CVE3371 Capstone Project : Final Report BEng (Hons) Civil Engineering (Joint - Degree with University of Glasgow) Year 3 Trimester 2 (AY2021/2022) Date of Submission: 20 th July 202 2 T itle: Evaluate Chloride Resistance and compressive strength of Concrete with GGBS Name: Cheah Nian Sheng Student ID: 1901554 Project ID: CVE21010 Contents CHAPTER 1 INTRODUCTION ................................ ................................ ................................ ..................... 4 1.1 Background ................................ ................................ ................................ ................................ ....... 4 1.2 Research p roblem statement ................................ ................................ ................................ ........... 4 1.3 Project objective and Research questions ................................ ................................ ........................ 5 1.4 Project limitations ................................ ................................ ................................ ............................. 5 1.5 Dissertation structure ................................ ................................ ................................ ....................... 5 CH APTER 2 LITERATURE REVIEW ................................ ................................ ................................ ............. 7 2.1 Cementitious material ................................ ................................ ................................ ...................... 7 2.1.1. Ordinary Portland Cement (OPC) ................................ ................................ .............................. 7 2.1.2. Ground Granulated Blast Furnace Slag (GGBS) ................................ ................................ ......... 8 2.1.3. Various types of cement ................................ ................................ ................................ ......... 11 2.2 Hydration Process ................................ ................................ ................................ ........................... 11 2.2.1. Defining Hydration ................................ ................................ ................................ .................. 11 2.2.2. What contributes to the strength? (Chemically) ................................ ................................ .... 12 2.2.3. Rate of heat evolution during hydration of Portland cement ................................ ................ 13 2.2.4. What contributes to the strength? (physically) ................................ ................................ ...... 14 2.2.5. What contributes to the dur ability of the concrete? ................................ .............................. 16 2.3 Relationship between chloride and concrete ................................ ................................ ................. 16 2.3.1. Define concrete durability ................................ ................................ ................................ ...... 16 2.3.2. Define Chloride attack ................................ ................................ ................................ ............ 16 2.3.3. Factors of concrete durability ................................ ................................ ................................ 17 2.3.4. Negative impact of Chloride attack ................................ ................................ ........................ 17 2.3.5. Prevention of Chloride attack ................................ ................................ ................................ 17 2.3.6. Concluding remarks ................................ ................................ ................................ ................ 18 CHAPTER 3 : Research Methodology ................................ ................................ ................................ ..... 18 3.1 Chapter overview ................................ ................................ ................................ ............................ 18 3.2 Research Design ................................ ................................ ................................ .............................. 18 3.3 Quantitative data collection: Experimental research ................................ ................................ ..... 18 3.3.1. Material data of OPC and GGBS ................................ ................................ .............................. 18 3.3.2. Early age strength deve lopment of GGBS concrete ................................ ................................ 19 3.3.3. GGBS Concrete’s chloride resistivity ................................ ................................ ....................... 19 CHAPTER 4 : Testing/Experimental program ................................ ................................ ......................... 19 4.1 Chapter overview ................................ ................................ ................................ ............................ 19 4.2 Concrete material ................................ ................................ ................................ ........................... 19 4.2.1. Source of materials ................................ ................................ ................................ ................. 19 4.2.2. Chemical properties and composition of cement ................................ ................................ ... 19 4.2.3. Aggregates ................................ ................................ ................................ .............................. 20 4.2.4. Sup erplasticizer ................................ ................................ ................................ ....................... 20 4.3 Mix design ................................ ................................ ................................ ................................ ....... 20 4.3.1. Design mix composition ................................ ................................ ................................ .......... 20 4.4 Specimen preparation ................................ ................................ ................................ ..................... 21 4.4.1. Apparatus used for preparing specimens for test ................................ ................................ .. 22 4.5 Experimental testing approach ................................ ................................ ................................ ....... 25 4.5.1. Cement compressive test ................................ ................................ ................................ ........ 25 4.5.2. Cement Flexural tests ................................ ................................ ................................ ............. 26 4.5.3. Concrete compressive test ................................ ................................ ................................ ...... 27 4.5.4. Rapid Chloride Permeability Test (RCPT) ................................ ................................ ................ 29 CHAPTER 5 RESULTS and DISCUSSION ................................ ................................ ................................ ... 33 5.1 Early compressive strength of Cement ................................ ................................ ........................... 33 5.2 Early flexural strength of cement ................................ ................................ ................................ .... 34 5.3 Compressive strength of Concrete ................................ ................................ ................................ 35 5.3.1. Results of Compressive Strength ................................ ................................ ............................ 35 5.3.1.1. 100mm mould compressive strength value ................................ ................................ ... 36 5.3.1.2. 150mm mould compressive strength value ................................ ................................ ... 37 5.3.2. Classification ................................ ................................ ................................ ........................... 38 5.3.3. Discussion of compressive strength ................................ ................................ ........................ 38 5.4 Chloride permeability of concrete ................................ ................................ ................................ .. 45 5.4.1. Results & Analysis of Chloride Resistivity ................................ ................................ ............... 45 5.4.2. Discussion of Chloride Resistivity ................................ ................................ ............................ 47 CHAPTER 6 Conclusion ................................ ................................ ................................ ........................... 48 6.1 Summary of findings ................................ ................................ ................................ ....................... 48 6.2 Recommendation for future studies ................................ ................................ ............................... 48 CHAPTER 1 INTRODUCTION 1.1 Background The worldwide construction industry has been a threat to sustainable development, it has contributed a wide margin of carbon emission ( Globalabc , 2021 ) . The word sustainability has a plethora of meaning across the globe; however, most of the definition are gen erally to the capacity of Earth’s biosphere and human civilization co - existence. Concrete is used in large quantities because simply it is an extraordinary material used for building, comparing with other material such as steel, it is in fact lower in carb on footprint. The huge carbon footprint from concrete comes from the quantities being used, the second to water, with average of three tons being used per person a year ( Gagg C ,2014) Portland cement (CEM I), an ingredient of concrete that can be applie d to all binder material. It boils down to the earliest time, where builders use binder, in conjunctin of rock and stone to form stable structure. Simple ingredient like mud is incorporated as the binder, and up till today, it is still being use in parts o f the world today ( Gagg C ,2014) . Portland Cement, the modern man - made material binder that is commonly used, made from heating up limestone in a high temperature of 1,500 degree Celsius. The intense heating process requires massive amount of fuel, causing the limestone to chemically decompose calcium oxide (used in final cement product) and carbon dioxide (Greenhouse gasses); an ingredient of concrete when mixed with water, consistently found in the construction of everything, from all buildings and bridge s to road and all kinds of modern infrastructure ( Harvey, C ,2018) While cement is widely used across the globe, the industry faces many challenges that threatens sustainability, it generates between five to ten percent of the global greenhouse gasses t hat damages the atmosphere . ( Adobor .C et al. ,2016). By 2050, the expected greenhouse gas produced to be 4807 million metric tons of carbon dioxide, which are 5 times more than the previous year (Eia.gov ,2021) , there seems to be a concerning situation in the future. In the present day, cement and concrete industry are constantly searching for ways to meet the increasing demand of the world while reducing the carbon footprint of the concrete produced. Hence, there is a need to str ategize in reducing greenhouse gases. These are the following techniques that are being used to reduce greenhouse gases, they are Carbon Capture and Storage (CCS) , material substitution, alternative fuels and energy sufficient technologies have been narro wed down as some of the approaches in producing more sustainable cement ( Poudyal, L., & Adhikari, K. , 2021) 1.2 Research problem statement Chloride attack in a concrete mix can be resolved using material substitution, which is a common technique used in the sustainable development era. The Ground Granulated Blast - furnace slag (GGBS), the partial replacement of GGBS could reduce the demand for Ordinary Portland Cement (OPC or CEM I), the carbon footprint of a concrete mix and mitigate chloride attack reaction Chloride attack commonly impose a concern in a concrete mix, this is due to the chemical reaction that occurs between chloride ions and the steel rebars in the concrete mix. The produced product called hydrochloric acid eats away the steel reinforcemen t, causing concrete cracking, spalling and eventually failure ( Stanish et al., n.d. ) . With the effect of GGBS on the concrete mix, GGBS increases the durability of the mix by decreasing the porosity, this result in the active pozzolanic addition that lower s the permeability of the paste impeding the ingress of potentially harmful agents from the environment ( Prince Arulraj, M., & Carmichael, J. , 2019) . Thus, GGBS are regarded as the better choice against Portland Cement (CEM I) with respect to the resistance against acid medium like chloride and sulphate attacks. 1.3 Project objective and Research questions The primary objective of this project is to inve stigate the early strength of concrete mix and the effect of GGBS in concrete, with regards to resistance of Chloride attacks. Below are the follow components to that we will be focusing on for this project. 1. Study of performance of different ratio in concr ete mix with GGBS 2. Conducting tests that investigates the compressive strength and resistivity to chloride attacks. 3. Propose an optimum ratio of GGBS from the test results after analysis. 1.4 Project limitations 1. Limited testing machine to test for the detailed composition 2. Limited sample preparation machine/facility/storage. 3. Availability of school’s equipment machine 1.5 Dissertation structure Chapter One align the reader with the background, research problem and objective. Chapter Two reviews the literatur e content of strength and durability of cement/concrete. Chapter Three shows the research design and methodologies adopted for this dissertation Chapter Four shows the method and testing program of the experiment Chapter Five Discuss and analyze results c ollected from the lab experiments Chapter Six concludes the study and discussion for limitation, summary, and recommendation for future research The flow chart of the report will be reference to Figure 1 Research design for this dissertation CHAPTER 2 LITERATURE REVIEW 2.1 Cementitious material There are various types of cement serving different applications. Through time, the different types of standard and methods are to categories different cement types. Chapter 2 will be discussing the properties of Ordinary Portland Cement (OPC) and Ground granulated Furnace Slag (GGBS). 2.1.1. Ordinary Portland Cement (OPC) The typical oxides compounds found in OPC are the bridge in understanding the complex process of hydration process. Below are the table shown to denote the oxides, and content in percentage. The data will be referenced from Engro Corporation, as I will be using OPC from EnGro Corporation Limited (Engro,2017) Oxide Formula Content % Calcium oxide CaO 63 - 67 Silicon dioxide SiO 2 20 - 24 Aluminum oxide Al 2 O 3 3 - 7 Iron III oxide Fe 2 O 3 2.1 - 4.1 Sulfur trioxide SO 3 1.0 - 3.0 Magnesium oxide MgO 1.0 - 4.0 Potassium oxide K 2 O 0.2 - 1.0 Sodium monoxide Na 2 O 0.1 - 1.0 Manganese trioxide Mn 2 O 3 0.1 - 0.4 Table 1 Typical oxide composition of OPC (Engro,2017) Ordinary Portland cement (OPC) has four main types of minerals that governs hydraulic cement, a cement that sets and hardens with addition of water. Below are the table that shows the ch emical composition of the four main minerals. Cement compound Chemical equation Short form Weight (100%) Properties Tricalcium aluminate Ca 3 Al 2 O 6 C 3 A 10 Contributes to lots of heat during the early stage of hydration , doesn’t contribute much to the cement’s strength. Gyp sum slows down the hydration rate of C 3 A. Low in C 3 A also meant is sulfate resistant Tetracalcium aluminoferrite Ca 4 Al 2 Fe 2 O 10 C 4 AF 8 Fluxing agent which reduces the melting tem perature of the raw materials in the kiln. ( From 3,000 o F to 2,600 o F ) It also hydrates rapidly and does not contribute much strength to the cement paste. Belite or dicalcium silicate Ca 2 SiO 5 C 2 S 20 Hydrates , harden and the reactivity is slow However, it contributes largely on strength gain after a week. Alite or tricalcium silicate Ca 3 SiO 4 C 3 S 55 Hydrates and hardens rapidly, responsible for initial setting and early strength gain. Sodium oxide Na 2 O N Up to 2 It increases the workability,reduce setting time and compressive strength of the cement Potassium oxide K 2 O K Gypsum CaSO 4 .2H 2 O C S H 2 5 Table 2 OPC chemical compound properties (Steve K. & William P.,1988) Ordinary Portland Cement’s can be evaluated by various methods, one of the ways are X - ray Fluorescence (XRF) spectroscopy. The technique enables us to determine the elemental composition of materials (Steve , K. & William ,P. ,1988) . Bogue calculations (Boug e, 1947), are able to aid in converting it to cement chemical composition. Below are the following calculations used commonly in the industry. BOGUE CALCULATION C3S = 4.0710CaO - 7.6024SiO2 - 1.4297Fe2O3 - 6.7187Al2O3 C2S = 8.6024SiO2+1.0785Fe2O3+5.0683Al2O3 - 3 .0710CaO C3A = 2.6504Al2O3 - 1.6920Fe2O3 C4AF = 3.0432Fe2O3 However, it should be stressed that the Bogue calculations is just the estimation of the four main clinkers presented in OPC, the estimation will still be useful and commonly adopted in the cement industry. 2.1.2. Ground Granulated Blast Furnace Slag (GGBS) Ground granulated blast furnace slag (GGBS) is a common cementitious material used in the cement and concrete industry, a material that is known being a sustainable material. The by - product of steel and iron production that is operated in the blast furnace , raw materials like iron ore, coke and limestone were mixed in together in thousand and five hundred degrees Celsius. The molten liquid that was produced after will be quenched with large volume of water to produce granules like coarse sand, the product will then further be dried and ground into fine powder to what is being commonly used for construction materials. As it has cementitious properties that enable the material to be used for construction. (Siddique,2012) Below will be based on reference on Engro’s expected properties based on what EnGro’s VCEM GGBS production promised , with compliance with SS EN 15167:2008 and have certificate of analysis upon request. GGBS Physical and Chemical properties Physical Properties Fineness 430 - 460 Bulk Density 1 - 1.2 mt/m^3 Specific gravity 2.8 - 2.95 Colour Beige to white powder Table 3 Physical properties of GGBS (Engro Global Corporation , n.d. ) Chemical Properties Calcium oxide 30 - 50% Silica 30 - 40% Alumina 7 - 17% Magnesia 2 - 14% CaO+MgO+SiO 2 76.0 – 84.0% (CaO+MgO)/SiO 2 1.25 – 1.40 Table 4 Chemical properties of GGBS (Engro Global Corporation , n.d. ) Figure 2 Ground Granulated Blast - Furnace Slag (GGBS) , (ibmd.tatasteel, n.d.) Ground Proportion Following BS EN 197 - 1:2011, Granulated blast furnace slag proportion consist of a minimum two - third total mass of calcium oxide (CaO), magnesium oxide (MgO) and silicon dioxide (SiO 2 ). The other remaining mass shall contain aluminum oxide (Al 2 O 3 ) together with other compounds. In addition, the ratio by mass within the two - third will follow the formula of (CaO+MgO)/(SiO 2 ) not exceeding 1,0 By GGBS itself, it’s a material that requires combination of an activator to harden efficiently. Usually, its typically being used together with Ordinary Portland Cement (OPC) and with reference to Singapore Standards type CEM I cement, GGBS is used as direct replacement for OPC on a one - to - one ratio. There is various combination ratio of GGBS, the common combination is 50% GGBS with 50% OPC, the properties of the concrete will not only have an increase in strength in the long term as compared to a conventional concrete, but the durabilit y of the concrete are also able to prevent chemical attacks. With reference to Singapore Standards, the percentages used in Singapore are ranged from 20 to 90% GGBS replacement. The higher replacement of GGBS will have a more denoting effect on the concret e’s properties. GGBS effect on the concrete : 1.Strength The Ground granulated blast furnace slag have shown to have greater compressive and flexural strength and comes with greater workability as compared to the conventional concrete. (Limbachiya et al. ,2016) With the replacement of GGBS in the design mix, the properties of GGBS are able to decrease the size of Ca(OH)2 crystals in the aggregate - paste interface, this makes the microstructure within the aggregate transition zone stronger and denser 2.Mixture needed for Hydration product The impermeable coating of amorphous silica and alumina found on GGBS particles can delay the reaction between quenched glass, water, and alkali compounds such as Calcium Hydroxide or Sodium silicate (NaSiO 3 ), which is used as an activator. The hydration products of Ca(OH) 2 that ac tivates the slag hydration only requires low mixture of CaO/SiO 2 (C/S) ratio, CaO - SiO 2 - H 2 0(C - S - H) and AFm (cementitious product from the reaction of reactive alumina and calcium hydroxide, Al 2 O 3 – Fe 2 O 3 – mono ) phases. In addition, the pozzolanic reaction can increase the C/S ratio to about 1.7 in slag - cement blends, because of the unstable low mixture of C - S - H and Ca(OH) 2 3. Permeability and chemical stability The tests that took place containing GGBS have shown that the permeability and penetration of chlori de ions in the specimens have been reduced. (Basheer et al. , 2001) Because of its finer pore structure, the reaction to the excess calcium hydroxide can form a finely dispersed gel, this fills the larger pores. With the reduction of calcium hydroxide which makes it more chemically stable, and the pore structure can limit the ability of chemicals diffusing out of concrete. (CSMA, n.d.) 4.Setting time and consistency The use of slag as supplementary cementitious also increases the initial, final setting time and decreases consistency according to the experiment done by Huisheng and XiaoLu (2010). In the experiment, the author compared using two specimens, one with conventional plain cement concrete, another with GGBS partial replacement with up to 20 - 50%. It is being shown that the consistency decreased from 27% to 26.4% when GGBS is being used. GGBS has proven to delay initial and final setting time from 200 to 260 minutes and their final setting time from 340 minutes to 450 minutes respectively. This is adva ntageous as the warm weather in Singapore will require more time to remain workable, it could also reduce the risk of cold joints which affects the quality of the concrete. 2.1.3. Various types of cement There are several types of cement that serve different appl ications and there are different standards that categorize the cement types based on the industry needs. The variation of concrete usage has urged the industry to develop more specialized and specific cement types for different applications, also known as performance - based cements. With different blends of OPC and other mineral admixtures like slag, fly ash, silica fume and limestone. Shilstone, J.M (2002) mentions how ultimately, we must identify the project performance objective and intended function, so to meet industry needs. (Shilstone, J. M., 2002) Singapore standards for Cement types There are a lot of different standards ranging from America, British, Europe and others. The standard that Singapore take reference from is European standard EN 197 - 1:2014, Part 1: Composition, specification, and conformity criteria for common cement. Below are the types of Portland cement that SS - EN 197 - 1 characterized. Types of Portland Cement (SS EN 197 - 1: 2014) CEM I Ordinary Portland Cement 95 - 100% Portland cement 0 - 5% Minor Additional constituents CEM II Portland - Composite Cement ≥65% Portland cement ≤35 Supplementary Cementitious material CEM III Blast Furnace Cement 5 - 64% Portland cement 36 - 95% Blast furnace slag (GGBS) CEM IV Pozzolanic Cement Portland cement with up to 55% of selected Pozzolanic constituents CEM V Composite Cement Portland cement blended with addition of GGBS or fly ash and pozzolanic material Table 5 Types of Portland Cement ( SS EN 197 - 1:2014 ) Singapore Standards SS EN 197 - 1:2014 has detailed list of Portland cement types, with respective percentage range of constituents of the types of common cement. The dissertation focus will be on CEM III, which is the use of GGBS in cement. 2.2 Hydration Process As the strength of the concrete have correlation with hydration, we will see how the strength are formed from the chemical process of hydration. 2.2.1. Defining Hydration Hydration is a chemical reaction between the main compound found i n cement and water molecules, forming hydration products. Below are the following five main compound compositions listed by weight percentage and chemical formula. Cement compound Weight in % Chemical formula Tricalcium silicate 50 Ca 3 SiO 5 or 3CaO SiO 2 D icalcium silicate 25 Ca 2 SiO 4 or 2CaO SiO 2 Tricalcium aluminate 10 Ca 3 Al 2 O 6 or 3CaO Al 2 O 3 Tetracalcium aluminoferrite 10 Ca 4 Al 2 Fe 2 O 10 or 4CaO Al 2 O 3 Fe 2 O 3 Gypsum 5 CaSO 4 2H 2 O Table 6 Composition of Portland Cement with chemical composition and weight percentages (matse1, n.d.) 2.2.2. What contributes to the strength? (Chemically) After the water is being added to the cement, each of the compound listed in Table 6 contributes to the final hydration concrete product, do note that calcium silicates are the main contribution to strength. Explanation below is with reference to ( Bye & G. C. , 1983 ; Hewlett, P. C., & Young, J. F. , 1987) Tricalcium silicate Tricalcium silicate the main contributor to the early strength, usually we are seeing 7 days for early strength. When it reacts with water, it forms Calcium silicate hydrate, Calcium hydroxide and heat. In short, it releases calcium and hydroxide ions and large amount of heat. Tricalcium silicate + Water --- >Calcium silicate hydrate+ Calcium hydroxide + heat 2 Ca 3 SiO 5 + 7 H 2 O --- > 3 CaO 2SiO 2 4H 2 O + 3 Ca(OH) 2 + 173.6kJ The pH very quickly changed to over 12 as there is a release of alkaline hydroxide (OH - ) ions. This initial hydrolysis will decrease with reduction of heat after. The formation of the calcium hydroxide and calcium silicate hydrate creates “seeds”, which more calcium silicate hydrate (C - S - H) can form. The crystals of calcium silicate hydrate (C - S - H) will grow thicker, making it harder for the water molecules to diffuse through the coating of calcium silicate hydrates (C - S - H). As the coating thickens over time, causing the dimin ishing production of calcium silicate hydrate (C - S - H). ( Mindess, S., and Young, J.F. , 1981) Figure 3 Schematic illustration of the pores in calcium silicate through different stages of hydration (matse 1, n.d.) Dicalcium silicate Dicalcium silicate the vice versa of tricalcium silicate in terms of reaction with water molecules. It reacts with water slower and the heat released are significantly lesser than tricalcium silicate, because of the reactivity of Dicalci um silicate. However, the products of Dicalcium silicate remains the same as Tricalcium silicate. Dicalcium silicate + Water --- >Calcium silicate hydrate + Calcium hydroxide +heat 2 Ca 2 SiO 4 + 5 H 2 O --- > 3 CaO 2SiO 2 4H 2 O + Ca(OH) 2 + 58.6 kJ Tricalcium alumina te and Tetracalcium aluminoferrite Both compounds listed also reacts with water, but it does not contribute significantly to the strength gain, hence, it will be neglected in this review. The compounds are generally complex as they involve Gypsum, which ma kes the hydration chemistry more complicated. ( Mindess, S., and Young, J.F. , 1981) Rates of hydration of the compounds Tricalcium aluminate > Tricalcium silicate > Tetracalcium aluminoferrite > Dicalcium silicate 2.2.3. Rate of heat evolution during hydration of Portland cement Heat is evolved and different throughout cement hydration, the breaking and making of chemical bonds during hydration is what causes the heat. Below Figure 4 shown below is the heat over a function of time. Explanation below is with reference to ( Skalny, J. , 1992 ; Matse,n.d.) Figure 4 Rate of heat evolution during the hydration of Portland cement (Skalny, J. ,1992; Matse,n.d.) The hydration process can be split into 5 stages. How different stages varies between minutes, hours, or days in different heat evolution. Stage I Rapid hydrolys is of the cement compound occurs with an increase of temperature in several degree for around 15 minutes Stage II Also known as Dormancy period, the evolution slows down drastically compared to previous stage and usually last up to 1 - 2 hours. During this p eriod, the concrete is usually in plastic state for it to be transported and placed without any major difficulty. This is crucial to know if one work in the construction industry, as placing the concrete will not impose any major difficulty. Stage III This is where initial and final setting happens at the start and end respectively. The heat will increase in a steadily rate, and the concrete will start to harden. Tricalcium silicate, previously mentioned at 2.2.2 , calcium silicate hydrate (C - S - H) crystallization starts forming as shown in Figure 3 . The process will usually last for around 12 hours. Stage IV Once the peak of hydration has reached, the initial hydrolysis will decrease, reduction of heat after. The calcium silicate hydrate (C - S - H) coating as mentioned from Figure 3 will grow thicker, making it harder for water molecules to diffuse through the thick coating. Hence, the diminishing production of calcium silicate hydrate (C - S - H) ultimately slowing down the hydration reaction. Durin g this period, it usually lasts for around 20 more hours. Stage V Usually reached after approximately 36 hours, depending on the different types of cement. The hydration heat level will be like stage II, whereby the heat remains low. The formation of hydrates product will still occur as long water and un - hydrated silicates are present. 2.2.4. What contributes to the strength? (physically) As water play an important role in the strength of concrete, particularly on the amount being used. The process of hydrat ion requires only a specific amount of water, and when the concrete gets sufficient water to fill the microstructure pore space, the concrete will have sufficient workability and strength will be gained through the process. Explanation below is with refere nce to ( Abercrombie, S. 1977 ; Skalny, J. , 1992) Figure 5 Schematic drawings to demonstrate the relationship between water cement ratio and porosity. (Abercrombie, S. 1997 ; Skalny,J.,1992) Water/cement (w/c) ratio Low water cement ratio will lead to high strength but low workability. Whereas high water cement ra tio will lead to low strength but high workability. Hence, compacted concrete which is closely related to porosity are important. As shown in Figure 6 , the empty spac e, which is the porosity is determined by w/c ratio. (Js Jeff.,2020) Figure 6 a plot of concrete strength over water cement ratio ( Js Jeff,2020) Physical characteristic of aggregates The aggregates shape, texture, and size can i ndirectly affect the strength due to the workability of the concrete. Workability in the concrete will dictates whether the contactor will require to add in more water to make the concrete workable but lower in strength. Time Time is another crucial factor to take note, concrete hardens as time passersby. It takes great amount of time to hydrate the un - hydrated tricalcium silicate hydrate as mentioned from 2.2.2 The dicalcium silicate will take a long time for all the bonds to determine the concrete’s strength. Admixture Admixtures are substance that was added during the mixing process, and it could affect the concrete’s strength depend ing on admixture. Different list of admixture has their different application usage, it will be selected based on the need of the concrete user. Type Function Example Air entraining Improves durability and workability. Reduces bleeding, reduces freezing/thawing problems Special detergents Super - plasticizers Increases strength and reduces water for the need of workable concrete. Special polymers Retarding Delays setting time, more long - term strength, offsets adverse h igh temperature; hot weather. Sugar Accelerating Speeds setting time, more early strength, offsets adverse low temperature; cold weather. Calcium chloride Mineral Admixture Improves workability, plasticity, strength. Fly ash Pigment Adds colour. Metal oxides Table 7 List of admixtures, function, and their examples. (theconstructor.org,n.d.) 2.2.5. What contributes to the durability of the concrete? Durability is a major concern in given application, the service life of the concre te will depend largely on the durability of the concrete. There is different contributor to the durability of concrete, constituent materials, construction practices, physical properties, environment exposure conditions, and loading conditions. (Brant Jr. et al., 2009) As the study focus will be on chloride resistivity and early strength, the research has found the test of Rapid Chloride Penetration Test (RCPT) are able to measure chloride ion in the shortest duration of time. 2.3 Relationship between chlori de and concrete 2.3.1. Define concrete durability Concrete Durability is the ability to resist chemical attacks, weathering action condition, and other form of deterioration. While preserving the desired physical properties of a concrete, and the determination of concrete’s lifespan and its serviceability when exposed to such environment. ( American Concrete Institute , 2021) Its dependent on the degree of exposure, the concrete grade or strength, and the cement content. As the concrete to protect the reinforcement bars from harmful ions, that may subject the bars to corrosion. ( C.R. Bayliss, B.J. Hardy , 2012) 2.3.2. Define Chloride attack The ion of Chloride (CL - ) is formed when the element undergoes a process in gaining an electron , or when the compound such as hydrogen chloride reacts with the dissolved water Concrete with high concentration of chloride ions can be detrimental , as due to the chemical nature of chloride ions, the ions will break down the passive layer of reinforcing steel , not dropping the pH level. Corrosion occurs when chloride ions react with the steel and the surrounding passive material , the reaction forms hydrochloric acid. The harmful acid eats away the steel reinforcement causing the concrete to crack , spall ing and failure. The two main s ource of chloride ions are the concrete mix components and surrounding environment . Concrete mix of unwashed aggregate s, sand, admixtures and even the use of seawater in the concrete processing Lastly, the exposure to marine environment such as sea salt spray, direct seawater wetting, and contact with soil with rich chloride deposits. All the mentions above are the proce ss of diffusion that chloride penetrates the concrete. ( SHI, X. ,et al. , 2011) 2.3.3. Factors of concrete durability Durability is a major concern in given application, the service life of the concrete will depend on the durability of the concrete. There is diffe rent contributor to the durability of concrete, constituent materials, construction practices, physical properties, environment exposure conditions, and loading conditions. (Brant Jr. et al., 2009) 2.3.4. Negative impact of Chloride attack The corrosion of steel causes the spalling of the concrete cover. The corrosion causes the oxide of the reaction to be very porous and expand up to 10 times the volume of the steel , this break and cracks the concrete. Resulting the acceleration of corrosion process when the corr osion agents have better access to the steel reinforcement bars. One key indication of chloride attacks is when there are rust stains observed around the cracks and spalls. It will also latter be shown that the steel forms black colored rusting, where the hydrochloric acid reacts with the metal reinforcement bars. The two main types of corrosion are vertical and horizontal cracks. Vertical crack occurs when the tensile stre ngth of the steel is exceeded . While the horizontal crack occurs when the oxide formation and the loss of concrete cover causes the material interface. (Robuschi et al.,2021) 2.3.5. Prevention of Chloride attack There are different methods in prevention against chloride attacks . Below are the different strategies for newer structures and existing structures to minimize or prevent the effects of chloride attacks from occurring. For newer structures • Increase concrete cover (min 50mm) • Use epoxy coat rebars • Use stain less steel rebars • Cathodic protection • Use low water/cement ratio • Apply of anti - carbonation concrete coating For existing structure • Apply of anti - carbonation concrete coating to slow down the corrosion process • Use of corrosion inhibitors • Install a cathodic protection system • In the case of extensive spalling or section loss, a comprehensive concrete repair or a section replacement wi ll be required 2.3.6. Concluding remarks Topcu, I., & Bilir, T. (2010) mentioned that the inclusion of GGBS to the concrete can have drastic improvement in durability and strength, as it refines and disconnects pore in concrete and reduces the thickness of the interfacial transition zone between matrix and aggregate. The dif fusivity of concrete can be reduced with the use of slag, depending on unitary content. Although the early age strength and long - term strength is inverted to conventional concrete, it is still advisable to use GGBS if the application requires chloride atta ck to be tackled. CHAPTER 3 : Research Methodology 3.1 Chapter overview This chapter will discuss about the details and approach to the research methodologies adopted to achieve what Chapter 1 established. The research methods will be used, including literature review, laboratory experimentation of early strength and chloride resistivity. 3.2 Research Design The research design for this dissertation will be discuss below. Several lite rature reviews have been completed to understand the material composition and complex chemical process, how could be a better alternative to a conventional cement concrete. The literature review was also conducted to identify how strength is gained chemica lly and physically and concluded that GGBS does meet the research objective. Further research has also been completed in understanding the harmful occurrence in concrete’s lifespan, such as chloride attacks. Following the literature review, quantitative re search through experimental research will be adopted to meet the research objective. All the findings and experiments will be conducted with reference to Singapore Standards and relevant source described in Chapter 4 : Preliminary results. 3.3 Quantitative data collection: Experimental research In this dissertation, lab experimentation was developed to collect relevant quantifiable data on the effect of GGBS in early str ength concrete and chloride resistivity. The lab experimentation is conducted at EnGro Corporation Limited’s Research and Develop, and Quality Check laboratory. The following experiments samples will have only one independent variable, the percentage of GG BS in the cement or concrete. 3.3.1. Material data of OPC and GGBS Under SS EN 197 - 1 table 6: properties, test methods and minimum testing frequencies for t h e auto control testing by the manufacturer, and the statistical assessment procedure , it’s a common practice in the manufacturer company to