Mechanical and Durability Properties of Geopolymer Concrete A Thesis Submitted in Partial Fulfillment of the Requirements of the Degree of Master of Science in Structural Engineering By Eng

Mechanical and Durability Properties of Geopolymer Concrete

A Thesis
Submitted in Partial Fulfillment of the Requirements of the Degree of Master of Science in Structural Engineering

By
Eng. Mohammed Hosni Abdel Hammed Sharabash
Civil Engineer, B.Sc. Faculty of Engineering, Ain Shams University

Abstract

Concrete is one of the most commonly used construction materials. It is produced by using Ordinary Portland Cement (OPC) as the binder; a highly energy consuming product which releases carbon dioxide (CO2) that contributes about 7 % of the world’s carbon dioxide emissions. Thus new binders with low CO2 emissions are needed for concrete to meet the environmental demands. Among these new binders the geopolymers are highly potential solutions.
Geopolymers as binding materials consist mainly of a source material and an alkaline activator. The source materials for geopolymers based on alumina-silicates should be rich in silicon (Si) and aluminum (Al). These could be natural minerals such as kaolinite or clays or byproduct materials such as fly ash, silica fume or slag. The choice of the source materials depends on factors such as availability, cost and type of application. The alkaline liquids are from soluble alkali metals that are usually sodium or potassium based. The most common alkaline liquids used in geopolymers are combinations of sodium hydroxide or potassium hydroxide and sodium silicate or potassium silicate. Using geopolymers in concrete as binding materials, and studying the strength and durability properties of the geopolymer concrete is the aim of this research. To achieve this goal a review of previous studies and an experimental investigation were carried out and were illustrated in details throughout the different chapters of this thesis.
The literature review included the previous investigations and researches on the subjects concerning the environmental benefits of using geopolymers and geopolymer concrete, the geopolymer concrete constituents, the manufacture, the properties of geopolymer concrete.
The experimental study included 24 geopolymer concrete mixtures produced using locally available kaolinite minerals and imported fly ash as source materials, the alkaline liquid being a mixture of sodium hydroxide and sodium silicate. The main variables in the metakaolin based geopolymer concrete mixture were the content of the metakaolin in the mixture, the ratio of the silicate in the alkaline liquid to the source material and the curing temperature. As for the fly ash based geopolymer concrete mixture the main variables were the content of the fly ash in the mixture, the ratio of the alkaline liquid to the fly ash content and the molarity of the sodium hydroxide solution. The slump, density and compressive strength of the mixtures were recorded for all mixture. For the optimum fly ash mixture other mechanical tests were performed including density, compressive strength, indirect tension and modulus of elasticity. The resistance of the fly ash based geopolymer concrete to corrosion of steel reinforcement was also studied.
The investigation concluded that for metakaolin-based geopolymer concrete the influencing factor on the compressive strength was the sodium silicate/metakaolin ratio where the increase in sodium silicate/metakaolin increased the compressive strength, also the increase in content of metakaolin, increased in compressive strength. Curing was an important factor in increase compressive strength where oven curing gave highest compressive strength than ambient curing. It was also concluded that for fly ash based geopolymer concrete the influencing factor on the strength was the alkaline liquid to fly ash ratio and the fly ash content where both increased the strength. The increase in morality of NaOH solution, increased the strength, also fly ash based geopolymer concrete showed a high resistance to corrosion of steel reinforcement.

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Chapter (1)
Introduction

1.1 General
Due to the increasing demand on concrete, the cement production is expected to increase enormously in the near future 1.
Cement production has a negative effect on the environment. It consumes large amounts of energy in the manufacturing process, uses large amounts of natural resources in the form of virgin aggregates and emits carbon dioxide into the atmosphere. Global warming, which is a serious environmental problem, is caused by greenhouse gas emissions. Carbon dioxide is one of the major contributors of the greenhouse gases. Every ton of cement approximately emits one ton of CO2 into the atmosphere; thus the cement industry is accountable for about 6% of the overall CO2 emissions 2, 3.
On account of the abovementioned environmental drawbacks of cement, many researchers are now seeking the development of alternative binders in order to reduce the use of Portland cement in concrete. Alternative binders include blended cements in which materials such as fly ash, silica fume, granulated blast furnace slag, rice-husk ash and metakaolin are used as partial replacement of the clinker in the cement production. Alternative binders also include alkali activated cements and geopolymers.
Geopolymer technology offers an opportunity to obtain an environmentally friendly binder for the concrete. The use of geopolymers as binders may reduce the carbon dioxide emissions caused by the cement industry by about 80% 4 5.
1.2 Scope
This thesis presents a research work concerning the investigation of the mechanical and durability properties of geopolymer concrete. The scope of this research includes:
1. The manufacturing procedure of metakaolin–based geopolymer concrete (MKGC) and fly ash–based geopolymer concrete (FAGC)
2. The parameters influencing the workability and compressive strength of MKGC and FAGC.
3. The mechanical and durability properties of FAGC.

1.3 Objectives
The objectives of this research are therefore studying the effect of the following parameters on the mechanical and durability properties of MKGC and FAGC.
1- Studying the manufacturing procedure of MKGC and FAGC.
2- Investigating the effect of the metakaolin content in the concrete mixture, the ratio of the silicate in the alkaline liquid to the source material on workability and compressive strength of MKGC.
3- Investigating the effect of FA content in the concrete mixture, the ratio of the alkaline liquid to the FA content and the molarity of the sodium hydroxide on the workability and compressive strength of FAGC.
4- Studying other mechanical properties including density, compressive strength, indirect tension, modulus of elasticity for the optimum FAGC mixture. Also, studying the corrosion resistance for the optimum FAGC mixture as a measure for durability.

1.4 Contents
The thesis consists of five chapters the contents of which are as follows:
Chapter One: Introduction, indicating the significance of the research and its main goals.
Chapter Two: Literature review, including a summary of the previous researches on the subject of geopolymer concrete.
Chapter Three: Experimental work, explaining in details the experimental program, the materials used geopolymer concrete mixture proportions, manufacture and curing of the test specimens, test parameters, test procedures and equipment used for conducting the tests.
Chapter Four: Analysis of experimental work, including the analysis and discussion of the test results.
Chapter Five: Conclusions and recommendations, giving a brief summary, conclusions based on the results of the experimental work done in this research, and recommendations for future studies in the same field.

Chapter (2)
Literature Review

This chapter provides a survey on the various topics included in this research, such as the relation between the concrete and the environment which emphasizes the need for developing alternative binders to cement. The materials involved in producing such alternative binders are thoroughly reviewed together with previous literature on geopolymers and geopolymer concrete.
2.1 Concrete and the environment
Portland cement concrete is one of the most famous of construction materials in the world. Portland cement is not considered an environmentally friendly binding material, 6.
Global warming is a result of the green-house gas emissions; mainly carbon dioxide emissions. Such a phenomenon causes serious environmental problems. The Portland cement industry contributes to the carbon dioxide emissions by about 1.5 million tons per year or about 8% of the total generated greenhouse gas emissions to the atmosphere of the Earth 7. Cement is also among the construction materials that consumes large amounts of the energy, during its manufacture, after the aluminium and steel. Cement also consumes large amounts of aggregates and materials which are natural resources that need preserving for future generations.

Moreover, the durability properties of OPC are still being investigated. Many concrete structures, built in severe exposure conditions begin to deteriorate after 20 to 35 years, although the service life had been designed for more than 60 years 8.

Figure (2-1) Cement production emissions 8
For the production of environmentally friendly concrete, it has thus been suggested to use less natural resources, minimize the energy and reduce the carbon dioxide emissions 9.
It has also been suggested that the amount of carbon dioxide (CO2) emissions from the cement industry can be reduced by decreasing the production of the amount of calcined material, as well as by reducing the amount of cement in concrete, and reducing the constructions using cement 10.
To reduce the amounts of used cements, other waste materials may be used after activation such as FA resulting from the burning of the coal in the electrical and nuclear power plants to act as new binding materials.

Figure (2-2).Huge volumes of FA from power plants 8
2.2 History of geopolymer technology
In 1978, Davidovits invented the term geopolymer to represent abroad range of materials characterized by chains or networks of inorganic molecules 11.
Another scientist, Demortier, subjected the pyramid blocks to X-ray and nuclear magnetic resonance (NMR) analyses and concluded that pyramids may have been made from ‘concreting’ operations 12.
The concept of alumino-silicate activation started in the 1930s. Alkali oxides were used to react with slags to produce new binding material 13.
Sodium chloride and sodium hydroxide were used in 1950s to activate slag to produce binder for use in Military applications by the US army 14
In 1965 it was observed that during alkali activation of slag alumino-silicate hydrates are formed as solid binder products and these are also noticed during alkali treatment of rock and clay minerals. The binders were named ‘soil cements’ and concrete as ‘soil silicate concretes’ 15.
A patent on ‘siliface process’ was filed in 1974 which involved use of NaOH, quartz, kaolinite, and water.
2.3 Terminology and chemistry
As previously mentioned, Davidovits in 1978 16 was the first to use the term ‘geopolymer’; Sialate is an abbreviation for silicon-oxo-aluminates”.
2.4 Constituting materials of geopolymer
The geopolymer binders mainly consist of a source material and an alkaline solution to activate it. This will be discussed in the following sections.
2.4.1Source materials
Geopolymers based on alumino-silicates should be rich in silicon (Si) and aluminium (Al). The source materials are natural minerals such as metakaolinites and clays. Since 1972, scientists 17 tried to produce geopolymers with kaolinite as a source material and with alkalis such as sodium hydroxide and potassium hydroxide as activating solutions.
Many patents disclosed the technology for making geopolymer concrete under the name”SILIFACE-Process”. Another pure kaolinite was introduced, calcined for 6 hours at 750oC, performed better in making geopolymers called KANDOXI (kaolinite, nacrite, dickiteoxides)18
The study included more than 10 natural minerals, as well as garnet, mica, clay, feldspar, zeolite and zeolite mineral groups. It has been shown that a wide range of natural alumino silicate minerals provide potential sources to form geopolymers 19.
Between the natural waste or by-product materials, FA and slag are more potential sources of polymers. It has been reported that many studies related the use of these source materials to the manufacture of geopolymer binders.
2.4.1.1Fly ash
Aside from the chemical composition, the loss on ignition (LOI), fineness and uniformity are the other important characteristics of fly ash. As an example, the production of Fain Australia in 2000 was approximately12milliontons; only 5.5 million tons have been utilized 20.
From the environmental point of view using FA in concrete has many advantages.It uses less cement, thus reduces the amount of energy,uses less natural resources and also reduces the carbon dioxide emissions from the cement production. It also solves the problem of landfills by using most of the produced ash 21.
It was reported that the main factors affecting the properties of geopolymers are the calcium content, particlesize, origin of fly ash,alkali-metal content and amorphous content22 .The strength development is greatly affected by the calcium content in FA and also the final compressive strength ; faster strength development and higher compressive strength are achieved by the presence of a high calcium content. The polymerization setting rate is also affected by the amount of calcium in fly ash; also the amount of calciumin FA alters the micro structure.

2.4.1.2 Metakaolin
The pozzolanic properties of metakaolin make it suitable to be added to lime mortar mixes, thus improving the characteristics for use in conservation mortars. For this particular application cement mortars are inadequate, due to their excessive brittleness, low plasticity, high elastic modulus and high content of soluble salts23.Kaolinitic clays are available all over the world; thusa growing scientific interest is developing to use metakaolin in mortars and concretes, in order to improve mechanical strength or reduce alkali-silica reaction 24.
2.4.1.3 Other
Other materials same as FA and metakaolin can be used as source materials for the production of geopolymers such as silica fume and rice husk ash.
2.4.2 Activating solutions
Activating solutions play an important role in the geopolymerization process. They are mainly alkaline solutions, the most common of which is a combination of sodium hydroxide (NaOH) or potassium hydroxide (KOH) and sodium silicate (Na2SiO3)or potassium silicate (K2SiO3).Increase in molarity of NaOH as an alkaline activator appears to provide better compressive strength when compared with lesser molarity25.
2.4.2.1Sodium hydroxide solution
A combination of sodium hydroxide (KOH) and sodium silicate (Na2SiO3) is considered the most common alkaline activator used in geopolymerization. The dissolution of the source material is affected by the type and concentration of alkaline solution.
In the case of FA as a source material, sodium hydroxide solution causes the leaching of Al3+andSi4+ions more effectively compared to potassium hydroxide solution. Therefore, alkali concentration affects the leaching of alumina and silica from FA particles, also affects the geopolymerization process and the resulting mechanical properties of the hardened geopolymer.The presence of NaOH in the activating solution causes the reaction to proceed more rapidly and the gel becomes less mooth 26.
2.4.2.2Preparation of alkaline solutions
The most effective factor regarding the compressive strength of geopolymers is the morality of the sodium hydroxide. The most commonly used molarities are (8M, 12M, 16M).
2.5The polymerization and microstructure
The exact mechanism of setting and hardening of the geopolymer material is not clear until this moment.Geopolymer can take one of the three basic forms as shown in Figures (2-3) and (2-4).

Figure (2-3). The three basic forms of geopolymers 27

Figure (2-4) Polymeric structures from polymerization of monomers 28

2.6 Properties of geopolymer cements
It was reported based on laboratory tests that geopolymer cement hardens rapidly at room temperature. The compressive strength was found to be around 20 MPa after only 4 hours at 20oC and around 70-100 MPa after 28 daysD129.
Tests were made to demonstrate the behaviour of geopolymers regarding heat and fire resistance. It was found that the performance of geopolymeric cement was better than that of Portland cement. As for the shrinkage behaviour, it has also been shown that geopolymers had extremely low shrinkage compared to Portland cement 30.
It is generally known that ordinary Portland cement incorporating amounts of alkalis may cause the harmful alkali aggregate reaction phenomenon. However the geopolymeric system does not have the same effect even with higher alkali content.
As for acid resistance, geopolymers perform very well in acidic solutions, because unlike the Portland cement, geopolymer cements do not rely on lime and are not dissolved by acidic solutions. Researchers concluded that geopolymer concrete is better than ordinary Portland cement concrete. Observing the weight loss after acid exposure, it was found that as the weight loss is much lower for geopolymer concrete specimens 31.
2.7. Fields of applications
The applications of geopolymers in civil engineering are numerous. Geopolymers are used in the precast concrete domain. Geopolymers are used to develop sewer pipeline products and railway sleepers 32.Geopolymers are also used in industrial applications such as in the automobile and aerospace, nonferrous foundries and metallurgy 19.
An overview and related test results of the potential of the use of geopolymer technology in toxic waste management was reported by many researchers 33.
Table 2.1 Influence of Si:Al ratio on geopolymer applications 34
Si:Al ratio
Applications
1
– Bricks
– Ceramics
– Fire protection

2
– Low CO2 cements and concretes
– Radioactive and toxic waste encapsulation

3
– Fire protection fibre glass composite
– Foundry equipments
– Heat resistant composites, 200oC to 1000oC
– Tooling for aeronautics titanium process

>3
– Sealants for industry, 200oC to 600oC
– Tooling for aeronautics SPF aluminium
20 – 35
– Fire resistant and heat resistant fibre composites

2.8 Geopolymer concrete
2.8.1 Constituting materials
Geopolymer concrete consists of aggregate and a geopolymeric binder. As previously discussed the geopolymeric binder consists of a source material and an alkaline liquid for its activation. The most popular source materials for geopolymers should be rich in silicon (Si) and aluminium (Al). These could be natural minerals such as metakaolinite and clay, or waste materials such as slag, fly ash or silica fume.

Figure (2-5) Constituents of geopolymer concrete 35
2.8.2 Water content of geopolymer mixtures
Based on tests performed on geopolymer pastes using calcined kaolin as the source material , it was found that the optimum composition occurred when the ratio of Na2O/SiO2 was 0.25 and the ratio of H2O/Na2O was 10.024.The mixture proportions for tests were derived from many trial mixes. The test variables were H2O:Na2O molar ratio and the Na2O:SiO2 molar ratio.
2.8.3Properties of geopolymer concrete
The properties of geopolymer concrete are herein discussed based on researches made recently worldwide.
2.8.3.1 Fresh concrete properties
Water, when present in the mixture, is used in geopolymer concrete to improve the workability; never the less, itin creases the porosity in concrete due to the evaporation of water during the curing process at the elevated temperature.
It was reported that an increase in sodium hydroxide and sodium silicate concentration reduces the flow of mortar 23. To improve the workability of mortar, super plasticiser or extra water can be added. However, the use of super plasticiser has an adverse effect on the strength of geopolymer. As such, extra water gives greater strength than the addition of super plasticiser. Workability of geopolymer concrete decreases as the metakaolin content in creases,butin crease in fly ash content does not affect the workability19.

Figure 2-6 Water in geopolymers to improve workability 25

It was also reported that as the morality of the NaOH solution increases, the workability of concrete decreases 23.
2.8.3.2 Hardened concrete properties
The development and properties of low-calcium fly-ash based geopolymer concrete were studied 19. The research report described the development, the mixture proportions and the short-term properties of low calcium FA based geopolymer concrete. It was concluded that low-calcium FA-based geopolymer concrete had excellent compressive strength, suffer very little drying shrinkage and low creep.

Figure (2-7) Drying shrinkage and low creep of geopolymer concrete 36

2.8.4 Durability of geopolymer concrete
2.8.4.1Sulphate attack
The properties of low calcium fly ash-based geopolymer concrete were studied 37.It was concluded that low-calcium FAGC had excellent resistance to sulphate attack, and good acid resistance.

Figure (2-8) Resistance to sulphate attack of geopolymer concrete 38

2.8.4.2Corrosion of embedded steel
The corrosion potential and polarisation resistances for steel electrodes embedded in a Portland cement mortar and two FA mortars, one activated with NaOH and the other activated with a combination of sodium silicate and NaOH solution, was studied. FAmortarshelpedpassivatethesteelreinforcementasquicklyandeffectivelyasPortlandcementmortars.Thepolarizationcurvesandtheresponsetoshort-term anodic current pulses confirmed the full passivation of the steel 22.
Results of the corrosion of a steel bar located inside in FAGC (GPC) in an accelerated corrosion test were reported compared to those of ordinary Portland cement concrete (OPC). All the GPC mixes had higher compressive strengths than conventional concrete (10 to 16 MPa). The test results included the half-cell potential and cross sectional loss of steel bar and in both the respects GPCs performed better. It was concluded that at 72 hrs, the GPC specimens gave the half-cell potential value of -175mV which is comparable to that of OPC value (-200 mV)22.

Figure (2-9) Corrosion of geopolymer concrete 39

2.8.4.3Acid attack
The corrosion of geopolymer concrete exposed to sulphuric acid was studied. It was concluded that GPC is highly resistant to sulphuric acid;

Figure (2-10) Acid resistance test of geopolymer concrete 10
2.8.4.4Fire resistance
Experiments carried out on geopolymers using fly ash found them to be fire resistant with compressive strengths of 5 to 51 MPa. The factors affecting the compressive strength were the mixing process and the chemical composition of the fly ash. The microstructure thus increased the compressive strength. Besides, the water-to-fly ash ratio also influenced the strength. It was found that as the water-to-fly ash ratio decreased, the compressive strength of the binder increased 40.

Figure (2-11) Fire resistance of geopolymer concrete 41

The fire resistance of geopolymers used in carbon fiber composites was also discussed. The fire response of a potassium alumina silicate matrix was monitored at irradiance levels of 50 kW/m2 similar to the heat flux in awell-developed fire. Glass or carbon-reinforced polyester, epoxy, ignited readily and released appreciable heat and smoke, while carbon-fibre reinforced geopolymer composites did not ignite, burn, or release any smoke even after extended heat flux exposure42.

Chapter (3)
Experimental Work

3.1 Introduction
1. The review of literature presented in chapter (2) has demonstrated the need for further research to investigate the mechanical and durability properties of geopolymer concrete. There are many factors that affect the mechanical properties of geopolymer concrete. In this study the following factors are taken into consideration in the experimental study: 1) type and content of the source material, 2) mixture proportioning,3) alkaline liquid, 4) curing method. This chapter includes the objectives of the research together with the details of experimental program. The details of the tests are also included in this chapter.
3.2 Objectives
2. The main objective of the current research is to study the properties of geopolymer concrete. The specific objectives of the research plan are:
1. Studying the manufacturing procedure of the MKGC and FAGC.
2. Studying the effect of the content of the metakaolin in the mixture, the ratio of the silicate in the alkaline liquid to the source material and the curing temperature on the workability and compressive strength of the metakaolin-based geopolymer concrete.
3. Studying the effect of the fly ash content in the mixture, the ratio of the alkaline liquid to the FA and the molarity of the sodium hydroxide on the workability and mechanical properties of the FAGC.
4. Studying the different properties of geopolymer concrete including density, compressive strength, indirect tension, flexural strength, modulus of elasticity and the corrosion resistance for the optimum FAGC mixture.
3.3 Experimental Program
The experimental work is the study investigates both MKGC and FAGC. An experimental plan was designed to include twenty four concrete mixtures. Twelve mixtures used metakaolin as a source material and the other twelve mixtures used FA as a source material.
3.3.1 Metakaolin-based geopolymer concrete mixtures
Twelve mixtures were designed using the absolute volume. The variables for the mixtures were the metakaolin content, the ratio of silicate in alkaline liquid to metakaolin content and the curing temperature. The details of the mixtures are as shown in Figure (3-1) and Table (3-1).
The tests performed on the metakaolin- based geopolymer concrete mixtures are the slump test, unit weigh test and the compressive strength test at age of 7 and 28 days.
.
3.
Figure (3-1) Experimental program of MKGC mixtures

Table (3-1) Proportions of metakaolin–based geopolymer concrete mixtures
Mix. No.
Metakaolin
Fine aggregate
Coarse aggregate
Total
water
Silicate Solution/ Metakaolin
Curing Temp.
oC
M1
1
2.07
4.13
0.5
0.04
Ambient
25
M2

0.05

M3

0.06

M4
1
2.07
4.13

0.5
0.04
60
M5

0.05

M6

0.06

M7
1
1.40
2.8
0.5
0.04
60
M8

0.05

M9

0.06

M10
1
1.20
2.2
0.5
0.04
60
M11

0.05

M12

0.06

3.3.2 Fly ash-based concrete mixtures
Twelve mixtures were designed by the absolute volumes with varying FA content, varying morality of the sodium hydroxide solution, varying ratio of silicate in alkaline liquid to FA content and varying curing temperature. The details of the mixtures are as shown in Figure (3-2) and Table (3-2).
The tests performed on the FA based geopolymer concrete mixtures are the slump test, unit weigh test and the compressive strength test at age of 7 and 28 days.
In the FA based geopolymer concrete and after choosing the optimum mixture more tests were performed such as indirect tension test, flexural strength tests, and the determination of the modulus of elasticity.

4.
5. Figure (3-2) Experimental program of FAGC mixtures
6.
7.
8.
Table (3-2) Proportions of fly ash–based geopolymer concrete mixtures
Mix.
No.
Fly ash
Fine aggregate
Coarse aggregate
Alkaline Liquid/Fly ash ratio
Molarities of NaOH
M13
1
1.67
3.33
0.3
8
M14

12
M15

16
M16
1
1.67
3.33
0.3
8
M17

12
M18

16
M19
1
1.29
2.58
0.4
8
M20

12
M21

16
M22
1
1.29
2.58
0.5
8
M23

12
M24

16

3. 4 Testing
The tests performed on the majority of the metakaolin based-geopolymer concrete mixtures and the FAGC mixtures are the slump test, unit weigh test and the compressive strength test.
In the FA based geopolymer concrete and after choosing the optimum mixture, from the point of view of compressive strength, more tests were performed such as in direct tension test, flexural strength test, and the determination of the modulus of elasticity of the concrete. Also the corrosion resistance test was performed as a measure of the durability.
3.4.1Slump test of fresh concrete
The slump test method was developed to provide a technique to observe the consistency of fresh concrete.Means of the conventional slump was used to measure the workability of the fresh concrete (Figure 3-3) according to the ASTM C 249. The slump was recorded in cm and to the nearest 0.5cm

Figure (3-3) Slump test for geopolymer concrete

3.4.2 Hardened concrete tests
3.4.2.1 Compressive strength test
The compressive strength test was performed in accordance with ACI C31 41 on three cubes (10x10x10cm) and tested after 7 and 28 days using a 200 t capacity testing machine. The test is as shown in Figure (3-4)

Figure (3-4). The compressive strength test

3.4.2.2. Indirect tension test
Tensile strength of geopolymer concrete was calculated using the indirect tensile strength test. Three test specimens were made and tested for each mixture after 28 days. A steel cylinder mould of interior dimensions 10×20 cm was used. The splitting strength of the geopolymer concrete may be calculated according to the following equation and as shown in Figure (3-5)
Ft= (2*P)/ (? *D*H) kg/cm2 …………………………… eq. (3-1)
Where,
P= maximum load carried by the specimen (kg)
D= mean diameter of the specimen (cm)
H= mean length of the specimen (cm)

Figure (3-5) Tensile strength of geopolymer concrete 43
D2
3.4.2.3 Modulus of elasticity and stress-strain relationship in compression
Five 100x 200 mm concrete cylinders were cast for each mixture. The elastic modulus and Poisson’s ratio was determined for three of the cylinders. The average compressive strength was determined for other two cylinders. All the specimens were prepared in accordance with the ASAS 101243. A 2500KNcapacity universal test machine was used in these tests.
The axial deformations of the concrete cylinders were measured using the displacement-control mode available in the test machine.
3.4.3 Durability tests
3.4.3.1Accelerated reinforcement corrosion test
A laboratory accelerated electrochemical process was used for corrosion monitoring. The test beams had dimensions of 150X150X500 mm, in which one deformed steel bar of 16 mm diameter and 500 mm length was embedded for each beam. The steel bars were placed into beams keeping only 400 cm of its length embedded in the concrete beams. The test specimens were immersed in saline solution to simulate chemical attack in order to accelerate the corrosion process. A constant DC potential was used to simulate the different degrees of corrosion of the steel bars, which were embedded in the geopolymer concrete beams. The schematic diagram of the experimental setup of the accelerated corrosion system used is shown in Figure (3-6), while the test as performed in the laboratory is shown in Figure (3-7).

Figure (3-6) Schematic diagram of accelerated corrosion test setup

Figure (3-7) Accelerated corrosion monitoring
3.5Properties of used materials
9. The properties of the materials used to produce geopolymer concrete are hereafter indicated.
3.5.1 Source materials
As previously indicated the source materials used in this study are locally extracted metakaolin subjected to processing techniques and imported class F fly ash.

3.5.1.1 Metakaolin
The metakaolin was obtained from the calcinations of kaolinitic clays at temperatures in the range of 700-800 ?C. The high temperature enabled the formation of a glassy structure suitable for the reaction.
The metakaolin used in this study was acquired from the Middle East Mining Investment Company and the chemical composition is as given in the results of the x-ray diffraction test shown in Figure (3-8) and X-ray Fluorescence (XRF) given in Table (3-3).
Table (3-3) X-ray Fluorescence (XRF) of used metakaolin
Material
SiO2
Al2O3
Fe2O3
CaO
MgO
SO3
K2O
Na2O
Kaolin before
calcination
49.36
34.1
0.30
0.09
0.26
0.59
0.02
0.03
Kaolin after
calcination
57.53
38.63
0.35
0.11
0.30
0.56
0.03
0.01

Figure (3-8) X-Ray diffraction pattern of kaolin before and after calcinations

3.5.1.2 Fly Ash
In the hydration of Portland cement, the excess lime is generated. The highly pozzolanic class F FA reacts with excess lime. ASTM C618 requires that the class F FA contains at least 70% pozzolanic compounds (silica oxide, alumina oxide, and iron oxide) according to ASTM C618 34 .
The chemical composition of the used FA type F is as shown in Table (3-4).
Table (3-4) Chemical composition of used fly ash
Cons.
Al2O3
SiO2
CaO
Fe2O3
K2O
MgO2
P2O5
TiO2
BaO2
MnO
%
27.00
48.80
6.20
10.20
0.85
1.40
1.20
1.30
0.19
0.15

3.5.2 Aggregate
The fine aggregate used in this study was sand. The coarse aggregate was obtained from crushed stone having a MNS of 19 mm. The grading of the two types of aggregates together with the combined grading used is given in Table (3-5) compared to the Egyptian standard specification limits 44.
Table (3-5) Grading of Combined Aggregate
Sieve Size
mm
Coarse
Aggregate
Fine
Aggregate
Combined
Aggregate
19.00
93.34
100.00
99.00
9.50
3.89
100.00
69.03
4.75
0.90
100.00
37.77
2.36
0.88
100.00
31.63
1.18
0.87
99.99
31.01
600 µm
0.85
79.58
24.67
150 µm
0.75
16.53
5.57
150 µm
0.54
1.11
0.72

3.5.3 Super plasticizer
The naphthalene sulphate super plasticizer was used to improve the workability of the fresh geopolymer concrete.
3.5.4 Alkaline Solution
The alkaline solution used in this study, is a combination of sodium hydroxide and sodium silicate. Sodium based solutions were chosen because they are cheaper than Potassium based solutions. Generally sodium hydroxide and sodium silicate are readily available in market in the form of pellets and gel (liquid) as shown in Figure (3-9)

Sodium hydroxide solution
Sodium silicate solution.
Figure (3-9) Activating solution components

3.5.4.1 Preparation of alkaline solution for metakaolin-based geopolymer concrete
The sodium hydroxide solution and sodium silicate solution are mixed together at least one day prior to casting. The quantity of alkalis needed for the mixtures was taken to be 10% of the metakaolin quantity in the mixture, while the total amount of water in the mixture is 50% of the source material (metakaolin). The ten percent is divided into:-
1- 5% of sodium silicate (available in solution)
2- 5%flakes of sodium hydroxide(calculated by mass)
In a mixture, for 300 kg of metakaolin, the alkalis required are 30 kg. The 30 kg are divided into 15 kg sodium hydroxide flakes and 15 kg sodium silicate in solution and the amount of water is 150 kg. This amount of water is equally divided, 50% free water and 50% for mixing the alkalis 45. Thus in this example 75 kg are mixed with the alkalis and 75 kg are free water for mixing. Since the sodium silicate is available in solution then the amount of water left for dissolving the sodium hydroxide flakes is 75-15=60 kg.
3.5.4.2 Preparation of alkaline solution
The flakes or the pellets were dissolved in water to prepare the sodium hydroxide (NaOH) solution. The weight of NaOH solids in a solution depended on the concentration of the solution expressed in terms of molar, M. For example, NaOH solution with a concentration of 8M consisted of 320 grams of NaOH solids per litre of the solution, where 40 is the molecular weight of NaOH.
Sodium silicate solution (commercially found under the name Vitroso lD) was used.

Figure (3-10) Mixing of alkaline solution

The sodium hydroxide solution and sodium silicate solution are mixed together at least one day prior to casting. The quantity of alkalis needed for the mixtures was taken to be (30%,40%,and 50%) of the FA quantity in the mixture, while the ratio between sodium silicate solution to sodium hydroxide solution was 1:1.5 as shown in Figure (3-5).
In a mixture, for 375 kg of fly ash, the alkalis required are112.8 kg consisting of 45 kg sodium hydroxide solution at morality (8, 12 and 16) and 67.8 kg sodium silicate in solution and the amount of water is 22.5 kg. This amount of water is added to improve workability 22
3.6 Geopolymer concrete mix design
Based upon previous research on geopolymer concrete, the following guidelines were taken into consideration during the design of the geopolymer concrete mixtures according to the absolute volume method with processed metakaolin and low calcium fly ash.
1- Coarse and fine aggregates, in the range of approximately 75 % to 80% of the entire mixture by mass. This value is similar to that used in OPC concrete.
2- Ratio of sodium silicate solution-to-sodium hydroxide solution, by mass, in the range of 0.4 to 2.5. This ratio was fixed at 1.5 for most of the mixtures because the sodium silicate solution is considerably cheaper than the sodium hydroxide solution.
3- Super plasticizer, in the range of 0 % to 2% of fly ash, by mass and extra water was added – in mass– to achieve the certain degree of workability (slump range 100-120 mm).

The quantities of the metakaolin- based geopolymer concrete and the FA based geopolymer concrete are as shown in Tables (3-6) and (3-7) respectively.
Table (3-6) Quantities/m3 of metakaolin–based geopolymer concrete
Mixture
No.
Metakaolin kg/m3
Fine aggregate kg/m3
Coarse aggregate kg/m3
Silicate solution/ MetakaolinRatio
NaOH kg/m3
Na2SiO3
kg/m3
Water kg/m3
Temp.
oC
M1
300
620
1240
0.04
63
12
75
Amb.
M2

0.05
60
15

M3

0.06
58
18

M4
300
620
1240
0.04
63
12
75
60
M5

0.05
60
15

M6

0.06
58
18

M7
400
560
1120
0.04
84
16
100
60
M8

0.05
80
20

M9

0.06
76
24

M10
450
540
1080
0.04
94.5
18
112.5
60
M11

0.05
90
22.5

M12

0.06
85.5
27

Table (3-7) Quantities/m3 of fly ash–based geopolymer concrete
Mixture
No.
Fly ash kg/m3
Fine aggregate
kg /m3
Coarse aggregate kg/m3
Alkaline liquid
Water
kg/m3
Amb
Temp.
oC

NaOH solution
Na2SO3 solution
kg/m3

molar
kg/m3

M13
375
625

1250

8
45
67.8
22.5
60
M14

12

M15

16

M16
450
580
1160
8
45
67.8
22.5
60
M17

12

M18

16

M19
450
580
1160
8
72
108
36
60
M20

12

M21

16

M22
450
580
1160
8
90
135
45
60
M23

12

M24

16

3.7 Manufacture of geopolymer concrete
The manufacture of the geopolymer concrete mixtures was executed at the Properties and Testing of Materials Laboratory, Faculty of Engineering, Ain Shams University.
3.7.1Batching
The batching of the necessary solid quantities was made by weight to the nearest gram, while the activating solution was prepared one day before casting as previously explained.
3.7.2 Mixing, casting and compaction
A pan mixer of 20 litres capacity with fixed blades was used for mixing the geopolymer concrete constituents as shown in Fig (3-11). The MKGC was off-white in colour (due to the off-white colour of the metakaolin) while the freshly mixed FAGC was darker. Both mixtures were cohesive. When the mixing time was long, mixtures with high water content bled and segregation of aggregates and the paste occurred. This phenomenon was usually followed by low compressive strength of hardened concrete.

Figure (3-11) Pan Mixer for mixing geopolymer concrete

Figure (3-12) Addition of activating solution
The following steps were used in mixing
1- Coarse and fine aggregate were dry mixed for 1 minute. Half the amount of the alkaline liquid was then added and mixing was resumed for another two minutes (total duration 3 minutes).
2- The metakaolin is then added and the other half of the alkaline liquid and mixing resumed for another 3 minutes (duration 3 minutes)
3- Whenever the workability was poor, a super plasticizer was used up to 2% of the metakaolin ratio. The mixing continued for 2 minutes. Thus the total time of mixing is 8 minutes
Casting of the geopolymer concrete mixtures was made directly after mixing in the prepared moulds Figure (3-13)

Figure (3-13) Casting in moulds
Compaction of fresh concrete in the steel moulds was achieved by using the vibrating table for ten seconds as shown in Figure (3-14)

Figure (3-14) Compaction using vibrating table

Figure (3-15) Finishing of moulds
3.7.3 Curing
3.7.3.1 Curing of metakaolin-based geopolymer mixtures
The first 3 mixture were cured in the ambient temperature about 25oC for 7 and 28 days after rest period (period enabling initial setting of the concrete and form removal). The rest of the specimens were cured in the oven at 60oC for 24 hours.

3.7.3.2 Curing of fly ash-based geopolymer mixtures
All mixtures were oven cured at 60oC for 24 hours after a rest period which was nearly one day in FA based concrete mixtures.
Curing of the fly ash-based geopolymer mixtures was done in EPRI (Egyptian petroleum research institute) following the chart shown in Figure (3-16).

Figure (3-16) Temperature in curing oven

Chapter (4)

Experimental Results and Discussion

4.1. Introduction
As previously explained in chapter 3, an experimental program was designed to test the properties of geopolymer concrete. This program involved two types of geopolymer concrete, from the point of view of source material, mainly MKGC and FAGC.
In this chapter the results of the performed tests are reviewed and the effect of the various parameters of the study are discussed.

4.2Metakaolin-based geopolymer concrete
The tests performed on the MKGC mixtures are the slump test, unit weight test and the compressive strength test. The obtained results from the experimental investigation are given in the following section.

4.2.1 Test results
The values of slump, unit weight and the compressive strengths of three concrete cubes tested at ages 7, 28 days are given in tables (4-1) to (4-8). The main variables, as previously discussed in chapter 3, are the content of metakaolin, the ratio of the silicate solution to the metakaolin content and the method of curing.

Table (4-1) Metakaolin based geopolymer concrete results at 7 days – ambient curing-metakaolin content = 300 kg/m3
Mixture
No.
Silicate solution/ Metakaolin
content
Slump
(mm)
Unit Weight(kg/m3)
Compressive
Strength
(MPa)
M1
0.04
136
2200
12.0

2210
12.5

2300
13.0
M2
0.05
135
2250
14.0

2310
15.2

2330
15.6
M3
0.06
138
2220
16.0

2340
17.0

2325
17.5

Table (4-2) Metakaolin based geopolymer concrete results at 28 days – ambient curing-metakaolin content=300kg/m3
Mixture
No.
Silicate solution/ Metakaolin
content
Unit Weight(kg/m3)
Compressive
Strength
(MPa)
M1
0.04
2200
15.0

2210
15.5

2300
16.0
M2
0.05
2250
17.0

2310
18.5

2330
19.0
M3
0.06
2220
20.0

2340
21.0

2325
22.0

Table (4-3) Metakaolin based geopolymer concrete results at 7 days -oven curing at temp. 60oC for 24 hours-metakaolin content=300 kg/m3
Mixture
No.
Silicate solution/ Metakaolin
content
Slump
(mm)
Unit Weight
(kg/m3)
Compressive
Strength
(MPa)
M4
0.04
138
2200
21.0

2210
22.0

2300
23.0
M5
0.05
140
2250
25.0

2310
26.0

2330
27.0
M6
0.06
141
2220
27.5

2340
28.5

2325
30.0

Table (4-4) Metakaolin based geopolymer concrete results at 28 days – oven curing at temp. 60oC for 24 hours- metakaolin content = 300 kg/m3
Mixture
No.
Silicate
solution/ Metakaolin
content
Unit Weight
(kg/m3)
Compressive
Strength
(MPa)
M4
0.04
2200
27.0

2210
28.0

2300
29.0
M5
0.05
2250
29.5

2310
30.5

2330
31.5
M6
0.06
2220
32.0

2340
33.0

2325
34.0

Table (4-5) Metakaolin based geopolymer concrete at 7 days – oven curing at temp. 60oC for 24 hours – metakaolin content=400kg/m3
Mixture
No.
Silicate solution/ Metakaolin
content
Slump
(mm)
Unit Weight(kg/m3)
Compressive
Strength
(MPa)
M7
0.04
136
2200
21.0

2210
22.0

2300
23.0
M8
0.05
135
2250
25.3

2310
26.2

2330
27.6
M9
0.06
138
2220
27.2

2340
28.1

2325
30.1

Table (4-6) Metakaolin based geopolymer concrete results at 28 days – oven curing at temp. 60oC for 24 hours – metakaolin content=400kg/m3
Mixture
No.
Silicate solution/ Metakaolin
content
Unit Weight(kg/m3)
Compressive
Strength
(MPa)
M7
0.04
2200
26.0

2210
27.0

2300
29.0
M8
0.05
2250
29.5

2310
30.5

2330
31.5
M9
0.06
2220
31.3

2340
32.5

2325
33.3

Table (4-7) Metakaolin based geopolymer concrete results at 7 days -oven curing at temp. 60oC for 24 hours-metakaolin content=450kg/m3
Mixture
No.
Silicate solution/ Metakaolin
content
Slump
(mm)
Unit Weight
(kg/m3)
Compressive
Strength
(MPa)
M10
0.04
136
2200
21.0

2210
22.2

2300
24.0
M11
0.05
135
2250
25.3

2310
27.0

2330
27.6
M12
0.06
138
2220
27.2

2340
28.1

2325
32.0

Table (4-8) Metakaolin based geopolymer concrete results at 28 days – oven curing at temp. 60oC for 24 hours – metakaolin content = 450kg/m3
Mixture
No.
Silicate solution/ Metakaolin
content
Unit Weight
(kg/m3)
Compressive
Strength
(MPa)
M10
0.04
2200
26.0

2210
27.0

2300
29.0
M11
0.05
2250
29.5

2310
30.5

2330
31.5
M12
0.06
2220
31.3

2340
32.6

2325
33.8

4.2.2Discussion of test results
The values of slump and mean value of the compressive strengths at ages 7and 28 days for MKGC mixtures are given in Table (4-9).

Table (4-9) Mean compressive strength (MPa) and slump values for metakaolin at 7 and 28 days
Mixture
No.
Silicate solution/
Metakaolin
content
Content of metakaolin
(kg)
Type of curing
average compressive strength (MPa)
Slump (mm)

7
days
28
days

M1
0.04
300
ambient
12.5
15.5
136
M2
0.05
300
ambient
15.0
18.2
135
M3
0.06
300
ambient
17.0
21.0
138
M4
0.04
300
oven
21.0
27.0
138
M5
0.05
300
oven
26.0
29.0
140
M6
0.06
300
oven
28.5
30.0
141
M7
0.04
400
oven
22.0
27.3
136
M8
0.05
400
oven
26.3
30.5
135
M9
0.06
400
oven
28.4
31.5
138
M10
0.04
450
oven
22.4
28.0
136
M11
0.05
450
oven
26.6
31.5
135
M12
0.06
450
oven
29.1
33.0
138

4.2.2.1 Effect of the ratio of sodium silicate-to-metakaolin content on the compressive strength
Figures (4-1), (4-2), (4-3), (4-4), (4-5) & (4-6) represent the effect of ratio of sodium silicate-to-metakaolin content on the mean compressive strength, for all specimens at the ages of 7 and 28 days. The values of 0.04 ratio of sodium silicate-to-metakaolin content were taken as a reference value (i.e. 100%). The percentage of mean compressive strength of 0.05 and 0.06 ratio of sodium silicate-to- metakaolin content were compared to those of 0.04 ratio of sodium silicate-to-metakaolin content.

Figure (4-1).Compressive strength vs. content of metakaolin (kg/m3) at 7 days (oven curing).

Figure (4-2).Compressive strength vs. silicate solution/metakaolin content at 7 days (oven curing)

Figure (4-3).Percentage of compressive strength vs. content of metakaolin (kg/m3) at 7 days (oven curing)

Figure (4-4).Compressive strength vs. content of metakaolin (kg/m3) at 28 days (oven curing)

Figure (4-5).Compressive strength vs. silicate solution/ metakaolin content at 28 days (oven curing)

Figure (4-6).Percentage of compressive strength vs. content of metakaolin at 28 days (oven curing)

Based on the calculated values of mean compressive strength, which are represented graphically in Figures (4-1) to (4-6), the following points were observed:
At age 7 days and content of metakaolin 300 kg/m3, the mean compressive strength for 0.05 and 0.06 ratio of sodium silicate-to-metakaolin content were 23.8 and 35.7% higher than that of the 0.04 ratio of sodium silicate-to-metakaolin content respectively. Also, at content of metakaolin 400 kg/m3, the mean compressive strength for 0.05 and 0.06 ratio of sodium silicate-to-metakaolin content were 19.5 and 29.1% higher than that of the 0.04 ratio of sodium silicate -to-metakaolin content respectively. Also, at content of metakaolin 450 kg/m3, the mean compressive strength for 0.05 and 0.06 ratio of sodium silicate -to-metakaolin content were 18.9 and 29.9% higher than that of the 0.04 ratio of sodium silicate-to-metakaolin content respectively. This means that, the ratio of sodium silicate-to-metakaolin content has a remarkable effect on compressive strength at age 7 days. This is also due to the oven curing at the first 24 hours.
At age 28 days and content of metakaolin 300 kg/m3, the mean compressive strength for 0.05 and 0.06 ratio of sodium silicate-to-metakaolin content were 7.4 and 11.1% higher than that of the 0.04 ratio of sodium silicate-to-metakaolin content respectively. Also at content of metakaolin 400 kg/m3, the mean compressive strength for 0.05 and 0.06 ratio of sodium silicate-to-metakaolin content were 11.7 and 15.4% higher than that of the 0.04 ratio of sodium silicate-to-metakaolin content respectively. Also at content of metakaolin 450 kg/m3, the mean compressive strength for 0.05 and 0.06 ratio of sodium silicate-to-metakaolin content were 12.5 and 17.9% higher than that of the 0.04 ratio of sodium silicate-to-metakaolin content respectively. This means that, the ratio of sodium silicate-to-metakaolin content has a pronounced effect on compressive strength at age 28 days. This is also related to oven curing at first 24 hours.
Generally, the compressive strength increases when the ratio of sodium silicate-to-metakaolin content increase. Nevertheless, the increase in the compressive strength at early ages is higher than the increase in the compressive strength at later ages.

4.2.2.2 Effect of metakaolin content on compressive strength of the metakaolin based geopolymer concrete
Figures (4-7), (4-8), (4-9), (4-10), (4-11)&(4-12) represent the effect of the content of metakaolin on the mean compressive strength for all specimens at ages 7 and 28 days. The values of 300kg/m3 content metakaolin were taken as a reference value (i.e. 100%). The percentage of mean compressive strength of 400and 450kg/m3content of metakaolin were compared to that of content 300 kg/m3metakaolin.

Figure (4-7).Compressive strength vs. silicate solution/metakaolin content at 7 days (oven curing).

Figure (4-8).Compressive strength vs. content of metakaolin (kg/m3) at 7 days (oven curing).

Figure (4-9).Percentage of compressive strength vs. silicate solution/metakaolin content at 7 days (oven curing).

Figure (4-10).Compressive strength vs. silicate solution/ metakaolin content at 28 days (oven curing)

Figure (4-11).Compressive strength vs. content of metakaolin at
28 days (oven curing)

Figure (4-12).Percentage compressive strength vs. silicate solution/ metakaolin content at 28 days (oven curing)

Based on the calculated values of mean compressive strength, which are represented graphically in Figures. (4-7) to (4-12), the following points were observed:
At age 7 days and ratio of sodium silicate-to-metakaolin content 0.04, the mean compressive strength for contents of metakaolin 400, 450 kg/m3were 4.8 and 6.7% higher than that of 300kg/m3content of metakaolin respectively.
Also at ratio of sodium silicate-to-metakaolin 0.05, the mean compressive strength for content of metakaolin 400, 450 kg/m3were 1.2 and 2.3% higher than that of 300 kg/m3 content of metakaolin respectively. Also at ratio of sodium silicate-to-metakaolin 0.06, the mean compressive strength for content of metakaolin 450 kg/m3 was2.1% higher than that of 300 kg/m3content of metakaolin. Nonetheless, at ratio of sodium silicate-to-metakaolin 0.06, the mean compressive strength for content of metakaolin 400kg/m3 was 3.4% lower than that of 300 kg/m3 content of metakaolin.
At age 28 days and ratio of sodium silicate-to-metakaolin 0.04, the mean compressive strength for content of metakaolin 400 and 450 kg/m3 was 1.1 and 3.7% higher than that of 300 kg/m3 content of metakaolin respectively. Also at ratio of sodium silicate-to-metakaolin 0.05, the mean compressive strength for content of metakaolin 400 and 450 kg/m3was 5.2 and 8.6% higher than that of 300 kg/m3 content of metakaolin respectively. Also at ratio of sodium silicate-to-metakaolin 0.06, the mean compressive strength for content of metakaolin 400 and 450 kg/m3were 5 and 10 % higher than that of 300kg/m3content of metakaolin respectively.
Generally, the compressive strength increases slightly when the content of metakaolin increases.
4.2.2.3 Effect of type of curing on compressive strength of the metakaolin based geopolymer concrete
Figures (4-13), (4-14), (4-15), (4-16), (4-17) and (4-18) represent the effect of the curing method of metakaolin based geopolymer concrete on the mean compressive strength for all specimens at ages 7 and 28 days. The values of ambient curing were taken as a reference value (i.e. 100%). The percentage of mean compressive strength at oven curing was compared to those of ambient curing.

Figure (4-13).Compressive strength vs. silicate solution/metakaolin content at 7 days (ambient and oven curing).

Figure (4-14).Compressive strength vs. silicate solution/metakaolin content at 7 days (ambient and oven curing).

Figure (4-15).Percentage compressive strength vs. silicate solution/ metakaolin content at 7 days (ambient and oven curing).

Figure (4-16).Compressive strength vs. silicate solution/metakaolin content at 28 days (ambient and oven curing).

Figure (4-17).Compressive strength vs. silicate solution/metakaolin content at 28 days (ambient and oven curing).

Figure (4-18).Percentage compressive strength vs. silicate solution/ metakaolin content at 28 days (ambient and oven curing).

Based on the calculated values of mean compressive strength, which are represented graphically in Figures. (4-13) to (4-18), the following points were observed:
At age 7 days and ratio of sodium silicate-to-metakaolin content 0.04, 0.05 and 0.06, the mean compressive strengths for the oven curing of metakaolin at content of metakaolin 300kg/m3was 68, 37.3 and 67.6 % higher than that of ambient curing respectively.
At age 28 days and ratio of sodium silicate-to-metakaolin content 0.04, 0.05 and 0.06 the mean compressive strength forthe oven curing of metakaolin at content of metakaolin 300 kg/m3 was 74.2, 59.3 and 42.9% higher than that of ambient curing respectively.
Generally, this means that, the difference of type of curing has a remarkable effect on compressive strength. The compressive strength of metakaolin based geopolymer concrete increase when the types of curing change from ambient to oven curing.
4.2.2.4 Compressive strength gain
Figure (4-19) gives the compressive strength for all specimens at ages 7 and 28 days and Figure (4-20) represent strength gain of metakaolin based geopolymer concrete on compressive strength. The values of compressive strength of metakaolin at 7 days were taken as a reference value (i.e. 100%).

Fig (4-19).Compressive strength vs.MKGC mixtures

Fig (4-20).Percentage compressive strength vs.MKGC mixtures

The compressive strength of metakaolin based on geopolymer concrete mixtures at 28 day increased in the range of 5-28% than the compressive strength at 7 days.
4.3 Fly ash-based geopolymer concrete
The tests performed on the fly ash-based geopolymer concrete mixtures are the slump test, unit weight test and the compressive strength test for three concrete cubes tested at ages 7 and 28 days. The main test variables, as discussed in chapter 3, are FA content, ratio of alkaline liquid to FA content, and the molarity of NaOH solution. After choosing the optimum mixture more tests were performed such as indirect tension test, and the determination of the modulus of elasticity. Also the accelerated corrosion test was performed as a measure of the durability.
4.3.1 Compressive strength test results
The values of slump, unit weight and the compressive strength of three concrete cubes tested at ages 7 and 28 days for FA-based geopolymer concrete mixtures are given in Tables (4-10) to (4-17).

Table (4-10) Results of FAGC mixtures at 7 days – cured at temp. 60oC for 24 hours- FA content=375kg/m3
Mixture
No.
Alkaline
liquid/
Fly ash
content
Morality of NaOH
Slump
(mm)
Unit Weight
(kg/m3)
Compressive
Strength
(MPa)
M13
0.3
8
160
2100
29.0

2150
30.0

2200
31.0
M14

12
165
2150
32.0

2350
33.0

2250
34.0
M15

16
168
2210
35.0

2310
36.0

2350
37.5

Table (4-11) Results of FAGC mixtures at 28 days –cured at temp. 60oC for24 hours – FA content=375 kg/m3
Mixture.
No.
Alkaline
liquid/
Fly ash content
Morality of NaOH
Unit Weight
(kg/m3)
Compressive
Strength
(MPa)
M13
0.3
8
2100
33.0

2100
34.0

2150
34.5
M14

12
2100
35.0

2250
37.0

2150
45.0
M15

16
2200
41.0

2300
43.0

2330
45.0

Table (4-12) Results of FAGC mixtures at 7 days – cured at temp. 60oC for 24 hours – FA content=450 kg/m3
Mixture.
No.
Alkaline
liquid/
Fly ash content
Morality of NaOH
Slump
(mm)
Unit Weight
(kg/m3)
Compressive
Strength
(MPa)
M16
0.3
8
160
2200
35.0

2210
37.0

2300
37.5
M17

12
165
2250
37.5

2310
38.0

2330
38.2
M18

16
170
2220
38.0

2340
39.0

2325
41.0

Table (4-13) Results of FAGC mixtures at 28 days – cured at temp. 60oC for 24 hours – FA content=450kg/m3
Mixture
No.
Alkaline
liquid/
Fly ash content
Morality of NaOH
Unit Weight
(kg/m3)
Compressive
Strength
(MPa)
M16
0.3
8
2200
40.0

2210
41.0

2300
42.0
M17

12
2250
42.5

2310
43.5

2330
44.0
M18

16
2220
44.2

2340
44.5

2325
45.8

Table (4-14) Results of FAGC mixtures at 7 days – cured at temp. 60oC for 24 hours – FA content=450kg/m3
Mixture.
No.
Alkaline
liquid/
Fly ash content
Morality of NaOH
Slump
(mm)
Unit Weight
(kg/m3)
Compressive
Strength
(MPa)
M19
0.4
8
145
2200
36.0

2210
38.0

2300
38.5
M20

12
148
2250
37.0

2310
38.0

2330
38.2
M21

16
150
2220
38.5

2340
40.0

2325
42.0

Table (4-15) Results of FAGC mixtures at 28 days – cured at temp. 60oCfor 24 hours – FA content=450kg/m3
Mixture.
No.
Alkaline
liquid/
Fly ash content
Morality of NaOH
Unit Weight
(kg/m3)
Compressive
Strength
(MPa)
M19
0.4
8
2200
39.0

2210
41.0

2300
42.0
M20

12
2250
42.0

2310
43.5

2330
44.0
M21

16
2220
45.5

2340
46.0

2325
45.5

Table (4-16) Results of FAGC mixtures at 7 days – cured at temp. 60oC – for 24 hours – FA content=450kg/m3
Mixture
No.
Alkaline
liquid/
Fly ash content
Morality of NaOH
Slump
(mm)
Unit Weight
(kg/m3)
Compressive
Strength
(MPa)
M22
0.5
8
140
2200
36.0

2210
38.0

2300
38.5
M23

12
145
2250
37.0

2310
38.0

2330
38.2
M24

16
150
2220
38.5

2340
39.5

2325
41.0

Table (4-17) Results of FAGC mixtures at 28 days – cured at temp. 60oC -for 24 hours – FA content = 450kg/m3
Mixture
No.
Alkaline
liquid/
Fly ash content
Morality of NaOH
Unit Weight
(kg/m3)
Compressive
Strength
(MPa)
M22
0.5
8
2200
40.0

2210
41.0

2300
42.0
M23

12
2250
42.5

2310
43.5

2330
44.0
M24

16
2220
48.0

2340
49.0

2325
50.0

4.3.2 Discussion of compressive strength test results
The value of slump and mean value of compressive strengths at ages 7and 28 days of all cubes of FAGC mixtures are given in Table (4-18).

Table (4-18) Mean value of compressive strength and value of slump for FAGC mixtures
Mixture.
No
Alkaline
liquid/
Fly ash content
Content of fly ash
Morality of NaOH
Mean compressive strength
(MPa)
Slump (mm)

7 day
28 day

M13
0.3
375
8
30.0
34.0
160
M14
0.3
375
12
33.0
37.0
165
M15
0.3
375
16
36.0
40.0
168
M16
0.3
450
8
36.5
41.0
160
M17
0.3
450
12
37.5
43.0
165
M18
0.3
450
16
39.0
44.0
170
M19
0.4
450
8
37.5
42.5
145
M20
0.4
450
12
38.0
44.0
148
M21
0.4
450
16
40.2
46.0
150
M22
0.5
450
8
38.5
44.0
140
M23
0.5
450
12
39.2
46.5
145
M24
0.5
450
16
42.0
49.0
150

4.3.2.1 Effect of alkaline liquid/FA content ratio on compressive strength
Figures (4-21), (4-22), (4-23), (4-24), (4-25) and (4-26) represent the effect of the ratio of alkaline liquid to FA content on compressive strength of FA based geopolymer concrete, for all specimens at 7 and 28 days. The values of 0.3 ratio of alkaline liquid to FA content were taken as reference values (i.e. 100%). The percentage of mean compressive strength at ratio 0.4 and 0.5 were compared to 0.3 ratio of alkaline liquid to fly ash content.

Figure (4-21).Compressive strength vs. morality of NaOH at different ratios of alkaline liquid/FA content and fly ash content =450 kg/m3at age 7days

Figure (4-22). Compressive strength vs. ratio of alkaline liquid/FA content at different NaOH moralities and for fly ash content = 450 kg/m3at age 7 days

Figure (4-23).Percentage compressive strength vs. morality of NaOH at different ratios of alkaline liquid/FA content and for fly ash content = 450kg/m3 at age7 days

Figure (4-24).Compressive strength vs. morality of NaOH for fly ash content=450 kg/m3 at age 28 days

Figure (4-25).Compressive strength vs. ratio of alkaline liquid/FA content at different NaOH moralities and FA content = 450 kg/m3at age 28 days

Figure (4-26).Percentage compressive strength vs. morality of NaOH at content FA=450 kg/m3 at age 28 days

Based on the calculated values of mean compressive strength, which are represented graphically in Figures (4-21) to (4-26), the following points were observed:
For the age 7 days, morality of NaOH 8molar and content of FA 450kg/m3, increasing the ratio of alkaline liquid/FA content from 0.3 to 0.4 and 0.5 increased the mean compressive strength by 2.7 and 5.5% respectively. Also, for morality12 molar of NaOH and content of FA 450kg/m3, increasing the ratio of alkaline liquid/FA content from 0.3 to 0.4 and 0.5 increased the mean compressive strength by 1.3 and 4.5% respectively. Similarly, for morality 16 molar of NaOH and content of FA 450kg/m3, increasing the ratio of alkaline liquid/FA content from 0.3 to 0.4 and 0.5 increased the mean compressive strength by 3.1 and 7.7% respectively

At age 28 days, morality 8molar of NaOH and content of FA 450 kg/m3, increasing the ratio of alkaline liquid/FA content from 0.3 to 0.4 and 0.5 increased the mean compressive strength by 3.7 and 7.3% respectively. Also, for morality 12 molar of NaOH and content of FA 450kg/m3, increasing the ratio of alkaline liquid/FA content from 0.3 to 0.4 and 0.5 increased the mean compressive strength by 2.3 and 8.1% respectively. Similarly, for morality of 16 molar NaOH and content of FA 450kg/m3, increasing the ratio of alkaline liquid/FA content from 0.3 to 0.4 and 0.5 increased the compressive strength by 4.5 and 11.4% respectively
This means that, increasing the ratio of the alkaline liquid/FA content has a remarkable effect on compressive strength at age 28 days. Generally, the compressive strength increases when the ratio alkaline liquid/FA content increases.

4.3.2.2 Effect of morality of sodium hydroxide solution on compressive strength
Figures (4-27), (4-28), (4-29), (4-30), (4-31) and (4-32) represent the effect of morality of sodium hydroxide solution on compressive strength of FAGC for all specimens at ages 7 and 28 days. The values of 8 molar of sodium hydroxide solution were taken as a reference value (i.e. 100%).The percentage of mean compressive strength at molar 12 and 16 were compared to 8 molar of alkaline liquid to fly ash.

Figure (4-27).Compressive strength vs. alkaline liquid/fly ash content for fly ash content = 450 kg/m3 at age 7 days

Figure (4-28).Compressive strength vs. morality of NaOH for fly ash content = 450 kg/m3 at age 7 days

Figure (4-29).Percentage compressive strength vs. ratio of alkaline liquid for fly ash content = 450 kg/m3 at 7 days

Figure (4-30).Compressive strength vs. Alkaline liquid/fly ash content for fly ash content = 450 kg/m3 at 28days

Figure (4-31).Compressive strength vs. morality of NaOH for fly ash content = 450 kg/m3 at 28 days

Figure (4-32).Percentage compressive strength vs. ratio of alkaline liquid for fly ash content = 450 kg/m3 at 28 days

Based on the calculated values of mean compressive strength, which are represented graphically in Figures (4-27) to (4-32), the following points were observed:
At age 7 days, alkaline liquid ratio 0.3, content of fly ash 450kg/m3, the mean compressive strength at morality of NaOH 12, 16 molar was 2.7, 5.5% higher than that for morality of NaOH 8 molar respectively. Also at alkaline liquid ratio 0.4, content of FA 450 kg/m3the mean compressive strength at morality of NaOH 12, 16 molar was 1.3, 4.5% higher than that for morality of NaOH 8 molar respectively. Also at the alkaline liquid ratio 0.5, content of fly ash 450kg/m3 the mean compressive strength at morality of NaOH 12,16 molar was 1.8, 9.1% higher than that for morality of NaOH 8 molar respectively.
At age 28 days, alkaline liquid ratio 0.3, content of FA 450 kg/m3, the mean compressive strength at morality of NaOH 12, 16 molar was 4.9, 7.3% higher than that for morality of NaOH 8 molar respectively. Also at alkaline liquid ratio 0.4, content of FA 450kg/m3the mean compressive strength at morality of NaOH 12, 16 molar was 3.5, 8.2% higher than that for morality of NaOH 8 molar respectively. Also at the alkaline liquid ratio 0.5, content of FA 450kg/m3 the mean compressive strength at morality of NaOH 12, 16 molar was 5.7, 11.4% higher than that for morality of NaOH 8 molar respectively.
This means that, the molarity of sodium hydroxide has a remarkable effect on compressive strength at age 28 days. Generally, the compressive strength increase when the morality of sodium hydroxide solution of fly ash-based geopolymer increases.

4.3.2.3 Effect of content of FA on compressive strength
Figures (4-33),(4-34), (4-35), (4-36), (4-37) and (4-38) represent the effect of the content of fly ash in FAGC mixtures on compressive strength – for all specimens at 7 and 28 days. The values of 375 kg/m3 content of FA were taken as a reference value (i.e. 100%). The percentage of mean compressive strength at 450 kg/m3 was compared to that of 375 kg/m3content of fly ash.

Figure (4-33).Compressive strength vs. molarity of NaOH at 7days

Fig (4-34).Compressive strength vs. molarity of NaOH at 7days

Figure (4-35).Percentage compressive strength vs. morality of NaOH at 7 days

Figure (4-36).Compressive strength vs. morality of NaOH at 28 days

Figure (4-37).Compressive strength vs. morality of NaOH at 28 days

Figure (4-38).Percentage compressive strength vs. morality of NaOH at 28 days

Based on the calculated values of mean compressive strength, which are represented graphically in Figures (4-27) to (4-32), the following points were observed:
At age 7 days, morality of NaOH 8 molar, the mean compressive strength forcontent of fly ash 450 kg/m3was21.7% higher than that for content of fly ash 375kg/m3 for FA based geopolymer concrete. Also at morality of NaOH 12 molar, the mean compressive strength forcontent of fly ash 450 kg/m3was15.2% higher than that content of FA 375kg/m3. Also at morality of NaOH 16 molar, the mean compressive strength for content of fly ash 450 kg/m3was 8.3% higher than that for content of fly ash 375kg/m3 for FA based geopolymer concrete.
At age 28 days, morality of NaOH 8 molar, the mean compressive strength forcontent of FA equals 450 kg/m3was 20.6% higher than that for content of FA 375 kg/m3 for FA based geopolymer concrete.Also at morality of NaOH 12 molar, the mean compressive strength forcontent of FA 450 kg/m3 was13.5% higher than that for content of FA 375kg/m3 for FA based geopolymer concrete. Also at morality of NaOH 16 molar, the mean compressive strength forcontent of FA 450 kg/m3was 7.5% higher than that for content of FA 375 kg/m3for FA based geopolymer concrete.
Generally, the compressive strength increase when the content of FA increases.
4.3.2.4 Compressive strength gain
Figure (4-39) gives the compressive strength for all specimens at ages 7 and 28 days and Figure (4-40) represent strength gain of FA based geopolymer concrete on compressive strength. The values of compressive strength of fly ash mixtures at 7 days were taken as a reference value (i.e. 100%).

Figure (4-39).Compressive strengths vs.FAGC mixtures

Figure (4-40).Percentage compressive strengths vs.FAGC mixtures

The compressive strengths of mixtures of fly ash-based geopolymer concrete at 28 day increased about 11.1-18.6% compared to the compressive strengths at 7 days.

4.3.3 Optimum FAGC mixture
Based on the previous compressive strength results the mixture M24 had highest results in compressive strength. It had a FA content of 450 kg/m3, alkaline liquid/FA content 0.6 and a molarity of the NaOH 16 molar. Thus M24 was used in the other tests conducted on the FA based geopolymer concrete to monitor hardened and durability properties.

4.3.4 Results and discussion of hardened concrete tests
Tests were performed on the optimum mixture of the FAGC to determine the modulus of elasticity and Poisson’s ratio, stress-strain relationship in compression, indirect tensile strength and density.
4.3.4.1 Modulus of elasticity and Poisson’s ratio
The modulus of elasticity, Ec, of FAGC was determined as the secant modulus. It was measured at the stress level equal to 40 percent of the average compressive strength of concrete cylinders. Tests were carried out in accordance with the Australian Standard 43

Table 4-19: Young’s modulus and Poisson’s ratio
Mixture
No.
Highest
compressive
strength
(MPa)
Age of
concrete
(days )
Modulus of
elasticity
(GPa)
Poisson’s
ratio
M24
49
28
24.5
0.135

Table 4.19 shows the values of modulus of elasticity and Poisson’s ratio of specimens from Mixtures 24 .The modulus of elasticity increased as the compressive strength of concrete increased.
For geopolymer concrete, the Australian standard 43 recommends the following expression to calculate the value of the modulus of elasticity with in an error ± 20%:-
Ec= ? 1 .5x (0.024 ? fc m + 0.12)………………………… Eq. (4.1)
Where:
Ec is modulus of elasticity
? is the density of concrete in kg/ m3.
fcmis the mean compressive strength in MPa.

American Concrete Institute (ACI) 50 has recommended the following expression to calculate the modulus of elasticity:-
Ec= 3320 ? fcm + 6900………………………………….Eq. (4.2)
The average density of fly ash-based geopolymer concrete was 2350 kg/m3. Table4.20 shows the comparison between the measured value of modulus of elasticity of fly ash-based geopolymer concrete with the values determined by Equation 4.1 and Equation 4. 2.

Table 4.20: Comparison between calculated values using Equation 4.1, Equation 4.2 and measured values of Modulus of Elasticity
fcm
Ec measured
(GPa)
Ec(Eq.4.1)
(GPa)
Ec(Eq.4.2)
(GPa)
47
26.50
34??7.9
30.8
46
25.50
33??7.2
30.3
45
24.50
32??6.8
29.5

As shown in Table 4.20, the measured values were consistently lower than the values calculated using Equation 4.1 and Equation 4.2. This may be due to the difference in the type of coarse aggregates used in the manufacture of geopolymer concrete.
The Poisson’s ratio of geopolymer concrete falls between 0.12 and 0.16 (Table 4.19).For Portland cement concrete, Poisson’s ratio is usually between 0.11 and 0.21,with the most common value taken as 0.15 for high strength concrete and 0.22 for low strength concrete. These ranges are similar to those measured for the fly ash-based geopolymer concrete.
4.3.4.2 Stress-Strain relationship in compression
Tests to obtain the stress-strain curves in compression were performed on100X200 mm concrete cylinders using the displacement-control mode available in the test machine. It took approximately 50 to 90 minutes to complete each test in order to obtain both the ascending and the descending branches of the stress-strain curves.
According to ACI 232 31, loading in compression over a period between 30 and 240 minutes has been found to cause about 15% reduction in the measured value of the compressive strength of test cylinders. The loading rate also influences the measured compressive strength of concrete.

Figure (4-41). Stress-strain relations of geopolymer concrete
The values of compressive strength, the strain at peak stress, and the modulus of elasticity obtained from the stress-strain curve are given in Table 4.21.
Table (4-21)Results from stress-strain curves
Mixture
No.
Highest
compressive
strength (MPa)
Strain at peak
stress
Modulus of
elasticity
(GPa)
M24
49
0.0005
30.6

The values in table (4-21) are comparable to those found in literature ACI 232 31.

4.3.4.3 Indirect tensile strength
The tensile strength of FAGC was measured by performing the cylinder splitting test on 150×300 mm concrete cylinders. The test results show that the tensile splitting strength of FA based geopolymer concrete is comparable to that of Portland cement concrete.
ACI (41) recommends the following design expression to determine the characteristic principal tensile strength of geopolymer concrete.
fct = 0.4(fcm)*0.5 (MPa) ……………………………… Eq. (4.4)
fct= 0.3 (fcm)2/3 (MPa) ………………………………… Eq. (4.5)

Table (4-22). Indirect tensile test results
Mixture
No.
Compressive
strength
(MPa)
Mean indirect tensile
strength
(MPa)
Characteristic
tensile
strength
Equation (4.4) (MPa)
Splitting strength Equation (4.5)
(MPa)
M24
49
5.45
3
4.34

Table (4-22) shows that the indirect tensile strength of FA-based geopolymer concrete is larger than the values recommended by the Australian Standards 43 and Aitcin 17 for geopolymer concrete.
4.3.4.4 Density
The density of concrete primarily depends on the unit mass of aggregates used in the mixture. Because the type of aggregates in all the mixtures did not vary, the density of fly ash-based geopolymer concrete varied only marginally between 2330 to 2430 kg/m3
4-4 Durability of FA based geopolymer concrete (Accelerated reinforcement corrosion)
As mentioned earlier in chapter (3), eight beams were tested in the accelerated corrosion test. The schematic of the experimental setup and of the electrochemical system used are shown in Figures (4-42) and (4-43)

Figure (4-42) Schematic of the accelerated corrosion test setup

Figure (4-43) Accelerated corrosion-monitoring at a typical test setup in the Lab

The beam specimens were tested after 28 days of curing. The specimens were immersed partially into a saline solution at room temperature. The specimens were pre-wetted to keep the initial D.C. to a low value. The steel bars were connected to the positive terminal of a constant 30volt D.C. power supply, to make the steel bars act as anodes. A stainless steel mesh was connected to the negative terminal of the DC power source and the mesh was used as the cathode, and isolated from the beams. The mesh was placed near the beams in the solution and landed on a stainless steel plate placed beneath the beams. Periodically, the mesh was cleaned to prevent the deposition of calcium, on the surface. The beam was considered to be cracked due to corrosion when a sudden rise in the current intensity was observed. Thus the corrosion time, which is the time at which the cracking of the beam by corrosion occurred, is determined by recording the intensity of the electric currents at different time intervals.
Daily, the beams were visually inspected for cracks while the current flow was continuously monitored using an ammeter. The weight of the steel bar was measured, and recorded for weight loss measurement before the accelerated corrosion test was started.
4-4-1 Corrosion current and cracking behavior
Current/time for specimens was the same. A decrease for approximately 80 hours was monitored, and for the remaining duration of the test it remained quasi-constant.
The results after 1 day showed that the mean current in the specimens decreased from 85 µA to 23 µA, from 110 µA to 20 µA in the M24 specimens, and then remained almost steady. It is suggested that the filling of the voids by salt caused the initial decrease. Then a current path was created and a decrease in the electrical resistivity of the beam occurred when chloride solution reached the bar interface.

Figure (4-44). Beam after 80 hours of accelerated corrosion testing
After 80 hours, the specimens began to crack, as shown in Fig 4-44. A sudden increase was recorded, after a decrease in current for a period of time, which matched with the cracking at the bottom of the beams. Corrosion products floated on the surface of the chloride solution. The reading currents continued to decrease. The visual inspection showed no sign of corrosion attack. After 100 hours, the cracks were observed on the top of the beams. The cracking was associated with a total current rise in the power supply ammeter.
4-4-1-3 Measurements of mass loss
The mass loss measurement is the most accurate method to determine the degree of corrosion in embedded steel. After test, the specimens were broken beams in order to determine the mass loss of the corroded bars. The beams were completely broken to retrieve the entire rebar, and the final mass was recorded as shown in Table (4-23).
Table (4-23). Percentage mass losses of reinforcing bars after accelerated corrosion exposure
Specimen
type
Initial
mass
(gm)
Final
mass
(gm)
Mass
loss
(%)
Beam-1
570
550
3.50
Beam-2
560
550
1.80
Beam-3
590
560
5.10
Beam-4
530
520
1.90
Beam-5
520
505
2.90
Beam-6
540
528
2.20
Beam-7
530
516
2.60
Beam-8
540
523
3.10

Figure (4-45).Mass of steel bars vs. FAGC beams

Figure (4-46).Percentage mass loss vs. FAGC beams

Figure (4-45) and Figure (4-46) show variations of 1.8 % and 5.1% for FAGC after the 100 hours of corrosion testing. The FAGC beams started to crack about 80 hours from the beginning of the test.
By reviewing the previous researches of the OPC concrete subjected to accelerated corrosion at same test conditions 31, the percentage mass losses after accelerated corrosion testing for 300 hours were 51% to 71.2%. The OPC concrete specimens took about 60 hours to crack and the width of crack was 5 mm at the end of corrosion testing 22.
Therefore, it may be assumed that fly ash geopolymer concrete has a better corrosion resistance than ordinary Portland cement concrete.
It is also recommended that the same accelerated corrosion specimens be re-examined and compared to similar ordinary Portland cement specimens made from local materials.

Chapter (5)
Summary, Conclusions and Recommendations

5.1Summary
10. This chapter presents a summary of the present study, the major conclusions, the environmental and economic benefits of using metakaolin-based and FAGC and finally the proposed recommendations for future research.
11. When this study started in 2010, the published literature contained only limited knowledge and know-how on the process of making geopolymer concrete. In this study an attempt was made to locally manufacture geopolymer concrete and outline its major properties.
The experimental work in this study investigated both metakaolin- based and fly ash-based geopolymer concrete. An experimental plan was designed to include twenty four concrete mixtures. Twelve mixtures using metakaolin as a source material and the other twelve mixtures using FA as a source material.
The metakaolin-based geopolymer mixtureswere designed by the absolute volume method with varying metakaolin content, varying ratio of silicate in alkaline liquid to metakaolin content and the curing temperature. The fly ash mixtures were also designed by the absolute volume method, with varying fly ash content, varying ratio of alkaline liquid- to fly ash content and difference molarity of solution.
The tests performed on the metakaolin-based geopolymer concrete mixtures and the fly ash based geopolymer concrete mixtures were made to determine the workability, unit weigh and the compressive strength.
Further tests were conducted on the fly ash-based geopolymer concrete, after choosing the optimum mixture, to determine the indirect tensile strength, stress-strain relationship and modulus of elasticity. Also the corrosion resistance of the fly ash-based geopolymer concrete was investigated.
5.2Conclusions
Based on the experimental work reported in this study, the following conclusions are drawn:
5.2.1 Metakaolin based geopolymer concrete
1. Increasing the ratio of sodium silicate/metakaolin content from 0.04 to 0.05, and 0.06 increases the compressive strength about 18-35% for 7 days and 7-17% for 28 days for the different contents of metakaolin. When the concentration of activating solution increase the compressive strength of metakaolin based-geopolymer concrete increase. The increase in the compressive strength at early ages is higher than the increase in the compressive strength at later ages.
2. Increasing the metakaolin contents from 300 to 400, and 450 kg/m3 increase the compressive strength about 1-6% for 7 days, and1-10% for 28 days for the different sodium silicate/metakaolin content ratios. The compressive strength increases when the content of metakaolin increases.
3. The curing at temperature 60OC showed much better results than ambient curing. The compressive strength increased about 67-73% for 7 days and42-74% for 28 days for the different alkaline liquid ratios. Thus, the difference of type of curing has a remarkable effect on compressive strength; the compressive strength of metakaolin-based geopolymer concrete increase when the type of curing changes from ambient to hot curing.
4. The strength gain of the compressive strength from 7 days to 28 days for all tested metakaolin-based geopolymer concrete mixtures was in the range of 5-28%.
5.2.2 FA-based geopolymer concrete
1. Increasing the alkaline liquid/fly ash content ratios in the mixture from 0.3 to 0.4, and 0.5 increases the compressive strength about 1-7% for 7 days, 3-11% for 28 days for the different molarities of NaOH. The increase in the ratio of the alkaline liquid/FA content has a remarkable effect on compressive strength at age 28 days. Generally, the compressive strength increases when the ratio alkaline liquid/FA content increases.
2. The moralities of sodium hydroxide activating solution,if increased from 8 to 12 and 16 increase the compressive strength about 1-9% for 7 days; 3-11% for 28 days for the different alkaline liquid/fly ash contents. This means that, the sodium hydroxide ratio has a remarkable effect on compressive strength at age 28 days. Generally, the compressive strength increase when the morality of sodium hydroxide solution of fly ash-based geopolymer increases.
3. Increasing the fly ash contents from 375 to 450 kg/m3 increase the compressive strength about 8-21% for 7 days and 7-20% for 28 days for the different molarities of NaOH. The compressive strength increase when the content of FA increases.
4. The slump value of the fresh fly-ash-based geopolymer concrete increases with the increase of extra water added to the mixture.
5. The average density of fly ash-based geopolymer concrete is the same of OPC concrete.
6. The strength gain of the compressive strength, from 7days to 28 days, for all tested fly ash-based geopolymer concrete mixtures was in the range of 11-18%.
7. The modulus of elasticity of fly ash-based geopolymer concrete with compressive strength of 49 MPa was 24.5 MPa. The measured value is higher than that recommended by the Egyptian code.
8. The Poisson’s ratio of fly ash-based geopolymer concrete with compressive strength in the range of 41 to 49MPa falls between 0.12 and 0.16.These values are the same as those of Portland cement concrete.
9. The indirect tensile strength of fly ash based-geopolymer concrete is a fraction of the compressive strength, as in the case of Portland cement concrete.
10. The durability of fly ash-based geopolymer concrete, from the point of view of resistance to corrosion, is better than that of ordinary Portland cement concrete.

5.3 Environmental and economic benefits
1. The use of geopolymer concrete is considered environmentally beneficial. It reduces the demand for the cement, the binding material for concrete, thus reducing the carbon dioxide emissions, saving energy and natural recourses.
2. Metakaolin-based geopolymer concrete offers economic benefits because it uses kaolin as a cheap and available material in Egypt, especially in the region of Sinai. On the other hand, for fly ash-based geopolymer concrete, the cost of 1 ton of fly ash is considerably less than the cost of 1 ton of Portland cement.
3. It has been estimated that the cost of chemicals needed to react one ton of fly ash is approximately 800 LE and for metakaolin approximately 650 LE. This is significantly lower than the current price of Portland cement.

5.4 Recommendations for further studies
1- More studies are needed to investigate the guidelines of mix design of geopolymer concrete.
2- The mechanical properties of geopolymer concrete and mortar should be investigated for the different parameters involved in the mixtures.
3- The behaviour of geopolymer reinforced concrete elements under different loads should be investigated.
4- The different durability aspects of geopolymer concrete and mortar should be thoroughly studied.

D1Are there no figures in the literature for the properties ?!!!
D2