AN ABSTRACT OF THE PROJECT REPORT OF

Anika T. Sarkar for the degree of Master of Science in Civil Engineering presented on July 19, 2019.

Title: Assessing Durability of Concrete and Ettringite Accelerated Cementitious System

Abstract approved: ______Jason H. Ideker

The goal of the first part of this project was to investigate the influence of aggregate source and entrained air on the transport properties of concrete. Currently, there are several ASTM standards available that provide systematic procedures to evaluate mass transport properties of concrete. ASTM C642-13 (ASTM 2013), often referred to as the standard for measurement of pore volume, has been used in assessing durability. Another standardized test method, ASTM C1556-11a (ASTM 2016), allows determination of the apparent chloride diffusion coefficient of concrete, which is generally used to assess the resistance to chloride penetration and predict service life of concrete. To assess the durability of concrete in this project, these were the two experimental techniques used. Two aggregate sources, river gravel, and carbonate limestone, were investigated along with three water/cement ratios; with and without air entrainment. Results indicated that aggregate types influenced the porosity and chloride ingress of concrete. Limestone concrete showed a lower apparent diffusion coefficient than the river gravel counterpart. However, no significant effect was observed in the concrete mixtures due to the addition of air entrainment.

The second goal of this project was to investigate the stability of ettringite accelerated cementitious systems subjected to different environmental conditions. Ettringite, the major hydrated phase of

these systems, may have durability issue when subjected to environmental exposure. Ettringite accelerated systems have distinct advantages including rapid set and hardening as well as shrinkage compensation. Durability concerns have reason as these systems have moved from indoor application to interest in using these systems in outdoor applications, especially for rapid repair and construction. Until now, most of these systems were designed for indoor application (e.g., self-leveling floor screeds, tile adhesives, and grouts). Therefore, there is insufficient data on the performance of ettringite accelerated system, particularly as repair material in transportation infrastructure. Recently, the durability of portland cement rich ettringite accelerated systems was determined for different exposures. However, in this research the focus is on calcium aluminate cement rich systems. In this research, the cementitious systems consist of portland cement, calcium aluminate cement, and calcium sulfate were exposed to four environmental conditions. For completeness, both portland cement rich and calcium aluminate cement rich systems were evaluated to enable direct comparison. The dimensional stability, mechanical properties, and mineralogical compositions were examined in this study.

©Copyright by Anika T. Sarkar July 19, 2019 All Rights Reserved

Assessing Durability of Concrete and Ettringite Accelerated Cementitious System

by Anika T. Sarkar

A PROJECT REPORT

submitted to

Oregon State University

in partial fulfillment of the requirements for the degree of

Master of Science

Presented July 19, 2019 Commencement June 2019

Master of Science project report of Anika T. Sarkar presented on July 19, 2019.

APPROVED:

Major Professor, representing Civil Engineering

Head of the School of Civil & Construction Engineering

Dean of the Graduate School

I understand that my project report will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my project report to any reader upon request.

Anika T. Sarkar, Author

Acknowledgments

I would like to extend my sincerest thanks to the following people and organizations, without whom this document would never have been completed.

I want to begin by thanking my advisor Dr. Jason H. Ideker. Professor Ideker has taught me a lot about not giving up when everything seems to be going wrong and holding on to the determination to learn. Under his mentorship, I have arrived where I am today and learned to strive to have an impact in my field while remembering the importance of family.

I would also like to thank my committee members, Dr. O. Burkan Isgor and Dr. Erdem Coleri, for your time and valuable input in the course of my graduate learning.

I would also like to express my gratitude to the Ideker Research group for always being around. Special thanks to Samantha for laying the groundwork for my research on the PCA project. Thank you, Siva for your encouragement and sharing thoughtful life lessons. To all the undergrads, Jeremy, Gabe, Joe, and Matt, thank you for the hard work and support and still managing to smile after spending hours in the lab.

To Kerneos and to the Department of Civil and Construction Engineering for helping me navigate through the vast wilderness of administration so that I could make it this far on schedule.

To the OASE intern team, for lifting me up and for always being there to encourage me.

To Ammu, thank you for always having faith in me and for bearing through those panicked phone calls. It would have been so much harder to survive through this journey without your constant motivation and calming voice. I would like to write a lot more, but I believe you already know. Abbu, your drive, and passion for your work has always inspired me to work harder. You have been a true motivation.

Last but not least, thank you to my best friend and husband, Sa’ad. You have been a constant encouragement and inspiration to me. Thank you for all you have done to support me during my graduate student journey. I am so excited to start the next stage in our lives, together.

Contribution of Authors

Dr. Jason H. Ideker advised on data interpretation of Chapter 2. Samantha Whatley assisted in data collection, analysis of Chapter 2.

Table of Contents

1 General Introduction ...... 15

Scope and Layout of Thesis ...... 15

Notation...... 16

Cement chemistry notation for oxide compounds ...... 16

Materials...... 16

Background and Introduction ...... 16

Manuscript 1 ...... 16

Manuscript 2 ...... 17

2 Manuscript 1 ...... 19

Effect of air entrainer and aggregates on the apparent diffusion coefficient of concrete ...... 19

Introduction ...... 20

Apparent Diffusion Coefficient ...... 21

Materials and experimental methods ...... 22

Raw materials and mixture characteristics ...... 22

Experimental Methods ...... 24

Results and Discussion ...... 26

Conclusions ...... 31

Acknowledgments ...... 32

References ...... 32

Appendix A ...... 35

Appendix B ...... 37

List of Figures

Figure 1. Porosity of each mixtures with respect to water-cement ratio at 182 days ...... 26

Figure 2. Chloride profiles after exposure for 182 days for concrete mixtures with (a) Limestone and cement A (b) Limestone and cement B (c) River Gravel and cement A (d) River gravel and cement B ...... 27

Figure 3. Correlation of w/c with porosity and apparent diffusion coefficient of limestone concrete ...... 30

Figure 4. Correlation of w/c with porosity and apparent diffusion coefficient of river gravel concrete ...... 30

List of Tables

Table 1. Aggregate Properties ...... 23

Table 2. Chemical and mineralogical compositions (%) ...... 23

Table 3. Mixture composition (kg/m3) and air content of the individual mixes (%) ...... 24

Table 4. Depth Interval for chloride profile grinding ...... 25

Table 5. Apparent diffusion coefficient and surface chloride for all concrete mixtures ...... 28

List of Appendices

Appendix A ...... 35

Additional Data: Manuscript 1 ...... 35

Appendix B ...... 37

Influence of temperature and relative humidity on the stability of ettringite accelerated systems38

B.1. Introduction ...... 39

B.1.1. Application of ettringite accelerated systems ...... 39

B.1.2. Hydration in Portland cement blended with CAC and calcium sulfate ...... 40

B.2. Stability of ettringite accelerated systems ...... 44

B.2.1. Structure of ettringite ...... 44

B.2.2. Influence of temperature ...... 45

B.2.3. Influence of relative humidity ...... 48

B.2.4. Carbonation ...... 49

B.2.5. Influence of pH ...... 51

B.2.6. Impact of latex ...... 52

B.2.7. Conclusion ...... 54

B.3. Experimental investigation ...... 54

B.3.1. Materials and formulations ...... 54

B.3.2. Specimen Preparation and Curing ...... 55

B.4. Testing ...... 56

B.4.1. Dimensional stability ...... 56

B.4.2. Flexural and compressive strength measurement ...... 56

B.4.3. Hydration stoppage ...... 56

B.4.4. Thermogravimetric Analysis ...... 57

B.4.5. X-ray diffraction...... 57

B.5. Results and discussion ...... 58

B.5.1. Dimensional stability ...... 58

B.5.2. Mass loss measurement ...... 58

B.5.3. Mechanical behavior ...... 58

B.5.4. Microstructural analysis ...... 58

B.6. Conclusion ...... 58

B.7. Reference ...... 58

List of Appendix Figures

Figure A. 1. Total chloride content profile in various concrete mixtures after 182 days of ponding (a) RG _C-A (b) RG_C-B (c) L_C-A (d) L_C-B ...... 35

Figure A. 2. Apparent diffusion coefficient of various concrete mixtures (a) River Gravel (b) Limestone ...... 36

Figure B. 1. Ternary diagram of CAC-PC-C$ blends [1] ...... 40

Figure B. 2. Possible hydrates of CAC-PC-C$ system [1] ...... 40

Figure B. 3. Strength development of PC and CAC based systems ...... 41

Figure B. 4. (a) Crystal structure of ettringite viewed along the c axis direction. Aluminate ions (AlO3 3−) are shown as blue octahedra, sulfate ions (SO4 2−) are shown as yellow tetrahedra, and calcium ions are inside orange polyhedra. Water and hydroxyl groups are denoted with red and white sticks for O and H atoms, respectively. (b) Detail of a calcium-aluminate column. [5] ..... 45

Figure B. 5. Reversibility of ettringite decomposition and reformation at 10 kPa water vapor pressure [4] ...... 47

Figure B. 6. Curves of ettringite decomposition at various PH2O for the decomposition and formation reactions. Numbers marked along curves indicate the uncertainties in temperature (°C), of data points. Equations of best fit for formation and decomposition are ln P= 1.89 + 0.047T and lnP=_1.61 + 0.075T, respectively. [4] ...... 47

Figure B. 7. The formation of ettringite at pH>10.7 [2] ...... 51

Figure B. 8. The formation of ettringite at pH>10.7 [3] ...... 52

List of Appendix Tables

Table B. 1 Chemical and mineralogical composition of the materials ...... 54

Table B. 2 Binder composition of the investigated mixes ...... 55

1 General Introduction Scope and Layout of Thesis This technical report follows the manuscript option for the Oregon State University Graduate School Thesis Guide for 2018-2019. The technical report contains an investigation into durability of concrete and cementitious systems. The scope of this report covers the influence of aggregate source and air entrainment on the transport properties of concrete. Mass transport tests are more and more used as an indicator of performance, durability, and service-life prediction models. The work presented in this technical report was undertaken to study the apparent diffusion coefficient of various concrete mixtures with and without air entraining agent. Moreover, this report explores the stability of ettringite in portland cement, calcium aluminate cement, and calcium sulfate ternary system, which is presented in Appendix B. The impact of different temperature and relative humidity on the dimensional stability, mechanical properties, and mineralogical compositions were evaluated in this study. The report consists of two chapters and two appendices.

Chapter 1: Background and Introduction- This chapter contains an introduction as well as the motivation for the two individual studies. Also, cement chemistry notations and abbreviations are provided which are used in the report.

Chapter 2: Manuscript 1- The first manuscript, titled “Effect of air entrainer and aggregates on the apparent diffusion coefficient of concrete,” examines the apparent diffusion coefficient of concrete. Mixture designs and curing parameters were determined to study the impact of different aggregate source, water/cement, and air entrainment on the apparent diffusion coefficient. In addition, pore volume was measured to establish a relationship between porosity and apparent diffusion coefficient.

Appendix A: Additional data- This section includes additional data that was not presented in manuscript 1 but was collected as a part of the research.

Appendix B: Manuscript 2- The manuscript included in Appendix B is titled “Influence of temperature and relative humidity on the stability of ettringite accelerated systems”. This manuscript presents a preliminary investigation on ettringite accelerated systems that were formulated by portland cement, calcium aluminate cement, and calcium sulfate. This study

examines the influence of different temperature and relative humidity on the early age properties of ettringite accelerated system. Future work will be carried out to generate long-term data of such different formulations.

Notation

Cement chemistry notations are extensively used in this technical report. The following is a list of the cement chemistry notation and other abbreviations used in the report.

Cement chemistry notation for oxide compounds

A Al2O3 C CaO S SiO2 F Fe2O3 $ SO3 H H2O

Materials

PC Portland cement

CAC Calcium aluminate cement

CSA Calcium sulfoaluminate cement

Background and Introduction Manuscript 1 Air entrainment has been widely used to improve the performance of concrete against freeze-thaw damage[6]. Although air void system in concrete is described by both air content and the average spacing of the air voids, it is typical to only specify total air content in fresh concrete as a quality control measure. The recommended air content ranges from 3 to 7%, depending on the size and type of aggregates and the severity of the freeze-thaw cycle [7].

Previous research heavily studied the characterization of air void system and the requirement for frost resistance. Minimal work is done to understand the influence of air entrainment on the mass transport processes in concrete [8, 9]. Furthermore, limited work is present on the combined effect of air entrainment and aggregates on the mass transport process. As mass transport tests are indicative of performance, durability, and service-life prediction models, it is crucial to understand the role of aggregate source and air entrainment on the transport process.

The transport properties of concrete are related to the microstructure which consists of narrow ribbons (of the order of 80 to 150 µm) of cement paste separating sand, coarse aggregate grains and frequent interruption of air voids [10]. Previous studies showed that a small amount of air entrainment could cause a significant change to the microstructure of the cement paste. In general, air voids are considered as isolated inclusion in the matrix due to the large size of air voids compared to the gel pores and capillary pores. However, air voids have shown to increase permeability and gas diffusivity of the concrete [9]. Several authors have reported that the interfacial transition zone (ITZ) between aggregate and cement paste influences the transport process [11, 12]. Work by Caré showed that ITZ content and tortuosity, depending on the volume fraction of aggregates, and the aggregate size distribution, influence the effective diffusion in concrete [13].

ASTM guidelines to estimate the transport properties of concrete include ASTM C642 (porosity), ASTM C 1585 (sorptivity), ASTM C1202 (electrical migration of ions) and ASTM C1556 (bulk diffusion). This research evaluates the transport properties by measuring the porosity and apparent diffusion coefficient as described by ASTM C642 and ASTM C1556 respectively and studies the influence of aggregate types and air entrainment on the transport properties of concrete.

Manuscript 2 Ternary blends, formulated of portland cement (PC), calcium aluminate cement (CAC) and calcium sulfate (C$) have been successfully used in interior applications, such as self-leveling floor screeds, tile adhesives and mortar, and grouting industry. There is a growing interest in using these cementitious systems to exterior environment as repair material. These ternary blends are commonly termed as ‘ettringite accelerated systems’.

In most of these applications, the combined system containing CAC, with calcium sulfate and or PC, the calcium aluminate cement is a precursor to ettringite formation. Ettringite is the major hydrated phase in such blends. However, a wide variety of hydrate assemblages may occur depending on the relative proportions of CAC, PC, and C$. As such, the durability of these systems may vary widely.

The presence of ettringite is not a durability concern. Like any hydrated phase, it can be durable or not durable depending on its exposure condition. Ettringite has similar stability compared to

calcium silicate hydrate concerning temperature and relative humidity [14]. Structurally, ettringite contains around 46% water, which makes it more susceptible to decomposition due to high temperature and low relative humidity.

Although many studies have determined the precise conditions under which ettringite is stable or unstable, no definite correlation could be established as different approaches were taken to study the decomposition mechanism. Some research studied the thermal stability under hydrothermal condition, yet most of them were done at uncontrolled vapor pressure.

Recent studies consider both temperature and vapor pressure, as they are critical variables of any decomposition process. Baquerizo and co-workers reported that at 25 °C ettringite was stable in a relative humidity greater than 18%, at 50 and 80 °C the limit of stability was around 30% and 45% RH respectively [15]. In the previous relevant research, most of the work was done on purely synthesized ettringite samples. There is a substantial lack of data regarding the stability of ettringite in ternary blends. Moreover, most studies reflected on extreme vapor pressure, either very low pressure or vacuum or vapor pressure at saturation [16-22]. This research focused on the more realistic conditions of temperature humidity range within commercially formulated ettringite accelerated systems.

2 Manuscript 1

Effect of air entrainer and aggregates on the apparent diffusion coefficient of concrete

Anika Tabassum Sarkar1, Samantha Whatley1, Johnny Ye1, Jason H. Ideker1 1 School of Civil and Construction Engineering, Oregon State University, Corvallis OR 97330, USA

Abstract Air entrainers have been extensively used as a mitigation technique for freeze-thaw damage, but minimal research has been done to study the effect of this increased porosity on the diffusion of chloride into concrete. The objective of this research was to study the effect of water-cement ratios (w/c), air entrainment and two different aggregate types on the apparent diffusion coefficient of concrete. The apparent diffusion coefficient in Portland cement concrete was measured by acid- soluble chloride digestion for different w/c, aggregate types and concrete with and without air entrainment. The test results indicate that air entrainer and aggregates modify the microstructure and hence the diffusion of chloride. The role of aggregate (high purity limestone versus alumino- siliceous river gravel) will be presented. Preliminary results show that there is no significant difference in apparent diffusion coefficient due to the addition of air entraining agents. Moreover, limestone mixtures have a lower apparent diffusion coefficient than the river gravel mixtures.

Keywords: Apparent Diffusion Coefficient, Air Entrainment, Aggregate, Mass Transport

Accepted to the 15th International Congress on the Chemistry of Cement

To be held at Prague, Czech Republic, September 16-20, 2019

Introduction Many authors have reported the individual effects of aggregate, water content and air entrainment on mass transport of concrete (Delagrave et al. 1997, Garboczi & Bentz 1997, Caré 2003, Hobbs 1999, Shi 2004, Toutanji 1998 Wong et al. 2011, Song et al. 2008). This study aims to investigate both the influence of aggregate and the presence of entrained air voids on the mass transport properties of concrete. Given that mass transport tests are increasingly used as indicators for performance, durability, and service-life prediction models, it is imperative to understand the role of air entrainment and aggregate types on the chloride ingress of concrete. Currently, there are many ASTM standards to estimate transport properties of concrete, such as ASTM C642 (porosity), ASTM C1585 (sorptivity), and ASTM C1202 (electrical migration of ions). This study focused on evaluating the transport properties by measuring the porosity (pore volume) and apparent diffusion coefficient of concrete as described by ASTM C642 and ASTM C1556 respectively. The pore volume or the porosity is an essential parameter in understanding the transport properties of a porous material; thus it is correlated with apparent diffusion coefficient in this research. The method to measure porosity can be easily performed but has been criticized in the past for the exclusion of some of the entrained air voids when compared to porosity measured through vacuum saturation (Bu et al. 2014). Therefore, vacuum saturation was carried out to measure porosity accurately.

Air entraining admixtures (AEAs) have been extensively used to improve the freeze-thaw resistance of concrete (Kosmatka et al. 2011, ACI 201.2R-16 2016, ACI 212.3R-16 2016), and to a lesser extent, the workability, consistency and the bleeding and segregation tendency of fresh concrete (Pigeon 1995, Hover 2006). Although Powers identified that air void size distribution plays a significant role in frost resistance, it is typical to only specify total air content in fresh concrete as a quality control measure due to the difficulty in obtaining air void size and distribution (1954). The size and the volume of entrained air void are affected by many factors, such as materials, mixing action and proportions, placing techniques, the type and amount of air entraining agent (Mielenz et al. 1958). These influencing factors, parameters and, the mechanism of air entrainment and, the concepts related to freeze-thaw resistance have been reviewed in many research studies and guidance documents (Du et al. 2004, Pigeon 1995, ACI 201.2R-16 2016, ACI 212.3R-16 2016).

Extensive research has been devoted to the development of AEAs, characterization of air void system and the requirement for frost resistance. However, minimal studies have been carried out to understand the effect of air entrainment on the mass transport processes of concrete (Song et al. 2008, Wong et al. 2011). Even though air voids are penetrable, these are often treated as inert inclusions as these voids are not generally interconnected (Wong et al. 2011). So, transport of ions solely through these voids is unlikely. Toutanji reported that air entrainment increased the permeability of silica fume concrete containing 2-15% entrained air per test results of AASHTO T277 (1998). Wong and co-workers estimated that every 1% air content increases the transport coefficient by about 10% or decreased it by 4%, depending on whether air voids acted as conductors or insulators (2011). Research completed by Song et al. indicated an increase in diffusion coefficient and a decrease in surface chloride, resulting from the additional air void content (2007).

Several studies have reported the influence of aggregate on chloride ingress is due to the interfacial transition zone (ITZ) (Delagrave et al. 1997, Garboczi & Bentz 1997). Caré showed the effective diffusion coefficient as a function of ITZ content and the tortuosity. Caré pointed out that the ITZ content depended on the volume fraction of aggregates, the aggregate size distribution, and the thickness of ITZ and the tortuosity relied only on the volume fraction of aggregate (2003). However, there is still a lack of data on the role of aggregate type on the chloride ingress.

The objective of this paper is to investigate the influence of AEA and aggregate types on the transport properties of concrete under saturated conditions. The work presented focuses on the apparent diffusion coefficient of concrete and porosity which are vital for the development of more durable concrete and accurate service life prediction models. Thus, it is essential to understand how the aggregate types and air entrainment influence the apparent diffusion coefficient and porosity of the concrete.

Apparent Diffusion Coefficient Chlorides can penetrate concrete through the concrete pore solution by three mechanisms: a) permeation: pressure gradient, b) absorption: movement of water due to capillary suction and c) diffusion: concentration gradient. It is known that when the concrete is fully saturated, chloride is transported by diffusion and it is referred to as the effective diffusion process. Due to the difficulty of separating different transport mechanisms, it is typically assumed that chloride ingress in

concrete takes place by diffusion. Therefore, the “apparent” diffusion coefficient term has been used (Song et al. 2013).

The apparent diffusion coefficient is necessary to predict the service life of a concrete structure. This coefficient is often determined by curve fitting profiles of acid-soluble chloride concentration v e x C(x, t)= (C -C0)*(erf )+C0 0.1 r s 2Dat s Where: u The s Materials and experimental methods

Raw materials and mixture characteristics t Six h Table e Aggregate Absorption Specific Source Mineralogical d Limestone 0.64 2.67 Washington, Carbonate e Limestone 0.25 2.58 Washington, Carbonate p t River 2.58 2.44 Oregon, Alumino- h River 3.08 2.41 Oregon, Alumino-

t o Table

SiO Al O Fe O CaO MgO SO Na O CO Lime C S C S C A C AF Blaine F 2 2 3 2 3 3 2 2 3 2 3 4 i A 20.2 4.7 3.3 63.7 0.7 3.1 0.56 1.8 4.1 52 18 7 10 383 cB 20.2 4.8 3.5 65.3 2.1 2.7 0.45 0.7 2.3 66 0 7 11 419 k

’ s The

S e c o

Table Aggregate W/C Cement Water Coarse Fine Air Cement Cement No With No With River 0.40 356 142 924 832 2.7 7.3 2.1 5.1

River 0.45 356 160 924 790 1.9 6.5 1.6 7.0

River 0.50 356 178 924 747 2.3 6.1 1.7 6.1

Limestone 0.40 356 142 927 972 1.2 5.8 3.1 5.1

Limestone 0.45 356 160 927 927 1.2 6.8 1.4 5.7

Limestone 0.50 356 178 927 880 1.5 6.5 2.3 5.0

Experimental Methods Porosity Measurement The porosity was determined at 182 days according to ASTM C642-13 with the exception that vacuum saturation was used instead of placing the samples into boiling water (Bu et al. 2014). At first, the samples were placed in an oven at 110°C for seven days, and the oven-dried mass was recorded (mOD). Then the specimens were placed in a vacuum saturator at 380 Torr pressure. In total, the samples were kept in the chamber for 4 hours; during the final hour, de-aired water was added. The specimens remained immersed in the de-aired water for an additional 24 hours. The samples were then removed and toweled to saturated surface dry at which their mass was recorded

(mSS). Finally, the samples were suspended in water by a wire to weigh the apparent mass in water

(mSSB). The volume of permeable pore space for each sample was determined using Volume of permeable pore %=�SS−�OD�SS−���� ∗ 100 0.2.

Volume of permeable pore %= ∗ 100 0.2

Where: �=saturated surface dry mass, �= oven dry mass, � =the mass of sample in water

Diffusion Test After 28 days of curing, the specimens were cut in half, rinsed with tap water and air dried at 23 ° C and 50% RH for no more than 24 hours. One half was ground for measuring the initial chloride content, and the other half was epoxy coated on all sides and one end, leaving one end exposed. Subsequently, the epoxied samples were vacuum saturated with saturated lime water for 3 hours until the mass of the sample stabilizes. Then the samples were removed from the lime water, rinsed immediately and placed to 165g/L NaCl solution for one-dimensional exposure. After 182 days of immersion, the specimens were taken out of the solution, washed with tap water and dried for 24 hours at 23 ° C and 50% RH. Then powder samples were obtained by grinding off material in 8 layers parallel to the exposed surface (Table 4). After grinding, the powder was stored in sealed polypropylene plastic bags in a refrigerator set at 5 °C until the time of testing. The total chloride profile was determined according to ASTM C1152. Finally, the measured chloride profile was f i t Table 4. Depth Interval for chloride profile grinding t e Depth 1 0 – 1 mm d Depth 2 1 – 2 mm w Depth 3 2 – 3 mm i Depth 4 3 – 5 mm t h Depth 5 5 – 8 mm

Depth 6 8 – 12 mm F i Depth 7 12 – 16 mm c Depth 8 16 – 20 mm k ’ s s e c o n

Results and Discussion The porosity of three samples of each mixture was measured at 182 days. The results of the average porosity are shown in Figure 1, where the error bar represents the standard deviation of each data set.

30 RG_C-A (No AEA) RG_C-A (with AEA) RG_C-B (No AEA) RG_C-B (With AEA) L_C-A (No AEA) L_C-A (with AEA) L_C-B (No AEA) L_C-B (with AEA) 25

20

15 Porosity (%) 10

5

0 0.4 0.45 0.5 W/C Figure 1. Porosity of each mixtures with respect to water-cement ratio at 182 days

It was observed that the mixtures with river gravel had higher porosity than their limestone counterpart. As the water-cement ratio increased, the limestone mixtures showed a slightly higher porosity. At low w/c, air entrainment had negligible influence on limestone mixtures, but the influence appeared more prominent at high w/c and also with low cement fineness. Cement A had a lower cement fineness compared to cement B, as stated in Table 2. However, similar porosity was seen in river gravel mixtures at all w/c and with the addition of air entrainment.

The chloride content measured at 182 days for the different series is displayed in Figure 2.

1.6 1.6 (a) L_C-A_0.4 L_C-A_0.4-Air (b) L_C-B_0.4 L_C-B_0.4-Air L_C-A_0.45 L_C-A_0.45-Air L_C-B_0.45 L_C-B_0.45-Air 1.4 1.4 L_C-A_0.5 L_C-A_0.5-Air L_C-B_0.5 L_C-B_0.5-Air 1.2 1.2

1.0 1.0

0.8 0.8

0.6 0.6

0.4 0.4

0.2 0.2 Chloride Content Chloride (mass Content % of concrete)

0.0 Chloride (Content mass % of concrete) 0.0 0 5 10 15 20 0 5 10 15 20 Layer Depth (mm) Layer Depth (mm) (c) 1.6 (d)1.6 RG_C-A_0.4 RG_C-A_0.4-Air RG_C-B_0.4 RG_C-B_0.4-Air 1.4 RG_C-A_0.45 RG _C-A_0.45-Air 1.4 RG_C-B_0.45 RG_C-B_0.45-Air RG_C-A_0.5 RG_C-A_0.5_Air RG_C-B_0.5 RG_C-B_0.5-Air 1.2 1.2

1.0 1

0.8 0.8

0.6 0.6

0.4 0.4

0.2 0.2 Chloride Content Chloride (Content mass % of concrete) Chloride Content Chloride ( Content mass % of concrete)

0.0 0 0 5 10 15 20 0 5 10 15 20 Layer Depth (mm) Layer Depth (mm) Figure 2. Chloride profiles after exposure for 182 days for concrete mixtures with (a) Limestone and cement A (b) Limestone and cement B (c) River Gravel and cement A (d) River gravel and cement B Results showed that the concrete was more resistant to chloride penetration by diffusion at the low water-cement ratio. This trend agrees with literature that higher water/cement typically results in increased chloride penetration. In addition to this, concrete containing limestone mixtures were more resistant to chloride penetration than that seen in the concrete containing river gravel. This might be due to the lower porosity of limestone concrete compared to river gravel concrete.

Moreover, the surface texture of the limestone aggregate provided more surface area to bond with the cement paste compared to the smooth surface of the river gravel aggregate. The rougher surface texture of the crushed particles results in a better bond due to mechanical interlocking (Neville 1995). Therefore, the bond between the crushed limestone aggregate and cement paste may be more significant than river gravel. Additionally, a possible chemical interaction between calcite in limestone and calcium hydroxide in hydrated cement paste may account for a less porous interfacial transition zone in the limestone concrete (Monteiro & Mehta 1986). It is often assumed that the ITZ facilitates penetration of deleterious species into concrete. Thus, an improved ITZ in limestone aggregate concrete may have contributed to the lower chloride penetration compared to river gravel mixture.

Table 5 presents the test results of the apparent diffusion coefficient and surface chloride concentration of concrete with and without air entrainment.

Table 5. Apparent diffusion coefficient and surface chloride for all concrete mixtures

Mix Apparent Diffusion Coefficient Surface Chloride (%) (m2/s)

No AEA AEA No AEA With AEA

RG_C-A_0.4 2.099E-11 2.020E-11 0.852 0.770

RG_C-A_0.45 2.504E-11 3.550E-11 0.809 1.138

RG_C-A_0.5 1.838E-11 2.220E-11 1.233 1.034

RG_C-B_0.4 8.597E-12 8.789E-12 0.920 0.865

RG_C-B_0.45 2.576E-11 6.790E-12 0.877 1.102

RG_C-B_0.5 1.087E-11 1.143E-11 1.039 1.068

L_C-A_0.4 1.850E-11 2.160E-11 0.612 0.581

L_C-A_0.45 1.796E-11 1.724E-11 0.681 0.928

L_C-A_0.5 1.695E-11 3.108E-11 0.711 0.985

L_C-B_0.4 1.401E-11 1.542E-11 0.581 0.535

L_C-B_0.45 1.631E-11 1.685E-11 0.535 0.627

L_C-B_0.5 1.171E-11 1.963E-11 0.969 0.757

In almost all the cases, similar apparent diffusion coefficient values were observed between air and non-air entrained concrete. In addition to this, no trend was found for the surface chloride concentration for either concrete containing limestone or river gravel as aggregate. However, mixtures with alumino-siliceous river gravel resulted in a higher apparent diffusion coefficient than the limestone concrete mixes. This again corresponded with the lower porosity of limestone concrete. Furthermore, apparent diffusion coefficient increased between the low and high w/c in both aggregate mixtures.

Concrete specimens made of cement A had slightly higher apparent diffusion coefficient than that made of cement B. This may be due to the higher fineness of cement B (419 m2/kg) than cement A (383 m2/kg). High fineness results in an increased surface area which leads to rapid hydration at early ages (Neville 1995). Finer cement may influenced the microstructure of the concrete through pore refinement. Thus a decrease in porosity occurred.

Figure 3 and Figure 4 show the correlation of water-cement ratio with porosity and apparent diffusion coefficient of limestone and river gravel concrete.

Porosity_AEA_C-B Porosity_No AEA_C-B Porosity_AEA_C-A Porosity_No AEA_C-A Da_AEA_C-B Da-No AEA_C-B Da_AEA_C-A Da_No AEA_C-A 25 8.E-11 /s) 7.E-11 2 20 6.E-11

15 5.E-11

4.E-11 Porosity (%) 10 3.E-11

2.E-11 5

1.E-11 Apparent Diffusion Coefficient (m

0 0.E+00 0.4 0.45 0.5 W/C Figure 3. Correlation of w/c with porosity and apparent diffusion coefficient of limestone concrete

Porosity_AEA_C-B Porosity_No AEA_C-B Porosity_AEA_C-A Porosity_No AEA_C-A Da_AEA_C-B Da-No AEA_C-B 25 Da_AEA_C-A Da_No AEA_C-A 8.E-11 /s) 7.E-11 2 20 6.E-11

5.E-11 15

4.E-11 Porosity (%) 10 3.E-11

2.E-11

5 Apparent Diffusion Coefficient (m 1.E-11

0 0.E+00 0.4 0.45 0.5 W/C Figure 4. Correlation of w/c with porosity and apparent diffusion coefficient of river gravel concrete

Limestone aggregate concrete showed an increase in porosity and apparent diffusion coefficient between low and high w/c. The change in porosity in river gravel mixtures was not so prominent as the limestone mixtures, but the apparent diffusion coefficient showed a definite increase between 0.4 and 0.5 w/c.

Air-entraining the concrete mixtures did not show a significant change in apparent diffusion coefficient values. However, a notable change in the apparent diffusion coefficient was observed in the two different types of aggregates used in this study. In almost all cases, river gravel mixtures showed a higher apparent diffusion coefficient. As a result, a higher chloride penetration depth was observed in Figure 2 (c-d).

Conclusions This paper presented the apparent diffusion coefficient and porosity of air entrained and non-air entrained concrete made with limestone or river gravel. Fick’s second law was used to determine the apparent diffusion coefficient per ASTM C1556. The following conclusions were drawn from this research:

• Water to cement ratio played an influential role in chloride ingress of concrete, especially between 0.40 and 0.50. Resistance to chloride penetration decreased with an increase of water-cement ratio. • Concrete with or without air entrainment had similar apparent diffusion coefficient values. Thus, the use of air entrainment had little influence on the transport properties of concrete as measured in this study. • Air entrainment increased the porosity of the concrete containing limestone aggregate at high w/c; however, no trend could be observed between the apparent diffusion coefficient and the addition of air entraining agent. • Concrete made with higher cement fineness resulted in a relatively lower apparent diffusion coefficient than that made with lower fineness. • Concrete cast with limestone aggregate showed slightly increased resistance to chloride diffusion than the concrete made with alumino-siliceous river gravel. The higher resistance of the limestone aggregate concrete is attributed to the lower porosity, increased bond, and improved ITZ of the concrete microstructure.

Acknowledgments The authors would like to thank the Portland Cement Association for the financial support for this project.

References ACI Committee 201 (2016). Guide to durable concrete (ACI 201.2R-16). American Concrete Institute, Farmington, Hills, Mich, pp 12.

ACI Committee 212 (2016). Report on Chemical Admixtures for Concrete (ACI 212.3R-16). American Concrete Institute, Farmington, Hills, Mich, pp 11.

Ann, Ki Yong, & Ha-Won Song (2007). Chloride threshold level for corrosion of steel in concrete. Corrosion Science, Volume 49, Issue 11, pp 4113-4133.

Beaudoin, J. J., Ramachandran, V. S., & Feldman, R. F. (1990)). Interaction of Chloride and C-S- H. Cement and Concrete Research, Volume 20, Issue 6, pp 875-883.

Birnin-Yauri, U. A., & Glasser, F. P. (1998). Friedel’s salt, Ca2Al (OH)6(Cl, OH)·2H2O: its solid solutions and their role in chloride binding. Cement and Concrete Research, Volume 28, Issue 12, pp 1713-1723.

Bu, Y., Luo, D., & Weiss, J. (2014). Using Fick's Second Law and Nernst–Planck Approach in Prediction of Chloride Ingress in Concrete Materials. Advances in Civil Engineering Materials, Volume 3, Issue 1, pp 566-585.

Bu, Y., Spragg, R., & Weiss, W. J. (2014). Comparison of the pore volume in concrete as determined using ASTM C642 and vacuum saturation. Advances in Civil Engineering Materials, Volume 3, Issue 1, pp 308-315.

Delagrave, A., Bigas, J. P., Ollivier, J. P., Marchand, J., & Pigeon, M. (1997). Influence of the interfacial zone on the chloride diffusivity of mortars. Advanced Cement Based Materials, Volume 5, Issue 3-4, pp 86-92.

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 sodium

chloride salt. Transportation Research Record: Journal of the Transportation Research Board, Volume 2441, pp 81-90.

Garboczi, E. J., & Bentz, D. P. (1997). Analytical formulas for interfacial transition zone properties. Advanced Cement Based Materials, Volume 6, Issue 3, pp 99-108.

Hobbs, D. W. (1999). Aggregate influence on chloride ion diffusion into concrete. Cement and Concrete Research, Volume 29, Issue 12, pp 1995-1998.

Hooton, R. D., & McGrath, P. F. (1995).Issues related to recent developments in service life specifications for concrete structures. Chloride Penetration into Concrete, Published as a part of proceedings of the International RILEM Workshop in St-Remy-les-Chevreuse, France, pp. 10.

Hover, K. C. (2006). Air content and density of hardened concrete. Significance of Tests and Properties of Concrete and Concrete-Making Materials, STP169D-EB, Lamond, J. and Pielert, J., Ed. ASTM International, West Conshohocken, PA, pp. 288-308.

Kosmatka, S. H., Kerkhoff, B., & Panarese, W. C. (2011).Design and control of concrete mixtures, Portland Cement Association (14th ed.), Skokie, Illinois.

Luping, T., & Nilsson, L. O. (1993). Chloride binding capacity and binding isotherms of OPC pastes and mortars. Cement and concrete research, Volume 23, Issue 2, pp 247-253.

Martın-Pérez, B., Zibara, H., Hooton, R. D., & Thomas, M. D. A. (2000). A study of the effect of chloride binding on service life predictions. Cement and Concrete Research, Volume 30, Issue 8, pp 1215-1223.

Monteiro, P. J. M., & Mehta, P. K. (1986). Interaction between carbonate rock and cement paste. Cement and Concrete Research, 16(2), 127-134.

Mielenz, R. C., Wolkodoff, V. E., Backstrom, J. E., & Flack, H. L. (1958). Orgin, Evolution, and Effects of the Air Void System in Concrete. Part 1-Etrained Air in Unhardend Concrete. Journal Proceedings, Volume 55, Issue 7, pp. 95-121).

Neville, A. M. (1995). Properties of concrete. Vol. 4. London: Longman.

Pigeon, M. (1995). Modern Concrete Technology 4, Durability of Concrete in Cold Climates. Theories of Frost Action and De-icer Salt Scaling Mechanisms, pp 11-30.

Powers, T. (1949). The air requirement of frost-resistant concrete. Chicago: Portland Cement Association. Research and Development laboratories, Development Department. Bulletin 33.

Shi, C. (2004). Effect of mixing proportions of concrete on its electrical conductivity and the rapid chloride permeability test (ASTM C1202 or ASSHTO T277) results. Cement and Concrete Research, Volume 34, Issue 3, pp 537-545.

Song, H. W., Lee, C. H., & Ann, K. Y. (2008). Factors influencing chloride transport in concrete structures exposed to marine environments. Cement and Concrete Composites, Volume 30, Issue 2, pp 113-121.

Suryavanshi, A. K., Scantlebury, J. D., & Lyon, S. B. (1996). Mechanism of Friedel's salt formation in cements rich in tri-calcium aluminate. Cement and concrete research, Volume 26, Issue 5, pp 717-727.

Toutanji, M. (1998). Technical note The influence of air entrainment on the properties of silica fume concrete. Advances in cement research, Volume 10, Issue3, pp 135-139.

Appendix A

Additional Data: Manuscript 1

This section presents additional data for Chapter 2: Manuscript 1. The mixture names are as designated in Chapter 2. The results showed in this section are an average of two data sets. These results are discussed in Chapter 2.

(a) (b) 1.8 1.8 0.4 0.4 1.6 1.6 0.4 Air 0.4 Air 1.4 0.45 1.4 0.45 0.45 Air 0.45 Air 1.2 1.2 0.5 0.5 1.0 0.5 Air 1.0 0.5 Air

0.8 0.8

0.6 0.6

0.4 0.4

(mass % of concrete) of % (mass concrete) of % (mass

TotalChloride Content TotalChloride Content 0.2 0.2

0.0 0.0 0 2 4 6 8 10 12 14 16 18 20 0 2 4 6 8 10 12 14 16 18 20 Layer Depth from the Exposed Surface (mm) Layer Depth from the Exposed Surface (mm) (c) (d) 1.8 1.8 0.4 0.4 1.6 0.4 Air 1.6 0.4 Air 1.4 0.45 1.4 0.45 0.45 Air 0.45 Air 1.2 0.5 1.2 0.5 1.0 0.5 Air 1.0 0.5 Air

0.8 0.8

0.6 0.6

0.4 0.4

(mass % of concrete) of % (mass concrete) of % (mass

TotalChloride Content TotalChloride Content 0.2 0.2

0.0 0.0 0 2 4 6 8 10 12 14 16 18 20 0 2 4 6 8 10 12 14 16 18 20 Layer Depth from the Exposed Surface (mm) Layer Depth from the Exposed Surface (mm) Figure A. 1. Total chloride content profile in various concrete mixtures after 182 days of ponding (a) RG _C-A (b) RG_C-B (c) L_C-A (d) L_C-B Figure A. 1 shows the total chloride profile of concrete mixtures with different mixture proportions.

(a)6 C-A_No Air C-A_Air C-B_No Air C-B_ Air

4

2

/s) 2

m 0 -11 (b) 0.4 0.45 0.5 6

(X 10 (X C-A_No Air C-A_Air C-B_No Air C-B_ Air

4

2 ApparentDiffusion Coefficient of Concrete

0 0.4 0.45 0.5 Water/Cement Figure A. 2. Apparent diffusion coefficient of various concrete mixtures (a) River Gravel (b) Limestone Figure A. 2 shows the apparent diffusion coefficient of various concrete mixtures at 182 days.

Appendix B

Manuscript 2

Influence of temperature and relative humidity on the stability of ettringite accelerated systems

Anika T. Sarkar1, Jeremy Asher1 and Jason H. Ideker1

1 School of Civil and Construction Engineering, Oregon State University, Corvallis OR 97330, USA

Abstract

Ettringite accelerated systems are increasingly used in building chemistry application due to a wide range of properties including fast setting and hardening, rapid drying and shrinkage compensation. These systems are formulations of portland cement, calcium aluminate cement, and calcium sulfate in combination with different types of additives to modify setting and volume stability. Such systems, producing ettringite as the primary hydrated phase, have shown concerns about long-term stability due to the possible degradation in the presence of high temperature and low relative humidity. The objective of this research was to investigate the stability of ettringite within commercially formulated systems subjected to different temperature and relative humidity. The study focused on both portland cement rich and calcium aluminate cement rich systems. Cement pastes from each mix were evaluated for dimensional change, mechanical properties, and mineralogical composition.

Keywords: Ettringite, Calcium aluminate cement, Ternary blends. Stability, Temperature, Relative humidity, Strength, Expansion

To be submitted to: Advances in Civil Engineering Materials

B.1. Introduction

Ettringite accelerated systems are typically comprised of calcium sulfoaluminate cement (CSA) or blends of calcium sulfoaluminate cement with belite (C2S) or portland cement, or blends of portland cement (PC), calcium sulfate (C$) and calcium aluminate cement (CAC). High early strength, usually 20 MPa (3000 psi), can be achieved in such systems within the first three hours of hydration through the rapid formation of ettringite (C3A.3C$.H32). Later-age strength gain (e.g., beyond ~24 hours) may occur as a result of hydration of portland cement phases in the blends [23]. Moreover, blending calcium sulfoaluminate cement with portland cement can decrease carbon footprint and cost [24]. This research is concerned with the performance of ettringite accelerated system that constitutes portland cement, calcium aluminate cement, and calcium sulfate.

B.1.1. Application of ettringite accelerated systems

Ettringite accelerated systems have a wide range of application associated with building and construction such as flooring installation and concrete repair which is commonly termed as ‘Building Chemistry’ by the dry-mix mortar industry. Application of this system depends on the composition of each component. In a portland cement rich system, CAC is mainly used as a setting and hardening accelerator. Important applications of CAC rich systems are in the non-structural application by contributing unique technical properties such as rapid hardening or setting, rapid reduction of internal humidity (drying) and shrinkage compensation. Ternary blends PC-CAC- C$ have been used successfully in interior applications for self-leveling floor screeds, tile adhesives, and mortar and grouting industry [25]. This mixture is usually dry blended with other materials such as limestone and/or fine siliceous sand as well as several admixtures and sold as mortars ready to mix with water [26]. Accelerated PC based binders using calcium aluminate cement is currently being used as repair materials in structures such as bridge decks and columns, parking structures, and pavement which requires a high early strength within few hours of hydration and suitable working time to ensure proper placement [23].

B.1.2. Hydration in Portland cement blended with CAC and calcium sulfate

Relative proportions of CAC, PC, and C$ provide general guidance on the formation of different hydrates and their properties [25] (See Figure B. 2). Combination of CAC-PC-C$ blends can broadly be identified according to their locations within a ternary diagram. Typically, the composition falls into two zones, as presented in Figure B. 1.

Figure B. 2. Possible hydrates of CAC-PC- Figure B. 1. Ternary diagram of CAC- C$ system [1] PC-C$ blends [1]

Mixtures in zone 1 are PC rich (≈70%) and contributes to the high early strength (e.g. 20 MPa at 3 h) without compromising long-term strength gain and also allows shrinkage compensation to large horizontal surfaces. Mixtures in zone 2, which are predominantly CAC and C$, are characterized by high early strength, better shrinkage compensation and self-drying capacity [25]. In order to better understand the properties of such ternary blends, it is crucial to learn the hydration products formations by the reaction of CAC-PC-C$ at different zones. The hydration characteristics of PC-CAC-C$ systems are significantly different from the sole hydration of PC or CAC. In the CAC system, the hydration of monocalcium aluminate (CA), the main constituent of calcium aluminate cement, initially results in the formation of metastable hydrate CAH10 at temperatures below approximately 15°C [27-29]. With increasing temperature, between 15 and 30° C, AH3 is formed along with the metastable hydrates CAH10 and C2AH8 [30,

31]. C2AH8 usually dehydrates within a few hours to C2AH7.5 [31-33]. As the concrete matures with time, CAH10, C2AH7.5 eventually converts to stable C3AH6 and AH3 [34, 35]. However, if the

temperature is above 30°C, C3AH6 and AH3 are favorable hydration products [35]. The hydration reactions of CA is presented in Equation 1-5, and similar reactions may be written for C12A7, which is the most reactive constituent of certain CACs.

CA + 10H→CAH10 Equation 0.1

2CA+11H→C2AH8+AH3 Equation 0.2

3CA+12H→C3AH6+2AH3 Equation 0.3

3C2AH8→2C3AH6+AH3+9H Equation 0.4

3CAH10→C3AH6+2AH3+18H Equation 0.5 In 100% CAC, a process called conversion occurs where metastable hydrates convert to stable hydrates. During this conversion, water is released increasing porosity and can result in a significant reduction in strength. Conversion can be detrimental if not accounted for, but it can be avoided by the addition of PC, C$, and/or supplementary cementitious materials (SCMs) [36] (See Figure B. 3).

Figure B. 3. Strength development of PC and CAC based systems

In the hydration of CSA cement, the main phase, ye’elimite (C4A3$), reacts with the interground calcium sulfate to form ettringite and aluminum hydroxide and when the calcium sulfate is

depleted, monosulfoaluminate forms. No later age strength gain is observed due to the absence of OPC.

C4A3$+2C$Hx+(38-2x)H→C3A.3C$.H32+2AH3 Equation 0.6

C4A3$+18H→C3A.C$·H12+2AH3 Equation 0.7

The early age hydration reaction in a CSA blended with portland cement system (PC-CSA-C$) is the same as the sole hydration of CSA cement. However, in the later ages, ettringite content decreases and the OPC clinker phase, alite, reacts to form strätlingite, C-S-H, and monosulfoaluminate, as will be presented in this section later [37]. The hydration in a ternary blend (PC-CAC-C$) is driven by the reaction between different calcium aluminate phases and calcium sulfate and also between the calcium aluminates from the portland cement and the calcium sulfate during the first 24 hours, shown in Equation 6-7.

3CA+3C$Hx+(38-3x)H→C3A.3C$.H32+2AH3 Equation 0.8

C3A+3C$Hx+2C+(32-3x)H→C3A.3C$.H32 Equation 0.9

Here, x=0 is anhydrite, x=0.5 is hemihydrate, and x=2 is gypsum. In a PC rich system, usually anhydrite and CAC-C$ rich system, hemihydrate or gypsum is used. It has been reported that the dissolution rate of calcium sulfate could be a key parameter in the morphology or spatial distribution of the hydrates. In the rapid dissolution scenario (hemihydrate and gypsum), short crystals of ettringite forms on the surface of CAC grains while in the slow dissolution (anhydrite) long thin needles of ettringite forms [38].

Once all the calcium sulfate is consumed, the unreacted calcium aluminate phases (C3A, CA) react with ettringite to form monosulfoaluminate (3C3A·C$·H12 or AFm) as

C3A.3C$.H32+6CA+16H→3C3A.C$·H12+4AH3 Equation 0.10 Between 1 to 28 days, the hydration products are mainly the result of PC hydration, C-S-H being the main hydration product and other minor constituents are ettringite (C3A.3C$.H32), and AFm phases (monosulfoaluminate, hemi and monocarbonaluminates) (Equation 8-11). Depending on the amount of lime present in the system, either aluminum hydroxide (AH3) or calcium hydroxide

(CH) will exist. However, it is not thermodynamically possible for AH3 and CH to co-exist. Thus

depending on the existing phases present in the system, different hydrates are formed. If calcium sulfate is present, ettringite is formed, and if calcium carbonate is present, monocarboaluminate is formed (Equation 12-13). If no other phase is present, AH3 and CH form hydrogarnet (C3AH6)

(Equation 14). Moreover, AH3 can react with alite (C3S), the main phase of PC, to form strätlingite

(C2ASH8) and CH (Equation 15). In the presence of calcium carbonate, ettringite is consumed to precipitate either monocarboaluminate (equation 16) or hemicarboaluminate (Equation 17).

C3S+(y+1.3)H→C1.7SHy+1.3H Equation 0.11

C2S+(y+0.3)H→C1.7SHy+0.3H Equation 0.12

C3S+3C$Hx+(32-3x)H→C3A.3C$.H32 Equation 0.13

3C4AF+12C$Hx+(132-12x)H→C3(A,F).3C$.H32+2(A,F)H3 Equation 0.14

AH3+3CH+3C$Hx+(26-3x)H→3C3A.3C$.H32 Equation 0.15

AH3+3CH+CČ+5H→3C3A.CČ.H11 Equation 0.16

AH3+3CH→C3AH6 Equation 0.17

AH3+C3S+6H→C2ASH8+CH Equation 0.18

3C3A.3C$.H32+2C3A+3CČ+7H→ 3C3A.CČ.H11+3C$H2 Equation 0.19

3C3A.3C$.H32+2C3A+1.5 CČ+10H→ 3C3A.CČ0.5.H12+3C$H2 Equation 0.20

In the blended systems, if the OPC content is low (<~20%), the hydration products will be similar to pure CAC system, and at the same time, if CAC content is low (<~20%), the final hydrated assemblage will be reflecting the pure PC system. The hydrates developed in between these two extremities is complex, and the mechanisms are not yet well defined [39, 40]. Ettringite is the primary hydration product in all of the systems in the early ages. As a minor nevertheless common product in the hydration of a portland cement system, the stability of ettringite was studied quite extensively, many of which revealed inconsistencies [16-22]. Due to the growing interested in using the ettringite accelerated system in outdoor applications, the need to study the behavior of ettringite in practical circumstances is utmost important. The next section

presents the stability concerns and data previously developed in OPC, CSA, and ternary blend systems.

B.2. Stability of ettringite accelerated systems

Ettringite contains more water (~46% water) than any other cement-based hydrates. Therefore, the activity of water is especially crucial to ettringite stability. The stability of a hydrate is usually expressed in terms of temperature, pressure, and activities of its component, including water activities which are influenced by the presence of dissolved components [4]. Although many studies have been done to determine the precise conditions under which ettringite is stable or unstable, no definitive correlations have been established between these studies. Moreover, in most of the previous work, the curing conditions were either termed “wet” meaning the samples were immersed in water or “dry” where the exposure to a relative humidity less than fully immersed in water but can be relatively high. So, the ‘dry’ samples indicated a broad range of relative humidity condition. Numerous studies have reported ettringite to be stable at varying temperature and humidity conditions. To fully understand the stability of ettringite under different conditions, it is vital to study the structure of the hydrate.

B.2.1. Structure of ettringite

Ettringite is reported as a complex calcium sulfoaluminate hydrate. Its structure is widely studied and well reported in cement chemistry in the past. Taylor and Moore first reported the structure of this hydrous calcium-alumina-sulfate mineral before 1970, and Goetz-Neunhoeffer and Neubauer revised the structural model in the more recent crystallographic work [41, 42]. The general molecular formula of ettringite is [Ca3(Al)(OH)6.12H2O]2.(SO4)3.2H2O or C3A.3C$.H32 according to cement chemistry notation. Ettringite crystals are hexagonal prisms, often elongated to needle- like or rod-like shapes [43]. As shown in Figure B. 4, the crystal structure is composed of four

3+ positively charged columns ([Ca3(Al)(OH)6.12H2O] ) running parallel to the c axis, the aluminum atoms are octahedrally coordinated with hydroxyl groups and intercalated between planes with three calcium atoms. Each Ca atom is also coordinated to four hydroxyl group of aluminum and four H2O molecules. The columns are connected by channels containing sulfate and zeolitic water [17].

Figure B. 4. (a) Crystal structure of ettringite viewed along the c axis direction. Aluminate ions (AlO3 3−) are shown as blue octahedra, sulfate ions (SO4 2−) are shown as yellow tetrahedra, and calcium ions are inside orange polyhedra. Water and hydroxyl groups are denoted with red and white sticks for O and H atoms, respectively. (b) Detail of a calcium- aluminate column. [5]

The stoichiometric composition of an ettringite phase contains 32 H2O molecules, of which two zeolitic water are loosely bound in the channels [20]. Some studies show ettringite containing up to 6 zeolitic water, giving a total of 36 water molecules [44]. However, most researchers agree on ettringite having a maximum of 32 water molecules.

B.2.2. Influence of temperature

Numerous researchers have taken different approaches to study the thermal stability and the decomposition mechanism of ettringite, some under vacuum, some under hydrothermal condition, yet most of these conditions are at uncontrolled partial vapor pressure [16-22]. Generally, the studies indicate that ettringite becomes unstable when the temperature increases above 50° C. The role of moisture also significantly affect dehydration and/or decomposition processes as well. As the relative humidity decreases below ( at 13%) the two interchannel zeolitic water molecules are removed from ettringite at room temperature without causing any significant change in unit cell size or crystallinity [19]. The withdrawal of two water molecules was also observed at 18 ° C and 0.103 kPa [20]. It is generally not considered to represent decomposition [45]. Skoblinkskaya and

co-workers explained the decomposition of ettringite under vacuum and identified the removal of covalently combined water (30 molecules) in the columns and the structural changes associated with it in three stages: at first, the water linked to the Ca atom was lost from n=30 → n=18 and subsequently to n=6 H2O, and finally the ettringite was completely decomposed [17, 20]. In the 3+ first step, the columns [Ca3Al(OH)6] , were preserved, but as the intercolumnar water was lost, the individual columns moved closer. In the second step, the structure collapsed in the course of water loss and became amorphous [45]. Shimada and Young observed that ettringite lost three water molecules below 60° C, a gradual loss of 20 water molecules occurred at 70° C, and water molecules were removed rapidly at a temperature above 120° C [19]. Deb et al. investigated the thermal decomposition of synthesized ettringite using Raman spectroscopy and X-ray diffraction. The study revealed that the onset of dehydration takes place suddenly at 53° C when it is heated under ambient condition, and complete destabilization of ettringite crystal occurs at a temperature higher than 175° C [22]. Using differential hydrothermal analysis, Satava and Veprak determined the spontaneous decomposition of ettringite at 111±1° C [21]. The experiments carried out in these studies were characterized by controlling the temperature, whereas the water vapor pressure was not monitored. Therefore, it is impossible to generalize on the stability of ettringite from their findings. Moreover, failure to demonstrate the reversibility of ettringite decomposition and reformation in the literature, the thermal stability, mechanisms and reaction kinetics of ettringite were not well known until the twenty-first century [4, 45]. As temperature and water vapor pressure both are critical variables of a decomposition process, recent studies in the literature have focused on describing the stability of ettringite as a function of temperature and water vapor pressure. Hall et al. claimed that ettringite rapidly decomposed into monosulfoaluminate and basanite at 114° C at a calculated water vapor pressure of 163 kPa [18]. Nerad et al. concluded that ettringite was stable up to 107° C in the presence of water and at a pressure of 150 kPa [16]. In a C4A3$ and gypsum system, ettringite was found to be stable up to 130-150° C at a water pressure of 690-4137 kPa [46]. Work by Ndiaye and co-workers showed that ettringite in CSA paste could lose its crystallinity from around 60° C, between 3-5% RH, and completely converted to metaettringite after three days [47].

In a more recent study, Zhou and Glasser described the physiochemical stability of ettringite and reversibility of ettringite decomposition, as presented in Figure B. 5.

Figure B. 5. Reversibility of ettringite decomposition and reformation at 10 kPa water vapor pressure [4] They found that hysteresis of decomposition and reformation occurred at a temperature between 55 and 95° C and in the range of 4-53 kPa water vapor pressure [2]. They proposed a composite diagram, as seen in Figure B. 6, to assess the possibility of ettringite decomposition in different environment [4].

Figure B. 6. Curves of ettringite decomposition at various PH2O for the decomposition and formation reactions. Numbers marked along curves indicate the uncertainties in temperature (°C), of data points. Equations of best fit for formation and decomposition are ln P= 1.89 + 0.047T and lnP=_1.61 + 0.075T, respectively. [4]

Very little work has been done on the stability of ettringite using thermodynamic modeling. One study investigated the stable zone of ettringite in the aqueous CaO-Al2O3-CaSO4 system at 25, 50 and 85° C, result of which showed that at a temperature above 45° C, monosulfoaluminate becomes increasingly stable at the expense of ettringite. However, in these studies, the activity of water was fixed by the dissolution of the solid components in response to self-generated solubility [48, 49]. In the early twenty-first century, researchers began to incorporate experimental investigation to validate the modeling calculations and assumptions. Kaufmann and co-workers indicated that ettringite in a pure CSA system was stable up to 90° C under steam curing conditions and was expected to convert at 93±17° C (from thermodynamic modeling). However, experimentally it decomposed to monosulfate (no belite) and katoite (with belite) at a higher temperature between 100-110° C [50]. [48, 49]. Pourchez and co-workers proposed kinetic modeling of thermal decomposition of ettringite into metaettringite between 20 and 140° C based on Arrhenius law. Moreover, they examined the decomposition of 15 mg of ettringite to metaettringite at 50° C isothermal condition or a 0.5° C /min heating rate at a very low water vapor pressure [51]. In previous relevant studies, primarily pure synthesized ettringite was prepared to obtain data sets on the thermal stability. Although some researchers reported ettringite decomposition in a CSA system, there is a considerable lack of data regarding the stability of ettringite in a ternary blend dominated by calcium aluminate cement. The composite diagram proposed by Zhou and Glasser, presented in Figure B. 6, was developed by investigating on synthesized ettringite samples only. No further study was carried out on ettringite produced in cementitious systems to validate this research. Furthermore, it is important to study the stability of ettringite in the influence of other hydrated phases in the system.

B.2.3. Influence of relative humidity

Decomposition of ettringite releases water, which can result in locally elevated partial vapor pressure or in the appearance of transient liquid water, or both depending on the sample size, packing, and geometry [45]. The presence of water in the structure complicates the decomposition mechanism. Hartman et al. reported a simultaneous loss of both water and hydroxyl group in the decomposition pathway when ettringite was dried over saturated LiCl solution in 11% RH [52]. This not only contradicts the sequential water loss concept but also refutes the suggested

metaettringite structure [17, 20, 45]. In recent times, the relative humidity condition of the system was incorporated while studying the thermal stability of ettringite. Additionally, this approach was adopted when investigated with phase diagram software by Albert and co-workers [53]. T. Grounds was one of the first researchers who experimentally studied the stability of ettringite in different storage conditions, maintaining both temperature and RH [54]. He pointed out that ettringite was stable at 25° C under all humidity conditions (11%, 53%, 100%) but showed greater susceptibility to drying at 50° C and 53% RH in when produced from a supersulfated cement paste [55]. Renaudin and co-workers reported that the structure of ettringite appeared similar at 35% and 100% RH at 22° C [56]. Baquerizo and co-workers indicated that higher temperature was required for a high humidity system to retain stability. They reported that at 25° C ettringite was stable down to a relative humidity greater than 18%, at 50° C the theoretical stability limit was ~30 % and at 80° C, the limit increased to greater than 45% [15]. Fridrichová and co-workers studied the long-term stability of ettringite from ye’elimite hydration at 21° C in two moisture condition: one at 40% RH and another in saturated water vapor pressure. It was noted that approximately 30% of ettringite gradually converted to metaettringite at 40% RH and under saturated water vapor, ettringite content increased to a maximum at 50 days exposure with stability after that for 160 days until the experiments were stopped [57].

B.2.4. Carbonation

When systems are exposed to CO2, coupled with high relative humidity, carbonation can occur. Carbonation can lower the pH which in turn dissolves ettringite. Other decomposition can occur when CO2 directly reacts with ettringite. In order to carry out carbonation of ettringite, Nishikawa and co-workers mixed the synthesized ettringite with distilled water at various water/solid ratios

(0-3.5) and placed it inside a CO2 incubator. The incubator was maintained at 5% CO2, 25° C and 95% RH. They reported that the carbonation mechanism was attributed to the excess or the lack of water in or around ettringite. Ettringite remained mostly stable with fine gypsum and calcium carbonate forming on the surface at water/solid~ 0, whereas with excess water, ettringite completely dissolved into gypsum, calcium carbonate, alumina gel and water, as following [58].

3C3A.3C$.H32+3CO2→3CaCO3+3C$H2+AHx+(26-x)H Equation 0.21

Relative humidity can control the rate of dehydration and carbonation. If the relative humidity is low, the rate of carbonation is low, but dehydration can occur, resulting in the formation of metaettringite. When relative humidity increases, the rate of carbonation increases. As carbonation causes ettringite to convert into a denser, less space occupying products, it results in a loss of strength and increased porosity. Grounds and co-workers investigated ettringite decomposition by carbonation at various temperature in a moist environment (100% RH) and reported the time taken to achieve complete decomposition was influenced by temperature as 25 > 50 > 95 > 75° C.

Furthermore, they showed that at 95° C ettringite is inherently unstable even in the absence of CO2 [59]. Zhou and Glasser showed that ettringite abruptly degraded to gibbsite and vaterite between

2 and 5 hours when exposed to 100% CO2, 25° C, and 88% RH [60]. Carbonation of ettringite in a ternary cement system (40 % FA/ 20% C$/ 40% CAC) caused the formation of rapidsceekite

(Ca2(SO4)(CO3)·4H2O), CaCO3, Al(OH)3 [61]. According to Gastaldi et al., at 20° C, 60% RH, and environmental CO2 exposure, penetration depth followed the order: CSA-Portland Limestone Cement > CSA > CSA-OPC after one year with the highest penetration depth being 16 mm. Carbonate ions can also replace sulfates in the interlayer of AFm phase, and the released sulfate ions can contribute to the formation of new ettringite. This may result in increasing compressive strength [62]. The carbonation depth increases as the proportion of OPC in the blended system goes down as there is less portlandite to react with CO2. Lamberet exposed different variation of

PC-CAC-C$ ternary systems to 25° C, 65% RH, 0.3% CO2 condition and reported that CAC-rich binders were more sensitive to carbonation than PC-rich systems. However, no adverse effect on mechanical strength was observed, which might be due to the formation of AH3 [1]. Moffat and

Thomas showed that CSA-C2S binders carbonated at a much faster rate under 55±5 % RH, 22±1°

C conditions than PC-CAC-C$ and PC systems in both accelerated (4% CO2) and atmospheric carbonation. Like CSA based binder, PC-CAC-C$ contains a significant level of ettringite; however, the presence of 70% PC results in the formation of portlandite, which acts as a buffer to carbonation [63]. After three years of exposure in an aggressive marine exposure site (Treat Island, Maine, USA), Moffat and Thomas reported that carbonation depth and the corrosion rate was the highest in samples comprised of CSA-C2S blend (>10% risk of corrosion) than samples made of PC-CAC-C$, CSA-OPC and high early strength portland cement (HEPC) [64]. Likewise, a similar trend was also observed for samples in an outdoor exposure site up to two years in Austin, Texas

[65]. Recent work by Ndiaye and co-workers showed that 71% of the ettringite was carbonated in crushed CSA paste in 10 days after exposed to 4% CO2, 25° C and 65% RH [47]. Although carbonation will not be carried out in this research, it is essential to understand the mechanism and previous relevant literature, which will be important for future research of PC- CAC-C$ system.

B.2.5. Influence of pH

The pH of a well-hydrated portland cement paste ranges from 12.5 to 13.5, depending on the concentration of different ions [66]. Calcium aluminate cement has fewer alkalis present than PC, and does not produce portlandite as a hydration product which results in a lower pH than PC. Therefore, the pH of the blended system varies depending on the relative proportions of PC, CAC, and C$. Gabrisová and co-workers dispersed synthesized ettringite in water at a water/solid ratio of 100, and used saturated calcium hydroxide solution and 0.02 M H2SO4 at regular intervals to regulate the pH of the water. The study revealed that ettringite was stable above pH= 10.7 in water and below pH=10 only gypsum and aluminum sulfate were stable phases [67]. This work was further

Figure B. 7. The formation of ettringite at pH>10.7 [2] carried out by Havlica and Sahu, who described the mechanism of ettringite formation in

C4A3$ reaction as a function of pH (Figure B. 7). A liquid interlayer was reported between solid

C4A3$ phase and ettringite crystal. When the thickness of the layer was about 1.4 µm, a saturated solution of ettringite was created by topotactic mechanism, and when the thickness was about 10 µm, ettringite then crystallized in the solution of pH>10.7 [2]. However, ettringite can also exist at pH values <10.7, but only in association with gypsum and aluminum hydroxide [68]. Hampson and Bailey found an upper limit (about pH 12.5) at which the crystal structure of ettringite is

disordered and the fiber length is reduced compared to that of ettringite formed at pH=11.5 [69].

Ettringite is stable in the CaO-Al2O3-SO3-H2O system at the following temperatures within pH ranges indicated [49]: 25°C: 10.43

Figure B. 8. The formation of ettringite at pH>10.7 [3] Thermodynamic investigation with GEMS showed that the solubility of ettringite decreased until a pH of 12.7 and then increased after that [71].

B.2.6. Impact of latex

Latex polymers have been used in civil engineering application to improve fresh cement properties, increase flexural strength, cracking resistance, impermeability, cohesion and adhesion to the solid substrate and durability [72]. The most commonly used latex polymers are made from

styrene-butadiene (SBR), styrene-acrylate (SA), ethylene-vinyl acetate (EVA) ,etc. and are used either in the form of an aqueous dispersion or re-dispersible powder [73]. Wang et al. studied the effect of SBR latex on portland cement hydration and observed that SBR promotes the reaction of calcium aluminate with gypsum and thus enhanced the formation and stability of ettringite, meanwhile inhibiting the formation of C4AH13 [74]. Wang and co-workers also investigated the effect of styrene-acrylate (SAE) copolymer in cement paste and concluded similar results [75]. Moreover, Kong et al. indicated a retardation mechanism on cement hydration using styrene-acrylate based polymer latexes [76]. Work done by Silva and co-workers showed that ethylene-vinyl acetate (EVA) retards all cement hydration reactions of portland cement and leads to the formation of Hadley Grains and big rods of ettringite [77]. However, these experiments were only limited to portland cement. Ukrainczyk and Rogina investigated the effect of SBR latex on calcium aluminate cement mortars. The study showed that SBR latex markedly retarded the hydration kinetics, and the retardation was more significant with higher addition of polymer content. Moreover, the compressive strength decreased due to the conversion process in CAC based materials, but a noticeable increase in flexural strength was observed [78]. Furthermore, Bentivegna and co-workers showed the addition of SB latex to plain CAC retarded the hydration reaction. Though lithium sulfate accelerated the reaction of the mixture with SB latex, it was not as much as the mixture without the latex [79]. In a more recent study, Baueregger et al. investigated the influence of styrene-butadiene copolymer on the hydration of PC and ternary binder system PC/CAC/C$. The study demonstrated that SB latex significantly accelerated ettringite formation in a ternary binder system, compared to that of ordinary portland cement where a strong delay of silicate reaction and almost complete suppression of ettringite formation was observed [80]. Previous studies showed that tailor-made latex polymers could improve the properties of fresh and hardened cementitious systems, such as adhesion, flexural strength. However, no work has been done dealing with the influence of latex polymers on the performance of ternary binders dominated by calcium aluminate cement. The widespread use of latex in the building chemistry industry makes it relevant to investigate its impact on CAC rich ettringite accelerated systems.

B.2.7. Conclusion

In the present study, ettringite stability was researched in a PC-CAC-C$ system. Mixture designs and curing parameters were decided by considering the temperature and partial vapor pressures of the cementitious systems in their service environments. As most of the previous studies reflected on vapor pressure either on the two extremes: very low vapor pressure or vacuum and water vapor pressure at saturation, this study focused on the more realistic conditions of a temperature- humidity range to the performance of ettringite accelerated systems in service environments.

B.3. Experimental investigation

B.3.1. Materials and formulations

Three pre-blended ettringite accelerated systems were obtained from Kerneos. A single source of ordinary portland cement (OPC) and two commercial calcium aluminate cements, Ciment Fondu and Ternal EP, referred to as CAC1 and CAC2 respectively, and calcium sulfate were used as raw materials to produce the individual system. Table B. 1 shows the chemical and mineralogical compositions of the cements. Table B. 1 Chemical and mineralogical composition of the materials

Al2O3 CaO SiO2 Fe2O3

OPC CAC1 > 37.0 < 39.8 < 6.0 < 18.5 CAC2 >34 <51 <6 <9

A ternary formulation reported in the past, composed of 76% ordinary portland cement, and 24% CAC1:C$ (2.2:1) was considered as the control mixture [1, 23, 65]. PC dominates the control system whereas, the other two systems are highly rich in calcium aluminate cement. Two types of calcium sulfate were used: anhydrite for PC dominant mix and hemihydrate for CAC dominant mix. The weight proportions of the three different formulations are summarized in Table B. 2.

Table B. 2 Binder composition of the investigated mixes Mix PC (wt %) CAC (wt %) C$ (wt %)

Control 76 16.5 7.5 CAC2:C$ 0 61 39 CAC1:C$:OPC 13 60 27

For the CAC2:C$ and CAC1:C$:OPC mixtures, powdered citric acid was used as a retarder at a dose of 0.38% by mass of binder.

B.3.2. Specimen Preparation and Curing

Paste was prepared in the laboratory at an ambient temperature of 23 ± 2 °C with a constant water/binder ratio of 0.35. Pastes were cast according to the norm ASTM C305-14. The dry material was added to distilled/deionized water (ASTM Type II water) and allowed to rest for 30 s for the absorption of water. The following mixing procedure was used: 30 seconds on slow speed, rest for 15 seconds and finally mix for 60 seconds at medium speed [81]. The paste was poured in a 25 x 25 x 152.4 mm moulds in two layers; each layer was compacted using 25 jolts. Finally, the moulds were covered with plastic sheet and wet burlap, and placed at 22 ± 1 °C and 100% RH climatic chamber for 24 hours. The samples were demolded and exposed to four simulated environmental conditions: (i) 20 °C and 22% RH (ii) 38 °C and 22% RH (iii) 20 °C and 33% RH

(iv) 38 °C and 33% RH. A saturated salt solution of MgCl2 was used to equilibrate the samples at 33% RH and for 20% RH, environmental test chambers were utilized. The temperature and relative humidity was monitored using Lascar USB data logger. The samples were tested at regular interval (4 hours, and 1, 3, 7, 14, 28 days) following the techniques outlines in section B.4.

B.4. Testing

B.4.1. Dimensional stability

The initial length of the samples was recorded after demolding at 24 hours. The samples were taken from the different exposure conditions periodically to measure the length change using the following formula: (L -L ) 0.22 V = t 0 X 100 d G

Where, Vd is variation in dimension, L0 is initial length, Lt is length at certain age and G is nominal gauge length.

B.4.2. Flexural and compressive strength measurement

The flexural and compressive strength was determined according to BS EN 196-1 [82]. At first, a center-point loading method was used to determine the flexural strength followed by compression testing on the half prism (obtained in the flexural test). The flexural and compressive strength results at each time are an average of three prisms. Statistical analysis will be carried out to validate the results as a part of future work.

B.4.3. Hydration stoppage

To evaluate microstructural characteristics of the samples at a specific period, hydration was stopped using the solvent exchange method. The fractured sample obtained from the strength test was crushed to a particle size of 4-6 mm. Around 5 g of the crushed sample was then immediately immersed in 100 ml of acetone. After 24 hours, the solvent was replaced with fresh acetone, sealed and stored for 48 hours. Then, the sample was vacuum filtered with less than 2 µm pore size (blended system without latex).The residue was rinsed with diethyl ether thrice, dried in air and finally stored in a low vacuum desiccator over silica gel to avoid carbonation until the time of testing. The crushed samples were ground and sieved with a 0.75 µm size before running thermogravimetric and X-ray diffraction analysis.

B.4.4. Thermogravimetric Analysis

Thermogravimetric analysis (TGA) was carried out using a TA Instruments TGA Q50. Around 30 mg of ground sample was placed in a platinum crucible over the temperature range of 25-1000 °C with a heating rate of 20 °C/min under N2 atmosphere to prevent carbonation. The TGA-DTG technique analyzed the nature of the hydration products and the changes in chemical composition or decomposition. The amount of a single phase present is related to the weight loss of that phase with the following equation mk 0.23 wk= WLk X mwater

Where, wk is the weight fraction of phase k present in sample, WLk is the weight loss due to evaporation of water, mk is the molar mass of phase k and mwater is the molar mass of water

B.4.5. X-ray diffraction

X-ray diffraction analysis will be carried out for some samples at different conditions at room temperature with a Bruker D8 Advance Diffractometer (CuKα radiation, λ = 1.54) working in Bragg-Bentano geometry with a 2θ-range of 5°–65°. Fine powder samples were scanned with a 2θ-range of 5°–65°.

(Preliminary results to be included during the presentation)

B.5. Results and discussion

B.5.1. Dimensional stability

B.5.2. Mass loss measurement

B.5.3. Mechanical behavior

B.5.4. Microstructural analysis

B.6. Conclusion

B.7. Reference

[1] S. Lamberet, Durability of ternary binders based on Portland cement, calcium aluminate cement and calcium sulfate, EPFL, (2004) pp.

[2] J. Havlica, S. Sahu, Mechanism of ettringite and monosulphate formation, Cement and concrete research, 22 (1992) pp. 671-677.

[3] R. Perkins, C. Palmer, Solubility of ettringite (Ca6[Al(OH)6]2(SO4)3z26H2O) at 5–75°C, Geochimica et Cosmochimica Acta, 63 (1999) pp. 1969-1980.

[4] Q. Zhou, F.P. Glasser, Thermal stability and decompostition mechanisms of ettringite at <120 C, Cement and Concrete Research, 31 (2001) pp. 1333-1339.

[5] H. Manzano, A. Ayuela, A. Telesca, P.J.M. Monteiro, J.S. Dolado, Ettringite Strengthening at High Pressures Induced by the Densification of the Hydrogen Bond Network, The Journal of Physical Chemistry C, 116 (2012) pp. 16138-16143.

[6] G.W. Scherer, J. Valenza, Mechanisms of frost damage, Materials science of concrete, 7 (2005) pp. 209-246.

[7] ACI, Guide to durable concrete, (2008) pp.

[8] L. Song, W. Sun, J. Gao, Time dependent chloride diffusion coefficient in concrete, Journal of Wuhan University of Technology-Mater. Sci. Ed., 28 (2013) pp. 314-319.

[9] H. Wong, A. Pappas, R. Zimmerman, N. Buenfeld, Effect of entrained air voids on the microstructure and mass transport properties of concrete, Cement and Concrete Research, 41 (2011) pp. 1067-1077.

[10] S. Diamond, Cement Paste Microstructure in Concrete, (1986) pp.

[11] A. Delagrave, J. Bigas, J. Ollivier, J. Marchand, M. Pigeon, Influence of the interfacial zone on the chloride diffusivity of mortars, Advanced Cement Based Materials, 5 (1997) pp. 86-92.

[12] E.J. Garboczi, D.P. Bentz, Analytical formulas for interfacial transition zone properties, Advanced Cement Based Materials, 6 (1997) pp. 99-108.

[13] S. Caré, Influence of aggregates on chloride diffusion coefficient into mortar, Cement and Concrete Research, 33 (2003) pp. 1021-1028.

[14] J.H. Ideker, B. Touzo, H. Fryda, K.L. Scievener, Calcium Aluminate Cements, in: P.C. Hewlett (Ed.) Lea's Chemistry of Cement and Concrete, (2018).

[15] L.G. Baquerizo, T. Matschei, K.L. Scrivener, Impact of water activity on the stability of ettringite, Cement and Concrete Research, 79 (2016) pp. 31-44.

[16] I. Nerád, S. Šaušová, L. Števula, The CaO-Al2O3-CaSO4-H2O System Equilibrium States, Cement and concrete research, 24 (1994) pp. 259-266.

[17] N. Skoblinskaya, K. Krasilnikov, L. Nikitina, V. Varlamov, Changes in crystal structure of ettringite on dehydration. 2, Cement and Concrete Research, 5 (1975) pp. 419-431.

[18] C. Hall, P. Barnes, A.D. Billimore, A.C. Jupe, X. Turrillas, Thermal decomposition of ettringite Ca6[Al(OH)62(SO4)3.26H2O, J.Chem. Soc., 92 (1996) pp. 2125-2129.

[19] Y. Shimada, J. Young, Structural changes during thermal dehydration of ettringite, Advances in cement research, 13 (2001) pp. 77-81.

[20] K.K. N. Skoblinskaya, Changes in crystal structure of ettringite on dehydration. 1, Cement and Concrete Research, 5 (1975) pp. 381-393.

[21] V. ŠATAVA, O. VEPŘEK, Thermal Decomposition of Ettringite Under Hydrothermal Conditions, Journal of the American Ceramic Society, 58 (1975) pp. 357-359.

[22] R.A. Livingston, P.J.M. Monteiro, S.K. Deb, M.H. Manghnani, K. Ross, Raman scattering and X-ray diffraction study of the thermal decomposition of an ettringite-group crystal, Physics and Chemistry of Minerals, 30 (2003) pp. 31-38.

[23] E. Moffat, Durability of rapid-set (ettringite-based) concrete, University of New Brunswick, (2016) pp.

[24] F. Winnefeld, B. Lothenbach, Hydration of calcium sulfoaluminate cements — Experimental findings and thermodynamic modelling, Cement and Concrete Research, 40 (2010) pp. 1239-1247.

[25] J.H. Ideker, B. Touzo, H. Fryda, K.L. Scievener, Calcium Aluminate Cements, in: P.C. Hewlett (Ed.) Lea's Chemistry of Cement and Concrete, (2019).

[26] R. Kwansny-Echterhagen, L. Amathieu, F. Estinenne, Calcium aluminate cement: A polyvalent binder for various applications in the building industry, International conference on dry mixesSt. Petersbourg, 2003.

[27] F. Buttler, H. Taylor, 433. The system CaO–Al 2 O 3–H 2 O at 5°, Journal of the Chemical Society (Resumed), (1958) pp. 2103-2110.

[28] M. Crowley, Effect of Starting Materials on Phase Relations in the System CaO—Al2O3— H2O, Journal of the American Ceramic Society, 47 (1964) pp. 144-148.

[29] J. d'Ans, H. Eick, Das System CaO–Al2O3–CaSO4–H2O bei 20 C, Zement-Kalk-Gips, 6 (1953) pp. 302-311.

[30] R. Edmonds, A.J. Majumdar, The hydration of monocalcium aluminate at different temperatures, Cement and Concrete Research, 18 (1988) pp. 311-320.

[31] 159-169F. Goetz-Neunhoeffer, Hydration kinetics of calcium aluminate cement in the presence of Li2CO3 in: C. Fentiman, R. Mangabhai, K. Scrivener (Eds.) Calcium Aluminate Cements: Proceedings of Cenentary Conference, IHS BRE Press, Avignon, France, 2008, pp. 159- 169.

[32] 123-138H. Pöllmann, Wenda, R., Fylak, M., & Göske, J., Cryo-SEM-FEG investigations on calcium aluminate cements, in: C. Fentiman, R. Mangabhai, K. Scrivener (Eds.) Calcium Aluminate Cements: Proceedings of the Centenary Conference, IHS BRE Press, Avignon, France, 2008, pp. 123-138.

[33] S. Rashid, Barnes, P., Bensted, J., & Turrillas, X. , Conversion of calcium aluminate cement hydrates re-examined with synchrotron energy-dispersive diffraction.=, Journal of materials science letters, 13 (1994) pp. 1232-1234.

[34] B. Lothenbach, L. Pelletier-Chaignat, F. Winnefeld, Stability in the system CaO–Al2O3– H2O, Cement and concrete research, 42 (2012) pp. 1621-1634.

[35] K.L. Scrivener, A. Capmas, Calcium aluminate cements, in: P.C. Hewlett (Ed.) Lea's Chemistry of cement and concrete, Elsevier- Butterworth-Heinemann, Oxford,UK, (1998), pp. 713-782.

[36] J.H. Ideker, C. Gosselin, R. Barborak, An alternative repair material, Concrete international, 35 (2013) pp. 33-37.

[37] L. Pelletier, F. Winnefeld, B. Lothenbach, The ternary system Portland cement–calcium sulphoaluminate clinker–anhydrite: Hydration mechanism and mortar properties, Cement and Concrete Composites, 32 (2010) pp. 497-507.

[38] J. Bayoux, A. Bonin, S. Marcdargent, M. Verschaeve, R. Mangabhai, Study of the hydration properties of aluminous cement and calcium sulphate mixes, Calcium aluminate cements. London: E. &F. N. SPON, (1990) pp.

[39] K.L. Scievener, A. Capmas, Calcium Aluminate Cements, in: P.C. Hewlett (Ed.) Lea's Chemistry of Cement and Concrete, (1998), pp. 713-782.

[40] D. Torréns-Martín, L. Fernández-Carrasco, Effect of sulfate content on cement mixtures, Construction and Building Materials, 48 (2013) pp. 144-150.

[41] F. Goetz-Neunhoeffer, J. Neubauer, Refined ettringite (Ca 6 Al 2 (SO 4) 3 (OH) 12· 26H 2 O) structure for quantitative X-ray diffraction analysis, Powder diffraction, 21 (2006) pp. 4-11.

[42] A.E. Moore, H.F.W. Taylor, Crystal structure of ettringite, Acta Crystallographica Section B, 26 (1970) pp. 386-393.

[43] D.D. Walker, T.B. Hardy, D.C. Hoffman, D.D. Stanley, Innovations and uses for lime, ASTM, 1992.

[44] H. Pollmann, Characterization of different water contents of ettringite and kuzelite, Proceedings of 12th International Congress on the Chemistry of Cement, Montreal, Canada, 2007.

[45] Q. Zhou, E.E. Lachowski, F.P. Glasser, Metaettringite, a decomposition product of ettringite, Cement and Concrete Research, 34 (2004) pp. 703-710.

[46] K. Ogawa, D.M. Roy, C4A3S hydration ettringite formation, and its expansion mechanism: I. expansion; Ettringite stability, Cement and Concrete Research, 11 (1981) pp. 741-750.

[47] K. Ndiaye, M. Cyr, S. Ginestet, Durability and stability of an ettringite-based material for thermal energy storage at low temperature, Cement and Concrete Research, 99 (2017) pp. 106- 115.

[48] D. Damidot, F.P. Glasser, Thermodynamic investigation of the CaO-Al2O3-CaSO4-H2O system at 25 C and the influence of Na2O, Cement and Concrete Research, 23 (1993) pp. 221- 238.

[49] D. Damidot, F.P. Glasser, Thermodynamic investigation of the CaO-Al2O3-CaSO4-H2O system at 50C and 85C, Cement and Concrete Research, 22 (1992) pp. 1179-1191.

[50] J. Kaufmann, F. Winnefeld, B. Lothenbach, Stability of ettringite in calcium sulfoaluminate based cement pastes at elevated temperatures, Advances in cement research, 28 (2016) pp. 251- 261.

[51] J. Pourchez, F. Valdivieso, P. Grosseau, R. Guyonnet, B. Guilhot, Kinetic modelling of the thermal decomposition of ettringite into metaettringite, Cement and Concrete Research, 36 (2006) pp. 2054-2060.

[52] M.R. Hartman, S.K. Brady, R. Berliner, M.S. Conradi, The evolution of structural changes in ettringite during thermal decomposition, Journal of Solid State Chemistry, 179 (2006) pp. 1259- 1272.

[53] B. Albert, B. Guy, D. Damidot, Water chemical potential: A key parameter to determine the thermodynamic stability of some hydrated cement phases in concrete?, Cement and Concrete Research, 36 (2006) pp. 783-790.

[54] T. Grounds, The stability and durability of supersulphated cement paste and their relationship to ettringite, Hatfield Polytechnic, (1985) pp.

[55] T. Grounds, D. Nowell, F. Wilburn, The influence of temperature and different storage conditions on the stability of supersulphated cement, Journal of thermal analysis, 41 (1994) pp. 687-699.

[56] G. Renaudin, Y. Filinchuk, J. Neubauer, F. Goetz-Neunhoeffer, A comparative structural study of wet and dried ettringite, Cement and Concrete Research, 40 (2010) pp. 370-375.

[57] M. Fridrichová, K. Dvořák, D. Gazdič, J. Mokrá, K. Kulísek, Thermodynamic Stability of Ettringite Formed by Hydration of Ye’elimite Clinker, Advances in Materials Science and Engineering, 2016 (2016) pp. 1-7.

[58] T. Nishikawa, K. Suzuki, S. Ito, K. Sato, T. Takebe, Decomposition of synthesized ettringite by carbonation, Cement and Concrete Research, 22 (1992) pp. 6-14.

[59] T. Grounds, H. Midgley, D. Novell, Carbonation of ettringite by atmospheric carbon dioxide, Thermochimica Acta, 135 (1988) pp. 347-352.

[60] Q. Zhou, F. Glasser, Kinetics and mechanism of the carbonation of ettringite, Advances in Cement Research, 12 (2000) pp. 131-136.

[61] S. Martínez-Ramírez, L. Fernández-Carrasco, Carbonation of ternary cement systems, Construction and Building Materials, 27 (2012) pp. 313-318.

[62] D. Gastaldi, F. Bertola, F. Canonico, L. Buzzi, S. Mutke, S. Irico, G. Paul, L. Marchese, E. Boccaleri, A chemical/mineralogical investigation of the behavior of sulfoaluminate binders submitted to accelerated carbonation, Cement and Concrete Research, 109 (2018) pp. 30-41.

[63] E.G. Moffatt, M.D.A. Thomas, Effect of Carbonation on the Durability and Mechanical Performance of Ettringite-Based Binders, ACI Materials Journal, 116 (2019) pp.

[64] E.G. Moffatt, M.D.A. Thomas, Performance of rapid-repair concrete in an aggressive marine environment, Construction and Building Materials, 132 (2017) pp. 478-486.

[65] R.D. Lute, Durability of calcium-aluminate based binders for rapid repair applications, University of Texas, Austin, (2016) pp.

[66] P.K. Mehta, P.J. Monteiro, Microstructure, properties and materials, McGraw-Hill Professional, New York, (2006) pp.

[67] A. Gabrisova, J. Havlica, S. Sahu, Stability of calcium sulphoaluminate hydrates in water solutions with various pH values, Cement and Concrete Research, 21 (1991) pp. 1023-1027.

[68] S.C. Myneni, S.J. Traina, T.J. Logan, Ettringite solubility and geochemistry of the Ca (OH) 2–Al2 (SO4) 3–H2O system at 1 atm pressure and 298 K, Chemical Geology, 148 (1998) pp. 1- 19.

[69] C. Hampsoim, J. Bailey, On the structure of some precipitated calcium alumino-sulphate hydrates, Journal of Materials Science, 17 (1982) pp. 3341-3346.

[70] F.P. Glasser, The stability of ettringite, in: K. Scrivener, J. Skalny (Eds.) International RILEM Workshop on Internal Sulfate Attack and Delayed Ettringite Formation, RILEM Publications SARL, (2004), pp. 43 - 64.

[71] J. Bizzozero, Hydration and dimensional stability of calcium aluminate cement based systems, ÉCOLE POLYTECHNIQUE FÉDÉRALE DE LAUSANNE, (2014) pp. 189.

[72] Y. Ohama, Handbook of polymer-modified concrete and mortars: properties and process technology, William Andrew, (1995) pp.

[73] D. Urban, K. Takamura, Polymer dispersions and their industrial applications, Wiley-VCH, (2002) pp.

[74] R. Wang, X.-G. Li, P.-M. Wang, Influence of polymer on cement hydration in SBR-modified cement pastes, Cement and Concrete Research, 36 (2006) pp. 1744-1751.

[75] R. Wang, L. Yao, P. Wang, Mechanism analysis and effect of styrene–acrylate copolymer powder on cement hydrates, Construction and Building Materials, 41 (2013) pp. 538-544.

[76] X. Kong, S. Emmerling, J. Pakusch, M. Rueckel, J. Nieberle, Retardation effect of styrene- acrylate copolymer latexes on cement hydration, Cement and Concrete Research, 75 (2015) pp. 23-41.

[77] D.A.d. Silva, H.R. Roman, P. Gleize, Evidences of chemical interaction between EVA and hydrating Portland cement, Cement and concrete research, 32 (2002) pp. 1383-1390.

[78] N. Ukrainczyk, A. Rogina, Styrene–butadiene latex modified calcium aluminate cement mortar, Cement and Concrete Composites, 41 (2013) pp. 16-23.

[79] A.F. Bentivegna, J.H. Ideker, K.J. Folliard, Latex-modified calcium aluminate cement, in: C. Fentiman, R. Mangabhai, K. Scrivener (Eds.) Calcium aluminates: Proceedings of the international conference, IHS BRE Press, Avignon, France, 2014.

[80] S. Baueregger, M. Perello, J. Plank, Impact of carboxylated styrene–butadiene copolymer on the hydration kinetics of OPC and OPC/CAC/AH: The effect of Ca2+ sequestration from pore solution, Cement and Concrete Research, 73 (2015) pp. 184-189.

[81] C. ASTM, Standard practice for mechanical mixing of hydraulic cement pastes and mortars of plastic consistency, ASTM West Conshohocken, PA, 2014.

[82] B.E. 196-1, Methods of testing cement. Determination of strength, BSI, 2016.