Fly Ash, GGBS and RHA based geopolymer synthesis project with detailed methodology, chemical analysis & compressive and flexural strength properties

BRUNEL UNIVERSITY

Development of Low Carbon and Low Energy Geopolymer-based Cement

free Construction Materials

Shakir Mahboob

Supervisor: Dr. Xiangming Zhou

3/22/2014

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Acknowledgements

In the Name of my Creator, The Beneficent, The Merciful. The accomplishment of this project would

not have been possible without the guidance of my Creator. I thank Him. All the best elements of this

project are from Him. All the mistakes in this are from me.

Working with materials and being able to use the state of the arts facilities with such immense freedom

made this very difficult project one of the best experiences of my life. I would like to thank all the staff

at Brunel University, specifically the Civil Engineering department for this wonderful opportunity. I

would like to thank all the authors whose literature and research I utilised to understand this exciting

topic.

I would like to thank Dr. Xiangming (Michael) Zhou for suggesting this project. He directed me to

some crucial and excellent sources of information. His critical assessments were an excellent

motivation.

I would also like to thank Professor Mizi Fan who taught me the Materials module during my degree.

Much of the information I had earlier learnt from him were utilised throughout the project.

I would also like to thank Dr. Philip Collins, Professor John Bul, Dr. Katherine Cashell and Dr. Nuhu

Braimah at Brunel University who helped me to cultivate my learning methodologies and application of

the knowledge in writing over the years with their brilliant individual teaching styles. I would also like

to thank the technicians at Brunel.

I would also like to thank my parents. If they ever see this, I hope they are proud of me.

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Contents

Abstract

Acknowledgements

Contents ..................................................................................................................................................... 0

1. INTRODUCTION ............................................................................................................................. 4

1.1 Introductory Background ........................................................................................................... 4

1.2 Global Perspectives, Challenges and Solution .......................................................................... 4

1.3 Project Structure & Synopsis ..................................................................................................... 5

2. LITERATURE REVIEW .................................................................................................................. 7

2.1 Cement, Concrete and the Status of AACs and Geopolymers ........................................................ 7

2.1.1 Overview of Cements ............................................................................................................... 7

2.1.2 Comparison between Alkali Activated Cements (AAC), Geopolymers and Ordinary Portland

Cement ............................................................................................................................................... 8

2.1.3 Status of Geopolymers and Alkali Activated Cements in the Industry .................................. 10

2.2 Chemical, Microstructure & Molecular Theory ............................................................................ 11

2.2.1 Discussion of the Polymerisation Stages ................................................................................ 11

2.3 Geopolymer Frameworks and Bonds ............................................................................................ 15

2.3.1 General [Si-O-Al] 3 dimensional Framworks ........................................................................ 15

2.3.2 The Significance of Si:Al Ratios on Geopolymer Frameworks ............................................. 17

2.3.3 Geopolymer Bond Type – Covalent vs Ionic ......................................................................... 19

2.4 Geopolymer Constituent Materials and Classifications ................................................................ 20

2.4.1 Geopolymer and Alkali Activated Cement Classification through Constituent Materials ..... 20

2.4.2 Differentiating between Alkali Activated Cements and Geopolymers................................... 21

3. MATERIALS & METHODOLOGY .................................................................................................. 22

3.1 Sample Preparation & Manufacture .............................................................................................. 22

3.1.1 Alkali Activator Solution Synthesis ....................................................................................... 22

3.1.2 Mortar Sample Creation ......................................................................................................... 23

3.1.3 GGBS Impact Compaction ..................................................................................................... 25

3.1.4 Mixed PFA and GGBS geopolymers ..................................................................................... 25

3.2 Sample Formulation ...................................................................................................................... 26

3.2.1Formulae Used to Calculate Sample Synthesis Parameters..................................................... 26

3.2.2 Geopolymer Sample Mixtures ................................................................................................ 27

3.3 Sample Curing Processes............................................................................................................... 28

3.3.1 Uncontrolled Exposed Ambient Temperature Curing ............................................................ 28

3.3.2 Curing Cabinet Curing............................................................................................................ 29

3.3.3 Oven Curing ........................................................................................................................... 29

3.3.4 Dry Microwave Curing ........................................................................................................... 30

3.3.5 Combined Microwave & Oven Curing................................................................................... 30

3.3.6 Summary Listing of Samples to investigate Curing Parameters ............................................ 30

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3.3.7 Preliminary Experiments ........................................................................................................ 31

3.4 Sample Testing .............................................................................................................................. 33

3.4.1 Flexural 3 Point Strength Test ................................................................................................ 34

3.4.2 Mortar Compressive Strength Testing [BS EN 196-1:2005] ................................................. 35

3.4 General Health & Safety ............................................................................................................... 36

3.5 Sample Analysis ............................................................................................................................ 36

3.5.1 Scanning Electron Microscope [SEM]/ Energy-Dispersive X-ray Spectroscopy [EDX] ...... 37

3.5.2 X-ray Diffraction [XRD] ........................................................................................................ 38

4. RESULTS, OBSERVATIONS & CONSIDERATIONS.................................................................... 38

4.1 Research & Investigations Outline ................................................................................................ 38

4.2 Material Analysis & Preliminary Qualitative Investigation into the Rice Husk Ash (RHA),

Pulverised Fly Ash (PFA) and Ground Granulated Blast Slag (GGBS) waste materials for potential

use as alkali activated binder ............................................................................................................... 39

4.2.1 Preliminary Qualitative Analysis of Geopolymer & Pozzolanic Feedstock .......................... 40

4.2.2 Chemical and Microstructure Analysis of the Geopolymer Feedstock Source Materials ...... 41

4.2.3 Analysis of XRD patterns of Geopolymer Feedstock ............................................................ 45

4.3 Investigation of Curing Methods in relation to geopolymer characteristics ................................. 46

4.3.1 Experimental Results of Oven Cured Materials ..................................................................... 46

4.3.2 Room temperature Curing in uncontrolled conditions & inside a controlled curing cabinet . 48

4.3.3 Microwave Curing & Combination Curing ............................................................................ 50

4.4 Investigation into the performance implications of different ratios of Ground Granulated Blast

Furnace Slag and Fly ash mixed in a single geopolymer mixture ....................................................... 53

4.5 Investigation into optimisation and augmentation methods to increase flexural and compressive

capabilities of geopolymers ................................................................................................................. 54

5. DISCUSSION ................................................................................................................................. 56

5. 1 Surface Carbonation and Loss of Cohesion ................................................................................. 56

5.2 Unreacted Materials ...................................................................................................................... 57

5.3 Co-existance, Interactions & Interrelationships between C-S-H and aluminosilicate geopolymers

............................................................................................................................................................. 59

5.4 Nano Crystallisation within the Fly Ash Geopolymer Matrices ................................................... 60

5.5 GGBS cracking characteristics – relate to low flexural strength .................................................. 61

5.5.1 Leaching ................................................................................................................................. 62

5.5.2 Dehydration of C-S-H phase .................................................................................................. 62

5.5.3 Interruption of Geopolymer 3 dimensional networks ............................................................ 62

5.6 The Effect of Magnesium on Geopolymer .................................................................................... 62

5.7 The Effects of Liquid Expulsion from the Geopolymer ................................................................ 62

5.8 Uneven Heating ............................................................................................................................. 63

5.9 Evaluation of Errors ...................................................................................................................... 64

6. CONCLUSIONS ................................................................................................................................. 65

7. References…………………………………………………………………………………………….65

Appendix

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1. INTRODUCTION

1.1 Introductory Background

Concrete is the most widely used material in the world, with Ordinary Portland Cement being the

current most utilised concrete binder. Although there are variations in the estimates of the total global

concrete production, roughly 2.55 billion tonnes of Portland cement was recorded to have been

manufactured in 2006. (Glasby, 2012). This rate of concrete usage is increasing semi-exponentially due

to continuous global industrialisation. The current usage is estimated at 3 tonnes per capita (Kumar,

2009). Concrete’s environmental impact, especially during the manufacturing process, is ranked as one

of the worst in the world as 1 tonne of Portland Cement production results in 1 tonne of CO2 emissions.

Portland Cement manufacture therefore accounts for 5-8% of global man-made CO2 emissions.

(Glasby, 2012)

Different stakeholders are approaching this sustainability issue from various perspectives. Strategies

that have been formulated to address this problem include:

increasing the life cycle of concrete

finding curative measures to improve and restore existing structures

encouraging sustainable design and manufacturing practice in the construction industry

using waste and recycled components for concrete production

utilising different procedures and materials to synthesise alternative cementitious composites

One such strategy is the development of a substitute Ordinary Portland Cement (OPC) that has been

termed as geopolymers. The term ‘geopolymer’ covers a wide range of materials with variations in the

constituents and their ratios. Unlike OPC which uses hydration to obtain its properties, Geopolymer

cements are created by reacting aluminosilicate materials with alkali to activate their latent cementitious

properties. This project aims to understand the chemical nature and relationships of such materials and

then develop and manufacture samples of varying compositions in laboratory conditions. The samples

are cured or synthesised in different variables and then tested for their flexural and compressive

strengths. Their economic and feasibility prospects are also briefly discussed.

1.2 Global Perspectives, Challenges and Solution

The current global population has gone past 7 Billion (Dungus, 2011) and is growing exponentially.

Countries such as China and India are densely populated with 1.351 billion and 1.237 billion

respectively. This inevitable increase of population has been accompanied by rapid mega-scale

industrialisation and urbanisation in most parts of the world. Upon further analysis, these seemingly

progressive conditions hide many problems and challenges for the engineering community.

Air pollution is one of the one of the main problems caused by the aforementioned global changes, with

concrete production contributing to global emissions. In addition, human and industrial activity

produces various waste products. Disposal of these waste products vary according to their country of

origin and most of them are disposed of in landfills, by combustion and other wasteful methods. The

unplanned spurts in population growth has also resulted in poor utilisation of space and unequal

standards of living, growth of high density slum areas and a lack of adequate housing due to economic

reasons. Infrastructure management is also becoming inefficient and problematic in developed parts of

the world and some places have no access to roads at all. Ordinary Portland Cement is reliant on mining

processes for raw material e.g. limestone extraction, which causes heavy damage on the ecology and

environment. Also, OPC is subject to performance problems such as low corrosion resistance, spalling

caused by Alkali-silica reaction, sulphate attacks etc.

The broad hypothesis being examined in this project is the statement that ‘all of the aforementioned

problems can be addressed through the development, utilisation and commercialisation of geopolymer

in construction.’ According to literature, using geopolymer can cut carbon emissions by 9% to 80%

depending on the measures taken, geographical factors and methodology used (Turner et all, 2013). Fly

ash, Ground Granulated Blast Furnace Slag (GGBS) and rice husk ash are all viable examples of

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industrial by-products and alumina and silicate rich materials that can be geopolymerised. Commercial

utilisation of geopolymer could allow for mega scale recycling of industrial waste and also reduce

limestone usage. With the correct economies of scale, geopolymer structures could be significantly

cheaper, potentially providing a solution to the need for cheaper housing. Its faster setting times along

with the aforementioned benefits could make it more suitable for infrastructure creation, pothole repair

etc. Finally, geopolymer material can be significantly more durable and resistant to corrosion, ASR,

sulphate attacks and even synergised with admixtures to provide fire resistance, radiation containment

and other favourable characteristics (Davidovits, 2011).

1.3 Project Structure & Synopsis

There is a multitude of existing research and literature on the subject of AACs and geopolymers.

However, due to the relatively recent influx of interest in this topic, comparing the available research

and literature often results in contradictory or inconsistent information. Projects based on the use of

waste materials have an inherent inconsistency due to the potential variation in material micro

composition. Therefore it is important to question whether the conclusions made from these projects are

universal to all AACs and geopolymers. Much of the information, especially on the chemical and

molecular aspects of geopolymerisation, are still theories. Some of these theories are basic and are open

to further elaboration and some have been challenged and reinforced by academics and critics.

Taking these factors into consideration, the literature review attempts to incorporate the various

viewpoints on many of the subtopics in an objective manner. Although this can deduct from the

conciseness of the literature review, it allows for a more judicious view on the information that is

available. The learning outcomes of literature review are as follows:

Gaining an overview of the options available when synthesising concrete or cement and the

industry standing of geopolymers

The rudimentary differences between Ordinary Portland Cement & geopolymers

A look at the past and present documented uses of geopolymers for construction purposes

The implications, conflicts and complications of defining and differentiating between

geopolymers and AACs.

An explanation and dissection of incongruities of the chemistry, microstructure and molecular

theory of geopolymers.

An understanding of the constituent materials that are used to produce geopolymers.

The project establishes that results from any experiment lose much of their credibility when there is a

discrepancy in the methodology. Unfortunately, a large number of researches available on this topic

contains ambiguous methodologies; does not elaborate on the methodology or fails to mention potential

areas of error and measures taken to mitigate them e.g. no mention of compaction on mortar samples

etc. Therefore, the methodology in this project is in-depth. The materials, equipment, quantities, times

etc. are explicitly mentioned. Not all the steps are necessary but are taken to ensure optimum working

efficiency and precision. Justification for these steps is also provided. This allows any critics to be able

to re-enact, optimise and critically analyse all the experiments on this project.

The constituent materials such as Fly Ash are subjected to qualitative and quantitative bulk analysis (X-

ray Diffraction and X-ray Fluorescence) to add a chemical dimension to the investigation. The

chemical composition and silica, alumina content are linked to performance characteristics of the

produced geopolymers using the understanding of the chemical theory from sections 2.2- 2.3. Also, the

chemical composition of waste products and pozzolanic and ash components can be highly variable.

Separating them into different samples and determining the standard deviation in the contents clarifies

implications of the reliability of using them for practical construction purposes.

Microscopic analysis such as Scanning Electron Microscopy is performed on the constituent materials,

geopolymer mixtures and the cured samples. The observations taken during the various sample

production stages allow for commentary on visual changes on the microstructure and how these

changes can relate to the chemical theory. Once the samples are made, tests are performed to determine

the following performance characteristics:

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Flexural Strength

Compressive Strength

The complete scope of the research is provided in the research outline but the areas that are investigated

are:

Preliminary Investigations

Investigation into the viability of several pozzolanic materials

Analysis and Characterisation of Raw Materials

Main Investigations

Investigation into the effects of various curing times of oven cured geopolymers

Investigation into samples cured in ambient temperature

Investigation into the performance implications of different ratios of Ground Granulated

Blast Furnace Slag and Fly ash

Investigating Microwave Curing (although similar experiments have been done on Fly Ash

samples, this curing method has not been tested with GGBS and Fly Ash

Use of impact compaction GGBS

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2. LITERATURE REVIEW

2.1 Cement, Concrete and the Status of AACs and Geopolymers

2.1.1 Overview of Cements

When using the term ‘cement’ or ‘concrete’, by default, the material is assumed to be Ordinary Portland

Cement (OPC) in common language. This is understandable as OPC has been monopolised in the

construction industry since the beginning of the last century. Even in this age of technological

supremacy, different industry experts sometimes fail to reach a consensus on whether some structures

were cast using cement agglomeration or stonework e.g. the Pyramids of Giza (Davidovits, 2004) which

shows that there is a lot more to learn.

In reality, the topic of cements and concrete is open to interpretation according to the industry type,

professional expertise, academic proficiency etc. Some chemistry experts believe that geopolymers

should not be specified as a sub-category of cements but rather, simply as ‘geopolymers’. This project

is based on a Civil Engineering perspective and focuses more on the mechanical properties and practical

implications of materials and the following basic definitions are accepted and implied throughout:

Concrete – Concrete is the universal solid material consisting of an active binder ingredient

i.e.calcium silicate cements, aluminosilicates ; coarse and/or fine aggregates of various grading,

sizes, mineral types etc. and water. The mixture of these ingredients result in various chemical

reactions such as hydration (Domone, 2010), polymerisation and polycondensation. Concrete

can be steel and fibre reinforced.

Cement – Cement denotes the binder material in dry powder form. It can range from Ordinary

Portland Cement to Pozzolanic materials, Aluminosilicate etc. according to the reaction type

being discussed. Different types of cement materials can mixed together to obtain specific

material characteristics (Domone,2010).

Cement paste (also known as Grout) – Traditionally, this refers to a mixture of cement and

water. Although it will harden and gain strength, it is not usually used for structural purposes

(Domone, 2010). However, for the purpose of this project, cement paste can also describe a

mixture of aluminosilicate e.g. fly ash, alkali activator solution and/or water.

Mortar – Mortar is the mixture of cement paste with fine aggregate such as sand. The majority

of the investigations in this project are based around characteristic testing of mortar samples.

Aggregate - Aggregates with a particle diameter lower than 4mm is classed as fine aggregate

and anything bigger is classed as coarse aggregates. They form the bulk of concrete usually

constituting from 60-80% of the mix (Domone, 2010).

Admixtures - Concrete may also contain admixtures which can change or provide additional

characteristics (Domone, 2010) such as super- plasticisers which improve workability and

retarders which allow for longer setting times.

Alkali Activated Cement (AAC) – This refers to pozzolanic aluminosilicate materials that are

reacted (or activated) with an alkali to provide a cementitious binder. To avoid unnecessary

complexity, this term is used interchangeably with the term Geopolymer.

Evidence of various types of concrete and cements has been discovered across the world. Furthermore,

each type of cement can be differentiated into further subclasses. Figure 1 below is a list of cement

types and subtypes (The red arrows indicate materials that are essentially the same or similar but fall

under similar or disputed classification:

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Figure 1: Segmentation of Cement Types

This clearly shows that there is a multitude of cement materials available, each with their own set of

advantages and drawbacks. However, the materials of interest for this project are the geopolymer and

alkali activated cements types. They encompass a wide range of cements using various constituent

materials, resulting in many potential characteristics not unlike OPC.

2.1.2 Comparison between Alkali Activated Cements (AAC), Geopolymers and Ordinary Portland

Cement

Ordinary Portland Cement is the most widely used cement across the world making it logical to draw

comparisons between it and AACs and geopolymer cements. There are fundamental differences

between the chemical processes by which Alkali Activated Cements or geopolymer and Ordinary

Portland Cement gains strength.

Portland cement can consist of various phases and compounds but the main constituents are tricalcium

silicate [3CaO-SiO2] and dicalcium silicate [2Cao-SiO2]. They are also termed calcium hydrate, calcium

silicate hydrate, hydraulic cement etc. because its strength gain is dependent on its reaction with water

(Callister & Rethwisch, 2011). Although there are various hydration reactions, the general term can

equate to the following:

2CaO-SiO2 + xH2O 2CaO-SiO2-xH2O (1)

Equation 1 denotes the general term where x represents variable compounds that are dependent on the

water content, presence of other compounds such as sulphate content etc. The primary phase that exists

within the cement structure is known as Calcium Silicate Hydrate or C-S-H. This phase is a major

contributor to OPC’s strength. C-S-H is a general phase with no strict specific formula with over 30

known crystalline formations e.g. Jennite which equates to Ca9(Si6O18)(OH)6-8H2O, (Chen et al,

2004). The phases can vary from crystalline to pseudo-amorphous. Although the cement materials that

are synthesised for this project do not contain any OPC, a primary ingredient that is utilised, GGBS is

rich in Ca and Si. Therefore, almost certainly, the GGBS geopolymer will contain C-S-H phases within

the matrix. The characteristic of CSH that is the most significant to this study is that the bonds are

dependent on SiO2 and the intake of H2O.

Grouping all Alkali Activated Cements (AAC) in an indiscriminate manner for comparison purposes

will lower the understanding of the material. AACs and geopolymer can vary in composition from a

raw material perspective, activator type and the oxides and atoms involved in the bond. A further

discussion into the complex reactions for AACs and on subcategorising the geopolymer types is

provided in section 2.2 and 2.3. However in general, a geopolymer is formed when aluminosilicate raw

materials containing Si2O3 and Al2O3 (or other compatible Metal Oxides such Fe2O3) is reacted with an

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Alkali such as Na or K. The reaction results in dissolution of the Si2O3 and Al2O3 oxides into atoms. The

dissolved Si and Al species become a gel with the presence of water (which serves the primary purpose

of being used as a mixing agent for the alkali). The atoms within the gel are free to move and therefore

begin to form monomers, followed by polymers and oligomers, eventually 3dimensional chain

networks if the correct ratio of Si:Al is present within the mix. The polymeric bonding continues until a

solid hardened structure emerges. Unlike for the reaction in OPC (C-S-H) phase, geopolymerisation

expels water to form the bond. This process is coined ‘dehydroxilation’. The function of water is purely

for capillary reasons i.e. transportation of the oligomeric species within the gel matrix to form bonds

(Davidovits, 2011; Abdullah et al, 2011). The final geopolymer characteristics are dependent on various

factors. A generalised equation for Geopolymerisation reaction is as follows (Davidovits, 2011;

Wovchko, 1995):

[R]-O-Si-(OH) [R]-Si-O-[r] + H2O (2)

Where [R] = Atoms connected to –O-Si-OH such as Al or Fe

[ r ] = new chain sequences connecting to the [R]-Si-O- to form a bigger chain

The ‘+ H2O’ indicates the expulsion of water in order for the bonds to form. The geopolymer gains its

strength from the creation of long 3-dimensional chain networks, which results in the initial utilisation

of a large amount of capillary H2O, followed by its expulsion once a suitable bond can be formed. This

essentially means that OPC(C-S-H) and Geopolymers(Si-O-Al-O-{r}; Si-O-{r}) gain strength by

opposing processes. Figure 2 shows a more detailed equation mentioned by Wallah (2006) show the

process by which the powder particles dissolve into the alkali to produce the reactant product in

equation (2):

Figure 2: The dissolution of Aluminosilicates, (Na, K) Hydroxide, Water and addition silicate to gel

form, followed by dehydroxilation process to form geopolymer network (Wallah et al, 2006)

Ultimately, both OPC and Geopolymers fulfil the same function. They share similarities as well as

distinct differences. Some of these issues are highlighted below:

Strength gain mechanisms - C-S-H gains strength through hydration while geopolymerisation gains

strength by dehydroxilation. These are opposite processes. However, Both C-S-H and Geopolymer

create bonds incorporating SiO2 to gain strength.

Cost – OPC costs vary according to the locality, quality of the product and the economies of bulk

applied. Many geopolymer feedstock are actually free waste products e.g. Fly Ash. However, some

AAC raw materials like GGBS can cost as much as OPC. They also provide higher performance

characteristics as determined by this project.

Chemical constituency – OPC is generally highly different from geopolymer constituents such as

phosphates and ashes in composition. However, they are similar to GGBS due to its calcium

compounds as determined by EDX in this project. (Brunel ETC, 2014; Callister & Rethwisch, 2011).

Sustainability- The main advantage of geopolymers over OPC is its sustainability and low carbon

potential. OPC requires milling, mining, calcining (Domone,2010) and a multitude of emissions causing

processes. Geopolymers on the other hand make use of waste products that are usually combusted in

landfills, effectively reversing potential carbon emissions.

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On top of this, geopolymers have the following performance and durability advantages over OPC as

verified by the relevant studies (Wallah et al, 2006; Davidovits, 2011; Olivia, 2013 ):

Sulphate Resistance

Increased heat resistance

Increased sustainability

Limitations of in situ casting

Less Creep

Setting Times

Raw Material Availability

Water penetrability (Olivia, 2013)

Alkali-Silica Reaction

Safety issues

2.1.3 Status of Geopolymers and Alkali Activated Cements in the Industry

Regardless of the large amount of research on geopolymers, its commercialisation is still at a fledgling

state in relation to the cement industry. Naturally there is more than one perspective to this situation.

Although, the various viewpoints have subtle differences, they can usually be generalised into the

following categories:

1. The outlook of many scientists and sustainability conscious engineers is that geopolymers and

AACs are superior to Portland cement in terms of performance and sustainability and should be

utilised globally and on a major scale. (Davidovits, 2002)

2. The decision to use materials as major structural components is often influenced by analysing

huge amounts of previous data. Many engineers and companies that work more conservatively

do not believe there is sufficient long term data to safely analyse and deduce the risks and

benefits of the use of geopolymers and AACs. (Deventer et al, 2012)

3. Some critics are neutral or apathetic about the commercial aspects of geopolymer but are

interested in its scientific and engineering potential.

The first two viewpoints have their merits and flaws in terms of their practicality. Either viewpoint loses

much of its validity when the geopolymer materials are generalised and not sub-categorised according

to their merits and flaws. Geopolymers of different constitutions display high variability in terms of

their performance and durability characteristics as been proven by this project. Not appreciating this

issue, could lead to failure of structures as the material could be too weak; uneconomical design when

materials are much stronger than estimated or incorrect dismissal of superior materials e.g. Alkali

activated GGBS can give superior strength to OPC while lower quality Fly Ash can give relatively poor

strengths to OPC.

Furthermore, Fly Ash production, quality etc. are variable in different parts of the world due to the

difference in combustion methods, degree of pulverisation and chemical composition of the coal being

burnt. Therefore, in order to create an optimised and flexible network of geopolymer usage, it would be

advantageous to have global trade links that allow the transfer of different materials to places where it

can be utilised. Most advocates of the first perspective on geopolymer use do not take the political and

regulatory implications of this into account. Fly Ash is classified as a waste product and is thus

governed by the Basel Convention [Sections A2060 and B2060]. This causes limitations and

complications when attempting to transport fly ash globally. Furthermore, the suggestion of global

mega scale utilisation of geopolymer materials idealises the situations further and does not take into

account that the waste materials are dispersed disproportionately across the globe. For example, China

produces approximately 395 Mt of coal combustion products and utilises approximately 67% whereas

Africa produces 31.1 Mt and utilises 10.5% (Heidrich, 2013). These disproportionalities in conjunction

with the limitations against the ability to transport these materials work against each other to hinder the

practical prospects of global utilisation of fly ash waste based geopolymers.

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Finally, geopolymers require the use of metal hydroxides (potassium, sodium, lithium etc.) as well as

silicates. These products are relatively unsustainable and typically not waste products. In 2004, Sodium

Hydroxide production was estimated at 60 million tonnes with a demand of 51 million tonnes (Bittner,

2005). Assuming that the 51 million tonnes were used for non geopolymer related uses, only 9 million

metric tonnes would be available for global use. Even if the estimation would allow for an additional 10

million metric tonne increase during the last 10 years, there would still be a huge deficiency in terms of

hydroxide supply for globalised large scale geopolymer material use. Potassium Hydroxide production

was estimated at 1 million tonnes per anum in 1994. (Lakhanisky, 2001). Estimating the production has

increased to 5 million, its viability for geopolymer synthesis would still be negligible on a global scale.

The second perspective also has problems. There are actually several historical instances where similar

alkali activated materials have been used. Alkali activated pozzolans similar to geopolymers have been

used in ancient Egypt and Rome to build structures of cultural significance such as the Pyramids and the

Coliseum. (Davidovits, 2011; Davidovits, 1988). Although there is a level of resistance to accepting

this theory, this project has evaluated the evidence to support this idea and accepts it to be true. More

recently, Alkali activated slag cement was used to construct several structures and apartments in

Ukraine in 1960 (Shi et al, 2006). These buildings are still functioning.

2.2 Chemical, Microstructure & Molecular Theory

Understanding the chemical processes involving geopolymer allows for a more scientific approach to

geopolymer synthesis. The base materials will surely vary in terms of their chemical constitution,

especially because they are waste materials and not purposefully manufactured to be turned into

cement. Therefore, having an understanding on a molecular level will enable the engineer to determine

optimal amounts of alkali activator, Alkali Modulus, Alkali Dosage, manipulation of the Si:Al ratios

with the use of external Al2O3 or SiO2 after ascertaining the chemical composition of the raw material

and the way they function.

2.2.1 Discussion of the Polymerisation Stages

The chemical processes behind geopolymerisation are not completely understood and the available

explanations of the entire process are simplifications. Several theories have been proposed and some of

them are discussed throughout the project. Figure 3 below illustrates the multi-sequence of events that

cause geopolymerisation.

Figure 3: A) Geopolymerisation sequences from aluminosilicate raw material to geopolymer.

(Duxson et al, 2007) B) Illustration of dissolution of the small Aluminosilicate framework of

aluminosilicate feedstock and the speciation equilibrium formation resulting in large 3d network

(Yao et al, 2009)

A B

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The process of geopolymerisation is not simply polymerisation, but rather a chain of reactions and a

mixture of phases that culminates in the formation of oligomer chain networks. Although the exact

process can vary for each type of geopolymer, the following sections discuss the mechanisms behind

the simplified geopolymerisation model (Yao et al, 2009):

2.2.1.1 – Deconstruction/ Destruction/ Depolymerisation/ Dissolution

This occurs when the alkali solution is introduced to the aluminosilicate, resulting in alkaline

hydrolysis. The dissolution of the molecular bonds and structure of amorphous aluminosilicates, results

in a complex and varied mixture of aluminate, silicate and aluminosilicate species. It is important to

note that the dissolution process only occurs to ions in amorphous phases and not the inert crystalline

phases (Davidovits, 2011). This relates to the poor reactivity of the project’s fly ash sample as it has

very high levels of crystalline phases as determined by the XRD. The primary factor behind the

amorphosity to crystallinity of the pozzolanic material is the temperature range at which they are

calcined or combusted in in. For example, Rice Husk Ash becomes crystalline when combusted above

800◦C (Chemtrader Conference, 2010) but Fly Ash resists crystallisation even when combusted at

1000◦C to 1400◦C. Therefore, when choosing a pozzolanic material, the crystalline content should be

minimised as they will have poor reaction rates or not react at all.

Several studies indicate increased alkalinity or Sodium Hydroxide molarity results in a general trend of

higher strengths (Barnet et al, 2011). These stages can occur simultaneously, making it difficult to

examine each phase separately (Palomo et all, 1999) but the project makes a logical assumption that a

higher pH results in a higher rate of dissolution. The result of this hydrolysis based dissolution is a

supersaturated aluminosilicate solution. In a separate study by Yifei Zhang,(2003), it was concluded

that in supersaturated aluminosilicate solutions, silica attains supersolubility and secondary reactions of

the nucleation of aluminosilicates also occur (Zhang, 2003). As the other stages may occur

simultaneously, an improved rate of dissolution should hypothetically be correlational to the final

strength of the concrete as it would mean less of the feedstock would remain unreacted. If stages 2, 2b

and 3 occur prematurely around partially dissoluted material, it could possibly result in more unreacted

feedstock and lower final strength in samples.

Figure 4: A) Fly Ash particle in the process of dissolution (Palomo et al, 1999) B) Illustrated Model

of dissolution stages and alkali activation of fly ash (Fernandez-Jiminez et al., 2005)

2.2.1.2 – Speciation Formation, Gelation and Reorganisation

These are the main actions that occur once the geopolymer mix comes into contact with the activator.

They occur constantly using the water as a capillary medium where the aluminosilicate species

rearrange and reorganise as necessary to form increasing chains and bonds. There are a multitude of

species that constantly change to form bigger networks. The formation of the aluminosilicate species

can vary due to factors, such as base feedstock composition, type, amount and molarity of alkaline

activator, water availability, temperature of initial reactions etc. Figure 5 illustrates a few of the

orthosilicate species.

A B

13 | P a g e

Figure 5: Ortho-silicon-oxo-aluminate species within a Potassium Hydroxide (K

+) based alkali

activator solution, (North& Swaddle,2000).

2.2.1.3 – Polymerisation/ Polycondensation

The deconstruction stage results in a saturated aluminosilicate solution. The monomers then begin to

form oligomers and the process continues to occur resulting in an increasingly solid structure. Although

many publications have stated that the reaction can be very fast or even instantaneous (Bakri et al,

2011), the actual total reaction rates can be highly variable. This is validated by the experiments in this

project. GGBS based geopolymers can harden within 12 – 24 hours according to literature but the

experiments showed hardening after as early as 4- 7 hours. However, Fly Ash based geopolymers can

remain plastic for as long as 7 days at uncontrolled temperatures even with relatively high levels of

alkali. This variation in hardening times is an indicator of the raw material quality.

A study into the kinetics of silicate exchange reveals that the polymerisation of oligomeric silicon-oxo-

aluminates (Si-O-A) produce the significantly faster reaction times mentioned in the publications

(North & Swaddle, (2000). Subsequently, ortho-silicates (SiO4) and oligo-siloxo (silica: alumina ratio

of 2:1) react relatively slower. (Davidovits, 2011) In practical terms, this means that most geopolymers

synthesised from readily available waste materials will polymerise at variable and slower speeds. Fly

Ash and GGBS are an exception as they are pulverised, ground and granulated respectively. Other

pozzolanic feedstock that dissolves in alkali into oligomeric silicon-oxo-aluminate species that are

specifically engineered for the purpose react within seconds to milliseconds to provide extremely fast

reactions e.g. MK750 (Davidovits, 2011). MK750 is kaolin clay that is calcined at an optimal

temperature of 750°C. This also means that within the same geopolymer matrix, both reactions can

occur, resulting in both slow speed and high speed polymerisation. Raw materials such as fly ash could

continue to polymerise and gain strength over a long period of time similar to concrete.

Waste materials such as fly ash and GGBFS can vary in their composition, particle size etc. due to the

lack of quality control. Furthermore, the complex and hypothesis-based scientific methodology (Al and

Si NMR spectroscopy) needed to determine the aluminosilicate species present in the samples means it

may not be economic or practical to determine the microstructure of species each time before utilising a

material for geopolymer purposes.

It is important to note that during the polymerisation stage, the geopolymer mixture can still be in gel

form as explained in Figure 3. However, the gel substance still displays small degrees of cohesion,

especially with GGBS, as discovered during geopolymer synthesis, which is indicative of early

oligomeric formations.

2.2.1.4 – Secondary Phase Formations

Most of the geopolymerisation models proposed (Davidovits. 2008; Davidovits (2011); Barbosa, 2000)

are idealisations. In practical terms, the pozzolanic materials are not just aluminosilicates, but also

14 | P a g e

contain Iron, Magnesium, Calcium, potassium species etc. This is reinforced by the EDX scans in

sections 4.1 of the project. When a substantial amount of these secondary elements are present in the

feedstock, additional phases and characteristics may arise. Although there have not been many studies

into this phenomenon, a study by C.K. Yip (2004) determines that substantial calcium sources present

in the feedstock can cause the formation of Calcium Silicate Hydrate (CSH) phases and precipitates

within the geopolymer structure upon alkali activation. Yip initially states that the combination of both

geopolymeric gels and CSH in the same matrix results in increased mechanical strength. (Yip et al,

2004) However further studies into this phenomenon reveals that the type of calcium silicate in the

mixture is critical to any strength increase. Increased amount of crystalline calcium silicate results in

more unreacted phases within the geopolymer matrix causing an overall decrease in strength (Yip,

2008).

Figure 6. Concept of secondary phase formations in the presence of Non-aluminosilicate

constituents within the aluminosilicate geopolymer constituents (Yip et al, 2004)

In addition, to the above factors, this project determines that the type of complementary geopolymer

feedstock and ratios of Calcium to Aluminosilicates affect how much of the CSH cross-links with other

geopolymers and how much of it separates from the matrix to form C-S-H precipitates and large

sections of non-cross-linked, phase separated C-S-H. This type of C-S-H formation within the interface

of the geopolymer matrix could either positively or negatively effect of the strength. These findings are

highlighted in sections 4 and 5. Further studies into the topic are warranted.

This project assumes that some synthesis conditions (Si: Ca ratios, curing temperatures, water: binder

ratios) can result in calcium precipitates whereas some synthesis conditions result in cross-linking of

C-S-H and geopolymer phases at a matrix level. This hypothesis is further evaluated in sections 4-5.

2.2.1.5 – Dehydroxilation/ Stabilisation/ Polymer Network Creation – amorphous/crystalline

The final stage results in a hardened cement-like solid. This occurs when the oligomers formed in the

polymerisation/polycondensation phase joins together to form large 3 dimensional networks. The

physical indicative manifestation of this is the liquid leaching or evaporation (especially during

accelerated synthesis with higher temperatures as realised in the experiments) which indicates the

expulsion of H2O which was repeatedly observed during the experiments in section 3. Figure 7 by

Davidovits (2011) illustrates how the large 3d structures are formed through dehydroxilation.

Figure 7: Large olygomers forming even larger 3d networks by dehydroxilation (Davidovits,2011)

15 | P a g e

The formulaic explanation for this is given below in figure 8 also by Davidovits (2011). The formula

not only shows dehydroxylation represented by [-n H2O] but also equilibrium of the negative charges in

Al- species by the Alkali Na+. This stabilisation is what causes the geopolymers structure to complete

its reaction and slowly become inert 3 dimensional solids.

Figure 8: Detailed illustration of formation of [Si-O-Al-O] oligomer chain through dehydroxilation

(Davidovits, 2011)

It is important to note that although Figure 7 shows K+ (potassium) and figure 8 shows Na

+ (sodium) as

the alkali activators, these chemicals can be used interchangeably for explanation and synthesis

purposes i.e. Sodium Hydroxide and Potassium Hydroxide both work similarly as alkali activators.

2.2.1.6 – Al Coordination Changes

Although this is not explicitly mentioned in Yao’s (2009) model of geopolymerisation in figure 3,

another important stage occurs during the process. Many studies show that the Al coordination in the

constitute material are usually mostly of V and VI as determined by 27 Al NMR Spectroscopy. The

coordination number represents the total number of attachments. The Al coordination changes from V

and VI to IV. This project hypothesises that this change in Al coordination occurs mostly during the

oligomerisation and 3d chain formation phases. A study by P. Singh et al (2005) into the NMR spectra

of geopolymers can be used to reinforce this hypothesis.

Figure 9: Al Coordination III (76), IV (58), V (28) and VI (10) (Singh et al, 2005)

Using the time and temperature of curing as reference, it can be determined that 24 hours at room

temperature and 16 hours at 80°C, a degree of polycondensation has occurred. The complete shift in Al

coordination to tetrahedron is represented by 58 ppm.

2.3 Geopolymer Frameworks and Bonds

2.3.1 General [Si-O-Al] 3 dimensional Frameworks

One of the major determinant factors of the characteristic and behaviours of the geopolymer material is

its 3 dimensional frameworks it comprises of which is discussed in section 2.2.1.5. There are a

multitude of frameworks that can form depending on the available atoms, monomers, alkali activator

16 | P a g e

type etc. However, there are two main theories for the general 3 dimensional framework settings of

aluminosilicate geopolymer. They are shown in the illustration below.

Figure 10: A) Davidovits’ general model of aluminosilicate geopolymer framework denoting the use

of Potassium alkali activator. (Davidovits, 2011) B) Barbosa’s suggestion of geopolymer framework

using Sodium Activator (Barbosa et al, 2000)

Although the two models are seemingly identical, the main difference lies in the inclusion of free H2O

and Na within the matrix as well as some[ O-Al-OH] bonds in Barbosa’s model, whereas Davidovit’s

model denotes a perfect arrangement of [Si-O-Al-Si-O-{r}] bonds. In morphological terms, Davidovit’s

model resembles geopolymer models with near perfect crystallinity, whereas Barbosa’s model is of a

more seemingly amorphous structure. In practical terms, Davidovit’s model would be highly unlikely

and only occur when the materials are of extremely high quality, perfect Si:Al ratio of 3:1 to 1:1,

perfect quantification of the use of the alkali medium, no unreacted materials, perfect mixing etc.

Furthermore, this type of behaviour is also unlikely in geopolymers cured at room temperature and is

more accurate for describing heat cured and dehydrated geopolymer matrices.

Barbosa’s model is less idealised and takes the possibility of phase disorder, low reactivity, existence of

LOI and inert crystalline within the raw materials etc into consideration. It is more accurate when

describing geopolymer samples that are cured at room temperature. An important thing to note is that

this is not a fixed model and is in a transitional process to be more like the model described in figure

10.A. [O-Al-OH] bonds at the end of the 3d oligomer network will eventually undergo a hydrolysis

reaction to connect to more [O-Si-O-Al-O] bonds. The edges ending with [O-Al-O] or [O-Si=O]

likewise have the potential to form more bonds with oligomers ending with [OH-Al-O] etc. and expand

the 3d network.

A

B

17 | P a g e

2.3.2 The Significance of Si:Al Ratios on Geopolymer Frameworks

There are various generic and unspecific formulae developed through trial and error that are widely

available. Even commercialised geopolymer mixtures have been developed using trial and error at some

stage. (Banacrete, 2014) This has resulted in a standardisation of geopolymer mixes. However, using

the Si:Al ratios correlations can be used to define optimal geopolymer mixtures and the resulting

oligomer networks.

Figure 11: Three basic geopolymer framework formations categorised according to their Si:Al ratios

(Chanh et al, 2010)

The 3 frameworks illustrated above can form within a geopolymer matrix depending on their Si:Al

ratios. The framework shape undoubtedly affects the morphology, strength characteristics and general

behaviour of the geopolymer. The frameworks in figure 11 above are examples of Sodium polysialate

Sodalite framework, Potassium polysialate-siloxo Leucite framework and Potassium polysialate

disiloxo Sanydine framework (Davidovits, 2011). Chanh states that “a geopolymer can take 3 basic

forms” and illustrates his point in figure 11. However, this statement is questionable at best. Chanh’s

frameworks are subjective to the alkaline activator that is utilised. The first one is dependent on the use

of Na whereas the other 2 forms when K is utilised. Chanh would have been more accurate in

describing them as ‘Three basic geopolymer frameworks dependant on Aluminosilicate source material

and Na and K alkali activator. In terms of physical characteristics, longer chains of 3d framework

would result in more polymeric, flexible, elastic or ductile behaviour and better reaction to flexural

loads, whereas shorter and smaller 3d frameworks would result in denser packing, a more brittle

material and subsequently stronger reaction against compressive loads. Finally, Geopolymer reactions

can still occur at Si: Al ratios above 3. This is reinforced by figure 12 (Davidovits, 2008).

18 | P a g e

Figure 12: Explanation of the type of materials that can be synthesised from geopolymeric reactions

of aluminosilicates with different Si:Al ratios (Davidovits, 2008)

The project comprises of two main raw materials being synthesised i.e. Fly Ash and GGBS. Fly Ash

has a Si: Al ratio of 2:1 as determined by EDX in section 4.1. Therefore the likely framework that it

will consist of is Phillipsite frameworks Sodium Poly(sialate-siloxo). The reactions within GGBS

geopolymers are more complex and can consist of non-geopolymer C-S-H phases as well as secondary

and tertiary geopolymers. However, it is possible that Anorthite frameworks form within the GGBS

geopolymer phases. Both frameworks are illustrated below.

Figure 13: A) Illustration of Phillipsite framework (Unknown author, 2010) B) Anorthite

framework, which can occur within GGBS geopolymer (Chanh et al, 2010)

A B

19 | P a g e

2.3.3 Geopolymer Bond Type – Covalent vs Ionic

Some studies imply that the geopolymer bonds between the monomers i.e. Si4, O

- and Al

3+ are ionic.

However, this project does not accept the ionic bond theory in its entirety. A study by Rowles (2004)

challenges this theory via the utilisation of X-ray scattering on polysilicon-oxo-aluminates formed from

metakaolin. Rowles measured the values for the bonds in the polysilicon-oxo-aluminates in Angstroms.

Davidovits uses the results of this research to create a comparison between the calculated values for

ionic bonds of the Si4+

, Al3+

and O- and concludes that the geopolymer bonds are covalent and not

ionic. This is illustrated below in figure 14.

Figure 14: Calculation of ionic radii in geopolymers (Davidovits, 2011)

Although the calculations are correct, the values used in the table require further scrutiny. The

determination of ionic radii involves estimation, interpolation and extrapolation of data. Furthermore,

the values for ionic radius can vary according to the ionic coordination (Shannon, 1976). The table does

not specify the coordination number either but using the Al NMR in Figure 9, the Al is assumed to be

coordination IV. The following table is an alternative calculation of Ionic Radii with the consideration

of their coordination:

Table 1: Evaluation of Bond Calculations Using a different source

Davidovit's Bond Calculations (Å)

Project Calculations using Shannon's (1976) data (Å)

Ionic Bond Ionic Bond

Si4+ 0.39 0.26

O- 1.32 1.38

Al3+ 0.57 0.535

Calculated Ionic Bond Radii(Å)

Calculated Ionic Bond Radii(Å)

Measured Radius (Royles, 2004)

Si-O 1.71 1.64 1.6

Al-O 1.89 1.915 1.75

Si-O-Al 3.6 3.55 3.35

Ultimately, regardless of the small differences with Davidovit’s data in figure 14, the project accepts

that geopolymeric bonds themselves are covalent as the theory still holds. However, the covalent bond

theory by Davidovits is based on an idealised model of geopolymers. Most geopolymers, especially

those synthesised from waste materials, contain a level of unreacted or poorly reacted SiO2 and Al2O3 as

well as contaminants and secondary constituents such as Fe2O3 (Brunel ETC, 2014) which can form

alternative types of bonds. The project hypothesises that some of these particles can potentially form

ionic bonds within the matrix. However, the project acknowledges that there is more evidence to

support Davidovits’ covalent bond theory rather than oppose it.

20 | P a g e

2.4 Geopolymer Constituent Materials and Classifications

2.4.1 Geopolymer and Alkali Activated Cement Classification through Constituent Materials

The geopolymer and AAC type can vary according to their synthesis process, curing method, activator

molarity, base material type and other factors that directly affect the types of frameworks that it consists

of. Hypothetically, any silica based compound can be utilised to create a polymerisation reaction, so

there is a possibility of the existence of undiscovered geopolymer cement combinations. Figure 15

below illustrates possible combinations that can be used to produce AAC and geopolymers:

Figure 15: Categorisation of Geopolymer and constituent materials

This project recognises the multiple and often conflicting forms of classification given to AACs and

geopolymers. The classification can be according to the base material, alkali type, mechanical

characteristics, molecular properties, polymeric bond types etc. Many of these classifications can be

used interchangeably and does not necessarily contradict each other. The Institut Géopolymère in Saint

Quentin France classifies geopolymers using two systems. The first type is classification through 3

dimensional geopolymer framework discussed in section 2.3. The second classification type is based on

the raw materials and utilised in the book ‘Geopolymer Chemistry & Applications’ (Davidovits, 2011).

The classification dictates geopolymers can be grouped as:

1. Waterglass based geopolymer – based on the use of sodium silicate (waterglass) solutions

2. Kaolinite based geopolymer – when kaolinite based clays are utilised. It is generally more

sustainable as calcination is not required but provides weaker geopolymers.

3. Metakaolin geopolymer – based on the usage of metakaolin or calcined kaolinite clay. Generally

provides better characteristics than kaolinite based geopolymer. (Davidovits, 2011)

4. Calcium based geopolymer- relating to the use GGBS or doping the geopolymer with Ca or

OPC.

5. Rock-based geopolymer – relating to the use of rock based minerals.

6. Silica-based geopolymer- denoting the use of pure silica such as silica fume, metasilicate etc.

7. Fly ash-based geopolymer- based on the use of Pulverised Fly Ash from power stations.

8. Ferro-sialate-based geopolymer – based on feedstock containing high amounts of Ferric

elements which results in formations of [Fe-O-Si-O-{r}] bonded geopolymers. (Davidovits,

2011)

9. Phosphate-based geopolymer- resulting from the synthesis of geopolymer in an acidic medium

containing phosphoric acid as opposed to an alkali medium. The phosphate partially or

completely replaces the Si within the geopolymer bonds (Sadangi et al, 2013)

21 | P a g e

10. Organic-mineral geopolymer – based on non-synthetic materials, usually synthesised in an

acidic medium similar to phosphate based geopolymers. (Davidovits, 2011)

Although only two main types of geopolymers are synthesised i.e. Fly Ash and GGBS, due to

secondary Fe2O3 in the matrix and the use of waterglass, they can actually be put into categories 1, 4, 7

and 8.

2.4.2 Differentiating between Alkali Activated Cements and Geopolymers

As mentioned earlier, J. Glukhovsky investigated ancient cement fabrication techniques used in Rome,

leading to publications on reacting pozzolanic materials with alkali (Glukhovsky, 1959). The

theoretical information was published in 1959, using the term ‘geocement’ in 1965. Professor J.

Davidovits also did research in this field and in 1979, the term ‘geopolymer’ was ultimately devised,

but as a commercial designation. Although technically, geopolymer is a type of alkali-activated

cement, Professor Davidovits insists that the two types of cements are categorised as separate

substances (Davidovits, 2005). This is because alkali activated cement is a holistic concept, whereas

geopolymers are essentially an optimised and more commercially viable form of AAC. The main

differences between AAC and Geopolymer are:

1. The discovery of AAC was a result of open experimentation with cements by Glukhovsky. The

research behind geopolymers was initiated with the objective purpose of creating a

commercially viable cement product. (Davidovits, 2005)

2. AAC is based around the concept of reacting pozzolanic and/or alluminosilicate materials with

many indiscriminate alkali solutions. This concept means any alkali can be used to facilitate the

reaction. This means many AAC mixtures entail the use of corrosive and user hostile

components e.g. pure Calcium Oxide, Potassium Hydroxide, Sodium Hydroxide etc.

Geopolymer instead involves the use of user friendly alkali, mainly silicates that are only irritant

but not corrosive, as opposed to pure hydroxides. The practical implications behind this are that

AAC can potentially cause problems, injury or lawsuits when used by field workforce. Insurance

costs could also increase because of this. Therefore, Geopolymers are less dangerous and more

commercially viable because of this. Although Davidovits has revised his definition of

geopolymers several times, as a general rule, materials utilising silicate solutions with a molar

ratio of SiO2:M2O less than 1.45 is considered user hostile and thus categorized as AAC.

Silicates with molar ratios of SiO2:M2O greater than 1.45 are considered user friendly. Silicates

used in geopolymers should ideally be between molar ratio SiO2 : M2O of 1.45 to1.85.

(Davidovits, 2005)

3. Both AACs and Geopolymers utilise waste materials for their pozzolanic properties e.g. fly Ash,

Ground Granulated Blast Furnace Slag (GGBFS) etc. These components are not produced for a

purpose but are by-products of other reactions. This means that two samples of the same waste

material could differ in their chemical constitution. The presence of impurities could alter the

chemical reaction to be something other than polymerisation or polycondensation. For example,

the alkali activated polymerisation reaction in Fly ash and Metakaolin results in the formation of

aluminosilicate oligomers from silica and alumina monomers which finally becomes an

amorphous aluminosilicate polymer. (Provis et all, 2005). However, alkali activation of some

samples of Ground Granulated Blast Furnace Slag (GGBFS) results in a different and more

complicated chemical reaction as it contains Calcium Silicate Hydrate(Yip et al, 2005), high

levels of Calcite, hydrocalcite and lower levels of Alumina (Puertas et all, 2000).

The classification of Geopolymers and AACs is not a closed subject. There are many unknown

variables in the context of differentiating the two types of materials due to the sheer variety of potential

mixture combinations, raw material variability, synthesis conditions etc.

Authors such as Paloma have argued that the term geopolymer is a commercial label and therefore

should not be used for scientific purposes in the Portugal UTAD conference (2004). However, this is

impractical as the terminology of ‘Ordinary Portland Cement’ also began as a commercial label and is

22 | P a g e

now widely used and understood amongst engineers. Furthermore, the term ‘geopolymer’ is patented

and has been used and is generally accepted by a wide range of scientists and researchers.

This project takes a different approach and concludes that AACs and Geopolymers are essentially the

same material and uses the two terms interchangeably.

3. MATERIALS & METHODOLOGY

3.1 Sample Preparation & Manufacture

3.1.1 Alkali Activator Solution Synthesis

3.1.1.1 Materials/Equipment

Sodium Hydroxide Powder – General Grade

Sodium Silicate Solution (Waterglass), 38.3% Water; Si:Na2O -2:1

Filtered Water

4 500 ml beakers

Measuring Scale

Spatula

Plastic alkali resistant containers [for storage]

{Fume Cabinet}

PPE

3.1.1.2 Methodology

1. The beakers are labelled appropriately according to the chemical it will be used to handle. Each

beaker is used consistently for one type of solution ingredient to avoid reduction of accuracy due

to material cross- contamination, human errors etc.

2. Using the scale, water, Sodium Hydroxide Powder and Sodium Silicate solutions are measured

and poured into their appropriate beakers. Consult table 3 for measurement values.

3. The 3 beakers containing the measured ingredients and collected into the plastic containers. They

are stored inside the fume cabinet.

4. The fume cabinet fan is left on. The alkali solution can release vapours that cause irritation.

5. The weight of the beaker with the combined ingredients is measured to determine any weight loss

due to liquid staying inside containers because of frictional cohesion, spillage etc. This value is

recorded as the error margin.

6. The solutions are left to mix for 24 hours.

7. The mixed alkali solution can crystallise and become unusable if not used within 8-9 days.

Figure 16: A) All mixing occurs in fume cabinet B) Sodium Silicate solutions C) Sodium Hydroxide

solids form D) Storage in alkali resistant containers E) Crystallisation of Alkali activator solution

A

B C

D E

23 | P a g e

Health and Safety

1. All work is to be carried out inside the fume cupboard.

2. Lab coat, gloves and eye protective goggles are worn at all times.

3. Solutions are mixed carefully to avoid unnecessary spillage

4. Mixing the sodium hydroxide and water will release heat. Solution are handled carefully.

5. Alkali is corrosive and an irritant. In case of exposure, area is immediately washed with special

hand wash.

3.1.2 Mortar Sample Creation

3.1.2.1 Materials

Raw Materials as specified in table 3 and 4

Hobart Planetar mixer

3 X 160mm X 40mm X 40 mm steel moulds + Glass Plates

Trowel

Compactor Machine

Mould Oil + Brush

PPE

3.1.2.2 Methodology

1. The appropriate amounts of Pozzolanic binder, sand and alkali activator were first weighed in

the respective containers. All measurements are in section 3.2.2.

2. A Hobart Planetar Mixer was used for mixing the geopolymer paste. The sand and pozzolanic

binder was first dry mixed for 3 minutes at speed 1. The alkali activator is then added and

mixed together for 5 Minutes at Speed 2. Preliminary experiments found this to be the optimal

mixing settings and technique. Slower speeds and less time results in potential unreacted

materials and higher speeds results in spillage and dust emissions. Dry mixing the solids first

before adding the alkali activator was also proven to reduce unreacted material, lower strength

standard deviations and ensure homogeneity. A smaller mixer was also used to mix smaller

amounts (for preliminary experiments etc.). The smaller mixer was set at level ‘Manual-2’ and

mixed for 5 minutes.

Figure 17: A) Hobart Planetar mortar mixer; B) Time setting; C) Speed settings; D)Alternative

small mixer for preliminary experiments; E) Dry mixed binder and sand; F) Addition of alkali

solution to solids; G) Mixed geopolymer paste

A

B C D

E F G

24 | P a g e

3. A relatively large amount of mould oil was applied to the mould as geopolymers are more prone

to sticking to the mould surface than OPC.

4. Using a trowel, the mortar mix was poured into the mortar moulds [40mm x 40mm x 160 mm].

Fill beyond the mould’s top to allow for compaction.

5. The mortar mould was placed onto the compactor and compacted at a frequency of 36.

Compaction results in increased density to volume ratios and more homogeneity in the geopolymer

samples. It also reduces the probability of voids. As discussed in the preliminary experiments,

compaction results in a more uniform statistical data of compressive and flexural strengths. Uncompact

mortar samples also show weaker cohesion near the outer surface, especially within the first 7 days of

ambient curing. As discussed in the literature review, some of the studies conducted does not utilise

compaction to create the samples which reduces the reliability of their data.

Figure 18: A) Compactor B) Frequency of 36 used for settings

6. Any excess mortar mix from the moulds is removed after compaction using the trowel.

7. The moulds are covered with a flat glass panel and leaft for 24 hours before removing from the

mould for GGBS. For Fly Ash samples, de-moulding occurs after 7 days. The fact that each of

the geopolymers requires different setting times makes comparative scientific analysis more

complex.

Figure 19: A) Work area with bucket with geopolymer mix, mortar moulds, mould oil, trowel, mixing

stick; B) Work area prepared for mass production of samples; C) Importance of excessive oil on

mould; D)Mould filled with fly ash geopolymer mortar mix E) Glass panel on top of mould to provide

A

B

C

D

E

F

G

A B

25 | P a g e

smooth surface area and prevent contamination; F) De-moulded GGBS and PFA mixed sample G)

De-moulded GGBS sample

Health and Safety

1. PPE is worn at all times

2. Mortar mix contains residual alkalinity so must be handled carefully

3. Plastic sheets are set under the working area in case of spillage

4. Contact with skin or eyes can be irritant and must be washed off immediately

5. Care must be taken when using potentially dangerous machinery e.g. mixer, compactor etc.

6. Due to handling of heavy objects such as steel moulds, steel toe cap boots are worn

3.1.3 GGBS Impact Compaction

3.1.3.1 Materials

30 cm X 2 cm X 2cm impact hammer

3.1.3.2 Methodology

GGBS with a relatively low water to binder ratio (0.35– 0.37) was shown to solidify into elastic clay-

like consistency within 1 to 2 hours when mixed in larger volumes (approximate total weight of solids

of 12 kg). The project utilises a novel augmentation method where the GGBS samples are mixed at this

ratio, placed inside the steel moulds, and after 1 hour, 45 minutes, manually hit repeatedly with an

impact hammer to achieve compaction. As the samples become more compressed, additional

geopolymer paste is used to fill in the voids. These samples are termed GGBS Impact Compacted

Samples. The mixture composition for these mixtures is identical to the normal ‘GGBS 100’ specimens

and only the moulding technique is different.

Figure 20: A) Impact Hammer utilised for compaction; B) Manual hammering process

3.1.3.3 Health & Safety

This process can be dangerous if not done carefully, the hammering is done slowly and systematically

to avoid accidents.

3.1.4 Mixed PFA and GGBS geopolymers

A segment of the investigation required testing the outcomes of mixing Fly Ash and GGBS in the same

geopolymer matrix. In order to do so, mortar samples were mixed using the steps from section 3.1.2.

However, the pozzolanic binders in table 4 were mixed in the following ratios in table 3. These

measurements were used to manufacture three 160mm 40mm 40mm mortar samples per 500 grams

of total pozzolanic feedstock.

A B

26 | P a g e

Table 3: PFA and GGBS Mix Ratios

Pulverised Fly Ash Ground Granulated Blast Furnace Slag

Sample Designation (%) (grams) (%) (grams)

Geopolymer Mix 2080 20 100 80 400

Geopolymer Mix 4060 40 200 60 300

Geopolymer Mix 6040 60 300 40 200

Geopolymer Mix 8020 80 400 20 100

3.2 Sample Formulation

3.2.1Formulae Used to Calculate Sample Synthesis Parameters

In order to quantify sample variables and mixture ratios, several formulae has been used. Their

explanations are as follows:

Alkali dosage, [%Na2O] , represents the mass ratio of total sodium oxide (Na2O) in the

activating solution to the amount of pozzolanic binder in the geopolymer mix.

PFA

ONaONa 2

2% (3)

Alkali modulus, [AM], signifies the mass ratio of sodium oxide to silica (SiO2) in the

activating solution only. The alkali modulus does not take the SiO2 content of the pozzolanic

material into consideration.

2

2

SiO

ONaAM

(4)

Binder/ Aggregate Ratio, [B/A Ratio], defines the weight ratio of the pozzolanic binder e.g.

fly ash, GGBFS etc. to the amount of fine aggregate e.g. pumice, plaster sand etc.

(5)

Water/ Solid Ratio, [W/S Ratio], defines the ratio of total mass of water to the mass of

pozzolanic material and alkali solids. This ratio is not holistic and does not take the mass of the

fine aggregate into account.

(6)

Total Water/Solid Ratio [T.W.S Ratio], is the second parameter to measure the ratio of total

water to solids. Unlike the W/S Ratio, the T.W.S. Ratio takes the mass of fine aggregate into

account.

27 | P a g e

(7)

Na2O Present in NaOH [Na2O in NaOH], is the calculation of Sodium Oxide within the

Sodium Hydroxide solids. Sodium Hydroxide [NaOH] is in pellet form and it is necessary to

calculate Na2O in order to procure the values for Alkali Modulus and Alkali Dosage

parameters. The formulaic method of calculating the Na2O is as follows:

Na2O in NaOH solids =

(8)

=

H2O Present in NaOH [H2O in NaOH], is the calculation of Water within the Sodium

Hydroxide solids. Sodium Hydroxide [NaOH] is in pellet form and it is necessary to calculate

H2O in order to procure the values for Alkali Modulus and Alkali Dosage parameters. The

formulaic method of calculating the Na2O is as follows:

H2O in NaOH solids =

(9)

=

Oxides Present in Water Glass (Sodium Silicate) Solution [Na2O in Na2O3Si Solution], is

the calculated amount of Na2O present in the sodium silicate solution. Although a similar

formula utilising the molar mass of the molecules as seen above can be used, the percentage

oxide composition of the water glass is already provided :

Composition of Water Glass Solution: 61.7% Water (H2O), 25.5% Silicon Dioxide (SiO2) 12.7%

Sodium Oxide (Na2O)

Na2O in Sodium Silicate =

SiO2 in Sodium Silicate =

H2O in Sodium Silicate =

3.2.2 Geopolymer Sample Mixtures

Table 4: Geopolymer Sample Mixture table

Mortar Sample Designation

PFA

100

GGB

S 100

FA EN450

100

GeoMix

2080

GeoMix

4060

GeoMix

6040

GeoMix

8020

[Alkali

Modulus]Na2O/SiO2 1.250707

[Alkali Dosage] Na2O

(%) 12.5295

Unregulated PFA

(kg/m3)/(g)

500 +

2 0.0 0.0 100 + 2 200 + 2 300 + 2 400 + 2

GGBFS(kg/m3)/(g) 0.0 500+ 2 0.0 400 + 2 300 + 2 200 + 2 100 + 2

BS EN450-S

PFA(kg/m3)/(g) 0.0 0.0 500 + 2 0.0 0.0 0.0 0.0

28 | P a g e

Sand(kg/m3)/(g) 1375 + 2

NaOH(kg/m3)/(g) 48.7 + 0.4

Na2O in

NaOH(kg/m3)/(g) 37.73033

H2O in

NaOH(kg/m3)/(g) 10.96359

WaterGlass(kg/m3)/(g) 196.20000 + 0.3

Na20 in

Waterglass(kg/m3)/(g) 24.91740

SiO2 in Waterglass

(kg/m3)/(g) 50.03100

H2O in Waterglass

(kg/m3)/(g) 121.05540

Added Water

(kg/m3)/(g) 95.00000 + 0.3

w.s Ratio 0.37054

Total Water

(kg/m3)/(g) 227.01899

Total Solids

(kg/m3)/(g) 1987.67873

The samples were measured using a small scale for accurate measurements. However, there were still

observable differences in the actual measurements from the calculated measurements. This is accounted

for in the table with ‘+ x’. Also, a majority of the variables were kept identical. Only the amount of

pozzolanic feedstock was changed for each sample type. This is illustrated in the table by allowing one

row of information to represent all the geopolymer mixes. The measurements can be interpreted as

kg/m3 for scientific basis or grams for small scale preparation. If calculated in grams, the above

measurements based on 500g of pozzolanic feedstock results in the synthesis of three 160 mm X 40 mm

X 40 mm mortar samples. For the purpose of the experiment, in order to manufacture 21 samples in one

session, the measurements were multiplied by 7.

Also, it is important to note that oxides such as SiO2 and Na2O are calculated using molecular

mathematics (highlighted in equations 8 and 9). The water to solids ratio was selected after the

preliminary investigation to achieve a balance between workability, setting times and representative

compressive and flexural strengths.

3.3 Sample Curing Processes

One of the main investigative points of this project was the effect of various curing conditions on

geopolymer characteristics. The methodologies involving the different curing methods are detailed in

the following sections.

3.3.1 Uncontrolled Exposed Ambient Temperature Curing

Although according to traditional scientific notions, uncontrolled samples should not be used to gauge a

material’s characteristic, the project included a set of samples cured in variable (but monitored)

29 | P a g e

temperatures and humidity. This allows for an appreciation of how the material would perform in

practical applications where there is a likelihood of exposure to unfavourable and variable conditions.

3.3.2 Curing Cabinet Curing

Sets of samples are cured inside a curing cabinet at 95% relative humidity and 20°C temperature.

However, the leaching silicate solution can mix with the steam inside the cabinets and ultimately

solidify inside the pipes, resulting in machinery malfunction. The samples are wrapped inside plastic

bags to stop this from happening. This had unintentional effects on the dehydroxilation process due to

the hindrance of pressure gradient reactions that can form inside the bag as well as liquid precipitations

inside the bag. Therefore, instead, the geopolymers were cured inside the cabinet without any plastic

bags, but in very small quantities (6 at a time) this solved the problem without affecting the experiment.

Figure 21: Curing Cabinet used for experiment

3.3.3 Oven Curing

1. The oven is first preheated at the appropriate temperature for 30 minutes. This is to remain

consistent in terms of scientific variables and ensure that the samples are cured at the actual

temperature for the full duration of the process.

2. The mortar samples are prone to leaching. Instead of using aluminium trays, enamel trays which

are resistant to alkali are used to put the mortars inside.

3. The mortars are left inside at appropriate temperatures for the relevant time intervals.

4. The samples are removed using oven gloves for safety purposes.

5. The samples are allowed to cool down and stabilise for 17 hours before testing. Too much rest

time would allow the sample to gain strength in a different curing condition whereas too little

would mean that the aluminosilicate species are not fully stabilised. This time was chosen as a

compromise. The samples would have been tested after 12 hours, but laboratory opening times

and usage restrictions did not allow for this.

Figure 22: A) Oven Exterior B) Oven Interior C) Enamel trays used for curing purposes

A B C

A

30 | P a g e

3.3.3.1 Health & Safety

Heat is an issue so oven gloves are worn during handling of the specimens. Also the enamel tray is

chosen as it does not conduct heat as much.

3.3.4 Dry Microwave Curing

1. The mortar samples are placed inside the microwave. They are not placed inside any containers

or trays as they have been shown to distort the heating process as substantiated by preliminary

experiments.

2. The samples are microwaved at the appropriate powers and times.

3. The samples are removed out of the microwave using oven gloves for safety purposes.

4. The samples are allowed to cool down and stabilise for 17 hours before testing.

Figure 23: Domestic Microwave used for curing purpose

3.3.4.1 Health & Safety

Microwave curing geopolymers in a domestic microwave can have unpredictable results. In general the

user is advised to stay away from the device until the entire process is complete. Some of the

geopolymers exploded due to a build-up of heat pressure, but this was contained inside the microwave.

Gloves and PPE was worn at all times.

3.3.5 Combined Microwave & Oven Curing

1. The samples are first heated in a microwave at 350 Watts at 10 minutes.

2. The samples are removed out of the microwave using oven gloves for safety purposes.

3. They are then immediately cured in an oven using the same steps from section 3.3.3. The oven

is preheated in advance.

4. The samples are allowed to cool down and stabilise for 17 hours before testing.

3.3.6 Summary Listing of Samples to investigate Curing Parameters

As observable from the previous sections, there are a multitude of samples being synthesised under

different variables to investigate different factors. Each test requires multiple repetitions to establish

validity of the results. Therefore, the total number of samples being manufactured is detailed below in

table 5. Some of the investigations require the samples to be put through more than one type of curing

in stages. This is accounted for in the table. Furthermore the PFA EN 450 and Impact compacted GGBS

is only tested using the optimal curing sub-variables of each synthesis process to make more efficient

use of time and resources. This is also apparent on the table.

31 | P a g e

Table 5: List of Mortar samples and variables and sub-variables tested

No. of Mortar Samples Required

Synthesis Process Sub-Variables Unregulated

PFA

GGBS PFA BS-

EN450-

S

Impact

Compacted

GGBS

Uncontrolled Exposed

Ambient

Temperature Curing

7 days 3 3 0 0

28 days 3 3 0 0

Curing Cabinet

Curing

7 days 3 3 0 0

28 days 3 3 0 0

Oven Curing

60°C, 7 hours 3 3 0 0

80° C, 7 hours 12 12 0 0

120°C, 7 hours 3 3 0 3

60°C, 24 hours 3 3 0 0

80°C, 24 hours 3 3 3 0

120°C, 24 hours 3 3 0 0

80°C,60 hours 3 3 0 0

Dry Microwave

Curing*

750 Watts 5 Minutes 6 6 0 0

540 Watts 5 Minutes 3 3 0 0

350 Watts 5 Minutes 3 3 0 0

350 Watts 10 Minutes 3 3 0 0

Combined Microwave

& Oven Curing

350 Watts 10 Minutes

+ 80°C 24 Hours Oven

3 3 0 0

3.3.7 Preliminary Experiments

3.3.7.1 Mortar Mixing Technique Optimisation

In order to determine the optimum technique for mixing the mortar, the basic fly ash and GGBS

geopolymer mixes were mixed together at various speeds and times. Mixing speeds above 2 resulted in

spillage and wastage of geopolymer paste. Mixing for times lower than 3-4 minutes resulted in

unreacted fly ash and GGBS binder within the paste. Ultimately, 5 minutes at Speed 2 was chosen as an

optimal mixing speed.

Furthermore, dry mixing the sand and binder for 3 minutes at a slow speed (speed 1) before adding the

alkali activator, as opposed to mixing all the ingredients in one stage resulted in minimal unreacted

materials and homogeneity throughout the mix.

Mortar samples made using the different methods of mixing were tested for their flexural and

compressive strength. Although they all showed very similar values, the optimised technique resulted in

the lowest standard deviation amongst the sample strength values.

3.3.7.2 Use of containers for microwave curing

Plastics and containers are assumed to interfere with the microwave radiation heating process.

Preliminary experiments were carried out by placing fly ash samples inside the microwave inside

plastic containers and simply by itself without any containers. The samples inside the containers were

found to be emitting less heat and ultimately had lower compressive strengths in comparison to the

samples that were placed inside directly without any containers. Subsequently all samples that were

microwave cured were placed directly inside the microwave without any containers.

32 | P a g e

3.3.7.3 Rest time between curing and testing – mainly affects flexural strength

In order to save time between the project, the samples were initially tested directly after heat curing.

However, this resulted in a lack of correlation and high standard deviations between their compressive

strength. Therefore a set of Fly Ash samples were tested for compressive strength directly after oven

curing and another set were tested after a 12 hour cool down period. The 12 hour rest period resulted in

a much more correlative result as well as a lower standard deviation for the strengths. However, the

overall strengths also increased. It must be taken into account, whether the overall strength increased

due to molecular and granular stabilisation or due to additional geopolymerisation action. Subsequently,

all heat treated samples were allowed to cool down for 12 hours before testing.

3.3.7.4 Oven curing inside steel mould

As the fly ash takes approximately 5-7 days before they can be de-moulded, some samples were heat

cured inside the steel moulds in the oven while still at a plastic state. The resulting geopolymer samples

were stronger in terms of both compressive and flexural strength even though they incurred surface

damage during de-moulding. Using this process, even after heavy oiling of the moulds, the geopolymer

would get stuck to the side of the moulds. This caused damage to the samples as they had to be de-

moulded more forcefully, resulting in an uneven surface area. Ultimately, this method was not utilised

regardless of the increased strength because the uneven surface area would distort the accuracy of the

data.

Figure 24: A) Scraped off and damaged sample sides B) Deep crack on the top surface of sample

The above illustration highlights the damaged surface area which causes additional residual stress and

would distort the data. A variation in coloration is also present as the lower portion that was surrounded

by the steel mould is light grey whereas the upper exposed surface area is dark grey. This could be due

to steel being conductive of the heat and more overall heat being applied to the bottom area. A further

implication of this curing method is that the leaching pathway is directly upwards as opposed to the

entire three dimensional volume. This causes an increased leaching velocity due to decreased area of

water expulsion from dehydroxilation. The result of this can also be seen in figure 24 B where there is a

deep crack on the upper surface.

3.3.7.5 Optimal Time for GGBS Impact Compaction

Impact compaction cannot be used on mortar samples while they are at a plastic state. Similarly,

waiting too long for the geopolymer to harden before using impact compaction will result in material

separation and interface weakness resulting in residual stresses and weaker cohesion. Preliminary

experiments were conducted to determine that hammering the samples after they have been allowed to

set for 1 hours and 45 minutes allows for optimal compaction and mitigates for poor interface bonding

when additional mortar paste is added after compaction.

A B

33 | P a g e

3.4 Sample Testing

All the samples are tested for their flexural and compressive strength using the Instron Bluehill 5584

System [System ID: 5584K4212].

Methodology

1. Before both the flexural and compressive tests, a plastic mat is placed onto the Instron machine

to mitigate the effects of debris, dust etc.

2. The relevant jig is then fitted into the main rig.

3. All samples are weighed and their mass is recorded before the destructive testing. Furthermore,

samples are individually analysed for anomalies, unique characteristics etc. In cases where

samples were found to have defects/cracks before testing, they were discarded and replaced

with new samples.

4. All samples are sanded using sandpaper in order to make the contact surface smooth. Placing

samples with rough surfaces onto the test jigs causes additional residual stress and early failure,

especially during compressive testing.

Figure 25: Instron 5584 System used for sample strength testing with close-up of Instron console

used to position instron in correct alignment with sample

34 | P a g e

3.4.1 Flexural 3 Point Strength Test

Flexural 3 point strength test was conducted on the 160mm 40mm 40mm mortar samples at a load

rate of 3000N/minute. This was one of the primary testing methods of the project and the values from

this test were used to characterise and evaluate the usefulness of the samples.

Figure 26: Illustration of the flexural test parameters being set up using the Instron Bluehill

Software Interface

Flexural Strength Can be equated to:

(10)

Where, F = Flexural Strength, P = Maximum Loading Force (N), L= support span length (mm) , b =

Sample width (mm), d = sample depth (mm)

Methodology

1. After the 3 point jig has been fitted into the rig, the mortar sample is placed onto it. The sample

is aligned to be symmetrical, to ensure accurate results.

2. Using the console, the top rig is brought down until it just makes contact with the mortar

sample. If the rig does not make contact, the results may show the sample to be more resistant

to the load than it actually is. However, if the rig is brought down too much, premature cracking

can occur which will also distort the data.

3. The crack pattern is observed. The sample is then removed.

4. The debris are brushed off the mat and the rig after each sample to ensure they do not affect the

ensuing specimen.

35 | P a g e

Figure 27: A) Mortar Sample in flexural testing B) Samples after undergoing flexural testing

3.4.2 Mortar Compressive Strength Testing [BS EN 196-1:2005]

40mm 40mm 40mm of the mortar sample volumetric area was subjected to compressive strength

testing at a rate of 144kN/minute. The results from this test were also used as a primary factor to judge

the overall usefulness and rank of the geopolymer samples in question.

Figure 28: Illustration of the test parameters being set up inside the Instron Bluehill Software

Interface

Methodology

1. The samples broken in half during the flexural testing are used for compressive testing.

Although this may be distort the data due to residual cracks from the flexural and additional

shear stress caused by the increased mortar sample length, this method of testing provides a lot

more data, requires less time and raw material resources in comparison to creating individual

40mm 40mm 40mm mortar samples for each test.

2. After the compressive jig has been fitted into the rig, the mortar sample is placed onto it. The

sample is aligned to ensure that the contact area is in the middle of the sample to negate

eccentricities. This will also place the contact area further away from the uneven surface caused

by flexural testing.

A B

36 | P a g e

3. Using the console, the top rig is brought down until it just makes contact with the mortar

sample. If the rig does not make contact, the results may show the sample to be more resistant

to the load than it actually is. However, if the rig is brought down too much, premature cracking

can occur which will also distort the data.

4. The residue is quantitatively analysed. Any observations are recorded. Pieces from the test are

labelled and stored for microscopic (SEM and EDX) analysis.

5. The debris are brushed off the mat and the rig after each sample to ensure they do not affect the

ensuing specimen.

Health & Safety

The resulting dust and debris from the geopolymer compressive test can be very fine and hazardous if

breathed in. Therefore eye protection and breathing mask is worn during the tests.

Figure 29: A) Compressive Test Jig B) Mortar sample inside jig C) Crushed sample after testing

3.4 General Health & Safety

The project follows a general health and safety stance as well as contextual health and safety awareness,

which are mentioned in the appropriate sections. The geopolymer materials should not come into

prolonged contact with the body. The alkali activator, geopolymer paste and even the hardened samples

are alkali in nature. Therefore, during all stages of the sample preparation, manufacture, curing and

testing; Personal Protective Equipment (PPE) is worn. These items are highlighted in figure 30.

Figure 30: List of PPE worn throughout the project during stages 3.1 – 3.3

3.5 Sample Analysis

In order to gain an insight on a chemical level for both the pozzolanic feedstock and the geopolymers,

Scanning Electron Microscopy [SEM] was utilised. Energy Dispersive X-ray Spectroscopy [EDX] was

also used to determine the chemical oxide composition etc. X-ray Diffraction was used to determine the

crystallinity and amorphism properties of the materials.

1. Eye and Face

protective

helmet

2. Gloves, Soft

3. Breathing Mask

4. Lab Coat

5. Heavy Duty

Gloves

A B C

37 | P a g e

3.5.1 Scanning Electron Microscope [SEM]/ Energy-Dispersive X-ray Spectroscopy [EDX]

A Supra 35VP Scanning Electron Microscope [SEM] was used in order to analyse the pozzolanic

feedstock as well as the geopolymer microstructure. Energy-Dispersive X-ray [EDX] capabilities were

also utilised to confirm the chemical composition of the different components isolated during

microscopy. Finally, EDX line-scans were conducted for the combined PFA and GGBS mixed

geopolymers (GeoMix 8020, 4060, 6040 and 2080) in order to establish the level of cross linking

between any C-S-H and geopolymer or oligomeric phases as opposed to the formation of isolated C-S-

H phases and Calcium precipitate formations within the matrix.

Methodology

1. For the powdery pozzolanic binder specimens, only a small 8mm radius plate amount of sample

was required to be inserted into the SEM. However, for the geopolymer small intact non powder

chunks were attached to the plate and inserted into the SEM.

2. First, the 8mm plates were prepared by putting carbon tape onto their surface. This is necessary to

provide a surface that will not charge and distort the surface morphology.

3. The powdery samples were then dabbed onto the sticky carbon tape surface. The non-powder

geopolymer chunks were broken into small sizes and also stuck to the carbon tape. During the EDX

chemical analysis, there are large carbon peaks in the graphs. This is directly a result of the carbon

tape and is ignored until the EDX is conducted discriminately at a very small scale on individual

particles (10-50 μm)

4. The samples were then sputter coated with gold to make the specimens more conductive. Sputtering

with a conductive metal is necessary in order to omit electron charging, sample burning and

distortion of surface morphology.

4.1. A sputtering rate graph [Graph SC7640] was used to determine the rate and time of sputtering

required.

4.2. A voltage of 15kiloVolts and a vacuum pump system was used.

4.3. The samples were sputtered for a total of 2 minutes in bursts of 30 seconds (to help dissipate

heat inside the machine) at a sputter rate of 5 nanometers per minute. Therefore the total

coating was approximate 10 nanometers of gold.

4.4. During the EDX chemical analysis, Au (gold) is displayed on the graphs. The Au peaks are

resulted directly due to the sputtering process and is ignored.

5. The gold sputtered samples are placed on a larger plate and then put inside the Supra SEM machine.

6. The materials are then studied using the analogue controller.

7. Energy Dispersive X-ray Spectroscopy (EDX) is used at a bulk level as well as on individual

segments to determine the chemical details of the samples, crystallinity, unreacted particles , phase

changes etc. EDX Line scans are also used to take a spectrum across an entire sample as a means of

determining cross linking and isolation between different phases.

A B C

D

E

F

G

H

38 | P a g e

Figure 31: A) Gold sputter machine B) Geopolymer sample broken and organised into SEM

compatible size C) Raw material samples prepared on plates D) Carbon tape and SEM plates E)

Samples fixed into larger secondary plate F) SEM Equipment G) SEM Monitor in use H) Gold

sputtering graph SC7640

3.5.2 X-ray Diffraction [XRD]

A Bruker D8 Advance powder diffractometer was used in order to determine the crystallinity and

amorphism characteristics of the pozzolanic feedstock. The resulting data was used to determine the

correlations between the crystalline presence and geopolymeric potential and compressive strength of

resulting alkali activated materials. Although it would have been beneficial to use XRD to confirm the

crystalline presence within geopolymers, this could not be done due to time, authority and financial

constraints within the project.

Methodology

1. The XRD sample holders were first thoroughly cleaned using acetone in order to remove any

contaminants.

2. They were then placed inside the container and flattened to ensure a smooth surface using a thin

glass card. While they were waiting to be put into the XRD machine, they were covered in a

glass case to negate contamination.

3. The containers were then inserted into the diffractometer, where they were analysed for 2 hours

each.

4. ‘Diffrac.Suite’ software was used to study the Two Theta curves, match crystalline patterns and

to calculate and interpolate crystallinity in-between peaks.

Figure 32: A) Pozzolanic binder powder samples prepared in container and secured in glass cases

B)XRD Samples being put into Bruker D8 Advance powder diffractometer

4. RESULTS, OBSERVATIONS & CONSIDERATIONS

4.1 Research & Investigations Outline

There are already a myriad of research available on the chemical composition, performance and

synthesis variables of specific geopolymers, but it is difficult to find clear and concise sources

providing a guideline to optimised geopolymer production. The research integrates several

investigations in order to provide guidelines for producing high quality, low cost and low carbon

cementitious materials. Novel curing methods are also investigated in relation to their performance

enhancement capabilities. A synopsis of the investigative research is as follows:

A B

39 | P a g e

Using the methodologies highlighted in sections 3.1 to 3.5 in an organised and systematic manner, this

project investigates several hypothesis and parameters that are relevant to the synthesis of low carbon

geopolymer materials. Some of these investigations have been done before with different variables by

other authors but a few of the investigations are original and involve testing new methods to improve

the materials’ performance. These topics of investigations are outlined as follows:

Preliminary Investigation - Investigation into the viability of several pozzolanic materials for

potential use as alkali activated binder - The preliminary investigation involves X-ray Diffraction

(XRD) analysis of several samples of potential pozzolanic feedstock to determine their oxide

compositions and their crystalline/amorphous structure. They are then reacted with a pre-determined

alkali activator solution to see how well they respond to alkali activation. RHA does not react

favourably. The possible reasons for the results are theorized. Microstructural characteristics are also

analysed and commented upon.

Investigation 1 – Investigation of Curing Methods in relation to geopolymer characteristics – Fly

Ash, GGBFS and GGBFS/Fly Ash Mixture samples are synthesised under various curing condition. In

addition to normal room temperature and oven curing, a combination of novel curing methods i.e.

microwave curing is also investigated. All the samples are tested for their density, flexural and

compressive strengths and water absorption parameters.

Investigation 2 - Investigation into the performance implications of different ratios of Ground

Granulated Blast Furnace Slag and Fly ash mixed in a single geopolymer mixture– Fly Ash and

GGBFS differ in a multitude of ways. In this investigation, samples consisting of various ratios of fly

ash GGBFS are mixed and synthesised with oven curing and tested for their density, flexural and

compressive strengths and water absorption parameters. The results are evaluated from an economic

and sustainable perspective in addition to the performance parameters. A holistic optimum ratio is

determined and subsequently used as the GGBFS/Fly Ash Mixture samples for the other investigations.

Investigation 3- Investigation into optimisation and augmentation methods to increase flexural

and compressive capabilities of geopolymers – The final investigation evaluates the viability of

impact hammer compaction for GGBS based geopolymer samples and Alkali coating and Alkali

Submersion synthesis augmentation methods to improve the flexural and compressive strengths of the

geopolymers.

The project involved the handling of an enormous amount of raw data. Including all the raw data

without adding context to it would result in a loss of coherence. Therefore the presentation of the results

has been divided according to the investigation it relates to. Furthermore, most segments of the report

do not require the complete set of data in order to establish a correlation so the means for all the data are

summated to present the results. However, some segments require a thorough look at the data in its

entirety in order to appreciate the range and deviations from the mean amongst samples of the same

subgroups. Therefore, the majority of the quantitative data is included in the appendix. Some synthesis

methods ultimately result in a large variance in the characteristics of the geopolymers due to the

somewhat non-sequenced nature of the geopolymerisation stages. The standard deviations of the means

are included in the appendix to allow for judgements into the reliability of the data. All the flexural

strength tests were repeated 3 times and the compressive tests were repeated 6 times unless otherwise

stated.

4.2 Material Analysis & Preliminary Qualitative Investigation into the Rice Husk Ash (RHA),

Pulverised Fly Ash (PFA) and Ground Granulated Blast Slag (GGBS) waste materials for

potential use as alkali activated binder

The initial stages of the project involved qualitatively evaluating the 4 different pozzolanic materials for

their geopolymeric potential. The four pozzolanic materials were:

Unregulated and uncontrolled Pulverised Fly Ash [PFA]

Commercial Pulverised Fly Ash conforming to BS-EN450 [PFA-EN450]

Ground Granulated Blast Slag [GGBS]

40 | P a g e

Rice Husk Ash [RHA]

Understanding the main ingredient of the geopolymer at an in-depth level in addition to alkali activation

allows for a better understanding of the resulting geopolymers. The resulting information is discussed

below.

4.2.1 Preliminary Qualitative Analysis of Geopolymer & Pozzolanic Feedstock

The 4 Samples of pozzolanic feedstock (without sand) were mixed with alkali activator solutions of

Alkali Modulus of 1.25 and Alkali Dosage of 12.5% Na2O and water to solids ratio of 0.375. The two

Fly Ash samples and the GGBS sample polymerised, albeit at highly different rates. However, the RHA

sample did not solidify.

Table 6: Table illustrating preliminary geopolymeric capabilities of materials

Pozzolanic

Binder

Geopolymeric Viability [based on initial

speed of reaction, workability etc.]

Initial Solidification

Time (hours)

Relative

Cost

PFA Average 60 Free

PFA-EN450 Excellent 32 Cheap

GGBS Excellent 4 Expensive

RHA Did not geopolymerise - Free

It is important to note that the ‘Initial Solidification Time’ refers to very early cohesion. Samples were

plastic although highly prone to damage at this stage. Furthermore, although PFA is free,

commercialised PFA-EN450 costs can vary between 20% - 60% of the bulk price of Ordinary Portland

Cement.

Figure 33: A) Geopolmyerised Fly Ash binder B) Geopolymerised GGBS Binder C) Rice Husk Ash

saturated with alkali solution but not polymerising D) Unregulated PFA E) PFA BS EN450 F)

GGBS E)RHA

Figure 33.A and 33.B shows the PFA and GGBS specimens in solid form. However, although RHA

seems cohesive on the image, the paste was soft and elastic even after 15 days. Closer inspection shows

light brown organic materials and a fibrous consistency. The project deduces that these organic pieces

are the main reason behind the failure of the geopolymerisation process as they have a much higher

liquid absorption capacity. This causes them to absorb the alkali activator solution, which critically

A B C

D E F G

41 | P a g e

increases the liquid requirements of the mixture. The ash show white strands that resembles uncrushed

but burnt rice husk. These parts are pseudo-organic and show high silica content after EDX analysis in

the following section in Figure 34. This suggests that the RHA was combusted in low temperatures and

not crushed or ground. In comparison PFA was combusted at a higher temperature. According to

literature, the PFA is usually pulverised before being combusted. It should be noted that even visually,

the uncontrolled PFA looks coarser than the PFA- EN450.

4.2.2 Chemical and Microstructure Analysis of the Geopolymer Feedstock Source Materials

Using the Electron Dispersive X-ray Spectroscopy (EDX) function of the Scanning Electron

Microscope (SEM), the chemical oxides of the various pozzolanic materials were analysed. It is

important to note that these values are taken from precise micro-samples (as discussed in the

methodology section) and normalised during processing through oxygen by stoichiometry. The results

of Loss on Ignition(LOI), which represent unburnt carbon, is estimated using the carbon peaks in the

EDX spectra that could be interpolated as LOI and thus is beyond the total 100% value. This data is

based on normalised mean values and the full set of raw data can be found in the Appendix section A1.

The comparative mean values are illustrated below in table 7.

Table 7 Comparative Table of Chemical Oxides present in Pozzolanic Feedstock Material

BS EN450 PFA[Drax

Power Station]

Unregulated PFA

(Drax Power Station)

Rice Husk

Ash [RHA]

GGBS

(Scunthorpe)

SiO2 (%) 46.52 49.1 90.36 33.23

Al2O3 (%) 27.136 25.718 - 12.642

Fe2O3 (%) 9.666 10.756 0.014 0.55

K2O (%) 4.636 3.746 0.04 0.442

CaO (%) 2.818 4.054 0.04 42.212

Na2O (%) 2.418 1.34 0.23 0.292

SO3 (%) 1.882 2.44 - 2.17

TiO2 (%) 2.89 1.36 - 0.628

MgO (%) 0.476 1.482 1.246 7.834

MnO (%) 0.04 - 0.1 -

LOI (%) 4 8 7.8 -

4.2.2.1 Rice Husk Ash

The table shows a stark contrast between the four materials. Although all of them contain significant

amounts of SiO2, it is important to note that not all of the SiO2 will be reactive. This could be

considered as a topic suitable for further study. Furthermore, in the case of RHA, the lack of Al2O3 in

RHA would limit its capability to undergo a geopolymerisation reaction even if it wasn’t stopped by

other factors such as too much carbon content. The bonds would contain just [Si-O-Si-O] bonds.

Although these bonds are stronger, with a complete lack of [Si-O-Al] bonds, larger 3 dimensional

structure formations would be severely limited or even non-existent.

[ Note – In the following figures containing EDX information, the Carbon (C) peaks and Gold (Au)

peaks should be ignored or normalised, as they are an effect of carbon taping and gold sputtering,

discussed in section 3.5.1]

42 | P a g e

Figure 34: A) Typical Rice Husk Composition B) EDX showing high silica and oxygen peaks and

relatively low carbon peak. There is no indication of Al present

The above figure shows that the RHA has an overall higher level of silica than carbon which denotes

that the amount of unburnt carbon is not as high. The Si and C levels are relatively similar and

consistent with the peaks of PFA. However the SEM scan shows that the particles are very large as well

non spherical in shape. Even if they were pulverised and crushed after the combustion process, there

would be poorly combusted areas that would become exposed from within the larger matrix. This leads

to the conclusion that for RHA to be truly effective for use as geopolymer feedstock, they should be

crushed and pulverised before the combustion process akin to PFA to achieve the spherical

morphology. This is not practiced and could significantly increase its energy requirements. The SEM

and EDX scans in figure 35 are further evidence that the RHA has been combusted to an acceptable

level. It is possible that this morphology of Ash makes it difficult for the alkali to react due to a lower

surface area to volume ratio, which affects the initial dissolution process for geopolymerisation.

Figure 35 A) LOI unburnt carbon within RHA B) closer analysis of unburnt carbon C) EDX of LOI

carbon

4.2.2.2 Pulverised Fly Ash

Although the two PFA samples are from the same source, there is a relatively large difference in the

SiO2 percentages. The processed PFA EN450 actually has a lower amount of SiO2 but an overall

increase in other trace oxides. This could be due to sieving and separation process as larger SiO2 is

separated resulting in an overall imbalance in the total chemical composition. Ultimately, BS EN450

resulted in geopolymer samples with improved strength characteristics which show that other factors

e.g. overall particle size, particle size uniformity etc. are more significant than a small decrease in SiO2.

A B

A B C

43 | P a g e

Figure 36: A) Unregulated PFA particles B) LOI in Unregulated PFA C) EDX scan of LOI

D) Particles of PFA conforming to BS EN450 E) LOI in PFA EN450 F)EDX scan of LOI

The above illustration confirms that PFA EN450 has a significantly more uniform particle grading in

comparison to uncontrolled PFA. The majority of the PFA EN450 is 1 – 10 μm whereas uncontrolled

PFA is 3-20 μm. The effects of particle size are two-fold. Smaller particle sizes react better with the

alkali due to a larger surface area to volume ratio. However, it is inevitable that there will be unreacted

particles within the geopolymer matrix, in which case larger PFA particles act as micro-aggregates and

contribute to the overall strength. The image also shows the existence of LOI carbon matter within the

ash bulk and their status as LOI being confirmed with EDX scans. The smaller particles are still

aluminosilicates but with higher counts of oxygen which insinuates the existence of different valences

of Si in the material bulk.

Figure 37: A) Ferric Fly Ash particle B) Confirmation of ferric properties in EDX through Fe peaks

Due to the varied compositions of the two PFA and GGBS samples, there is a huge possibility that the

oligomeric bonds within their structures are not just [Si-O-Si-O-{r}] and [Si-O-Al-O-{r}], where {r}

denotes the continuation of the oligomeric chain. Both samples of PFA contain significant amounts of

Fe2O3 which could result in the existence of small amounts of poly ferro-silicon-oxo-aluminate bonds of

sequences of [-Fe-O-Si-O-Al-O-{r}]. This is assuming that the Fe atoms take up a tetrahedral position

within the sequence due to the similarity of the oxides Al2O3 and Fe2O3 and due to relative atomic

concentrations in the EDX in figure 39. There are no major studies with conclusive information on the

effects of the existence of small amounts of ferric aluminosilicate geopolymers within the matrix. BS-

EN450 in fact states a minimum amount of the combination of SiO2+Al2O3+Fe2O3 to be determined

A B C

D E F

A B

44 | P a g e

from EN 196-2 section 5.2.1, but still do not provide enough understanding into the effects of Fe2O3 on

the final properties of the geopolymer. This is a subject that is highly eligible for further studies.

4.2.2.3 Ground Granulated Blast Slag

Figure 38 A) General view SEM of GGBS particles B) Small GGBS particles C) Larger GGBS

particles D) Small ferric elements in GGBS

GGBS is a relatively uniform consisting of 3 main particle types ash shown in the above figure. The

majority of the bulk consists of 2μm small particles and 14- 30 μm larger particles. However, the larger

particles do not impair the reaction as Ca reacts with H2O as well as the Na2O to make it a lot more

reactive to the alkali activator. Small ferric elements of 200nm are also present within the GGBS which

are the possible residues of the iron slag process. The existence of Fe also suggests the possibility of [-

Fe-O-Si-O-Al-O-{r}] sequences within the subsequent geopolymer structure. Ultimately, the two

smaller particles are responsible for the faster initial reaction, due to their smaller size and their

increased chemical reactivity (ascertained from the high Oxygen count in the EDX in figure 39. The

larger particles contribute to the reaction more slowly and serve a secondary purpose as micro-

aggregate.

Figure 39 A) EDX of Large Particles in GGBS B) EDX of Smaller particles in GGBS C) EDX of

Ferrous particles in GGBS

A

B

C

D

A B C

45 | P a g e

4.2.3 Analysis of XRD patterns of Geopolymer Feedstock

In order to achieve a complete understanding of the raw materials, the XRD patterns are scrutinised.

The 2 Theta waves were matched for similar crystals diffraction to provide crystal identification. In

addition, the ‘Diffrac.suite’ software’s crystallinity calculation function is utilised to provide an

estimate of the percentage of crystallinity in the materials. Quantifying the crystallinity from the XRD

and the LOI from the EDX provides a rudimentary estimate of the amount of reactive material in the

feedstock. No further analysis of RHA is done and the material is omitted from the rest of the

investigations.

Figure 40 A) XRD of Unregulated PFA B) XRD of PFA- EN450

The XRD patterns in the above figure show the presence of Mullite and the crystallised Silicon Oxide

within the raw materials. According to the peak calculations similar to the one in figure 41, the total

amount of crystalline elements in unregulated PFA is approximately 66.2 % but reduced to 31.7% for

the PFA BS EN450. This is because the crystalline elements are larger in size than the particles and are

reduced during the sieving process. This is a primary reason why BSEN450 reacts quicker as well as

provides a better geopolymer. Accounting for the estimated LOI, the total reactive materials for

Unregulated PFA is approximately 74.2% and 35.7% for PFA EN450. This is denoted in the following

equation.

Total Unreacted Material (TUM) = Crystalline Components + Loss on Ignition Compounds (11)

TUMPFA = 66.2 + 8 = 74.2 % (12)

TUMPFA-BSEN450 = 31.7 + 4 = 35.7% (13)

In comparison, GGBS shows XRD patterns that are on the opposite end of the spectrum. The material is

highly amorphous with approximately 13.2% crystalline content. This means in terms of reactivity,

GGBS is superior to both Fly Ashes. However, an important factor that these analyses do not account

for are the sizes of the crystals. As the crystal elements essentially act as micro aggregates, a relatively

large amount of small crystals would elicit different mechanical properties in comparison to a small

amount of large crystals. The size of the crystals within the binder feedstock is a topic that warrants

further study. A balancing factor to the improved properties of GGBS is that they can cost almost the

same as OPC whereas PFA is free or significantly cheaper.

Unregulated PFA XRD PFA –EN 450

XRD

46 | P a g e

4.2.1 Oven Curing

Figure 41: XRD of GGBS and software calculations showing amorphosity

4.3 Investigation of Curing Methods in relation to geopolymer characteristics

4.3.1 Experimental Results of Oven Cured Materials

Unprocessed PFA and GGBS samples were tested for flexural and compressive strengths under

different time and temperature variables. There was a repetition of 3 samples for flexural 3 point

bending test and 6 samples for compressive testing for each sub-variables which results in a total of 108

sets of raw data. Presenting this much raw data is not practical, therefore the mean values were

determined to represent the information. Table 8 shows the mean compressive values. All the

corresponding raw data can be found in the Appendix A2.

Table 8: Compressive Strengths of Oven Cured Geopolymers

Uncontrolled PFA GGBS

Curing

Times Temperature

Compressive

load (kN)

Compressive

stress(MPa)

Compressive

load (kN)

Compressive

stress(MPa)

7

Hours

60°C 9.080 5.675 58.144 36.340

80°C 12.123 7.577 50.718 31.699

120°C 12.437 7.773 61.286 38.304

24

Hours

60°C 19.980 12.487 51.451 32.157

80°C 24.888 15.555 51.532 32.208

120°C 19.102 11.939 60.773 37.983

When analysing material strengths, it is important to consider strains in conjunction with the stress

values. However, the strain characteristic is more individualised and vary greatly between the samples.

Applying strains to these standardised mean sets of information will result in a distortion of the data and

having all the strain data is unnecessary. Instead, relevant strain graphs are highlighted within its

context in the following sections. Also, flexural Modulus, which is indicative of the strains and

brittleness or ductility of the material, is included. Table 9 highlights the flexural data of the samples.

47 | P a g e

Table 9 : Flexural Strength properties of Oven Cured Geopolymers

Uncontrolled PFA GGBS

Curing

Times Temperature

Flexural

Load (N)

Maximum

Stress

(N/mm²)

Flexural

Modulus

(N/mm²) Maximum

Load (N)

Maximum

Stress

(N/mm²)

Flex

Modulus

(N/mm²)

7

Hours

60°C 455.973 1.069 227.533 974.217 2.283 783.29

80°C 687.543 1.611 329.373 786.957 1.844 634.6067

120°C 750.433 1.759 310.640 786.957 1.889 634.6067

24

Hours

60°C 1754.430 4.112 1233.083 646.103 1.516 315.5667

80°C 1555.880 3.650 838.690 614.570 1.440 276.49

120°C 1186.040 2.780 286.050 638.307 1.496 381.55

Graph 1: Mean Compressive & Flexural strengths of Oven Cured PFA and GGBS Samples

This data initially reveals the following things:

Both PFA and GGBS geopolymers are weak in flexural strength and strong in compression in a

similar manner to concrete.

The PFA compressive strength increases by approximately 48.73% from 7 hours to 24 hours at

80°C. This is considered to be the optimum temperature. Strength gains are diminished at

120°C.

60°C 80°C 120°C 60°C 80°C 120°C

7 Hours 24 Hours

PFA Compressive 5.675 7.577 7.773 12.487 15.555 11.939

PFA Flexural 1.069 1.611 1.759 4.112 3.650 2.780

GGBS Compressive 36.340 31.699 38.304 32.157 32.208 37.983

GGBS Flexural 2.283 1.844 1.889 1.517 1.440 1.497

0.000

5.000

10.000

15.000

20.000

25.000

30.000

35.000

40.000

45.000

Max

imum

Str

ess

Val

ues

(M

pa)

Graph Highlighting Mean Maximum Stress Capabilities in relation to Curing Parameters

48 | P a g e

Although, the correlation is not very strong, GGBS slightly loses strength after 24 hours. The

flexural strength loss is approximately 21.9% at 80°C and 20.8% at 120°C from 7 to 24 hours.

The loss in compression strengths is negligible as they are less than 1% for 120°C. The

compression strength gain at 80°C does not fit into any correlation.

The optimum temperature and time for flexural strength and compressive strength are different.

The optimum curing condition for Fly Ash is 80°C at 24 hours which results in a mean

Compressive strength of 15.6 MPa.

The optimum curing condition for the best flexural strength for fly ash is 60°C for 24 hours

which provides a mean of 4.112 MPa.

The optimum curing condition for GGBS is 120°C at 7 hours which give compressive strengths

of 38.304 MPa. The Flexural strengths of the GGBS samples are negligible

The fact that GGBS has a higher compressive strength but lower flexural strength can be due to

the fact that it has more C-S-H phases with shorter oligomer chain networks. Also, the surface

cracking characteristics discussed in section 5.5 affect the flexural strength more than

compressive strength.

4.3.2 Room temperature Curing in uncontrolled conditions & inside a controlled curing cabinet

Although traditional scientific practice for engineering purposes suggests the use of a temperature and

humidity controlled curing cabinet, it is necessary to include uncontrolled samples that are exposed to

the atmosphere within the evaluation parameters. Both GGBS and PFA are synthesised in these

conditions and the results of their compressive and flexural strengths are as follows. Table 10 and 11

show the mean values and the raw data in its entirety is in the Appendix.

Table 10 Compressive Strengths of Room temperature cured Geopolymers

Maximum

Compressive load

(kN)

Compressive

stress(MPa)

Uncontrolled

Samples Cured in

Open

Atmosphere

Ground Granulated

Blast Slag (GGBS)

7 days 55.194 34.497

28 days 70.750 44.219

Pulverised Fly Ash

(PFA)

7 days 7.698 4.811

28 days 27.541 17.213

Controlled

Variables in

Curing Cabinet

Ground Granulated

Blast Slag (GGBS)

7 days 66.122 41.326

28 days 82.131 51.332

Pulverised Fly Ash

(PFA)

7 days 7.902 4.939

28 days 34.457 21.535

49 | P a g e

Table 11 Flexural Strengths of Room temperature cured Geopolymers

Maximum

Load (N)

Maximum

Stress (N/mm²)

Flex

Modulus

(N/mm²)

Uncontrolled

Samples

Cured in

Open

Atmosphere

Ground Granulated

Blast Slag (GGBS)

7 days 2376.657 5.570 1256.123

28 days 2914.773 6.832 1947.073

Pulverised Fly Ash

(PFA)

7 days 687.350 1.611 482.493

28 days 2093.777 4.907 1569.233

Controlled

Variables in

Curing

Cabinet

Ground Granulated

Blast Slag (GGBS)

7 days 2242.150 5.255 1435.723

28 days 3239.516 7.592 1978.620

Pulverised Fly Ash

(PFA)

7 days 840.040 1.969 629.717

28 days 3217.533 7.541 2188.073

Graph 2: Mean Compressive & Flexural strengths of PFA and GGBS Samples cured at low

temperatures

The following observations can be made from this data:

The strength of both geopolymers are higher when cured in the cabinet. The reasons for this are

determined to be as follows:

7 days 28 days 7 days 28 days 7 days 28 days 7 days 28 days

GGBS PFA GGBS PFA

Atmosphere Cabinet

Compressive stress 34.497 44.219 4.811 17.213 41.326 51.332 4.939 21.535

Flexural Stress 5.570 6.832 1.611 4.907 5.255 7.593 1.969 7.541

0.000

10.000

20.000

30.000

40.000

50.000

60.000

Stre

ss V

alu

es (

Mp

a)

Graph Highlighting Stress Capabilities of Samples cured exposed to uncontrolled atmoshphere and controlled curing cabinet at room temperature

50 | P a g e

o Surface carbonation occurs for Fly Ash geopolymers as discussed in section 5.1

o The C-S-H phases in GGBS are hydrated in the curing cabinet, resulting in a significant

strength gain

o The overall temperature in the curing cabinet is consistent and warmer. The

geopolymeric reaction improves with higher temperatures.

Discounting the factor of time, both the final compression and flexural strengths of the two

geopolymers are significantly higher when oven curing is not utilised. In fact, oven curing

potentially limits the final strength of the material to a lower threshold.

The flexural strengths of both geopolymers are lowered significantly when oven curing is used.

The fact that oven curing lowers the overall strength of the materials can be attributed to:

o Increased unreacted materials as the time of reaction is faster, allowing for less time for

materials to geopolymerise. Also, as capillary water is removed through evaporation as

well as dehydroxilation, the speciation equilibrium and polymerising capabilities are

diminished.

o Higher velocity of leaching causes porosity within the geopolymer matrix. Velocity of

leaching can be equated to amount of geopolymerisation reaction/ time. As the time

becomes less and the same amount of geopolymerisation occurs, a higher velocity of

water is expelled from the material matrix. This is discussed in section 5.7.

o Less nano crystallisation was observed within the Fly Ash samples in the oven heated

samples. This is discussed in section 5.4. Furthermore, this suggests that nano crystals

are a contributory factor to material strength.

4.3.3 Microwave Curing & Combination Curing

As heat was a major precursor in speeding up the geopolymeric reaction, the geopolymer mortar

samples were microwaved for different amounts of time in order to ascertain the potential for

alternative curing methods. The samples were microwaved after 3 days of setting time, and were

allowed to cool down for 5-8 hours before testing. Out of the different variables that were tested, some

settings caused the geopolymer to remain cold and unchanged. Higher power and time settings caused

the geopolymer to break apart, disintegrate etc. Table 12 shows the microwave settings that were

successful and Tables 13 show the subsequent strength characteristics.

Table 12 Results of Sample state after Microwave curing

Power

Time 350 Watts 540 Watts 750 Watts

5 Minutes X S S

10 Minutes S D D

15 Minutes D D D

Key: X = negligible effect, D = sample destruction; S = Successful

Microwaving is a more complex and unpredictable source of heating in comparison to simple

conduction in an oven. Furthermore, the complex heating characteristics are influenced by the type of

material as well as the moisture content of the materials. Due to the inherent unpredictable nature of

microwave heating, approximately 1 out 3 samples of the fly ash gained strength. The GGBS on the

other hand all gained relative amounts of strength. Furthermore, some of the PFA samples became

51 | P a g e

damaged due to disintegration of the granular bonds. The reasons behind this are discussed in detail in

section. It is important to see the detailed table of Microwave Cured sample strengths in the Appendix.

Tables 13 and 14 simplify and normalises this data. The highest strength values are chosen for the Fly

Ash samples whereas a mean is used for RHA. Although this reduces the statistical significance of the

data, it allows for an improved understanding.

Table 13 Compressive & Flexural Strengths of Microwave cured Fly Ash and GGBS

Fly Ash GGBS

350 Watts 540 Watts 750 Watts 350 Watts 540 Watts 750 Watts

Maximum

Load (N)

405.83 112.62 217.27 1751.95 1079.90 1448.28

Maximum

Stress

(N/mm²)

0.95 0.26 0.51 4.11 2.53 3.39

Flex

Modulus

(N/mm²)

135.18 124.76 71.87 1052.02 819.94 989.92

Maximum

Compressive

load (kN)

8.00 6.01 6.96 59.26 45.128 63.29

Compressive

stress(MPa)

5.62 3.7541 4.35 37.04 28.21 39.56

This shows that microwaving, at least by itself is a poor curing process for Fly Ash geopolymers.

Approximately 1 out of 3 samples disintegrated during the microwaving process. However, the

mechanics are reversed for GGBS. The flexural strength loss by this method of curing is relatively low

in comparison to oven curing. The maximum compressive strength may seem high at initial inspection,

however, GGBS typically has similarly high strengths without any curing process. It is highly possible

that the relative compressive strength remained unchanged from microwave curing.

Figure 42 A) Discolorations suggest excessive leaching through microwaved samples B) Thermal

cracking and higher levels of porosity in microwaved sample. C) Disintegrated Fly Ash sample D)

High porosity and surface damage of GGBS sample.

A B

C

D

52 | P a g e

Graph 3: Flexural & Compressive Strength characteristics of microwave cured geopolymers

One of the problems with curing with the microwave is that it reacts differently to Fly As and GGBS. It

was observed that Fly Ash samples suffered from thermal cracking, material distortion as well as

disintegration of the samples. This could be due to the extremely high velocity of leaching that the

microwave causes. It could also be due to the heat destroying the granular cohesion within the Fly Ash

matrix.

This shows that microwaving is highly ineffective for curing Fly Ash but it works relatively well for the

short duration to increase the strength of GGBS. However, in order to further understand the potential

of the microwave’s compatibility with geopolymer, the samples are microwaved for 10 minutes with

350 watts of power and then cured via oven heating at a temperature of 80°C for 7 and 24 hours. The

results are as follows:

Table 14 Compressive & Flexural Strengths of Fly Ash and GGBS geopolymer samples cured

through conduction in an oven after microwave curing at 350 Watts

Fly Ash GGBS

7 hours 24 hours 7 hours 24 hours

Maximum Load (N) 2587.135 765.216 1458.21 451.024

Maximum Stress (N/mm²) 6.0636 1.793475 3.417 1.057

Flex Modulus (N/mm²) 2115.371 498.772 1341.718 257.191

Maximum Compressive load (kN) 42.215 17.831 113.645 86.125

Compressive stress(MPa) 26.384 11.144 71.028 53.828

These results are a lot more favourable. The data suggests that microwaving prior to conduction heating

using an oven can effectively reduce the curing time of 24 hours to 7 hours to give improved

compressive and flexural strengths in comparison to un-microwaved samples. For the Fly Ash and

GGBS samples, both the flexural and compressive strengths are highly improved. However, continuing

the heating process up to 24 hours serves to diminish the strength gains of both geopolymers. The

results are illustrated on Graph 4.

350Watts

540Watts

750Watts

350Watts

540Watts

750Watts

Fly Ash GGBS

Flexural Strength (N/mm²) 0.95 0.26 0.51 4.11 2.53 3.39

Compressive stress(MPa) 5.62 3.75 4.35 37.04 28.21 39.55

0.005.00

10.0015.0020.0025.0030.0035.0040.0045.00

Stre

ss V

alu

es

Graph showing strength characteristics of microwaved geopolymers

53 | P a g e

Graph 4: Compressive and Flexural strength of Fly Ash and GGBS samples after combined

Microwave and Oven Curing

4.4 Investigation into the performance implications of different ratios of Ground Granulated

Blast Furnace Slag and Fly ash mixed in a single geopolymer mixture

The mixed geopolymers were similarly tested for their compressive and flexural strengths and these

were the results:

Table 15: Table showing Flexural & Compressive Strengths of Mixed Geopolymers

7 Hours Curing at 80°C

GGBS:FA -

100:400

GGBS:FA -

200:300

GGBS:FA-

300:200

GGBS:FA-

400:100

Maximum Load (N) 722.46 998.22 404.19 72.25

Maximum Stress (N/mm²) 1.69 2.34 0.95 0.17

Flex Modulus (N/mm²) 508.53 325.82 401.49 69.86

Maximum Compressive load (kN) 21.533 30.522 47.578 41.266

Compressive stress(MPa) 13.458 19.078 29.736 25.791

The correlation for this set of data is low. However the general trend is that the compressive strength

increases with higher levels of GGBS and flexural strength is better with increasing levels of PFA. The

reason why GGBS:FA 300-200 performed better is possibly because of the extra Al species that

become available due to the addition of PFA, which results in a better Si:Al ratio. The reasons why

there is no distinct correlation between the mixed samples is due to unpredictability in the percentage of

the mixture that becomes C-S-H and the percentage that becomes a geopolymer. This is further

discussed in section 5.3.

7 hours 24 hours 7 hours 24 hours

Fly Ash GGBS

Flexural Stress (N/mm²) 6.0636 1.793475 3.417 1.057

Compressive stress(MPa) 26.384 11.144 71.028 53.828

0

10

20

30

40

50

60

70

80

Stre

ss V

alu

es

Graph showing strength of geopolymers after combined curing

54 | P a g e

4.5 Investigation into optimisation and augmentation methods to increase flexural and

compressive capabilities of geopolymers

4.5.1 Utilising PFA BS EN450 in comparison to Unregulated PFA

First, PFA BS EN450 was evaluated for their flexural and compressive loading. In order to save time

and evaluate the most optimum condition, the BS EN450 PFA was cured at 24 hours at 80◦C. The

results are presented in table 16 with the strengths of Unregulated PFA for ease of comparison as

follows.

Table 16: Compressive Strengths of Unregulated PFA and PFA BS EN450

PFA BS-EN450 Unregulated PFA

Maximum Compressive

load (kN)

Compressive

stress(MPa)

Maximum Compressive

load (kN)

Compressive

stress(MPa)

103.215 64.509375 24.74114 15.46321

97.345 60.840625 29.82714 18.64196

88.216 55.135 28.18163 17.61352

92.231 57.644375 27.39552 17.1222

85.123 53.201875 19.89637 12.43523

94.126 58.82875 19.28742 12.05464

93.376 58.36 24.8882 15.55513

Graph 5: Graph of Comparison of Compressive strengths in Unregulated PFA and PFA BS

EN450

Table 17:Flexural Strengths of Unregulated PFA and PFA BS EN450

PFA BS EN 450 Unregulated PFA

Sample Maximum

Load (N)

Maximum

Stress (N/mm²)

Flex

Modulus

(N/mm²)

Sample Maximum

Load (N)

Maximum

Stress

(N/mm²)

Flex

Modulus

(N/mm²)

1 3465.21 8.121586 2345.174 1 1865.36 4.37 1111.84

2 3864.12 9.056531 2671.21 2 1520.02 3.56 785.83

3 4184.12 9.806531 2174.12 3 1282.25 3.01 618.41

Mean 3837.817 8.994883 2396.835 Mean 1555.877 3.646667 838.6933

1 2 3 4 5 6 7

PFA BS-EN450 Compressivestress(MPa)

64.51 60.84 55.14 57.64 53.20 58.83 58.36

Unregulated PFA Compressivestress(MPa)

15.46 18.64 17.61 17.12 12.44 12.05 15.56

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

Stre

ss V

alu

es

Compressive strengths of PFA BS-EN450 and Unregulated PFA

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Graph 6: Graph of Comparison of Flexural strengths in Unregulated PFA and PFA BS EN450

As expected, BS EN45 unregulated is superior to unregulated PFA in both compressive and flexural

strengths. The reasons have been discussed in sections 4.1 but can be summarised as follows:

There are less crystalline elements in PFA EN 450. The lack of crystallinity means more of the

raw materials will react and geopolymerise

The PFA EN450 particles are smaller, resulting in better reactivity due to larger surface area

to volume ratio. Smaller and uniform particle size also results in better compaction..

PFA EN 450 has less LOI. This also means there are less unreacted contaminants within the

geopolymer.

Even visually, the PFA BS EN450 is highly different to the normal PFA. It is less porous, has a

smoother surface and geopolymerises a lot quicker. The visual differences between the two

geopolymers are illustrated below in figure 43.

Figure 43 A) Unregulated PFA B) PFA BS EN 450

The final stage of the process involves testing the proposed optimised methods of geopolymer

synthesis. Using all the results, GGBS was determined to be holistically superior to the PFA

geopolymer. It was determine that the surface cracking of GGBS (discussed in section 5.5) was causing

1 2 3 4

PFA BS-EN450 Flexural Stress(N/mm²)

8.121586 9.056531 9.806531 8.994883

Unregulated PFA Flexural Stress(N/mm²)

4.37 3.56 3.01 3.646667

0

2

4

6

8

10

12

Stre

ss V

alu

es

Flexural strengths of PFA BS-EN450 and Unregulated PFA

A B

56 | P a g e

weakness within its structure. Therefore, impact compaction was used as augmentation methods for an

improved geopolymer. The results were successful to a certain degree. Although the flexural strength of

the GGBS was improved, the compressive strength was relatively unchanged. The results are compiled

into Graph 5. The material was still very brittle.

Graph 5: Graphs Showing Increased flexural strength and relatively low compression strength of

augmented GGBS geopolymer

5. DISCUSSION

During the project, several observations were made regarding the nature of the geopolymers. Some of

these observations were often overlooked and are critical to understanding the nature, shortcomings and

advantages of this material. Many of these concepts can be studied further and used to optimise and

augment the synthesis of AACs.

5. 1 Surface Carbonation and Loss of Cohesion

This is a phenomenon have not had much mention in the studies that are available on geopolymers. It is

assumed that this is because most geopolymers are synthesised in controlled conditions and with high

quality fly ash. However, the reality is much of the fly ash that are available for utilisation are of

unpredictable quality and are prone to defects and unexpected behaviour. Some of the samples that

were cured in the uncontrolled environment began to show a flaking behaviour that is indicative of a

loss of reaction. This is illustrated in figure 44.

Figure 44 A) Geopolymer indicating surface flaking/carbonation behaviour. B) Normal geopolymers

for comparison

A B

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Approximately 6 out of 10 of the samples that were cured outside displayed this behaviour so it can be

ascertained that it is likely to occur frequently during practical uncontrolled geopolymer synthesis.

There are two theories as to what this is.

The first hypothesis is that this is an effect of surface carbonation. Sodium hydroxide reacts with CO2 in

the atmosphere to produce Sodium Carbonate and Water. Sodium Carbonate is amphoteric, which means

it can be both acidic and basic i.e. Sodium Carbonate can react with water to give both Sodium Hydroxide and

Carbonic Acid. This is presented in the equation below.

2 NaOH + CO2 -----> Na2CO3 + H2O (14)

Na2CO3 + 2 H2O --> H2CO3 + 2 NaOH (15)

If the reaction from equation 14 occurs, the pH is lowered significantly. There is also capillary water within the

geopolymer matrix. This can cause the carbonates in the surface to react with the water further inside the

geopolymer to produce carbonic acid as shown in equation 15. The resulting NaOH would be drawn further into

the geopolymer framework while the H2CO3 remains on the surface, thus interrupting the geopolymer process.

Carbonic acid would interrupt the oligomer chains

There is a rate at which hydroxylation and geopolymerisation occurs and there is a rate at which surface

carbonation occurs. The material quality of the fly ash results in a lower rate of geopolymerisation in

relation to surface carbonation of the mixture’s alkali content. Surface carbonation will not occur if the

rate of geopolymer bond creation and dehydroxilation processes are fast and efficient which would

mean the necessary cations for equations 14 and 15 to occur would not be available.

The second theory is that the surface capillary water was separated from the geopolymer matrix for

reasons other than dehydroxilation i.e. evaporation. This results in a lack of capillary water, which

impedes the aluminosilicate dissolution, speciation equilibrium etc. essentially stopping polymerisation

activities at the surface.

The surface carbonation phenomenon was prevalent when the samples’ water to binder ratios were too

high which had a reciprocal effect of diluting the alkali content, and more leaching. Ultimately , this

behaviour significantly reduces the strength of the geopolymer samples which is evident from the

results of Tables 10 and 100 and graph 2 which show lower strengths for the uncontrolled samples in

relation to the cabinet cured ones.

The main reasons why surface carbonation can occur when a combination of these factors occur

simultaneously:

Low Alkali Modulus, which results in a lower rate of geopolymerisation

High water to binder ratio, which dilutes the alkali content

Combination of temperature, humidity and atmospheric CO2 contents which encourage

carbonation or evaporation

Ultimately, if geopolymers were to employed in the industry or practical reasons, this is a possibility

that the user should be aware of and mitigate.

5.2 Unreacted Materials

Most of the geopolymer process models highlighted in the literature review are idealised and show the

occurrence of perfect reactions. However, in reality, both Fly Ash and GGBH geopolymers contain

varying degrees of unreacted materials. Unreacted materials results in the reduction of both flexural

and compressive strengths as they cause distortions within the large 3 dimensional network bonds.

However larger unreacted materials can also act as micro aggregate within the geopolymer structure,

inadvertently adding to their strength. Some of the reasons behind unreacted materials are:

Lack of Al or Na species to complete the oligomeric chains.

Lack of reactions during the dissolution process – this can be caused by the alkali solution

58 | P a g e

being too weak, lack of capillary water

Capillary liquid not reaching the feedstock material – this becomes a major issue when the

water to solids ratio is too low. The water is absorbed quickly within the initial geopolymer and

inert material matrix and some materials do not come into enough contact with the water or

alkali activator solution.

Larger particle size of binders

Amount of inert compounds in comparison to reactive binder

Amount of non-reactive silica

Physical Irregularity of feedstock particles

Partial reactions- sometimes fly ashes are only partially reacted and due to reasons such as

premature casing by surrounding geopolymer or relative weakness of surrounding alkali, the

dissolution stays incomplete.

Figure 45 illustrates how unreacted materials can manifest itself within geopolymer matrices.

Figure 45: A) Large amounts of unreacted fly ash within geopolymer matrix B) Partially dissoluted

fly ash particle C) Unreacted GGBS particles D) Unreacted GGBS particle within geopolymer matrix

visible without microscopy

Typically, the GGBS samples contain much less unreacted materials in comparison to the PFA samples.

In the PFA geopolymers, the larger fly ash particles are more prone to being unreacted. This relates to

the lower strength of the uncontrolled PFA in comparison to the PFA BS EN450. There is another

correlation in the amount of unreacted materials in geopolymers. Geopolymers that have been

synthesised using accelerated methods e.g. microwave and oven have higher levels of unreacted

materials than materials cured at room temperature. However, this project was focused towards

A B

C D

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performance characteristics i.e. compressive and flexural strength and not enough data was acquired on

unreacted materials to substantiate this observation.

5.3 Co-existence, Interactions & Interrelationships between C-S-H and aluminosilicate

geopolymers

The existence of Calcium in the geopolymer mix results in C-S-H phases to occur alongside the

geopolymer [Si-O-Al-{r}] and [Ca-O-Si-{r}] bonds. Having these two phases within the same material

matrix can result in either cross-linking at a micro-level, cross linking of larger chunks of C-S-H and

geopolymer or phase separation and Calcium precipitates. All three types of behaviour were observed

throughout the project and they are highlighted below in figure 46.

Figure 46: A) Phase separation of CSH and pseudo-nano crystals in Geopolymer mixed at ratio

GGBS:FA 400:100. B) C-S-H- phase separation from mixed geopolymer matrix in GGBS:FA

200:300 C) Good cross-linking of GGBS and FA at a micro-level D) Lower cracking characteristics

of GGBS due to Fly Ash addition

These different types of cross-linking and phase separation characteristics show that the addition of

GGBS to PFA can result in areas of increased strengths as well as areas of inherent weakness. In order

to further ascertain the level of cross linking within the geopolymer mixture matrices, EDX Line scans

were taken across the surface of the samples. The results are as follows.

Figure 47: A) Line Scan of GGBS:PFA ratio 300:200 B) Line scan of GGBS:PFA ratio 200:300

A B

C D

A B

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The trough found in figure 47.A indicates the formation of phase separation whereas the more constant

EDX lines in figure 47.B is indicative of better cross linking throughout the entire surface even though

the line scan looks relatively uniform. The Ca requires Al to form geopolymer chains. A lower level of

GGBS and a higher level of Fly Ash introduce more Al cations into gel phase. This means that the Ca

has an increased possibility of geopolymerising by bonding with Al as opposed to forming C-S-H

bonds.

From figure 46.B and D, it is apparent that the mixed geopolymer matrix has taken up the predominant

characteristics of GGBS and micro-cracking has occurred. However, the cracking phenomenon is

relatively lower than 100% GGBS geopolymers.

As discussed in the literature review, section 2.1.2, C-S-H and geopolymer phases essentially gain

strength from opposing processes i.e. hydration vs dehydroxylation. This could result in a symbiotic

relationship between the two phases, where the dehydroxilated water from the geopolymer is absorbed

by the C-S-H to gain strength. However, there is also a possibility that the C-S-H absorbs the water

prematurely resulting in less capillary water which could halt the speciation equilibrium for

geopolymers, effectively shortening the geopolymer chains. Ultimately, there is a large level of

uncertainty to how the geopolymer and C-S-H phases will form within a matrix, as there are no solid

correlations detected from the data.

5.4 Nano Crystallisation within the Fly Ash Geopolymer Matrices

A critical observation was the presence of zones with nano-crystal formations. Some literatures have

reported the growth of zeolitic nano crystals. The observations along with an EDX scan of the

qualitative chemical analysis is shown in figure 48. There were no observable nano crystal formations

in the GGBS.

Figure 48: A) Nano crystal formation in oven cured sample microwave sample B) Nano crystal

formation in Mixed GGBS and Fly Ash geopolymer C) Very fine (1 micron) Nano crystal formation

D) EDX of nano crystal showing small Mg peaks

A B

C

D

61 | P a g e

Factors that were considered were:

The size of the nano crystals

The frequency of the nano crystals

Growth characteristics of the crystals

Whether the crystals were phase separated or cross-linked with the geopolymer

The initial theory was that these were sodalite formations. However, the EDX scan shows the existence

of Magnesium (Mg) in conjunction with the Sodium (Na), Aluminium (Al) and Silicon (Si). This poses

the question of whether the geopolymer can be dosed with additional Mg to increase nanocrystallisation

and whether the process will increase the final material strength.

There were no formations of nano crystals within the GGBS matrices. However, the mixed Fly Ash and

GGBS geopolymers showed evidence of unique formations that are similar to crystalline phases but

only in mixes where the Fly Ash percentage was higher than the GGBS percentage. The observations

made suggests that cross linking disrupts the crystallisation process.

The nano crystal formations were the highest in the PFA EN 450. The PFA EN 450 samples were also

superior in terms of flexural and compressive strength. Although enough experiments have not been

done in this project to explain the solid correlations, it can be said that the nano crystal formations work

to increase the strength of fly ash geopolymers.

5.5 GGBS cracking characteristics

The GGBS samples across all the variables displayed very low flexural strength in relation to their high

compressive strength. There are several reasons for this, but a major factor is the occurrence of cracks

and micro-cracks within the surface as well as the interior matrix. This is illustrated below in figure 49.

Figure 49 A) Cracking phenomenon within GGBH matrices B) Increased cracking in heat treated

Samples C),D) Microcracks within the matrix

This type of material is more consistent with Davidovits’ model of geopolymer framework, although it

most likely retains the phase disorder of Barbosa’s model as discussed in section 2.3.1. The surface

cracks were more severe in samples that were heat cured in the oven as shown in figure 49.B. In

addition, SEM scans show micro cracks in the geopolymer interior. There are several theories as to why

this occurs:

A B

C

D

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5.5.1 Leaching

As the geopolymer dehydroxilises, H2O is expelled from within the matrix. This expulsion of water

leaves voids within the geopolymer as they travel outwards. Normally, the geopolymer re-polymerises

by additional dehydroxilation at the surface. However, heat treating causes the surface water to

dehydroxilate or evaporate first, thus limiting the re-polymerisation capabilities. This explains the

reduced cracking on figure 49A, where the sample was cured in the oven at 80◦C for 7 hours.

5.5.2 Dehydration of C-S-H phase

It is inevitable that some of the alkali activated slag contains C-S-H phases. These phases gain strength

through hydration while heat treatment results in the loss of water through evaporation as well as

dehydroxilation. These opposite work to weaken the C-S-H phases resulting in cracking.

5.5.3 Interruption of Geopolymer 3 dimensional networks

Geopolymers gain strength due to the formation of large 3 dimensional networks as discussed in

sections 2.2 and 2.3. The existence of two different geopolymer bonds i.e. [Ca-O-Si-O-{r}] and

[O-Si-O-Al] along with C-S-H increases the likelihood that the formation of long 3 dimensional

networks are interrupted.

Using the EDX readings of the chemical constituents in section 4.1.2, it can be determined that there is

a relatively low concentration of Al2O3. This reinforces the above theory and suggests that larger 3

dimensional networks stop forming after the Al cations are utilised within geopolymeric bonds, after

which Ca-O-Si or C-S-H bonds begin forming. The lack of larger frameworks coupled with dehydration

of the material results in the microcracks

There are additional observations made on the cracking phenomenon. There was no cracking in any of

the mixed GGBS and PFA geopolymers. Furthermore, the surface cracking was minimal at 120◦ at 24

hours. This could be because cracking occurs more for when the GGBS geopolymer contains more C-S-

H phases and less for [Ca-O-Si-O-Al] or [O-Si-O-Al-O] as there are no cracking for the Fly Ash

geopolymer. This would lead to the theory that higher temperature curing leads to more geopolymer

phase formation and less C-S-H phase formation.

Ultimately this becomes a major issue as micro-cracks makes the GGBS prone to localised fracture,

which explains its low flexural stress capabilities. For further work, it would be possible that brushing

the samples with alkali at intervals and alkali immersion curing could both works to reduce or

eliminate surface cracks as well as microcracks. Mixing PFA with the GGBS also reduces the cracks

but also reduces the compressive strength in the process.

5.6 The Effect of Magnesium on Geopolymer

The trace element magnesium seems to play an interesting role within the geopolymer matrix. The

smaller size particles for GGBS, assumed to be responsible for faster reactions are rich in Magnesium,

shown by the illustrations and Mg peaks. Similarly the nano crystals in Fly Ash particles display small

Mg peaks as shown by figure 48,D. This shows the possibility that Mg has a more significant role in

geopolymerisation capabilities than previously thought. This is a topic that is highly suggested for

further studies. Quick setting magnesium phosphate cements are already commercially available, which

suggests the cementitious properties of the compound. It is possible that Mg works in a similar manner

to strengthen the oligomeric bonds or decrease the setting times.

5.7 The Effects of Liquid Expulsion from the Geopolymer

The dehydroxylation results in physical leaching of water from the geopolymer. This has a tertiary

effect of damaging the geopolymer if the velocity of leaching is too high. The velocity of leaching can

be higher if the geopolymerisation rate is increased through temperature. However, the geopolymer has

the ability to re-geopolymerise over the damaged surfaces, but only if the damage is relatively small and

the geopolymerisation capabilities of the material is high. Liquid can also be lost through evaporation

during heat treatment, this causes less surface damage but also reduces the capillary water within the

63 | P a g e

geopolymer framework. The studied effects of leaching are shown below in figure 50. The voids left

from dehydroxylation are more detrimental to flexural strength than compressive strength due to the

distortion of the stress fields during bending moments because of the residual defects.

Figure 50: A) Porosity and surface damage caused by leaching in PFA binder B) Porosity and

surface damage caused by leaching in PFA mortar.

5.8 Uneven Heating

Heat treatment in an oven is through conduction. This results in an increased level of surface heating as

opposed to the interior core. Therefore the geopolymerise is exposed to different conditions throughout

its structure, resulting in uneven hardening and composition. This can result in residual stresses during

loading.

Microwave curing effectively cures the interior of the geopolymer and when combined with the outside

temperature differential heating of oven heating, causes a relatively even level of geopolymerisation

throughout the interior layer. This is similar to normal curing, where the geopolymer has an evenly

cured matrix, resulting in superior flexural strength.

Figure 51: A) Combined Microwave and Oven cured geopolymer show relatively even characteristic

due to both interior and exterior heating gradients B) GGBS samples cured at room temperature in

cabinet C) GGBS Samples cured at 80◦C for 24 hours D) GGBS Samples cured at 120◦C for 24

hours

A B

C D

A B

64 | P a g e

Figure 51 illustrates how different curing conditions result in different heat distribution profiles which

has a knock on effect on how evenly the samples are cured. This behaviour can be attributed to why

heat treatment has a lower maximum potential strength in comparison to room temperature cured

samples. The samples possibly display the two geopolymer framework models propose by Davidovits

(2011) and Barbosa (2000) in figure 9. The darker areas represent Barbosa’s model, while the lighter,

dehydrated areas are more similar to Davidovit’s model. The compressive strengths are relatively

unaffected by having two different models within the geopolymer matrix, however the flexural

strengths are greatly affected as this sort of dual material characteristics can cause residual shear

stresses at the interface where the two phases meet.

5.9 Evaluation of Errors

The possibility of errors have been highlighted throughout the project in context and preliminary

experiments highlighted in section 3.3.8 were conducted to mitigate some of these issues. However

there are still a possibility of error within this data that can be attributed to the following factors:

1. Human Error – caused due to errors regarding the interpretation of data etc.

2. Environmental Factors – e.g. temperature humidity etc.

3. Accidental error- damage of samples through accident.

4. Instrumental error- error from test instruments e.g. faulty scales, instron etc.

The project makes an active effort to minimise these errors using systematic guidelines and

methodologies in the project. It is important to note that not all anomalous results need to be considered

as errors due to the surprising and unpredictable nature of geopolymers. Standard deviation calculations

were used on all the means and the data was deemed satisfactory except in the case of microwave cured

samples in section 4.3.3. Alternative methodologies for data representation were used for this section

and this is explicitly mentioned.

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6. CONCLUSIONS

The following conclusions have been derived from the data in the project:

1. Not all aluminosilicate will react with alkali to form cementitious materials. The reaction and

reaction quality is dependent on a multitude of factors, such as Si:Al ratios within the feedstock,

particle size of raw materials, alkali activator type, levels of LOI within the material etc.

2. Geopolymer synthesis is an inherently inconsistent process due to the variability of the

feedstock material according to their geographical location. Therefore, it is more than likely

that several experiments with similar feedstock and variables can produce highly inconstant

results. A prime example of this is the use of RHA to create geopolymers where some

experiments have reported degrees of success whereas several including the one in this project

results in critical failure.

3. Fly Ash and many other geopolymer feedstock are waste materials and not subject to quality

control. This results in low quality synthesised geopolymer. However, if the materials were

quality controlled, simple steps such as particle size reduction can greatly improve their

geopolymeric potential. In this context, Pulverised Fly Ash conforming to BS EN 450 is

superior to regular PFA even though they were from the same source (Drax Power Station).

4. The reason that not all feedstock can be geopolymerised is due to several factors such as

particle size, particle uniformity, temperature of calcination/combustion, crystallinity etc. Most

of these factors are interlinked.

5. Heat treatment and accelerated curing methods usually result in the overall reduction in

material strength, due to uneven curing, excessive liquid expulsion etc.as discussed in section

5.8.

6. GGBS is higher in compressive strength and lower in flexural strength.

7. Combined microwaving and oven heating can reduce the curing time and increase material

strength.

8. The reasons why geopolymers (using the conclusive evidence in the project) can be weakened

are:

a) Voids and matrix damage due to leaching,

b) Premature or excessive dehydration of the geopolymer which reduces the capillary

water which assists in speciation equilibrium and transportation of oligomers.

c) Interruption of geopolymer 3d chain networks due to secondary phases.

d) Unreacted materials

e) Surface carbonation

f) Uneven curing during heat treatment

g) Poor quality geopolymer feedstock. The quality of geopolymer raw materials can be

determined by:

i. Non-reactive crystalline components within the materials

ii. Unburnt carbon or organic materials

iii. Non-uniform particle composition

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iv. Excessively large particle sizes

v. Poor Si:Al ratio

h) Dehydrated C-S-H phases within the geopolymer matrix

i) Poor cross linking between C-S-H and geopolymer phases

9. Nano crystallisation within fly ash geopolymers could contribute to its strength.

These are the basic conclusions drawn from the project. However, much of the knowledge regarding

geopolymers should not be summed up as absolute and definitive statements but rather as open

discussions, questions and potential possibilities, included largely in the ‘discussion’ and ‘results’

section. Although the experiments in the project were highly intensive, the bulk of the conclusions

simply result in more questions and the need for further research and experimentation. Some possible

prospects of further work are listed below.

Investigation into the nano crystallisation particles of geopolymers and their relationship to

strength

Further scrutiny into existing research on geopolymers and what causes the high variability in

the strength of geopolymers synthesised from seemingly similar raw materials under analogous

conditions.

Microcrack mitigation in GGBS geopolymers

Investigation into C-S-H and geopolymer cross linking

Methods required to utilise RHA as a viable geopolymer. RHA is abundant in third world

countries and solid research into this material could be ground-breaking in terms of Civil

Engineering and sustainability.

Further research into geopolymer matrices with mixed raw materials

Magnesium seems to play an interesting role in geopolymers. This element is already utilised in

magnesium phosphate cements. There is a potential relationship between this element and

geopolymers that has not been looked into and presents for potential new discoveries. Common

sense and rudimentary knowledge of chemistry would suggest that magnesium doping could

potentially result in faster reactions due to its catalytic and exothermic reactive properties.

There are no major studies with conclusive information on the effects of the existence of small

amounts of ferric aluminosilicate geopolymers within the matrix. BS-EN450 in fact states a

minimum amount of the combination of SiO2+Al2O3+Fe2O3 to be determined from EN 196-2

section 5.2.1, but still do not provide enough understanding into the effects of Fe2O3 on the final

properties of the geopolymer. This is a subject that is highly eligible for further studies.

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69 | P a g e

Appendix

A1. Tables showing EDX Raw Data for chemical composition of Pozzolanic Materials

BS EN450 [Drax Power Station]

Sample 1

Sample 2

Sample 3

Sample 4

Sample 5

Mean Value

SiO2 (%) 47.49 46.4 48.88 44.82 45.01 46.52

Al2O3 (%) 27.22 28.64 25.52 27.35 26.95 27.136

Fe2O3 (%) 10.01 9.59 9.82 9.56 9.35 9.666

K2O (%) 4.52 4.39 4.62 4.92 4.73 4.636

CaO (%) 3.25 2.56 2.84 2.62 2.82 2.818

Na2O (%) 2.18 2.43 2.52 2.61 2.35 2.418

SO3 (%) 2.01 1.75 1.82 1.91 1.92 1.882

TiO2 (%) 2.51 2.84 3.08 2.99 3.03 2.89

MgO (%) 0.44 0.51 0.48 0.47 0.48 0.476

MnO (%) 0.05 0.06 0.03 0.05 0.01 0.04

Rice Husk Ash [Gloucestershire]

Sample 1

Sample 2

Sample 3

Sample 4

Sample 5

Mean Value

SiO2 (%) 90.01 89.95 90.24 91.52 90.08 90.36

Al2O3 (%) – – – – –

Fe2O3 (%) 0.02 0.02 0.01 – 0.02 0.014

K2O (%) 0.08 – 0.05 0.04 0.03 0.04

CaO (%) 0.04 0.05 0.06 0.05 – 0.04

Na2O (%) 0.24 0.21 0.19 0.25 0.26 0.23

SO3 (%) – – – – –

TiO2 (%) – – – – –

MgO (%) 1.36 1.14 1.25 1.16 1.32 1.246

MnO (%) 0.2 0.1 – 0.2 – 0.1

LOI 8.04 8.12 8.08 6.74 8.12 7.82

Trace Elements 0.01 0.41 0.12 0.04 0.17 0.15

Ground Granulated Blast Slag [Heidelberg Cement Group, Scunthorpe]

Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Mean Value

SiO2 (%) 33.59 32.82 31.67 33.86 34.21 33.23

Al2O3 (%) 12.94 14.28 11.92 12.59 11.48 12.642

Fe2O3 (%) 0.62 0.49 0.55 0.58 0.51 0.55

K2O (%) 0.44 0.48 0.39 0.41 0.49 0.442

CaO (%) 41.47 41.25 44.28 41.84 42.22 42.212

Na2O (%) 0.31 0.25 0.37 0.21 0.32 0.292

SO3 (%) 2.08 2.28 1.98 2.23 2.28 2.17

TiO2 (%) 0.66 0.61 0.66 0.52 0.69 0.628

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MgO (%) 7.89 7.54 8.18 7.76 7.8 7.834

Unregulated Pulverised Fly Ash (Hargreaves Coal Combustion Products, Drax)

Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Mean Value

SiO2 (%) 49.93 49.07 48.48 49.89 48.13 49.1

Al2O3 (%) 25.43 25.27 25.73 26 26.16 25.718

Fe2O3 (%) 10.37 11.8 11.57 9.82 10.22 10.756

K2O (%) 3.83 3.89 3.7 3.52 3.79 3.746

CaO (%) 3.91 3.6 3.92 4.34 4.5 4.054

Na2O (%) 1.43 1.18 1.46 1.29 1.34 1.34

SO3 (%) 2.02 2.2 2.61 2.46 2.91 2.44

TiO2 (%) 1.46 1.49 1.13 1.29 1.43 1.36

MgO (%) 1.62 1.48 1.41 1.38 1.52 1.482

A2. SEM and EDX results

Evaluation of Carbon Elements within RHA

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Crystallinity Calculations for FA and GGBS

72 | P a g e

A3. Raw Flexural Data for Oven Cured Samples

A3.1 Fly Ash

Flexural Strength

7 Hour Oven Cured 60°

Fly Ash Maximum Load (N) Maximum Stress (N/mm²) Flex Modulus (N/mm²)

Sample 1 560.15 1.312851563 250.99

Sample 2 315.19 0.738726563 117.67

Sample 3 492.58 1.154484375 313.94

Mean 455.9733333 1.0686875 227.5333333

Range 244.96 0.574125 196.27

Flexural Strength

7 Hour Oven Cured 80°

Fly Ash Maximum Load (N) Maximum Stress (N/mm²) Flex Modulus (N/mm²)

Sample 1 653.18 1.530891 321.85

Sample 2 582.14 1.364391 413.11

Sample 3 827.31 1.939008 253.16

Mean 687.5433 1.61143 329.3733333

Range 245.17 0.574617 159.95

Flexural Strength

7 Hour Oven Cured 120°

Fly Ash Maximum Load (N) Maximum Stress (N/mm²) Flex Modulus (N/mm²)

Sample 1 821.25 1.924805 401.24

Sample 2 761.86 1.785609 314.56

Sample 3 668.19 1.56607 216.12

Mean 750.4333 1.758828 310.64

Range 153.06 0.358734 185.12

Flexural Strength

24 Hour Oven Cured 60°

Fly Ash Maximum Load (N) Maximum Stress (N/mm²) Flex Modulus (N/mm²)

Sample 1 1982.64 4.6468125 1353.25

Sample 2 1549.21 3.630960938 1061.13

Sample 3 1731.44 4.0580625 1284.87

Mean 1754.43 4.111945313 1233.083333

Range 433.43 1.015851563 292.12

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Flexural Strength

24 Hour Oven Cured 80°

Fly Ash Maximum Load (N) Maximum Stress

(N/mm²) Flex Modulus (N/mm²)

Sample 1 1865.36 4.37 1111.84

Sample 2 1520.02 3.56 785.83

Sample 3 1282.25 3.01 618.41

Mean 1555.877 3.646667 838.6933333

Range 583.11 1.36 493.43

Flexural Strength

24 Hour Oven Cured 120°

Fly Ash Maximum Load (N) Maximum Stress (N/mm²) Flex Modulus (N/mm²)

Sample 1 2137.21 5.009086 822.19

Sample 2 1271.44 2.979938 611.87

Sample 3 951.17 2.229305 536.14

Mean 1453.273 3.406109 656.7333333

Range 1186.04 2.779781 286.05

GGBS

Flexural Strength

7 Hour Oven Cured 60°

GGBS Maximum Load (N) Maximum Stress (N/mm²) Flex Modulus (N/mm²)

Sample 1 927.16 2.17 885.67

Sample 2 1091.68 2.56 688.97

Sample 3 903.81 2.12 775.23

Mean 974.2166667 2.283333333 783.29

Range 187.87 0.44 196.7

24 Hour Oven Cured 60°

GGBS Maximum Load (N) Maximum Stress (N/mm²) Flex Modulus (N/mm²)

Sample 1 553.32 1.3 382.67

Sample 2 711.22 1.67 405.17

Sample 3 673.77 1.58 158.86

Mean 646.1033333 1.516666667 315.5666667

Range 157.9 0.37 246.31

Flexural Strength

7 Hour Oven Cured 80°

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GGBS Maximum Load (N)

Maximum Stress

(N/mm²) Flex Modulus (N/mm²)

7 hour 80 1015.25 2.379492 681.25

7 hour 80 643.11 1.507289 772.84

7 hour 80 702.51 1.646508 449.73

Mean 786.9567 1.84443 634.6066667

Range 372.14 0.872203 323.11

24 Hour Oven Cured 80°

GGBS Maximum Load (N)

Maximum Stress

(N/mm²) Flex Modulus (N/mm²)

Sample 1 428.21 1.003617 215.28

Sample 2 1001.34 2.346891 105.98

Sample 3 414.16 0.970688 508.21

Mean 614.57 1.440398 276.49

Range 587.18 1.376203 402.23

Flexural Strength

7 Hour Oven Cured 120°

GGBS Maximum Load (N)

Maximum Stress

(N/mm²)

Flex Modulus

(N/mm²)

7 hour 120 915.64 2.146031 584.17

7 hour 120 789.21 1.849711 319.52

7 hour 120 713.15 1.671445 422.73

Mean 786.9567 1.84443 634.6066667

Range 202.49 0.474586 264.65

24 Hour Oven Cured 120°

GGBS Maximum Load (N)

Maximum Stress

(N/mm²)

Flex Modulus

(N/mm²)

Sample 1 544.99 1.28 237.31

Sample 2 443.5 1.04 666.05

Sample 3 926.43 2.17 241.29

Mean 638.3067 1.496667 381.55

Range 482.93 1.13 428.74

Raw Compressive Data for Oven Cured Samples

75 | P a g e

Compressive Strength

Fly Ash 7 Hour Oven Cured 60°

Maximum Compressive load (kN) Compressive stress(MPa)

Sample 1 8.12997 5.081231

Sample 2 6.42263 4.014144

Sample 3 10.74294 6.714338

Sample 4 10.68735 6.679594

Sample 5 10.79168 6.7448

Sample 6 7.7065 4.816563

Mean 9.080178333 5.675111

Fly Ash 24 Hour Oven Cured 60°

Maximum Compressive load (kN) Compressive stress(MPa)

Sample 1 21.71937 13.57461

Sample 2 17.25132 10.78208

Sample 3 18.19857 11.37411

Sample 4 14.1832 8.8645

Sample 5 22.58494 14.11559

Sample 6 25.94067 16.21292

Mean 19.97967833 12.4873

Compressive Strength

GGBS 7 Hour Oven Cured 60°

Maximum Compressive load (kN) Compressive stress(MPa)

Sample 1 60.82108 38.01318

Sample 2 71.86731 44.91707

Sample 3 43.04732 26.90458

Sample 4 55.07631 34.42269

Sample 5 65.95573 41.22233

Sample 6 52.09433 32.55896

Mean 58.14368 36.3398

GGBS 24 Hour Oven Cured 60°

Maximum Compressive load (kN) Compressive stress(MPa)

Sample 1 56.54603 35.34127

Sample 2 47.04577 29.4036

Sample 3 52.61163 32.88227

Sample 4 43.65448 27.28405

Sample 5 53.19404 33.24628

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Sample 6 55.65275 34.78297

Mean 51.45078333 32.15674

Compressive Strength

Fly Ash 7 Hour Oven Cured 80°

Maximum Compressive load (kN) Compressive stress(MPa)

Sample 1 11.16485 6.978031

Sample 2 12.65456 7.9091

Sample 3 10.85617 6.785106

Sample 4 13.98465 8.740406

Sample 5 11.06917 6.918231

Sample 6 13.00873 8.130456

Mean 12.12302 7.576889

Fly Ash 24 Hour Oven Cured 80°

Maximum Compressive load (kN)

Sample 1 24.74114

Sample 2 29.82714

Sample 3 28.18163

Sample 4 27.39552

Sample 5 19.89637

Sample 6 19.28742

Mean 24.8882

Compressive Strength

GGBS 7 Hour Oven Cured 80°

Maximum Compressive load (kN) Compressive stress(MPa)

Sample 1 58.19854 36.37409

Sample 2 67.1431 41.96444

Sample 3 29.6733 18.54581

Sample 4 45.31821 28.32388

Sample 5 54.28874 33.93046

Sample 6 49.68401 31.05251

Mean 50.71765 31.69853

GGBS 24 Hour Oven Cured 80°

Maximum Compressive load (kN) Compressive stress(MPa)

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Sample 1 62.18765 38.86728

Sample 2 31.58161 19.73851

Sample 3 58.16565 36.35353

Sample 4 58.96137 36.85086

Sample 5 52.17935 32.61209

Sample 6 46.11762 28.82351

Mean 51.53221 32.20763

Compressive Strength

Fly Ash 7 Hour Oven Cured 120°

Maximum Compressive load (kN) Compressive stress(MPa)

Sample 1 12.69456 7.9341

Sample 2 11.96153 7.475956

Sample 3 7.94561 4.966006

Sample 4 14.72613 9.203831

Sample 5 12.14567 7.591044

Sample 6 15.14568 9.46605

Mean 12.43653 7.772831

Fly Ash 24 Hour Oven Cured 120°

Maximum Compressive load (kN) Compressive stress(MPa)

Sample 1 20.44391 12.77745

Sample 2 20.57301 12.85813

Sample 3 12.45026 7.78141

Sample 4 20.32903 12.70564

Sample 5 20.40754 12.75471

Sample 6 20.41024 12.7564

Mean 19.10233 11.93896

Compressive Strength

GGBS 7 Hour Oven Cured 120°

Maximum Compressive load (kN) Compressive stress(MPa)

Sample 1 50.71765 31.69853

Sample 2 58.14368 36.3398

Sample 3 75.21743 47.01089

Sample 4 68.6941 42.93381

Sample 5 58.31985 36.44991

Sample 6 56.62184 35.38865

Mean 61.28576 38.3036

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GGBS 24 Hour Oven Cured 120°

Maximum Compressive load (kN) Compressive stress(MPa)

Sample 1 72.82151 45.51344

Sample 2 68.63384 42.89615

Sample 3 58.94657 36.84161

Sample 4 53.24846 33.28029

Sample 5 37.67883 23.54927

Sample 6 73.3062 45.81637

Mean 60.77257 37.98286

Raw Compressive Data for Room temperature cured Samples

Unregulated Fly Ash

Maximum Compressive load (kN)

Compressive stress(MPa)

Uncontrolled Samples Cured in Ambient

Temperature and Open

Atmosphere

7 days

Sample 1 9.47315 5.92071875

Sample 2 4.86195 3.03871875

Sample 3 7.13001 4.45625625

Sample 4 6.50843 4.06776875

Sample 5 10.8963 6.8101875

Sample 6 7.31981 4.57488125

Mean 7.698275 4.811421875

Standard Deviation 2.158896786 1.349310491

28 days

Sample 1 25.471108 15.9194425

Sample 2 37.19635 23.24771875

Sample 3 22.88804 14.305025

Sample 4 35.48731 22.17956875

Sample 5 29.61773 18.51108125

Sample 6 14.58621 9.11638125

Mean 27.54112467 17.21320292

Standard Deviation 8.419542829 5.262214268

Samples Stored in

Curing Cabinets

7 days

Sample 1 12.55076 7.844225

Sample 2 6.89214 4.3075875

Sample 3 9.57467 5.98416875

Sample 4 4.69875 2.93671875

Sample 5 5.99315 3.74571875

Sample 6 7.70291 4.81431875

Mean

4.938789583

Standard Deviation 2.80616348 1.753852175

28 days

Sample 1 19.59123 12.24451875

Sample 2 25.31374 15.8210875

Sample 3 37.32656 23.3291

Sample 4 41.28374 25.8023375

Sample 5 43.59316 27.245725

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Sample 6 39.63145 24.76965625

Mean 34.45664667 21.53540417

Standard Deviation 9.691990779 6.057494237

GGBS Maximum Compressive load (kN) Compressive stress(MPa)

Uncontrolled Samples Cured in Ambient

Temperature and Open

Atmosphere

7 days

Sample 1 58.21595 36.38496875

Sample 2 76.12541 47.57838125

Sample 3 61.25828 38.286425

Sample 4 43.26991 27.04369375

Sample 5 35.68413 22.30258125

Sample 6 56.61325 35.38328125

Mean 55.19448833 34.49655521

Standard Deviation 14.20468104 8.87792565

28 days

Sample 1 74.65198 46.6574875

Sample 2 69.01853 43.13658125

Sample 3 66.4881 41.5550625

Sample 4 82.14732 51.342075

Sample 5 55.27328 34.5458

Sample 6 76.91959 48.07474375

Mean 70.7498 44.218625

Standard Deviation 9.422089297 5.88880581

Samples Stored in

Curing Cabinets

7 days

Sample 1 64.19565 40.12228125

Sample 2 66.85465 41.78415625

Sample 3 67.49523 42.18451875

Sample 4 74.39156 46.494725

Sample 5 59.91501 37.44688125

Sample 6 63.88197 39.92623125

Mean 66.122345 41.32646563

Standard Deviation 4.85928888 3.03705555

28 days

Sample 1 84.1647 52.6029375

Sample 2 79.6712 49.7945

Sample 3 91.19472 56.9967

Sample 4 87.71556 54.822225

Sample 5 64.584119 40.36507438

Sample 6 85.45319 53.40824375

Mean 82.1305815 51.33161344

Standard Deviation 9.406964022 5.879352514

Raw Flexural Data for Room temperature cured Samples

Unregulated Fly Ash Maximum Load (N)

Maximum Stress

Flex Modulus

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(N/mm²) (N/mm²)

Uncontrolled Samples Cured in Ambient

Temperature and Open

Atmosphere

7

Sample 1 743.25 1.741992188 459.32

Sample 2 517.16 1.21209375 316.88

Sample 3 801.64 1.87884375 671.28

Mean 687.35 1.610976563 482.4933

Standard Deviation 150.2525377 0.352154385 178.3328

28 days

Sample 1 2762.15 6.473789063 1921.18

Sample 2 1531.72 3.58996875 1148.67

Sample 3 1987.46 4.658109375 1637.85

Mean 2093.776667 4.907289063 1569.233

Standard Deviation 622.0666535 1.457968719 390.7993

Samples Stored in

Curing Cabinets

7

Sample 1 605.28 1.418625 710.83

Sample 2 1102.18 2.583234375 557.23

Sample 3 812.66 1.904671875 621.09

Mean 840.04 1.96884375 629.7167

Standard Deviation 249.578947 0.584950657 77.16252

28 days

Sample 1 3381.48 7.92534375 2311.76

Sample 2 2522.91 5.913070313 1833.15

Sample 3 3748.21 8.784867188 2419.31

Mean 3217.533333 7.54109375 2188.073

Standard Deviation 628.8870365 1.473953992 312.0412

Maximum Load (N)

Maximum Stress

(N/mm²)

Flex Modulus

(N/mm²)

Uncontrolled Samples Cured in Ambient

Temperature and Open

Atmosphere

7 day

Sample 1 2394.15 5.611289063 992.13

Sample 2 2914.18 6.830109375 1543.41

Sample 3 1821.64 4.26946875 1232.83

Mean 2376.656667 5.570289063 1256.123333

Standard Deviation 546.4800321 1.280812575 276.3771773

28 days

Sample 1 3531.89 8.277867188 1726.18

Sample 2 2889.53 6.772335938 2517.41

Sample 3 2322.9 5.444296875 1597.63

Mean 2914.773333 6.8315 1947.073333

Standard Deviation 604.8901755 1.417711349 498.0905647

Samples Stored in

Curing Cabinets

7 days

Sample 1 2621.64 6.14446875 1753.67

Sample 2 1894.77 4.440867188 1090.49

Sample 3 2210.04 5.17978125 1463.01

Mean 2242.15 5.255039063 1435.723333

Standard 364.497309 0.854290568 332.4309699

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Deviation

28 days

Sample 1 2961.65 6.941367188 1534.23

Sample 2 2992.89 7.014585938 1968.46

Sample 3 3764.01 8.821898438 2433.17

Mean 3239.516667 7.592617188 1978.62

Standard Deviation 454.4930439 1.065218072 449.5561145

Microwaved Samples Flexural Data

Maximum Load (N)

Maximum

Stress (N/mm²) Flex Modulus (N/mm²)

Fly Ash

350 Watts*

Sample 1 405.83 0.95 135.18

Sample 2 91.66 0.21 70.07

Sample 3 66.18 0.16 70.36

540 Watts

Sample 1 112.62 0.26 124.76

Sample 2 30.23 0.07 26.74

Sample 3 Sample Damaged

Sample Damaged Sample Damaged

750 Watts

Sample 1 80.69 0.19 30.74

Sample 2 52.46 0.12 41.58

Sample 3 217.27 0.51 71.87

GGBS

350 Watts*

Sample 1 1643.22 3.85 1026.57

Sample 2 1726.31 4.05 1073.52

Sample 3 1886.31 4.42 1055.96

540 Watts

Sample 1 1143.85 2.68 843.25

Sample 2 1058.27 2.48 801.26

Sample 3 1037.58 2.43 815.31

750 Watts

Sample 1 1448.58 3.4 950.91

Sample 2 1546 3.62 990.38

Sample 3 1350.25 3.16 1028.47 *350 watts was cured for 10 minutes. All others were cured for 5 minutes

Microwaved Samples Compressive Data

Maximum Compressive load (kN) Compressive stress(MPa)

Fly Ash

350 Watts*

Sample 1 5.07565 3.17228

Sample 2 1.16632 0.72895

Sample 3 8.98847 5.61779

Sample 4 1.84865 1.1554

Sample 5 1.43624 0.89765

Sample 6 0.98923 0.61827

540 Watts

Sample 1 3.19601 1.99751

Sample 2 6.00656 3.7541

Sample 3 1.06161 0.6635

Sample 4 0.00061 0.00038

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Sample 5 0.74596 0.46622

Sample 6 0.66232 0.41395

750 Watts

Sample 1 0.94042 0.58776

Sample 2 1.00064 0.6254

Sample 3 0.94367 0.58979

Sample 4 1.00251 0.62657

Sample 5 2.56873 1.60546

Sample 6 6.95724 4.34827

GGBS

350 Watts*

Sample 1 70.26411 43.91506875

Sample 2 69.16715 43.22946875

Sample 3 37.59632 23.4977

Sample 4 68.55912 42.84945

Sample 5 67.29642 42.0602625

Sample 6 42.68931 26.68081875

540 Watts

Sample 1 49.63273 31.02045625

Sample 2 35.18628 21.991425

Sample 3 46.26993 28.91870625

Sample 4 47.69344 29.8084

Sample 5 38.14381 23.83988125

Sample 6 53.84315 33.65196875

750 Watts

Sample 1 56.65964 35.41227

Sample 2 61.44218 38.40136

Sample 3 64.06541 40.04088

Sample 4 66.47507 41.54692

Sample 5 65.04627 40.65392

Sample 6 66.03515 41.27197