Utilization of Municipal Solid Waste Incineration Residues in Concrete

Home , Concrete slab, Construction aggregate, Flow table test

Shipeng Zhang

Department of Civil Engineering and Applied Mechanics McGill University, Montréal, Québec, Canada Aug. 2019

A thesis submitted to McGill University in partial fulfillment of the requirements of the degree of Doctor of Philosophy

©Shipeng Zhang, 2019

Abstract

The global generation of municipal solid wastes (MSW) has been dramatically increasing as a

result of industrialization and rise in population. The conventional waste treatment method,

landfilling, can be problematic because of the long-term land occupation and the potential

environmental risks from underground water pollution, soil contamination, and/or methane and

odor emissions. Because of that, many countries adopted incineration as an alternative solution for waste treatment. Incineration has the advantages of reducing mass and volume of the waste and collecting energy from the combustible content simultaneously. However, this is not the final

solution. Considering the extensive amount of MSW generated every day, after incineration, there

are still ash residues that pose challenges to disposal. Moreover, some of the incineration residues

are hazardous and thus need to be treated and further landfilled. This process is costly and has the

possibility of presenting ecological risks. To solve this problem, this thesis successfully demonstrated the feasibility of using municipal solid waste incineration (MSWI) residues, namely bottom ash (BA), boiler ash (BLA), and APC lime, in concrete for different applications. Firstly the dried and pulverized bottom ash (BA) residue was successfully applied in dry-cast concrete as cement replacement. This material exhibited good pozzolanic reactivity, which led to improved strength and durability. Secondly an eco-cement was synthesized exclusively from MSWI residues that had shown both CO2 reactivity and latent hydraulic behavior. All types of residues were

utilized as raw materials of the eco-cement. The performance of the eco-cement to partially and

entirely replace ordinary Portland cement was examined under both hydration and carbonation

curing conditions. This concept was further proved in pilot-scale production of full-size concrete masonry units. The results indicated that the eco-cement can work as either standalone binder

(under carbonation curing) or supplementary cementitious material (under hydration or

carbonation curing) in concrete products. Thirdly, attempt has been made to use as-received

bottom ash (BA) as aggregate in concrete. A green concrete that combined BA aggregate and

synthesized eco-cement was developed to maximize the usage of MSWI residues. It was concluded that the proposed MSWI residues utilization techniques can replace the costly and environmental harmful landfill disposal method and convert the wastes to value-added products.

Résumé

Le taux de production mondial de déchets solides municipaux a considérablement augmenté en raison de l'industrialisation et de l'augmentation de la population. La méthode conventionnelle de traitement des déchets, la mise en décharge, peut être problématique en raison de l'occupation du sol à long terme et des risques environnementaux potentiels liés à la pollution de l'eau souterraine,

à la contamination du sol et / ou aux émissions de méthane et d'odeurs. À cause de cela, de nombreux pays ont adopté l'incinération comme solution alternative pour le traitement des déchets.

L'incinération présente les avantages de réduire la masse et le volume des déchets et de collecter simultanément l'énergie calorifique du contenu combustible. Cependant, ce n'est pas la solution finale. Compte tenu de la quantité considérable de déchets solides municipaux générés chaque jour, après l'incinération, il reste encore des résidus de cendres qui posent des problèmes d'élimination. En outre, certains des résidus incinérés sont dangereux et doivent donc être traités et ensuite mis en décharge. Ce processus est coûteux et peut présenter des risques écologiques.

Dans le but de résoudre ce problème, cette thèse a démontré avec succès la possibilité d'utiliser des résidus d'incinération des déchets solides municipaux, à savoir des cendres résiduelles (BA), des cendres de chaudière (BLA) et de la chaux APC, dans le béton. Le résidu de cendre inférieure séchée et pulvérisée (BA) a été appliqué avec succès dans du béton coulé à sec en remplacement du ciment. Ce matériau a présenté une bonne réactivité pouzzolanique, ce qui a permis d’améliorer la résistance et la durabilité. Un éco-ciment dérivé de résidus MSWI presque entièrement synthétisé a pour la première fois une activation de CO2 et des comportements hydrauliques latents. Tous les types de résidus ont été utilisés comme matières premières du ciment écologique.

La performance du ciment écologique pour remplacer partiellement et entièrement le ciment

Portland ordinaire a été examinée à la fois par les méthodes de durcissement par hydratation et par

5 carbonatation. Ce concept a également été prouvé à l’échelle pilote avec des spécimens d’unités de maçonnerie en béton de taille industrielle. Les résultats ont indiqué que l’éco-ciment peut fonctionner soit comme liant autonome (durcissement par carbonatation), soit comme matériau de ciment supplémentaire (durcissement par hydratation ou carbonatation) dans les produits en béton.

De plus, on a tenté d'utiliser du BA tamisé comme agrégat dans le béton. Un béton écologique associant agrégat BA et éco-ciment de synthèse a été mis au point pour optimiser l'utilisation des résidus de MSWI. Il a été conclu que les techniques d’utilisation des résidus MSWI proposées peuvent remplacer la méthode d’élimination des décharges coûteuse et nocive pour l’environnement et convertir les déchets en produits à valeur ajoutée.

Acknowledgements

Foremost I would like to express my sincere gratitude to my supervisor, Prof. Yixin Shao. He has

given me tremendous amount of knowledge, perspective, and guidance throughout the many years of this thesis. His inspiration, encouragement, and continuous help made this work possible.

I would like to express my special thanks to Dr. Zaid Ghouleh for his superb mentorship, both

academically and personally. I sincerely appreciate all his contributions of time and ideas which

lead me into research.

I owe my gratitude to Dr. Lingling Hu for her generous help on XRF and heat of hydration tests.

Moreover, I would like to acknowledge John Bartczak, Bill Cook and David Liu for the technical

support. Thanks to my colleagues and friends for all the unforgettable memories we had over the

past three years.

I would like to express my deepest gratitude to my parents and brother. This journey would not

have been possible without the support and encouragement from them. I must thank my wife,

Mengjie Wang. Thank you for your kindness and always being by my side.

Thank you to our Industrial sponsors and collaborators, Mr. Paul Hargest of Boehmers Block,

Emerald Energy from Waste (EFW) incinerator. I would lastly like to thank NSERC for its

generous financial support.

Table of Contents Abstract ...... 3 Résumé ...... 5 Acknowledgements ...... 7 List of Figures ...... 13 List of Tables ...... 15 Chapter 1. Introduction ...... 16 1.1 Overview ...... 16 1.2 Research Objectives ...... 19 1.3 Thesis Structure ...... 19 References ...... 21 Chapter 2. Literature review ...... 23 2.1 Municipal Solid Waste Incineration ...... 23 2.2 MSWI Residues ...... 24 2.3 MSWI Residues Reutilization ...... 24 2.4 Bottom Ash as Aggregates...... 25 2.5 Bottom Ash as Cement Additive ...... 26 2.6 MSWI Residues Derived Cement ...... 28 2.7 Carbonation Curing ...... 29 2.8 Supplementary Cementitious Material ...... 30 2.9 Belite Cement ...... 32 2.10 Dry-cast Concrete ...... 32 References ...... 33 Chapter 3. Use of municipal solid waste incineration bottom ash as supplementary cementitious material in dry-cast concrete ...... 46 Preface...... 46 3.1 Introduction ...... 47 3.2 Experimental Program ...... 50 3.2.1 Materials, mix proportions, sample preparation ...... 50 3.2.2 Laser Diffraction Particle Size Analysis ...... 51 3.2.3 Pozzolanic Reactivity Assessment ...... 51 3.2.4 Gas-release evaluation ...... 52 3.2.5 Mini-slump Test ...... 52

3.2.6 Compressive Strength ...... 53 3.2.7 Thermal Analysis ...... 53 3.2.8 Microstructure ...... 54 3.2.9 Freeze-thaw resistance ...... 54 3.3 Results and Discussion ...... 55 3.3.1 Material Characteristics ...... 55 3.3.2 Pozzolanic Reactivity Assessment ...... 56 3.3.3 Gas Release Evaluation...... 57 3.3.4 Strength Performance of Paste ...... 58 3.3.5 Thermogravimetric analysis (TGA) ...... 60 3.3.6 Isothermal calorimetry ...... 61 3.3.7 Scanning electron microscope (SEM) ...... 62 3.3.8 Concrete compressive strength ...... 63 3.3.9 Freeze-thaw scaling resistance ...... 65 3.4 Conclusion ...... 65 References ...... 67 Chapter 4. Performance of Eco-concrete Made from Waste-derived Eco-cement ...... 85 Preface...... 85 4.1 Introduction ...... 86 4.2 Materials and Methods ...... 88 4.2.1 Raw Materials ...... 88 4.2.2 Materials Characterization ...... 88 4.2.3 Eco-cement Clinkering ...... 89 4.2.4 Sample Preparation and Curing Scenarios ...... 91 4.2.5 Scanning Electron Microscopy (SEM) ...... 92 4.2.6 Concrete slab performance tests ...... 92 4.2.7 Pilot-Scale Production ...... 94 4.2.7.1 Pilot-scale Eco-cement Clinkering ...... 94 4.2.7.2 CMU Sample Preparation ...... 95 4.2.7.3 CMU Performance Tests ...... 95 4.3 Results and Discussion ...... 96 4.3.1 Raw Material Compositional Analysis ...... 96 4.3.2 Eco-cement QXRD Analysis, Particle size Analysis and Morphology Analysis .... 96 9

4.3.3 Eco-cement Performance Under Hydration and Carbonation Curing ...... 97

4.3.3.1 Compressive Strength and CO2 Uptake ...... 97 4.3.3.2 Mineralogical Analysis of Paste Samples ...... 98 4.3.4 Lab-scale Concrete Performance Tests ...... 99

4.3.4.1 Concrete CO2 Uptake and Compressive Strength ...... 99 4.3.4.2 Leaching Performance ...... 100 4.3.4.3 Concrete Surface Resistivity ...... 101 4.3.4.4 Freeze-thaw Scaling Resistance ...... 102 4.3.4.5 Concrete Linear Drying Shrinkage ...... 103 4.3.5 Pilot-scale Concrete Performance Tests ...... 103 4.3.5.1 Mineral analysis (QXRD) of Eco-cement Produced at Pilot-scale ...... 103 4.3.5.2 Full-size CMU Performance ...... 104 4.4 Conclusion ...... 105 References ...... 107 Chapter 5. Use of Eco-cement Derived from MSWI Ashes as Supplementary Cementitious Material in Concrete ...... 124 Preface...... 124 5.1 Introduction ...... 125 5.2 Materials and Methods ...... 127 5.2.1 Materials ...... 127 5.2.2 Eco-cement Raw Material Characterization ...... 128 5.2.3 Synthesis of Eco-cement ...... 128 5.2.4 Chemical Compositions (XRF) of OPC, Eco-cement and NewCem Plus...... 129 5.2.5 Mix Proportions and Specimen Casting ...... 130 5.2.6 Curing Scenarios ...... 130 5.2.7 Cement Paste consistency and Setting Time ...... 131 5.2.8 Quantitative X-ray Diffraction Analysis ...... 131 5.2.9 Microstructure Analysis (SEM) ...... 132 5.2.10 Lab-scale Concrete Performance Analysis ...... 132 5.2.11 Full-size Concrete Masonry Units (CMU) Preparation and Curing ...... 133 5.2.12 CMU Performance Test ...... 134 5.3 Results and Discussion ...... 134 5.3.1 Laser Particle Size Analysis on Raw Binding Material ...... 134

5.3.2 Consistency and Setting time ...... 134 5.3.3 Eco-cement’s Hydration and Carbonation Strength ...... 135

5.3.4 Paste Compacts with Blend Cement’s CO2 Uptake and Compressive Strength ... 135 5.3.5 Quantitative X-ray Diffraction Analysis ...... 137 5.3.6 Microstructure Analysis (SEM) ...... 138

5.3.7 Concrete CO2 Uptake and Compressive Strength ...... 139 5.3.8 Freeze-thaw Scaling Resistance ...... 141 5.3.9 Leaching Performance ...... 142 5.3.10 Pilot-scale Test ...... 142 5.3.10.1 Compressive Strength Test ...... 142 5.3.10.2 Density, Absorption and Linear shrinkage ...... 143 5.4 Conclusion ...... 144 References ...... 146 Chapter 6. Use of Bottom Ash as Aggregate and Eco-cement as Binding Material in Concrete163 Preface...... 163 6.1 Introduction ...... 164 6.2 Experimental Program ...... 166 6.2.1 Materials ...... 166 6.2.2 Bottom Ash Stabilization Methods ...... 166 6.2.3 Bottom Ash Aggregates Characterization ...... 167 6.2.4 Mix Proportions and Concrete Preparation...... 168 6.2.5 Compressive Strength Test ...... 169 6.2.6 Concrete Density, Absorption and Permeable Voids Content ...... 169 6.2.7 Concrete Leaching Performance ...... 170 6.2.8 Microstructure Analysis (SEM) ...... 170 6.3 Results and Discussions ...... 171 6.3.1 BA Treatment Methods...... 171 6.3.2 Aggregate Characterization ...... 172 6.3.3 BA Aggregate Application Ratio ...... 173 6.3.4 Compressive Strength and Carbon Uptake ...... 174 6.3.5 Concrete Density, Absorption and Permeable Voids Content ...... 176 6.3.6 Interfacial Transition Zone ...... 176 6.3.7 Leaching Performance ...... 177 11

6.4 Conclusion ...... 178 References ...... 179 Chapter 7. Conclusions, Future Work and Originality ...... 191 7.1 Conclusions ...... 191 7.2 Future work ...... 194 7.3 Originality ...... 195

List of Figures

Figure 3. 1: Typical compaction voids in dry-cast concrete (OPC batch at 90 days)...... 76 Figure 3. 2: Gas over water set-up ...... 76 Figure 3. 3: Miniature slump test ...... 77 Figure 3. 4: SEM image of (a) primed BA and (b) Class CI fly ash ...... 77 Figure 3. 5: Laser particle size analysis ...... 78 Figure 3. 6: Lime-pozzolan test specimens; (a): Standard ASTM C593 (water/(hydrated lime + additive) = 65%); (b): Modified Lime-pozzolan (water/(hydrated lime + additive) = 35%) ...... 78 Figure 3. 7: Lime-pozzolan compressive strength (28 days samples); (a): strength from standard ASTM C593 test; (b): strength from modified lime-pozzolan test ...... 79

Figure 3. 8: Cumulative gas releasing from BA (100 gram) in alkaline solution (Ca(OH)2 solution with pH value of 12.07) ...... 79 Figure 3. 9: Gas chromatography for the gas released from BA ...... 80 Figure 3. 10: Compressive strength of paste compacts...... 80 Figure 3. 11: TGA and DTG curve of BAOPC batch ...... 81 Figure 3. 12: Isothermal calorimetry curves ...... 81 Figure 3. 13: SEM Images for polished surface of paste compacts at age of 28 days; (a): BAOPC; (b) OPC ...... 82 Figure 3. 14: SEM Images for fracture surface of paste compacts at age of 28 days; (a): BAOPC; (b) OPC ...... 82 Figure 3. 15: Concrete compressive strength ...... 83 Figure 3. 16: Concrete freeze-thaw scaling test ...... 83 Figure 3. 17: Concrete subjected to 30 freeze-thaw cycles; (a): Typical concrete before test; (b): Concrete after test ...... 84

Figure 4. 1: Eco-cement making process (Steps: 1. Pulverizing of raw meals and Mixing; 2. Nodulizing; 3. Clinkering; 4. Final pulverizing of clinkers) ...... 117 Figure 4. 2: Laboratory scale carbonation curing set-up ...... 118 Figure 4. 3: Nodule clinkering in pilot-scale; (a) Industrial furnace; (b) Nodules before clinkering; (c) Nodules after clinkering ...... 119 Figure 4. 4: Pilot-scale carbonation curing set-up ...... 119 Figure 4. 5: (a) Fresh Eco-cement CMU blocks made from industrial block machine; (b) blocks being loaded into carbonation kiln for carbonation curing; (c) Eco-cement blocks after carbonation curing ...... 120 Figure 4. 6: Cements particle size analysis ...... 120

Figure 4. 7: Clinker Morphology: SEM image with EDS point analysis ...... 121 Figure 4. 8: Cement paste compact compressive strength and CO2 uptake ...... 121 Figure 4. 9: Concrete slabs compressive strength and CO2 uptake ...... 122 Figure 4. 10: Concrete slabs surface resistivity test ...... 122 Figure 4. 11: Concrete slabs freeze-thaw resistivity ...... 123 Figure 4. 12: Concrete slabs linear shrinkage ...... 123

Figure 5. 1: Types of specimens produced ...... 156 Figure 5. 2: Laboratory-scale carbonation curing set-up ...... 156 Figure 5. 3: Pilot-scale carbonation curing set-up ...... 157 Figure 5. 4: Laser particle size analysis ...... 157 Figure 5. 5: Paste compacts compressive strength of 100% eco-cement ...... 158 Figure 5. 6: Paste compacts compressive strength of OPC and blend cement ...... 158 Figure 5. 7: Eco-cement paste microstructure: (a) SEM images with EDX analysis: 1: Raw Eco- cement; 2: ECB-H at 28 days; (b) SEM images of ECB-C up to 90 days: 1: 1 day (mag. 100,000×), 2: 1 day (mag. 50,000×), 3: 28 days (mag. 50,000×), 4: 90 days (mag. 50,000×); (c) EDX point analysis ...... 160 Figure 5. 8: Concrete slabs compressive strength ...... 161 Figure 5. 9: Freeze-thaw scaling resistance of concrete slab ...... 161 Figure 5. 10: Compressive strength of full-size CMUs ...... 162

Figure 6. 1: Carbonation set-up ...... 185 Figure 6. 2: Target aggregate size distribution ...... 185 Figure 6. 3: Negative effect for concrete with as-received bottom ash: a. Pitting; b. Foaming; c. Corrosion; d. Mold forming ...... 186 Figure 6. 4: BA before and after 200 °C drying ...... 186 Figure 6. 5: BA sieve analysis before and after pyrolysis ...... 187 Figure 6. 6: BA aggregates retained on different sieves ...... 187 Figure 6. 7: Fracture surface of a 50BA-OPC-H ...... 188 Figure 6. 8: 1 day compressive strength for BA aggregate concretes with OPC under hydration curing ...... 188 Figure 6. 9: Concrete slab with 50% BA aggregates and 100% Eco-cement ...... 189 Figure 6. 10: Comparison of eco-cement - BA aggregate concretes with reference concretes .. 189 Figure 6. 11: SEM image of ITZ; a: Granite-OPC-H; b: Litex-OPC-H; c: BA-OPC-H; d: BA- Eco-C ...... 190

List of Tables

Table 3. 1 :Mixture Proportions of paste compacts and concrete ...... 73 Table 3. 2 : Mixture proportions of pozzolanic reactivity assessment ...... 73 Table 3. 3: Chemical compositions (XRF) of BA, FA and OPC ...... 74 Table 3. 4: Quantitative X-ray Diffraction (QXRD) analysis for BA ...... 74 Table 3. 5: Miniature paste slump test ...... 75 Table 3. 6: Percentage TGA mass loss and CH content (wt%) ...... 75

Table 4. 1: Chemical compositions (XRF) of the MSW incinerator residues ...... 112 Table 4. 2: Raw feed proportion for clinker ...... 113 Table 4. 3: Mixture proportions for cement paste and concrete ...... 113 Table 4. 4: Mineral compositions (QXRD) of raw binders and paste compacts ...... 114 Table 4. 5: Leaching performance ...... 115 Table 4. 6: Mineral compositions (QXRD) of Eco-cement produced in pilot-scale ...... 116 Table 4. 7: Compressive strength, density, absorption and linear shrinkage of CMU made from pilot-scale produced eco-cement...... 116

Table 5. 1: Chemical compositions of MSWI ashes ...... 151 Table 5. 2: Mix design of clinker ...... 151 Table 5. 3: Chemical compositions of OPC, eco-cement and NewCem Plus ...... 152 Table 5. 4: Mixture proportions for pastes and concretes ...... 153 Table 5. 5: Consistency and setting time ...... 153 Table 5. 6: Mineral compositions (QXRD) of OPC, eco-cement and their blend pastes at age of 24 hours ...... 154 Table 5. 7: Leaching Performance ...... 155 Table 5. 8: Density, absorption and linear shrinkage of CMU ...... 155

Table 6. 1: Mix proportions ...... 182 Table 6. 2: Chemical compositions (XRF) of as-received BA and pyrolysis treated BA ...... 183 Table 6. 3: Absorption, relative density and loose bulk density of aggregates ...... 183 Table 6. 4: Concrete bulk density, absorption and volume of permeable voids ...... 184 Table 6. 5: Leaching performance ...... 184

Chapter 1. Introduction

1.1 Overview

Municipal solid waste (MSW), which is defined by “Environment Canada” as “Solid waste

includes residential, light industrial, commercial and institutional waste that is collected by a

municipality or by contracted collectors on behalf of the municipality.” After the industrial

revolution in the 19th century, the rapid growth of urbanization and industrialization led to fast

economic development and population boost. The MSW generation level is increasing promptly

every year. There were 1.3 billion tonnes of MSW generated in the year of 2012 worldwide, and

it was expected to grow to 2.2 billion tonnes by 2025 (Bhada-Tata, 2012). The most common

disposal solution, landfilling, is facing significant challenges including limited dumping area near

urban areas, surrounding environment contamination, odor emissions and greenhouse gas –

methane releasing (Dou et al., 2017; Makarichi et al., 2018; Muangrat, 2013). At the meantime,

harsher regulations were issued to control the dumping area and landfilling process. So, more

sustainable waste management methods were needed, and incineration seems to be a good option,

which has already been adopted by many countries. This technique offers an efficient way to

reduce the solid waste by 90% in volume and 70% in weight (Lynn et al., 2017), and it also has

the capacity to recover a considerable amount of energy through high-pressure steam (Shih et al.,

2003). However, it is still not the final solution. Although incineration can still diminish a

considerable amount of the solid waste, the MSW incineration (MSWI) residues are still

substantial, namely bottom ash (BA), boiler ash (BLA) and air pollution control (APC) lime.

Landfilling is a common method to treat these ashes. However, BLA and APC lime contain

leachable heavy metal, chloride content, and toxic organic contaminants. Landfilling them requires

special pre-treatment to protect the dumping area, and therefore, it makes the process costly and

environmental pollution risk still remains. Thus, new methods should be developed to treat or even utilize these residues and get benefit from them.

With the advantages of easy access ingredients, high durability, low maintenance cost, and high

fire resistance, concrete has been used as a construction material for thousands of years. Nowadays, concrete has become the world’s most used synthetic material with around ten billion metric tons produced each year, and most of them are made by ordinary Portland Cement (OPC) (Assi et al.,

2018). Cement manufacture is an extensive energy consumption process. Moreover, it releases an

enormous amount of greenhouse gas CO2. About one ton of CO2 generated for the production of

one ton OPC (Hanein et al., 2018). Half of the CO2 discharge in cement making contributed during

the heating process when limestone (CaCO3) converts to lime (CaO), and the rest half is emitted

from the fossil fuel burning to heat the kiln. Globally, 5% of CO2 emission is from the cement

industry (Supino et al., 2016). The high content of CO2 is the main reason that global warming passed over its limit in 2015 (Szulejko et al., 2017). Therefore, actions have to be taken to reduce

CO2 emissions.

Attempts have been made to save the energy and lower the CO2 discharge simultaneously in the

cement industry. One of them is the use of supplementary cementitious material (SCM) in concrete, which has been applied extensively over the past two decades. Many SCMs are originally by-products from industries, for example, coal fly ash, silica fume, blast furnace slag etc. Use of these SCM not only reduces the by-product wastes but also improves the mechanical and durability performance of the concrete, since the SCM generates extra C-S-H gel that densifies the concrete microstructure. Meanwhile, usage of SCM reduces the construction cost, which is another motivation for the industry to adopt it. The invention of new clean binding materials to replace

ordinary cement is another focus to reduce the environmental impact from the construction sector.

For instance, belite cement that clinkered under low temperature (Staněk & Sulovský, 2015), steel slag that activated by carbonation curing could be one of the possible options (Humbert & Castro-

Gomes, 2019), a green cementitious material was made from flue gas desulfurization gypsum

(Rust et al., 2012) and much more.

In addition to SCM and environmentally friendly new cement that can reduce the emission of CO2,

a technique has been developed to absorb and store CO2 in concrete, which is so-called

“carbonation curing”. Altered from conventional hydration curing, carbonation curing is a method

that exposes fresh concrete products to the high concentration of CO2 under relatively high

pressure condition. Instead of damage the concrete in the case of weathering carbonation,

introducing concrete to carbon dioxide gas at an early age has proved that concrete can benefit

from rapid strength gain and improved durability properties (Zhang et al., 2017). Considering the

large amount of concrete used annually, implementing this curing method can permanently

consume enormous amount of CO2 in concrete.

In this study, a novel approach was explored that could potentially use incineration residues to

produce cementing material, supplementary cementitious materials, and construction aggregates.

This research will help to reduce the volume of MSWI residues, eliminate the costly landfill,

convert waste into a value-added product, and therefore generate revenues at the same time. This

will further decrease the carbon footprint in the construction industry. Furthermore, for incinerator

companies, instead of paying costly landfill fee to dispose of ashes, they can give or even sell the

by-products to cement and/or masonry industries and make benefits from this proposed solution

1.2 Research Objectives

This study aims to develop feasible methods to utilize municipal solid waste incineration (MSWI) residues in concrete products from different perspectives, including SCM, synthesized binding material (eco-cement) and aggregates. The property of pulverized BA added as SCM will be evaluated. The characterization of the low-energy waste derived eco-cement will be investigated when it is applied in concrete to replace ordinary cement partially and entirely. BA will also be tested in the use of aggregates in concrete and a “green concrete” was produced with BA aggregate and synthesized eco-cement. Carbon dioxide gas will be served as an activator for the eco-cement concrete through carbonation curing with the advantage of sequestrating a considerable amount of greenhouse gas. The concepts will be further proved under the pilot-scale test. The practicability of manufacturing eco-cement on a large scale will be assessed, and the properties of eco-cement based full-size concrete masonry units (CMUs) made from a real concrete masonry plant will be examined.

1.3 Thesis Structure

This thesis follows a manuscript-based structure. Each chapter presents in the way of a standalone paper. Therefore, repetitions could not completely be avoided, especially in the introduction sections. Every chapter includes a preface to explain the objectives, background information, and the connections to other chapters.

Chapter 1 serves as the introduction to the background information of this research and describes the proposed objectives and structure of the thesis.

Chapter 2 presents a detailed literature review on past studies with topics related to this thesis

research.

Chapter 3 investigates the feasibility of using MSWI bottom ash (BA) as supplementary

cementitious material (SCM) in dry-cast concrete products. The chemical instability of BA under

alkaline condition was studied and the associated cracking problem was successfully avoided using

the dry-cast concept. Thermal analyses, microstructure analysis, strength test, and durability

assessment were employed to evaluate the performance of the BA additive.

Chapter 4 describes the process of synthesizing a low energy, MSWI residues derived, carbonation

reactive eco-cement, and its performance in concrete. The concept was further proved in a pilot- scale test.

Chapter 5 presents another application scenario of eco-cement that is used as SCM to replace ordinary portland cement. The research in this chapter is to find more applications of eco-cement developed in chapter 4, including both of hydration curing and carbonation curing of eco-cement.

Chapter 6 focused on applying the MSWI BA as aggregate component in concrete. Ordinary

Portland cement was used first to exam the BA aggregate performance in normal binding system.

Then, the BA aggregate was used with eco-cement that synthesized in this study to create a green concrete that almost all the components were originally made from MSWI ashes.

Chapter 7 summarizes the main conclusions in this thesis and the originality of the work.

References

Assi, L., Carter, K., Deaver, E., Anay, R., & Ziehl, P. (2018). Sustainable concrete: Building a greener future. Journal of Cleaner Production, 198, 1641-1651. doi:https://doi.org/10.1016/j.jclepro.2018.07.123

Bhada-Tata, P. H., Daniel A. (2012). What a waste: A Global Review of Solid Waste Management. In Urban development series knowledge papers (pp. 15): World Bank, Washington, DC. © World Bank. .

Dou, X., Ren, F., Nguyen, M. Q., Ahamed, A., Yin, K., Chan, W. P., & Chang, V. W.-C. (2017). Review of MSWI bottom ash utilization from perspectives of collective characterization, treatment and existing application. Renewable and Sustainable Energy Reviews, 79, 24- 38. doi:https://doi.org/10.1016/j.rser.2017.05.044

Hanein, T., Galvez-Martos, J.-L., & Bannerman, M. N. (2018). Carbon footprint of calcium sulfoaluminate clinker production. Journal of Cleaner Production, 172, 2278-2287. doi:https://doi.org/10.1016/j.jclepro.2017.11.183

Humbert, P. S., & Castro-Gomes, J. (2019). CO2 activated steel slag-based materials: A review. Journal of Cleaner Production, 208, 448-457. doi:https://doi.org/10.1016/j.jclepro.2018.10.058

Lynn, C. J., Ghataora, G. S., & Dhir Obe, R. K. (2017). Municipal incinerated bottom ash (MIBA) characteristics and potential for use in road pavements. International Journal of Pavement Research and Technology, 10(2), 185-201. doi:https://doi.org/10.1016/j.ijprt.2016.12.003

Makarichi, L., Jutidamrongphan, W., & Techato, K.-a. (2018). The evolution of waste-to-energy incineration: A review. Renewable and Sustainable Energy Reviews, 91, 812-821. doi:https://doi.org/10.1016/j.rser.2018.04.088

Muangrat, R. (2013). A review: utilization of food wastes for hydrogen production under hydrothermal gasification AU - Muangrat, Rattana. Environmental Technology Reviews, 2(1), 85-100. doi:10.1080/21622515.2013.840682

Rust, D., Rathbone, R., Mahboub, K. C., & Robl, T. (2012). Formulating Low-Energy Cement Products. 24(9), 1125-1131. doi:doi:10.1061/(ASCE)MT.1943-5533.0000456

Shih, P.-H., Chang, J.-E., & Chiang, L.-C. (2003). Replacement of raw mix in cement production by municipal solid waste incineration ash. Cement and Concrete Research, 33(11), 1831- 1836. doi:https://doi.org/10.1016/S0008-8846(03)00206-0

Staněk, T., & Sulovský, P. (2015). Active low-energy belite cement. Cement and Concrete Research, 68, 203-210. doi:https://doi.org/10.1016/j.cemconres.2014.11.004

Supino, S., Malandrino, O., Testa, M., & Sica, D. (2016). Sustainability in the EU cement industry: the Italian and German experiences. Journal of Cleaner Production, 112, 430- 442. doi:https://doi.org/10.1016/j.jclepro.2015.09.022

Szulejko, J. E., Kumar, P., Deep, A., & Kim, K.-H. (2017). Global warming projections to 2100 using simple CO2 greenhouse gas modeling and comments on CO2 climate sensitivity factor. Atmospheric Pollution Research, 8(1), 136-140. doi:https://doi.org/10.1016/j.apr.2016.08.002

Zhang, D., Ghouleh, Z., & Shao, Y. (2017). Review on carbonation curing of cement-based materials. Journal of CO2 Utilization, 21(Supplement C), 119-131. doi:https://doi.org/10.1016/j.jcou.2017.07.003

Chapter 2. Literature review

2.1 Municipal Solid Waste Incineration

Municipal solid waste (MSW) is dramatically increased along with the industrialization of nations and the rise in population. Globally, 1.3 billion tons of MSW were generated in the year of 2012, and it was expected to rise to 2.2 billion tons by 2025 (Bhada-Tata, 2012). Limited space and potential negative environmental impacts, including underground water pollution, soil contamination, odor emission, and etc. (Saikia N, 2006), make the conventional landfill waste

management no longer satisfy the needs for modern society.

Incineration technique has been adopted by many countries as one of the waste management

options that has the advantages of reducing the landfilling material and recovering energy from

the combustible fraction in the MSW. Several combustion systems exist in the market, but they

can be generally divided into two types: mass burning and refuse derived fuel (RDF). Mass burning

means to burn the waste in its “as-received” status without any pre-conditioning like size

separation and material recycling (Chandler et al., 1997b). On the other side, the RDF system

adopted several pre-treatment processes to remove and/or recover the non-combustible fractions

in the solid waste, for instance, ferrous, certain plastics and aluminum materials (Chandler et al.,

1997b). The mass burning combustion system can be further divided into the European type and

the modular type. The mass burning system with “starved air” incineration system is going to be

emphasized since the raw materials used in this study were collected from this type of incinerator.

The modular type or so-called “two-stage” burning system consists of the connected primary and

secondary chamber. The primary chamber runs under insufficient air level and creates high

pyrolysis air that will be burned with excess oxygen in the secondary chamber (Chandler et al.,

1997b). This well adopted incineration system has the advantages of low capital cost and low suspension particles in flue gas. However, the energy conversion rate is low (55-60%) (Chandler et al., 1997b). Moreover, the bottom ash that comes from the primary chamber has a high carbon content and LOI value due to the incomplete combustion, which will be problematic to reutilize this residue.

2.2 MSWI Residues

Three MSWI residues are generated from the incineration process, namely, bottom ash (BA), boiler ash (BLA) and air pollution control (APC) lime. BA represents the majority (90%) of the

total residues (Giro-Paloma et al., 2017), which is the residue underneath furnace grate after the

completion of the combustion process. Water quenching is normally adopted to lower the

temperature, therefore, the recovered BA usually has a high moisture content (Todorovic & Ecke,

2006). Furthermore, as mentioned before, due to the design of the “two-stage air-starved” burning

chamber, the BA from this type of incinerator has even higher carbon content and LOI value. The

composition of BA varies depending on the area and the type of incinerator, but it mainly consists

of glass, ceramics, metals and unburned organic matter (del Valle-Zermeño et al., 2017). Residues

from the Heat Recovery Steam Generator (HRSG) and Electrostatic Precipitator (ESP) system are

often mixed together and called boiler ash. APC lime comes from the downstream flue gas cleaning

system, which contains products of the reaction between the flue gas and the lime sorbent

(Todorovic & Ecke, 2006).

2.3 MSWI Residues Reutilization

With the rapid increase in solid waste generation and the strict regulation developed by different

countries, incinerated residues disposal has become the challenge in waste management.

Especially for the hazardous class boiler ash and APC lime, which consists of leachable heavy

metals, chloride content and toxic organic contaminants (Tang et al., 2018). Because of that, these

residues need to be treated and stabilized before landfill. New disposal solution of MSWI residues has been attracted attentions to developing a new method to utilize these by-products in a more environmentally sustainable and economically beneficial way.

2.4 Bottom Ash as Aggregates

Due to the granular shape and relative compactable nature of bottom ash, attempts were made to

use this residue as aggregates in road construction. European countries have been the first to adopt

the technique that using BA as unbound aggregates in pavement and embankment construction

(Leenders, 2000). However, this move raised concern about the heavy metal and salts leaching to

the surrounding soil and water, resulting in a polluted area that effects the plant growth along the

road (Baldwin et al., 1997). Vegas et al. (2008) confirmed that the fresh BA could also be a feasible

road base aggregate as long as it didn’t consist of a high concentration of soluble salts. Forteza et

al. (2004) suggested that the BA needed weathering treatment for at least a month before use as

aggregate in order to fulfill the environmental regulation and the mechanical properties. Early age

carbonation was used by Van Gerven et al. (2005) to decrease the heavy metal leaching during

aggregate application in road construction. Cement solidification might further eliminate the

environmental impact potential of BA, therefore, attempts had been made to use BA as aggregate

in cement bound sub-base and road base (Paine et al., 2002; York, 2000). However, expansion and

swelling were observed when BA was used in portland cement concrete due to the instability of

BA under alkaline condition created by cement hydration (Pecqueur et al., 2001). Furthermore,

fine BA has a high water absorption rate and a higher concentration in contaminants. Therefore,

size separation was suggested to use the coarse portion of BA only (Chandler et al., 1997b).

Asphalt mixtures were another considered application for BA, Eymael et al. (1994) observed that

it is acceptable to replace 25% of natural aggregate with BA in asphalt design, but higher

bituminous binder content was required.

Furthermore, BA was also attempted to use as aggregate component in concrete mix in building

construction. However, studies reported expansion and cracking problem for concrete with raw

BA, as a result of hydrogen gas generation from the reaction of metallic aluminum in BA under

high pH pore solution created by cement hydration, which consequently damaged the concrete

product (Lynn et al., 2017; Pera et al., 1997) . To make stable BA aggregates for concrete, several

pre-treatment methods had been proposed. A minimum of six weeks of weathering and aging was

suggested by van Beurden et al. (1997) to stabilize the fresh BA before being used in concrete.

Another possible solution is to chemically treat BA aggregate with sodium hydroxide solution

which was introduced to consume the aluminum fraction and release hydrogen gas in advance

(Pera et al., 1997). Sintering or vitrifying can stabilize the BA in high temperature. Cheeseman et

al. (2005) created a BA lightweight aggregate making process by sintering the material in a rotary

furnace under a temperature range of 900-1080°C, and the produced product had the similar

property to a commercial lightweight aggregate product on the market. Ferraris et al. (2009) made

a new type of aggregate from vitrifying the BA at 1450°C, and the performance of it was found to

be comparable to the natural aggregate in an evaluation period of 2 years.

2.5 Bottom Ash as Cement Additive

The chemical composition of MSWI bottom ash is mainly comprised of amorphous silica, alumina, iron oxide, and calcium oxide, which is similar to that of many supplementary cementitious materials (SCMs) that possess pozzolanic behavior. Consideration is, therefore, being given to

using bottom ash as cement replacement in Portland concrete products, and several studies have

been carried out with this objective. Again, similar to the observation in BA aggregates applications, expansion, swelling, and cracking have been reported for concrete with BA additive, resulting from hydrogen gas releasing from the reactive aluminum content in BA under alkaline condition created by the hydration of cement in concrete (Bertolini et al., 2004; Kim et al., 2016;

Pera et al., 1997). The severity of the chemical instability of the BA material depends on the incineration processing system adopted. For the most common “mass burning” system, the collected waste is burned in its “as-received” condition without any pre-screening (Chandler et al.,

1997b). The reactive non-combustibles are inevitably left in the bottom ash residue, manifesting in the form of expansion in the BA added concrete. Therefore, the BA must be stabilized, and some methods have been proposed. Long term weathering and aging could be a possible solution by converting the metallic aluminum fraction into stable oxide (Chandler et al., 1997b). Sodium

hydroxide washing is another proposed treatment method, the expansion in concrete with BA

could be successfully eliminated by allowing the hydrogen gas released in advance in sodium

hydroxide solution (Kim et al., 2015). Lin et al. (2008) suggested a high temperature method by

melting the bottom ash at 1400°C for 30 minutes to create a slag that needed further pulverization

before applying. With a replacement of 10% and 20% of cement, the BA blended paste developed

a comparable strength with OPC references (Lin et al., 2008). Bertolini et al. (2004) developed a

wet-grinding method to pre-treat the BA. The as-received BA was ground with water to facilitate

gas release, and the 30% blended concrete was found to impart enhancements in concrete

properties.

2.6 MSWI Residues Derived Cement

MSWI residues can be potential raw materials to produce cement since they contain a certain amount of lime, silica, and alumina, which are the basic ingredients of cement raw feeds (Lederer et al., 2017). A new type of binding material, “eco-cement’, made from MSWI residues was created that consist of certain amount of chlorine (Odler, 2003). Attempts have been tried to use the MSWI by-products in this related project (Ampadu & Torii, 2001; Ferreira et al., 2003;

Ghouleh & Shao, 2018; Guo et al., 2014; Kikuchi, 2001; Lederer et al., 2017; Li et al., 2018; Li et al., 2016; Wu et al., 2012). Here are details for some of the studies. Ampadu and Torii (2001) came up a cement that 50% of the raw material was MSWI ashes with similar manufacture process with

OPC cement. Guo et al. (2014) investigated the durability and microstructure of a calcium sulphoaluminate (CSA) cement made with 30-40% MSWI boiler ash under a temperature of

1250°C. Alinite cement was created by Wu et al. (2012) incorporated 30% of MSWI residues in

the raw material and 2 hours of 1200°C clinkering process was performed. Kikuchi (2001)

concluded that it was feasible to contain 50% of MSWI ash in the cement production and a pilot-

scale test was further proved this concept. Ghouleh and Shao (2018) demonstrated a carbonation

reactive eco-cement that 85.5% of the raw material came from the MSWI residues. With silica

sand and calcium hydroxide served as extra source additions to adjust the raw feed chemical

composition, two major CO2 reactive minerals, chlorellestadite (CE) and belite (C2S), were

synthesized under a clinkering temperature of 1000 °C. Under carbonation curing, the eco-cement

could permanently sequestrate greenhouse gas CO2 and gain mechanical strength rapidly at the

same time. Moreover, the MSW incinerators usually run at 800-1000°C, which means with a

proper design, the whole eco-cement making process can be performed inside incinerator without

using extra energy resource.

2.7 Carbonation Curing

Weathering carbonation is a common durability issue for concrete. Atmospheric carbon dioxide

penetrates into the harden concrete in service and react with the two major cement hydration

products, calcium hydroxide, and C-S-H gel, leading to structural failure as a result of softened paste matrix (Groves et al., 1991).

Curing of fresh cast concrete is an important process in the precast industry to maintain the early age concrete in adequate humidity and temperature condition in order to ensure proper strength and durability properties development. Carbonation curing is a curing technique by introducing the freshly cast concrete to high purity CO2 gas under pressurized condition. Unlike weathering

carbonation that causing damage to concrete paste matrix, curing of concrete with CO2 at early

age increases the strength development rate and considerably enhances the concrete durability

properties (Rostami et al., 2011; Young et al., 1974). The CO2 that penetrated the concrete reacts

with anhydrous cement phases alite (3CaO· SiO2) and belite (2CaO· SiO2), and the reactions are shown in Eqs. 2.1 to 2.2 (Berger et al., 1972a). Instead of forming the normal hydration product calcium hydroxide, calcium carbonates are generated with CO2 permanently fixed in this mineral.

The reactions between CO2 and calcium silicates take place in a very short time (Zhang et al.,

2017), the resulting C-S-H gel and calcium carbonates give significate contribution to the early age strength development. Therefore, the carbonated concrete exhibits a rapid strength gain. The

precipitation of extra CaCO3 crystals further densify the microstructure, leading to a lower permeability and the durability performance of the concrete in service life is therefore enhanced

(Rostami et al., 2012). Short term carbonation is not able to consume all the calcium silicates in the cement. Therefore, subsequent hydration potential is still available to the concrete that subjected carbonation curing (Klemm & Berger, 1972).

Besides, carbonation curing can activate γ-C2S (Bukowski & Berger, 1979; Saito et al., 2010),

which is one of the polymorphs of belite that formed during low temperature clinkering. Since it does not hydrate under conventional curing scenario, it is a form that shall be avoided during cement production. With carbonation activation, carbonation curing provides a possibility to lower the clinkering temperature and to activate γ-C2S binder, so that it can reduce the energy

consumption in the cement industry (Guan et al., 2016).

3 + (3 ) + + (3 ) (2.1)

𝐶𝐶𝐶𝐶𝐶𝐶 ∙ 𝑆𝑆𝑆𝑆𝑂𝑂2 − 𝑥𝑥 𝐶𝐶𝑂𝑂2 𝑦𝑦𝐻𝐻2𝑂𝑂 → 𝑥𝑥𝑥𝑥𝑥𝑥𝑥𝑥 ∙ 𝑆𝑆𝑆𝑆𝑂𝑂2 ∙ 𝑧𝑧𝐻𝐻2𝑂𝑂 − 𝑥𝑥 𝐶𝐶𝐶𝐶𝐶𝐶𝑂𝑂3 2 + (2 ) + + (2 ) (2.2)

𝐶𝐶𝐶𝐶𝐶𝐶 ∙ 𝑆𝑆𝑆𝑆𝑂𝑂2 − 𝑥𝑥 𝐶𝐶𝑂𝑂2 𝑦𝑦𝐻𝐻2𝑂𝑂 → 𝑥𝑥𝑥𝑥𝑥𝑥𝑥𝑥 ∙ 𝑆𝑆𝑆𝑆𝑂𝑂2 ∙ 𝑧𝑧𝐻𝐻2𝑂𝑂 − 𝑥𝑥 𝐶𝐶𝐶𝐶𝐶𝐶𝑂𝑂3 The degree of carbonation during carbonation curing is quantified as CO2 uptake that measured

through the mass gain method proposed by El-Hassan et al. (2013). As shown in Eq. 2.3, the CO2

uptake is a ratio of the mass of CO2 sequestrated by the specimen as a fraction of the initial mass

of cement added in the mix design.

arbon (%) = × 100% (2.3) �𝑊𝑊𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐+𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙�−𝑊𝑊𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 𝐶𝐶 𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈 𝑊𝑊𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶

Where is the weight of the specimen after carbonation, is the water

𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 retrieved𝑊𝑊 from the chamber, is the weight of the specimen𝑊𝑊 before carbonation,

𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 and is the weight of𝑊𝑊 the dry cement used for a specimen.

𝑊𝑊𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 2.8 Supplementary Cementitious Material

Ordinary Portland cement is the second most consumed material after water by human beings and

the recorded amount of cement production was around 4.1 billion tons in the year of 2015

worldwide (Miller, 2018). Concerns have been raised for the environmental impacts of the cement

production process that not only consumes a great amount of energy but also heavily contributes

to the greenhouse gas emission. It was estimated that the cement industry counted 2-3% global

energy consumption and 8-9% of CO2 emission (Monteiro et al., 2017). In addition, the cement raw clinkering feeds mainly consist of limestone and clay or shale (Taylor, 1997) that mined from the natural resources. The cement production also leads to a huge consumption on these raw materials. In order to alleviate some of these negative impacts, the concrete industry has been working to promote the incorporation of industrial by-products in concrete mixtures to serve as alternative binding materials. For instance, coal fly ash, silica fume, and ground granulated blast furnace slag (GGBFS) were blended with cement clinker as supplementary cementitious materials

(SCM). Silica fume originally from silicon metal and alloy industries, and coal fly ash comes from the residue of coal burning power plants and has been proven that they exhibited pozzolanic reaction in cement-fly ash cementing system in concrete products (Mehta & Monteiro, 2017). The contained silica and/or alumina reacts with one of the hydration products – calcium hydroxide, with the presence of water, to form C-S-H gel. Use of pozzolan in concrete has the advantages of improvement in workability, enhancing the later age strength, reducing heat generation during concrete setting, increasing the durability resistance due to the refined microstructure (Tokyay,

2016b). Based on the total amount of silicon dioxide, aluminum oxide and iron oxide, the fly ash is classified into three different classes (N, F, C) according to ASTM C618 standard. On the other side, Canadian CSA A-3000 standard divided the fly ash into F, CI, CH, according to its calcium oxide content ranging from low to high.

GGBFS is a residue from the production of iron collected from the blast furnace. Rapid cooling is required to form the glassy phase. After pulverization, GGBF slag has the ability to react with

water directly at later age to produce aluminum-substituted calcium silicate hydrate (Tokyay,

2016b).

2.9 Belite Cement

Calcination is the conventional method to produce Ordinary Portland cement clinkers by heating the grounded raw mix (limestone, clay, etc.) at a temperature of 1450 °C. The main component of

Portland cement -alite (C3S) is thereafter formed. However, this process releases a great amount

of CO2. Each ton of Portland cement production releases 0.95 ton of CO2 (Ludwig & Zhang, 2015).

The CO2 emission in cement production comes from two sources, the first one is the fuel burning

in order to increase the temperature of the kiln, the second one is the decomposition of CaCO3 to

obtain CaO. Efforts have been made to increase the belite (C2S) ratio in the cement, or even,

completely replace alite in the so-called “belite cement”. Belite formation needs a much lower clinkering temperature of 1000-1100 °C, and the low CaO ratio of this mineral leading to a low

CO2 release during synthesizing in the kiln (Ávalos-Rendón et al., 2018). Comparing to C3S,

production of each ton of belite reduces 120 kg of limestone and saves 220 KJ of energy (Odler,

2000).

2.10 Dry-cast Concrete

Dry-cast concrete concept has been broadly used in many concrete products, for example, concrete masonry unit (CMU), paving blocks, retaining wall units, pipes, hollow core slabs, etc.

Distinguished from conventional wet-cast, dry-cast has a much lower water-cement ratio and cement content, leading to a zero-slump fresh concrete mix. Casting process of dry-cast involved pressure compaction with vibration, and the product can be demold right after casting, which effectively increases the production cycles (Sulistyana et al., 2014). Resulting from the different

32 in mix design and casting method, dry-cast concrete exhibits a distinct microstructure. Other than the capillary and gel pores in the bulk cement paste that can also be found in wet-cast concrete, the second pores system, the compaction voids, which consists of large, irregular, continuous voids formed during the compaction process can be observed in the dry-cast concrete (MacDonald, 2000;

Pigeon & Pleau, 1995). This type of pores is normally inevitable since the dry-cast concrete does not have enough hydration products to fill all the pores between aggregates due to the low cement content mix design (Pigeon & Pleau, 1995). Therefore, the dry-cast has a higher intrudable porosity compared to the normal conventional concrete (Marchand et al., 1996). The high porous natural of dry-cast concrete makes it an ideal product to perform carbonation curing, the compaction voids provide sufficient path for CO2 gas to penetrate at early age, and, therefore, leading to a high degree of uptake.

References

A. Harnik, U. M., A. Roesli. (1980). Combined influence of freezing and deicing salt on concrete—physical aspects. Durability of Building Materials and Components， ASTM International.

Alkemade, M., Eymael, M., Mulder, E., & Wijs, W. (1994). How to prevent expanstion of MSWI bottom ash in road construction? In J. J. J. M. Goumans, H. A. van der Sloot, & T. G. Aalbers (Eds.), Studies in Environmental Science (Vol. 60, pp. 863-876): Elsevier.

Ampadu, K. O., & Torii, K. (2001). Characterization of ecocement pastes and mortars produced from incinerated ashes. Cement and Concrete Research, 31(3), 431-436. doi:https://doi.org/10.1016/S0008-8846(00)00467-1

Ávalos-Rendón, T. L., Chelala, E. A. P., Mendoza Escobedo, C. J., Figueroa, I. A., Lara, V. H., & Palacios-Romero, L. M. (2018). Synthesis of belite cements at low temperature from silica fume and natural commercial zeolite. Materials Science and Engineering: B, 229, 79-85. doi:https://doi.org/10.1016/j.mseb.2017.12.020

Baldwin, G., Construction Industry, R., & Information, A. (1997). Use of industrial by-products in road construction - water quality effects. London: Construction Industry Research and Information Association.

Bentz, D. P. (2009). Influence of internal curing using lightweight aggregates on interfacial transition zone percolation and chloride ingress in mortars. Cement and Concrete Composites, 31(5), 285-289. doi:https://doi.org/10.1016/j.cemconcomp.2009.03.001

Berger, R. L., Young, J. F., & Leung, K. (1972a). Acceleration of Hydration of Calcium Silicates by Carbon Dioxide Treatment. Nature Physical Science, 240(97), 16-18. doi:10.1038/physci240016a0

Berger, R. L., Young, J. F., & Leung, K. (1972b). Acceleration of Hydration of Calcium Silicates by Carbon Dioxide Treatment. Nature Physical Science, 240, 16. doi:10.1038/physci240016a0

Berger, R. L., Young, J. F., & Leung, K. J. N. P. S. (1972c). Acceleration of Hydration of Calcium Silicates by Carbon Dioxide Treatment. 240(97), 16-18. doi:10.1038/physci240016a0

Bertolini, L., Carsana, M., Cassago, D., Quadrio Curzio, A., & Collepardi, M. (2004). MSWI ashes as mineral additions in concrete. Cement and Concrete Research, 34(10), 1899- 1906. doi:https://doi.org/10.1016/j.cemconres.2004.02.001

Bhada-Tata, P. H., Daniel A. (2012). What a waste: A Global Review of Solid Waste Management. In Urban development series knowledge papers (pp. 15): World Bank, Washington, DC. © World Bank. .

Bukowski, J. M., & Berger, R. L. (1979). Reactivity and strength development of CO2 activated non-hydraulic calcium silicates. Cement and Concrete Research, 9(1), 57-68. doi:https://doi.org/10.1016/0008-8846(79)90095-4

Chandler, A. J., Eighmy, T. T., Hartlén, J., Hjelmar, O., Kosson, D. S., Sawell, S. E., . . . Vehlow, J. (1997a). Chapter 2 - Municipal solid waste. In Studies in Environmental Science (Vol. 67, pp. 15-57): Elsevier.

Chandler, A. J., Eighmy, T. T., Hartlén, J., Hjelmar, O., Kosson, D. S., Sawell, S. E., . . . Vehlow, J. (1997b). Municipal Solid Waste Incinerator Residues

Elsevier.

Cheeseman, C. R., Makinde, A., & Bethanis, S. (2005). Properties of lightweight aggregate produced by rapid sintering of incinerator bottom ash. Resources, Conservation and Recycling, 43(2), 147-162. doi:https://doi.org/10.1016/j.resconrec.2004.05.004

Choudhary, A., Shah, V., & Bishnoi, S. (2016). Effect of low cost fillers on cement hydration. Construction and Building Materials, 124, 533-543. doi:https://doi.org/10.1016/j.conbuildmat.2016.07.088

Cyr, M., Lawrence, P., & Ringot, E. (2005). Mineral admixtures in mortars: Quantification of the physical effects of inert materials on short-term hydration. Cement and Concrete Research, 35(4), 719-730. doi:https://doi.org/10.1016/j.cemconres.2004.05.030

Deja, J. (2003). Freezing and de-icing salt resistance of blast furnace slag concretes. Cement and Concrete Composites, 25(3), 357-361. doi:https://doi.org/10.1016/S0958-9465(02)00052- 5 del Valle-Zermeño, R., Gómez-Manrique, J., Giro-Paloma, J., Formosa, J., & Chimenos, J. M. (2017). Material characterization of the MSWI bottom ash as a function of particle size. Effects of glass recycling over time. Science of The Total Environment, 581-582, 897- 905. doi:https://doi.org/10.1016/j.scitotenv.2017.01.047

Deschner, F., Winnefeld, F., Lothenbach, B., Seufert, S., Schwesig, P., Dittrich, S., . . . Neubauer, J. (2012). Hydration of Portland cement with high replacement by siliceous fly ash. Cement and Concrete Research, 42(10), 1389-1400. doi:https://doi.org/10.1016/j.cemconres.2012.06.009

Egüez Álava, H., De Belie, N., & De Schutter, G. (2016). Proposed mechanism for the formation of oxychloride crystals during sodium chloride application as a deicer salt in carbonated concrete. Construction and Building Materials, 109, 188-197. doi:https://doi.org/10.1016/j.conbuildmat.2016.01.047

El-Hassan, H., Shao, Y., & Ghouleh, Z. (2013). Reaction Products in Carbonation-Cured Lightweight Concrete. 25(6), 799-809. doi:doi:10.1061/(ASCE)MT.1943-5533.0000638

Erol, M., Küçükbayrak, S., & Ersoy-Meriçboyu, A. (2007). Production of glass-ceramics obtained from industrial wastes by means of controlled nucleation and crystallization. Chemical Engineering Journal, 132(1), 335-343. doi:https://doi.org/10.1016/j.cej.2007.01.029

Eymael, M. M. T., de Wijs, W., & Mahadew, D. (1994). The use of MSWI bottom ash in asphalt concrete. In (Vol. 60, pp. 851-862).

Farnam, Y., Bentz, D., Hampton, A., & Weiss, W. (2014). Acoustic Emission and Low Temperature Calorimetry Study of Freeze and Thaw Behavior in Cementitious Materials Exposed to NaCl Salt. Transportation Research Record, 2441. doi:10.3141/2441-11

Ferraris, M., Salvo, M., Ventrella, A., Buzzi, L., & Veglia, M. (2009). Use of vitrified MSWI bottom ashes for concrete production. Waste Management, 29(3), 1041-1047. doi:https://doi.org/10.1016/j.wasman.2008.07.014

Ferreira, C., Ribeiro, A., & Ottosen, L. (2003). Possible applications for municipal solid waste fly ash. Journal of Hazardous Materials, 96(2), 201-216. doi:https://doi.org/10.1016/S0304-3894(02)00201-7

Forteza, R., Far, M., Seguı́, C., & Cerdá, V. (2004). Characterization of bottom ash in municipal solid waste incinerators for its use in road base. Waste Management, 24(9), 899-909. doi:https://doi.org/10.1016/j.wasman.2004.07.004

Gao, J. M., Qian, C. X., Liu, H. F., Wang, B., & Li, L. (2005). ITZ microstructure of concrete containing GGBS. Cement and Concrete Research, 35(7), 1299-1304. doi:https://doi.org/10.1016/j.cemconres.2004.06.042

Ghouleh, Z., & Shao, Y. (2018). Turning municipal solid waste incineration into a cleaner cement production. Journal of Cleaner Production, 195, 268-279. doi:https://doi.org/10.1016/j.jclepro.2018.05.209

Giro-Paloma, J., Ribas-Manero, V., Maldonado-Alameda, A., Formosa, J., & Chimenos, J. M. (2017). Use of municipal solid waste incineration bottom ash and crop by-product for producing lightweight aggregate. IOP Conference Series: Materials Science and Engineering, 251, 012126. doi:10.1088/1757-899x/251/1/012126

Groves, G. W., Brough, A., Richardson, I. G., & Dobson, C. M. (1991). Progressive changes in the structure of hardened C3S cement pastes due to carbonation. Journal of the American Ceramic Society, 74(11), 2891-2896.

Guan, X., Liu, S., Feng, C., & Qiu, M. (2016). The hardening behavior of γ-C2S binder using accelerated carbonation. Construction and Building Materials, 114, 204-207. doi:https://doi.org/10.1016/j.conbuildmat.2016.03.208

Guo, X., Shi, H., Hu, W., & Wu, K. (2014). Durability and microstructure of CSA cement-based materials from MSWI fly ash. Cement and Concrete Composites, 46, 26-31. doi:https://doi.org/10.1016/j.cemconcomp.2013.10.015

Hoornweg, D. B.-T., Perinaz. (2012). What a Waste : A Global Review of Solid Waste Management. Urban development series;knowledge papers no. 15. World Bank, Washington, DC. © World Bank.

Jerga, J. (2004). Physico-mechanical properties of carbonated concrete. Construction and Building Materials, 18(9), 645-652. doi:https://doi.org/10.1016/j.conbuildmat.2004.04.029

Kikuchi, R. (2001). Recycling of municipal solid waste for cement production: pilot-scale test for transforming incineration ash of solid waste into cement clinker. Resources, Conservation and Recycling, 31(2), 137-147. doi:https://doi.org/10.1016/S0921- 3449(00)00077-X

Kim, Jinyoung, Boo Hyun Nam, Baig A. Al Muhit, Kazi M. Tasneem, & An, J. (2015). Effect of chemical treatment of MSWI bottom ash for its use in concrete. Magazine of Concrete Research, 67(4), 179-186. doi:https://doi.org/10.1680/macr.14.00170

Kim, J., An, J., Nam, B. H., & Mimmi, K. M. T. (2015). Investigation on the side effects of municipal solid waste incineration ashes when used as mineral addition in cement-based material (Vol. 17).

Kim, J., An, J., Nam, B. H., & Tasneem, K. M. (2016). Investigation on the side effects of municipal solid waste incineration ashes when used as mineral addition in cement-based material. Road Materials and Pavement Design, 17(2), 345-364. doi:10.1080/14680629.2015.1083463

Kim, T., & Olek, J. (2012). Effects of Sample Preparation and Interpretation of Thermogravimetric Curves on Calcium Hydroxide in Hydrated Pastes and Mortars. 2290(1), 10-18. doi:10.3141/2290-02

Klemm, W. A., & Berger, R. L. (1972). Accelerated curing of cementitious systems by carbon dioxide: Part I. Portland cement. Cement and Concrete Research, 2(5), 567-576. doi:https://doi.org/10.1016/0008-8846(72)90111-1

Lam, L., Wong, Y. L., & Poon, C. S. (2000). Degree of hydration and gel/space ratio of high- volume fly ash/cement systems. Cement and Concrete Research, 30(5), 747-756. doi:https://doi.org/10.1016/S0008-8846(00)00213-1

Lederer, J., Trinkel, V., & Fellner, J. (2017). Wide-scale utilization of MSWI fly ashes in cement production and its impact on average heavy metal contents in cements: The case of Austria. Waste Management, 60, 247-258. doi:https://doi.org/10.1016/j.wasman.2016.10.022

Leenders, P. (2000). MSW BOTTOM ASH - EXPERIENCES IN THE NETHERLANDS. In Sustainable Construction: Use of Incinerator Ash (pp. 227-234).

Li, X.-G., Lv, Y., Ma, B.-G., Chen, Q.-B., Yin, X.-B., & Jian, S.-W. (2012). Utilization of municipal solid waste incineration bottom ash in blended cement. Journal of Cleaner Production, 32, 96-100. doi:https://doi.org/10.1016/j.jclepro.2012.03.038

Li, X., Liu, Z., Lv, Y., Cai, L., Jiang, D., Jiang, W., & Jian, S. (2018). Utilization of municipal solid waste incineration bottom ash in autoclaved aerated concrete. Construction and Building Materials, 178, 175-182. doi:https://doi.org/10.1016/j.conbuildmat.2018.05.147

Li, Y., Hao, L., & Chen, X. (2016). Analysis of MSWI Bottom Ash Reused as Alternative Material for Cement Production. Procedia Environmental Sciences, 31, 549-553. doi:https://doi.org/10.1016/j.proenv.2016.02.084

Lin, K. L., Chang, W. C., & Lin, D. F. (2008). Pozzolanic characteristics of pulverized incinerator bottom ash slag. Construction and Building Materials, 22(3), 324-329. doi:https://doi.org/10.1016/j.conbuildmat.2006.08.012

Lo, T. Y., & Cui, H. Z. (2004). Effect of porous lightweight aggregate on strength of concrete. Materials Letters, 58(6), 916-919. doi:https://doi.org/10.1016/j.matlet.2003.07.036

Ludwig, H.-M., & Zhang, W. (2015). Research review of cement clinker chemistry. Cement and Concrete Research, 78, 24-37. doi:https://doi.org/10.1016/j.cemconres.2015.05.018

M.M. C. ALkemade , M. M. T. E., E. Mulder , W. de Wijsb. (1994). How to prevent expansion of MSWI bottom ash in road constructions? Environmental Aspects of Construction with Waste Materials, 60.

MacDonald, K. A., and Lukkarila, M.R. (2000). Freezing and thawing resistance of dry compacted segmental retaining wall units. Paper presented at the the Twenty-second International Conference on Cement Microscopy, Montre´al, Quebec, Canada.

Marchand, J., Hornain, H., Diamond, S., Pigeon, M., & Guiraud, H. (1996). The microstructure of dry concrete products. Cement and Concrete Research, 26(3), 427-438. doi:https://doi.org/10.1016/S0008-8846(96)85030-7

Mehta, P. K., & Monteiro, P. J. (2017). Concrete Microstructure, Properties and Materials. In.

Mehta, P. K., & Monteiro, P. J. M. (2006). Concrete microstructure, properties, and material: McGraw-Hill Professional.

Miller, S. A. (2018). Supplementary cementitious materials to mitigate greenhouse gas emissions from concrete: can there be too much of a good thing? Journal of Cleaner Production, 178, 587-598. doi:https://doi.org/10.1016/j.jclepro.2018.01.008

Mo, L., & Panesar, D. K. (2012). Effects of accelerated carbonation on the microstructure of Portland cement pastes containing reactive MgO. Cement and Concrete Research, 42(6), 769-777. doi:https://doi.org/10.1016/j.cemconres.2012.02.017

Monkman, S., & Shao, Y. (2006). Assessing the carbonation behavior of cementitious materials. Journal of Materials in Civil Engineering, 18(6), 768-776.

Monteiro, P. J. M., Miller, S. A., & Horvath, A. (2017). Towards sustainable concrete. Nature Materials, 16(7), 698-699. doi:10.1038/nmat4930

Mostafa, N. Y., & Brown, P. W. (2005). Heat of hydration of high reactive pozzolans in blended cements: Isothermal conduction calorimetry. Thermochimica Acta, 435(2), 162-167. doi:https://doi.org/10.1016/j.tca.2005.05.014

Müller, U., & Rübner, K. (2006). The microstructure of concrete made with municipal waste incinerator bottom ash as an aggregate component. Cement and Concrete Research, 36(8), 1434-1443. doi:https://doi.org/10.1016/j.cemconres.2006.03.023

Odler, I. (2000). Special inorganic cements. London ;: E & FN Spon.

Odler, I. (2003). Special Inorganic Cements: Taylor & Francis.

Ohsawa, S., Asaga, K., Goto, S., & Daimon, M. (1985). Quantitative determination of fly ash in the hydrated fly ash - CaSO4·2H2O  Ca(OH)2 system. Cement and Concrete Research, 15(2), 357-366. doi:https://doi.org/10.1016/0008-8846(85)90047-X

Omotoso, O. E., Ivey, D. G., & Mikula, R. (1995). Characterization of chromium doped tricalcium silicate using SEM/EDS, XRD and FTIR. Journal of Hazardous Materials, 42(1), 87-102. doi:https://doi.org/10.1016/0304-3894(95)00012-J

Paine, K., Dhir, R., & Doran, V. (2002). Incinerator Bottom Ash: Engineering and Environmental Properties as a Cement Bound Paving Material. International Journal of Pavement Engineering, 3(1), 43-52. doi:10.1080/10298430290023458

Paris, J. M., Roessler, J. G., Ferraro, C. C., DeFord, H. D., & Townsend, T. G. (2016). A review of waste products utilized as supplements to Portland cement in concrete. Journal of Cleaner Production, 121, 1-18. doi:https://doi.org/10.1016/j.jclepro.2016.02.013

Pecqueur, G., Crignon, C., & Quénée, B. (2001). Behaviour of cement-treated MSWI bottom ash. Waste Management, 21(3), 229-233. doi:https://doi.org/10.1016/S0956- 053X(00)00094-5

Pera, J., Coutaz, L., Ambroise, J., & Chababbet, M. (1997). Use of incinerator bottom ash in concrete. Cement and Concrete Research, 27(1), 1-5. doi:https://doi.org/10.1016/S0008- 8846(96)00193-7

Pigeon, M., & Pleau, R. (1995). Durability of concrete in cold climates (1st ed. ed.). London: E. & F.N. Spon.

Quenee, B., Li, G., Siwak, J. M., & Basuyau, V. (2000). The use of MSWI (Municipal solid waste incineration) bottom ash as aggregates in hydraulic concrete. In G. R. Woolley, J. J. J. M. Goumans, & P. J. Wainwright (Eds.), Waste Management Series (Vol. 1, pp. 422- 437): Elsevier.

Rostami, V., Shao, Y., & Boyd, A. J. (2011). Durability of concrete pipes subjected to combined steam and carbonation curing. Construction and Building Materials, 25(8), 3345-3355. doi:https://doi.org/10.1016/j.conbuildmat.2011.03.025

Rostami, V., Shao, Y., Boyd, A. J., & He, Z. (2012). Microstructure of cement paste subject to early carbonation curing. Cement and Concrete Research, 42(1), 186-193. doi:https://doi.org/10.1016/j.cemconres.2011.09.010

Saikia N, K. S., Kojima T. (2006). Production of Cement Clinkers from Municipal Solid Waste Incineration (MSWI) Fly Ash. Waste Management, 27, 1178-1189.

Saint-Jean, S. J., Jøns, E., Lundgaard, N., & Hansen, S. (2005). Chlorellestadite in the preheater system of cement kilns as an indicator of HCl formation. Cement and Concrete Research, 35(3), 431-437. doi:https://doi.org/10.1016/j.cemconres.2004.05.028

Saito, T., Sakai, E., Morioka, M., & Otsuki, N. (2010). Carbonation of γ-Ca2SiO4 and the Mechanism of Vaterite Formation (Vol. 8).

Shao, Y., & Lin, X. (2011). Early-Age Carbonation Curing of Concrete Using Recovered CO2. Concrete International, 33(9).

Sulistyana, Purwanto, Widoanindyawati, V., & Pratama, M. M. A. (2014). The Influence of Compression Applied during Production to the Compression Strength of Dry Concrete: An Experimental Study. Procedia Engineering, 95, 465-472. doi:https://doi.org/10.1016/j.proeng.2014.12.206

Suraneni, P., Jafari Azad, V., Isgor, O., & Weiss, W. (2016). Calcium oxychloride formation in pastes containing supplementary cementitious materials: Thoughts on the role of cement and supplementary cementitious materials reactivity (Vol. 1).

Tan, Z., Bernal, S. A., & Provis, J. L. (2017). Reproducible mini-slump test procedure for measuring the yield stress of cementitious pastes. Materials and Structures, 50(6), 235. doi:10.1617/s11527-017-1103-x

Tang, J., Ylmén, R., Petranikova, M., Ekberg, C., & Steenari, B.-M. (2018). Comparative study of the application of traditional and novel extractants for the separation of metals from MSWI fly ash leachates. Journal of Cleaner Production, 172, 143-154. doi:https://doi.org/10.1016/j.jclepro.2017.10.152

Taylor, H. F. W. (1997). Cement chemistry (2nd ed. ed.). London: T. Telford.

Todorovic, J., & Ecke, H. (2006). Treatment of MSWI Residues for Utilization as Secondary Construction Minerals: A Review of Methods. Minerals & Energy, 20(3/4), 45-59. doi:10.1080/14041040500504277

Tokyay, M. (2016a). Cement and Concrete Mineral Admixtures. Boca Raton: CRC Press.

Tokyay, M. (2016b). Cement and concrete mineral admixtures. In. doi:10.1201/b20093

Valenza, J. J., & Scherer, G. W. (2007). A review of salt scaling: I. Phenomenology. Cement and Concrete Research, 37(7), 1007-1021. doi:https://doi.org/10.1016/j.cemconres.2007.03.005

van Beurden, A. C., BV, R. M. F., Born, J. G., van Afvalverwerkers, V., Colnot, E. A., & Keegel, R. H. (1997). High Standard Upgrading and Utilization ofMSWI Bottom Ash Financial Aspects.

Van Gerven, T., Van Keer, E., Arickx, S., Jaspers, M., Wauters, G., & Vandecasteele, C. (2005). Carbonation of MSWI-bottom ash to decrease heavy metal leaching, in view of recycling. Waste Management, 25(3), 291-300. doi:https://doi.org/10.1016/j.wasman.2004.07.008

Vegas, I., Ibañez, J. A., San José, J. T., & Urzelai, A. (2008). Construction demolition wastes, Waelz slag and MSWI bottom ash: A comparative technical analysis as material for road construction. Waste Management, 28(3), 565-574. doi:https://doi.org/10.1016/j.wasman.2007.01.016

Wu, K., Shi, H., Schutter, G. D., Guo, X., & Ye, G. (2012). Preparation of alinite cement from municipal solid waste incineration fly ash. Cement and Concrete Composites, 34(3), 322- 327. doi:https://doi.org/10.1016/j.cemconcomp.2011.11.016

York, D. M. (2000). MSWI plants: sustainable qurries. In Sustainable Construction: Use of Incinerator Ash (pp. 259-265).

Young, J. F., Berger, R. L., & Breese, J. (1974). Accelerated Curing of Compacted Calcium

Silicate Mortars on Exposure to CO2. Journal of the American Ceramic Society, 57(9), 394-397. doi:doi:10.1111/j.1151-2916.1974.tb11420.x

Zhang, D., Cai, X., & Shao, Y. (2016). Carbonation Curing of Precast Fly Ash Concrete. 28(11), 04016127. doi:doi:10.1061/(ASCE)MT.1943-5533.0001649

Zhang, D., & Shao, Y. (2016). Effect of early carbonation curing on chloride penetration and weathering carbonation in concrete. Construction and Building Materials, 123(Supplement C), 516-526. doi:https://doi.org/10.1016/j.conbuildmat.2016.07.041

Ziaei-Nia, A., Tadayonfar, G.-R., & Eskandari-Naddaf, H. (2018). Effect of Air Entraining Admixture on Concrete under Temperature Changes in Freeze and Thaw Cycles. Materials Today: Proceedings, 5(2, Part 1), 6208-6216. doi:https://doi.org/10.1016/j.matpr.2017.12.229

CSA 8000 – 18, Cementitious Materials Compendium, CSA Group, 2018

Chapter 3. Use of municipal solid waste incineration bottom ash as supplementary

cementitious material in dry-cast concrete

Preface

This chapter evaluates the feasibility of partially replacing Portland cement in concrete with

bottom ash (BA) from municipal solid waste incineration (MSWI). The challenge with this ash

lies in its property to react expansively in alkaline conditions, leading to cracking when used in

conventional high-slump concrete. This expansive behavior was confirmed to be the result of the

dissolution of the ash’s aluminum metal content and consequent formation of hydrogen gas. The

aim of this study was to explore the suitability of BA as a cementitious additive in zero-slump dry-

cast concrete instead. The premise was that dry-cast could better diffuse the generated gas and

avoid internal pressure build-up. Results from isothermal calorimetry and thermal gravimetric

analysis (TGA) clearly correlate enhancements in early-age cement hydration and pozzolanic reactivity. Scanning electron microscope (SEM) images revealed voids channels and larger aggregation formation in the BA applied concrete paste. Dry-cast concrete containing 20% BA replacement of cement exhibited higher strengths than ordinary Portland cement (OPC) reference samples at every test age up to 90 days, with the ultimate strength of BA concrete being 18% higher than that of OPC concrete. The addition of BA also improved resistance to freeze-thaw damage. The study found that MSWI-BA can impart enhancements to dry-cast concrete, qualifying it as a potentially suitable supplementary cementitious material. Use of this otherwise landfilled ash as raw feedstock in concrete-making demonstrates a greener approach to building – scoring favorably in environmental performance for being relevant to resource conservation, landfill diversion, and waste-recycling.

3.1 Introduction

With the industrialization of nations and rise in population, a palpable and direct consequence has

been a dramatic increase in municipal solid waste (MSW) generation, which is anticipated to further intersify in coming years. According to a most recent publication on the topic by the World

Bank, global MSW production in 2012 was estimated at 1.3 billion tons (Bt), and is projected to reach 2.2 Bt by 2025 (Bhada-Tata, 2012). Landfilling is the most commonly used method for

MSW disposal. However, conventional landfilling entails the long-term occupation of vast

stretches of land and the possibility of presenting ecological risks from underground water

pollution, soil contamination, and/or methane and odor emissions (Saikia N, 2006). Alternatively,

MSW could be incinerated. This practice that has been gaining more attention in recent years and

mostly adopted by space-restricted urban regions. Incineration presents an effective way to reduce

the volume and mass of MSW, whilst generating heat energy from the pyrolysis of the waste’s

organic content. Proper recovery and use of the generated energy presents a more sustainable

substitute to burning virgin fossil fuels (Chandler et al., 1997b). While incineration reduces a

waste’s volume by 90% and mass by 70% (Lynn et al., 2017), it still leaves behind ash residues

that make up another disposal challenge by themselves. Bottom ash (BA) constitutes the majority

of the generated residues (80 – 90% by mass) (Lin et al., 2008). It is the subject of various

reclamation initiatives that aim to divert this residue from redundant land disposal.

On another note, concrete is the most widely used construction material in the world. Utilize BA

in concrete production seems attractive to manage large amount of residue. Meanwhile, energy

and carbon footprints can be considerably reduced with this waste alternative. Efforts to utilize BA

as an aggregate material have been attempted (Alkemade et al. (1994); Pecqueur et al. (2001);

Müller and Rübner (2006); Pera et al. (1997); and Kim et al. (2015)). Furthermore, since BA

mainly consists of amorphous silica, alumina, iron oxide, and calcium oxide – compositional traits similar to pozzolanic additives used in concrete – it has also been explored as a supplementary cementing material (SCM) (Bertolini et al., 2004; Kim et al., 2016). However, researchers have reported damaging impacts of expansion and cracking in their studies. Investigations identified the cause of expansion to be a reaction between aluminum and hydrating cement paste (Lynn et al.,

2017; Müller & Rübner, 2006; Pera et al., 1997). When aluminum metal remnants found in ash are exposed to such highly alkaline aqueous environments, they react to form hydrogen gas.

Failure to inhibit this deleterious mechanism will likely lead to the cracking and eventual failure of BA-containing concrete. Several treatment methods have been proposed by researchers to solve this problem. One method entails subjecting BA to long-term weathering/aging such that all metallic Al is transformed into a stable oxide. This would, in effect, halt the ash’s propensity to form gas in the event of alkali-activation (Chandler et al., 1997b). Another suggested method

involves a priming step of washing with a sodium hydroxide solution in order to fully react BA’s

aluminum content (Kim et al., 2015; Pera et al., 1997). Moreover, Bertolini et al. (Bertolini et al.,

2004) proposed wet grinding as an effective stabilization method that also weathers BA and

renders it stable, thus preventing cumulative buildup of internal stresses when BA is used in

concrete. Their study successfully demonstrated cement replacements of up to 30% with treated

BA and reported tangible performance improvements in the resulting concrete.

Dry-cast concrete covers a sizable segment of the construction market, and include products such

as concrete masonry units (CMU), paving blocks, retaining walls, pipes, hollow core slabs, etc.

Unlike ready-mix (or wet-cast) concrete, dry-cast concrete consists of a lower water-to-binder ratio

and cement content, yielding zero-slump when freshly cast. Therefore, mechanical compaction

and vibration are required when casting these products to ensure proper placement and

48 consolidation. The very low workability of dry-cast concrete allows demolding and dismantling of formworks in a very short time after compaction casting (Sulistyana et al., 2014). Due to the difference in mix design and manufacturing procedure from wet-cast concrete, dry-cast products exhibit a distinct pore distribution and microstructure. Compaction voids, consisting of large, irregular, and continuous voids, formed during the compaction process can be clearly observed

(MacDonald, 2000; Pigeon & Pleau, 1995). These are usually persistent and unavoidable even with subsequent hydration since dry-cast concrete does not have enough binder material to fill all the empty spaces between aggregates (Pigeon & Pleau, 1995). Research by Marchand et al.

(Marchand et al., 1996) revealed that dry-cast concrete had much higher intrudable porosity than wet-cast concrete. Figure 3. 1 illustrated a SEM image a typical compaction voids formed in an

OPC dry-cast concrete made in this study. Large pores could be observed, especially at locations around the aggregates.

The interconnected nature of the compaction voids in dry-cast concrete could potentially present a diffusion-related solution to the problem of using as-received BA in concrete. The connected pore structure could facilitate the outward diffusion and release of hydrogen gas during concrete setting, thereby avoiding internal stress buildup, and cracking. This would help make BA more readily usable and recyclable, without needing to employ cumbersome pre-treatment procedures.

To that end, this paper aimed to investigate the more practical direct-use of BA as a partial cement replacement in dry-cast concrete. Both paste compact and concrete samples were examined. A modified lime-pozzolan test was developed to evaluate the pozzolanic potential of BA. The BA-

OPC binding system was characterized by thermogravimetric analysis (TGA), isothermal calorimetry, scanning electron microscope (SEM), compressive strength, and freeze-thaw scaling resistance.

3.2 Experimental Program

3.2.1 Materials, mix proportions, sample preparation

The MSW incineration residue of bottom ash (BA) was collected from the Emerald Energy-from-

Waste incinerator facility located in Brampton, Ontario, Canada. The as-received BA was wet and

was dried at 200°C until no change in weight was observed. To qualify for use as an SCM, the dried ash was pulverized into a fine powder using a ring-and-puck mill. The final powder had an average particle size of 9.3 µm. Type GU ordinary Portland cement (from Cement Quebec) was used for this work, and granite as the aggregate material. Fly Ash (FA), classified Class CI by

CSA (Canadian Standards Association), from a coal-burning power plant was chosen as the commercial pozzolanic additive control. Compositional and mineralogical analyses of BA were carried out using X-Ray fluorescence (XRF) and quantitative X-Ray diffraction (QXRD), respectively.

Two types of specimens were tested in this work, paste and concrete. The mix proportions of the

two are presented in Table 3. 1. Cylindrical paste samples with diameters of 15 mm and 30 mm

heights were individually formed by compacting moistened binder powders (water-to-binder ratio

of 0.15) in a mold using a pressure of 3 MPa. Cement replacement with either BA or FA was

limited to 20% the weight of overall cementitious material. For the concrete specimens, a dry-cast

CMU (concrete masonry unit) mix design was adopted from a local producer. Fine and coarse

aggregate materials consisted of granite obtained from the Bauval CCM quarry in Montreal,

Canada. The concrete specimens were formed in molds by manual vibration compaction, yielding

slabs with final dimensions of 100 mm × 76 mm × 31 mm. A slab thickness of 31 mm was critical

in simulating the web and/or shell wall of a masonry block. For both paste and concrete specimens,

50 cement replacement with either BA or FA was limited to 20 % the weight of overall cementitious material in the mix. Curing took place in a moisture-controlled room with 100% relative humidity.

3.2.2 Laser Diffraction Particle Size Analysis

The particle size distribution of the raw materials (BA, FA, and OPC) were measure with the aid of a Horiba LA-920 particle size analyzer. The powder sample was dispersed in isopropanol with an ultra-sonic time of 1 minute.

3.2.3 Pozzolanic Reactivity Assessment

In order to examine the pozzolanic reactivity of BA, ASTM C593 testing protocol was carried out and compared to commercial FA, which served as the experimental control. The mixture proportions of test samples are given in Table 3. 2. As instructed by the standard, the amount of mixing water had to be justified such that the fresh mix (pozzolan material plus hydrated lime) achieved a flow of 65 to 75% (percentage of increase in average base diameter to the original base diameter). This equated to a water-to-binder ratio of 0.65 for OPC and 0.58 for BAOPC based on the flow table test according to ASTM C1437. To derive more relevancy to the scope of this study, a modified lime pozzolan test (based on ASTM C593) was additionally carried out in parallel. This test differed in the amount of water proportioned in preparing the test specimens, which were adjusted to have a similar consistency to zero-slump dry-cast concrete. This modification followed the study’s hypothesis of overcoming BA’s deleterious effect by facilitating gas diffusion in a more porous medium. The water-to-binder ratio for the modified lime-pozzolan test was therefore lowered to 0.35. In addition, the casting method was switched from “hand tamping” to vibration compaction. To understand and quantify the contribution of this modified method of casting to strength, an identical reference batch of specimens was prepared only instead of using a pozzolan,

51 non-reactive granite powder was used when making the specimens. All specimens were placed in a sealed zip-bags and placed in an oven for 7 days at 54°C to accelerate the pozzolanic reaction.

The specimens were supplemented with moisture by spraying water into the zip-bags twice a day.

After oven-heating was completed, the specimens were stored in a 100% relative humidity moisture-controlled room for 21 days for further curing.

3.2.4 Gas-release evaluation

Understanding that the aluminum content of BA could potentially release H2, a gas-over-water apparatus was constructed to determine the rate and volume of gas generated by BA when suspended in an alkaline solution. 100 g of BA was immersed in a saturated calcium hydroxide solution in a sealed flask allowed to bubble into an inverted water-filled graduated cylinder (Fig.

3. 2). The solution was periodically supplemented with calcium hydroxide powder to ensure a constant pH of 12.07 was maintained. The pH was measured using an Extech PH110 pH meter.

The gas generated in the reaction flask ends up displacing the water in the graduated cylinder. To confirm that H2 was the gas being generated by the reaction, an Agilent Gas Chromatography (GC) analyzer was employed, with argon serving as the carrier gas. Pure hydrogen and atmospheric air were used as references.

3.2.5 Mini-slump Test

One of the objectives of this study was to examine dry-cast concrete’s ability to overcome the expansive damage associated with BA’s addition to the mix. It was decided that a comparative correlation between the study’s concrete and paste specimens should also exist. To ensure that the

paste specimens had the same form and physical consistency of the fresh dry-cast concrete, a mini- slump test method (Tan et al., 2017) was adopted to determine the water-to-binder ratio that would yield the same slump in concrete. A miniature slump cone was fabricated for this test, which had

a downscaled Abrams cone geometry. As shown in Fig. 3. 3, the cone had a height of 57 mm with

tapered interior walls, where one end had a diameter of 19 mm and the other 38 mm. Three water- to-binder ratios were tested for the paste specimens, and these were 0.35, 0.25, and 0.15. For the test, the cone had to be placed on a flat, level, moist, and nonabsorbent surface. The freshly mixed paste was poured into the cone over two passes, with each layer tamped by rod 15 times. The cone was then carefully lifted and placed next to the slumped paste for height reference. A digital image was taken and the slump (the vertical difference between the top of the mold and the center of the top surface of the specimen) was measured.

3.2.6 Compressive Strength

Uniaxial compressive strength was measured for the lime-pozzolan, paste, and concrete specimens using an MTS-SINTECH 30/G Compressive Tester equipped with a 150 kN load cell, and according to ASTM C39. Values were calculated from the maximum load and dimensions of the loading area, measured using a digital Vernier caliper.

3.2.7 Thermal Analysis

A TAM Air 8-channel (TA Inc.) isothermal conduction calorimeter was used to measure the heat

of hydration at 20 °C. In order to mimic the paste scenario in concrete, 20% of cement was replaced

by FA and BA. And the water-to-binder ratio was chosen to be the same as that of the concrete

specimens (i.e. 0.35). Moreover, a Mettler Toledo Thermal TGA/DSC 1 analyzer was used to conduct thermogravimetric analysis (TGA). Paste samples were fully dried and pulverized, and approximately 5 – 10 mg of material was collected for each test. The temperature profile spanned

30-1000°C at a heating rate of 5°C/min, with nitrogen as the purging gas. The mass loss curves

(TG) along with their corresponding derivatives (DTG) were plotted. The weight percent of

calcium-hydroxide (CH) in the specimens was calculated using Eq. 1 (Kim & Olek, 2012), which

correlates the loss of bound water over the temperature range that corresponds to thermal

decomposition of CH,

. CH (%) = × × 100% . (1) 74 1 𝑀𝑀𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 18 0 𝑀𝑀𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖

where 74.1/18.0 is the molar mass ratio of CH to its molecularly-bound water; Mloss is the mass

lost within the CH decomposition temperature range; and Minitial is the initial mass of the sample.

3.2.8 Microstructure

The surface morphology of the primed BA powder and fracture surfaces of hardened paste and concrete samples were examined by Scanning Electron Microscope (SEM) using an FEI Inspect

F50 FE-SEM. Due to the material’s non-conductive nature, a 5nm Pt coating was applied to the surfaces being examined.

3.2.9 Freeze-thaw resistance

Freeze-thaw scaling test in accordance with ASTM C672 was carried out to appraise the extent of

resistance to frost damage by the different concrete specimens. Mature specimens aged 60 days

were fully submerged in a solution containing de-icing salt, sodium chloride. Each 100 mL of solution contained 4 g sodium chloride. The freeze-thaw cycles were repeated daily, with 16-18

hours of freezing and 6-8 hours of thawing. The scaled concrete pieces were collected and further dried in oven before measuring the mass every five cycles. Then, the final retained concrete mass

was recorded at the end of the test. The mass retained percentage from each five freeze-thaw cycle

was calculated based on the total mass of the concrete and the recorded mass loss.

3.3 Results and Discussion

3.3.1 Material Characteristics

The chemical compositions determined by XRF are presented in Table 3. 3. The oxides of silicon, aluminum, and iron are generally the most crucial for pozzolanic reactivity. The total percentage of the above-mentioned minerals in BA amounts to 49.31 %, which is slightly lower than the

ASTM C618 standard requirement for Class C fly ash (50%).

Table 3. 4 summarizes the mineral makeup of the BA residue. The analysis relates a total X-ray

insensitive amorphous content of 57.1 wt. %, with calcite as the second most abundant phase

amounting to 22.7 wt. %. The QXRD technique was unable to resolve the entire mineralogy of the

ash. Cross-referencing these results with the oxide compositions in Table 3. 3, the authors postulate

that the unidentified portion of the ash (or amorphous phase) seemingly consists of components

that are SiO2 and/or Al2O3-rich and exhibit crystallinities below the detection threshold. It is also

quite probable that minor metallic inclusions in the ash may also be reporting to this unidentified

portion. Whether these components contribute to pozzolanic and/or cementitious behaviors

remains to be examined by this study. Figure 3. 4 is an SEM image of the primed BA (a) and FA

powder. BA powder appears to consist of irregularly shaped particles with a smaller size

distribution range than the FA, which exhibits approximate spherical in shape. Figure 3. 5 shows

the particle size distribution for OPC, FA, and BA with an average particle size of 12.4 µm, 21.3

µm, and 9.3 µm, respectively. The smaller sized particles of the primed BA powder suggests an increased surface area of exposure, which can accelerate hydration if reactive, and increases the effective water-to-binder ratio in a blended cement, further promoting early-age hydration (Cyr et al., 2005; Deschner et al., 2012).

3.3.2 Pozzolanic Reactivity Assessment

The lime-pozzolan test was carried out using BA and FA as prescribed by standard ASTM C593.

However, as shown in Fig. 3. 6(a), the cube specimens of BA experienced significant cracking

upon setting. Multi-layered horizontal cracking was observed on all four sides. Moreover,

expansion in the form of a bulging protrusion of the top surface was also clearly discernible. The

FA specimen shown in Fig. 3. 6(b), on the other hand, was perfectly intact. The performance of

the two materials was more clearly differentiated by the compressive strength results shown in Fig.

3. 7(a), where the FA cubes recorded a strength of 9.1 MPa (ASTM C593 requires a minimum of

4.1 MPa), while the BA batch yielded no strength due to severe cracking. Evidently, the BA

specimens were physically compromised from the expected generation of H2 gas, which inflicted

a delamination-type damage. Therefore, the true potential of BA as a pozzolanic material could

not be assessed due to the overriding expansive effect caused by gas build-up within the specimens.

The cast-in-place nature of the standard lime-pozzolan test (ASTM C593) was clearly not suitable

for BA. The authors wanted to examine whether a dry-cast approach to casting would offer more

tolerance to gas generation, with an understanding that the consistency of dry-cast products may

better diffuse the generated H2 outward through its pore structure. To that end, a minor

modification was made to the lime-pozzolan test, where the water-to-binder ratio was reduced

from 0.65 to 0.35 to create a zero-slump fresh mix. Since this new mix-design necessitated

compaction forming, a baseline had to be established that would determine the contribution of

compaction alone to strength. To investigate that, a third batch of cubes was prepared, only using

inert granite powder (GP) instead of a pozzolanic material to simulate the physical effect of

compaction. The granite powder was pulverized to a similar particle size distribution to BA. As

shown in Fig. 3. 6(b), none of the specimen batches experienced cracking. The corresponding

compressive strength values for the FA, BA, and granite-powder specimens were 17.39 MPa, 7.62

MPa, and 1.40 MPa, respectively (Fig. 3. 7(b)). It is safe to say that any strength above the

compaction-baseline-strength of 1.40 MPa can be considered the result of pozzolanic reactivity.

Interestingly, the BA did display pozzolanic behavior after all, provided that the damage from gas

generation was effectively neutralized by using a zero-slump dry-cast approach. No cracking nor

expansive bulging was observed for the BA batch. This appears to support the proposition that

dry-cast is more efficient in providing internal paths for gas to escape, which acts as a relief to

internal stresses. While the pozzolanic strength from BA was markedly lower than the strength

obtained from commercial FA, the tangible contribution to strength by BA opens promising new

avenues for the beneficial recycling of this material in dry-cast concrete products.

3.3.3 Gas Release Evaluation

A gas-over-water apparatus was designed (Fig. 3. 2) to collect H2 gas generated. Two hours after

immersing BA into the saturated lime solution (pH = 12.07) a gas started bubbling inside the

inverted cylinder. A considerable amount of gas was collected over a monitoring period of 200

hours. In fact, Fig. 3. 8 displays the profile of gas volume released over time. No reaction seemed

to take place at first, a dormancy likely attributable to the passivation layer that naturally forms around metallic aluminum. This period of dormancy lasted for two hours presumably until the oxide layer was fully dissolved. After 170 hours, BA was fully reacted as observed from the clear

pleateau in the volume of gas released. Cumulatively, 76 ml of gas was collected from an original

amount of 100 g of BA. In other words, one gram of BA generated 0.76 ml of gas. The collected

gas was positively identified as hydrogen gas from gas chromatography (GC). The chromatogram

is shown in Fig. 3. 9, with the most prominent peak perfectly matching pure H2 gas retention time

8.2 min. The other two peaks matched the atmospheric air reference, indicating that the test sample had entrained some air. While a number of metals could be responsible for the cathodic process of generating H2, this study’s attention was mainly focused on aluminum since XRF results (Table 3.

3) identified this as the highest metal oxide, and was found consistent with previous works

(Bertolini et al., 2004; J. Kim et al., 2015; M.M. C. ALkemade 1994; Müller & Rübner, 2006; Pera

et al., 1997; Quenee et al., 2000; Vegas et al., 2008). The corresponding overall anodic/cathodic

reactions for generating H2 from an aluminum metal are presented in the following equations

(Bertolini et al., 2004),

Anodic reaction: + 2 + 4 + 3 (2) − + − 𝐴𝐴𝐴𝐴 𝐻𝐻2𝑂𝑂 → 𝐴𝐴𝐴𝐴𝑂𝑂2 𝐻𝐻 𝑒𝑒 Cathodic reaction: 2 + 2 + 2 (3) − − 𝐻𝐻2𝑂𝑂 𝑒𝑒 → 𝐻𝐻2 𝑂𝑂𝐻𝐻 3.3.4 Strength Performance of Paste

Following the dry-cast approach from the previos section, paste specimens were similarily

prepared to have a zero-slump consistency. The water-to-binder ratio was justified by carrying out

the mini-slump test described in Section 2.2. The results of the test are summarized in Table 3. 5.

A water-to-binder of 0.15 was chosen for mixing since that achieved zero-slump for all paste

batches. After mixing, the paste powders was formed into cylindrical compacts in a mold and a

load of 3 MPa.

Three batches of compacts were prepared, a control batch using 100% OPC, a BA batch using

20% BA and 80% OPC (BAOPC), and an FA batch using 20% commercial FA and 80% OPC

(FAOPC). The BAOPC paste specimens experienced no cracking or expansive damage up to an age of 90 days. The pore distribution in the paste, during and after setting, seemed to suffice in diffusing the gas outside of the specimen, and in so doing preventing any internal pressure buildup.

Fig. 3. 10 profiles the strength of OPC, FAOPC, and BAOPC pastes from 1 day to 90 days. All three batches were fully reacted by the 60-day mark, with a consistent plateau between 60 and 90 days. The ultimate strength at 90 days for BAOPC and FAOPC pastes were quite comparable, respectively recording 76.51 MPa and 78.97 MPa. At 20% cement replacement, these specimens achieved 88.3% and 85.5% the ultimate strength of straight OPC paste as per the specific experimental conditions adopted in this study. The lower values could be a result of having less overall cementitious content in the pastes, thus implying reduced generation of hydration products.

Quiet interestingly, the BAOPC specimens displayed much smaller deviations from the reference strength of OPC during early curing. It was only at the 60-day mark that FAOPC overtook BAOPC in terms of strength. What this seems to suggest is that BA played a more active role during early cement hydration displaying features similar to the function of common hydration accelerators. In comparison, Class CI fly ash remained dormant until its contribution to strength was only observed by the 60-day mark. This was consistent with previous works that similarly showed FA’s major pozzolanic reaction take place after 28 days of hydration (Lam et al., 2000; Ohsawa et al., 1985).

Compared to this commonly used pozzolanic additive, incineration-derived BA performed exceptionally well, yielding markedly higher early-age strength than the FAOPC specimens and comparable ultimate strength. According to the testing protocols of this study, BA evidently displayed features that are both cementitious and, arguably, pozzolanic. At 20% cement

replacement, dry-cast BAOPC specimens displayed no cracking and ultimate strength values

virtually identical to the benchmark FAOPC specimens. A foreseeable advantage of using BA may lie in its demonstrated ability to increase the rate of strength development, where the BAOPC specimens achieved 82.7% of their ultimate strength at 28 days, compared to 57.4% for FAOPC

at the same age.

3.3.5 Thermogravimetric analysis (TGA)

A typical TGA curve and its corresponding derivative function (DTG) are presented in Fig. 3. 11

for BAOPC. The analysis was repeated for all paste specimens aged 1 and 28 days. Mass loss

experienced between 30°C and 105°C was attributed to the vaporization of unbound water, and

losses between 105°C and 470°C associated to the decomposition of chemically bound water.

Interpretations of graphical features in the TGA-DTG curves helped further divide the latter range

into two distinct phase-specific regions: 105°C to 350°C to correlate to the decomposition of the

hydration product C-S-H ; and 350°C to 470°C to correspond to the decomposition of calcium

hydroxide (CH). The decomposition of CH results in the release of water, leaving behind calcium

oxide (CaO). The CH content of a specimen was therefore back calculated from the respective

water loss experienced though molecular conversion and expressed as a weight percent. The final

temperature range between 470°C and 950°C was linked to the decarbonation of calcium carbonate

and associated mass loss from the release of carbon dioxide. Table 3. 6 presents a numerical

rendition of the mass losses experienced over the identified temperatures ranges, and associated

CH content calculated for each specimen. After one day of hydration, BAOPC experienced the

highest mass loss indicative of C-S-H decomposition and, hence, the highest content of binding

hydration product. Interestingly, BAOPC also contained the lowest CH content (5.82%) compared

to OPC (7.15%) and FAOPC (6.51%), an anticipated outcome resulting from the consumption of

CH by a pozzolanic-type activation and/or from the reaction with active aluminum found in the raw BA. BAOPC also experienced the largest loss in mass over the 470 – 950°C range seemingly due to the high content of carbonates in the raw BA (Table 3. 4). The same exact trend was observed for BAOPC at the age of 28 days but slightly more amplified, with the highest C-S-H content (4.21%) out of the three samples and the lowest CH content (10.35%) after FAOPC

(10.58%) and OPC (12.97%). FAOPC expectedly recorded the lowest C-S-H content within the course of 28 days, which was consistent with observations from compressive strength measurements.

TGA results confirmed BA’s active role as supplementing additive to cement paste, with observable contributions to early hydration and strength, consistently reporting the highest amount of C-S-H up to the monitored period of 28 days.

3.3.6 Isothermal calorimetry

The partial addition of BA to cement is anticipated to affect the heat of hydration in four possible ways, inducing any one or all of a heterogeneous nucleation effect, pozzolanic activation, redox reaction involving metallic aluminum, and dilution effect. The former three associate an increase in heat output. The dilution effect on the other hand prompts a decrease in heat output primarily as result of reducing the content of the hydraulically-active C3S (tri-calcium silicate, the main cementitious component of OPC) (Mostafa & Brown, 2005).

Figure 3. 12 graphically depicts the rate of heat evolution during the hydration of pastes made with

100% OPC and ones with 20% substitutions by FA and BA additives. During the acceleratory period, the heat generation rate for FAOPC was markedly lower than OPC due to the aforementioned dilution effect. However, this was not the case for BAOPC, who’s curve closely

61 shadowed that of the pure cement reference (OPC), even at a 20% dilution factor. This unexpected exothermic behavior of BAOPC could not have been attributed to the redox reaction involving aluminum since not enough CH would have formed at this point to make the pore solution sufficiently alkaline, nor would the passivation film surrounding metallic Al be extensively dissolved this early into hydration. Moreover, considering that the pozzolanic reaction also needs a high CH concentration, this increased heat generation was very likely attributed to a heterogeneous nucleation effect. The addition of BA provided effective nucleation sites for C-S-

H to form, and therefore, increased the heat output rate during the acceleratory period (Choudhary et al., 2016; Mostafa & Brown, 2005). Relative to the principal peak of OPC, the peaks for the

FAOPC and BAOPC curves measured 77.0% and 94.3%, respectively. The additives seemed to incur a shift in the principal peak and a faintly observable shoulder before the deceleration portion of the curves. The lower amounts of hydraulically-active components in FAOPC and BAOPC likely lacked the heat signature of OPC, incurring a delay in the critical heat buildup that defines the curve’s principal peak. The peak broadening effect clearly observed for FAOPC was mainly due to additional heat evolution from the pozzolanic reaction of FA. At this point in time, sufficient concentrations of CH would have been formed as a result of cement hydration. For BAOPC, the heat signature beyond the principal peak is likely a combination of redox and pozzolanic reactions, contributing to a more emphasized “shoulder” feature.

3.3.7 Scanning electron microscope (SEM)

Both polished and fractured cross-sections of OPC and BAOPC paste compacts at an age of 28 days are shown in the SEM micrographs (SE) of Figure 3. 13. Polished surface of BAOPC (Fig.

3. 13(a)) and OPC (Fig. 3. 13(b)) generally exhibited similar morphologies except that BAOPC had a more uniformly dispersed microstructure with larger aggregations than OPC. Larger grain

sizes are usually the result of more profound or prolonged crystal growth. This could be explained

as an accelerated cement hydration effect and/or a doping effect induced by BA that promotes

faster C-S-H generation and grain growth (Omotoso et al., 1995). As observed, the outcome is a

microstructure that is more efficiently spatially-filled with a surface morphology that appears to

be more tightly emulsified than that of the fine-grained OPC. The notion of having a higher overall

volume of C-S-H for BAOPC is also supported by findings from TGA (Table 3. 6), where after 28

days of hydration the BAOPC paste reported a mass loss of 4.212% over the C-S-H -specific

temperature range of 105-350°C, compared to 3.827% for the OPC paste.

The fracture surfaces of the two pastes were similarly examined (Figure 3. 14 (a)&(b)).

Microscopic air voids with ranging diameter sizes can be seen randomly dispersed throughout the

revealed microstructures of BAOPC. The voids are round and presumably represent the cross-

sections of hollow channels that form during initial setting of as a result of H2 gas permeating

through the soft paste before it sufficiently hardened. The channels are thought to pour into a larger

macro-pore network that acts as the main pressure-relief mechanism responsible for dispersing the

generated H2 gas outside of the paste matrix. Like in dry-cast concrete, this pore network feature

of dry-cast paste is what effectively eliminates cracking and expansion seen in wetter mixes.

3.3.8 Concrete compressive strength

Since BA was originally intended for use in dry cast applications, compressive strength results of

concrete slab specimens served as the primary indicator to appraise the practical suitability of the

projected use. The slabs were made from a zero-slump mix design provided by a local CMU manufacturer. At a cement substitution rate of 20 wt.% by BA, no cracking was observed for any

of the slab specimens for all hydration ages. Strength results for the different concrete mixes are

summarized in Fig. 3. 15, up to a hydration age of 90 days. Surprisingly, the BAOPC batch showed

remarkable performance at all ages, indicating a measurable enhancement in strength. As expected,

and due to the latent nature of typical pozzolanic activation, FAOPC yielded the lowest strength at one-day, which averaged 12.35 MPa. In contrast, BAOPC achieved the highest strength of 15.04

MPa, unexpectedly higher than OPC’s 13.92 MPa. Signs of pozzolanic reactivity were observed at the later ages of hydration for both the blended batches, where FAOPC and BAOPC recorded strengths that exceeded OPC at 28, 60, and 90 days. The FAOPC batch displayed the highest differential strength gain, where it caught up and slightly overtook BAOPC by the 90-day mark.

The values for BAOPC and OPC plateaud after 60 days of hydration, indicating that the batches reached their ultimate natural strengths according to this study’s experimental conditions.

Comparatively, however, the strength of the BAOPC batch was higher than the OPC reference at all tested ages, with an ultimate strength that is 18.4% higher than the OPC commercial benchmark.

This clearly suggests that BA associates an improvement in overall the compressive strength of dry-cast concrete during the early and late stages of curing. This recorded benefit may possibly attribute to two main reasons. First, BA seemingly contained components that lent cementitious and pozzolanic-like reactivity, thus promoting increased C-S-H generation and therefore strength.

Another noteworthy observation was the coarser grain structure observed in Figure 3. 13 (a), which may have been the result of C-S-H crystal growth induced by a sort of doping component in the

BA (Omotoso et al., 1995). Another main reason likely involves a reduced CH content in the paste resulting from the aforementioned pozzolanic reaction and additionally from the chemical redox engagement with active aluminum to generate hydrogen gas. CH is not generally known to be a major contributor to strength; in fact, some studies specifically link the reduced presence of CH crystals in the interfacial transition zone (ITZ) to improved concrete strength (Gao et al., 2005;

Mehta & Monteiro, 2006).

3.3.9 Freeze-thaw scaling resistance

The pozzolanic reactivity and any associated resilience of the BA additive was also indirectly

appraised by means of a destructive freeze-thaw scaling resistance test. Figure 3. 16 is a graphical representation of the test with the retained concrete mass expressed in percentage and plotted against the number of freeze-thaw cycles. Figure 3. 17 shows images of a typical concrete

specimen prior to testing and after experiencing 30 cycles. No significant scaling occurred during the first 10 cycles for all specimens. Only after this point did the damage begin to gradually accrue.

By 30 consecutive freeze-thaw cycles, the average mass percentages retained by the OPC, FAOPC, and BAOPC concrete slabs were 42.6%, 49.46%, and 68.33%, respectively. The OPC reference batch experienced the most severe deterioration, losing more than half its original weight. The

FAOPC batch performed slightly better than OPC; while BAOPC was the best of the three. The improved resistance of BAOPC could likely be attributed to the coarsened morphology, increased

C-S-H content, and/or the result of damage dissipation from the channel pathways generated by

the hydrogen gas during initial setting, similar to the function of commercial air entraining admixtures (AEA) (Ziaei-Nia et al., 2018).

3.4 Conclusion

This study successfully demonstrated the feasibility of using pulverized MSWI BA as a supplementing cement replacement in dry-cast paste and concrete. The dried and pulverized BA can be directly used without having to employ laborious treatment steps that could incur secondary environmental pollutants. BA blended mortars undergoing the standardized ASTM Pozzolan test suffered a great deal of expansion and cracking, confirming BA’s instability under alkaline

65 conditions. This study proposed adopting a zero-slump mix design approach to alternatively assess the suitability of BA in dry-cast concrete products. Consequently, the testing protocols were modified to incorporate the dry-cast approach for all paste and concrete specimens used in this study. With the low water-to-binder ratio and vibration-compaction casting method, deleterious expansion and cracking were effectively mitigated, and even avoided. This allowed evaluating BA more objectively as a potential cement additive in building applications. The main conclusions drawn from this study are:

1. The BA residue used in this study was chemically unstable when exposed to alkaline

conditions. The metallic aluminum component commonly found in this type of ash material

was confirmed as the culprit behind the generation of hydrogen gas. One gram of BA was

found to generate 0.76 ml of hydrogen gas when experimentally immersed in a Ca(OH)2

saturated solution having a pH of 12.07.

2. The damage from gas-induced expansion and cracking of BA-containing cement

specimens was successfully prevented by modifying the mix design to a zero-slump dry-

cast paste and concrete specimens. The final pore network of those specimens, comprising

macro compaction voids and microscopic channels in the paste, seemed to serve as a

pressure-relief mechanism from hydrogen gas generated within the specimens.

3. As a supplementing additive, BA was found to enhance early-age hydration and also

performed comparably well to commercial Class CI fly ash in the later stages of hydration.

This was particularly the case for the intended real-life use in dry-cast concrete, with BA-

supplemented concrete yielding an ultimate 90-day strength that is 18.4% higher than the

benchmark OPC concrete batch.

4. From SEM, a more continuous microstructure and larger aggregations were observed in 66

the BA-supplemented paste sample in comparison to the OPC reference. Observations

strongly suggest that BA likely contained components that act as dopants that accelerate

cement hydration and promote crystal growth.

5. The perforations in the BA-supplemented paste, created from the permeation of hydrogen

gas, didn’t seem to compromise the freeze-thaw scaling resistivity of the concrete. On the

contrary, resistance was improved. They may have been attributed to any or all of a reduced

CH content, increased C-S-H gel formation, and AEA-like effect from the modified void

network system.

6. The specific use of BA as a supplementing additive in dry-cast concrete products holds

both environmental and economic merits.

References

Alkemade, M., Eymael, M., Mulder, E., & Wijs, W. (1994). How to Prevent Expanston of MSWI Bittom Ash in Road Constructions? In J. J. J. M. Goumans, H. A. van der Sloot, & T. G. Aalbers (Eds.), Studies in Environmental Science (Vol. 60, pp. 863-876): Elsevier.

Bhada-Tata, P. H., Daniel A. (2012). What a waste: A Gllobal Review of Solid Waste Management. Urban development series knowledge papers, 15.

Chandler, A. J., Eighmy, T. T., Hartlén, J., Hjelmar, O., Kosson, D. S., Sawell, S. E., . . . Vehlow, J. (1997). Municipal Solid Waste Incinerator Residues

Elsevier.

Choudhary, A., Shah, V., & Bishnoi, S. (2016). Effect of low cost fillers on cement hydration. Construction and Building Materials, 124, 533-543. doi:https://doi.org/10.1016/j.conbuildmat.2016.07.088

Kim, Jinyoung, Jinwoo An, Nam, B. H., & Tasneem, K. M. (2016). Investigation on the side effects of municipal solid waste incineration ashes when used as mineral addition in cement-based material. Road Materials and Pavement Design, 17(2), 345-364. doi:10.1080/14680629.2015.1083463

Kim, J., An, J., Nam, B. H., & Mimmi, K. M. T. (2015). Investigation on the side effects of municipal solid waste incineration ashes when used as mineral addition in cement-based material (Vol. 17).

Kim, T., & Olek, J. (2012). Effects of Sample Preparation and Interpretation of Thermogravimetric Curves on Calcium Hydroxide in Hydrated Pastes and Mortars. 2290(1), 10-18. doi:10.3141/2290-02

M.M. C. ALkemade , M. M. T. E., E. Mulder , W. de Wijsb. (1994). HOW TO PREVENT EXPANSION OF MSWI BOTTOM ASH IN ROAD CONSTRUCTIONS ? Environmental Aspects of Construction with Waste Materials, 60.

P. Kumar Mehta, P. J. M. M. (2006). Concrete microstructure, properties, and material: McGraw-Hill Professional.

Pecqueur, G., Crignon, C., & Quénée, B. (2001). Behaviour of cement-treated MSWI bottom ash. Waste Management, 21(3), 229-233. doi:https://doi.org/10.1016/S0956- 053X(00)00094-5

Pera, J., Coutaz, L., Ambroise, J., & Chababbet, M. (1997). Use of incinerator bottom ash in concrete. Cement and Concrete Research, 27(1), 1-5. doi:https://doi.org/10.1016/S0008- 8846(96)00193-7

Pigeon, M., & Pleau, R. (1995). Durability of concrete in cold climates (1st ed. ed.). London: E. & F.N. Spon.

Saikia N, K. S., Kojima T. (2006). Production of Cement Clinkers from Municipal Solid Waste Incineration (MSWI) Fly Ash. Waste Management, 27, 1178-1189.

Standard References

ASTM C593-06(2011), Standard Specification for Fly Ash and Other Pozzolans for Use With Lime for Soil Stabilization, ASTM International, West Conshohocken, PA, 2011, www.astm.org

ASTM C1437-15, Standard Test Method for Flow of Hydraulic Cement Mortar, ASTM International, West Conshohocken, PA, 2015, www.astm.org

ASTM C39 / C39M-18, Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens, ASTM International, West Conshohocken, PA, 2018, www.astm.org

ASTM C672 / C672M-12, Standard Test Method for Scaling Resistance of Concrete Surfaces Exposed to Deicing Chemicals, ASTM International, West Conshohocken, PA, 2012, www.astm.org

ASTM C618-19, Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete, ASTM International, West Conshohocken, PA, 2019, www.astm.org

Table 3. 1 :Mixture Proportions of paste compacts and concrete

Paste Concrete

Mixture component OPC FAOPC BAOPC OPC FAOPC BAOPC

Cement [wt%] 87 69.6 69.6 9.7 7.76 7.76

Fly ash [wt%] - 17.4 - - 1.94 -

Bottom ash [wt%] - - 17.4 - - 1.94

Water [wt%] 13 13 13 3.4 3.4 3.4

Coarse aggregate [wt%] - - - 28.9 28.9 28.9

Fine aggregate [wt%] - - - 58 58 58

Water/ (cement + additive) 0.15 0.15 0.15 0.35 0.35 0.35

Table 3. 2 : Mixture proportions of pozzolanic reactivity assessment

ASTM C593 Modified test

Mixture component FA BA GP FA BA

Hydrated lime [wt%] 7.59 7.71 8.15 8.15 8.15

Fly ash [wt%] 15.18 - - 16.3 -

Bottom ash [wt%] - 15.43 - - 16.3

Granite powder [wt%] - - 16.3 - -

Graded standard sand [wt%] 62.42 63.43 67 67 67

Water [wt%] 14.8 13.42 8.56 8.56 8.56

Water/ (Hydrated lime + additive) 0.65 0.58 28.9 28.9 28.9

Table 3. 3: Chemical compositions (XRF) of BA, FA and OPC

Oxides BA FA OPC

CaO 22.91 10.93 62.01

SiO2 28.64 54.98 22.67

Al2O3 14.18 23.81 5.62

Fe2O3 (T) 6.49 3.7 4.33

MnO 0.17 0.04 0.08

MgO 2.62 1.07 2.6

Na2O 2.63 2.68 0.14

K2O 1.12 0.69 0.57

TiO2 2.88 0.7 0.15

P2O5 2.34 0.11 0.21

LOI 14.87 1.28 1.62

Table 3. 4: Quantitative X-ray Diffraction (QXRD) analysis for BA

Mineral Formula BA

Calcite CaCO3 22.7

Quartz SiO2 4.7

Plagioclase Ca(Al2Si2O8) 5.1

Rutile TiO2 2.2

Halite NaCl 2.4

Anhydrite CaSO4 4.2

Hematite Fe2O3 1.6

Amorphous - 57.1

Table 3. 5: Miniature paste slump test

Batch water/binder ratio [%] Slump [mm]

0.35 23.30 OPC 0.25 12.53

0.15 0.00

0.35 24.74 FAOPC 0.25 10.20

0.15 0.00

0.35 24.49 BAOPC 0.25 7.23

0.15 0.00

Table 3. 6: Percentage TGA mass loss and CH content (wt%)

Mix Age (days) 105°C to 350°C 350°C to 470°C 470°C to 950°C CH Content

1 2.72 1.74 3.30 7.14 OPC 28 3.83 3.15 3.42 12.97

1 2.57 1.58 3.06 6.50 FAOPC 28 3.38 1.87 3.01 7.67

1 2.76 1.41 5.10 5.81 BAOPC 28 4.21 2.52 6.17 10.34

Figure 3. 1: Typical compaction voids in dry-cast concrete (OPC batch at 90 days)

Figure 3. 2: Gas over water set-up

Figure 3. 3: Miniature slump test

Figure 3. 4: SEM image of (a) primed BA and (b) Class CI fly ash

8 7 6 BA

5 Cement 4 FLY ASH 3 Percentage [%] 2 1 0 0 50 100 150 200 250 Diameter (µm)

Figure 3. 5: Laser particle size analysis

Figure 3. 6: Lime-pozzolan test specimens; (a): Standard ASTM C593 (water/(hydrated lime + additive) = 65%); (b): Modified Lime-pozzolan (water/(hydrated lime + additive) = 35%)

10 20 9.1 17.39 8 16

6 12 7.62 4 8

2 4

ompressive strength [MPa] strength ompressive 1.4 Compressive strength [MPa] strength Compressive C 0 0 FA BA Granite FA BA a b

Figure 3. 7: Lime-pozzolan compressive strength (28 days samples); (a): strength from standard ASTM C593 test; (b): strength from modified lime-pozzolan test

80 70 60 50 40 30

Gas Volume [mL] Volume Gas 20 10 0 0 50 100 150 200 Time [hours]

Figure 3. 8: Cumulative gas releasing from BA (100 gram) in alkaline solution (Ca(OH)2 solution with pH value of 12.07)

6000

4000 Air

Pure Hydrogen 2000 Test Sample 0 Response -2000

-4000

-6000 7.5 8 8.5 9 9.5 10

Retention Time [min] Figure 3. 9: Gas chromatography for the gas released from BA

100 89.43 80 78.97 76.51

40 OPC FAOPC 20 BAOPC Compressive strength [Mpa] strength Compressive

0 1 day 28 days 60 days 90 days Hydration age

Figure 3. 10: Compressive strength of paste compacts

6.9 0 6.8 -0.002 6.7 -0.004 6.6 -0.006

6.5 TGA -0.008 6.4 -0.01 DTG

TGA [mg] 6.3 -0.012 DTG [mg/min] DTG 6.2 -0.014 6.1 -0.016 6 -0.018 0 200 400 600 800 1000 Temperature [°C] Figure 3. 11: TGA and DTG curve of BAOPC batch

2.5

1.5 OPC 1 BAOPC FAOPC

Rate of Heat Generation [mW/g] 0.5

0 0 10 20 30 40 50 60 70 Time [hours] Figure 3. 12: Isothermal calorimetry curves

Figure 3. 13: SEM Images for polished surface of paste compacts at age of 28 days; (a): BAOPC; (b) OPC

Figure 3. 14: SEM Images for fracture surface of paste compacts at age of 28 days; (a): BAOPC; (b) OPC

35 32.79 32.02 30 27.04 25

20 OPC 15 FAOPC BAOPC 10 Compressive strength [MPa] strength Compressive 5

0 1 day 28 days 60 days 90 days Hydration age

Figure 3. 15: Concrete compressive strength

100 90 80 70 60 50 40 30

Mass Percentage[%] OPC 20 FAOPC 10 BAOPC 0 0 5 10 15 20 25 30 Number of Cycles

Figure 3. 16: Concrete freeze-thaw scaling test

Figure 3. 17: Concrete subjected to 30 freeze-thaw cycles; (a): Typical concrete before test; (b): Concrete after test

Chapter 4. Performance of Eco-concrete Made from Waste-derived Eco-cement

Preface

Three types of Municipal solid waste incineration (MSWI) residues are generated. They are bottom ash (BA), boiler ash (BLA) and air pollution control (APC) lime. Although BA represents the majority (90%) of the residues, FA and APC lime also pose disposal challenges due to leachable heavy metals, chloride content and toxic organic contaminants (e.g. furans, dioxins). In this chapter, an MSWI waste-derived eco-cement was developed using more than 93% of all types of

MSWI by-products which generated from different steps during the incineration process as raw clinkering materials. Moreover, this newly synthesized eco-cement can be activated by carbon dioxide and gain early strength rapidly while permanently sequestrating CO2. This eco-cement

also exhibited latent hydraulic property in the long term. The feasibility to fully replace ordinary

Portland cement (OPC) cement in concrete products that made under both lab and pilot-scale was

further investigated. It was found that a comparable mechanical compressive strength of eco- concrete was achieved with OPC references. Leaching test confirmed that there is no risk of heavy metal and chloride leaching from the Eco-concrete according to Canadian and U.S. EPA regulations. In addition, the freeze-thaw scaling resistivity was improved for concrete with eco- cement compared to that of conventional hydration OPC reference. Linear shrinkage test carried out in lab showed that eco-concrete exhibited the lowest dimensional change. A pilot-scale Eco- concrete production was demonstrated, and the produced full-size CMUs passed all four physical requirements defined by Canadian and U.S. standards, including compressive strength, density, absorption, and linear shrinkage. It is conclusive that the eco-cement synthesized in this research is feasible to be an economically and environmentally friendly new building material.

4.1 Introduction

Due to the rapid population growth and industrialization, the generation of Municipal Solid Waste

(MSW) was 1.3 billion tonnes in the year of 2012 worldwide, and the number was expected to

increase to 2.2 billion tonnes by 2025 (Bhada-Tata, 2012). As the widest adopted disposal method

(Bhada-Tata, 2012), landfilling is facing multiple challenges including limit dumping area, surrounding soil and groundwater contamination potential, odor emission and methane release

(Dou et al., 2017; Makarichi et al., 2018; Muangrat, 2013). Alternatively, incineration treatment offers a means of managing MSW, and now it is employed by many countries because of the high efficiency in waste volume reduction, considerable waste energy recovery, and maturity in technology (Chandler et al., 1997a; Dou et al., 2017). However, it is not the final solution, substantial amounts of unstable residues are generated during this treatment, which can be divided into bottom ash (BA), Boiler ash (BLA), and air pollution control (APC) lime. Ashes collected downstream from the air treatment process (BLA and APC lime) contain leachable heavy metals, chloride content and toxic organic contaminants (Erol et al., 2007; Ferreira et al., 2003; Li et al.,

2012), and thus, stabilization and/or solidification is required before final disposal.

On the other side, these by-products contain a certain amount of lime, silica, and alumina, and could be potential raw materials in cement production (Lederer et al., 2017). Researches have been done to utilize them in this field (Ampadu & Torii, 2001; Ferreira et al., 2003; Ghouleh & Shao,

2018; Guo et al., 2014; Kikuchi, 2001; Lederer et al., 2017; Li et al., 2018; Li et al., 2016; Wu et

al., 2012). Ampadu and Torii (2001) accessed a cement made by 50% of MSWI ashes with similar

manufacture process with OPC cement. Guo et al. (2014) analyzed the durability and

microstructure of a calcium sulphoaluminate (CSA) cement sintered from 30-40% of boiler ash as

raw material at 1250°C. Alinite cement was generated by the effort of Wu et al. (2012) under 1200

°C for 2 hours with 30% fly ash as raw feed. Ghouleh and Shao (2018) demonstrated a sustainable

binder made from 85.5% of MSWI ashes. This binder was clinkered at 1000°C and it consists of

two major CO2 reactive minerals, chlorellestadite (CE) and belite (C2S). Under carbonation curing,

this new binding material could permanently sequestrate greenhouse gas CO2 and gain mechanical

strength rapidly at the same time. Moreover, the MSW incinerators usually run at 800 - 1000°C,

which means the whole treating process can be done inside the facility without extra energy input.

Carbonation curing is an accelerated curing process by exposing the freshly cast concrete to CO2

gas at an early age. Different from weathering carbonation that causing damage to cement matrix, in OPC cement carbonation curing, strength develops rapidly during the carbonation process due

to the generation of C-S-H and CaCO3 from the extensive reaction between CO2 gas and calcium silicates (C3S and C2S), and the reactions are shown in Eqs. 1 to 2 (Young et al., 1974).

Precipitation of calcium dioxide crystals leads to a lower permeability and the durability

performance of concrete is therefore enhanced (Rostami et al., 2012). Short term carbonation

cannot completely consume all the calcium silicate in the concrete. Therefore, strength can further develop in the later age, the effect links to cement subsequent hydration (Klemm & Berger, 1972).

3 + (3 ) + + (3 ) (2.1)

𝐶𝐶𝐶𝐶𝐶𝐶 ∙ 𝑆𝑆𝑆𝑆𝑂𝑂2 − 𝑥𝑥 𝐶𝐶𝑂𝑂2 𝑦𝑦𝐻𝐻2𝑂𝑂 → 𝑥𝑥𝑥𝑥𝑥𝑥𝑥𝑥 ∙ 𝑆𝑆𝑆𝑆𝑂𝑂2 ∙ 𝑧𝑧𝐻𝐻2𝑂𝑂 − 𝑥𝑥 𝐶𝐶𝐶𝐶𝐶𝐶𝑂𝑂3 The purpose of this paper is to evaluate the feasibility of using eco-cement, which was synthesized

from MSWI residues, to make concrete products under lab and pilot-scale. Eco-cement clinker’s raw materials that proposed by Ghouleh and Shao (2018) were modified, and a novel eco-cement

with latent hydraulic behavior was synthesized with all types of MSWI residues involved, namely, bottom ash, boiler ash and APC lime. A small portion (6.2%) of calcium hydroxide was served as

the only extra additive in the clinker raw feeds. Clinkers quality was first verified through paste

compacts’ mineral compositions, mechanical strength, and degree of carbonation. Then, the eco-

cement binding performance in concrete was evaluated on both of laboratory-scale (concrete slabs)

and pilot-scale (full-size concrete masonry units) through compressive strength, leaching

performance, freeze-thaw scaling resistance, and linear shrinkage.

4.2 Materials and Methods

4.2.1 Raw Materials

Municipal Solid Waste Incineration (MSWI) residues, named bottom ash (BA); boiler ash (BLA);

and air pollution control (APC) lime, were obtained from an incinerator located in Ontario,

Canada. The bottom ash came from the incineration platform is mainly irregular in shape. Sieve

analysis was performed on this material in order to remove pieces larger than 10 mm. BLA was

collected in the heat transfer system in the facility and APC lime was recovered from the baghouse further downstream in the air pollution control system. All collected residues were thoroughly

dried in an oven in the lab before use. ACROS organics TM 98% pure calcium hydroxide (CH) served as the only supplemental material in eco-cement making. CAN/CSA-A3001 (Canadian

Standards Association) Type GU ordinary Portland cement (Lafarge) (OPC) was used for reference control batch. Granite (Bauval CCM query, Montreal, Canada) was chosen to be the aggregate material for concrete with a maximum size of 5 mm.

4.2.2 Materials Characterization

Chemical composition analysis was conducted by X-Ray Fluorescence with the help of a

Panalytical PW2440 Spectrometer (MagiX PRO Series), which is presented in Table 4. 1. ASTM

D7348 was followed to determine the loss on ignition (LOI) value. Carbon and sulfur content in

raw material was measured using an ELTRACS-800 Carbon/Sulfur Analyzer. Chlorine content was quantified using instrumental neutron activation analysis (INAA).

“Quartering” sampling method from ASTM C702 was adopted to ensure the representativity of the collected residues for element analysis. For each residue, the collected sample was mixed thoroughly and shoveled the sample into a conical pile. Then, the flattened pile was divided into

quarters. Two opposite quarters were retained, while the other two quarters were rejected. Repeat

this process until 20 g of representable test sample was obtained from each residue.

The particle size distribution of final eco-cement was measured using laser diffraction analysis by a Horiba LA-920 Particle size analyzer. The powder sample was dispersed in isopropanol with an ultra-sonic time of 1 minute.

4.2.3 Eco-cement Clinkering

Chemical parameters based on the oxide compositions are indicators that show the characteristics of clinker. The eco-cement clinker synthesis compositional parameters, namely lime saturation factor (LSF); silica ratio (SR); and alumina ratio (AR), were adopted from the study done by

Ghouleh and Shao (Ghouleh & Shao, 2018). The equations for the compositional parameters are presented as Eqn. (1)-(3). On top of the BLA and APC lime that used in Ghouleh and Shao’s study,

BA was also introduced as a source of silica, making all three MSWI residues as the raw feeds in the eco-cement synthesized in this study. Furthermore, silica sand was removed from their clinker design, leaving CH the only external additive, which was counted 6.2%. The proportion of the raw feeds, including MSWI residues and additive, was adjusted based on the clinker compositional

parameters. Following this approach, the detailed blend mix design and the corresponding

parameters were presented in Table 4. 2.

= . . . Equation 1 𝐶𝐶𝐶𝐶𝐶𝐶 𝐿𝐿𝑆𝑆𝐹𝐹 2 8𝑆𝑆𝑖𝑖𝑂𝑂2+1 2𝐴𝐴𝑙𝑙2𝑂𝑂3+0 65𝐹𝐹𝑒𝑒2𝑂𝑂3 = Equation 2 𝑆𝑆𝑆𝑆𝑂𝑂2 𝑆𝑆𝑆𝑆 𝐴𝐴𝑙𝑙2𝑂𝑂3+𝐹𝐹𝑒𝑒2𝑂𝑂3 = Equation 3 𝐴𝐴𝑙𝑙2𝑂𝑂3 𝐴𝐴𝐴𝐴 𝐹𝐹𝑒𝑒2𝑂𝑂3 A total of 300 g raw material was first combined based on the clinker design and then further

pulverized for a duration of 2 minutes. The limitation on the weight of the raw material processed

each time was to ensure the desired particle size can be achieved. Prior to the nodulizing process,

the pulverized raw feed was moved into a V-shape blender for 3 hours mixing in order to get a

high uniformity material. A rotation granulator was used for nodule making, the water that added

into the granulator was precisely controlled to ensure a homogenous nodule size in an average diameter of 10 mm. Laboratory eco-cement clinkering was carried out with the help of a

Lindberg/Blue-M muffle furnace. Pre-heat was set-up to 800°C for 1 hour to remove all the organic content and decompose calcium carbonates. Then, the temperature was raised up to 1100°C to get the desired chemical compositions and desired cement properties. Cooling was performed inside the furnace for 12 hours before retrieving. The clinkers then further pulverized to powder with an

average of particle size of 6.6 μm. Figure 4. 1 schematically presents the eco-cement manufacture

process with images of material produced from each step.

4.2.4 Sample Preparation and Curing Scenarios

Batches were prepared depending on the cement type and curing scenario, including OPC under conventional curing (OPC-H); OPC under carbonation curing (OPC-C); eco-cement under hydration curing (Eco-H); eco-cement under carbonation curing (Eco-C). The mix proportions for the specimens were shown in Table 4. 3. In order to enhance the early age strength that was primarily contributed by carbonation curing, higher cement content was used in eco-cement batches. Furthermore, eco-cement did not absorb as much water as OPC, so the water-cement ratio was lowered to 0.1 for paste samples and 0.2 for concrete samples.

Cylinder paste compacts were prepared using an MTS machine to apply a uniaxial compact force of 3 kN. Compact specimens were 15 mm in diameter and 30 mm in height. Carbonation was carried out in an air-tight chamber (Fig. 4. 2) with a pressure of 1.5 bar pure CO2 (99.5%) for 2 h.

The specimens were then moved to a fog room with 100% relative humidity until the desired testing date of 1 day, 28 days, and 90 days. OPC-H compacts were served as control batch, which also experienced conventional hydration curing by storing in fog room right after casting.

Eco-cement concrete slab (100 mm × 31 mm × 76 mm) was vibration compacted with a cement

content of 12% and w/b of 0.23. On the other side, the OPC control batch adopted a commercial

zero-slump concrete mix design from a local CMU producer Boehmer’s with a cement content of

9.7% and w/b of 0.35. Carbonation curing on concrete had one more step than paste compacts. A

fan was used to dry the concrete to a targeted water loss first before moving into the pressure

chamber. The purpose was to remove a certain amount of water to make room for CO2 to penetrate.

A pressure of 0.07 MPa (10psi) was used, and the blocks were carbonated for a duration of 10

hours using the same set-up with compact carbonation that shown in Fig. 4. 2. The carbonated

concretes were further moved into the fog room for subsequent hydration.

The CO2 sequestration ability of OPC/eco-cement products was evaluated by measuring the amount of gas sequestrated during carbonation curing, using the mass gain method proposed by

Monkmand et al. (Monkman & Shao, 2006). The indicator- CO2 uptake was calculated based on

Eq.4.

(%) = × 100% �𝑀𝑀𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐+𝑀𝑀𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙�−𝑀𝑀𝐵𝐵𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 Equation 4 𝐶𝐶𝑂𝑂2 𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈 𝑀𝑀𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶

Where is the mass of the specimen after carbonation, is the mass of

𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 water retrieved𝑀𝑀 from the chamber, is the mass 𝑀𝑀of the specimen before

𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 carbonation, and is the mass 𝑀𝑀of the dry cement used for a specimen.

𝑀𝑀𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 4.2.5 Scanning Electron Microscopy (SEM)

The morphology of the clinkered eco-cement was investigated using Scanning Electron

Microscopy (SEM). A 5 nm platinum coating layer was applied on the surface to improve the conductivity. A dispersive X-ray spectroscopy (EDS) detector was used to analyze the mineralogical composition.

4.2.6 Concrete slab performance tests

The compressive strength of paste compacts and concrete slab samples was tested according to

ASTM C39, using an MTS-SINTECH 30/G compression machine with a loading capacity of 150 kN. The dimensions of the loading surface were recorded with the aid of a Vernier Caliper.

Environmental stability of the concrete is extremely important for a feasibility assessment of using material originally from MSWI. Therefore, heavy metal leaching test - Toxicity Characteristic

Leaching Potential Test (TCLP) Method 1311 described by US Environmental Protection Agency

(EPA) was conducted, targeting on Arsenic, Barium, Boron, Cadmium, Chromium, Lead,

Mercury, Selenium, Silver, and Uranium. After 28 days curing, the concrete slab was first crushed into the desired size, which could pass 9.5 mm sieve, before immersing in the extraction fluid. The

crushed sample was rotated with the extraction fluid at 30 ± 2 rpm for 18 ± 2 hours under 23 ± 2

°C ambient temperature. Inductively coupled plasma-mass spectrometry (ICP/MS) was used to

analyze the heavy metal leached out concentration. Chloride concentration in the leachate was also

measured by ion chromatography.

Surface scaling is a common durability issue for concrete structures facing a combination of de-

icing salts and repeated freeze-thaw cycles (Valenza & Scherer, 2007), especially in countries with

cold weather, like Canada. Concrete specimens were immersed in solution of 4 wt% sodium

chloride. As suggested by ASTM C 672, the freeze thaw cycle followed a daily base with 16 to 18

h of freezing and 6 to 8 h of thawing. The oven dried scaled concrete mass was collected and

recorded every five freeze-thaw cycles. Also, the oven dried final concrete retained mass was

recorded after the test finished. Then the mass retained percentage from each five cycle was

calculated based on the total mass of the concrete and the recorded mass loss each measuring cycle.

The permeability of concrete was evaluated through surface electrical resistivity of the water

saturated samples according to AASHTO TP 95. Concrete blocks were immersed in water for 48

hours and then surface dried before testing. A Proceq Resipod resistivity meter with four electrodes

was used.

Linear shrinkage property for the concrete slabs with gauge length of 100 mm was evaluated based on ASTM C426 (Standard test method for linear drying shrinkage of concrete masonry units). Two

spherical shape gauge plugs were aligned and mounted on the opposite surfaces of each concrete

slab samples. A comparator was used to test the concrete length change according to the standard

specified drying procedures in an oven with a temperature of 50 ± 0.9 °C. Sample weight was also

recorded simultaneously. Equilibrium conditions should be achieved in order to get the final

shrinkage value, which was defined as the length change less than 0.002% over 6 days of drying

and the weight change was less than 0.2% of 2 days of drying. The final shrinkage was calculated

for each batch by averaging the last three shrinkage values recorded.

4.2.7 Pilot-Scale Production

4.2.7.1 Pilot-scale Eco-cement Clinkering

Casting full-size CMU required a large amount of eco-cement (2.04 kg for each CMU), which was

over the limit of lab-scale production. Therefore, a scale-up mass production process was

developed which combined the laboratory nodule making and industrial size clinkering. Raw

nodules were prepared in lab using the same method introduced in the previous section. Batch

production was adopted for nodule making. 2 kg of nodules were prepared as one batch and stored

in separated buckets. A sample of 50 g of nodules was tested for each batch in lab, and paste compacts were made to test the 1 day mechanical compressive strength and CO2 uptake to ensure

a constant material quality. Batches that could not reach the quality control threshold (40 MPa in

compressive strength and 7.5% in CO2 uptake) were discarded and would not be used to make clinkers. As shown in Fig. 4. 3(a), the pilot-scale clinkering process was performed using an industrial scale gas charged furnace located in Ontario, Canada. Nodules before and after the

clinkering are shown in Fig. 4. 3(b). Heating process on nodules was identical for both laboratory-

scale and pilot-scale production. 1 day compressive strength and CO2 uptake were tested again for mass clinkered eco-cement to make sure it achieved 40 MPa and 7.5% respectively.

4.2.7.2 CMU Sample Preparation

For pilot-scale, the full-size standard concrete masonry units (CMU) with dimensions of 390 mm

× 190 mm × 190 mm, were made in Boehmers’ block manufacturing plant (Ontario, Canada).

They had the same mix design with the concrete slabs produced in the lab (Table 4. 3). Concrete

blocks were cast using an industrial production line from mixing to casting. As illustrated in Fig.

4. 4, carbonation curing was performed in an industrial scale kiln with the same pressure (0.069

MPa or 10 psi) and duration (10 h). Precondition drying and subsequent hydration were also conducted for CMUs. Figure 4. 5 shows the full-size CMU prepared using this work’s synthesized eco-cement.

4.2.7.3 CMU Performance Tests

Compressive strength, density, absorption, and linear shrinkage are the four parameters that used in evaluation criteria of commercial CMU based on ASTM C90 and CSA 165.1 standards. To investigate if the eco-cement CMUs satisfy the requirements of Canadian and U.S. standards, these parameters were tested for eco-concrete (Eco-C) batch. Compressive strength, density, and

absorption were examined by ASTM C140 and the linear shrinkage was determined through

ASTM C426.

4.3 Results and Discussion

4.3.1 Raw Material Compositional Analysis

XRF analysis was performed on raw materials and OPC, and the average oxide compositions results are given in Table 4.1. Raw bottom ash and boiler ash mainly consist of the three major components in cement synthesis CAS system (CaO-Al2O3-SiO2), while the air pollution control

lime primarily served as lime source. Both bottom ash and APC lime measured a high LOI value,

which suggested a high content of combustible residue content. All three MSWI residues contained

a certain amount of chlorine content. APC lime presented a 14.3% chlorine from Instrumental

Neutron Activation Analysis (INAA) test. This posed a challenge to fix the chlorine into the

clinkered phases in eco-cement. It also revealed the importance to check the chloride leaching

performance of the eco-cement concrete product.

4.3.2 Eco-cement QXRD Analysis, Particle size Analysis and Morphology Analysis

QXRD analysis on OPC and eco-cement made in lab condition are summarized in the first two columns of Table 4. 4. The clinker with the new raw feed design had been proved successfully synthesized the targeted mineral phases – chlorellestadite (CE) and belite. Except for amorphous content, CE and belite were the major components respectively counted for 16.9% and 25.5%. To be more specific, β-C2S is the polymorphs state of belite existed in the eco-cement, which had a

latent hydration property. Thus, it is beneficial to the concrete product from this mineral during

the subsequent hydration period.

Figure 4. 6 displays the eco-cement particle size distribution from laser diffraction analysis. It

revealed that the pulverized clinker had a higher range of finer particles than OPC. The particle

size D50 for eco-cement and OPC were 6.615μm and 12.314μm respectively. As seen from SEM

image (Fig. 4. 7), unreacted powdered state eco-cement had various shapes. EDS point analysis on

testing spot 1 and 2 showed a high content of calcium, silicate, oxygen, sulfur, and chlorine. It was

indicative that the crystal of CE was formed in the eco-cement. Carbon peak in the EDS graph was

due to the underneath holding carbon tape, and the platinum peak came from the conductivity

coating applied before testing. According to SEM image, the CE crystal has a longitudinal

monoclinic shape.

4.3.3 Eco-cement Performance Under Hydration and Carbonation Curing

4.3.3.1 Compressive Strength and CO2 Uptake

Eco-cement performance was assessed primarily based on the compressive strength and CO2

uptake of paste specimens, which are presented in Figure 4. 8, with OPC samples served as

reference.

In terms of CO2 reactivity, eco-cement displayed a higher CO2 uptake of 8.84% compared to 6.64% for OPC reference. Therefore, the eco-cement had a better CO2 sequestration capacity during

carbonation curing. It can be clearly observed that regardless of the binding material, the

carbonated samples always achieved a much higher strength at curing age of 1 day than

conventional hydrated references. For OPC, 1 day carbonated compacts achieved the same

strength level with the 28 days hydration cured samples (49.2 Mpa and 49.40 MPa respectively).

The rapid strength gain was due to the precipitation of C-S-H gel and CaCO3 when the cement was exposed to sufficiently carbonated pore solution (Rostami et al., 2012; Shao & Lin, 2011;

Young et al., 1974). The carbonated OPC batch also showed a subsequent hydration potential after carbonation by increasing to 62.53 MPa at age of 90 days compared to OPC-H at the same age

(55.95 MPa). Under hydration curing, eco-cement displayed a strength gain to a certain extent. It

developed 9.9 MPa after 1 day, 20.97 MPa after 28 days, and 33.33 MPa after 90 days. This

confirmed that the eco-cement is a cementitious material, which can build strength under

conventional hydration curing. The strength was mainly because of the hydration of C2S, which

reacted in a similar manner with C3S, but in a much slower speed (Tokyay, 2016a). On another

note, with the activation of carbonation curing, the uniaxial compressive strength of EC-C

dramatically raised up to 47.33 MPa after 1 day, which was comparable to OPC-C at the same age.

And the strength kept building up in subsequent hydration and reached 67.56 MPa at 90 days.

The compressive strength test revealed that eco-cement was able to gain strength under hydration

curing, but carbonation initiation was necessary. In one day, carbonated eco-cement samples can

reach the same strength level with 28 days hydration cured OPC (47.33 MPa and 49.40 MPa). And the long-term 90 days age EC-C sample achieved an even higher strength of 67.56 MPa. Due to the necessity of the carbonation activation in eco-cement, carbonation curing was the curing scenario that was focused in this study in concrete application assessment for eco-cement.

4.3.3.2 Mineralogical Analysis of Paste Samples

Table 4. 4 presents the mineral composition change in paste samples. The major hydration phases in OPC, C3S and C2S, were consumed after 1 day under both curing conditions. However, a higher

reduction can be noticed for these two minerals in carbonated blocks resulting from the reaction

with CO2. One of the hydration products, calcium hydroxide (CH), was fully consumed in OPC blocks under carbonation scenario and led to a higher content of CaCO3. Gaseous CO2 was

permanently converted to precipitated CaCO3 in OPC concrete.

The major components of eco-cement are chlorellestadite (16.9%) and C2S (25%), which are also

the dominant CO2 reactive minerals. Both were considerably consumed after 1 day after

carbonation curing. The amorphous content, calcite, and vaterite were the major products of

carbonation of eco-cement. Wadalite and periclase are minor minerals that could also be consumed

by carbonation. On the other side, under conventional hydration curing, CE was not reacted and

remained a constant content level. Meanwhile, a small reduction was noticed on belite due to

hydration. Mineral transformation was observed that the wadalite seemed to convert to Friedel’s

salt after 1 day hydration.

The results of the mineralogical analysis were suggestive that the rapid strength gain of carbonated

eco-cement came from the carbonation of CE and C2S. However, short term carbonation was not

able to react all the C2S, so the continuous hydration of C2S provided the latent strength

improvement.

4.3.4 Lab-scale Concrete Performance Tests

4.3.4.1 Concrete CO2 Uptake and Compressive Strength

The binding capacity of eco-cement in concrete made in lab was quantified by the compressive

strength at different curing ages. Figure 4. 9 presents the compressive strength and the CO2 uptake calculated by mass gain method. With regard to CO2 sequestration capacity, OPC displayed a

marginally higher uptake of 14.32±1.1% compare to eco-cement of 12.87±0.37%. Considering the

observation from paste compact samples that OPC showed a lower CO2 reactivity than eco-

cement, the increase in CO2 uptake of OPC in concrete test was probably due to the heat release from the carbonation reaction. Since the reaction of Portland cement with CO2 is an exothermic

process (Zhang et al., 2017), causing an increase in temperature inside the pressure chamber. The

elevated temperature could not only increase the CO2 diffusion rate but promote the mixing water

evaporation rate that makes it easier for CO2 to penetrate and then reacts inside the block.

However, in paste samples, the amount of cement for each sample was too small and this phenomenon is negligible.

At the age of 1 day, OPC-C displayed the highest mechanical strength due to the early age strength gain effect of carbonation curing, with an outcome of 25.84 MPa. Eco-C reached the same level

of strength development of 23.70 MPa with OPC-C. On the other side, the conventional OPC-H

batch only displayed a strength of 17.95 MPa. The hydration property of the eco-cement discovered in paste samples also been observed in concrete samples, resulting in a strength development on Eco-C samples during the subsequent hydration period. At 28 days, the eco- cement displayed the highest binding capacity in concrete which achieved strength of 33.28 MPa compare to OPC-H (33.03 MPa) and OPC-C (29.79 MPa). At 90 days, the strength gain for all three batches was small, but Eco-C still exhibited the best binding strength of 35.68 MPa.

It was worth noting that the Eco-C has displayed a great binding performance in concrete production using carbonation curing. It could not only absorb a considerable amount of CO2 but

gain strength rapidly. It reached a comparable strength with OPC-C after 1 day and became the

highest strength concrete after 28 days.

4.3.4.2 Leaching Performance

MSWI ashes contain leachable heavy metals and chlorine. It can be a potential environmental

problem while applying the residues as a raw material in clinkering. To ensure safe usage, Eco-

concrete’s leaching behavior was evaluated based on US Toxicity Characteristic Leaching

Procedure (TCLP) 1311 method. Table 4. 5 demonstrates the result of leached out heavy metal

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and chloride concentrations from carbonated eco-cement concrete. It shows that the concentration

of all the considered heavy metals in the leachate were far below the two North American

Regulations (Canada Ontario regulation 558 and US EPA 40 CFR 261.24). The heavy metals in

the raw MSWI ashes had been stabilized, thus resulting in no harm to the environment. In terms

of chloride, 125.8 mg/L was identified from the leachate. Even though not all of the chloride can

be fixed in the matrix, the leach out concentration of chloride still met the U.S. EPA freshwater

quality criterion (230 mg/L for chronic water; 860 mg/L for acute freshwater). To note, the TCLP

test was evaluated the leaching performance of the concrete under the worst-case scenario (crashed

sample that immersed in extraction fluid with continuous rotation in rotary agitation device), which

rarely happens in real service life. Therefore, the leaching performance of heavy metals and

chloride of eco-cement binder passed all the criteria. The stabilization was likely attributed to the

phase transformations during high temperature clinkering and matrix solidification through

carbonation curing.

4.3.4.3 Concrete Surface Resistivity

Concrete surface resistivity quantifies the degree of electrical resistivity of water-saturated concrete. Figure 4. 10 displays the surface resistivity test results on slab concrete samples up to 90 days. A higher surface resistivity indicates a lower permeability. At 1 day, carbonated OPC batch had shown a significant increase in surface resistivity comparing to other two batches due to the densified matrix structure from carbonates precipitation. Concrete with eco-cement measured a resistivity of 26.40 KΩ·cm which was doubled the value collected for OPC hydration reference

(10.07 KΩ·cm). Surface resistivity was increased gradually for all three batches with subsequent hydration since more hydrates formed in the microstructure. Eco-C exhibited the second highest

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surface resistivity at all testing ages, indicating that a less permeable structure was created compare to OPC-H. OPC-C displayed the best resistivity regardless of the hydration age.

4.3.4.4 Freeze-thaw Scaling Resistance

The percent mass retained for concrete that exposed to continuous freeze-thaw cycles is illustrated in Fig. 4. 11. Both of OPC-C batch and Eco-C batch displayed a better freeze-thaw resistivity than conventional cured ordinary Portland cement batch. For OPC-H batch, all the slabs were fully damaged after 30 freeze-thaw cycles in 4 wt% sodium chloride solution. On the other side, carbonated OPC blocks still retained almost 100% of its original mass while the Eco-C batch retained 94%. With the trend exhibited in the plot, both of OPC-C and Eco-C could stand far longer than OPC-H. The high frost resistance of Eco-C batch was likely due to the elimination of the calcium hydroxide mineral in its matrix system. In addition to salt scaling and reinforcement corrosion, the chloride-based de-icing salt also chemically reacted with the calcium hydroxide in concrete and forming expansive mineral phase calcium oxychloride (CAOXY) (Egüez Álava et al., 2016; Farnam et al., 2014). This effect process faster under a temperature just above freezing point and therefore causes expansion and cracking while concrete experiences freeze-thaw cycles.

SCMs was proposed to partially replace cement in order to reduce the CH content in the hardened concrete with the aim of decreasing the CAOXY formation (Suraneni et al., 2016). No CH existed in the Eco-C binding system that created in this study, so this deterioration mechanism was completely prevented. For OPC-C batch, as summarized in QXRD test, carbonation curing also consumed CH. Furthermore, the formed carbonates enhanced the microstructure of the concrete and led to a less permeability. With less water penetrated into the concrete, the freeze-thaw damage was therefore greatly mitigated in this batch.

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4.3.4.5 Concrete Linear Drying Shrinkage

Concrete displays dimensional instability when experiencing differential relative humidity

between the concrete and the ambient environment. The paste in concrete losses physically

adsorbent water during drying, resulting in shrinkage and its related cracking (Mehta & Monteiro,

2017). This characteristic was evaluated for concrete made by eco-cement under standard specified accelerated drying condition (ASTM C426). The results are exhibited in Fig. 4. 12. OPC-H had a comparable final shrinkage with OPC-C at equilibrium conditions, which calculated respectively as 0.0549% and 0.0498%. On the other side, the Eco-C batch exhibited a better shrinkage resistance with a final shrinkage of 0.0371%. The linear drying shrinkage could be reduced 32.4% by using eco-cement, comparing to conventional hydration OPC concrete. This might be due to the low water to binder ratio of the Eco-C batch. The water to binder ratio used for Eco-C and

OPC were 0.2 and 0.35. Lower water content in the Eco-cement mix had reduced the absorbed water amount in the Eco-cement gel, and therefore, reducing the degree of dimensional change.

4.3.5 Pilot-scale Concrete Performance Tests

4.3.5.1 Mineral analysis (QXRD) of Eco-cement Produced at Pilot-scale

Table 4. 6 summarizes the mineral compositions detected by QXRD for the eco-cement produced with an industrial furnace which served as binding material in full-size CMU production which was carried out at Beohmers Block plant. The results revealed that the mass produced eco-cement had similar chemical compositions with the material clinkered in lab condition, including the major carbonation active phases, belite and chlorellestadite.

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4.3.5.2 Full-size CMU Performance

Table 4. 7 displays the performance results for full-size CMU that were produced using an

industrial block production line in a masonry concrete plant. Four tests were performed including

compressive strength (with CO2 uptake), density, absorption and linear shrinkage. These are the

four specifications regulated by CSA 165.1 standard for commercial CMU blocks. In terms of strength, Eco-C CMU had gained a strength of 18.9 MPa after 1 day. At later hydration ages, the eco-cement demonstrated a subsequent hydration property. After 28 days of hydration, the strength of eco-concrete (Eco-C) increased from 18.9 MPa to 22.40 MPa. It proved that the MSWI ashes derived cement was able to provide a strength that met both CSA and ASTM criteria (15 MPa and

13.8 MPa, respectively). Furthermore, the Eco-C exhibited a good CO2 absorption property with

an averaged CO2 uptake of 17.67 % after 10 hours of carbonation curing. Considering the total

weight of a CMU was 17 Kg, each block was able to sequestrate 294 g of CO2 in its matrix.

Besides compressive strength, other three physical properties’ requirements of CMUs were set by

Canadian standard CSA 165.1, including density, absorption and linear shrinkage. Table 4. 7

presents the results of these properties for CMUs which used eco-cement as binding material.

Regulations from Canadian and US standards are listed as well, serving as evaluation criteria. A

density of 2101 Kg/m3 was measured, it was classified as “A” in CSA and “Normal weight” in

ASTM. It was clearly noted that, with an absorption 153.8 Kg/m3, Eco-C met the minimum

requirement. Lastly, Eco-C yielded a 0.027% shrinkage based on test method ASTM C426.

Therefore, this batch could be assigned to the most rigorous shrinkage classification in CSA with

a limitation of 0.03%. Furthermore, Eco-C CMUs also met the ASTM specification that at the time of delivery the linear shrinkage cannot exceed 0.065%. The standardized test performed was based

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on extreme wetting and drying scenario (ASTM C426), which do not occur in real service life,

and, therefore, the Eco-C batch was far beyond the ASTM requirement.

4.4 Conclusion

This study successfully demonstrated the feasibility of using the eco-cement as the binding

material in concrete and this concept had been further approved in pilot-scale test. The eco-cement developed in this study used all types of MSWI by-products that generated from different incineration steps as raw feeds. Only 6.2% of calcium hydroxide was added into the eco-cement clinkering design to serve as additive, and the rest 93.8% raw material consisted of bottom ash,

boiler ash and air pollution control lime. Paste compacts, concrete slab and full-size CMUs were adopted as experimental specimens to test the eco-cement performance. The eco-cement exhibited good carbonation reactivity under carbonation curing scenario, leading to improved compressive strength and durability properties, while permanently sequestrated gaseous CO2 in the paste matrix. The industrial produced CMU met all the commercial requirements indicated by Canadian and U.S. criteria. The main conclusions can be drawn:

1. An eco-cement with latent hydraulic behavior was developed. The raw clinker feed

consisted of all the types of residues from MSWI, and only 6.2% of calcium hydroxide

additive was added. With the new mix design, the eco-cement developed the target

minerals chlorellestadite and belite, which were the two major CO2 reactive phases. Fast

strength gain and CO2 sequestration made the eco-cement ideal to serve as binding material

in concrete with carbonation curing.

2. Besides carbonation reactivity, the synthesized eco-cement exhibited hydration property as

well, an effect linked to the existence of β-C2S. In hydration only scenario, eco-cement

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paste samples developed 33.33 MPa of compressive strength in 90 days. Under carbonation

curing, strength development was also observed with subsequent hydration ability. Short

term carbonation cannot fully react all the belite in the eco-cement, so strength kept

increasing because of the hydration of belite. This is a critical factor for concrete production

using carbonation curing since CO2 is unlikely to penetrate the entire block and fully react

with the core section. Subsequent hydration allows the cement matrix to keep hardening in

the core section, and higher strength can be developed during this period or even in the

later service life.

3. For concrete slab produced in lab condition, the eco-cement displayed a comparable

strength development with OPC reference. Both carbonated batches (OPC-C and Eco-C)

proved the rapid strength gain advantage of carbonation curing. Eco-C concrete achieved

a higher strength than OPC-C at 28 days, but their ultimate strengths were close at the age

of 90 days.

4. TCLP leaching test was conducted on Eco-C concrete slabs, and all the considered heavy

metals’ concentrations were much lower than the Canadian and U.S. regulations. Chloride

leaching also confirmed that the eco-cement concrete met U.S. EPA freshwater quality

criterion.

5. Compared to normal hydration OPC concrete, a better surface resistivity was achieved by

using eco-cement and carbonation curing. The freeze-thaw scaling resistance was

improved for concrete with eco-cement. OPC hydrated references were completely

destroyed after 30 freeze-thaw cycles, while the carbonated eco-cement concrete kept 94%

of the original mass. It was indicative that this material can be a good solution for cold

climate outdoor service applications. Linear shrinkage test concluded that the eco-cement

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binder has a better shrinkage resistance than OPC under both hydration and carbonation

curing scenarios.

6. This study also developed a pilot-scale process to demonstrate the industrial eco-cement

production. For Eco-C CMU, the ASTM strength requirement for load-bearing CMU

(15MPa) could be achieved in 1 day. The 28 days strength was even higher. The Eco-C

CMUs were also passed the commercial CMU requirements established by Canadian and

U.S. standards, according to the tested density, absorption and linear shrinkage. This

proved that Eco-C CMUs so produced are qualified as a commercial product.

References

Bhada-Tata, P. H., Daniel A. (2012). What a waste: A Gllobal Review of Solid Waste Management. Urban development series knowledge papers, 15.

Chandler, A. J., Eighmy, T. T., Hartlén, J., Hjelmar, O., Kosson, D. S., Sawell, S. E., . . . Vehlow, J. (1997). Chapter 2 - Municipal solid waste. In Studies in Environmental Science (Vol. 67, pp. 15-57): Elsevier.

Egüez Álava, H., De Belie, N., & De Schutter, G. (2016). Proposed mechanism for the formation of oxychloride crystals during sodium chloride application as a deicer salt in carbonated

107

concrete. Construction and Building Materials, 109, 188-197. doi:https://doi.org/10.1016/j.conbuildmat.2016.01.047

Lederer, J., Trinkel, V., & Fellner, J. (2017). Wide-scale utilization of MSWI fly ashes in cement production and its impact on average heavy metal contents in cements: The case of 108

Austria. Waste Management, 60, 247-258. doi:https://doi.org/10.1016/j.wasman.2016.10.022

Mehta, P. K., & Monteiro, P. J. (2017). Concrete Microstructure, Properties and Materials. In.

Monkman, S., & Shao, Y. (2006). Assessing the carbonation behavior of cementitious materials. Journal of Materials in Civil Engineering, 18(6), 768-776.

Shao, Y., & Lin, X. (2011). Early-Age Carbonation Curing of Concrete Using Recovered CO2. Concrete International, 33(9).

109

Tokyay, M. (2016). Cement and Concrete Mineral Admixtures. Boca Raton: CRC Press.

Valenza, J. J., & Scherer, G. W. (2007). A review of salt scaling: I. Phenomenology. Cement and Concrete Research, 37(7), 1007-1021. doi:https://doi.org/10.1016/j.cemconres.2007.03.005

Young, J. F., Berger, R. L., & Breese, J. (1974). Accelerated Curing of Compacted Calcium Silicate Mortars on Exposure to CO2. Journal of the American Ceramic Society, 57(9), 394-397. doi:doi:10.1111/j.1151-2916.1974.tb11420.x

Standard References

ASTM D7348-13, Standard Test Methods for Loss on Ignition (LOI) of Solid Combustion Residues, ASTM International, West Conshohocken, PA, 2013, www.astm.org

ASTM C702 / C702M-18, Standard Practice for Reducing Samples of Aggregate to Testing Size, ASTM International, West Conshohocken, PA, 2018, www.astm.org

ASTM C39 / C39M-18, Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens, ASTM International, West Conshohocken, PA, 2018, www.astm.org

110

ASTM C672 / C672M-12, Standard Test Method for Scaling Resistance of Concrete Surfaces Exposed to Deicing Chemicals, ASTM International, West Conshohocken, PA, 2012, www.astm.org

ASTM C426-16, Standard Test Method for Linear Drying Shrinkage of Concrete Masonry Units, ASTM International, West Conshohocken, PA, 2016, www.astm.org

ASTM C90-16a, Standard Specification for Loadbearing Concrete Masonry Units, ASTM International, West Conshohocken, PA, 2016, www.astm.org

CSA 165.1 Specification and General Specifications Notes, Canadian Concrete Masonry Producers’ Association, CSA Group, 2018

ASTM C140 / C140M-18a, Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units, ASTM International, West Conshohocken, PA, 2018, www.astm.org

Ontario Regulation 558/00 General-Waste Management, Environmental Protection Act, 2000

Code of Federal Regulations Title 40. Protection of Environment 264.24 Toxicity Characteristic, 1990

Ambient Water Quality Criteria for Chloride, United States Environmental Protection Agency, 1988

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Table 4. 1: Chemical compositions (XRF) of the MSW incinerator residues

Composition wt% Oxide Bottom ash Boiler ash APC Lime OPC

CaO 16.21 40.03 49.12 65.00

SiO2 26.69 27.34 2.44 20.54

Al2O3 9.66 15.16 1.42 4.57

Fe2O3(T) 6.20 4.50 0.31 3.11

MnO 0.14 0.31 0.02 0.10

MgO 2.27 4.08 1.22 2.80

Na2O 2.36 - - 0.24

K2O 1.00 0.05 0.65 0.68

TiO2 1.85 4.76 0.22 0.20

P2O5 1.74 3.42 0.12 0.26

Total-C 19.30 0.10 2.31 -

Total-S 0.59 2.06 1.01 -

Cl 2.14 0.20 14.82 -

LOI 29.74 0.15 29.65 2.49

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Table 4. 2: Raw feed proportion for clinker

Proportion (wt%) LSF SR AR

MSWI Residues Additive

Bottom ash Boiler ash APC Lime CH

24.8 27.6 41.4 6.2 0.79 1.46 2.27

LSF (lime saturation factor) = %CaO/[(2.8 × %SiO2) + (1.2 × %Al2O3) + (0.65 × %Fe2O3)].

SR (silica ratio) = %SiO2/ [(%Al2O3 + %Fe2O3)].

AR (alumina ratio) = %Al2O3/%Fe2O3.

Table 4. 3: Mixture proportions for cement paste and concrete

Paste Concrete Mixture component [%] OPC Eco OPC Eco

OPC Cement 85 - 9.7 -

Eco-cement - 90 - 12

Water 15.0 10 3.4 2.4

Aggregate (2-5 mm) - - 28.9 28.5

Aggregate (0-2 mm) - - 58.0 57.1

Water/binder ratio 17.6 11.1 35.1 20.0

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Table 4. 4: Mineral compositions (QXRD) of raw binders and paste compacts

Eco-cement Eco- Eco- Mineral Formula OPC OPC-H* OPC-C* (lab-scale) H* C*

Alite Ca3Si05 48.3 n.d. 27.5 25.1 n.d. n.d.

Belite β-Ca2SiO4 19.5 25.5 12.0 9.8 25.0 18.9

Tricalcium Ca3Al2O6 4.2 n.d. n.d. n.d. n.d. n.d. aluminate

Brownmillerite Ca2FeAlO5 7.8 n.d. 8.3 5.4 n.d. n.d. (C4AF)

Ca5(SiO4)1.5(SO4)1.5 Chlorellestadite n.d. 16.9 n.d. n.d. 17.8 10.7 Cl

Quartz SiO2 0.3 0.2 0.5 trace n.d. n.d.

Wadalite Ca12Al14O33 1.0 11.4 2.0 1.0 4.9 8.6

Periclase MgO 1.1 3.4 0.8 1.0 2.8 1.7

Calcite CaCO3 1.4 n.d. 2.7 15.3 n.d. 7.0

Vaterite CaCO3 n.d. n.d. n.d. n.d. n.d. 3.8

Gypsum CaSO4*2H2O 1.8 n.d. n.d. n.d. n.d. n.d.

Portlandite Ca(OH)2 n.d. n.d. 1.1 n.d. n.d. n.d.

Ca2Al(OH)6(Cl, Friedel’s salt n.d. n.d. n.d. n.d. 6.2 n.d. OH)·H2O

Amorphous 14.6 42.6 45.1 42.4 43.3 49.3

*OPC: Ordinary Portland cement; Eco: Synthesized Eco-cement; H: Hydration curing; C: Carbonation curing

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Table 4. 5: Leaching performance

U.S, EPA Eco-cement Canada, Ontario Regulation*2*3 Concrete slab Regulation 558*1 Parameter Parameter [mg/L] [mg/L] [mg/L]

Arsenic As 0.04 2.5 5.0

Barium Ba 0.75 100.0 100.0

Boron B 1.31 500.0 -

Cadmium Cd <0.001 0.5 1.0

Chromium Cr 0.78 5.0 5.0

Lead Pb 0.01 5.0 5.0

Mercury Hg <0.001 0.1 0.2

Selenium Se <0.01 1.0 1.0

Silver Ag <0.01 5.0 5.0

Uranium U <0.01 10.0 -

Chloride Cl− 125.8 - 230/860*3

*1: Canada Ontario regulation 558/00: General-waste management

*2: U.S. EPA 40 CFR 261.24 – Toxicity characteristic for heavy metals;

*3: U.S. EPA Ambient water quality criteria for chloride – 230 mg/L for chronic freshwater; 860 mg/L for acute freshwater

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Table 4. 6: Mineral compositions (QXRD) of Eco-cement produced in pilot-scale

Mineral Formula Eco-cement (pilot-scale)

Alite Ca3Si05 n.d.

Belite β-Ca2SiO4 25.7

Brownmillerite (C4AF) Ca2FeAlO5 n.d.

Chlorellestadite Ca5(SiO4)1.5(SO4)1.5Cl 18.4

Quartz SiO2 n.d.

Wadalite Ca12Al14O33 14.1

Periclase MgO 2.3

Calcite CaCO3 n.d.

Vaterite CaCO3 n.d.

Gypsum CaSO4*2H2O n.d.

Portlandite Ca(OH)2 n.d.

Friedel’s salt Ca2Al(OH)6(Cl, OH)·H2O n.d.

Amorphous 39.5

Table 4. 7: Compressive strength, density, absorption and linear shrinkage of CMU made from pilot-scale produced eco-cement

Parameters Eco-C CSA*1 ASTM*2

Compressive strength 1/28 days [MPa] 18.9/22.40 15 13.8

CO2 Uptake [%] 17.56 - -

Density [Kg/m3] 2101 class A*3 Normal weight*3

Absorption [Kg/m3] 153.8 175 208

Linear shrinkage [%] 0.027 0.03*4 0.065*5

*1：CSA 165.1 CSA standard on masonry units

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*2：ASTM C90 Standard specification for loadbearing concrete masonry units

*3：Blocks greater than 2000 Kg/m3 classified as “A” in CSA standard and “Normal weight” in ASTM standard

*4：The linear shrinkage classification defined by CSA standard

*5：Total shrinkage limitation at the time of delivery to the purchaser

Figure 4. 1: Eco-cement making process (Steps: 1. Pulverizing of raw meals and Mixing; 2. Nodulizing; 3. Clinkering; 4. Final pulverizing of clinkers)

117

Figure 4. 2: Laboratory scale carbonation curing set-up

(a)

118

(b) (c)

Figure 4. 3: Nodule clinkering in pilot-scale; (a) Industrial furnace; (b) Nodules before clinkering; (c) Nodules after clinkering

Figure 4. 4: Pilot-scale carbonation curing set-up

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Figure 4. 5: (a) Fresh Eco-cement CMU blocks made from industrial block machine; (b) blocks being loaded into carbonation kiln for carbonation curing; (c) Eco-cement blocks after carbonation curing

8 D50 7 OPC: 12.314μm 6 Eco-cement: 6.615μm 5

3 OPC Volume Percentage [%] Percentage Volume 2 Eco-cement

0 0 20 40 60 80 100 120 140 Partical Diameter [µm]

Figure 4. 6: Cements particle size analysis

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Figure 4. 7: Clinker Morphology: SEM image with EDS point analysis

100 CO2 Uptake 90 1day 28days 90days OPC-C: 6.10%; Eco-C: 8.84% 80 67.56 62.53 70 63.13 55.95 58.90 60 49.40 49.20 47.33 50 40 30.93 33.33 30 20.97

Compressive strength [MPa] strength Compressive 20 9.90 10 0 OPC-H Eco-H OPC-C Eco-C

Figure 4. 8: Cement paste compact compressive strength and CO2 uptake

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CO2 Uptake 45 1day 28days 90days OPC-C: 14.32%; Eco-C: 12.87% 40 34.74 34.83 35.68 35 33.28 30.03 29.79 30 25.84 23.70 25

20 17.95

Compressive strength [Mpa] strength Compressive 10

0 OPC-H OPC-C Eco-C

Figure 4. 9: Concrete slabs compressive strength and CO2 uptake

160 145.83 1 day 140 28 days 120 90 days Ω· cm] 100 81.13

80 53.90 60 48.63 35.43 40 27.30 Surface resistivity [K resistivity Surface 24.35 26.40 20 10.07

0 OPC-H OPC-C Eco-C Figure 4. 10: Concrete slabs surface resistivity test

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100 90 80 70 60 50 40 OPC-H Mass retained [%] 30 OPC-C 20 Eco-C 10 0 0 5 10 15 20 25 30 Freeze-thaw cycles Figure 4. 11: Concrete slabs freeze-thaw resistivity

0.0600% 0.0549% 0.0498% 0.0500%

0.0400% 0.0371%

0.0300%

0.0200% Linear Linear Shrinkage [%]

0.0100%

0.0000% OPC-H OPC-C Eco-C

Figure 4. 12: Concrete slabs linear shrinkage

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Chapter 5. Use of Eco-cement Derived from MSWI Ashes as Supplementary Cementitious

Material in Concrete

Preface

Even the eco-cement exhibited a certain degree of hydration property, under hydration curing

scenario, the strength of eco-cement as a standalone binder was relatively low compared to OPC.

Therefore, carbonation curing for 100% eco-cement products is a prerequisite. However, the

carbonating curing air-tight pressure kiln is not always available to concrete plants, since the

carbonation curing technique has not been fully adopted by concrete industry due to the

carbonation activation nature of the eco-cement, it might be hard for the industry to utilize this

waste-derived binding material as standalone binder because of the lacking of the facility.

Therefore, using eco-cement as partial cement replacement became another focused application in

this work. In this way, eco-cement may be used in concrete products under hydration curing,

which therefore widens the eco-cement application and opens up markets. At the same time, it is

also interesting to check the performance of eco-cement blend under carbonation curing. The

hydration phases available from ordinary cement in the blended concrete can make sure the quality

of concrete products even inadequate carbonation was performed.

The present study describes the results of a research aimed at investigating the feasibility of

applying an almost entire municipal solid waste incineration (MSWI) ashes derived eco-cement to

partially replace Portland cement. Beside of conventional hydration curing, carbonation curing which refers to introducing fresh cast concrete to CO2 was also performed. Influence of

substitution of 15% of cement with eco-cement, including mechanical property, leaching

performance, paste microstructure changing, freeze-thaw scaling resistance was investigated in

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lab-scale tests. This concept was further proved in the pilot-scale test by producing full-size

concrete masonry units (CMUs) in a real industrial concrete plant. The results collected from both

of lab-scale and pilot-scale tests proved that the eco-cement can work as supplementary

cementitious material to replace cement in concrete products under either hydration or carbonation curing scenario.

5.1 Introduction

The municipal solid waste (MSW) generation was 1.3 billion tons (Bt) globally in 2012, and this number was expected to increase to 2.2 Bt by 2025 (Hoornweg, 2012). Incineration is one of the most effective treatment methods of dealing with MSW, with the advantages of reducing volume, weight, and toxicity, as well as energy conversion (Makarichi et al., 2018). However, it is not the final solution due to the challenge of disposing of the substantial by-products, namely the bottom ash (BA), boiler ash (BLA) and air pollution control (APC) lime. Especially for BLA and APC lime, they are comprised of leachable heavy metals, chloride content and toxic organic contaminants (Erol et al., 2007; Ferreira et al., 2003; Li et al., 2012). Therefore, it is important to dispose of MSWI ashes in a proper and safe way. On the other hand, MSWI ashes contain a considerable amount of silica, calcium, and alumina, which are the basic constituents of the raw feed for the cement production (Shih et al., 2003; Tang et al., 2018). So, they have the potential to

be utilized as the raw material in cement making process. A carbonation active binding material

was produced from the MSWI ashes based on a study done by Ghouleh and Shao (Ghouleh &

Shao, 2018). This new binder was designed to use up to 86% of MSWI ashes with 14% of

hydrated-lime and silica sand as additives. The manufacturing process was almost the same with

Portland cement except that it adopted a lower clinkering temperature of 1000 °C, which could

save a great amount of energy. Two mineral phases produced in low temperature synthesis had

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shown the solidification properties activated by carbonation. First, the belite phase that also exists

in Portland cement. Second, the chloroellstadite (Ca10(SiO4)3(SO4)3Cl2) that fixed chloride and

sulfate into its structure. The cement so produced was not hydraulic but can only be activated by

carbonation.

Owing to the advantages of concrete, including easy access of raw ingredient, strong compressive

strength, good durability, construction shape flexibility, etc., Portland cement became the second

most widely used material after water with a production of four billion metric tons worldwide in

2014 (Paris et al., 2016). And the manufacture of cement consumed a great amount of energy and

contributed 8-9% of CO2 emission globally (Monteiro et al., 2017). Therefore, attentions have

been attracted to reduce environmental impact from the concrete sector. Carbonation curing seems

to be a possible solution, which refers to introduce carbon dioxide gas to fresh concrete. Unlike

weathering carbonation that leads to softened paste matrix due to the reaction between atmospheric

CO2 and hydration products (calcium hydroxide and C-S-H gel) (Groves et al., 1991), carbonation curing has been reported that it could offer an acceleration on strength gain and improvement in durability (Berger et al., 1972b; Jerga, 2004; Mo & Panesar, 2012; Rostami et al., 2011). In carbonation curing scenario, the CO2 reacts with anhydrous cement phases alite (C3S) and belite

(C2S) and generates C-S-H gel and calcium carbonates (Berger et al., 1972a), meanwhile, the

greenhouse gas was permanently sequestrated in the carbonated concrete. Another application that

can mitigate the negative environmental impact from the concrete industry is to use supplementary

cementitious materials (SCM) that have pozzolanic and/or cementitious properties. For instance, coal fly ash (FA), silica fume (SF), and ground granulated blast furnace (GGBF) slag are SCMs

that all originally industry by-products, which are able to increase the later age strength and durability resistance of the associated concrete (Tokyay, 2016a).

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In this study, an eco-cement mainly consisted of the carbonation active phases CE and C2S was synthesized to partially replace cement in concrete. Based on the study of Ghouleh and Shao

(2018), the clinkering mix design was further modified by using more than 94% of MSWI residues in the raw clinker mix and reduced the virgin additive to only calcium hydroxide by 6%. Then the feasibility of utilizing this waste derived eco-cement as supplementary cementitious material was successfully demonstrated in both laboratory and industrial scale. Carbonation curing was involved as one of the curing options to further reduce the carbon footprint of the concrete. The performance of compressive strength, leaching behavior, microstructure analysis, and freeze-thaw

resistance were studied for lab-scale paste compacts and concrete slabs. For full-size concrete masonry units (CMU) made from pilot-scale production, the physical requirements of commercial

CMU specified by Canadian standard association (CSA) were evaluated, including compressive strength, density, absorption, and linear shrinkage.

5.2 Materials and Methods

5.2.1 Materials

Three types of incineration residues, bottom ash (BA), boiler ash (BLA), air pollution control

(APC) lime were collected from an incinerator located in Ontario, Canada. Bottom ash, the bulk residue from the combustion unit, was collected from bottom ash bunker. Boiler ash was generated in the heat transfer system and APC lime was recovered from the baghouse further downstream.

ACROS® 98% pure calcium hydroxide was served as an additive raw material in making eco-

cement.

CAN/CSA-A3001 (Canadian Standards Association) Type GU ordinary Portland cement (Cement

Quebec) (OPC) was also used for this work. Larfarge NewCem ® Plus (NC) worked as a reference,

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which is a commercial SCM with 50% of coal burning fly ash and 50% of ground granulated blast

furnace slag. Granite (from the Bauval CCM query, Montreal, Canada) was chosen to be the

aggregate material for concrete with a size ranging from 0-5 mm.

5.2.2 Eco-cement Raw Material Characterization

X-Ray Fluorescence analysis was performed with the help of a Panalytical PW2440 Spectrometer.

The oxide form of major elements of bottom ash, boiler ash and APC Lime were determined by

XRF. The loss on ignition (LOI) value was determined based on ASTM D7348. An ELTRACS-

800 Carbon/Sulfur Analyzer was used to measure the carbon and sulfur content. In order to

minimize the variation between the analyzed sample selected and the large sample, “Quartering”

sampling method from ASTM C702 was adopted. The compositional analysis results are shown

in Table 5. 1 indicated that the MSWI residues comprised high contents of CaO, SiO2 and Al2O3,

which are the three main components in cement synthesis CAS system (CaO-SiO2-Al2O3). High

LOI value of BA expressed a considerable content of volatile in this by-product.

Laser particle analysis was conducted on the raw OPC and blended cements using a Horiba LA-

920 Particle size analyzer. The sample was dispersed in isopropanol with an ultra-sonic time of 1 minute.

5.2.3 Synthesis of Eco-cement

Raw clinker was designed based on the optimization values of cement compositional parameters, lime saturation factor (LSF), silica ratio (SR) and alumina ratio (AR), proposed by Ghouleh and

Shao (Ghouleh & Shao, 2018). Compared to their mix design, another type of residue BA was also added as calcium and silica sources, leaving the calcium hydroxide the only extra additive. Table

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5. 2 presents the detailed residue and additives combination mix design, and also the calculated

compositional parameters.

As-received bottom ash had a high moisture content due to the water quenching system in the incinerator. Pre-drying was performed for this residue under 105 °C for 24 hours, and it was further

passed through a 10 mm sieve to remove large chunks. Prior to moving into the mixing process,

all raw materials were mixed into the pulverizer based on Table 5. 2, and then pulverized for 2

minutes. A V-shape blender was used for mixing the raw blend material for 3 hours to ensure a

high uniformity material. Nodule making was carried out by a rotation granulator, water content

added into the raw blend was precisely controlled to ensure a homogenous nodules size in diameter

of 10 mm.

Clinkering process was performed in a Lindberg/Blue-M muffle furnace. Pre-heating was first

carried out by holding at 800°C for 1 hour to burn out all the organic content and decompose all

calcium carbonates. The temperature of the clinkers was then be increased to 1100°C and held for

another 1 hour in order to get the desired chemical compositions and cement properties. Upon on

completion, the clinkers were cooled down inside the furnace for 12 hours before retrieving and

pulverizing into powders.

5.2.4 Chemical Compositions (XRF) of OPC, Eco-cement and NewCem Plus

Table 5. 3 displays the chemical compositions of OPC, eco-cement, and NewCem Plus with the help of XRF. Eco-cement contained comparable compositions of CaO, SiO2, and Al2O3 to

NewCem Plus (53.88%, 18.72%, and 8.86% for eco-cement respectively).

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5.2.5 Mix Proportions and Specimen Casting

The production of blend cement was carried out with a V-shape blender. 3 hours of mixing

involved for blend cement with the replacement of 15% by weight of OPC with eco-cement or

NewCem Plus. The batch blend with eco-cement was named as ECB. The straight Portland cement batch (OPC) and commercial NewCem® Plus blend cement batch (NCB) were selected as control references.

Mix proportions of paste compacts and concrete are shown in Table 5. 4. For compacts, cylinder paste samples of 15 mm in diameter and 30 mm in height was prepared with an MTS machine using a uniaxial compact force of 3 kN. All compact batches used constant water to binder ratio of

0.15. A precast concrete mix design was adopted from a local CMU producer -Boehmer’s Block

Plant with water to binder ratio 0.35. The concrete slab specimens of 100 mm × 31 mm × 76 mm were vibration compact formed. These dimensions were selected as such to mimic the wall thickness of a concrete masonry unit. Figure 5. 1 shows the image of the lab made paste compacts and concrete slabs with dimensions labeled.

5.2.6 Curing Scenarios

Two different types of curing methods were performed in this project – conventional hydration curing and carbonation curing. For hydration curing, after 24 h initial curing, the samples were demolded and stored in moisture room with 100% relative humidity for further hydration. For carbonation curing, the procedures were split into three steps including: 1. Preconditioning; 2.

Carbonation curing; 3. Subsequent hydration. Preconditioning was carried out with the aid of a fan to dry the sample in order to remove free water and make rooms for carbon dioxide to penetrate and carbonates to precipitate. Mass was monitored during drying and 35% mix water loss was

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targeted. Lab-scale carbonation curing set-up is schematically illustrated in Figure 5. 2. A constant pressure of 0.069 MPa (10 psi) was maintained using a regulator to inject 99.5% purity CO2 for a

duration of 10 hours in the air-tight chamber. Mass was measured before and after carbonation.

The samples were then stored in the 100% relative humidity moisture room until the testing date

for subsequent hydration. For paste compact, no preconditioning was needed due to the nature of

the low water mix design.

The degree of carbonation was identified by carbon dioxide uptake using the mass gain method

proposed by Monkman and Shao (2006). The equation of CO2 uptake was governed in Eq. 1.

(%) = × 100% Equation �𝑀𝑀𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐+𝑀𝑀𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙�−𝑀𝑀𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 1 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈 𝑀𝑀𝐶𝐶𝑒𝑒𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚

Where is the mass of the specimen after carbonation, is the mass of

𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑖𝑖𝑖𝑖𝑖𝑖 𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 water retrieved𝑀𝑀 from the chamber, is the mass 𝑀𝑀of the specimen before

𝑀𝑀𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 5.2.7 Cement Paste consistency and Setting Time

The amount of water required to achieve normal consistency for the cement paste was determined

according to ASTM C187 with the help of a Vicat apparatus. Initial and final setting time of the

pastes with normal consistency were measured based on ASTM C191.

5.2.8 Quantitative X-ray Diffraction Analysis

The Quantitative X-ray diffraction (QXRD) analysis was performed on a Phnalytical X’Pert Pro

diffractometer, which is coupled with a Cu X-ray source and an X’celerator detector. The following X-ray conditions were chosen to run the analysis: Voltage: 40 kV; current: 40 mA; range

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5-70 deg 2θ; time per step: 50.165 sec. Paste compact samples at the age of 1 day were pulverized

before conducting the QXRD test.

5.2.9 Microstructure Analysis (SEM)

The micromorphology of the binding matrix was investigated by Scanning electron microscopy

(SEM), and a dispersive x-ray (EDX) detector was used to analyze the mineralogical composition.

Raw material powder samples and the fracture surface of the paste compact samples were coated

with 5 nm layer of platinum to improve the conductivity.

5.2.10 Lab-scale Concrete Performance Analysis

Mechanical compressive strength was assessed according to ASTM C-39 with the aid of an MTS-

SINTECH 30/G compression machine. The dimensions of the loading surface were measured with

a digital Vernier caliper. Each strength result represents the average of three samples.

For countries in cold climates in winter, like Canada, concrete faces a primary durability challenge

that involves physical deterioration mechanism: scaling of the concrete exposed to deicing salt under repeated freeze-thaw cycles(A. Harnik, 1980; Deja, 2003). ASTM C672 Freeze-thaw scaling test was conducted to estimate the concrete resistance to frost damage. Concrete specimens at the age of 28 days were covered with 6 mm of 4% of sodium chloride solution. The oven dried scaled concrete mass was collected and recorded every five freeze-thaw cycles. Also, the oven dried final concrete retained mass was recorded after the test finished. Then the mass retained percentage from each five cycle was calculated based on the total mass of the concrete and the recorded mass loss each measuring cycle.

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Use of MSWI residues as raw feed in eco-cement clinkers has urged necessity of checking the

environmental suitability of the concrete. Heavy metals, including arsenic, barium, boron, badmium, bhromium, lead, mercury, selenium, silver, and uranium have been determined by

Toxicity Characteristic Leaching Potential Test (TCLP). Concrete slabs at age of 28 days were first crushed into the desired size and then the TCLP Method 1311 described by United States

Environmental Protection Agency (EPA) was performed to evaluate the environmental impact of the blended cements. Acid digest method was used on leachate to analysis the heavy metal leached out concentration. It was also critical to test if the chloride content originally from the MSWI ashes could be fixed through high temperature clinkering and matrix solidification. Therefore, chloride concentration in the leachate from TCLP was also measure using ion chromatography.

5.2.11 Full-size Concrete Masonry Units (CMU) Preparation and Curing

In the interest of assessing the feasibility of using the eco-cement as an additive in real industrial scale, the standard concrete masonry units (CMU in Fig. 5. 1) were cast in Boehmer's block manufacturing plant (Ontario, Canada). The full-size CMU used the same mix design with the concrete slab produced in the laboratory scale. Two curing scenarios were also performed on

CMUs. Concrete blocks were stored in a moist room right after casting for hydration curing. For carbonation curing, as illustrated in Fig. 5. 3, an air-tight kiln was served as a carbonation chamber.

After losing 35% of mixing water from preconditional fan drying, the CMUs were delivered into the kiln and carbonated for 10 hours at 10 psi. All the carbonation curing parameters were chosen to be the same as the process conducted in lab condition. Blocks were further moved into the moist room for subsequent hydration.

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5.2.12 CMU Performance Test

As indicated by Canadian CSA 165.1, all the commercial CMUs must meet the four facets specified in the standard, including compressive strength, density, absorption, and linear shrinkage. Therefore, these four properties were tested on CMUs made in this study with blended cements. Before the compressive test, a sulfur mortar capping was placed on top of the block to ensure smooth, parallel surfaces perpendicular to the axial load. The capping also assures the uniformity of the distributed load. Compressive strength, density, and absorption were tested according to ASTM C140 and linear shrinkage was measured based on ASTM C426.

5.3 Results and Discussion

5.3.1 Laser Particle Size Analysis on Raw Binding Material

Figure 5. 4 shows the particle size distributions of cement containing different admixtures and raw eco-cement. As can be noted from the figure, the raw eco-cement had a smaller particle size

distribution with a mean value of 6.61 μm compared to that of ordinary OPC with a mean value of

12.31 μm. As a result of that, 15% of eco-cement decreased the overall grains’ size distribution in

EC blended cement to D50 of 11.61 μm. On the other hand, with 15% NewCem Plus replacement,

the NC blended cement displays a comparable distribution curve with OPC.

5.3.2 Consistency and Setting time

Table 5. 5 summarizes the consistency and the setting time for blended cement paste and OPC

paste reference. The weight percentage of the mixing water required was slightly decreased with

15% of eco-cement blended in, from 26% to 24%. All the blended cement paste showed

satisfactory initial setting values according to the limits specified by ASTM C595. An acceleration

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effect on setting time was revealed with the OPC replacement. Around 15% of initial setting time

and 17% of the final setting time were reduced with 15% of eco-cement.

5.3.3 Eco-cement’s Hydration and Carbonation Strength

Figure 5. 5 shows the strength development of paste compacts with eco-cement only under both

of hydration and carbonation curing. Under conventional hydration curing, the eco-cement

displayed some degree of cementitious property. The paste gained strength gradually during

hydration and eventually achieved 33.33 MPa at 90 days. This may be contributed by the hydration

phase, belite, in the eco-cement. On the other hand, the uniaxial compressive strength dramatically

raised up to 47.33 MPa after 1 day with an uptake of 8.84%. The pastes kept gaining strength

during subsequent hydration and they achieved a strength of 67.57 MPa at 90 days. The eco-

cement exhibited both of carbonation activation and cementitious behavior. Furthermore, this

binding material remained hydration potential after carbonation and 42.7 % more strength was

increased from 1 day to 90 days.

5.3.4 Paste Compacts with Blend Cement’s CO2 Uptake and Compressive Strength

Figure 5. 6 presents the averages of compressive strengths of blended cement paste compacts under hydration and carbonation curing scenarios with straight OPC as reference. Under conventional hydration scenario, at age of 1 day, the NCB-H pastes displayed a slight lower strength than hydrated OPC (OPC-H) due to the latent pozzolanic and cementitious properties of the fly ash and

GGBFS blended in. The SCMs in NCB-H reacted in the later age and its strength caught up after

28 days and became stronger than OPC control batch at age of 90 days (65.10 MPa for NCB-H compare to 55.95 MPa for OPC-H). On the other hand, with 15% eco-cement replacement, the strength of ECB-H was lower than OPC-H and NCB-H at age of 1 day, which was mainly due to

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the reduction of the C3S. At later curing ages of 28 days and 90 days, ECB-H showed a good

subsequent hydration property and reached almost equal strength with OPC-H. This was partially contributed by the extra C2S brought in by the eco-cement hydrated at later age.

The CO2 uptake is also included in this figure as an indication of the level of carbonation for

concrete batches under carbonation curing. NCB-C yield a lower carbonation uptake, a result associated with the reduction of C3S in this blended cement, which is a CO2 reactive component.

ECB-C exhibited the highest carbonation reactivity (uptake 7.70%), since the extra CE and C2S in

the eco-cement were also able to absorb gaseous carbon dioxide.

All paste samples were enhanced by carbonation curing at ages of 1 day and 28 days. However, at

90 days, the NCB-C paste showed a compressive strength of 56.43 MPa, which was lower than

that of conventional hydration cured NCB-H batch. It was indicative that the pozzolanic reaction

was weakened due to carbonation curing, which was in agreement with the previous study done

by Zhang et al. (2016). The strength was more significantly improved for ECB-C after

carbonation. The 1 day strength was dramatically increased to 61.23 MPa, reaching approximately

109% of OPC-H reference 90 days strength. This trend continued up to 90 days, which eventually

gained the highest strength of 71.1 MPa. In summary, ECB-C batch displayed the highest strength

in every testing age. The compressive strength advantage was contributed to the carbonation of

eco-cement. The injected CO2 was not only reacted with ordinary OPC grains in ECB-C, but also

the components in eco-cement (Chloroellestadite and Belite). The solidification from the

carbonation of eco-cement gave significant strength to the compact without sacrificing the long-

term strength. The eco-cement blended cement displayed a great mechanical advantage in every

age under carbonation curing scenario.

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5.3.5 Quantitative X-ray Diffraction Analysis

To determine the mineral phases in the raw eco-cement and products after carbonation and hydration curing, QXRD technique was adopted to analyze the paste samples of OPC batch and eco-cement blended batch at age of 1 day. The detected mineral phases are tabulated in Table 5.

Chloroellstadite (CE) and C2S were the most predominant crystalline minerals in the raw eco- cement in this study (16.9% for CE and 25.0% for Belite). Therefore, in EC blended cement, a reduction in alite and an increase in belite were observed. In addition, a small amount of CE (2.1%) was presented in the EC-blended cement. After 24 hours of hydration curing, alite and belite were the major hydration phases that had been consumed, along with the increase in amorphous content.

The semi-crystalline structure of C-S-H makes it hardly resolvable by standard diffraction techniques. Therefore, the C-S-H content cannot be accurately detected, and it composed part of amorphous value identified by XRD. The amorphous content in ECB-H (31.4%) was lower than

OPC-H (45.1%). This explained the paste compact compressive strength difference at age of 1 day.

Under carbonation curing scenario, due to the early age hydration acceleration effect (Berger et al., 1972c; Young et al., 1974; Zhang et al., 2016), the paste displayed higher C3S and C2S reduction compared to hydration cured samples. One of the hydration product-calcium hydroxide

(CH) was completely consumed by CO2 in all carbonated specimens. Calcium carbonate is the

product of the reactions between CO2 and regular components in ordinary cement (C3S, C2S and

CH). This mineral was higher in carbonated samples as predicted. Furthermore, for eco-cement blended samples, the injected CO2 reacted not only with the calcium silicate and CH but also with

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the eco-cement, reflecting by the reduction of CE after carbonation and less calcium carbonates

formation. To add, by parallel comparison, ECB-C had the highest amorphous content, which was

in agreement with the compressive strength test that ECB-C exhibited the highest strength development at age of 1 day.

5.3.6 Microstructure Analysis (SEM)

Analysis on the morphology of microstructure of eco-cement blended paste compacts at different ages was visualized by SEM and reported in Fig. 5. 7 (a), (b) and (c). The morphology transformation of the unique mineral in the eco-cement, chloroellstadite (CE), and its effect on the microstructure of the paste matrix were emphasized in this study.

In eco-cement’s unreacted powder state which is shown in Fig. 5. 7 (a)-1, the CE crystals were indicated with the help of EDX as longitudinal crystals, with a chemical composition of calcium, silicon, oxide, sulfur, and chlorine (spot 1). The hexagonal shape of CE also matched the description of this mineral by S. J. Saint-Jean et.al in their study (Saint-Jean et al., 2005). Figure

5. 7 (a)-2 displays that no morphology transformation was observed for CE crystals at age of 28 days for the eco-cement batch that under conventional hydration curing. Several distinct CE hexagonal crystals could still be found that partially embedded in the matrix with clear external surfaces. EDX results further confirmed the embedded crystals were CE at spot 2. It seemed that the CE crystals did not react under hydration curing condition, they stayed the same crystal morphology after 28 days hydration.

On the other side, as shown in Fig. 5. 7 (b)-1&2, at age of 1 day, a hexagonal columnar crystal could be found as CE crystal, which was confirmed by EDX analysis shown in Fig. 5. 7 (c) at

“spot 3” indicated in the same figure. An observation worth noting, a small cluster-like crystal

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formed on the surface of CE crystal. Furthermore, as highlighted in Fig. 5. 7 (b)-1, a portion of the

CE on the end of the columnar crystal had been consumed and left with a cavity with clusters.

Figure 5. 7 (b)-2,3,4 illustrate the microstructure change of the carbonated eco-cement blend under the same magnification (mag 50000×) from 1 day to 90 days. Image for the sample at 1 day was displayed again for better comparison with the others. Figure. 5. 7 (b)-3 presents the microstructure of the ECB-C compacts at age of 28 days. At this stage, CE crystal was no longer visible, and a network form of structure was identified instead. This kind of structure was believed due to the continuous growth of the cluster found at age of 1 day. Eventually, with 90 days of subsequent hydration, the network structure became much denser shown in Fig. 5. 7 (b)-4. It means that the

CO2 injected during carbonation curing reacted with CE and initiated the crystal transformation.

The cluster formed at the very beginning continuously grows into a network structure at age of 28 days. Due to the limitation of the voids space in the matrix, the cluster grown at later age kept densifying the framework, and finally formed into the impenetrable structure shown at 90 days.

The microstructure change could be the reason for the strength gain for ECB-C at 28 and 90 days.

The carbonated CE was continuously densifying the microstructure, resulting in a denser and less permeable matrix at later age, which was beneficial to the mechanical property of the compact and concrete. The porous network structure at the mid-age could be an issue for durability due to the cavities will increase the capillary suction in the concrete products.

5.3.7 Concrete CO2 Uptake and Compressive Strength

Figure 5. 8 presents the compressive strength results for concrete slabs with OPC, eco-cement

blend and NewCem Plus blend. For concrete under conventional hydration curing, ECB-H

displayed a comparable strength gain trend at 1 day and 28 days. However, the final strength of

139

ECB-H was 10.07% lower than OPC-H. This is linked to the fact that CE crystals had no

contribution to the strength gain under hydration curing, and the reduction on calcium silicates

resulted in lower final strength of ECB-H batch. To be noted, the strength requirement for

loadbearing concrete masonry units is 13.8 MPa based on ASTM C90. The 15% eco-cement

incorporated concrete could easily meet this criterion under hydration curing condition. NCB-H

yield a low strength at 28 days due to the latent hydraulic nature of the blended additives. This

batch eventually achieved more strength than ECB-H at later age of 90 days.

Consistent with the finding in paste compacts samples, concrete slabs with eco-cement blend exhibited the highest CO2 uptake of 16.15%, in comparison with uptake of 14.32% and 12.8% for

OPC-C and NCB-C respectively. This phenomenon is related to the carbonation of CE mineral in the ECB-C batch that absorbed more CO2 during the carbonation curing process. For NCB-C

batch, the reduction in carbonation active minerals- C3S and C2S led to a lower CO2 uptake.

All batches gained a higher strength after carbonation curing than hydration curing. A noteworthy

observation to mention was that a considerable strength was developed for carbonation cured

concrete with eco-cement. This batch displayed the highest strength at all testing ages. ECB-C

concrete was able to reach the one-day strength which took OPC batch 28 days by conventional

hydration curing. And it continually gained strength from subsequent hydration, leading to a 90

days strength of 38.93 MPa, which was 12.06 % stronger than that of OPC-H reference (34.74

MPa) at the same age. For NCB-C, similar to the paste compact samples, the strength development

for this batch was weakened due to carbonation, resulting in a slow strength increase rate and the

final strength was the lowest at 90 days.

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5.3.8 Freeze-thaw Scaling Resistance

Scaling resistance test was conducted on concrete slabs of OPC and eco-cement blended under

repeated freeze-thaw cycles in de-icing salt solution and Fig. 5. 9 displays the retained mass

percentage of the concrete. Due to the microstructure refinement phenomenon observed with the

help of SEM, carbonated eco-cement concretes at two curing ages were chosen in this test (28 days

and 90 days).

For batches with a hydration age of 28 days, OPC-C batch showed a good freeze-thaw resistance, and almost no mass loss after 30 repeated freeze-thaw cycles. At the meantime, conventional hydrated concretes (OPC-H and ECB-H) were completely destroyed. Carbonates precipitation in the cement matrix during carbonation curing created a denser microstructure which leads to a lower permeability on concrete (Rostami et al., 2011; Zhang & Shao, 2016). With less amount of salt solution penetration, the freeze-thaw damage was therefore greatly mitigated. However, the concrete with eco-cement exhibited a bad resistivity even after carbonation. This can be linked to the morphology change of eco-cement blend cement after carbonation, which was revealed by

SEM (Fig. 5. 7). At 28 days, as displays in Fig. 5. 7(b)-3, a porous networking structure was formed in blended cement after carbonation. These voids, therefore, increased the capillary suction property of the concrete and eventually caused severer damage under repeated freeze-thaw condition. Based on SEM (Fig. 5. 7(b)-4), a more compact structure was formed as an outcome of

the continuous phase transformation at later age. So, carbonated concretes with 15% of eco-cement

at age of 90 days were also evaluated to identify whether the densified structure can help the freeze-

thaw resistance. It turned out that the 90 days cured ECB-C concretes displayed a much better

performance. No obvious scaling could be observed after 30 freeze-thaw cycles. Therefore, longer

hydration is suggested for carbonated eco-cement concrete.

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5.3.9 Leaching Performance

Since the raw feeds of eco-cement were originally from MSWI ashes with leachable heavy metals

and chloride, the leaching performance of the blended concrete was therefore a critical factor

needed to be evaluated. To ensure safe usage, the eco-cement blended concrete, after 28 days of

curing, was subjected to the United States Environmental Protection Agency (U.S. EPA) toxicity

characteristic leaching procedure (TCLP) test. Table 5. 7 summarizes the results of leached out

heavy metals and chloride concentrations from the concrete with 15% eco-cement in its binding

material.

As can be noted from the table, the concentration of the ten monitored heavy metals in all leachate

solutions were found to be much lower than the Ontario and EPA limits. In terms of chloride, 10.6

mg/L was identified from the leachate from ECB-H and 3.4 mg/L from ECB-C, which were also much lower than the EPA regulation. Carbonation curing method mitigated the chloride leaching by 68% compare to hydration curing, but based on the criteria, the environmental impact should not be a concern regardless of the curing condition. To note, the TCLP test evaluated the leaching performance of the concrete under the worst-case scenario (concrete was crushed into smaller size and leaching in extraction solution), which rarely happens in real service life. The test revealed that the eco-cement had been stabilized through clinkering stabilization and mineral solidification.

5.3.10 Pilot-scale Test

5.3.10.1 Compressive Strength Test

The full-size CMUs that were produced in an industrial production line were tested for their

compressive strength. Figure 5. 9 displays the strength development of OPC and the blended

142 cement after curing duration of 1 day and 28 days. First of all, CMUs with 15% eco-cement additive by hydration curing displayed a slight strength reduction compared to OPC-H at all testing age, which resulted from the decrease of the hydration grains C3S in blended cement. But the reduction was acceptable, ECB-H achieved 87.1% of OPC-H’s strength at age of 1 day and 90.0% at age of 28 days. Moreover, the strength requirement from Canadian CSA and U.S. ASTM standards for load-bearing CMUs are 15 MPa and 13.8 MPa, respectively. Therefore, the blended concrete blocks under hydration curing were able to develop a required strength after 1 day.

Meanwhile, carbonation curing exhibited its advantage on early age strength gain and 1 day strength of carbonated concretes were rapidly developed. At 1 day, all carbonated concrete recorded a higher strength than the hydrated concrete from the same batch. With 15% of cement replaced with eco-cement, the ECB-C blocks yielded a comparable 1 day strength with OPC references, measured 34.7 MPa and 34.15 MPa respectively. For 28 days, OPC-C presented a marginally higher strength (48.1 MPa) compared to that of ECB-C (43.05 Mpa). It was suggestive that, in terms of compressive strength, the eco-cement was effective to serve as SCM to replace

15% of OPC in concrete regardless of curing scenarios.

5.3.10.2 Density, Absorption and Linear shrinkage

In addition to compressive strength, three more properties that were required by Canadian CSA

165.1 and U.S. ASTM C90 were tested. They included density, absorption, and linear shrinkage.

Therefore, these properties were analyzed in this study to ensure the eco-cement blend based

CMUs were suited to be a commercial product under the regulations. The results are presented in

Table 5. 8. The densities of ECB-H and ECB-C were 2172 Kg/m3 and 2214 Kg/m3 respectively, and both of batches classified as “A” in CSA code and “Normal weight” in ASTM standard.

143

According to the density, two standards defined the maximum allowable absorption which are

shown in the table. All the blended blocks met this requirement. ECB-H (120.1 Kg/m3) displayed a larger absorption than ECB-C (111.9 Kg/m3), an effect linked to the microstructure densification due to carbonation curing. Linear drying shrinkage was the last parameter that needed to take into consideration. With the tested shrinkage of 0.038% in ECB-H and 0.030% in ECB-C, these two batches assigned the second shrinkage classification based on CSA standard. Furthermore, their values were very close to the best shrinkage classification (0.03%) in CSA. ASTM required the total shrinkage limitation at the time of delivery to the construction site, which is 0.065%. The

experimentally measured drying shrinkage was based on extreme weathering condition

(continuous drying cycles under 50 °C based on ASTM C426), so the blended concrete blocks

well satisfied this provision.

5.4 Conclusion

This work has successfully demonstrated the feasibility of using almost entirely MSWI residue

derived eco-cement to partially replace cement in concrete produced in both lab and pilot-scale.

Paste compacts, concrete slabs, and full-size CMU were cast as experimental specimens to test the eco-cement performance. Conventional hydration curing and carbonation curing technique were involved in this study. Chemical composition analysis, microstructure morphology, compressive strength development, linear shrinkage, durability, and other physical requirements were tested in this work. The main conclusions can be drawn:

1. With 93.8% of raw feed from MSWI residues, the synthesized eco-cement additive mainly

consisted of crystalline mineral of CE and C2S, and the produced material had a smaller

particle size than OPC.

144

2. For concrete cast in lab, hydrated concrete with eco-cement blend could achieve

comparable strength with OPC references at 1 day and 28 days. Final strength decrease (10

% decrease compared to OPC reference) was observed for eco-cement blend batch due to

the reduction on hydration phases, but the blend concrete could easily achieve the strength

requirement for loadbearing concrete masonry units according to Canadian and U.S.

standards. The carbonated samples with eco-cement blended exhibited the highest

compressive strength compared to OPC and NewCem Plus blend concretes at all testing

ages. Carbonated eco-cement blend concrete developed 12.06 % more strength than OPC

control batch. It correlated with the strength contribution from the carbonation of CE and

C2S in the eco-cement, which was revealed by QXRD analysis and SEM analysis.

Therefore, in terms of strength, eco-cement can be used as SCM in cement regardless of

curing scenarios. Moreover, carbonation curing of blend concrete is more favorable in the

condition where a higher strength is needed than straight OPC.

3. Carbonation curing is not suggested to apply on concrete with NewCem Plus additive,

since it will weaken the strength development depended on the finding in this study.

4. SEM analysis confirmed that there was no morphology change of CE crystals in blend

cement during hydration. On the other hand, the early age carbonation consumed the CE

and formed small clusters on its surface at age of 1 day. Then, with the carbonation

initiation, the clusters kept growing at later age and densifying the structure due to the

limitation on the voids space, which was the reason for strength gain.

5. In terms of freeze-thaw resistance, there was no clear difference between hydrated eco-

cement blend concrete with OPC references. Carbonated eco-cement blended concrete

145

could gain high freeze-thaw damage resistance at later age because of the microstructure

densification from CE crystals.

6. The concretes containing eco-cement satisfied the requirements on heavy metals and

chloride content in leaching tests according to the criteria set by Ontario Regulation 558

and U.S. EPA regulation.

7. For the pilot-scale test, the hydrated and carbonated eco-cement blended full-size CMUs

that produced in a concrete block plant met all the physical requirements specified in

Canadian standard, including compressive strength, density, absorption and linear

shrinkage. The feasibility of using eco-cement as SCM in industry-scale production was

proved regardless of curing methods.

References

A. Harnik, U. M., A. Roesli. (1980). Combined influence of freezing and deicing salt on concrete—physical aspects. Durability of Building Materials and Components， ASTM International.

Berger, R. L., Young, J. F., & Leung, K. (1972a). Acceleration of Hydration of Calcium Silicates by Carbon Dioxide Treatment. Nature Physical Science, 240, 16. doi:10.1038/physci240016a0

Berger, R. L., Young, J. F., & Leung, K. (1972b). Acceleration of Hydration of Calcium Silicates by Carbon Dioxide Treatment. Nature Physical Science, 240(97), 16-18. doi:10.1038/physci240016a0

Deja, J. (2003). Freezing and de-icing salt resistance of blast furnace slag concretes. Cement and Concrete Composites, 25(3), 357-361. doi:https://doi.org/10.1016/S0958-9465(02)00052- 5

146

Hoornweg, D. B.-T., Perinaz. (2012). What a Waste : A Global Review of Solid Waste Management. Urban development series;knowledge papers no. 15. World Bank, Washington, DC. © World Bank.

Jerga, J. (2004). Physico-mechanical properties of carbonated concrete. Construction and Building Materials, 18(9), 645-652. doi:https://doi.org/10.1016/j.conbuildmat.2004.04.029

147

Monkman, S., & Shao, Y. (2006). Assessing the carbonation behavior of cementitious materials. Journal of Materials in Civil Engineering, 18(6), 768-776.

Monteiro, P. J. M., Miller, S. A., & Horvath, A. (2017). Towards sustainable concrete. Nature Materials, 16(7), 698-699. doi:10.1038/nmat4930

Tokyay, M. (2016). Cement and Concrete Mineral Admixtures. Boca Raton: CRC Press.

148

Zhang, D., Cai, X., & Shao, Y. (2016). Carbonation Curing of Precast Fly Ash Concrete. 28(11), 04016127. doi:doi:10.1061/(ASCE)MT.1943-5533.0001649

Standard References

ASTM D7348-13, Standard Test Methods for Loss on Ignition (LOI) of Solid Combustion Residues, ASTM International, West Conshohocken, PA, 2013, www.astm.org

ASTM C702 / C702M-18, Standard Practice for Reducing Samples of Aggregate to Testing Size, ASTM International, West Conshohocken, PA, 2018, www.astm.org

ASTM C187-16, Standard Test Method for Amount of Water Required for Normal Consistency of Hydraulic Cement Paste, ASTM International, West Conshohocken, PA, 2016, www.astm.org

ASTM C191-19, Standard Test Methods for Time of Setting of Hydraulic Cement by Vicat Needle, ASTM International, West Conshohocken, PA, 2019, www.astm.org

ASTM C39 / C39M-18, Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens, ASTM International, West Conshohocken, PA, 2018, www.astm.org

ASTM C672 / C672M-12, Standard Test Method for Scaling Resistance of Concrete Surfaces Exposed to Deicing Chemicals, ASTM International, West Conshohocken, PA, 2012, www.astm.org

149

ASTM C140 / C140M-18a, Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units, ASTM International, West Conshohocken, PA, 2018, www.astm.org

ASTM C426-16, Standard Test Method for Linear Drying Shrinkage of Concrete Masonry Units, ASTM International, West Conshohocken, PA, 2016, www.astm.org

ASTM C595 / C595M-19, Standard Specification for Blended Hydraulic Cements, ASTM International, West Conshohocken, PA, 2019, www.astm.org

ASTM C90-16a, Standard Specification for Loadbearing Concrete Masonry Units, ASTM International, West Conshohocken, PA, 2016, www.astm.org

CSA 165.1 Specification and General Specifications Notes, Canadian Concrete Masonry Producers’ Association, CSA Group, 2018

ASTM C140 / C140M-18a, Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units, ASTM International, West Conshohocken, PA, 2018, www.astm.org

Ontario Regulation 558/00 General-Waste Management, Environmental Protection Act, 2000

Code of Federal Regulations Title 40. Protection of Environment 264.24 Toxicity Characteristic, 1990

Ambient Water Quality Criteria for Chloride, United States Environmental Protection Agency, 1988

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Table 5. 1: Chemical compositions of MSWI ashes

Composition wt%

Oxide Bottom ash Boiler ash APC Lime

CaO 16.21 40.03 49.12

SiO2 26.69 27.34 2.44

Al2O3 9.66 15.16 1.42

Fe2O3(T) 6.20 4.50 0.31

MnO 0.14 0.31 0.02

MgO 2.27 4.08 1.22

Na2O 2.36 - -

K2O 1.00 0.05 0.65

TiO2 1.85 4.76 0.22

P2O5 1.74 3.42 0.12

Total-C 19.30 0.10 2.31

Total-S 0.59 2.06 1.01

Cl 2.14 0.20 14.82

LOI 29.74 0.15 29.65

Table 5. 2: Mix design of clinker proportions (wt%) LSF SR AR

MSW Residues Additive

Bottom ash Boiler ash APC Lime CH

24.8 27.6 41.4 6.2 0.79 1.46 2.27

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Table 5. 3: Chemical compositions of OPC, eco-cement and NewCem Plus

Oxides OPC Eco-cement NewCem Plus

CaO 65.00 53.88 51.56

SiO2 20.54 18.72 21.48

Al2O3 4.57 8.86 11.58

Fe2O3(T) 3.11 3.62 4.16

MnO 0.10 0.15 0.19

MgO 2.80 2.68 3.06

Na2O 0.24 < 0.01 < 0.01

K2O 0.68 < 0.01 < 0.01

TiO2 0.20 2.38 2.53

P2O5 0.26 1.90 2.01

LOI 2.49 7.81 3.41

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Table 5. 4: Mixture proportions for pastes and concretes

Concrete Paste (Slabs and Full-size CMU) Mixture component [%] OPC- NCB- ECB- OPC- NCB- ECB- H/C H/C H/C H/C H/C H/C

OPC Cement 85 72.2 72.2 9.7 8.24 8.24

NewCem Plus - 12.8 - - 1.46 - (FA+GGBFS)

Eco-cement - - 12.8 - - 1.46

water 15.0 15.0 15.0 3.4 3.4 3.4

Aggregate (2-5 mm) - - - 28.9 28.9 28.9

Aggregate (0-2 mm) - - - 58.0 58.0 58.0

Water/binder ratio 0.18 0.18 0.18 0.35 0.35 0.35

Notes:

1. OPC: Ordinary Portland cement; NCB: New-Cem blend (15% NewCem Plus + 85% OPC); ECB: Eco-cement blend (15% Eco-cement + 85% OPC) 2. H: Hydration curing; C: Carbonation curing

Table 5. 5: Consistency and setting time

OPC NCB-H ECB-H Limit

Normal consistency [%] 0.26 0.26 0.24 -

Minimum 45 and Time of initial setting [min] 120 105 103 maximum 420 *

Time of final setting [min] 180 165 150 -

* Specified by ASTM C595

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Table 5. 6: Mineral compositions (QXRD) of OPC, eco-cement and their blend pastes at age of 24 hours

Wt % Mineral Formula Eco-cement OPC OPC-H OPC-C ECB ECB-H ECB-C

Alite Ca3Si05 n.d. 48.3 27.5 25.1 37.9 28.2 18.2

Belite Ca2SiO4 25.5 19.5 12 9.8 20.7 19.8 12.1

Tricalcium aluminate Ca3Al2O6 n.d 4.2 n.d n.d n.d n.d n.d

Brownmillerite (C4AF) Ca2FeAlO5 n.d. 7.8 8.3 5.4 7.9 9.9 4

Chlorellestadite Ca5(SiO4)1.5(SO4)1.5Cl 16.9 n.d. n.d. n.d. 2.1 2.2 1.4

Quartz SiO2 0.2 0.3 0.5 trace 0.2 trace 0.2

Wadalite Ca12Al14O33 11.4 1 2 1 2.5 2.6 1.9

Periclase MgO 3.4 1.1 0.8 1 1.4 1.5 0.5

Calcite CaCO3 n.d. 1.4 2.7 15.3 2.4 3.7 11.7

Gypsum CaSO4*2H2O n.d. 1.8 n.d. n.d. 1.5 n.d. n.d.

Portlandite Ca(OH)2 n.d. n.d. 1.1 n.d. n.d. 0.7 n.d.

Amorphous 42.6 14.6 45.1 42.4 23.4 31.4 50

Notes:

1. OPC: Ordinary Portland cement 2. ECB: Eco-cement blend (15% Eco-cement + 85% OPC)

154

Table 5. 7: Leaching Performance

Canada,Ontario U.S. EPA ECB-H ECB-C Regulation 558*1 Regulation*2*3 Parameter Parameter [mg/L] [mg/L] [mg/L] [mg/L]

Arsenic As <0.01 <0.01 2.5 5.0

Barium Ba 0.34 0.65 100.0 100.0

Boron B 0.22 0.36 500.0 -

Cadmium Cd <0.001 <0.001 0.5 1.0

Chromium Cr 0.21 0.14 5.0 5.0

Lead Pb <0.01 <0.01 5.0 5.0

Mercury Hg <0.001 <0.001 0.1 0.2

Selenium Se <0.01 <0.01 1.0 1.0

Silver Ag <0.01 <0.01 5.0 5.0

Uranium U <0.01 <0.01 10.0 -

Chloride Cl− 10.6 3.4 - 230/860

*1: Canada Ontario regulation 558/00: General-waste management

*2: U.S. EPA 40 CFR 261.24 – Toxicity characteristic for heavy metals;

*3: U.S. EPA Ambient water quality criteria for chloride – 230 mg/L for chronic freshwater; 860 mg/L for acute freshwater

Table 5. 8: Density, absorption and linear shrinkage of CMU

*1 *2 Parameters ECB-H ECB-C CSA ASTM

Density [Kg/m3] 2172 2214 class A*3 Normal weight*3

Absorption [Kg/m3] 120.1 111.9 175 208

*4 Linear shrinkage [%] 0.038 0.030 0.03 - 0.045 0.065

*1：CSA 165.1 CSA standard on masonry units

155

*2：ASTM C90 Standard specification for loadbearing concrete masonry units

*3：Blocks greater than 2000 Kg/m3 classified as “A” in CSA standard and “Normal weight” in ASTM standard

*4：Total shrinkage limitation at the time of delivery to the purchaser

Figure 5. 1: Types of specimens produced

Figure 5. 2: Laboratory-scale carbonation curing set-up

156

Figure 5. 3: Pilot-scale carbonation curing set-up

8 D50 7 OPC: 12.31 μm NewCem Blend: 12.34 μm 6 Eco-cement Blend: 11.61 μm Eco-cement: 6.61 μm 5

4 OPC 3 NewCem Blend Volume Percentage [%] Percentage Volume 2 Eco Blend

Raw Eco additive 1

0 0 20 40 60 80 100 120 140 160 Partical Diameter [µm] Figure 5. 4: Laser particle size analysis

157

90 CO uptake 80 2 Eco-cement-C: 8.84% 63.13 67.56 70 Eco-cement-H 60 Eco-cement-C 50 47.33

40 33.33 30 20.97 Comressive strength [Mpa] strength Comressive 20 9.9 10

0 1 28 90 Curing age [days]

Figure 5. 5: Paste compacts compressive strength of 100% eco-cement

30 OPC-H OPC-C 20 NC-H CO uptake Compressive Strength Strength [Mpa]Compressive 2 NC-C 10 OPC-C: 6.10 %; NC-C: 5.72 %; EC-C: 7.70 EC-H % 0 0 20 40 60 80 100 Curing Age [Day]

Figure 5. 6: Paste compacts compressive strength of OPC and blend cement

158

(a)

(b)

159

(c)

Figure 5. 7: Eco-cement paste microstructure: (a) SEM images with EDX analysis: 1: Raw Eco- cement; 2: ECB-H at 28 days; (b) SEM images of ECB-C up to 90 days: 1: 1 day (mag. 100,000×), 2: 1 day (mag. 50,000×), 3: 28 days (mag. 50,000×), 4: 90 days (mag. 50,000×); (c) EDX point analysis

160

OPC-H OPC-C Compressive Strength Strength [Mpa]Compressive 20 NCB-H NCB-C CO2 uptake OPC-C: 14.32 %; NC-C: 12.80 %; EC-C: 16.15 % ECBH ECB-C 15 0 20 40 60 80 100 Curing Age [Day] Figure 5. 8: Concrete slabs compressive strength

120.00

100.00

80.00

60.00

（ 40.00 OPC-H 28 days) OPC-C（28 days) （

Mass retained [%] EC-H 28 days) 20.00 EC-C（28 days) EC-C (90 days) 0.00 0 5 10 15 20 25 30 35 Freeze-thaw cycles Figure 5. 9: Freeze-thaw scaling resistance of concrete slab

161

70 CSA criteria: 15 MPa 60 1D 28D ASTM criteria: 13.8 MPa

48.1 50 43.05

40 36.9 34.15 33.2 34.7 30 27.45 23.9

20 Compressive strength [Mpa] strength Compressive

0 OPC-H OPC-C EC-H EC-C

Figure 5. 10: Compressive strength of full-size CMUs

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Chapter 6. Use of Bottom Ash as Aggregate and Eco-cement as Binding Material in

Concrete

Preface

Concrete is made up of three basic components: cement, aggregate, and water. Aggregate is the primary ingredient that represents the highest weight fraction of the concrete. Especially in precast concrete with low cement content and low water-cement ratio, the aggregate constitutes more than

85% by weight of the concrete. Because of the extensive use of concrete worldwide every year, construction industry is facing challenge to find new sources of aggregates to substitute for the conventional aggregates. On another note, bottom ash represents the majority (90%) of the total by-product that incinerator generated. The granular shape and the relatively compact nature make it possible to use BA as an alternative for construction aggregate. In this chapter, the feasibility of using BA to partially replace natural aggregate was examined. LitexTM lightweight aggregate and

granite aggregates were used as references. Furthermore, the eco-cement synthesized in chapter 4

was also introduced in this study. A green concrete was developed with eco-cement and BA aggregate. Ordinary cement was used first as the binding material to examine the performance of

the BA aggregate in normal binding system. Then, the BA aggregate was used in concrete with

eco-cement. Due to the instability of the as-received BA, different pre-treatment methods were

evaluated and the most effective one – 200 °C heat treatment was adopted. Then the treated BA

aggregate was tested for its concrete compressive strength in both OPC and eco-cement binding

system. In addition, the environmental impact and microstructure of interfacial transition zone

(ITZ) were analyzed. The results concluded that with a 50% replacement ratio, it is feasible to use

BA to partially replace granite aggregate in concrete.

163

6.1 Introduction

Concrete is made up of three basic components: cement, aggregate, and water. Aggregate is the

primary ingredient that represents the highest weight fraction of the concrete. Especially in precast

concrete with low cement content and low water-cement ratio, the aggregate constitutes more than

85% by weight of the concrete. Considering the extensive use of concrete worldwide every year,

a great demand on natural aggregates is pressed from the construction industry. Driven by the fact

that there is a limitation on the natural resources, new material should be introduced to substitute

for conventional aggregates.

Three residues are produced from the municipal solid waste incinerator, which are bottom ash

(BA), boiler ash (BLA), and air pollution control (APC) lime. The bottom ash is not considered as

a hazardous material and no special treatment is needed before landfilling. However, it counts for

more than 90% (by mass) of incineration ashes and makes it also costly to landfill. Increased

restrictions and harsher growing regulatory codes pose numerous challenges for landfill practice.

On the other hand, BA can be used as aggregates in road construction and concrete production.

European countries have started to use BA as unbound aggregates in pavement and embankment

construction. However, the secondary pollution to the surrounding soil and underground water due

to the heavy metal and soluble salts leaching remains a concern (Baldwin et al., 1997). It was suggested that only coarse portion of the BA be used due to the higher contamination in fine particles (Baldwin et al., 1997). Vegas et al. (2008) proved that it is suitable to use fresh BA as road base aggregates if the material does not contain a high level of concentration of soluble salts.

More than one-month natural weathering was suggested by Forteza et al. (2004) to stabilize the

BA which could pass the mechanical and environmental regulations. Early age carbonation is

164

another treatment process that was proposed by Van Gerven et al. (2005) that can mitigate the

heavy metal leaching of BA as the base material in road construction.

Another possible application is to use the BA as aggregates in concrete for building construction.

But studies reported expansion and cracking problems for concrete with raw BA due to the

hydrogen gas releasing from the unstable aluminum in the BA under alkaline pore solution in the

concrete (Lynn et al., 2017; Pera et al., 1997). Different BA treatment methods were proposed to

eliminate the negative effect of BA in concrete. Again weathering concept was introduced by van

Beurden et al. (1997) that a six weeks of storage was a necessary for fresh BA before mixing with

cement. Sodium hydroxide solution treatment developed by Pera et al. (1997) could chemically

stabilize the BA aggregate by releasing hydrogen gas. Sintering and vitrifying were methods using

high temperature (1050 °C for sintering and 1450 °C for vitrifying) to make new forms of BA aggregate (Cheeseman et al., 2005; Ferraris et al., 2009). However, due to the high energy cost in these methods, it is not economically feasible to make BA aggregate while the market price of commercial aggregates is low.

In this study, five stabilization methods of as-received BA were evaluated, including weathering,

water washing, sodium hydroxide solution washing, early age carbonation, and 200 °C treatment.

The treated BA was then applied as concrete aggregate. OPC was first used as binding material to

test the performance of the BA aggregate with normal cement. Then, the waste derived eco-cement was added as binder to produce a green eco-concrete that all major components in concrete were originally from MSWI residues. Commercial Litex lightweight aggregates, which made from iron industry by-product, as well as the granite aggregates, were used as references. Besides of mechanical and environmental performance, the ITZ zone was also evaluated based on

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microstructure analysis. The technique provided in this study presents a solution that converting

all the MSWI residues into value-added building products.

6.2 Experimental Program

6.2.1 Materials

The MSWI bottom ash (BA) was collected from an incinerator located in Ontario, Canada.

Commercial Lafarge LitexTM lightweight aggregates were used as a reference, which is originally

from the iron industry by-product-expanded slag. The normal weight conventional granite

aggregates from the Bauval CCM query, Montreal, Canada were also used as reference.

CAN/CSA-A3001 (Canadian Standards Association) Type GU ordinary Portland cement

(Lafarge) (OPC) was chosen to be one of the binding materials. Eco-cement that synthesized in

the previous chapter was another binder that was used in this study.

6.2.2 Bottom Ash Stabilization Methods

According to the preliminary tests, the as-received BA was not suitable to be used directly in concrete due to the problems including low compressive strength, expansion, foam secretion, mold formation and red deposits generation. These problems occurred during the concrete subsequent hydration in the moist room. Therefore, treatment had to be done before utilizing this material as

aggregate into concrete. Physically, the ferrous fraction was first removed with the help of a

magnetic separator before any further treatment. Then, five stabilization treatments were

conducted and evaluated including weathering, water washing, sodium hydroxide washing,

carbonation, and 200 °C pyrolysis treatment.

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Weathering was conducted by aging the BA to the open atmospheric air for 3 months. Water

washing was performed by fully immersing the BA into water and stirring the solution and then

remove the upper solution after all the fine particles precipitated. New clean water was poured in

and this process was repeated for 5 times. Sodium hydroxide washing was another tested treatment.

The BA was immersed in 2 M sodium hydroxide solution for 15 days. After that, water washing

was adopted to remove the alkaline solution and the BA was further dried in an oven at 105 °C.

Carbonation process was conducted in an air-tight chamber (Fig. 6. 1) with a pressure of 1.5 bar

pure CO2 (99.5%) for 2 hours. The same set-up was used for concrete carbonation. BA was carried

by filter paper on top of a steel mesh stand in order to let CO2 penetrate on both of top and bottom

side during carbonation. Pyrolysis process was developed by treating the as-received BA at 200°C

for 72 hours to remove moisture as well as the leftover carbon content. The as-received BA was

wet because of the water quenching during the incineration process.

6.2.3 Bottom Ash Aggregates Characterization

The properties of BA aggregates were investigated first before being used in concrete application.

Chemical compositional analysis of as-received and treated BA was carried out using X-Ray

Fluorescence (XRF). Sieve analysis on the dried BA was performed based on ASTM C136, and the sieved aggregates were stored separately. The dry loose bulk density of the aggregates was determined using shoveling procedure according to ASTM C29. The pycnometer method described in ASTM C1761 was followed to determine the 72 hours absorption and oven-dried relative density of BA aggregate.

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6.2.4 Mix Proportions and Concrete Preparation

Pre-cast concrete slab was chosen to be the testing specimen in this work with a dimension of 31

×76×100 mm. The size of the concrete slab was designed to mimic the web portion of a concrete masonry unit (CMU). As presented in Table 6.1, a commercial CMU mix design was adopted with a cement content of 9.7 % and water/cement ratio of 0.35. With ordinary Portland cement. Granite concretes with BA aggregate replace percentages of 50%, 70%, and 100% were examined. With the most promising BA replacement ratio, the synthesized eco-cement was introduced as the binding material to make an eco-concrete that most of the materials originally from MSWI residues. For concretes made from both BA aggregate and granite, two aggregates mixed first before adding cement to get uniform distribution. As displayed in Fig. 6. 2, the concrete aggregate gradation was selected following a commercial CMU aggregate size distribution of Boehmers’

Block.

All the concretes were vibration compact formed before moving into the curing step. Two different curing methods were performed. Besides the conventional curing scenario that store the concretes into the fog room for further hydration, carbonation curing was also performed. For carbonation curing, preconditioning was fist conducted by drying the block with the help of a fan in order to remove a certain amount of water (50% of mixing water) to promote the penetration of CO2 gas.

Then the partially dried concrete moved into an air-tight chamber (Fig. 6. 1), and CO2 gas with

99.5% purity was injected to maintain a pressure of 0.069 MPa (10 psi) for a duration of 10 hours.

Concrete weights before and after the carbonation were recorded to calculate the CO2 uptake. The carbonated concrete slabs were then stored in the fog room until the testing date.

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The level of carbonation was determined by CO2 uptake using the mass gain method established

by (Monkman & Shao, 2006). The calculation equation based on the weight change of each sample

during the carbonation which was governed in Eq.1.

(%) = × 100% 1 �𝑀𝑀𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐+𝑀𝑀𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙�−𝑀𝑀𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈 𝑀𝑀𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝑡𝑡 Where is the mass of the specimen after carbonation, is the mass of

𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 water 𝑀𝑀evaporated during carbonation and retrieved from the 𝑀𝑀chamber after curing,

is the mass of the specimen before carbonation, and is the mass of

𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑖𝑖𝑖𝑖𝑖𝑖 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 t𝑀𝑀he dry cement used for a specimen. 𝑀𝑀

6.2.5 Compressive Strength Test

The concrete slabs were tested according to ASTM C30 with the aid of an MTS-SINTECH 30/G

compression machine with 150 kN loading cell. The loading surface dimensions were measured

using a Vernier Caliper.

6.2.6 Concrete Density, Absorption and Permeable Voids Content

The density, absorption and permeable voids content of hardened concrete at age of 28 days were

determined according to ASTM C642. The concrete oven dry mass “A” was measured after 48

hours drying in an oven at 105 °C and cooling down to room temperature. The 72 hours fully water

immersion was performed on concrete and the surface dry mass was recorded as “B”. The samples

were then put in boiling water for 5 hours in order to promote full absorption by the pores. The

boiled surface dry mass of concrete was then collected as “C”. Then, the apparent mass “D” was

measured by weighting the sample suspended in water to calculate the volume of the samples. The

targeted parameters were calculated through Eqn. 2 to 4. Three samples were tested for average.

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= × Equation 2 𝐴𝐴 𝐷𝐷𝐷𝐷𝐷𝐷 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝐶𝐶−𝐷𝐷 𝜌𝜌 (72 ) = × Equation 3 𝐵𝐵−𝐴𝐴 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 ℎ𝑟𝑟 𝐶𝐶−𝐷𝐷 𝜌𝜌 = × 100 Equation 4 𝐶𝐶−𝐴𝐴 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 𝐶𝐶−𝐷𝐷 Where = density of water = 1g/cm3

𝜌𝜌 6.2.7 Concrete Leaching Performance

Toxicity characteristic leaching potential test (TCLP) method 1311 from US environmental

protection agency (EPA) was adopted to evaluate the environmental impact of the eco-concrete

made from BA aggregates and eco-cement. After casting, concretes were first stored in the moist

room (100% RH) for 28 days before crashing into pieces that could pass 9.5 mm sieve. The crushed

sample was rotated with the extraction fluid at 30 ± 2 rpm for 18 ± 2 hours under 23 ± 2 °C ambient

temperature. Inductively coupled plasma mass spectrometry (ICP-MS) was used to detect heavy metal concentration in the leachate.

6.2.8 Microstructure Analysis (SEM)

The interfacial transition zone for different matrix systems was investigated by a FEI Quanta 450

Environmental Scanning Electron Microscope operating at 10 KV. Concrete (28 days) cross- sections were cut and mounted in epoxy before polishing by 1200 grit paper. A final polish was conducted using a 0.05 µm diamond suspension solution. The finished surfaces were coated with a 5nm layer of platinum to improve the conductivity.

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6.3 Results and Discussions

6.3.1 BA Treatment Methods

At the beginning, the BA was used in concrete in its as-received condition. The first obvious

drawback by doing it was the color alteration of the concrete caused by the black color from as-

received BA. The final concrete product became dark in color and therefore it may not be in favor

by the architects and customers. As presented in Fig. 6. 3, defects were observed during the

hydration period in the 100% relative humidity room, including pitting, foaming, corrosion and

mold forming. Furthermore, the compressive strength of the BA aggregate concrete was very low

even with a curing age of 90 days (1.62 MPa for concrete slab made with 100% as received BA).

Due to the instability of the as-received BA aggregates, different treatments were tried before

applying the BA in concrete. The red deposit found on the surface of the concrete related to the

iron content in the BA. Therefore, magnetic separation was performed to remove the metallic

components. This became the prerequisite process before any further treatment.

First, water washing was tried by cleaning the as-received bottom ash using tap water. Expansion

and color alteration could be mitigated after treatment. However, pitting and mold forming still

happened during the subsequent hydration period. And also, this process created a large amount

of wastewater, which may pose challenges to dispose. Second, sodium hydroxide solution washing

treatment was used by immersing the BA in 3% of sodium hydroxide solution for 72 hours. Then

tap water washing was adopted to remove the sodium hydroxide from the treated BA. This method

was proved that it can eliminate the expansion problem, however, mold forming and color

alteration remained unsolved. And the sodium hydroxide introduced could not be fully removed

even after applying repeated water washing. The remaining NaOH content may be problematic for

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the long-term durability performance for the concrete. Natural aging is another method tried in this

project. A barrel of bottom ash was stored for six months after collecting from the incinerator. No

noticeable improvement from this method was observed based on concrete performance. Some researchers revealed that the BA had the capacity to absorbing gaseous carbon dioxide and lead to a more stable material. With the accelerated carbonation set-up shows in Fig. 6. 1, the as-received

BA was mixed with different ratio of water, ranging from 0.1 to 1.0. No CO2 sequestration was

observed regardless of the carbonation pressure and duration. The last treatment method –pyrolysis

was conducted by placing BA aggregate in oven at 200 °C for 72 hours. This process was

successfully eliminated the undesired black color of the BA. The color change is shown in Fig. 6.

4. Sieve analyses were performed before and after pyrolysis presented in Fig. 6. 5, more fine

material was generated during this process leading to a higher passing percentage in the range

below 1 mm in size. More importantly, all the negative effects were eliminated. Table 6.2 presents

the chemical compositions of BA before and after pyrolysis treatment. The results indicated that

the carbon content and LOI value were greatly reduced. Therefore, the BA became more stable

after the treatment.

Therefore, 200 °C pyrolysis was adopted to be the treatment method applied before adding the BA

into the concrete. The granules were then sieved and stored separately based on their size classes,

as shown in Fig. 6. 6.

6.3.2 Aggregate Characterization

Table 6.3 displays the absorption, relative density and loose bulk density for the three aggregate

materials. From the relative density, which exhibited the volume to weight relationship for each

aggregate, granite was the densest material and comparable values were recorded for bottom ash

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aggregate and litex aggregate. Lightweight aggregate Litex measured a higher loose bulk density

of 1100.3 Kg/m3, comparing to bottom ash of 831.4 Kg/m3. They both met the maximum criteria

limit of 1120 Kg/m3 from ASTM standard C330. Therefore, bottom ash could be classified as lightweight aggregate as well. The lightweight nature of these BA aggregates owing to the porous

structure formed during the water quenching step in its process. Absorption is another critical

character that should be considered and compensated during the concrete mixing, since it can alter

the water-to-cement (w/c) ratio and consequently have influence on concrete performance

development. Bottom ash and Litex recorded higher absorption than the normal weight granite

aggregate. This was also associated with the high voids content in the lightweight aggregates.

Associated water content was added accordingly to each aggregate in order to reach saturated

surface dry (SSD) condition before mixing.

6.3.3 BA Aggregate Application Ratio

The compressive strengths of the concrete with fully or partially BA aggregate replacement were

tested and the 1 day strength results are shown in Figure 6. 8. In order to simplify the process of

changing parameters, OPC and conventional hydration curing were selected in this test. Batches

with 100% and 75% of BA aggregate exhibited a relatively low strength of 7.00 MPa and 7.71

MPa, while concretes with 50% BA aggregate measured 12.4 MPa strength. These data showed a

correlation between the strength and the replacement ratio, which was the more BA aggregate

involved in the concrete, the lower the strength developed in 1 day. This could be due to the low

compressive strength of BA aggregate itself. A failed concrete slab was photographed and

displayed in the Fig. 6. 7. An observation worth noting that many ruptured BA aggregate could be

located on the fracture surface instead of failing at the paste, suggesting the concrete failed at

aggregate and a lower strength than reference batches. Since the concrete with 50% BA aggregate

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had a close strength to the Litex aggregate batch, 50% replacement ratio was decided to use in this

project.

6.3.4 Compressive Strength and Carbon Uptake

With bottom ash used in concrete at levels of 50% by mass of the aggregate component, the

concretes were tested for its carbonation behavior and compressive strength at 28 days. Eco-

cement that synthesized in Chapter 2 was also used as another binding material to combine with

BA aggregate to test the feasibility of “green concrete” concept that maximized the usage of MSWI

residue in concrete. A typical “green concrete” is shown in Fig. 6. 9.

The results are displayed in Fig. 6. 10. For conventional hydration curing scenario, the BA

incorporated concrete exhibited a good long-term strength development. The strength increased to

25.3 MPa at 28 days, which was higher than the commercialized Litex aggregate concrete of 20.6

MPa at the same curing age. Even though natural granite aggregate provided the strongest concrete

product at 28 days, at 50% level of replacement, the BA aggregate concrete achieved 84.3% of

this granite reference. The high potential strength development in BA aggregate could be

contributed by the pozzolanic property of the fine particles. As confirmed in chapter 3, the

pulverized BA was confirmed that it behaved well as pozzolanic material, which could benefit the

concrete with a higher strength gain rate. This also reflected in this chapter, some fine particles in

the BA aggregate reacted as pozzolans in later hydration age and the extra C-S-H gel refined the microstructure, leading to an increased compressive strength.

In the case of carbonation curing, all the batches showed a certain capacity to absorb CO2. Concrete with eco-cement displayed the highest carbonation degree owing to the high CO2 reactivity of this

binding material. As concluded from Chapter 4, the chlorellestadite (CE) and belite (C2S) minerals

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in eco-cement reacted with gaseous carbon dioxide and formed a solidified matrix with

permanently CO2 embedment. For concrete containing 50% of BA aggregate and eco-cement binder, a 15.93% of uptake was achieved compared to 14.57% of Litex-OPC-C and 14.32% of

Granite-OPC-C. On the other side, a 11.42% of uptake was recorded for BA aggregate batch with

OPC cement. The lower degree of carbonation may due to the high water absorption of the aggregate. Aggregate was added in its SSD condition, and the pre-drying step of the carbonation curing was to dry the concrete to make paths for CO2 penetration. With a higher water content in

BA aggregate, the moisture ingredient may drive a certain amount of water discharged from the

aggregate in the concrete, and this water could block the pathway of the CO2 during carbonation.

Unlike granite concrete that gained strength rapidly at early age (1 day), only marginal strength

increased was observed for BA and Litex aggregate concrete. For 28 days, OPC carbonated

concrete reached the same level of strength compared to hydration scenario. Eco-cement concrete

also exhibited subsequent hydration property due to the C2S component that had not fully

consumed in the carbonation process. But the strength promotion was limited from 15.4 MPa to

18.5 MPa. Conclusion from Chapter 4 was that the major carbonation reaction of eco-cement did

not generate calcium hydroxide (CH), which was the critical mineral for pozzolanic reaction.

Therefore, the benefit of pozzolanic reactivity of BA cannot be taken in concretes with eco-cement

that consequently resulting in a limited strength gain. Considering the strength requirement of

concrete masonry block (CMU) from Canadian Standard Association (CSA) is 15 MPa, the green

concrete met the criteria in 1 day after carbonation. To sum, with 50% of aggregate replaced with

BA, the concrete could achieve an acceptable level of strength in 1 day and 28 days under hydration

and carbonation curing. The green concrete met the CSA standardized strength requirement in 1

day.

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6.3.5 Concrete Density, Absorption and Permeable Voids Content

BA aggregate concrete developed in this study were tested for density, absorption and permeable voids content in comparison with the normal use of hydration Litex and granite references and the results are shown in Table 6. 4. All BA aggregate contained concrete exhibited lower dry bulk density than OPC reference but was higher than Litex concrete. Although with 50% lightweight

BA aggregate, the BA batches were considered as normal weight concrete since the density higher than 2000 Kg/m3 according to the ASTM specification. Granite concrete displayed the lowest water absorption of 93.11 Kg/m3. BA concretes, regardless of curing condition and binder types,

demonstrated lower absorption than the commercial Litex aggregate concrete. But all the concretes met the water absorption requirement that particularized in ASTM standard (208 Kg/m3). In terms

of voids content, carbonation curing seemed to decrease the void content in concrete with 50% BA

aggregate from 18.49% (hydration curing) to 16.99%. The voids refinement probably due to the

calcium carbonates formation inside the paste matrix. Eco-cement binder BA concrete had shown

a slightly higher voids content than the concretes with OPC binding system, but it was comparable

with Litex-OPC-H.

6.3.6 Interfacial Transition Zone

The microstructure analysis of ITZ zone was performed on 28 days samples under conventional

hydration curing with OPC and also the batches with BA aggregates and eco-cement with

carbonation curing. The results are illustrated in Fig. 6. 11 with the help of SEM. As clearly

recognized in Fig. 6. 11 (a), the ITZ zone around the granite had a loose structure. On the contrary,

the boundaries were relatively indistinguishable around Litex and BA aggregate in Fig. 6. 11 (b)

and (c). The ITZ shown in these two cases demonstrated a good and continuous bond between the

176

aggregate and the cement matrix. This was possibly due to 1) less “wall effect”; 2) the internal

curing contributed by the high water absorption of the lightweight aggregates. For normal weight

aggregate, the size differences between cement and aggregates caused less cement grains near the

aggregate surface (“wall effect”), resulting in a porous structure indicated as ITZ zone. Second,

the drying of the cement paste in the later age will extract the water in the porous ITZ zone and

further resulting a low degree of hydration in this area. With lightweight aggregate, the “wall

effect” is eliminated, leading to a uniform ITZ zone with hydration products (Lo & Cui, 2004).

Furthermore, during the hydration period, the lightweight aggregate is able to continuously provide

the needed water to the surrounding ITZ, and therefore, forming a homogeneous and dense

structure. For the eco-cement binding system displayed in Fig. 6. 11 (d), the paste showed a highly

dense and emulsified matrix. Again, no clear transition zone could be observed around the BA

aggregate, a uniform paste was formed between the eco-cement and the aggregate. Even though the concrete with lightweight aggregate had a denser ITZ zone compared to granite aggregate, the compressive strength for conventional normal weight concrete was still higher. Since the compression force will partially close the ITZ zone and the strength of the paste and aggregate become the control parameters. The lightweight aggregates had lower strength that consequently resulting in a lower strength in concrete. However, the densified ITZ can increase the durability resistance of the concrete product (Bentz, 2009).

6.3.7 Leaching Performance

The environmental impact of the green concretes, with BA aggregate and waste-derived eco-

cement, was evaluated through the EPA TCLP leaching test. The heavy metal mobility was

investigated for the concrete under severe leaching condition and the results are shown in Table

6.5. Two criteria were also displayed in the same table, including Ontario Waste Management

177 regulation and United States Environmental Protection Agency (USEPA) regulation. It can be clearly concluded from the table, all ten monitored heavy metals in the leachate were much lower than the Ontario and EPA requirements. It meant that the “green concrete” concept had no negative environmental impact according to the TCLP test.

6.4 Conclusion

In order to maximize the usage of MSWI ashes in concrete products, the feasibility of partially utilizing bottom ash as aggregate in concrete was evaluated. Two binder systems were considered in this work, including OPC and eco-cement. Combining the eco-cement that synthesized from the previous chapter, a green concrete was developed with all the major components of concrete that originally came from the MSWI residues. The following conclusions are drawn.

1. As-received BA that collected from a “two-stage” mass burning incinerator was not

suitable to use as aggregate directly due to the negative effects of pitting, foaming,

corrosion and mold forming. Different treatment methods had been evaluated and a unique

process including magnetic separation and 200 °C pyrolysis treatment was confirmed to be

able to create stable BA aggregates for concretes.

2. A negative correlation was found between the BA replacement ratio and the compressive

strength. Concrete with a BA replacement level of 50% was able to develop a comparable

strength with Litex aggregate reference batch.

3. Under both hydration and carbonation curing scenario, concretes that consist of 50% BA

achieved a comparable strength with regular granite aggregate concrete at 28 days. Thanks

to the pozzolanic property of BA, the BA concrete experienced a considerable strength

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development from 1 day to 28 days, which led to a stronger product than commercial Litex

aggregate.

4. Bulk density and water absorption of BA aggregate concrete were proved that they met the

requirement specified by ASTM standard for loadbearing concrete masonry units.

Furthermore, the permeable voids content of BA concrete batches were comparable to the

Litex reference.

5. The “green concrete” concept was provided that the concretes could meet the minimum

strength requirement of concrete masonry block. Moreover, based on TCLP leaching test,

all the monitored heavy metals’ concentrations were far below the Canadian and U.S.

regulations.

6. Even though a denser ITZ zone was observed for concrete with lightweight aggregates

from SEM, the concretes containing the lightweight aggregates resulted in a weaker

concrete compared to granite concrete.

References

Baldwin, G., Construction Industry, R., & Information, A. (1997). Use of industrial by-products

in road construction - water quality effects. London: Construction Industry Research and

Information Association.

Bentz, D. P. (2009). Influence of internal curing using lightweight aggregates on interfacial

transition zone percolation and chloride ingress in mortars. Cement and Concrete

Composites, 31(5), 285-289. doi:https://doi.org/10.1016/j.cemconcomp.2009.03.001

179

Cheeseman, C. R., Makinde, A., & Bethanis, S. (2005). Properties of lightweight aggregate

produced by rapid sintering of incinerator bottom ash. Resources, Conservation and

Recycling, 43(2), 147-162. doi:https://doi.org/10.1016/j.resconrec.2004.05.004

Ferraris, M., Salvo, M., Ventrella, A., Buzzi, L., & Veglia, M. (2009). Use of vitrified MSWI

bottom ashes for concrete production. Waste Management, 29(3), 1041-1047.

doi:https://doi.org/10.1016/j.wasman.2008.07.014

Forteza, R., Far, M., Seguı́, C., & Cerdá, V. (2004). Characterization of bottom ash in municipal

solid waste incinerators for its use in road base. Waste Management, 24(9), 899-909.

doi:https://doi.org/10.1016/j.wasman.2004.07.004

Lo, T. Y., & Cui, H. Z. (2004). Effect of porous lightweight aggregate on strength of concrete.

Materials Letters, 58(6), 916-919. doi:https://doi.org/10.1016/j.matlet.2003.07.036

Lynn, C. J., Ghataora, G. S., & Dhir Obe, R. K. (2017). Municipal incinerated bottom ash

(MIBA) characteristics and potential for use in road pavements. International Journal of

Pavement Research and Technology, 10(2), 185-201.

doi:https://doi.org/10.1016/j.ijprt.2016.12.003

Monkman, S., & Shao, Y. (2006). Assessing the carbonation behavior of cementitious materials.

Journal of Materials in Civil Engineering, 18(6), 768-776.

Pera, J., Coutaz, L., Ambroise, J., & Chababbet, M. (1997). Use of incinerator bottom ash in

concrete. Cement and Concrete Research, 27(1), 1-5. doi:https://doi.org/10.1016/S0008-

8846(96)00193-7

180

van Beurden, A. C., BV, R. M. F., Born, J. G., van Afvalverwerkers, V., Colnot, E. A., &

Keegel, R. H. (1997). High Standard Upgrading and Utilization ofMSWI Bottom Ash

Financial Aspects.

Van Gerven, T., Van Keer, E., Arickx, S., Jaspers, M., Wauters, G., & Vandecasteele, C. (2005).

Carbonation of MSWI-bottom ash to decrease heavy metal leaching, in view of recycling.

Waste Management, 25(3), 291-300. doi:https://doi.org/10.1016/j.wasman.2004.07.008

Vegas, I., Ibañez, J. A., San José, J. T., & Urzelai, A. (2008). Construction demolition wastes,

Waelz slag and MSWI bottom ash: A comparative technical analysis as material for road

construction. Waste Management, 28(3), 565-574.

doi:https://doi.org/10.1016/j.wasman.2007.01.016

Standard References

ASTM C136 / C136M-14, Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates, ASTM International, West Conshohocken, PA, 2014, www.astm.org

ASTM C29 / C29M-17a, Standard Test Method for Bulk Density (“Unit Weight”) and Voids in Aggregate, ASTM International, West Conshohocken, PA, 2017, www.astm.org

ASTM C1761 / C1761M-17, Standard Specification for Lightweight Aggregate for Internal Curing of Concrete, ASTM International, West Conshohocken, PA, 2017, www.astm.org

ASTM C29 / C29M-17a, Standard Test Method for Bulk Density (“Unit Weight”) and Voids in Aggregate, ASTM International, West Conshohocken, PA, 2017, www.astm.org

ASTM C642-13, Standard Test Method for Density, Absorption, and Voids in Hardened Concrete, ASTM International, West Conshohocken, PA, 2013, www.astm.org

ASTM C330 / C330M-17a, Standard Specification for Lightweight Aggregates for Structural Concrete, ASTM International, West Conshohocken, PA, 2017, www.astm.org

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Table 6. 1: Mix proportions

75BA- 50BA- 50BA- Litex- Granite- Mixture component [%] 100BA-OPC OPC OPC Eco OPC OPC

OPC Cement 9.7 9.7 9.7 - 9.7 9.7

Eco-cement - - - 12 - -

Water 3.4 3.4 3.4 2.4 3.4 3.4

Granite Aggregate - 21.7 43.45 42.8 - 86.9

Litex Aggregate - - - - 86.9 -

Bottom ash Aggregate 86.9 65.2 43.45 42.8 - -

Water/binder ratio 0.35 0.35 0.35 0.20 0.35 0.35

Notes:

• 100BA/75BA/50BA: 100%; 75%; 50% BA aggregate replacement • Litex: Commercial Litex aggregate from Lafarge • Eco: Eco-cement synthesized in Lab based on Chapter 4

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Table 6. 2: Chemical compositions (XRF) of as-received BA and pyrolysis treated BA

Oxides As-received BA Pyrolysis treated BA

CaO 16.21 22.91

SiO2 26.69 28.64

Al2O3 9.66 14.18

Fe2O3 (T) 6.2 6.49

MnO 0.14 0.17

MgO 2.27 2.62

Na2O 2.36 2.63

K2O 1 1.12

TiO2 1.85 2.88

P2O5 1.74 2.34

Total-C 19.3 3.13

Total-S 0.59 1.17

LOI 29.74 14.87

Table 6. 3: Absorption, relative density and loose bulk density of aggregates

Parameters Bottom ash Litex Granite

Relative density 1.58 1.62 2.73

Loose bulk density [Kg/m3] 831.4 1100.3 1487.4

Absorption [%] 12.1 7.9 2.4

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Table 6. 4: Concrete bulk density, absorption and volume of permeable voids

50BA- 50BA- 50BA- Litex- Granite- Parameters ASTM * Eco-C OPC-H OPC-C OPC-H OPC-H

Bulk density, dry [Kg/m3] 2055.21 2045.71 2048.18 1908.22 2263.17 2000

Absorption (72hr) [Kg/m3] 130.82 144.04 133.03 155.87 93.11 208

Volume of permeable voids 19.68 18.49 16.99 19.04 16.01 - content [%]

*ASTM C90 Standard specification for loadbearing concrete masonry units

Table 6. 5: Leaching performance

50BA- Canada,Ontario US, EPA TCLP Parameter Parameter Eco-C Regulation 558 Regulation

Arsenic As <0.01 2.5 5.0

Barium Ba 1.4 100.0 100.0

Boron B 4.93 500.0 -

Cadmium Cd 0.033 0.5 1.0

Chromium Cr 0.03 5.0 5.0

Lead Pb 2.5 5.0 5.0

Mercury Hg <0.001 0.1 0.2

Selenium Se <0.01 1.0 1.0

Silver Ag <0.01 5.0 5.0

Uranium U <0.01 10.0 -

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Figure 6. 1: Carbonation set-up

110 100 90 80 70 60 50

40 % of passing 30 20 10 0 0.01 0.1 1 10 100 Sieve size [mm]

Figure 6. 2: Target aggregate size distribution

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Figure 6. 3: Negative effect for concrete with as-received bottom ash: a. Pitting; b. Foaming; c. Corrosion; d. Mold forming

Figure 6. 4: BA before and after 200 °C drying

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110 100 90 80 70 60 50

40 of % passing 30 As-received 20 Burned 10 0 0.01 0.1 1 10 100 Sieve size [mm]

Figure 6. 5: BA sieve analysis before and after pyrolysis

Figure 6. 6: BA aggregates retained on different sieves 187

Figure 6. 7: Fracture surface of a 50BA-OPC-H

20.0 18.0 14.0 15.0 12.4

7.0 10.0 7.7

5.0 Compressive strength [Mpa] strength Compressive

0.0

Figure 6. 8: 1 day compressive strength for BA aggregate concretes with OPC under hydration curing

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Figure 6. 9: Concrete slab with 50% BA aggregates and 100% Eco-cement

45 Hydration curing Carbonation curing 40 1 day 28 days

35 30.0 29.8 30 26.6 25.3 25.8 25 20.6 21.9 18.0 18.5 20 15.6 15.4 12.4 14.0 14.2 15 10 Compressive strength [MPa] strength Compressive 5 0

CO2 Uptake 50BA-OPC-C: 11.42%; Litex-OPC-C: 14.57%; Granite-OPC-C: 14.32%; 50BA-Eco-C: 15.93%

Figure 6. 10: Comparison of eco-cement - BA aggregate concretes with reference concretes

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Figure 6. 11: SEM image of ITZ; a: Granite-OPC-H; b: Litex-OPC-H; c: BA-OPC-H; d: BA- Eco-C

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Chapter 7. Conclusions, Future Work and Originality

7.1 Conclusions

This study has shown the feasibility of utilizing all types of MSWI residues, namely bottom ash

(BA), boiler ash (BLA) and Air pollution control (APC) lime in concrete as supplementary cementitious material (SCM), stand-alone cementing binder and/or structural aggregates. The techniques developed in this research not only save natural resources and energy, but also diversify the MSWI residues away from costly and environmental harmful landfill disposal. The following conclusions can be drawn.

1. Bottom ash (BA) collected from mass burning incineration was not considered as a good

SCM for traditional wet-cast concrete owing to its chemically unstable nature under

alkaline condition. The hydrogen gas releasing from the metallic aluminum content made

concrete vulnerable to expansion and cracking. However, these negative effects were

successfully prevented by using the dry-cast mix design with vibration compact forming

method. The BA powder exhibited certain pozzolanic behavior in lime-pozzolan test. It

seemed that the compaction voids created by dry-cast process provided enough releasing

paths for the hydrogen gas and this concept was further applied to paste and concrete.

2. It was found that dried and pulverized BA could increase the hydration speed of cement at

the early age and this material showed a comparable degree of pozzolanic activity with

class CI fly ash. In concrete, with 20% of cement replaced by BA, the concrete benefited

from strength enhancement from the pozzolanic reactivity and eventually achieved 17.8%

higher in strength than straight OPC references at the fully hydrated stage. At the same

time, the freeze-thaw resistance of BA blend concrete was improved.

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3. Once the negative expansion effect caused by BA can be prevented, this BA additive

exhibited good pozzolanic behavior. This study proved that the BA could be a well-suited

cement replacement in dry-cast concrete products, such as concrete masonry units (CMU),

paver blocks, retaining walls, pipes, hollow core slabs, etc.

4. An eco-cement with the properties of carbonation solidification activation and latent

hydration behavior was developed. The raw feeds consist of 93.8% of all type of MSWI

ashes and only 6.2% outsource calcium hydroxide. Chlorellstadite (CE) and belite (C2S)

were the two major carbonation reactive mineral phases. Under the early age carbonation

curing, the concrete with 100% eco-cement gained strength rapidly. The concrete could

further develop strength due to the latent hydration mineral phase belite. The strength

development potential after early age carbonation curing is a crucial advantage for eco-

cement developed in this thesis, since the CO2 gas was unlikely to penetrate through all

types of concrete products with different thickness. The latent hydration ensures the paste

matrix to keep hardening in the core section.

5. Under carbonation curing scenario, eco-cement concrete achieved a higher strength than

the OPC reference batch at 28 days, and the ultimate strengths for them were of close at

the age of 90 days. Toxicity characteristic leaching procedure (TCLP) leaching test was

performed on eco-cement concrete to assess the environmental impact. It was confirmed

that the heavy metals and chloride leaching met the Canadian and/or U.S. regulation.

Meanwhile, carbonated eco-cement concrete also exhibited better durability properties,

which included surface resistivity, freeze-thaw resistance, and linear shrinkage.

6. A pilot-scale experiment was conducted to demonstrate the industrial eco-cement CMU

production. The produced full-size CMU satisfied the commercial requirements

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established by Canadian and U.S. standards, according to the results of tested compressive

strength, density, absorption and linear shrinkage. It was conclusive that eco-cement can

be an ideal binding material in concrete with carbonation curing.

7. The synthesized eco-cement was also attempted to be used as a supplementary

cementitious material (SCM) in concrete to find wider applications, and the results

confirmed that it was feasible to use eco-cement to replace OPC under both of conventional

hydration curing and carbonation curing. Under hydration curing, the hydrated eco-cement

blend concrete could develop comparable strengths with OPC references at 1 day and 28

days. Although 10 % reduction was observed at 90 days compared to OPC, the eco-cement

blend concrete gained a much higher strength than the strength requirement for loadbearing

concrete masonry units (ASTM C90). On the other hand, the carbonated paste and

carbonated concrete that incorporated with 15% eco-cement had shown the highest

compressive strength at all testing ages comparing to NewCem Plus blend and OPC

references which linked to the carbonation of C3S, C2S, and CE.

8. Microstructure analysis revealed the morphology change process on CE crystals in the

blend cement matrix over time. Under conventional hydration scenario, CE crystals stayed

the same morphology during the 28 days hydration period. On the other side, it seemed

that the carbonation curing partially consumed CE crystals and formed small clusters on

the surface. Then the cluster kept growing and densifying the matrix because of the

limitation on the void spaces. Because of that, the carbonated eco-cement blend concrete

needed more time to build freeze-thaw resistance in correlates to the morphology change

and 90 days of curing was suggested. It was also confirmed that eco-cement blend concrete

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satisfied requirements on heavy metals and chloride content in the leaching test according

to Canadian and U.S. criteria.

9. Again, a pilot test was performed to test the feasibility of using eco-cement blend cement

in real industrial production. The full-size CMU met all requirements (compressive

strength, density, absorption, and linear shrinkage) specified in Canadian standard (CSA

165.1). This blend concept makes it easier for the concrete plants to adopt eco-cement

regardless of curing methods.

10. The use of BA as aggregate in concrete was demonstrated. Different treatment methods

were tried to eliminate the negative effects of pitting, foaming, corrosion and mold forming

when the as-received BA was used as aggregates in concrete. A magnetic separation and

pyrolysis process was developed that could effectively stabilize the BA.

11. A replacement ratio of 50% of BA aggregate to granite aggregates led to a comparable

strength with Litex aggregate reference batch. The BA aggregate concrete met the bulk

density and water absorption requirements according to ASTM standard. Eco-cement also

applied with BA aggregate to create a green concrete, which maximizes the usage of MSWI

residues. Compressive strength and TCLP leaching test were further validated for the green

concrete. These tested parameters met the criteria according to Canadian and U.S.

regulations. Denser interfacial transition zones (ITZs) were observed for concrete

incorporated with lightweight aggregates.

7.2 Future work

• Residues from other types of incinerator can be examined to check if the techniques

developed in this study can also be applied.

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• Long-term concrete durability tests for eco-cement need to be conducted to promote

commercialization and explore the market.

• Replace the outsource calcium hydroxide additive in eco-cement making with other

industrial waste to make all the raw feed entirely from waste materials.

• Develop flue gas carbonation curing by utilizing the low concentration CO2 gas directly

captured from the industry.

7.3 Originality

• MSWI bottom ash (BA) was successfully utilized in dry-cast concrete as a pozzolanic

additive. The utilization process developed in this study had prevented expansion and

cracking caused by the chemical reaction of BA under alkaline condition. Once the

expansion was prevented, this BA additive exhibited good pozzolanic behavior, leading to

enhanced strength and improved durability of the concrete.

• An eco-cement that had both of carbonation reactivity and latent hydration behavior was

successfully synthesized from MSWI residues for the first time. The eco-cement was

generated almost entirely from the waste with 93.8% of residues and only 6.2% outsource

calcium hydroxide. The eco-cement could be used as the stand-alone binding material in

concrete through carbonation activation. The full-size concrete masonry units (CMUs)

with eco-cement as an exclusive binder were cast in a real industrial concrete plant in the

pilot-scale test. The produced CMUs satisfied all commercial requirements.

• This study successfully demonstrated that eco-cement so developed could also be used a

supplementary cementitious material (SCM) to partially replace Portland cement under

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both hydration and carbonation scenarios. Concrete plants which are not equipped with air-

tight chamber can also adopt eco-cement as additive. A pilot-scale test was also performed

and further proved this concept in larger scale.

• This is the first time that a study was conducted to use BA as aggregate and eco-cement as

binder altogether to create a green concrete. The usage of the waste had been maximized

since the major components of concrete largely came from the MSWI residues. The

compressive strength, microstructure analysis, and leaching performance tests indicated

that the green concrete could be a unique and feasible option in MSWI residue

management.

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