Use of Sugarcane Bagasse Ash As Partial Cement Replacement in Interlocking Stabilized Soil Blocks (Issbs)

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October 2020

Use of Sugarcane Bagasse Ash as Partial Cement Replacement in Interlocking Stabilized Soil Blocks (ISSBs)

Adah Shair University of South Florida

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Use of Sugarcane Bagasse Ash as Partial Cement Replacement in Interlocking Stabilized Soil

Blocks (ISSBs)

Adah Shair

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Civil Engineering Department of Civil Engineering College of Engineering University of South Florida

Major Professor: James Mihelcic, Ph.D. Christopher Alexander, Ph.D. John Trimmer, Ph.D.

Date of Approval: October 29, 2020

Keywords: Sustainable Development Goals, Earth Technologies, Valorization of Waste, Natural Pozzolans, Cost-savings, Brick

Dedication

To the people of Masaka, Uganda.

Acknowledgments

I would like to thank every person who has been my support through this process. First, I would like to thank Dr. James Mihelcic for encouraging me and guiding me and without whom this thesis would not have been possible. Thank you, Dr. Christopher Alexander and Dr. John

Trimmer, for supporting me as members of my thesis committee.

I am grateful to Dr. Marc Sklar for giving me the opportunity to work with Brick by

Brick Construction Company Ltd. Thank you, David, Florence and Dorothy for your guidance, love and friendship in and out-of-the office. Thank you, Jinju and all masons of Brick by Brick

Construction, for helping me with the experimental study of this thesis. Thank you, Brick by

Brick Construction Company Ltd. for welcoming me and making me a part of the family.

A special thanks to my mother and husband for always being my strength.

Table of Contents

List of Tables iii

List of Figures v

Abstract vi

Chapter 1: Introduction 1 1.1 Introduction 1 1.2 Research Objectives 5

Chapter 2: Literature Review 8 2.1 Background on Uganda 8 2.1.1 Geographic, Socio-Economic, and Demographics of Uganda 8 2.1.2 Current Construction Methods and Their Drawbacks 9 2.1.2.1 Burned-clay Bricks 10 2.1.2.2 Wattled and Daub 11 2.1.2.3 Adobe Blocks 12 2.1.2.4 Concrete Construction 12 2.2 Interlocking Stabilized Soil Blocks (ISSBs) 13 2.2.1 Background 13 2.2.2 Properties of Interlocking Stabilized Soil Blocks 14 2.2.2.1 Dry and Wet Compressive Strength 14 2.2.2.2 Modulus of Rupture 15 2.2.2.3 Water Absorption 15 2.2.2.4 Initial Rate of Absorption 16 2.2.2.5 Efflorescence 17 2.2.3 Comparative Analysis and Advantages of Interlocking Stabilized Soil Blocks (ISSBs) 17 2.2.4 Barriers to Widespread Adoption of Interlocking Stabilized Soil Blocks Technology 18 2.3 Soil Properties and Need for Stabilization 20 2.4 An Overview of Sugarcane Bagasse Ash 21 2.5 Sugarcane Bagasse Ash a Primary and Auxiliary Stabilizer 23 2.5.1 Use of Sugarcane Bagasse as a Stabilizer in Interlocking Stabilized Soil Blocks 23

2.5.2 Use of Sugarcane Bagasse Ash as a Stabilizer in Compressed Earth Bricks/Blocks (CEB) 30 2.5.3 Sugarcane Bagasse Ash as a Stabilizer in Concrete and Mortar 36 2.5.4 Effect of Sugarcane Bagasse Ash Addition on Properties of Soil 38 2.5.5 Other Cost-effective Benefits of Utilizing Sugarcane Bagasse Ash 39 2.5.6 Sugarcane Bagasse Ash Used with Stabilizers Other than Cement 40 2.5.7 Use of Sugarcane Bagasse Ash as Cement Replacement in Other Products 43 2.6 Best Practices for Investigating the Use of Sugarcane Bagasse Ash as Partial Cement Replacement in Interlocking Stabilized Soil Blocks 45

Chapter 3: Methods 49 3.1 Mechanical Testing of Sugarcane Bagasse Ash Amended ISSBs 49 3.1.1 Material Selection and Preparation 49 3.1.1.1 Shrinkage Test for Marram 51 3.1.1.2 Preparing Soil Mixtures 53 3.1.2 Brickmaking 55 3.1.2.1 Material and Equipment Preparation 55 3.1.2.2 Batching and Mixing 55 3.1.2.3 Compressing the Mix 56 3.1.2.4 Brick Curing 57 3.1.3 Interlocking Stabilized Soil Blocks Testing 58 3.1.3.1 Wet Compressive Strength Test 59 3.1.3.2 Modulus of Rupture Test 59 3.1.3.3 Water Absorption Test 60 3.1.3.4 Initial Rate of Absorption Test 60 3.2 Cost Analysis of Sugarcane Bagasse Ash Amended ISSB Construction 61 3.3 Proposed Framework for Data Analysis 62

Chapter 4: Conclusions and Recommendations 66 4.1 Conclusion 66 4.2 Recommendations 67

References 69

Appendix A: Summary of Literature Review 75

Appendix B: Brick by Brick Construction Company Ltd. 2020 Standard Bill of Quantities (BOQ) 83

Appendix C: Copyright Permissions 87

List of Tables

Table 1 UN Joint Management Program (JMP) Sanitation Ladder 2

Table 2 Global Sanitation Coverage Rate (%) by Facility and Region 3

Table 3 Global Sanitation Coverage Rate (%) in Urban and Rural Areas 3

Table 4 Comparative Analysis of ISSBs and Other Construction Methods Used in Uganda 19

Table 5 Key Similarities in Investigations Conducted by Khobklang et al. (2008) And Greepala and Parichartpreecha (2011) 25

Table 6 Khobklang et al. (2008) Compressive Strength % Change with Addition of Sugarcane Bagasse Ash 26

Table 7 Greepala and Parichartpreecha (2011) Compressive Strength % Change with Addition of Sugarcane Bagasse Ash 27

Table 8 Khobklang et al. (2008) Compressive Strength for Sugarcane Bagasse Ash: Cement Ratio 29

Table 9 Greepala and Parichartpreecha (2011) Compressive Strength for Sugarcane Bagasse Ash: Cement Ratio 29

Table 10 Cement-Soil Mix Ratio Based on Linear Shrinkage of Soil 53

Table 11 Weight of a 15-L Bucket of Cement, Murram and Sand 54

Table 12 Sample Size Required for Testing 54

Table 13 Mix Design for Interlocking Stabilized Soil Blocks (ISSBs) with Sugarcane Bagasse Ash as Partial Cement Replacement 55

Table 14 Cement Cost Differences between Using Regular ISSBs and SBA ISSBs 62

iii

Table 15 Framework for Analyzing Wet Compressive Strength Test Results 63

Table 16 Framework for Analyzing Modulus of Rupture Test Results 63

Table 17 Framework for Analyzing Water Absorption Test Results 64

Table 18 Framework for Analyzing Initial Rate of Absorption Test Results 65

List of Figures

Figure 1 Map of the Republic of Uganda 8

Figure 2 Global Sugarcane Production in Metric Tonnes per Hectare in 2018 23

Figure 3 Comparison of 28-day Wet Compressive Strength Reported by Khobklang et al. (2008) and Greeepala and Parichartpreecha (2011) 27

Figure 4 Comparison of 28-day Wet Compressive Strength Reported by Lima et al. (2012), Khobklang et al. (2008), Greeepala and Parichartpreecha (2011) and Ali et al. (2016) 35

Figure 5 Comparison of the 28-day Compressive Strength with Minimum Compressive Strength Requirements Set by Thailand Industrial Standards (TIS), Bureau of Indian Standards (BIS) and Uganda National Bureau of Standards (UNBS) 36

Figure 6 Research Design Flowchart for Investigating the Impact of Sugarcane Bagasse Ash in Interlocking Soil Stabilized Bricks as Partial Cement Replacement 48

Figure 7 Location of Major Sugar Manufacturers in Uganda 50

Figure 8-A Steel Mold Box Used for Shrinkage Test 52

Figure 8-B Steel Mold Box Greased with Motor Oil for Shrinkage Test 52

Figure 8-C Steel Mold Filled in with Marram for Shrinkage Test 52

Figure 9 Marram Linear Shrinkage of 20 mm 53

Figure 10 Marram Being Sieved Using a 6 mm Sieve 57

Figure 11 Dry-mix of Marram, Cement and Sand 57

Figure 12 A Typical ISSB Press Machine 57

Figure 13 An ISSB Right after Production 57 v

Abstract Global infrastructure needs for adequate housing, water provision and improved

sanitation are on the rise. UN-Water estimates that 1 in 3 people still lack access to safe drinking

water and about 4.2 billion people across the globe lack access to safely managed sanitation

services. Rapid urbanization and the global refugee crisis have also increased the demand for

adequate and efficient housing. UN Sustainable Development Goals cannot be achieved until

these needs are met. Given the high environmental impact and cost of cement-heavy

construction, alternate construction techniques like appropriate earth technologies need to be

adopted. Interlocking stabilized soil blocks (ISSBs), a type of compressed earth block (CEB), is

one such technology that has recently gained recognition in East Africa. ISSBs are compressed

instead of burned to gain strength and thus do not require the use of firewood for production.

Moreover, ISSBs use less mortar than burned clay bricks, enable faster construction because of

their interlocking mechanism and can be made on site saving transportation costs. The

widespread adoption of ISSBs has been slow, however, due to higher unit costs (compared to burned clay bricks), lack of standardization and negative social attitude of people towards earth

construction.

To further reduce the cost and environmental impact of appropriate earth technologies,

natural pozzolans (e.g., sugarcane bagasse ash) have been studied for their potential to partially

replace cement as a soil stabilizer. This research presents an extensive literature review of the

current construction methods used in Uganda and their drawbacks, the comparison of traditional

construction methods with interlocking stabilized soil blocks (ISSBs) and the use of sugarcane

vi bagasse ash as a primary and auxiliary stabilizer in interlocking soil stabilized blocks (ISSBs)

and related products. Based on the findings of the literature review, this study proposes the

optimum content for sugarcane bagasse ash in interlocking stabilized soil blocks. Additionally,

this study contributes a best-practices research design flowchart and an experimental design for

assessing the use of sugarcane bagasse ash as partial cement replacement in interlocking soil

stabilized blocks.

vii

Chapter 1: Introduction

1.1 Introduction

Access to adequate housing is a basic human necessity and essential to a person’s well- being. United Nation’s Sustainable Development Goal (SDG) 11 Sustainable Cities and

Communities pertains to provision of housing and Target 11.1 is to “ensure access for all to adequate, safe and affordable housing” by year 2030. Globally, cities generate more than 75% of the world’s wealth and due to this economic pull, people are drawn to cities in large numbers for better opportunities. By year 2030, 60 percent of the world’s population is expected to be residing in urban areas and 90% of this urbanization is expected to take place in the Global South

(Asia, Africa and Latin America). Rapid urbanization has and will continue to increase the demand for adequate housing (About Us: UN-Habitat, 2020). Furthermore, the on-going global refugee emergency has further exacerbated the shelter crisis. With 70.8 million displaced people worldwide (UNHCR, 2020), the task for providing time-sensitive and adequate shelter poses a great challenge. Uganda in fact (the location of this research) hosts the third largest population of displaced people in the world (UNHCR, 2020).

The International Covenant on Economic, Social and Cultural rights defines adequate housing as more than just four walls and a roof. The right to adequate housing must also encompass access to safe drinking water and improved sanitation facilities (International

Covenant on Economic, Social and Cultural Rights, 1976). SDG 6 (Clean Water and Sanitation) pertains to the provision of water, sanitation and hygiene (WASH) facilities across the globe.

SGD Goal 6 Targets 6.1 and 6.2 aim to achieve universal access to safe and adequate drinking water and sanitation by the year 2030 (Water and Sanitation, 2020). This is important because currently, 1 in 3 people lack access to safe drinking water and more than half of the world’s population (4.2 billion) lack access to safely managed sanitization services (UN-Water, 2020).

Safely managed sanitation services are facilities that provide proper waste management either on-site or by transportation and treatment off-site. Table 1 defines the various levels of the

UN Joint Management Program (JMP) water and sanitation ladder.

Table 1: UN Joint Management Program (JMP) Sanitation Ladder (data from WHO/UNICEF, 2020) Sanitation Service Definition Examples Improved facilities that are not shared and that provide

proper waste management Safely Managed either on site or by Piped sewer system transportation and with flush toilets, treatment off-site septic tanks, Improved facilities that are ventilation improved Basic not shared pit latrines (VIP), pit latrines with a slab Improved facilities shared Limited between two or more households Facilities without proper Pit latrines without a separation of human platform or slab, Unimproved contact with human bucket latrines and excreta hanging latrines Human feces disposed in

the surrounding Open Defecation Not Applicable environment - fields, forests, bodies of water.

The affordability of water facilities like rainwater harvesting tanks and safely managed sanitation facilities like pit latrines (with a slab) play a critical role in their adoption by populations. Table 2 shows the global sanitation coverage rates by type of facility and region. As can be inferred from the data in this table, lower-income regions in Africa and Asia have the

2 highest rates of open defecation and lowest rates of accessibility to improved sanitation facilities.

Similar disparities can be seen in global sanitation coverage in urban and rural areas as shown in

Table 3.

Table 2: Global Sanitation Coverage Rate (%) by Facility and Region (data from WHO/UNICEF JMP, 2020)

Asia Africa World Zealand Oceania America Central andCentral Eastern and Sub-Saharan Southern Asia South-Eastern Latin America Northern AfricaNorthern and Asia Western Europe and North and the Caribbean Australia and New Open 20 20 14 4 2 2 <1 <1 9 defecation Unimproved 31 6 52 5 6 7 <1 2 9 Limited 18 12 4 4 5 6 <1 <1 8 (shared) At least basic 31 61 30 88 87 84 >99 98 74

Table 3: Global Sanitation Coverage Rate in Urban and Rural Areas (data from WHO/UNICEF JMP, 2020)

Open Safely Unimproved Limited Basic defecation managed

Urban 1 4 9 38 48 Rural 18 16 7 17 43

Building and construction to meet the global infrastructure needs for housing, water provision and improved sanitation, however, come at a heavy cost to the environment. For

example, the combined construction and building industry contributes to 39% of the world’s

carbon emissions, 28% of which are operational emissions and 11% is associated with the

material and construction process. Cement production alone contributes to 5% of world’s CO 2

3 emissions (New Report, 2019). Furthermore, Uganda’s traditional construction method of using burned clay bricks has led to significant deforestation and wetland deterioration in the country.

The construction industry thus plays an important role in sustainable development.

In order to provide speedy and durable infrastructure at a lower cost to both society and the environment, it is essential to promote appropriate construction technologies. Appropriate technologies utilize materials, knowledge and techniques that help protect the natural environment and take inspiration from the local culture to provide lower cost construction.

Interlocking Stabilized Soil Block (ISSB) technology is an example of an appropriate earth technology that has gained popularity in East Africa. Traditional bricks (burned-clay bricks) are produced using a wood fired kiln or a clamp (Mihelcic et al., 2009). This production process for traditional brick making requires one ton of firewood to manufacture 1,000 bricks (Impact

Reports, 2017). ISSB production foregoes traditional brick burning and utilizes a lower amount of cement for the mortar. ISSB also allows for on-site production of bricks and therefore reduces transportation needs and costs.

ISSB technology has gained momentum recently but still lags behind the use of conventional construction materials like cement. Major barriers to widespread adoption of ISSB technology are higher unit cost of blocks, lack of technical expertise and standardization, and social attitudes of people towards earth construction. To further promote use of ISSB technology, knowledge-sharing, standardization and additional quality control measures need to be established. Reducing the production and associated construction costs of ISSB will also help promote this technology over cement-heavy construction.

One potential cost-saving measure in ISSB production applicable to Uganda is to investigate the potential to replace a percent of the cement content in the brick with natural

4 pozzolans like Sugarcane Bagasse Ash (SBA). Pozzolan is a naturally occurring or artificial

material that does not have cementitious value by itself, but when combined with water forms

compounds with cementitious properties. Cementitious materials help hold concrete together and pozzolans can be used in bricks as auxiliary cementitious material (Mouli & Khelafi, 2008). The

overall goal of this study is to advance the use of interlocking stabilized soil block (ISSB)

technology in solving shelter and WASH challenges in low- and middle-income countries.

Countries like Uganda, Kenya and India have national standards for ISSBs, but no such

standards currently exist for ISSBs that utilize natural pozzolans in their mix.

1.2 Research Objectives

The growing need for sustainable materials and methods in construction necessitates further research into cost-effective and appropriate earth technologies like ISSBs. Accordingly, this research has three objectives. The first is to provide a literature review on: a) current brick construction techniques used in Uganda and their drawbacks; b) comparison of traditional brick construction methods and ISSB construction in terms of structural performance, environmental impact and cost of production; c) mechanical properties of ISSBs; d) barriers to widespread adoption of ISSB technology in Uganda; and e) experimental studies on the use of sugarcane bagasse ash as a primary and auxiliar stabilizer in interlocking soil stabilized bricks and related

materials.

The second objective is to develop and propose a detailed experimental plan, with field- based methods, to produce and test ISSB bricks with sugarcane bagasse ash as partial cement replacement that meet the Uganda National Bureau of Standards for ISSBs. Finally, the third objective is to provide a framework that uses collected data for comparing the structural

5 performance and cost of production between sugarcane bagasse ash interlocking soil stabilized bricks and control soil stabilized bricks.

ISSBs have been studied before for their cost-effectiveness for constructing water storage tanks and urine diverting toilets (Thayil-Blanchard & Mihelcic, 2015; Trimmer et al., 2016).

However, the use of ISSBs for more complex construction like multi-story buildings has not been studied extensively and would require standardization at a larger scale. Numerous studies

(Lima et al., (2012), Ali et al. (2016), Salim et al. (2014)) have been conducted on the use of sugarcane bagasse as partial replacement for cement in compressed earth blocks (CEB).

However, the literature on use of sugarcane bagasse ash as partial cement replacement in ISSBs is quite lacking. The limited number of studies that have been conducted involve study of only 1-

3 mechanical properties of ISSBs. Furthermore, these studies were found to not involve a cost- analysis and very few of these studies have been conducted in Uganda.

For this study, 29 peer-reviewed articles and reports on the use of sugarcane bagasse ash as a primary and auxiliary stabilizer were analyzed and compared to establish an optimum content for sugarcane bagasse ash addition. One contribution of this study is presentation of a test design that includes all essential mechanical properties of ISSBs; determines an optimum content of sugarcane bagasse ash for partial cement replacement for use in future studies and standardization; provides best practices and recommendations for future research of interlocking soil stabilized bricks amended with sugarcane bagasse ash for stabilization.

The author spent seven months working in Masaka, Uganda as an engineering consultant/intern for Brick by Brick Construction Company Ltd. Brick by Brick Construction

Ltd. is a social enterprise based in Masaka that specializes in design and construction using ISSB technology. This experience was part of her graduate studies with a concentration in Engineering

6 for International Development (Mihelcic et al., 2006). The author has firsthand experience using

ISSB technology and promoting its adoption to the community in and near Masaka. In March

2020, USF World activated an evacuation plan requiring all overseas students to return to the

United States due to the COVID-19 pandemic. Consequently, the author was unable to fully carry out the experimental methodology for this investigation and collect data in Uganda. The framework developed for this thesis research does provide a method on how to use data that is collected.

Chapter 2: Literature Review

2.1 Background on Uganda

2.1.1 Geographic, Socio-Economic, and Demographics of Uganda

The Republic of Uganda is a landlocked country in East-Central Africa bordered by

Kenya on the East, South Sudan on the North, Democratic Republic of the Congo on the West and Tanzania on the South. Uganda lies in the African Great Lakes region and shares Lake

Victoria with Tanzania and Kenya (The World Factbook: Uganda, 2018). Figure 1 demonstrates the main cities of Uganda including the capital city of Kampala and nearby city of Masaka where the thesis research was conducted.

Figure 1: Map of the Republic of Uganda (reprinted from The World Factbook, 2018. Royalty Free Standard License)

Uganda’s terrain is plateau with rim of mountains. It has fertile land with abundant water resources. The climate is tropical with two dry seasons that extend from December to February and from June to August. The 2018 population was estimated to be 42,729,000, with 25% of the population living in urban areas. Uganda has one of the youngest populations in the world and a high fertility rate of 5.8 children per woman (The World Factbook: Uganda, 2018). The country also hosts an estimated 1.1 million refugees (as of November 2018), mostly from South Sudan and Democratic Republic of the Congo (UNHCR, 2020). Its economy primarily depends on agriculture and exports. Government spending is mostly reserved for road and energy infrastructure spending whereas, investments in health and education rely on donor support. In

2017, Uganda ranked 159 out of 189 countries in the Human Development Index (HDI) (Human

Development Reports, 2019).

Uganda witnessed turbulent times after its independence from the United Kingdom in

1962. A lengthy civil war in Northern Uganda has caused mass casualties, rendered thousands of people without shelter and led to a loss of forest cover and deterioration of natural resources. The demand for shelter for the growing population, internally displaced people and refugees is rapidly increasing. Appropriate earth technologies and sustainable construction techniques that meet the housing needs of Uganda without relying heavily on the country’s natural resources are, thus needed (UN-Habitat, 2009).

2.1.2 Current Construction Methods and Their Drawbacks

Burned-clay bricks are the most common construction material used in urban areas of

Uganda. In rural areas, wattle and daub construction still dominates. Other construction materials like adobe bricks and cement are also used (UN-Habitat, 2009). A brief description of the

9 construction techniques used in Uganda along with their pros and cons is presented in the following subsections.

2.1.2.1 Burned-clay Bricks

Burned-clay brick production begins with clay extraction from wetlands. To make the extracted clay more homogenous and dissolve any soluble salts present in it, the clay is ground to a finer paste by stepping on it. The ground clay is then mixed with water to make a malleable paste. Sand may be added to the mix to reduce plasticity. The clay mix is then placed in molds to form bricks and allowed to air-dry. Air-dried bricks are fired in a kiln or clamp to increase durability (Mihelcic et al., 2009). Clamps are more commonly used in Uganda. In a clamp, about

20,000 bricks are stacked into a large pile with an opening where firewood is introduced and burnt for a period of 24 hours. The brick pile is plastered with mud on the outside to prevent heat loss. In this set-up, the bricks closest to the fire are over-burned while those farthest from the fire are under-fired. This leads to about 20% of the bricks (4,000 bricks) going to waste and is, thus, an inefficient production method (UN-Habitat, 2009). Burned-clay bricks may also get damaged during transportation to construction sites.

Burned-clay brick production in Uganda is still unstandardized at large. The bricks produced are mostly uneven and require up to 3 centimeters of mortar. Construction using burned-clay bricks is also unaesthetic and is often plastered over. The unit cost of burned-clay bricks is low; however, the added cost of cement for mortar and plaster makes this construction methodology expensive.

Burned-clay brick structures are durable and show resistance to elements; however, their production poses great environmental challenges. Clay extraction for brick making has proven detrimental for wetland cover in Uganda. According to Ministry of Water and Environment,

10 wetland area in Uganda has declined by 30% between 1994 and 2008 (Kaggwa et al., 2009).

Wetlands are a valuable natural resource that support and promote biodiversity. They also store carbon within their plants and soil instead of releasing it as carbon dioxide to the atmosphere

(EPA, 2018). Unmonitored clay extraction also creates burrows in wetlands. These burrows when left unattended collect water and become breeding grounds for mosquitoes, increasing the spread of malaria (UN-Habitat, 2009).

Burned-clay bricks also require a significant amount of firewood for their production.

One ton of firewood is used to produce 1,000 burned clay-bricks in clamps (Impact Reports,

2017). This rampant use of firewood has contributed to deforestation in Uganda, where the forest cover has reduced by approximately 1.3 million hectares from 1990 to 2005 (National Forestry

Plan, 2013). The Masaka district (location of this study) is the second-most deforested region in the country, with 31% of its 8,905 hectares of central forest reserves either degraded or deforested. Uganda’s National Environmental Management Authority (NEMA) estimates if deforestation in Uganda continues at the present rate, there will be no forests left in the country in 40 years (NEMA, 2008). Furthermore, Uganda’s increasing population and subsequent demand for housing is expected to worsen an already dire situation.

2.1.2.2 Wattle and Daub

Wattle and Daub (also known as mud and pole) is a common construction method used in

Uganda for its low-cost and use of readily available materials. Wattle and daub houses consist of a wood frame filled-in with earth walls. This construction method, although inexpensive, is not durable and provides weak resistance to elements. Extensive use of wood for the wattle and daub framework makes this construction method less environmentally friendly (Hashemi & Heather,

2015). These structures often require plastering on the outside for extending building life and enhancing aesthetic quality.

2.1.2.3 Adobe Blocks

Adobe blocks are sun-dried mud blocks commonly used in rural areas of Uganda and in camps for displaced people. Adobe construction does not require wood for the frame or for firing the bricks, making it an environmentally friendly technique. For improving durability, resistance to water and aesthetic quality, adobe construction is plastered with a mix of sand and mud or a mix of cassava and sand. Direct plastering with cement is avoided as it degrades quickly due to poor adhesion between cement and clay and high costs. Adobe construction provides weak to medium resistance to elements and can be durable if the structure is well-maintained and plastered (UN-Habitat, 2009). It has also been applied to water desalination (Manser & Mihelcic,

2013). Adobe construction, however, faces a social challenge of being considered as the

‘material of the poor.’ A higher social status is associated with living in brick or concrete houses

(Hashemi & Heather, 2015).

2.1.2.4 Concrete Construction

Concrete usage as a construction material has been rapidly increasing in Uganda, especially in urban areas. Concrete structures are durable and provide strong resistance to elements but have weak insulation capacity (Hashemi & Heather, 2015). Concrete is more expensive compared to other construction materials and remains unaffordable to a significant amount of the rural population in Uganda. Moreover, cement, that makes up a significant fraction of concrete, is energy intensive and contributes heavily to carbon dioxide emissions.

2.2 Interlocking Stabilized Soil Blocks (ISSBs)

2.2.1 Background

An earth block, also called a soil block, is a masonry unit made from soil. A Compressed

Earth Block (CEB) is a masonry unit made from the combination of soil and a stabilizing agent compressed under high pressure. An Interlocking Soil Stabilized Block (ISSB) is a type of compressed earth block.

The practice of making masonry units from compacted soil dates back thousands of years with the first compressed earth blocks produced using wooden tamps (Compressed Earth Blocks,

1985). After World War II, the invention of the CINVA-RAM press by the Chilean Engineer

Raul Ramirez was an evolutionary step towards producing uniform soil blocks in a time-efficient manner. However, the need for significant amount of cement for the mortar remained a drawback of the Compressed Earth Block (CEB) technology. In the early 1980’s, the Human

Settlements Division of the Asian Institute of Technology (HSD-AIT) and the Thailand Institute of Scientific and Technological Research (TIS-TR) modified the CINVA-RAM press to create interlocking soil blocks. The interlocks in the blocks worked like puzzle pieces that fit into each other. The interlocking soil blocks were used in wall construction and it was observed that the interlocking technology enhanced the structural stability of the wall while reducing the amount of cement required as mortar. Later in the 1990s, Dr Moses Musaazi from Makerere University

(Uganda) further enhanced the interlocking soil block technology by developing a double interlocking system for the bricks. Dr. Musaazi also developed curved interlocking soil stabilized blocks to construct rainwater harvesting tanks. This research focuses on the testing and adoption of straight interlocking soil stabilized blocks, commonly referred to as interlocking soil stabilized bricks (UN-Habitat, 2009).

2.2.2 Properties of Interlocking Stabilized Soil Blocks

A material that has the ability to undergo significant deformation and absorb large amounts of energy before fracturing is considered a ductile material (Segui, 2018). Brittle materials, on the other hand, do not yield significantly before breaking and typically have a strain value of less than 5% at fracture (Lindeburg, 2018). Examples of ductile material include steel and those of brittle material include unreinforced concrete and unreinforced masonry.

2.2.2.1 Dry and Wet Compressive Strength

Brittle materials are generally characterized as having low-tensile strength and high compressive strength. In other words, brittle materials can sustain higher compression loads as compared to tensile loads. Compressive strength is, therefore, the controlling factor in the design of masonry units.

The American Concrete Institute (ACI) Specification for Masonry Structures (Masonry

Society, 2005) defines compressive strength as the “maximum force resisted per unit of net cross-sectional area of masonry” (Masonry Society, 2005). Similarly, the Uganda Bureau of

National Standards for ISSBs defines compressive strength as:

= or = where,

CD = dry compressive strength, in N/mm

CW = wet compressive strength, in N/mm

WD = total load at which the dry specimen fails, in Newtons

WW = total load at which the wet specimen fails, in Newtons

A = the smaller bed face area, in mm

Wet compressive strength of a masonry unit is tested after the specimen is immersed in water for a period of 24 hours. Saturation reduces the compressive strength of ISSBs due to the build-up of pore water pressure and the dissolution of un-stabilized clay materials present in the block matrix. Strength testing in saturated conditions, thus, yields lower strength and is an

important measure of quality control for interlocking soil stabilized bricks (Walker, 1995).

2.2.2.2 Modulus of Rupture

Modulus of rupture is an important quality control measure in masonry for evaluating

cracking and deflection in beams. It is defined as the tensile strength in flexure or the stress at

which an interlocking soil stabilized brick is assumed to crack. The most used test method for

modulus of rupture is the three-point flexural test. Uganda National Bureau of Standards defines

modulus of rupture as:

where,

S = stress in specimen at midspan, in N/mm

W = maximum load at failure, in Newtons

l = distance between the supports, in mm

B = width, face to face, of the specimen, in mm

D = depth, bed face to bed face, in mm

2.2.2.3 Water Absorption

Interlocking soil stabilized bricks are porous and vulnerable to the effects of weathering.

Durability of an interlocking soil stabilized brick against environmental conditions can be

measured by the rate at which elements like water can penetrate exposed surfaces (Kelham,

1988). The rate at which bricks absorb water influences the strength of the bond between bricks and mortar (Khalaf & DeVenny, 2002) which in turn effects the overall stability of the structure.

The Uganda National Bureau of Standards defines water absorption as:

− = ∗ 100

where,

Aw = percentage of water absorption

M1 = mass of oven dry specimen, in grams

M2 = mass of saturated specimen after immersion in water for 24 hours, in grams

2.2.2.4 Initial Rate of Absorption

ASTM C67 (2020) defines initial rate of absorption as the amount of water (in grams)

absorbed in 1 minute over 30 square inches of brick bed area. ISSBs tend to draw water from the

mortar via a capillary mechanism formed by small pores in the bricks. If the initial rate of

absorption of a brick is over 1 gram per minute per square inch, it means the brick is too dry and

it will absorb water rapidly from the mortar during the drying process. This may lead to poor

adhesion and incomplete bonding between the bricks and mortar and reduced flexural bond

strength. ASTM C67 (2020) defines initial rate of absorption mathematically as:

= 30 ∗

Where,

IRA = initial rate of absorption, g/min/in 2

W = actual gain in weight of specimen, grams

L = length of specimen, in.

W = width of specimen, in.

2.2.2.5 Efflorescence

Efflorescence is a deposit of water-soluble salts generally found on the surface of bricks.

It is white and powdery in appearance and formed commonly from sulfate and carbonate salts of sodium, potassium, calcium and magnesium. The main source of these salts is the cement used in the mortar. Efflorescence can also be caused by the salts present in the sand used to make the brick and in water. For efflorescence to form, water-soluble salts need to come in contact with water for a sufficient time to dissolve and to be carried to the surface of bricks. Efflorescence affects the structural integrity of masonry structures. If the salts form below the surface of bricks, forces generated due to salt crystallization can cause cracking and spalling in the bricks. The use of water in the mortar makes it difficult to control efflorescence during the construction process.

Masonry design that prevents and minimizes water exposure and penetration is the most important factor in controlling efflorescence. Design details like capping and/or coping of walls and overhanging eaves are effective measures against efflorescence (Department of the Army,

1992)

2.2.3 Comparative Analysis and Advantages of Interlocking Stabilized Soil Blocks (ISSBs)

Table 4 provides a comparative analysis of the construction methods used in Uganda and interlocking stabilized soil blocks in terms of physical attributes, structural performance, cost- effectiveness and environmental impacts. As can be inferred from Table 4, ISSB wet compressive strengths are comparable with burned clay bricks and concrete masonry units.

ISSBs are also more durable compared to adobe bricks and wattle and daub construction.

Even though the unit cost of ISSBs is higher than burned clay bricks, the cost per square meter of construction is lower. As previously mentioned, the interlocking system of ISSBs reduces the amount of mortar needed for construction. Burned clay bricks typically require up to

3 centimeters of mortar between each brick (UN-Habitat, 2009). In comparison, interlocking stabilized soil blocks only require up to 1 centimeter of mortar (Nambatya, 2015), reducing the cost and environmental impact of construction. Furthermore, the interlocking mechanism of

ISSBs enables faster construction, reducing the labor cost. These attributes make ISSBs even cheaper than compressed earth blocks (CEB). ISSBs have a smooth and neat finish and, thus, do not require to be plastered over for aesthetic appeal (Rigassi, 1985). ISSBs can be made on site using a manual press which reduces the cost of transporting materials.

Though the full lifespan of ISSB construction is not known, it should be noted that the

ISSB construction projects completed by Brick by Brick Construction Company Ltd. since its inception in 2011 have not required maintenance and upkeep.

2.2.4 Barriers to Widespread Adoption of Interlocking Stabilized Soil Blocks Technology

A cross-sectional case study (Nambatya, 2015) was conducted in Uganda to investigate the underlying reasons for slow adoption of interlocking stabilized soil blocks technology. This study collected data through unstructured field interviews, observations and documentary evidence and found that cost of the blocks was one of the key factors affecting material selection.

People preferred burned clay bricks over interlocking stabilized soil blocks for their lower unit cost. This study also reported that developers were hesitant to use interlocking stabilized soil blocks for low-cost housing because they believed low-income earners would still not be able to afford the houses without government subsidies. The social attitude of end-users towards earth technology was another challenge reported by the study. People perceive soil to be a material for the poor and considered adding cement-an expensive material- to soil as a waste. Other barriers to widespread adoption of interlocking stabilized soil blocks reported by the study were lack of standardization and technical expertise.

Table 4: Comparative Analysis of ISSBs and Other Construction Methods Used in Uganda (price is for the year 2009) (Data from UN-Habitat, 2009 and Rigassi, 1985)

Wet Wet meter Impacts Material Durability (UGX): Per (UGX): Appearance Compressive Construction block sq. /Per Average price Average Environmental Strength (MPa) Dimensions (cm) Interlocking Stabilized Smooth 26.5 x 14 x 10 1-4 Good 350/ 35000 Low Soil Block and flat (ISSB) Compressed Smooth Earth Block 29 x 14 x 11.5 1-4 Good 400/45000 Low and flat (CEB) Burned Clay Rough Bricks 20 x 10 x 10 and 0.5-6 Good 150/55000 High powdery Adobe Rough 25 x 15 x 7 to Blocks and 0-5 Poor 50/10000 Low 40 x 20 x 15 powdery Concrete Course 40 x 20 x 20 0.7-5 Good 3000/75000 High blocks and flat Wattle and Daub N/A Rough N/A Poor N/A High

UN Habitat and Good Earth Test (UN-Habitat, 2009) conducted a series of case studies on various interlocking soil stabilized brick projects across Uganda. This study also reported lack of standardization and technical expertise and distrust of people in earth construction as some of the major challenges faced by interlocking stabilized soil blocks technology. This study recommended research on alternative stabilizers (other than cement and lime) be extended to help lower the overall cost of construction.

2.3 Soil Properties and Need for Stabilization

Soils in their natural state lack the strength and durability required for construction.

Stabilizing soils by mechanical compaction and addition of chemical binders like cement

overcomes these inherent deficiencies. Compaction increases the density of the block and

reduces its permeability. Stabilizing agents are supplementary materials added to the soil mixture

to increase its strength and durability to the elements (Walker, 1995).

The extent to which a soil can be stabilized for use in construction depends heavily on the

type of soil, type of stabilizer and content of stabilizer. Soils with a higher plasticity index (PI),

clays for example, are less suitable for stabilization. Plasticity is the extent to which a soil can be

distorted without crumbling or cracking and plasticity index (PI) is an indicator of the plastic behavior of the soil (Rigassi, 1985). Walker (1995) conducted an extensive study on the

influence of soil characteristics and cement content on the dry density, compressive and flexural

strength, durability and drying shrinkage of over 1500 cement stabilized compressed soil blocks.

Since interlocking soil stabilized blocks are a type of compressed earth block, the findings of this

study can be extended to interlocking soil stabilized blocks. Important insights from this study

are summarized below:

1. Saturated compressive strength and durability of cement stabilized soil bricks increases

with an increase in the cement content used for stabilization and decreases with an

increase in clay content of the soil.

2. Soils with a plasticity index higher than 25 show excessive dry shrinkage, low durability

and compressive strength and are not suitable for cement stabilization using manual

presses.

3. Soils with a plasticity index between 5 and 15 are most suitable for cement stabilized soil

block production.

4. Cement stabilization of greater than 10% (of dry soil weight) is uneconomical. On the

other hand, cement stabilization content of less than 5% (of dry soil weight) is inadequate

to reach desired strength characteristics using a manual press.

5. Saturation reduces the strength of stabilized compressed earth bricks due to the buildup

of pore water pressure and loss of inherent uniaxial dry compressive strength of clay.

Compressive strength testing must, hence, be conducted in saturated conditions.

6. Due to the inherent variability of soils, strength values should be calculated in terms of

95% characteristic instead of average values.

One or more stabilizing agents can be added to the soil mix. Generally, materials with the

strongest binding capacity like cement and lime act as the primary stabilizer and additional

materials act as auxiliary stabilizers. The most commonly used stabilizing agent in masonry

earth blocks, is Ordinary Portland Cement (OPC). However, given the previously mentioned

carbon-footprint associated with cement production, other pozzolanic materials are being

investigated for soil stabilization (James et al., 2016). Some of these materials include lime,

gypsum, fly-ash, rice husk ash and sugarcane bagasse ash.

2.4 An Overview of Sugarcane Bagasse Ash

Bagasse is the fibrous non-biodegradable material that remains after juice is extracted

from sugarcanes and is one of the major solid wastes generated by the sugar manufacturing process (James & Pandian, 2017). Bagasse is often used as a fuel by the sugar industry and when burned at high temperatures results in the generation of sugarcane bagasse ash. Many countries

generate a significant amount of sugarcane bagasse ash as a waste material. Sugarcane bagasse

21 ash generation in Kenya is estimated to be 1.6 million tons per year. Basika et al. (2015) reports

31,000 tons of sugarcane bagasse ash generated by Kakira Sugar Limited in Uganda goes unutilized every year. Due to its pozzolanic properties, sugarcane bagasse ash is a waste material of economic importance. It has been used in the manufacture of ceramics (Teixeira et al., 2008), in biomass ash filters (Umamaheshwaran et al., 2004), in concrete and recently as a stabilizer in compressed earth blocks.

Sugarcane bagasse ash is a natural pozzolanic material rich in silica, alumina and iron oxide. As per ASTM C618 (ASTM, 2001), natural pozzolans must consist of 70% silica, alumina and iron oxide. James and Pandian (2017) conducted a review on the valorization of sugarcane bagasse ash and reported that almost all studies reviewed show sugarcane bagasse ash meets this requirement. The silica (SiO 2) present in sugarcane bagasse ash reacts with the free lime (Ca

(OH) 2) released during the hydration of cement. The chemical equation for the hydration of

tricalcium silicate – major component of cement, is:

2 + 7 → 3. 2 . 4 + 3() +

+ → + ℎ +

Figure 2 shows the worldwide production of sugarcane crop in metric tonnes per hectare in 2018 . As can be seen in the figure, sugarcane is widely available across the globe . Uganda produced 67.67 metric tonnes per hectare of sugarcane in 2018.

Figure 2: Global Sugarcane Production in Metric Tonnes per Hectare in 2018 (map produced in ArcGIS using data from UN Food and Agriculture Organization, 2018)

2.5 Sugarcane Bagasse Ash as a Primary and Auxiliary Stabilizer

This section summarizes the research conducted on the use of sugarcane bagasse ash as a primary and auxiliary stabilizer in interlocking stabilized soil blocks, compressed earth blocks, soil and concrete.

2.5.1 Use of Sugarcane Bagasse Ash as a Stabilizer in Interlocking Stabilized Soil Blocks

Khobklang et al. (2008) studied the impact of utilizing sugarcane bagasse ash as partial cement replacement in interlocking stabilized blocks. In this study, interlocking soil stabilized blocks were admixed with 0% (control), 15%, 30% and 40% sugarcane bagasse ash by cement

23 weight replacement. The water absorption and wet compressive strength of the interlocking soil stabilized blocks were tested at 14, 28 and 90 days of strength. The results show that the 14-day and 28-day compressive strength of the blocks decreases with the addition of sugarcane bagasse ash as compared to the control. However, the 90-days compressive strength of blocks increases with the addition of sugarcane bagasse ash with the highest compressive strength achieved at the

30% sugarcane bagasse ash replacement level. This increase in strength with longer period of curing is in consensus with the findings of Deboucha and Hashim (2009).

Greepala and Parichartpreecha (2011) conducted a comparative study on the performance of fly ash, rice husk ash and sugarcane bagasse ash as partial cement replacement in lateritic sand-cement stabilized interlocking blocks. Fly ash was used to replace ordinary Portland cement up to 80% by weight in 10% increments, whereas rice-husk ash and sugarcane bagasse ash were used to replace the same up to 50% by weight in 10% increments. A sand-lateritic soil ratio of

1:1 was used in the mix-proportion. Sand-cement stabilized lateritic interlocking block with no auxiliary additives served as control. The blocks were tested for water absorption and wet compressive strength at 7 and 28 days.

The results of the study indicate that fly ash performed the best out of the three natural pozzolans and can be used as cement replacement up to 60% by weight of cement. The compressive strength of the blocks at 7 and 28 days decreased with an increase in sugarcane bagasse ash content. Blocks with sugarcane bagasse ash content higher than 40% by cement weight did not meet the compressive strength requirement of greater or equal than 7 MPa for

Thailand Industrial Standards (TIS) Class B Masonry Units. However, all blocks met the compressive strength requirement of greater or equal to 5 MPa for Class C Hollow Load-Bearing

Concrete Masonry Units. Blocks with sugarcane bagasse ash also showed the highest water absorption values when compared to fly ash and rice husk ash blocks.

Table 5: Key Similarities in Investigations Conducted by Khobklang et al. (2008) and Greepala and Parichartpreecha (2011)

mix) mix) source Source Testing Standard Sugarcane Laterite soilLaterite Bagasse Ash x mm xx mm) mm (by weight of weight mix) of Sand: soil ratio Brick Size (mm Cement Cement content Sand content (by Khobklang Kasetsart et al. (2008) University Chalermph Greepala Rerm-Udom Thailand rakeit 250 x and Sugar Industrial Sakon 12.5% 44.0% 1:01 120 x Parichartp- Factory in Standard Nakhon 110 reecha Thailand (TIS) Province (2011) Campus area

Khobklang et al. (2008) and Greepala and Parichartpreecha (2011) provide enough data to conduct a comparative analysis. However, the key similarities and differences between the two studies need to be understood first. Both studies share significant similarities in their design methodology, mix design and material selection as shown in Table 5

Khobklang et al. (2008) used sieve No. 200 (ASTM 2004b) for treating the bagasse ash, whereas Greepala and Parichartpreecha (2011) used sieve No. 325 (ASTM 2004b). Because both studies conducted 28-day wet compressive strength tests on the bricks, a comparative analysis of the results can be performed as shown in Table 6 and Table 7. The 28-day wet compressive strength for the control specimens (0% bagasse ash) in the two studies varies significantly. Both studies show a decline in the compressive strength of the bricks with the addition of sugarcane bagasse ash. However, the rate at which the compressive strength reduces is higher in Greepala

25 and Parichartpreecha (2011). In Khobklang et al. (2008), a 30% sugarcane bagasse ash replacement results in a 5% decline in compressive strength with respect to the control specimen.

The same sugarcane bagasse ash replacement in Greepala and Parichartpreecha (2011) results in a 54% reduction in compressive strength of the bricks with respect to the control specimen.

Even though the compressive strength of the control specimen in Greeepala and

Paricartpreecha (2011) is significantly higher, the compressive strength of the bricks in the two studies become comparable at 30% and 40% sugarcane bagasse ash content, as shown in Figure

3. At 30% bagasse ash content (by cement dry weight), the difference in 28-day wet compressive strength between the two studies is within 1.6%.

As previously discussed, finer ash additives show greater pozzolanic activity as smaller size particles tend to occupy the voids in the bricks making the bricks denser. The use of a finer sieve (No. 325/0.045 mm) by Greepala and Parichartpreecha (2011) could be a contributing factor to the higher compressive strength (compared to Khobkang et al. (2008)) achieved at early stages of sugarcane bagasse ash addition.

Table 6: Khobklang et al. (2008) Compressive Strength % Change with Addition of Sugarcane Bagasse Ash Khobklang et al. (2008) (Cement: 12.5% of total mix weight. Sand: 44% of total mix weight)

SBA % 28-day wet 28-day wet 28-day wet 28-day wet (by compressive compressive compressive compressive cement strength (ksc) strength strength % strength % weight) (MPa) change change w.r.t control 0 81.56 8.00 - - 15 78.35 7.68 -4% -4%

30 77.2 7.57 -1% -5% 40 72 7.06 -7% -12%

Table 7: Greepala and Parichartpreecha (2011) Compressive Strength % Change with Addition of Sugarcane Bagasse Ash Greepala and Parichartpreecha. (2011) (Cement: 12.5 % of total mix weight. Sand: 44% of total mix weight)

SBA % 28-day wet 28-day wet 28-day wet (by compressive compressive compressive cement strength (MPa) strength % strength % weight) change change w.r.t control 0 15.7 - - 10 11.7 -25% -25% 20 9.5 -19% -39% 30 7.7 -19% -51% 40 7.2 -6% -54% 50 6.8 -6% -57%

18.00

16.00 15.7

14.00

12.00 11.7

10.00 9.5 7.7 7.2 8.00 6.8 8.00 7.68 7.57 6.00 7.06

4.00

2.00

28-DAY 28-DAY WETCOMPRESSIVE STRENGTH,MPA 0.00 0 10 20 30 40 50 60

SUGARCANE BAGASSE ASH % (BY CEMENT WEIGHT) Khobkang et al. Greepala & Parichartpreecha

Figure 3: Comparison of 28-day Wet Compressive Strength Reported by Khobkang et al. (2008) and Greepala and Parichartpreecha (2011)

Onchiri et al. (2014) also investigated the performance of sugarcane bagasse ash as partial replacement for cement stabilization in interlocking soil stabilized bricks. This study was

conducted in Kenya and tested the compressive strength of the bricks at 7-day strength and 28-

day strength. The results of this study show that the maximum compressive strength for both 7-

days and 28-days was achieved at a sugarcane bagasse ash: cement ratio of 1:1.5 (3.2% of

sugarcane bagasse ash: 4.8% of cement). It is not clear if the sugarcane bagasse ash and cement

content is calculated as a percentage of the total weight of the mix.

The authors suggest that at this optimum sugarcane bagasse ash: cement ratio, the

sugarcane bagasse ash reacts completely with the calcium hydroxide (Ca (OH) 2) formed from the hydration of cement. Bricks with the sugarcane bagasse ash: cement ratio of 1:1.5 also met the minimum compressive strength requirement of 2.2 N/mm 2 (MPa) under the Kenyan Standard

Specification. This study does not include an investigation on the effect of sugarcane bagasse ash

as partial cement replacement on the water absorption behavior of the bricks. The following five

design parameters are not reported in this study:

1. Mix proportions used for the interlocking soil stabilized bricks samples.

2. Cement content used for the various design mix of the interlocking soil stabilized bricks.

It is not clear if the cement content is held constant at 4.8% for all mix proportions.

3. If the quantities of sugarcane bagasse and cement reported in the study are with respect to

the total mix weight.

4. If the compressive strength being evaluated is wet or dry compressive strength.

5. If sand is included in the brick design mix.

Since Khobklang et al. (2008) and Greepala and Parichartpreecha (2011) report the

design mix proportions, the sugarcane bagasse ash percentage by cement weight reported in

28 these studies can be evaluated as a weight ratio of sugarcane bagasse ash to cement. Tables 8 and

9 show the wet-compressive strength for the sugarcane bagasse ash: cement ratio for Khobklang et al. (2008) and Greepala and Parichartpreecha (2011), respectively.

Table 8: Khobklang et al. (2008) Compressive Strength for Sugarcane Bagasse Ash: Cement Ratio Khobklang et al.

Sugarcane Sugarcane 28-day wet bagasse ash bagasse ash: compressive % (by weight cement ratio. strength (MPa) of cement) 1:

0% - 8.00 15% 5.7 7.68 30% 2.3 7.57 40% 1.5 7.06

Table 9: Greepala and Parichartpreecha (2011) Compressive Strength for Sugarcane Bagasse Ash: Cement Ratio Greepala and Parichartpreecha

Sugarcane Sugarcane 7-day wet 28-day wet bagasse ash bagasse compressive compressive % (by ash: strength strength (MPa) (MPa) weight of cement cement) ratio. 1: 0% - 15.20 15.70 10% 9.0 11.00 11.7 20% 4.0 8.80 9.5 30% 2.3 7.10 7.7 1.5 6.5 7.2 40% 50% 1 5.7 6.8

As can be inferred from the data provided in Tables 8 and 9, the wet compressive strength in the studies conducted by Khobklang et al. (2008) and Greepala and Parichartpreecha

(2011) does not peak at a sugarcane bagasse ash: cement ratio of 1:1.5. The wet-compressive

29 strength drops steadily with the increase in bagasse ash content, providing contradictory evidence to Onchriri et al. (2014).

2.5.2 Use of Sugarcane Bagasse Ash as a Stabilizer in Compressed Earth Blocks (CEB)

Because the interlocking soil stabilized brick (ISSB) is a relatively new earth technology, studies conducted on the use of sugarcane bagasse ash as a stabilizer in interlocking soil stabilized bricks is limited. However, numerous studies have been conducted on the use of sugarcane bagasse ash in compressed stabilized earth blocks. James et al. (2016) studied the performance of 4% and 10% cement stabilized soil blocks admixed with 4%, 6% and 8% sugarcane bagasse ash by weight of dry soil, with plain cement stabilized blocks acting as control. Test specimens were subjected to compressive strength test, water absorption test and efflorescence test in accordance with the Bureau of Indian Standards (BIS). The results of this study indicated that the addition of sugarcane bagasse ash increased the compressive strength of the soil blocks. It was noted that the increase in compressive strength of the soil blocks was higher when sugarcane bagasse ash was added to the 4% cement soil blocks as compared to the increase in compressive strength in 10% cement soil blocks. This indicates the addition of sugarcane bagasse ash is more effective at lower cement content in terms of the resulting material’s compressive strength. Addition of sugarcane bagasse ash also caused a marginal increase in the water absorption of the soil blocks, while still meeting the Bureau of Indian

Standards (BIS) maximum water absorption criteria. It was noted that the water absorption was higher when Sugarcane Bagasse Ash was added to 10% cement content blocks as compared to the 4% cement content blocks, reinforcing the inference that sugarcane bagasse ash addition is more effective at lower cement content.

Another study conducted by Lima et al. (2012) indicated that sugarcane bagasse ash addition is also more effective at lower cement content. In this study, 6% and 12% cement stabilized soil blocks were amended with 0%, 2%, 4% and 8% sugarcane bagasse ash by weight of dry soil. Addition of Sugarcane Bagasse Ash to 6% cement stabilized soil blocks increased the compressive strength of the blocks when compared to the control (6% cement stabilized soil blocks with no sugarcane bagasse ash). On the other hand, addition of sugarcane bagasse Ash to

12% cement stabilized soil blocks decreased the compressive strength of the blocks as compared to the control (12% cement stabilized soil blocks with no sugarcane bagasse ash).

Ali et al. (2016) investigated the effect of sugarcane bagasse ash on the compressive

strength, water absorption, density and initial absorption rate of cement stabilized earth blocks.

In this study cement stabilized lateritic blocks with a cement: soil ratio of 1:6 were amended with

0% (control), 20%, 25% and 30% sugarcane bagasse ash by cement weight. Blocks with 20%

sugarcane bagasse ash showed an increase in compressive strength as compared to the control

specimen. However, compressive strength decreased with additional sugarcane bagasse ash

content. Water absorption and initial rate absorption increased with the addition of sugarcane bagasse ash and blocks with sugarcane bagasse ash were marginally lighter than the control

specimen.

Sugarcane bagasse ash has also been tested as the primary stabilizer in compressed earth blocks. Salim et al. (2014) studied the effect of sugarcane bagasse ash on the compressive

strength, failure pattern and shrinkage cracks of compressed earth blocks. Compressed soil blocks were stabilized with 3%, 5%, 8% and 10% sugarcane bagasse ash by weight of soil, with

un-stabilized (soil + water only) compressed earth blocks acting as control. The results of this

study show that the compressive strength of the stabilized soil blocks increased with the

31 sugarcane bagasse ash content in the admixture. At 10% sugarcane bagasse ash addition, the compressive strength was 65% higher than the control. Control earth blocks did not meet the 28- day compressive strength requirements of the Kenyan Standard Specification for Stabilized Soil

Blocks, whereas all stabilized earth blocks (from 3% to 10% sugarcane bagasse ash) met the minimum compressive strength requirement. Stabilized earth blocks exhibited compressive failure, similar to concrete’s failure pattern. Un-stabilized earth blocks, on the other hand, exhibited creep like failure where bricks disintegrated into smaller pieces.

Saranya et al. (2016) found contradictory evidence in the use sugarcane bagasse as primary stabilizer in compressed clay blocks. Compressed clay blocks were stabilized with equal proportions of sugarcane bagasse ash and rice husk ash ranging from 5% to 30% (of the total

mix) in increments of 5%. The bricks were tested for wet compressive strength at 7-days and 28-

days, water absorption and density. The compressive strength and density of the bricks decreased

with the addition of the ash content, whereas the water absorption increased with the addition of

ash content. In a similar study by Abner (2019), red coffee soil earth blocks were stabilized with

equal proportions of sugarcane bagasse ash and cassava peel. Bagasse ash and cassava peel were

each added to the bricks by 0% (control), 5%, 7.5% and 10% of the dry soil weight and the bricks were tested for compressive strength and water absorption. The compressive strength of

the bricks increased with the addition of bagasse ash and cassava peals, with 20% stabilizer bricks (10% bagasse ash+10% cassava peel) achieving the highest strength. Water absorption

decreased with the addition of stabilizers. This study also conducted Atterberg Limits test on the

stabilized soil mix and found the liquid limit and the linear shrinkage decreased and the plastic

limit increased with the addition of stabilizer.

Prashant et al. (2015) investigated the performance of compressed earth bricks admixed with different materials like sugarcane bagasse ash, lime, cement, fly ash, jaggery, quarry dust and coconut fiber in varying proportions. Each additive material was added individually to the earth bricks and tested for compressive strength. The results showed that 10% cement bricks produced the highest compressive strength followed by 5% quarry dust bricks and 5% fly-ash bricks. 5% sugarcane bagasse ash bricks produced compressive strength equivalent to 95% strength produced by 10% lime bricks. The study does not report the various percentage of the additives used in the bricks making it difficult to replicate and to be comparable with other studies. It is assumed the percentage of additives are given by weight of the total mix.

A comparison of the 28-day compressive strengths reported by Lima et al. (2012),

Khobklang et al. (2008), Greepala and Parichartpreecha (2011) and Ali et al. (2016) is shown in

Figure 3. Other investigations discussed were not included in the comparison because of insufficient data reported. Sugarcane bagasse ash content reported by Lima et al. (2012) was evaluated as a percent of the cement weight for comparing it to the other studies. Other than the variations in the soil type, bagasse ash quality and testing methodology, the key differences in these studies are:

1. Khobklang et al. (2008) and Greepala and Parichartpreecha (2011) compressive strength

values are for interlocking soil stabilized bricks, whereas Lima et al. (2012) and Ali et al.

(2016) values are for compressed earth/soil bricks.

2. Sand is included in the design mix of all studies except Ali et al. (2016).

3. All four studies except Ali et al. (2016) report the wet-compressive strength of the bricks.

It is unclear if the compressive strength values reported by Ali et al. (2016) are wet or dry

compressive strength. Please note wet compressive strength values are lower than dry

compressive strength.

4. The cement content decreases with the addition of sugarcane bagasse ash in Khobkang et

al. (2008) and Greepala and Parichartpreecha (2011). The cement content remains constant

in Ali et al. (2016) and Lima et al. (2012).

Figure 4 shows Lima et al. (2012) 6% cement content blocks show the least compressive strength and Ali et al. (2016) 16.7% cement content blocks show the highest compressive strength. As expected, compressive strength increases with the cement content in the blocks.

Figure 4 further shows that all studies except Lima et al. (2012) (6% cement) demonstrate an overall decline in the compressive strength of the blocks with the addition of sugarcane bagasse ash content. The figure also shows that the studies of Lima et al. (2012) show an increase in the compressive strength for both 6% and 12% cement mix when bagasse ash content increases beyond 60%.

In Figure 5, the results of these studies are further compared to the minimum compressive strength values for masonry units set by Thailand Industrial Standards (TIS), Bureau of Indian

Standards (BIS) and Uganda National Bureau of Standards (UNBS). Thailand Industrial

Standards (TIS) and Bureau of Indian Standards (BIS) were the most used standards in the literature review. Uganda National Bureau of Standards is used for reference because of this study’s location in Masaka, Uganda.

Figure 5 shows that all studies except Lima et al. (6% and 12%) exceed the Thailand

Industrial Standards (TIS) requirements for Class B (7 MPa) and Class C (5 MPa) masonry units.

Furthermore, all studies except the lower sugarcane bagasse ash content blocks of Lima et al.

(2012) 6% cement exceed the Uganda National Bureau of Standards (UNBS) minimum wet compressive strength of 1.5 MPa for interlocking stabilized soil blocks (ISSB).

18 Lima et al, 6% Cement

16 Lima et al, 12% Cement

14 Khobkang et al, 12.5% Cement

Greepala and Parichrtpreecha, 12.5% 12 Cement Ali et al., 16.7% Cement 10

28-DAY COMPRESSIVE STRENGTH COMPRESSIVE(MPA) 28-DAY STRENGTH 2

0 0 20 40 60 80 100 120 140

SUGARCANE BAGASSE ASH CONTENT (% BY CEMENT WEIGHT)

Figure 4: Comparison of the 28-day Compressive Strength Reported by Lima et al. (2012), Khobklang et al. (2008), Greepala and Parichartpreecha (2011) and Ali et al. (2016)

18 17 16 15 14 13 12 11 10 9 8 7 7 MPa, TIS Class B Masonry Units 6 5 MPa, TIS Class C Hollow Load-Bearing Concrete Masonry Units 5 4 2.94 MPa, BIS 1S 1725 Class 30 Blocks 28-DAY COMPRESSIVE28-DAY (MPA) STRENGTH 3 2 1.96 MPa, BIS 1S 1725 Class 20 Blocks

1 1.5 MPa, UNBS ISSB Wet Compressive Strength 0 0 20 40 60 80 100 120 140 SUGARCANE BAGASSE ASH CONTENT (% BY CEMENT WEIGHT) Lima et al, 6% Cement Lima et al, 12% Cement Khobkang et al, 12.5% Cement Greepala and Parichrtpreecha, 12.5% Cement Ali et al., 16.7% Cement Figure 5: Comparison of the 28-day Compressive Strength with Minimum Compressive Strength Requirements Set by Thailand Industrial Standards (TIS), Bureau of Indian Standards (BIS) and Uganda National Bureau of Standards (UNBS)

2.5.3 Sugarcane Bagasse Ash Used as a Stabilizer in Concrete and Mortar

To further understand the performance of sugarcane bagasse ash in relation with cement, studies conducted on the utilization of sugarcane bagasse ash as partial cement replacement in concrete and mortar are considered. In Uganda, Basika et al. (2015) investigated the compressive and flexural strength of mortars containing cement and sugarcane bagasse ash in proportions of

0% (control), 10%, 15%, 20%, 25%, 30% and 40% by cement weight replacement. Results of this study revealed that replacement of cement with sugarcane bagasse ash up to 20% by weight of cement increases the compressive strength of mortar. Highest compressive strength was

36 observed at 15% replacement levels. However, no statistically significant difference was found between compressive strength at 10% and 20% replacement, indicating that replacement up to

20% is feasible.

Sumesh and Sujatha (2018) investigated the effect of replacing 0% to 20% cement (in

increments of 5%) by sugarcane bagasse ash in concrete. Concrete specimens were tested for wet

compressive strengths at 7, 14 and 28 days, split tensile strength at 28 days, flexure strength, bond strength and resistance to sulphate attack. The results of the study showed an increased in

compressive strength and tensile strength at initial sugarcane bagasse ash addition of 5%,

followed by a decline in both properties with additional bagasse ash addition. The authors

recommend cement replacement by sugarcane bagasse ash by up to 10% (by weight of cement).

Additionally, sugarcane bagasse ash was not recommended as cement replacement in sulphate

attack prone areas. Srinivasan and Sathiya (2010) also found the compressive strength of

concrete increased at a 5% cement replacement by bagasse ash and decreased with additional bagasse ash content. However, the 28-day compression strength of 10% bagasse ash specimen

(by weight of cement) was still higher than the control specimen. The authors recommended that bagasse ash can be replace cement in concrete by up to 10%.

Another study conducted by Ganesan et al. (2007) also found that the compressive

strength of the concrete specimens increases at initial stages of bagasse ash addition followed by

a decline in strength. Cement was replaced by 5% to 30% by weight, in increments of 5% and

tested for 7-, 14-, 28- and 90-day compressive strength, splitting tensile strength, water

absorption, sorptivity, chloride penetration and chloride diffusion. The results show an increase

in compressive strength with up to 10% bagasse addition. At 20% bagasse addition, the

compressive strength drops and is equivalent to the value of the control specimen. The 7-

37 compressive strength of the 20% bagasse ash concrete specimen was equal to the 14-day compressive strength of the control specimen. A similar trend was seen in comparing the compressive strength of 20% bagasse ash specimen to that of the control specimen from the next curing period. This indicates the addition of bagasse ash develops high early strength in concrete.

The authors concluded a 20% replacement of cement by sugarcane bagasse ash is feasible without changing the properties of concrete.

Chusilp et al. (2009) found that the highest compressive is achieved at 20% cement replacement by sugarcane bagasse ash. In this study, cement was replaced by bagasse ash by

10%, 20% and 30% by weight and tested for 28- and 90- day compressive strength, water absorption and heat evolution. 20% bagasse ash concrete specimens achieved a 28 day- compressive strength 10% higher than the control specimen. Compressive strength dropped at

30% cement replacement but was still higher than the control specimen.

2.5.4 Effect of Sugarcane Bagasse Ash Addition on Properties of Soil

Onyelowe (2012) conducted a study to examine the effect of sugarcane bagasse ash on the maximum dry density and optimum moisture content of cement stabilized lateritic soil. 6% and 8% cement stabilized lateritic soil mixtures were admixed with 0% (control), 2%, 4%, 6%,

8% and 10% sugarcane bagasse ash by dry soil weight. Results indicated that at 4% cement content, the maximum dry density reduced with the addition of sugarcane bagasse ash. At 6% cement content, the maximum dry density increased with the addition of sugarcane bagasse ash.

The moisture content increased with the addition of sugarcane bagasse ash for both cement contents. Another study (Mohammed, 2007) showed an increase in optimum moisture content and decrease in maximum dry density of cement stabilized laterite soil with the addition of sugarcane bagasse ash. Mir et al. (2005) performed a similar study on cement stabilized soil (3%

38 and 6% cement by dry soil weight) amended with 7.5%, 15% and 22.5% sugarcane bagasse ash content. The results of the study show an increase in the optimum moisture content with the addition of sugarcane bagasse ash at both 3% and 6% cement, in support of the findings by

Onyelowe (2012) and Mohammed (2007). The maximum dry density reduced with the addition of bagasse ash for both cement contents, contradictory to the findings of Onyelowe (2012). Mir et al. (2016) suggests 7.5% sugarcane bagasse ash with 6% cement to be the optimum content for soil stabilization. Osinubi et al. (2009) investigated the effect of using sugarcane bagasse ash as the primary stabilizer in deficient laterite soil. Sugarcane bagasse ash up to 12% by weight of dry soil was added to laterite soil. The results showed an increase in optimum moisture content and decrease in maximum dry density with the addition of sugarcane bagasse ash. However, the results for unconfined compressive strength and California bearing ratio were lower that the required standards. The authors concluded that sugarcane bagasse ash cannot be used as the only stabilizer and should be used as an admixture.

2.5.5 Other Cost-effective Benefits of Utilizing Sugarcane Bagasse Ash

Sugarcane bagasse ash has also been investigated as a partial replacement for fine aggregates in concrete. Fine aggregates include sand and crushed stone. Modani and Vyawahare

(2013) investigated the effect of replacing 10% to 40% river sand by sugarcane bagasse ash, in increments of 10%. Concrete specimens were tested for 7- and 28-day wet-compressive strength,

28 day split tensile strength and captivity test. The results of the 28-day compressive strength test show an increase at 10% sugarcane bagasse ash content, followed by a decline in compressive strength with additional bagasse ash content. The increase in compressive strength at early stage of bagasse ash addition is similar to the findings by Ali et al. (2016) discussed earlier. The tensile strength of the concrete specimens decreases with the addition of sugarcane

39 bagasse ash. The authors conclude the 10% to 20% fine aggregates in concrete can be replaced by sugarcane bagasse ash. A similar study performed by Sales and Lima (2010) concluded that

sugarcane bagasse ash can be classified as fine sand based on sieve analysis. X-ray

diffractometry performed on the concrete samples admixed with sugarcane bagasse ash showed a

crystalline structure. The authors concluded that sugarcane bagasse ash can replace fine

aggregates which have inert properties but not cement which has binding properties.

Other than its use as a stabilizer in earth blocks, sugarcane bagasse ash has also been

studied as a means to reduce the weight of bricks. Singh and Kumar (2016) studied the impact of

replacing sand by sugarcane bagasse ash in earth blocks, while maintaining a constant cement

weight of 20% by total weight of mixture. Results of this study showed that the replacement of

sand with sugarcane bagasse ash resulted in lower weight bricks that still met the compressive

strength requirement of the Bureau of Indian Standards. Lower weight bricks will reduce the

dead load of structures, in turn reducing the among of structural steel and concrete required.

2.5.6 Sugarcane Bagasse Ash Used with Stabilizers Other than Cement

Sugarcane bagasse ash has also been studied in combination with stabilizers other than

cement. Alavez-Ramirez et al. (2012) conducted a comparative study on the use of cement, lime

and sugarcane bagasse ash as stabilizers in compacted soil blocks. In this study, soil blocks were

stabilized with 10% cement, 10% lime and combination of 10% lime + 10% sugarcane bagasse

ash with the control being soil blocks with no stabilizers added. Soil blocks were tested for

flexural strength and compressive strength in dry and saturated state. Results revealed that soil blocks stabilized with 10% lime + 10% sugarcane bagasse ash outperformed blocks stabilized with 10% lime alone in both flexural strength and compressive strength. This study also estimated the energy consumption, carbon dioxide emission and energy in transportation for each

40 of the ad-mix alternatives. Control soil blocks performed the best in terms of energy consumption and carbon dioxide emission followed by sugarcane bagasse ash + lime, lime alone and cement. In terms of energy consumed in transportation, combination of sugarcane bagasse ash and lime performed the best followed by control soil blocks, lime and cement. Compared to cement soil blocks, combination of sugarcane bagasse ash and lime blocks showed a 38%, 40% and 21% reduction in energy consumption, carbon dioxide emissions and energy in transportation, respectively. In comparison to lime blocks, combination of sugarcane bagasse ash and lime blocks showed a reduction of 19% in all three factors.

James and Pandian (2017) also investigated the effect of adding sugarcane bagasse ash to lime-stabilized earth blocks. The minimum lime content required to raise the pH value of soil to

12.4 is called the “initial consumption of lime” (James & Pandian, 2017) and is considered the amount required to modify soil properties for stabilization. In this study, the “initial consumption of lime” content was evaluated to be 6% using the Eades and Grim pH test. Six percent lime stabilized earth blocks were ad-mixed with 4%, 6% and 8% sugarcane bagasse ash by total weight of mixture. Blocks were tested for compressive strength at 28 days, water absorption and efflorescence in accordance with the Bureau of Indian Standards (BIS). As per BIS specification

IS 1725, there are two classes of stabilized blocks: Class 20 with a minimum required strength of

1.96 MPa and Class 30 with a minimum required strength of 2.94 MPa. The results of this study showed that the addition of sugarcane bagasse ash increased the compressive strength of blocks with 8% sugarcane bagasse ash blocks producing the maximum strength. However, none of the blocks met the minimum compressive strength requirements for Class 20 blocks. Comparing their study to earlier investigations that used higher lime contents and achieved better strength performance, the authors concluded that lime stabilization at the “initial consumption of lime” is

41 not sufficient to achieve required compressive strength and higher optimum lime content be used for future studies. The authors used the results of the study and regression analysis to forecast that a minimum sugarcane bagasse ash of 9.425% by weight of mix in combination with 6% lime is required to achieve a compressive strength of Class 20 blocks.

Madurwar et al. (2014) investigated the effect of using sugarcane bagasse ash as a partial replacement for quarry dust in lime stabilized soil blocks. In this study, admixtures of varying sugarcane bagasse ash and quarry dust proportions were prepared with 20% lime content by total weight of mixture held constant. 50% sugarcane bagasse ash and 30% quarry dust (with 20% lime) bricks were prepared for the first trial, with 5% of quarry dust replaced by sugarcane bagasse ash for each subsequent trial. A conventional clay brick was used as control. The results of this study showed that brick with sugarcane bagasse ash, quarry dust and lime ratio of

50:30:20 had the highest compressive strength of 6.59 MPa, which is 88.3% higher than that of burnt clay bricks.

In a similar study, Kulkarni et al. (2013) investigated the effect of using sugarcane bagasse ash as a partial replacement for fly ash in lime stabilized soil blocks. Sugarcane bagasse ash was used to replace fly ash up to 60% (by weight of fly ash) in increments of 10%. Lime content was held constant at 20% by total weight of mix for all trials of fly ash replacement with sugarcane bagasse ash. 10% quarry dust by total weight of mix was also used as an auxiliary stabilizer in the mix. Blocks were tested for compressive strength at 7, 14 and 21 days. The results indicate that the compressive strength of the blocks decreased with the addition of sugarcane bagasse ash as replacement for fly ash. However, all blocks met the minimum compressive strength requirements for Class 30 blocks (2.94 MPa). The results of this study

42 reinforce the inference by James and Pandian that lime content greater than the ‘initial consumption of lime’ is necessary to achieve required compressive strength requirements.

2.5.7 Use of Sugarcane Bagasse Ash as Cement Replacement in Other Products

Priyadarshini et al. (2015) investigated the effect of replacing cement in hollow concrete blocks by up to 30% by weight in increments of 10%. Silica fume was also used as a variable in the study and added to one set of bricks. The compressive strength test results indicate that bricks with 10% bagasse ash replacement and silica fumes as an admixture performed the closest to the control specimen. Water absorption also increased with the addition of sugarcane bagasse ash content greater than 10%. This study also performed a cost analysis to show sugarcane bagasse ash hollow concrete blocks could achieve a 63.7% profit ratio on sales.

Rajkumar et al. (2016) studied the effect of partial replacement of cement by sugarcane bagasse ash on the compressive strength of low traffic road paver blocks. Sugarcane bagasse ash was added to the concrete mix by 50% of the total weight of the mix. At the same time, the amount of cement used in the control trial was reduced by 50%. The compressive strength of the paver blocks reduced with the addition of sugarcane bagasse ash. However, the 7-day

compressive strength of sugarcane bagasse ash paver blocks was within 3.5% of the control

specimen compressive strength. A cost analysis performed in the study showed the sugarcane bagasse ash paver blocks were cheaper than conventional flexible pavement by 24.15%.

Table A1 in Appendix A summarizes the findings from the literature review of the use of

sugarcane bagasse ash as a primary and auxiliary stabilizer. The following knowledge gaps were

identified in the current literature:

1. Studies on the use of sugarcane bagasse ash as partial cement replacement in interlocking

stabilized soil blocks (ISSBs) are limited. Only three (3) such studies were identified for

this literature review.

2. Majority of the studies do not report all the important parameters that affect the

performance of the test specimens. For example,

a. Onchiri et al. (2014) and Prashant et al. (2015) do not report the cement

content used for the various brick mix-proportions.

b. In a few studies, it is unclear if the sugarcane bagasse ash percentage reported

is taken with respect to the total weight of the soil mix or with respect to the

weight of cement. If a total soil mix weight of 100 g with 10% cement content

is considered, 20% sugarcane bagasse ash with respect to total mix weight is

20 g and with respect to cement weight is 2 g.

c. A few studies either do not report if sand is included in the soil mix or do not

report the percentage of sand included. Sand also acts as a stabilizing agent in

compressed earth blocks affecting their compressive strength.

d. It is unclear if the compressive strength reported by a few studies is wet or dry

compressive strength. As previously noted, wet compressive strength is lower

than dry compressive strength.

e. A few studies report the test results only graphically. These studies cannot be

compared to other investigations because the exact values of the results are

not known.

These gaps in reported data hurt the standardization efforts for sugarcane bagasse ash

amended interlocking soil stabilized blocks (ISSBs). Issues (a), (b) and (c) can be easily

addressed by reporting the complete mix design used in the study.

3. In majority of the studies, the cement content used for the mix design is chosen

randomly. As recommended by Walker (1995), the cement content must be chosen based

on the soil properties. Soils with higher plasticity index require a higher cement content

for stabilization. By basing cement content on soil properties, discrepancies in test results

caused by the inherent variability of soils can be reduced.

4. Majority of the work has been done to study the compressive strength and water

absorption of sugarcane bagasse ash amended earth blocks. To promote adoption of

interlocking stabilized bricks, further investigation on the impact of sugarcane bagasse

ash on the modulus of rupture and initial rate of absorption of bricks is needed. Modulus

of rupture, or flexural strength, is critical to understand the resistance of ISSB

construction to lateral loads like wind and earth pressure and is especially important for

the construction of non-loading and free-standing walls. If the initial rate of absorption of

a brick is high (greater than 1 gram per minute per square inch), the brick will absorb

water rapidly from the mortar during the drying process. This disrupts the bond between

the brick and the mortar affecting the overall structural integrity.

2.6 Best Practices for Investigating the Use of Sugarcane Bagasse Ash as Partial Cement

Replacement in Interlocking Stabilized Soil Bricks

Figure 6 presents a research design flowchart for investigating the impact of sugarcane bagasse ash in interlocking soil stabilized bricks as partial cement replacement. This design flowchart is based on best practices learned from the literature review, procedures followed by

Brick by Brick Construction Ltd., and methodology prescribed by Uganda National Bureau of

Standards. The purpose of this flowchart is to provide a framework for future studies and to help avoid gaps in reported data, as described in the previous section. The flowchart is divided into three major sections and under each section, the required methods to conduct the investigations as well as the corresponding data that should be reported is specified.

For preparing the murram soil, it is recommended that a linear shrinkage test, Atterberg

Limits tests and/or other laboratory tests should be conducted to understand the soil properties and soil quality. If the linear shrinkage test is conducted, the linear shrinkage value of the murram sample should be reported. If the Atterberg Limits and/or other laboratory tests are conducted, Plasticity Index (PI) of the sample must be reported. Please note laboratory tests on the murram sample may not be feasible for field-based studies in low-resource settings.

For preparing the sugarcane bagasse ash, it is recommended to crush and sieve the ash.

Alavez-Ramirez et al. (2012) recommends using ASTM sieve No. 200 (0.075 mm). However, this flowchart recommends a sieve finer than No. 200 (0.075 mm). As previously discussed, finer ash additives show greater pozzolanic activity as smaller size particles tend to occupy the voids in the bricks making the bricks denser. The use of a finer sieve (No. 325/0.045 mm) by Greepala and Parichartpreecha (2011) compared to No. 200 (0.075 mm) by Khobklang et al. could be a contributing factor to the higher compressive strength achieved at early stages of sugarcane bagasse ash addition (See Figure 3). Additionally, laboratory tests to assess the chemical and mineralogical composition of the sugarcane bagasse ash should be conducted. James and

Pandian (2017) recommends calcination temperature of the bagasse ash, nature of silica present in the ash and loss on ignition percentage should be evaluated and reported. For low-resource

46 field-based settings, where laboratory tests for sugarcane bagasse ash may not be feasible, the sieve number and/or any other method of treatment used should be reported.

For determining the mix design of the sugarcane bagasse ash amended ISSBs, it is

recommended that the cement content should be based on soil properties (Walker, 1995). If

Atterberg Limits test is conducted on the murram sample, the cement content should be based on

the Plasticity Index (PI) of the soil as prescribed by Walker (1995). If the linear shrinkage test is

conducted on the soil sample, the cement content can be determined using Table 10 in Chapter 3.

Based on the findings of the literature review, 10% to 20% of cement weight replacement by sugarcane bagasse ash in interlocking soil stabilized bricks (ISSBs) is recommended. Sumesh and Sujatha (2018), Srinavasan and Sathiya (2010), and Priyadarshini (2015) all recommend a

10% sugarcane bagasse ash replacement of cement. Basika et al. (2015) and Ali et al. (2016) recommend up to 20% cement weight replacement by sugarcane bagasse ash. Greepala and

Parichartpreecha (2011) found that sugarcane bagasse ash replacement of cement greater than

40% reduced the compressive strength of the ISSB samples below the Thai Industrial Standards

Institute (TIS) Class B Masonry Units requirement. As can be seen from Figure 4 and Figure 5, compressive strength at higher sugarcane bagasse ash content reduces significantly. Furthermore, virtually all investigations concluded the water absorption rate of the test samples increases with the increase in sugarcane bagasse ash content.

Figure 6: Research Design Flowchart for Investigating the Impact of Sugarcane Bagasse Ash in Interlocking Soil Stabilized Bricks as Partial Cement Replacement

Chapter 3: Methods

The aim of this experimental study is to determine if ISSBs amended with 10% and 20% sugarcane bagasse ash by cement replacement weight meet the structural performance and durability requirements set by the Uganda National Bureau of Standards. Additionally, a cost- analysis on the benefits of using sugarcane bagasse ash as partial cement replacement in ISSBs is performed. For this analysis, the materials cost for constructing a 7-classroom block school building and a 30,000 L rainwater harvesting tank using regular ISSBs and using sugarcane bagasse ash amended ISSBs is compared.

3.1 Mechanical Testing of Sugarcane Bagasse Ash amended ISSBs

The ISSB testing methodology for this research is divided into three sections and is based on the research design flowchart presented in Figure 6. Please note that due to evacuation from project site because of the COVID-19 pandemic, only material selection and preparation, and brick making procedures were completed.

3.1.1 Material Selection and Preparation

The marram sample was excavated from Kalisizo, Uganda. According to the European

Soil Data Center (European Commission, 2020), the type of soil found in Kalisizo is mainly sandy loam ferrallitic soil. Ferrallitic soils are rich in iron and aluminum and are found in humid and tropical climates (Breeman & Buurman, 2002). This type of soil is also found in major portions of southern Uganda and in parts of east and west Uganda (European Commission,

2020). Fifty kg bags of Portland cement and sand were bought from a local hardware store in

Kalisizo. ISSB press machines, wheelbarrows, weighing scales and other equipment were loaned

49 from Brick by Brick Construction Company Ltd. Figure 7 shows the location of the five major sugar manufacturers in Uganda.

Figure 7: Location of Major Sugar Manufacturers in Uganda (map produced in ArcGIS using coordinated obtained from Google Maps)

As can be seen from the figure, most of the major sugar manufacturers are clustered in the eastern region of Uganda. It should be noted that other small sugar manufacturers and informal sugarcane vendors exist throughout the country. The nearest major sugar manufacturer to the study location (Masaka) is Sango Bay Estates Limited and it is located 1.5 hours away from Masaka. The cost for transporting sugarcane bagasse ash from Sango Bay Estates Limited to Maska outweighed the projected cost savings of replacing cement by sugarcane bagasse ash in

ISSBs. Hence, sugarcane bagasse was obtained from local vendors in Masaka and burned on site to produce sugarcane bagasse ash.

For construction projects located close to major sugar refineries in Uganda, it is recommended Brick by Brick Construction Company Ltd. obtain sugarcane bagasse ash directly from the refineries. For construction projects located farther away from the refiners, it is recommended to obtain sugarcane bagasse from local vendors and then field burn it to produce bagasse ash. To setup a supply-chain of sugarcane bagasse ash, Brick by Brick Construction

Company Ltd. can establish a relationship with local vendors in the Masaka/Kalisizo region wherein sugarcane bagasse is collected periodically from the vendors.

3.1.1.1 Shrinkage Test for Marram

A shrinkage test provides information to determine the amount of cement that must be added to the ISSB mixture for proper stabilization. To perform the shrinkage test, a long and narrow steel box mold with internal dimensions of 60 cm x 4 cm x 4 cm as shown in Figure 7-A was used. The mold’s interior was greased with locally sourced motor oil as shown in Figure 7-

B. Marram is a laterite soil rich in iron oxide and commonly found in regions with tropical and sub-tropical climate. The marram soil sample was mixed with water in a plastic container to form a smooth paste. The box mold was then filled-in with the moist marram and compacted hardily with the top levelled-off as shown in Figure 7-C. The mold was left to dry for a period of 7 days in a dry, shaded area.

After 7 days, the marram in the mold had solidified and shrunk. The marram was moved by hand to one end of the mold leaving a gap at the other end. Greasing the mold with oil ensures that the marram sample does not crack or stick to the mold when it is moved. As can be seen in

Figure 9, the gap left in the mold can be measured (in this case 20 mm in length) and it indicates

51 the linear shrinkage of the marram sample. Atterberg Limits test can be performed on the marram sample in place of the shrinkage test. Atterberg Limits test is used to determine the plastic limit, liquid limit, plasticity index and shrinkage limit of the soil sample and is a better indicator of soil properties than the shrinkage test. However, this study uses the shrinkage test because the appropriate soil and cement ratio used by Brick by Brick Construction Ltd. (shown in Table 10) is based on the shrinkage test. Moreover, the Casagrande cup used for the liquid limit test was not accessible in the study location at the time of testing.

Figure 8-A: Steel Mold Box Figure 8-B: Steel Mold Box Figure 8-C: Steel Box Mold Used for Shrinkage Test Greased with Motor Oil for Filled in with Marram for Shrinkage Test Shrinkage Test

Figure 9: Marram Linear Shrinkage of 20 mm

3.1.1.2 Preparing Soil Mixtures

Based on linear shrinkage, the appropriate mix ratio of soil and cement by volume was determined using Table 10. This table is used by Brick by Brick Construction Company Ltd. as standard procedure and was obtained from Makiga Engineering Services Ltd. Makiga is a Kenya based company and a major manufacturer of ISSB brick press machines in Africa. The mix proportions in this table are given in terms of a 15-L bucket to make field measurement of quantities easier. However, to make the mix-design of this study comparable with previously done work, the mass of a 15-L bucket of cement, murram and sand was measured and recorded in Table 11.

Table 10: Cement-Soil Mix Ratio Based on Linear Shrinkage of Soil Shrinkage (mm) Cement (15 L Murram +Sand No. of ISSBs bucket) (15 L bucket) Less than 12 mm 1 bucket 18 buckets 150 12 mm - 24 mm 1 bucket 16 buckets 130

25 mm - 39 mm 1 bucket 14 buckets 115 40 mm - 50 mm 1 bucket 12 buckets 100

Table 11: Weight of a 15-L Bucket of Cement, Murram and Sand 15 L bucket of Mass (kg)

Cement 18.5

Murram 19

Sand 24

As can be inferred from Table 10, a higher marram shrinkage value means more cement is required for stabilizing the ISSBs. Based on the table, a shrinkage value of 20 mm would require a cement: murram + sand mix ratio of 1:16 buckets (15 L). In other words, for every 15-L bucket of cement, 16 15-L buckets of soil are required to produce 130 ISSBs. Note the cement content in the table is given in relation to the murram and sand mix. As described in Chapter 2, sand is also used in the ISSB mix as auxiliary stabilizers. The marram: sand ratio is based on

Brick by Brick Construction Company Ltd.’s standard procedure.

The soil mix proportions will also depend on the number of ISSB samples required for testing. Table 12 shows the minimum number of samples required by Uganda National Bureau of Standards (UNBS) for each test.

Table 12: Sample Size Required for Testing (UNBS) Density Rupture Strength ISSB mix Absorption Modulus of Sample size Sample size Sample size Initial of Rate strength testing strength testing Weathering Test required each for Wet CompressiveWet Water AbsorptionWater required 28-day for required 14-day for 5 5 5 5 3 2 25 25 50

Based on the findings of the literature review, shrinkage test results and UNBS required sample sizes, the mix-design for sugarcane bagasse ash amended interlocking soil stabilized blocks was determined and is presented in Table 13.

Table 13: Mix Design for Interlocking Stabilized Soil Blocks (ISSBs) with Sugarcane Bagasse Ash as Partial Cement Replacement

(kg)

(kg) (kg) Mix Total Cement by Total Murram Murram Mix (Kg) Sand Weight of Weight of Weight of SBA% by Cement % Cement Cement Cement 247 kg (13 15-L 72 kg (3 15- Control 337.5 18.5 6.0% N/A buckets) L buckets) 247 kg (13 15-L 72 kg (3 15- 10% (1.85 SBA10% 337.5 16.65 5.0% buckets) L buckets) kg) 247 kg (13 15-L 72 kg (3 15- 20% (3.7 SBA20% 337.5 14.8 4.5% buckets) L buckets) kg)

3.1.2 Brickmaking

3.1.2.1 Material and Equipment Preparation

Marram was manually crushed until all big lumps were broken-off and was then passed through a 6-mm sieve, as shown in Figure 10. Marram soil retained on the sieve was further crushed and passed through the sieve again. Sugarcane bagasse was brought on site and field- burned to produce sugarcane bagasse ash.

3.1.2.2 Batching and Mixing

Marram soil, sand and cement for each mix were manually combined using a shovel as per the ratios obtained from the soil mix design. For the control mix, no additional materials were added. For the SBA10% and SBA20% mix, sugarcane bagasse was added to the mix as per the quantities described in the mix design. A weight scale was used to measure sugarcane bagasse ash quantities. The mixture of marram, sand, cement, and sugarcane bagasse ash was

55 dry-mixed until a uniform color of the mixture was obtained. Visually checking if the mixture has a uniform color serves as a quality control measure in the mixing process. After dry-mixing, water was added carefully such that it was enough to bind the materials but not too much to make the mix weak. Water quantity in the mix was tested by squeezing the mix in one hand to ensure water does not run through the fingers.

3.1.2.3 Compressing the Mix

A typical ISSB press machine is shown in Figure 12. The ISSB press machine mold was properly oiled with used motor oil to ensure ISSB mix does not stick to the mold. The mix was filled in the mold with the top flush and then compressed manually to produce an ISSB unit. The

ISSB was carefully removed from the mold and visually inspected for any issues. Bricks with overly rough texture and/or chipped-off ends were thrown back in the mix and re-compressed to ensure quality. Figure 13 shows a well-made ISSB right before it is ejected from the brick press mold. The same process was repeated to make the remaining ISSBs, which were then stacked in a maximum of five layers. Over stacking the bricks may lead to cracks as they have not developed their full strength yet.

Figure 10: Marram being Sieved Using a Figure 11 : Dry -mix of Marram, Ce ment and Sand 6 mm Sieve

Figure 12: A Typical ISSB Press Figure 13 : A n ISSB Right after Production Machine

3.1.2.4 Brick Curing

After a period of 24-hours, a field quality control measure prescribed by Brick by Brick

Construction Company Ltd. was conducted on the bricks. To conduct the field test, five ISSBs were randomly selected and two of the five ISSBs were laid flat on steady ground. These two

ISSBs act as supports for the third ISSB placed (lengthwise) on top and are separated by a

57 distance slightly less than the length of an ISSB. This field-based setup mimics the four-point bending (also known as two-point loading) setup of the laboratory conducted modulus of rupture test. To apply compressive load on the ISSB setup, one of the masons stood on top of the third

ISSB. The mason held the remaining two ISSBs (one in each hand) to increase the compressive load being applied to the setup. This field test was conducted to ensure ISSBs do not crack under the load applied. After the field-test was conducted, ISSBs were watered to begin the wet-curing process. Wet ISSBs were then properly covered with a transparent polythene sheet to ensure moisture does not leave the bricks and left to wet-cure for 7 days. This quality control measure of wet-curing the ISSBs is also followed by Brick by Brick Construction Company Ltd. before laying the bricks for construction. The polythene was removed after 7 days and the bricks were left to dry-cure for another 7 days. The 14-day testing sample set (50 ISSBs) was transported to the Uganda National Bureau of Standards (UNBS) facility in Kampala for mechanical testing and the remaining ISSBs (50 ISSBs) were left to cure longer and transported to Kampala at the end of the 28-day curing period.

3.1.3 Interlocking Soil Stabilized Blocks Testing

As previously mentioned, laboratory testing of the ISSBs was not carried out due to a

COVID-19 prompted evacuation from project site. This section describes the methodology that would have been undertaken for testing the sugarcane bagasse ash amended ISSB samples and is based on the procedures prescribed by the Uganda National Bureau of Standards (UNBS) and best practices learned from the literature review.

3.1.3.1 Wet Compressive Strength Test

Uganda National Bureau of Standards prescribes both dry and wet compressive strength testing for ISSBs. However, based on the recommendation of Walker (1995) only wet

58 compressive strength testing is proposed for this study. Wet compressive strength is lower than dry compressive strength due to the buildup of pore water pressure and loss of inherent uniaxial strength of dry clays.

Five ISSBs from each mix are measured and their surfaces cleaned of all loose debris.

ISSB specimens are then fully immersed in a water bath for 24 hours at a temperature of 15 o C to

30 o C. The water bath must be of sufficient size to ensure the ISSB specimens are not in contact

with each other. After 24 hours, specimens are removed from the water bath and wiped clean

with a piece of cloth. Each ISSB is then placed between two pieces of 3-mm thick plywood and

then set in the testing machine such that the center of the bed face coincides with the loading axis

of the machine. Load is applied to the ISSB specimen and increased continuously at a uniform

rate of 150 kN/min until the ISSB cracks. The load at which the ISSB fails is observed and

recorded.

3.1.3.2 Modulus of Rupture Test

Five ISSBs bricks from each mix are tested for modulus of rupture using a hydraulic

compression loading machine and a four-point bending setup, also known as two-point loading.

The width (B) and height/depth (D) of each ISSB is measured before testing. Each ISSB

specimen is laid flat on two roller supports placed in the machine test bed and is centered along

its longitudinal axis. The span length - distance between the two roller supports - is measured

and recorded. Span length should be approximately 25 mm less than the ISSB length. The

loading bar is then placed on the upper surface of the ISSB specimen and compressive load is

applied to the specimen at a uniform rate of 3kN/min until failure occurs. The maximum load at

which failure occurred is then recorded.

3.1.3.3 Water Absorption Test

Five ISSB specimens from each mix are fully immersed in a water bath for a period of

24 hours. The water bath is set at a temperature of 15 o C to 30 o C. After 24 hours, ISSB

specimens are removed from the water bath and wiped with a cloth. Within 3 minutes of their

removal from the water bath, each specimen is weighed to the nearest gram using a mass balance

and the mass is recorded as M 1. The saturated ISSB specimens are then dried in a ventilated oven

at 105 o C ± 5o C for 24 hours and until two successive weighings, at interval of 2 hours, show an increment of mass loss that is not greater than 0.2 % of the last recorded weight of the specimen.

Mass of the oven dried specimen is recorded as M 2.

3.1.3.4 Initial Rate of Absorption Test

Five ISSBs from each mix are oven dried for a period of 24 hours at a minimum

o temperature of 250 F. The samples are then weighed, and their mass recorded in grams as w 1. A tray with a cross sectional area of at-least 300 in2 (1935.5 cm 2) is filled with 1/8 in. (3mm) of

water. Starting with the first sample, the brick is placed in the tray for a period of 1 minute. After

1 minute, the brick is removed and gently dabbed on a rag cloth to remove excess water. The brick is weighed again, and its mass recorded as w 2. The same procedure is followed for the

remaining 4 samples.

A simple field test can also be performed to determine if the bricks need to be wetted before placement. A 25 mm (1 in.) circle is drawn on the brick bed using a wax pencil and a 200

UGX coin. An eyedropper is used to place twenty drops of water in the circle. After a period of

90 seconds, if all the water has been absorbed, the bricks is too dry with a high initial rate of absorption and needs to be wetted before placement (Slaton & Patterson, 2017).

3.2 Cost Analysis of Sugarcane Bagasse Ash amended ISSB Construction

To evaluate the cost-effectiveness of using sugarcane bagasse ash as partial cement replacement in ISSBs, the cement cost for constructing a 7-classroom block school building and a 30,000-L rainwater harvesting tank using regular ISSBs and using sugarcane bagasse ash amended ISSBs were compared. The cost estimates used for this analysis are based on Brick by

Brick Construction Company Ltd.’s Standard Bill of Quantities (BOQ) for 2020, shown in

Appendix B. Table 14 summarizes the result of the cost analysis.

As can be seen in Table 14, replacing 20% of the cement content in ISSBs by sugarcane bagasse ash for constructing a 7-classroom block school building results in cost savings of

864,600 UGX ($ 231.6). Even though the amount saved may seem meager in dollar value, the

amount in Ugandan shillings (864,600 UGX) is equivalent to the monthly salary of Brick by

Brick Construction Company Ltd.’s administrative staff and mid-level engineering and

architectural staff. The amount saved in Ugandan shillings for the 7-classroom block school building is also comparable to the monthly wages of five masons. Brick by Brick Construction

Company Ltd. could potentially save 2,000,000 UGX (536 $) per year if 20% of the cement in

ISSBs is replaced by sugarcane bagasse ash. This cost savings value is estimated based on the following:

• Total revenue of Brick by Brick Construction Company Ltd. in 2019.

• Assuming material cost to be 45% of the total project costs.

• Assuming cement cost for producing ISSBs to be 4.5% of the total material costs.

Given Brick by Brick Construction Company Ltd.’s commitment to providing economic

opportunities to local communities, 2,000,000 UGX could provide employment to one mason

for an entire year.

Table 14: Cement Cost Difference Between Using Regular ISSBs and Sugarcane Bagasse Ash (SBA) ISSBs 7-Classroom Block School Building ISSBs used for 7 classroom block school building 16917 ISSBs ISSBs produced per (50-kg) bag of cement 130 ISSBs No. of cement bags required for 16917 ISSBs 131 (50-kg) bags of cement Cement replaced by sugarcane bagasse Ash 20 % Cement required after replacement by SBA 105 (50-kg) bags of cement Cost of 1 (50-kg) bag of cement 33,000 UGX Cost of 131 (50-kg) bags of cement 4323000 UGX Cost of 105 (50-kg) bags of cement 3458400 UGX Cost Savings (UGX) 864600 UGX 231.6298 $ (1 $ = 3732.68 UGX, Cost Savings ($) October 2020) 30,000-L Rainwater Harvesting Tank ISSBs used for 30,0000 L rainwater harvesting tank 1800 ISSBs ISSBs produced per (50-kg) bag of cement 130 ISSBs No. of cement bags required for 1800 ISSBs 14 (50-kg) bags of cement Cement replaced by sugarcane bagasse ash 20 % Cement required after replacement by SBA 11 (50-kg) bags of cement Cost of 1 (50-kg) bag of cement 33,000 UGX Cost of 14 (50-kg) bags of cement 456923.1 UGX Cost of 11 (50-kg) bags of cement 365538 UGX Cost Savings (UGX) 91385 UGX 24.48231 $ (1 $ = 3732.68 UGX, Cost Savings ($) October 2020)

3.3 Proposed Framework for Data Analysis

This section provides a framework for analyzing the results obtained from the mechanical testing of sugarcane bagasse ash amended interlocking stabilized soil blocks.

Table 15: Framework for Analyzing Wet Compressive Strength Test Results

(MPa) 1.5 MPa 

≥

Value Mean Wet Mean Wet Compressive Compressive Check if 95% Sample Name Strength (MPa) Wet CompressiveWet Characteristic Wet Strength, Strength 95% Characteristic Standard Deviation C1 a1

C2 a2 OK/Not Control C3 a3  sa CI 1 a Good C4 a4 C5 a5 SBA10% 1 b1

SBA10% 2 b2 OK/Not SBA10% SBA10% b b s CI 3 3 b 2 Good SBA10% 4 b4 SBA10% 5 b5 SBA20% 1 c1

SBA20% 2 c2 OK/Not SBA20% SBA20% c c s CI 3 3 c 3 Good SBA20% 4 c4 SBA20% c 5 5

Table 16: Framework for Analyzing Modulus of Rupture Test Results

≥ ) ) 2 ) )  (mm) (mm) 0.5 MPa Rupture ( Sample Name Failure, W (N) Check if Mean Supports, l (mm) Distance between Mean Modulus of Depth Block, of D Width Block, of B Maximum Load at (S) = W*l/(2*B*D Modulus Rupture of Modulus Rupture of

C1 a11 a21 a31 a41 a51 OK/Not Control a C2 a12 a22 a32 a42 a52 Good

Table 16. (Continued)

C3 a13 a23 a33 a43 a53

C4 a14 a24 a34 a44 a54

C5 a15 a25 a35 a45 a55

SBA10% 1 b11 b21 b31 b41 b51

SBA10% 2 b12 b22 b32 b42 b52 OK/Not SBA10% SBA10% 3 b13 b23 b33 b43 b53 b Good SBA10% 4 b14 b24 b34 b44 b54

SBA10% 5 b15 b25 b35 b45 b55

SBA20% 1 c11 c21 c31 c41 c51

SBA20% 2 c12 c22 c32 c42 c52 OK/Not SBA20% SBA20% 3 c13 c23 c33 c43 c53 c Good SBA20% 4 c14 c24 c34 c44 c54

SBA20% 5 c15 c25 c35 c45 c55

Table 17: Framework for Analyzing Water Absorption Test Results

= w

1 2 ≤ 15% ) ) * 100 1  )/M 1 (%), ( (%), - M - 2 in M Water, Specimen, M Sample Name Mass Oven of Dry Mass Saturated of (M Absorption % Check if Mean Water Water Absorption,Water A Mean Water Mean Water Absorption Specimen after Immersion

C1 a11 a21 a31

C2 a12 a22 a32 OK/Not Control C3 a13 a23 a33  a Good C4 a14 a24 a34

C5 a15 a25 a35

SBA10% 1 b11 b21 b31

SBA10% 2 b12 b22 b32 OK/Not SBA10% SBA10% 3 b13 b23 b33 b Good SBA10% 4 b14 b24 b34

SBA10% 5 b15 b25 b35

Table 17. (Continued)

SBA20% 1 c11 c21 c31

SBA20% 2 c12 c22 c32 OK/Not SBA20% SBA20% 3 c13 c23 c33 c Good SBA20% 4 c14 c24 c34

SBA20% 5 c15 c25 c35

Table 18: Framework for Analyzing Initial Rate of Absorption Test Results (g) (g) 1

2 ) ) (g) (g) 2 2

1 1 g/min/in ) (g/min/in2)) ≤ - w - 2  = w Sample Name Width Block, of B (in) Length Block, of L (in) (30*W)/L*B (g/min/in Check if IRA Mean IRA, ( Immersion in w Water, Initial Absorption, of Rate IRA = Mass Saturated of Specimen after Change in Weight W Specimen, of Mass Oven of Specimen, Dry w

C1 a11 a21 a31 a41 a51 a61

C2 a12 a22 a32 a42 a52 a62 OK/Not Control C3 a13 a23 a33 a43 a53 a63  a Good C4 a14 a24 a34 a44 a54 a64

C5 a15 a25 a35 a45 a55 a65

SBA10% SBA10% 1 b11 b21 b31 b41 b51 b61

SBA10% 2 b12 b22 b32 b42 b52 b62 OK/Not SBA10% 3 b13 b23 b33 b43 b53 b63  b Good SBA10% 4 b14 b24 b34 b44 b54 b64

SBA10% 5 b15 b25 b35 b45 b55 b65

SBA20% 1 c11 c21 c31 c41 c51 c61

SBA20% 2 c12 c22 c32 c42 c52 c62 OK/Not SBA20% SBA20% 3 c13 c23 c33 c43 c53 c63 c Good SBA20% 4 c14 c24 c34 c44 c54 c64

SBA20% 5 c15 c25 c35 c45 c55 c65

Chapter 4: Conclusions and Recommendations

4.1 Conclusion

There is a growing global need for adequate housing, water provisions and improved sanitation. UN Sustainable Development Goals cannot be achieved until these needs are met.

Given the high environmental impact and high cost of cement-heavy construction, appropriate earth technologies present a viable alternative. Interlocking stabilized soil blocks (ISSBs), a type of compressed earth block (CEB), is one such technology that has gained recognition in East

Africa. ISSBs provide many advantages over traditional construction methods used in Uganda.

ISSBs require less mortar than burned clay bricks, enable faster construction because of their interlocking mechanism, can be made on site saving transportation costs and are compressed instead of burned to gain strength. However, widespread adoption of ISSBs has been slow due to higher unit costs, lack of standardization and technical expertise and social attitude of people towards earth construction.

To further reduce the cost and environmental impact of earth technologies, research investigations have been carried out on using natural pozzolans like sugarcane bagasse ash as partial cement replacement in compressed earth blocks (CEB). However, additional research needs to be conducted on the use of sugarcane bagasse ash as partial cement replacement in

ISSBs. Moreover, a more consistent research protocol needs to be followed while conducting and reporting investigations. Discrepancies in data collected and reported makes the data incomparable with other investigations and ultimately, hinders standardization efforts.

4.2 Recommendations

The following recommendations are proposed for future investigations on sugarcane bagasse ash as partial cement replacement in interlocking soil stabilized blocks (ISSBs):

• The research design flowchart presented in Figure 5 may be utilized as a framework for

future laboratory and/or field-based studies and can help avoid gaps in reported data.

• To promote adoption of interlocking stabilized bricks, further investigation on the impact

of sugarcane bagasse ash on the modulus of rupture and initial rate of absorption of

bricks is needed. Modulus of rupture is an important measure of the lateral resistance of a

masonry unit. The initial rate of absorption is an important quality control measure as

bricks that are too dry may absorb water from the mortar leading to structural

deficiencies.

• The cement content used in the design mix should be based on the soil properties, as

prescribed by Walker (1995). By basing cement content on soil properties, discrepancies

in test results caused by the inherent variability of soils can be reduced.

• Majority of the work has been done to study the impact of sugarcane bagasse ash addition

on the durability of individual blocks. To study the impact of sugarcane bagasse ash

addition on ISSB assemblages, compressive strength testing of ISSB prisms should be

conducted. Lima et al. (2012), for example, tested the compressive strength of

compressed earth block prisms (34 cm x 34 cm x 11 cm).

The following measures are proposed as recommendations for Brick by Brick

Construction Company Ltd:

• Conducting Atterberg Limit tests on the murram in addition to shrinkage test for quality

control. As per Walker (1995), soils with a plasticity index (PI) above 25 are not suitable

for stabilization and should be avoided for use in construction.

• Conducting field tests for initial rate of absorption as described in Chapter 3.

• Replacing up to 20% of the cement content in interlocking soil stabilized blocks (ISSBs)

to reduce the unit cost of bricks and the overall cost of construction.

The following measure is recommended for Uganda National Bureau of Standards

(UNBS):

• Require only wet compressive strength testing for ISSBs. Wet compressive strength is

lower than dry compressive strength and is, hence, the controlling value. Requiring both

strength tests may be redundant.

The following recommendations are proposed for moving forward with research in use of sugarcane bagasse ash (and other natural pozzolans) as partial cement replacement in ISSBS:

• Conduct the experiment proposed in this study in Masaka, Uganda and replicate it in

other parts of the world with significant sugarcane production.

• Conduct a life cycle assessment analysis on the use of sugarcane bagasse ash in ISSBs as

partial replacement for cement.

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Appendix A: Summary of Literature Review Table A1: Summary of Literature Review on Use of Sugarcane Bagasse Ash as Primary and Auxiliary Stabilizer

mm) mix? mix? by/of by/of Region Region Content Content Primary Primary Stabilizer, Stabilizer, x mm x x mm x SBA Content SBAContent Author name name Author Standard used Standardused Optimum SBA Optimum Block Size (mm (mm Size Block Content/Results Content/Results Tests performed performed Tests Sand included in Sand included Yes, Water absorption 30% SBA by 0% 38% Thai and wet cement (control), cemen Cement, of Industrial Khobkang 250 x 120 compressive weight Thailand 15%, t (100- total Standard et al. x 110 strength test at replacement 30% and weight SBA%) mix Institute 14, 28 and 90 for 90-day 40% weig (TIS) days strength ht > 40% SBA 0% Yes, by cement (control), 44% Water absorption Thai Greepala weight does 10%, cemen Cement, of and wet Industrial and 250 x 120 not meet TIS Thailand 20%, t (100- total compressive Standard Parichartpr x 110 requirement 30%, weight SBA%) mix strength test at 7 Institute eecha for Class B 40%, weig and 28 days. (TIS) Masonry 50% ht Units

0% (control), SCBA:OPC 1.6%, Compressive Onchiri et Cement, ratio of 1:1.5 Kenyan Kenya NR 3.2%, NR NR strength at 7 and al. NR (3.2% SBA: Standard 4.8%, 28 days 4.8% Cement) 6.4% and 8% 4% cement + 8% SBA meets Class 30 blocks Bureau of Cement, Wet compressive compressive Indian dry 4% and strength at 28 strength. 190 x 90 x 4%, 6% Standard James et al. India soil 10% by No days, water Slightly 90 and 8% Specifica weight weight of absorption and higher tions dry soil efflorescence contents of (BIS) cement and SBA for optimum combinations Prisms with bricks cut in half Cement, 12% cement Wet compressive with mortar dry 6% and needed to 0, 2, 4 strength test at Brazilian Lima et al. Brazil bond in soil 12% by No meet and 8% 28-days and Standards between. weight weight of Brazilian water absorption Brick dry soil Standards dimensions NR Cement, Compressive 0% cemen 20% SBA by Malaysia Malaysi 100 x 50 x 16.7% of Yes, strength test at 7 Ali et al. (control), t cement n a 40 soil NR and 28 days, 20%, weight weight Standards weight water absorption,

25% and density and 30% initial absorption rate Dry Dry compressive compressive 0% strength test at strength (control), weight Sugarcane 350 x 150 14, 21 and 28 increased with Kenyan Salim et al. Kenya 3%, 5%, of dry bagasse No x 100 days, shrinkage SBA addition Standard 8% and soil ash cracks and and with 10% failure pattern duration of curing Wet Sugarcane compressive bagasse strength and Bureau of Wet compressive 5% - weight ash and density Indian strength at 7 and Saranya et 190 x 90 x 30%, in of rice husk decreased Standard India No 28 days, water al. 90 incremen total ash in with addition Specifica absorption and ts of 5% mix equal of SBA, tions density proportion whereas water (BIS) s absorption increased 5% SBA Bureau of Sugarcane bricks achieve Indian Not bagasse Prashant et 200 x 100 Not Compressive compressive Standard India reporte ash. Other NR al. x 100 reported strength strength close Specifica d stabilizers to 10% lime tions also tested bricks. (BIS) 10% Compressive Lime+SBA Lime + strength for 7-, outperformed Alavez- weight 300 x 150 10% Cement 14- and 28-days, Lime. Sieve Ramirez et Mexico of dry No NR x 120 SBA and Lime flexural strength #200 is the al. soil (CALBA test, XRD and least energy ) SEM analysis, consuming

energy and most consumption, effective CO 2 emissions treatment for and energy in SBA. transportation Regression analysis used to forecast Bureau of Compressive 9.425% Indian total strength at 28- James and 190 x 90 x 4%, 6% SBA+6% Standard India weight Lime, 6% No days, water Pandian 90 and 8% Lime needed Specifica of mix absorption and to meet BIS tions efflorescence. Class 20 (BIS) Bricks requirement. SBA, quarry Density, dust and lime Bureau of 50% to Lime, compressive ratio of Indian total Madurwar 75%, in 20% of strength, water 50:30:20 Standard India weight No et al. incremen mix absorption, achieves Specifica of mix ts of 5% weight. energy per 1000 highest tions bricks equivalent compressive (BIS) strength Lime, 20% of Bureau of 10% SBA 10% to mix Indian weight Compressive replacement Kulkarni et 230 x 100 60%, in weight. Standard India of fly No strength at 7-, achieves al. x 75 incremen 10% Specifica ash 14- and 21- days highest ts of 10% quarry tions strength. dust as (BIS) admixture

4mm dia. cemen And 4 mm 0, 10, 15, Compressive Up to 20% t high 20, 25, (100 - strength and cement Basika et al. Uganda weight Yes NR cylindrical 30 and SBA%) flexural strength replacement replac concrete 40% test by SBA ement specimen Replacement of sand by Bureau of Compressive SBA results in Indian 15, 20, total strength at 7- lighter weight Singh and 225 x 110 Cement, Standard India 25, 30 weight Yes days, water bricks while Kumar x 70 20% Specifica and 35% of mix absorption and satisfying the tions dry weight requirement (BIS) for BIS Standards Not Not Maximum dry Applicable weight 2, 4, 6, 8 4% and appli density, Onyelowe Nigeria for soil of dry NR NR and 10% 6% cabl optimum stabilizatio soil e moisture content n Bureau of Not 0% Cement, 7.5% SBA Not Maximum dry Indian Applicable (control), weight 3% and (by dry appli density, Standard Mir et al. India for soil 7.5%, of dry 6% by dry weight of soil) cabl optimum Specifica stabilizatio 15% and soil weight of and 6% e moisture content tions n 22.5% soil cement (BIS) Decrease in Cement, Not liquid limit 0% 1%, 2%, Not Maximum dry Applicable weight and increase (control), 3% and appli density, Mohammed Nigeria for soil of dry in plastic limit NR 2%, 4%, 4% of dry cabl optimum stabilizatio soil and optimum 6%, 8% soil e moisture content n moisture weight content with

the addition of sugarcane bagasse ash

Particle size analysis, Sugarcane compaction, bagasse ash Not Not unconfined cannot be Applicable weight Sugarcane Osinubi et appli compressive used as the Nigeria for soil 0 - 12% of dry bagasse NR al. cabl strength (UCS), stand alone stabilizatio soil ash e California stabilizer in n bearing ratio laterite soil (CBR) and stabilization durability tests Wet- 150 mm weight 10% to 20% compressive dia., 300 10% to of Cement, fine aggregate strength for 7 Modani and mm high 40%, in sand 18% of can be India Yes and 28 days, 28 NR Vyawahare cylindrical incremen (fine total mix replaced by day split tensile concrete ts of 10% aggreg weight SBA in strength and specimen ate) concrete sorptivity test. SBA can be classified as fine sand Not based on sieve Sales and Not appli Brazilian Brazil analysis. SBA Lima Applicable cabl Standards can replace e fine aggregate, but not cement

Wet- compressive 150 mm strength at 7, 14 Bureau of concrete 0% to weight and 28 days, 28- Indian Cement, 10% SBA by Sumesh and cubes for 20% in of day split tensile Standard India (100- Yes cement Sujatha compressiv incremen cemen strength, flexural Specifica SBA%) weight e strength ts of 5% t strength, bond tions test strength and (BIS) resistance to sulphate attack. Wet- compressive Bureau of 0% to weight strength at 7- and Indian Cement, 10% SBA by Srinivasan 150 mm 25%, in of 28-days, split Standard India (100- Yes cement and Sathiya cubes incremen cemen tensile strength, Specifica SBA%) weight ts of 5% t flexural strength tions and modulus of (BIS) elasticity 20% (10% SBA and SBA+10% Atterberg limits, 0% Cassava Cassava Peel) weight compressive 215 x (control), peel ash in ash content Abner Kenya of dry Yes strength test at 102.5 x 65 5%, 7.5% equal resulted in soil 28-days and and 10% proportion maximum water absorption s compressive strength 7- and 28- days Bureau of compressive 5% to weight Indian Cement, strength, 20% SBA by Ganesan et 100 x 100 30%, in of Standard India (100- Yes splitting tensile cement al. x 100 incremen cemen Specifica SBA%) strength, water weight ts of 5% t tions absorption, (BIS) permeability

characteristics, chloride diffusion and resistance to chloride ion penetration 100 mm 28- 90-day wet Bureau of dia., 200 weight compressive Indian 10%, Cement, 20% SBA by Chusilp et mm high of strength, water Standard Thailand 20% and (100- Yes cement al. cylindrical cemen permeability and Specifica 30% SBA%) weight concrete t heat evolution of tions specimen concrete (BIS) Bureau of 10% SBA by weight Compressive Indian 10%, cement Priyadarshi of strength, water Standard India NR 20% and Cement No weight for ni cemen absorption and Specifica 30% short-term t density tions strength (BIS) Cement, Bureau of by reduced SBA paver Indian Compressive Rajkumar et total by 50% blocks Standard India NA 50% No strength, al. weight compared cheaper by Specifica Atterberg limits of mix to control 24.15%. tions specimen (BIS)

Appendix B: Brick by Brick Construction Company Ltd. 2020 Standard Bill of Quantities (BOQ)

Appendix C: Copyright Permissions

Below is the copyright permission for Figure 1 CIA World Factbook (2018).