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Faculty of Engineering Department of Civil Engineering
THE MIX DESIGN DEVELOPMENT OF GEOPOLYMER CONCRETE UNDER AMBIENT CURING CONDITIONS by
Darryl Hole 13110853
October 2009
Civil Engineering Project 461 & 462 Curtin University of Technology
Mix Design Development of Geopolymer Concrete
PROJECT DOCUMENTATION SHEET
Title: The Mix Design Development of Geopolymer Concrete Under Ambient Curing Conditions
Author: Darryl Hole
Date:
19th October 2009.
Supervisor:
Dr. Natalie Lloyd
ABSTRACT: Continued increase in the focus and restriction on global carbon dioxide emissions requires the research for a cleaner alternative to the use of Portland cement. The manufacture of this product is responsible for the release of millions of tons of carbon dioxide worldwide every year. Geopolymer concrete consists of 100% fly ash replacement of the ordinary Portland cement. A binder is formed by a reaction from an alkaline liquid and the aluminium and silicon present in this fly ash. The present report deals with advancing the mix design research in geopolymer concrete applications. The laboratory work carried out for this report was based upon developing geopolymer concrete mixes that were able to be used in an industry based application, and therefore having appropriate ambient curing properties. The conditions that would be found on a large scale concrete project within industry were replicated to form a comparison. Such measures taken included no specific aggregate preparation (saturated surface dry) or steam room curing. The aim initially was to consistently produce geopolymer concrete mixes that set quickly and exhibited a 28 day compressive strength of at least 30 MPa. Previously successful geopolymer concrete mix designs were used as a basis, with additives such as silica fume and calcium hydroxide included in anticipation of developing a faster setting concrete mix with a higher early strength. Seven concrete mixes were produced during the year with varying mix design properties. Experimental results were based on compressive strength primarily, with mixes being tested at 7, 14, 21 and 28 days of age in majority of situations. Tensile strengths were also tested for the first four mixes produced.
Indexing Terms: Geopolymer, concrete, ambient curing conditions, mix design.
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Civil Engineering Project 461 & 462 Curtin University of Technology
Mix Design Development of Geopolymer Concrete
ACKNOWLEDGEMENTS I would first of like to particularly thank both my project supervisor Dr. Natalie Lloyd, and Professor Arie van Riessen from the Curtin University Centre for Materials Research, for their assistance and direction throughout the year. Further to this, the assistance of Dr. Dan Churach from the Centre for Sustainable Resource Processing and Evan Jamieson of Alcoa is acknowledged. The majority of experimental work for this research was carried out in the Civil Engineering laboratories at Curtin University, Western Australia. For this I thank the technical staff including Mr. John Murray, Mr. Mike Ellis, Mr. Ashley Hughes and Mr. Mike Appleton. I would also like to thank Ms. Monita Olivia for the support and guidance throughout the year. The progress of this research would have been delayed significantly
without
the
assistance
of
these
individuals.
The assistance in this research from the Chemical Engineering laboratory at Curtin University is also acknowledged. Thank you to Ms . Karen Hayes and Ms. Ann Carroll for their support and assistance throughout the year. Further to this, I would also like to acknowledge the assistance provided from post‐graduate students from the Curtin Centre of Materials Research, in particular Ms. Emily Carter, Ms. Melissa Lee and Mr. Ross Williams. A final thank you goes to all my friends from the Curtin University Class of Civil Engineering 2009.
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Civil Engineering Project 461 & 462 Curtin University of Technology
Mix Design Development of Geopolymer Concrete
CONTENTS PAGE PROJECT DOCUMENTATION SHEET ......................................................................................... i ACKNOWLEDGEMENTS ........................................................................................................... ii CONTENTS PAGE .................................................................................................................... iii LIST OF FIGURES ...................................................................................................................... v LIST OF TABLES ....................................................................................................................... vi 1.
2.
3.
INTRODUCTION .............................................................................................................. 1 1.1
Background ........................................................................................................ 1
1.2
Geopolymer Concrete ........................................................................................ 2
1.3
Research Aims .................................................................................................... 3
1.4
About this Report ............................................................................................... 4
LITERATURE REVIEW ...................................................................................................... 5 2.1
Ordinary Portland Cement and the Environment .............................................. 5
2.2
Alternatives to Portland Cement in Concrete .................................................... 7
2.3
Fly Ash based Concretes .................................................................................... 9
2.4
Geopolymer Concrete ...................................................................................... 11
2.5
Mix Proportioning of Geopolymer Concrete ................................................... 14
2.6
Curing of Geopolymer Concrete ...................................................................... 15
2.7
Aiding the Early Strength of Concrete ............................................................. 17
EXPERIMENTAL PROCEDURE ........................................................................................ 20 3.1
Introduction ..................................................................................................... 20
3.2
Safety ................................................................................................................ 21
3.3
Materials .......................................................................................................... 22
3.3.1 Fly Ash ............................................................................................................. 22 3.3.2 Sodium Hydroxide ........................................................................................... 22 3.3.3 Sodium Silicate ................................................................................................ 23 3.3.4 Calcium Hydroxide .......................................................................................... 23 3.3.5 Silica Fume ....................................................................................................... 23 3.3.7 Alkaline Liquid ................................................................................................. 24 3.3.8 Aggregate ........................................................................................................ 24
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3.4
Mix Design Development of Geopolymer Concrete
Preliminary Laboratory Work ........................................................................... 26
3.4.1 Mixing Procedure ............................................................................................ 27 3.4.2 Mixture Proportions ........................................................................................ 29 3.4.3 Curing of Geopolymer Concrete ..................................................................... 33 3.5 4.
Testing of Concrete Specimens ........................................................................ 34
EXPERIMENTAL RESULTS AND DISCUSSION ................................................................. 35 4.1
Introduction ..................................................................................................... 35
4.2
Experimental Results Overview ....................................................................... 35
4.3
Compressive Strength and Observations of Geopolymer Concrete Mixes ..... 40
4.3.1 Initial Geopolymer Concrete Reference Mix ................................................... 40 4.3.2 The Use of Silica Fume to Aid Ambient Curing ............................................... 43 4.3.4 The Effect of Free Water Content on the Strength of Geopolymer Concrete . 48 4.3.3 The Use of Calcium Hydroxide to Aid Ambient Curing ................................... 53 4.4 5.
Indirect Tensile Strength of Geopolymer Concrete ......................................... 63
SUMMARY AND CONCLUSIONS ................................................................................... 68 5.1
Introduction ..................................................................................................... 68
5.2
Production of Geopolymer Concrete ............................................................... 68
5.2.1 Pre‐production Issues ..................................................................................... 68 5.3
Results and Observations ................................................................................. 69
5.3.1 The Use of Silica Fume to Aid Ambient Curing ............................................... 69 5.3.2 The Effect of Free Water Content on Geopolymer Concrete .......................... 69 5.3.3 The Use of Calcium Hydroxide to Aid Ambient Curing .................................... 70 5.3.4 Other Observations During Research ............................................................. 70 6.
RECOMMENDATIONS ................................................................................................... 72
REFERENCES ......................................................................................................................... 75 APPENDIX A .......................................................................................................................... 79 APPENDIX B .......................................................................................................................... 81
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LIST OF FIGURES Figure 2.1: Compressive Strength of 30% Fly Ash Substituted Concrete ....................... 18 Figure 3.1: Grading Curve of Combined Aggregates ....................................................... 25 Figure 3.2: Pan Mixer Used for Production of Concrete ................................................. 29 Figure 3.3: Setting of Wet Geopolymer Concrete........................................................... 29 Figure 3.4: Ambient Curing of Geopolymer Concrete .................................................... 33 Figure 3.5: Rough Surface of Cured Geopolymer Cylinder ............................................. 34 Figure 4.1: Compressive Strength of all Carried Out Mixes ............................................ 38 Figure 4.2: Indirect Tensile Strength of Mixes One to Four ............................................ 39 Figure 4.3: Compressive Strength of Mix One ................................................................ 41 Figure 4.4: Efflorescence Formed on the Outside of Cylinders ‐ Mix One at 14 days .... 42 Figure 4.5: Efflorescence on the Outside of Cylinders ‐ Mix One at 28 days .................. 43 Figure 4.6: Expansion of Mix Two (right) Relative to Mix One (left). ............................. 45 Figure 4.7: Expansion of Mix Two Cylinders ................................................................... 45 Figure 4.8: Compressive Strength for Mixes One and Two ............................................ 46 Figure 4.9: Excess Water in Geopolymer Concrete ........................................................ 51 Figure 4.10: Compressive Strength of Mixes One and Four ........................................... 52 Figure 4.11: Compressive Strength of Mixes Three and Four ........................................ 55 Figure 4.12 : Rapid Setting Effects and Efflorescence on Mix Three Cylinders .............. 56 Figure 4.13: Cross Section of Small Cylinder ‐ Mix Three ............................................... 56 Figure 4.14: Mix Six at Two Hours after Pouring ............................................................ 59 Figure 4.15: Mixes Seven (Left) and Six (Right) at One Hour after Pouring .................... 60 Figure 4.16: Compressive Strength of Mixes Five, Six and Seven (MPa) ........................ 61 Figure 4.17: Efflorescence Beginning to Form after De‐moulding ‐ Mix Five ................. 63 Figure 4.18: Indirect Tensile Strength of Mixes One to Four .......................................... 65
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Mix Design Development of Geopolymer Concrete
LIST OF TABLES Table 3.1: Grading of Combined Aggregates .................................................................. 26 Table 3.2: Free Water Content of Mixes One and Two .................................................. 31 Table 3.3: Mix Design Summary of Carried Out Research .............................................. 32 Table 4.1: Mix Design One .............................................................................................. 40 Table 4.2: Compressive Strength of Mix One (MPa) ....................................................... 41 Table 4.3: Mix Designs One and Two .............................................................................. 43 Table 4.4: Compressive Strength of Mix Two (MPa) ...................................................... 46 Table 4.5: Mix Design Four .............................................................................................. 48 Table 4.6: Free Water Content of Mix One ..................................................................... 49 Table 4.7: Free Water Content of Mix Four .................................................................... 50 Table 4.8: Compressive Strength of Mixes One and Four (MPa) .................................... 52 Table 4.9: Mix Design Three ............................................................................................ 53 Table 4.10: Compressive Strength of Mix Three ............................................................. 55 Table 4.11: Mix Designs Five, Six and Seven ................................................................... 58 Table 4.12: Compressive Strength of Mixes Five, Six and Seven (MPa) ......................... 62 Table 4.13: Indirect Tensile Strength of Mixes One to Four ........................................... 65 Table 4.14: Relationship Between Compressive and Tensile Strength .......................... 66
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1. INTRODUCTION
1.1
Background
Concrete is the most widely used structural material in the world, and therefore the production of it and its constituents are greatly relied upon in industry. The manufacture of ordinary Portland cement (OPC), the primary binder in a conventional concrete mix however, is well known for its environmental impacts. Approximately 1.35 million tons of greenhouse gases are emitted through the manufacture of OPC each year and therefore raises the concern for a cleaner alternative to be developed (Malhotra 2002). Continued increase in the focus and restriction on global carbon dioxide emissions requires the research for a cleaner alternative to the use of Portland cement. Concrete made using a binder that does not present such environmental issues has been investigated in the past using fly ash and an alkaline solution. The method of substituting fly ash for portions of cement in a concrete mix has been established and is well documented (Huntzinger and Eatmon 2009). However, the use of 100% fly ash made concrete is limited in industrial applications, partly due to the cost of fly ash and, in contrast, the availability and convenience of cement. Research fields though are well interested in the production of concretes with 100% fly ash because of the sustainability of using this industrial waste product for a construction material. This report investigates the effects of altering the mix design and properties of geopolymer concrete. Additives such as silica fume and calcium hydroxide have been used in anticipation of aiding the ambient temperature curing properties of the concrete. Further to this, properties of the concrete such as the effect the free water content has on the final strength have also been investigated. This research deals exclusively with the ambient curing of geopolymer concrete. This is to simulate site conditions that a concrete structure may be exposed to, and therefore investigate the feasibility of in‐situ cast geopolymer concrete.
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Mix Design Development of Geopolymer Concrete
1.2
Geopolymer Concrete
The investigation into the use of fly ash‐based geopolymer concretes has increased since 2000 due to the environmentally sustainable option of using an industrial waste to form a useful material. Research and industry groups are excited about the prospect of a concrete made from industrial by‐products that would therefore negate the need for waste disposal of these materials. The development of geopolymer concrete mix design has been carried out previously at Curtin University, Western Australia. Hardjito and Rangan (2005) investigated the effects of aspects such as alkaline parameters, water content and curing conditions in “Development and Properties of Low‐Calcium Fly Ash‐Based Geopolymer Concrete”. Further to this, the production and testing of low scale beams has also been carried out (Hardjito and Rangan, 2005). The physical properties of geopolymer concrete such as creep, drying shrinkage and sulfate and acid resistance were also researched at Curtin (Wallah and Rangan, 2006). The Centre of Materials Research at Curtin has investigated the use of including chemical additives to geopolymer pastes in order to increase the early strength under ambient curing conditions. This paste is essentially an aggregate‐less concrete that is made in much smaller quantities than the research for this current report. The mix design properties of geopolymer concrete were investigated by scaling up the production of geopolymer paste in the form of quantity and by adding aggregate to the product. The concrete produced consisted of 77% by mass of aggregate, which is bound by a geopolymer paste formed by the reaction of the silicon and aluminium within the fly ash and the alkaline liquid made up of sodium hydroxide and sodium silicate solutions. Specimens produced were cured only under ambient conditions within the Civil Engineering laboratory at Curtin University. Darryl Hole
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Civil Engineering Project 461 & 462 Curtin University of Technology
1.3
Mix Design Development of Geopolymer Concrete
Research Aims
The present study aims to carry out a scaling up exercise of past work with geopolymer pastes and mortars that was undertaken by the Materials Research Centre at Curtin University, and therefore furthering the mix design knowledge of geopolymer concrete applications. This exercise focuses on progressing towards the production of a geopolymer concrete with additives included in the mix designs to develop a quicker setting concrete mix with a higher early strength. It must be noted however, that the mixing procedure differs greatly between the paste and concrete, as the handling time and the quantity of material produced is much greater in the production of geopolymer concrete. The practical research for this report differs to many previous fly ash based concrete reports, as the fly ash based concrete is mixed using zero ordinary Portland cement. Although the production of fly ash does produce large amounts of carbon dioxide through the burning of coal, the use of it in concrete is seen as a sustainable option that negates the need for disposal of this waste. The aim initially was on achieving appropriate mix designs and a mixing procedure that would consistently provide a 28 day compressive strength of at least 30 MPa. A conventionally made geopolymer mix utilizing just sodium silicate and sodium hydroxide with no mix additives was made initially to act as a reference mix. All subsequent mixes produced were based primarily on this reference mix with materials either substituted in for fly ash or just as an additive. The mix designs are judged upon their compressive and tensile strengths accordingly. The main aims of the laboratory research for this thesis included: -
To familiarize with the making of fly ash based geopolymer concrete.
-
To develop an understanding of an appropriate mix procedure in the production of fly ash based geopolymer concrete.
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-
Mix Design Development of Geopolymer Concrete
To develop an understanding of appropriate mix proportioning in the production of fly ash based geopolymer concrete.
-
To observe the strength development of fly ash based geopolymer concrete under ambient curing conditions.
1.4
About this Report
This report is structured as follows; Chapter 2 presents a brief review of selected literature related to the environmental tribulations of ordinary Portland cement, the alternatives to mixing concrete utilizing OPC, and the previous research conducted in the use of fly ash‐based geopolymer concrete. The general background of geopolymer concrete production is investigated, along with mix proportioning, mixing procedures and curing properties. Chapter 3 describes the experimental process in conducting the research for this report. Attention is paid to the materials used, mix designs, mixing procedures, curing conditions and the method of testing the geopolymer concrete specimens produced. Chapter 4 presents and discusses the results of the research, drawing a comparison between the final strength and strength development of geopolymer concrete with varying mix designs cured under site conditions. Any observations noted during the experimental research being carried out are also stated, with explanations and justifications to clarify any unknowns. The present report’s summary and conclusions are included in Chapter 5. This section is based upon all results and observations discovered in the research throughout the year. Further to this, a list of recommendations is given in Chapter 6, detailing suggested steps in furthering the research in the mix design development of geopolymer concrete. Concluding this report is a list of references and all relevant appendices.
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Mix Design Development of Geopolymer Concrete
2. LITERATURE REVIEW Chapter 2 presents a background into the environmental impact of the manufacture of ordinary Portland cement (OPC) and other suggested alternatives to the use of cement. Research has been undertaken into the previous use of geopolymer concrete, and the mechanical properties resulting from mix design properties and different methods of curing. Research was also conducted into the sustainable qualities of the use of production by‐ products in the manufacture of geopolymer concrete.
2.1
Ordinary Portland Cement and the Environment
Disregarding water, concrete is the most widely used material in the world. Unfortunately, the manufacture of the integral constituent, ordinary Portland cement (OPC), proves to be unsustainable with regards to it’s the environmental impact due to the emissions of carbon dioxide (CO2) and large requirement of energy in the production procedure. However, due to the high demand for structural materials, the requirement for cement and concrete will be substantial until an equally effective and economic alternative is available, and therefore deeming it necessary to either overlook the environmental impact of standard concrete production, which is highly unlikely, or develop alternatives that will decrease these effects. Concrete International recognizes the situation at hand, and the article titled “Sustainable Development and Concrete Technology” quotes the current issues. ‘The contribution of ordinary Portland cement production worldwide to greenhouse gas emissions is estimated to be approximately 1.35 billion tons annually or approximately 7% of the total greenhouse gas emissions to the earth’s atmosphere (Malhotra 2002)’. The reason large amounts of CO2 are released during the manufacturing of cement is due in part to the immense heat that is required. The kiln used is heated to
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temperatures of up to 1400°C, and therefore energy requirements to yield this temperature account for approximately half of the released CO2 in the production of cement, the second half is released during the calcination process in which calcium carbonate is reduced to calcium oxide (Hendriks et al. 2003).
The production of cement alone accounts for approximately 5% of the worlds carbon dioxide emissions. According to the International Energy Agency, approximately 0.81 kilograms of CO2 is generated per kilogram of cement produced annually throughout the world. The production of cement also produces millions of tons of Cement Kiln Dust (CKD) which is harmful to the respiratory system (Hendriks et al. 2003). Due to the increasingly popular requirements for sustainable development within industry, research into methods of reducing greenhouse gas (GHG) emissions while maintaining the structural convenience of concrete has been carried out. The US Concrete Industry has addressed the current GHG emissions incorporated with the production of concrete in “Vision 2030: A Vision for the US Concrete Industry.” In this, focus is put on making concrete an environmentally friendly construction material whilst maintaining its status as the mostly widely used material in industry (Mehta 2001). In recent times, researchers have attempted to produce concrete as an environmentally friendly product by replacing amounts of ordinary Portland cement from the mix with industrial by‐products such as fly ash and blast furnace slag. Global warming continues to be a current concern within the public awareness, and what effects it will have on the human population in day to day life in the future. The continuing release of GHG through the burning of fossil fuels and land use change further increases the risk on earth of a rise in average surface temperatures and the flow on effects that it will have on sea levels. Huntzinger and Eatmon (2009) uses life‐cycle analysis (LCA) to evaluate the environmental impacts and therefore the ‘global warming factor’ of the manufacture of Portland cement and three other technologies. The three alternatives discussed Darryl Hole
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include, “blended cement (natural pozzolans), cement where 100% of the CKD is recycled into the kiln process, and Portland cement produced where CKD is used to sequester a portion of the process related to CO2 emissions.” It was discovered that the most environmentally solution of the three was the blended cement. Substituting natural pozzolans for OPC will effectively reduce the ‘global warming factor’ of the product proportional to the amount replaced. In reality though, it will be seen that in industry, because of the consistent high demand of cement, most kilns are operating at above their effective capacity. This therefore means that using ‘blended cement’ in industrial applications would not be likely to reduce the net emissions of carbon dioxide (Huntzinger and Eatmon 2009). As can be gathered through this review, most of the previous research available looks at the current situation of cement production and the damage it is causing to the atmosphere. The next logical step into this investigation is to either prevent this damage or offer alternatives to concrete using ordinary Portland cement. It is in the opinion of many, that the use of ordinary Portland cement in concrete is not going to slow down, despite the ongoing research into alternative binders. It would therefore be a sustainable decision to investigate further into the mix design of concrete whilst minimizing the volumes of OPC being used. It would be seen that if the use of OPC is going to remain strong over the coming decade, keeping its use to a minimum whilst retaining both durable and workable concrete would provide great benefit to the GHG emissions.
2.2
Alternatives to Portland Cement in Concrete
As the growth in the world of infrastructure continues, the demand for concrete that is usable in an industrial application will be high for the foreseeable future. Concrete using binders other than ordinary Portland cement that leave a smaller carbon footprint, are therefore heavily investigated within the cement and concrete industry. The use of these concretes within an industrial application is limited however, and it
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would be fair to say that concrete made without cement has not made a significant impact into the construction industry yet. The research into environmentally sustainable concretes is however not limited to replacing the OPC. Suggestions have been put forward into forming ‘blended cement’ where products such as pozzolans are added to OPC in order to reduce the environmental effect of the concrete. Concrete that has had OPC replacement commonly consists of industrial by‐products such as coal fly ash or ground blast furnace slag (GBFS). It has been suggested (Damtoft et al. 2008) that the cement and concrete industry is working positively in the hope of achieving sustainable solutions in environmentally friendly concrete. He suggests that using hydraulic binders, those which are based on Portland cement, have an incredible impact on the environment and sustainable development due to being easily the most widely used construction material worldwide. Damtoft et al. also discussed in which ways the industry is acting in order to provide sustainable development within the field of reducing the environmental impact of concrete production. The techniques discussed are as listed below: -
The addition of extra materials to the list of approved supplementary cementious materials (SCM’s) within current standards.
-
Allowing more complex composite cements within current cement standards. Greater attention to be paid to blending properties.
-
Development of methodology for the design of optimal performance for the use of blended cements.
Damtoft et al. (2008) clearly supports the use and further development of blended cements in industry, which directly reduces the CO2 emissions to the environment through replacing volumes of OPC. The current amount of research into the use of fly ash as a hydraulic binder is far from limited. The use of coal fly ash in concrete has been investigated for years with very Darryl Hole
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positive results for its use in industry. Unfortunately, apart from this research and a small amount of testing using blast furnace slag, there is little information regarding the use of other industrial wastes to substitute of ordinary Portland cement in concretes. The development of a concrete mixture using a new OPC substitute would greatly progress the process of producing an environmentally friendly concrete. This coincides with Damtoft’s discussion in which additional materials should be investigated into their effectiveness of working as a supplementary cementious material.
2.3
Fly Ash based Concretes
The production of concrete that incorporates the complete replacement of OPC with industrial by‐products such as coal fly ash has been developed, yet it is far from fully established. The use of waste products promises to be a sustainable option in any case, as it negates the need for disposal of these materials, which can become both costly and of an environmental concern. Fly ash is a residue that is formed during the combustion of coal. In the past fly ash was released to the atmosphere during production, but in recent times as research presents that this previously useless by‐product can be used for other applications, the capture of it has been instigated. Fly ash’s main constituents are amounts of silicon dioxide (SiO2), aluminium oxide (Al2O3) and iron oxide (Fe2O3). Fly ash that is destined for experimental use can be examined in more depth in order to determine its chemical composition. X‐ray Fluorescence (XRF) analysis is used to determine the proportions of materials present within the fly ash. The use of fly ash for concrete production is a popular option in theory, as it is available abundantly worldwide. The use of 100% fly ash based concrete however, is limited to date in structural uses. The Ash Development Association of Australia (ADAA) states that in 2007, Australia alone produced 14.5 million tons of fly ash, and that only 1.50 million tons (11%) was used in high valued applications such as cementious or concrete products (Coal Ash Matters 2009). Darryl Hole
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Though the practical use of 100% fly ash based in concrete is limited in structural applications, frequent laboratory work has been conducted into the investigation of mechanical properties of fly ash based concrete. A recent study at Montana State University, USA, discussed the method of preparation of fly ash based concrete. It should be noted that in their experiments, class F fly ash is utilized, in which the chemical reaction occurring is the hydration of water with the calcium in the fly ash (Cross, Stephens and Vollmer 2005). The major hurdle into the use of fly ash based concrete that was noted was the rapid rate of chemical reaction that occurs once water is added to the mix. It was discovered that the use of a retarder in these trials were essential, and that in the case that there was no retardation, hydration would occur immediately and that the concrete would ‘flash set’ in a matter of minutes. It was recommended to the researchers to attempt the use of borax to delay any setting of the mix, as has been discovered effective with OPC concretes. It then became an aim of the trials to gain an understanding of under which conditions the borax needs to be present to extend the placement time before setting (Cross, Stephens and Vollmer 2005). It was discovered that the effectiveness of borax was not determined equivalently to that in OPC based concretes. Rather than a simple relationship connecting the amount of borax required to the amount of cement used, it was determined that the effectiveness of the admixture was dependant on its physical properties and the rate at which it is added to the mix. When the relationships used for OPC based concretes were attempted to correspond to fly ash based concrete, it was found that the predicted setting times were largely inaccurate (Cross, Stephens and Vollmer 2005). The development of fly ash based concrete has a promising future. Laboratory research carried out worldwide are consistently yielding compressive strengths equal to or greater than equivalent mix designs utilizing Portland cement. In the above mentioned report, Cross and Stephens also discovered that fly ash based concrete
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gained strength at a rate equal to or faster than OPC concretes of similar mixes (Cross, Stephens and Vollmer 2005). One a physical level, it is thought that the rounded shape of the fly ash particles maintain the workability of the concrete prior to setting. Fly ash particles are also smaller in size than that of OPC and therefore produce and more compacted a denser concrete set. It should be recognised that the next step in the development of fly ash based concrete would be research into its durability as a structural material. To date, concretes with 100% fly ash have been limited to use on low strength applications. Before this material is to be introduced as a structurally safe and durable material though, development of mixes, prediction and control of strength, workability and set times must be obtained. The use of 100% fly ash concrete in these environments would require the knowledge that it develops soundly under site conditions, such as curing under ambient temperatures.
2.4
Geopolymer Concrete
Davidovits first proposed that concrete could be made with a hydraulic binder, where in which the silicon and aluminium from the inclusive fly ash would react with an alkaline liquid. The reaction that occurs, polymerization, is significantly faster due to the alkaline conditions. The resultant three dimensional structures consisting of Si‐O‐ Al‐O bonds is a polymeric chain (Davidovits 1999). The most conventional method of producing geopolymer concrete is the incorporation of a reaction between the fly ash and an alkaline solution formed from a metal hydroxide and silicate that forms an alkaline liquid. It is not uncommon for the constituents of the geopolymer alkaline solution to be sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). It is common practice in the mix design of geopolymer concrete, that aggregates occupy anywhere from 70 – 80% in volume by mass.
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Johnson (2008) states that, “Geopolymer consists of silicon and aluminium atoms bonded via oxygen into a polymer network. Geopolymers are prepared by dissolution and poly‐condensation reactions between alumino‐silicate binder and an alkaline silicate solution such as a mixture of an alkali metal silicate and metal hydroxide.” Again, in the research carried out by Johnson it was noted how quickly the chemical reactions take place with the addition of the alkaline solution to the fly ash in the mixing process, therefore limiting the able handling time before setting begins to occur. Therefore, an aim of the research became that of determining a mixing procedure that would enable sufficient handling time whilst maintaining a concrete of workable consistency and could be used in industrial applications. It was discovered that if a preliminary mixture of the total aggregate volume and the metal hydroxide solution were formed first, and then the fly ash added, no reaction would take place until the metal silicate solution was added to the mix. This process of mixing generally was found to extend handling time up to 45 minutes consistently, and therefore provide a more suitable application for use on site (Johnson 2007). Hardjito and Rangan (2005) concluded that it was favourable to mix the sodium hydroxide and sodium silicate solution at least one day prior to adding it to the dry materials. This was carried out under recommendation from Davidovits, who observed that when this was carried out, bleeding and segregation of the concrete no longer occurred. This combination was then added to the dry mixture. This is in contrast to advice given to the author of this report by Curtin post graduate student M. Olivia (personal communication, 25 May, 2009). She advised that the mixing of sodium hydroxide and sodium silicate solution should occur on the day of mixing the concrete, otherwise the solution may solidify and the production of concrete will be extremely difficult. She stressed that research has shown experiences of the alkaline solution crystallizing before it is to be added to the dry materials, therefore deeming the pour to be a failure. Situations had also occurred in which the concrete mix had hardened to a point that it is unable to be poured whilst still in the mixer. Darryl Hole
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Sofi et al. (2007) had similar findings to Johnson (2007) in the research paper entitled “Engineering Properties of Inorganic Polymer Concretes (IPCs).” In it, he praised the use of concrete utilizing materials other than OPC in terms of their mechanical properties. He suggests that inorganic polymer concretes comprising of materials such as fly ash, can exhibit superior mechanical properties to ordinary Portland cement concretes. This is heavily dependent though on the chemical composition of the fly ash used. The hurdle though, still stands at managing the quick setting nature of geopolymer concrete, and maintaining the concrete’s ultimate characteristics such as strength and durability is a prime concern when introducing mixture additions in order to retard the rapid setting. The fast setting characteristic of IPC, Sofi writes, can be taken as an advantage or disadvantage. Though the setting of IPC’s can occur rapidly, and the polymerization reaction occurs straight away, it continues over a length of time which extends beyond seven days. This contributes to the strength gaining characteristic of geopolymer which has a distinct behaviour in comparison to OPC based concretes. It was found within the IPC mixes that between 7 and 28 days, a development of compressive strength occurred of up to 15 MPa (Sofi et al. 2007). The use of Geopolymer, to date has only been limited to low strength applications. This seems to remain the case, when in fact a lot of researchers praise the characteristics of the product. Johnson (2007) writes in the aforementioned report that the heat, fire and acid resistance of geopolymer concrete will be greater than that of Portland cement based concrete. Johnson used the geopolymer’s fast setting characteristic as an advantage, as he proposed that it be used in the production of concrete pipes and poles. Such manufacturing requires the use of concrete with zero slump, and processes that involve centrifugal stages, roller suspension and vertical casting. It was discovered that by manipulating the mix design, and therefore producing ‘no slump’ concrete, it was possible to utilize geopolymer concrete in preparing pipes and other consolidated moulded products. Another issue that Johnson addressed in the use of geopolymer concrete was the well known rapid strength gain. He stresses that the time between placement and then Darryl Hole
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setting, and therefore losing any plasticity, must be long enough to incorporate any required transport of the product. This becomes important because if the concrete is at its hardened state during transport, cracking is likely to occur and therefore a reduction in the final strength will be experienced. To overcome the associated problems of rapid strength gain will require control of the setting times of the concrete, or reverting back to casting products on site or in‐situ, therefore making it unlikely to have the availability of steam rooms or kilns available for the particular application.
2.5
Mix Proportioning of Geopolymer Concrete
The aim of the research conducted for this report was to further the mix design of geopolymer concrete by improving its ambient curing properties. Therefore, the mix proportioning carried out for this research was in the form of using additives to the geopolymer concrete mix, rather than re‐establishing standard mixes again. This meant that initial mix designs were based largely upon previously successful geopolymer concrete mixes that had already yielded substantial results. It was found by Hardjito and Rangan (2005) that consistent results were gained upon keeping the alkaline solution at a sodium silicate‐to‐sodium hydroxide ratio of 2.5. This ratio was favoured over a lesser one because of the reliable results that it yielded, and because the sodium silicate solution is considerably cheaper than the sodium hydroxide pellets. A general proportion of alkaline solution‐to‐fly ash was settled upon at approximately 0.35. Upon investigation of the affects of the concentration of the sodium hydroxide solution, it was found that in mix designs of exact proportions, the mix with the higher concentration in molarity of the sodium hydroxide solution would yield a higher compressive strength. This was examined through the use of varying the molarity of the solution between 8 molars and 14 molars in mix designs of exact proportions. Liu reports how geopolymer concrete can be produced by using other industrial wastes such as bauxite residues. It is noted how past research into the re‐use of these Darryl Hole
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products such as bayer liquor has been used to produce materials such as ceramics, cements, clay bricks and glazes. In the production of unsintered construction and building products, Liu suggested that the optimal proportions of raw materials show following: Bauxite Residue
: 25 – 40%
Fly Ash
: 18 – 28%
Sand
: 30 ‐35%
Lime
: 8 – 10%
Gypsum
: 1 – 3%
Portland Cement
: 1%
This composition has been used to produce building materials that has reached the 1st grade of Chinese standards for a brick (Liu et al. 2009).
2.6
Curing of Geopolymer Concrete
The present report deals with the ambient curing of geopolymer concrete, yet changing the method of curing has previously researched in geopolymer concrete. The ability of concrete to cure at ambient temperatures becomes useful in industrial applications when concrete is cast in‐situ or on site, as the availability of a kiln, especially on larger scale projects, is unlikely. The conditions under which geopolymer concrete is cured directly relates to the durability and strength of the mix, as displayed by Hardjito et al. (2004). His results found that the curing of concrete at higher temperatures, up to 60°C, yielded a higher compressive strength than at a lower temperature, yet any increase in curing temperature over this threshold made no substantial difference to its strength. A proportional relationship was discovered between the length of curing time and compressive strength. The rate of setting of geopolymer concrete is well documented, yet it is likely that these cases were resultant upon short curing times. Hardjito et al. discovered the fast rate of polymerization only stalled the strength gain when the concrete was cured for short times, such as 24 hours. This contrasts with the strength development behaviour of OPC based concretes, which undergo a hydration process Darryl Hole
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over a length of time when being steam cured, therefore increasing in strength with age. This strength development over time can be achieved with geopolymer concrete when curing time is extended. It was discovered that as the curing time increases in the range of 6 hours to 96 hours (4 days), the polymerization process is improved and therefore yields a higher compressive strength. It is noted though, that the strength increase after 48 hours of steam curing is not significant. It is recommended that during curing of geopolymer concretes at elevated temperatures, samples should be wrapped and then sealed, this should be present for the duration that the samples are being cured at temperatures up to 100°C. This precaution has been suggested in order to prevent excessive evaporation of the samples during curing. This would cause a less dense concrete with a weaker compressive strength. It was also discovered that in wrapping the geopolymer concrete specimens, the mix did not harden immediately under ambient conditions. At room temperatures of below 30°C, hardening of the concrete did not occur for at least 24 hours (Hardjito and Rangan 2005). Whilst interesting to know that it is possible to achieve a time‐dependant, strength‐ development behaviour with geopolymer concrete, in industry, it would not be very applicable. Rarely would you see concrete cast and then kept under controlled curing conditions for any more than 24 hours, and if it was cast in situ, all curing would be under ambient conditions. In a rare situation where formwork turnover is not as critical in a precast concrete environment, it would be possible to achieve an extended curing time under controlled conditions. Wallah and Rangan (2006) reported how the strength development of geopolymer concrete varied with the conditions under which they were cured. Three batches of the same mix were produced at varying times in the year; May, July and September 2005, and cured under ambient conditions within the laboratory. The cylinders were released from their moulds one day after casting. It was discovered that specimens cured under ambient conditions exhibited significantly lower 7 day compressive strengths than those cured under elevated temperatures for the first 24 hours. Darryl Hole
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It was reported that under ambient curing conditions of geopolymer concrete, the 7th day compressive strength and subsequent strength gain with respect to age lies dependent upon the average ambient temperature at the time of curing. As the ambient temperature at casting increased, as did the 7th day and subsequent compressive strength’s tested at later dates. The compressive strength of the geopolymer concrete during July exhibited a 28 day strength of 31 MPa in comparison to 47 MPa for the mix poured in May. The average temperature experienced within July 2005 ranged from 8°C to 18°C, and 18°C to 25°C in May (Wallah and Rangan 2006).
2.7
Aiding the Early Strength of Concrete
The reaction between elements in fly ash based concretes is a slow process, and therefore only contributes to the strength development at later dates of age. This causes a problem in the utilization of fly ash concrete in ambient cured precast concrete applications, due to the low early strength and formwork turnover routines. Previous research in OPC based concretes has indicated that the inclusion of silica fume and hydrated lime (calcium hydroxide) yields positive results in increasing the early strength of concrete, as well as having the concrete mix set quicker. Barbhuiya et al (2009) investigated the use of including silica fume and calcium hydroxide to concretes with a fly ash substitution of 30% of the ordinary Portland cement based content. Silica fume was added to the mix at 5% by mass of the cement content as a final addition when mixing the concrete. Hydrated lime on the other hand was substituted at a rate of 5% by mass of the total cementious materials. In order to investigate the early strength development of this concrete specimens were tested at 3, 7 and 28 days after casting. Specimens were cured in curing rooms at constant temperatures. The first 24 hours were spent at 20°C and then transferred to a moist curing room at 23°C and kept in water until testing.
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Workability is seen to decrease upon the addition of hydrated lime, however to improve this, a super plasticiser was added. The addition of silica fume to the mix had no effect on the workability of a concrete mix. It was discovered that the addition of both silica fume and calcium hydroxide increased the early compressive strength of the concrete mixes. Testing at 3 days of age showed that the strength of both silica fume and hydrated lime mixes were equally higher, (30 MPa) than the standard concrete mix at 24 MPa. The major differences in compressive strengths were apparent at 28 days with a constant progression from the standard mix (49 MPa), fly ash inclusive of hydrated lime (53 MPa) and then the concrete mix incorporating silica fume with a 58 MPa 28 day compressive strength (Figure 2.1).
Figure 2.1: Compressive Strength of 30% Fly Ash Substituted Concrete
The use of calcium based additives into geopolymer pastes was researched by Temuujin, van Riessen and Williams (2009). Both calcium hydroxide and calcium oxide were substituted into geopolymer pastes for fly ash in order to accelerate the ambient curing (on average at 20°C) of the paste, and increase the compressive strength under these curing conditions. To form a proper comparison between the effects from curing conditions, specimens were oven cured being subjected to heats of 70°C.
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It was found that the addition of calcium compounds improved the mechanical properties of geopolymer pastes cured at ambient temperatures, yet reduced the strength of those cured under elevated temperatures. The results also showed that the addition of calcium hydroxide (Ca(OH)2) aided the ambient curing strength more so than calcium oxide (CaO). It is suggested that this is apparent because the calcium hydroxide is a reactive constituent of the geopolymer mixes. The use of calcium hydroxide would appear to present incomplete hydration of the product as it reacts with the alkaline solution in the formation of calcium hydroxide. Specimens with CaO added presented compressive strengths approximately 20% lower than those with calcium hydroxide. It is suggested that the lower compressive strength in the pastes that is cured under elevated temperatures is due to the water evaporation within the mix, exhibited by lower density and higher porosity. At elevated temperatures, it is also suggested that the presence of calcium doesn’t allow the formation of three dimensional geopolymer network due to the fast dissolution of the paste. This therefore results in reduced mechanical properties of the final product. Under ambient conditions, it was found that by increasing the percentage of added calcium compound, the compressive strength increased with it. With a 3% addition of calcium hydroxide the compressive strength of 29 MPa compared to a geopolymer paste with no calcium additive which exhibited a strength of 12 MPa. In comparison, geopolymer with a calcium hydroxide inclusion of 1% and 2% showed strength of 24 MPa and 28 MPa respectively (Temuujin, van Riessen and Williams 2009).
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3. EXPERIMENTAL PROCEDURE
3.1
Introduction
Chapter 3 presents the details of the research that was carried out in order to investigate the inclusion of additives in the development of geopolymer concrete mix design. Due to the limited research conducted using fly ash‐based geopolymer concrete with zero OPC, a large part of the experimental work for this report focused on the mix proportioning and procedure for developing this concrete. The project’s aim included mix design development that would constantly yield concrete mixes with a consistent compressive strength of at least 30 MPa. Due to the lack of previous mix design information using geopolymer concrete, initial mix design and procedures closely followed regular conditions for the production of geopolymer concrete using sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) to form the alkaline solution. A trial and error process was then used for fine tuning the strength of the mixes, including materials such as silica fume and calcium hydroxide in anticipation of developing a concrete mix that would cure faster and develop a higher compressive strength. Experimental results were based upon compressive and tensile strengths, this is not unusual because compressive strength has a fundamental importance in the design of concrete structures. Tests for these parameters were for the majority of the mixes conducted at 7, 14, 21 and 28 days after casting. This was conducted to observe the short term strength development in concrete with the primary binder not being cement. The current methods of producing and testing of ordinary Portland cement concrete were followed as closely as possible in the production of this geopolymer concrete.
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This was a key point in the research, as it was important that a relevant comparison between the two products was formed and therefore investigating whether geopolymer concrete would be suitable to be produced on site. This included a general aggregate quantity of 77% by mass within the mix. The aggregate used within the different mixes originate from the same source throughout the year, in order to minimize the effect of varying aggregate properties.
3.2
Safety
Prior to any research beginning, an aim for this report was to develop a geopolymer concrete mix utilizing bayer liquor. This product is an industrial waste that is formed in the stage of removing bauxite in the refining of alumina. It has previously been used in the production of geopolymer pastes by the Centre of Materials Research department at Curtin University. The aim was to carry out a scaling up exercise of this paste by adding aggregates to the mix and increasing the quantity produced. In order to gain access to the bayer liquor, numerous precautions needed to be carried out, due to the caustic nature of the product. The most important of these was the Edusafe risk analysis and compliance. This took into account what measures needed to be put in place so that safe handling procedures of this material could be carried out. A major influence that this programme had on the preparation was the requirement for a safety shower to be installed in the laboratory. Strict methods of storage and disposal also had to be planned that comply with the appropriate measures as outlined on the product’s Material Safety Data Sheet. Due to the unsafe nature of the product and the relatively tight schedule to put all safety measures in place, the bayer liquor was not able to be brought to Curtin for use in concrete. These measures were also carried out for production of the conventional geopolymer concrete, however the procedure for the bayer was quite a bit more stringent due to it never having been used in concrete at Curtin University.
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3.3
Mix Design Development of Geopolymer Concrete
Materials
3.3.1
Fly Ash
The carried out experimental work utilized low calcium Class F fly ash obtained from Collie Power Station located south of Perth, Western Australia. Throughout the research, the fly ash used was from the same delivered batch. The fly ash was obtained in bulk bags and measured from here into the respective amounts required. 3.3.2
Sodium Hydroxide
A sodium hydroxide solution was utilized in all mixes as a constituent in the alkaline reactor. The product was obtained from a local supplier in the form of pellets with a purity of 98%. The solution was prepared by dissolving the pellets into distilled water at specified concentration in molars, M, for the concrete. In the laboratory research carried out, the solution was prepared with a concentration of approximately 10 M by dissolving the sodium hydroxide solids into distilled water. To produce 1 kg of sodium hydroxide solution, 416.8 grams of pellets was dissolved into 583.2 grams of distilled water. The solid was added to the water gradually and stirred for approximately 20 minutes until all solid had dissolved. It was noticed that upon addition of the solid to water, the solution became hot as the exothermic reaction of dissolution carried out. Upon preparation of the first mix produced, the sodium hydroxide solution was prepared 4 days prior to its addition to sodium silicate, and then production of concrete. It was discovered that after 4 days of standing, some sodium hydroxide solids had appeared in the solution after being dissolved completely when initially combined, this required stirring of approximately half an hour to reduce the solid content. Subsequent sodium hydroxide solutions made throughout the year were not prepared to a schedule prior to mixing the concrete. Generally though, dilution of
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sodium hydroxide occurred a few days before concrete production in order to limit the time spent preparing the chemicals on the concrete mixing day. 3.3.3
Sodium Silicate
The sodium silicate was obtained in 30.5 kilogram pallets from a local chemical supplier, PQ Australia. The grade of material used is known as PQ‐D with a SiO2/Na2O ratio of 2.0. The pH of this liquid was 11.9 and was in the form of a heavy syrup. The weight analysis of this material was as given by the supplier:
Na2O : 14.7%
SiO2
Water : 55.9%
: 29.4%
No dilution was required, after being weighed out it was used in the concrete as delivered. 3.3.4
Calcium Hydroxide
The calcium hydroxide used in Mix Three is known as HYLIME by Cockburn Cement. It was an industrial grade powder obtainable from the local hardware store, typically used in masonry mortars or plastering applications. This product was used in anticipation of developing a faster curing concrete with a higher early strength. XRF analysis carried out on the product shows the majority of the composition of HYLIME to consist of 84% by mass of calcium oxide, 7.2% silicon dioxide and 5.3% magnesium oxide. 3.3.5
Silica Fume
Silica fume was used in Mix Two as a fly ash replacement in hope that it would aid the ambient curing properties of the concrete.
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The silica fume used was obtained from local supplier Simcoa, Western Australia. The product was delivered in bags of 10 kilograms, and was known just as Microsilica or densified silica fume. This same product is also used in concrete batching plants in Western Australia, in particular for marine applications. The silica fume is in the form of extremely fine particles and therefore makes the concrete less impermeable upon addition. 3.3.7
Alkaline Liquid
The alkaline solutions for all mixes produced during the research were prepared by combining the sodium hydroxide solution to sodium silicate gradually. This mixture was then stirred moderately for a few minutes and then sealed in the buckets with lids until addition to the concrete mix. This process took place immediately prior to beginning production of the concrete, the ratio of sodium silicate to sodium hydroxide was kept consistent at 2.5 upon recommendation from Hardjito and Rangan (2005). 3.3.8
Aggregate
The aggregate used was supplied by Cemex to Curtin University, stored outside uncovered in storage divisions. The aggregate supplied consisted of two components; coarse aggregate obtained from the Cemex Gosnells Quarry and a fine aggregate that originated from Baldivis Sand. For the purpose of this research, coarse aggregates were used with nominal sizes of 7mm, 10mm and 20mm, and fine aggregates in the form of sand. The aggregate was measured approximately a week prior to pouring and sealed in bins. The moisture content of the aggregate was measured at the time of being used in the concrete, and subsequently used to determine the free water content of the concrete mix.
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The aggregate proportions were found in accordance with utilizing British Standards BS 882.92 (Neville 2000, 172) grading requirement limits for all‐in aggregate. The grading curve was constructed in order to satisfy the grading limits with an application sourced from the University of Patras. As can be seen the sieve analysis of the utilized aggregate displayed a grading‐gap, which is displayed on the grading curve below (Figure 3.1). This made proportioning the aggregate components a more stringent process. Neville (2000) suggests that a grading curve closer to the bottom limit is comparatively workable, and can therefore be used in mixes with a low liquid/binder ratio. The results of sieve analysis and grading combinations of the utilized aggregates can be seen below in Table 3.1.
19
4.75
0.6
0.15
ISO Sieve
100
0.063
100 95
90
Percentage passing
80 70 60 50
50
40 35
30 27.5
30.1
30.5
30
20 10
10
5.5
6
0
1 0 0 . 0 1
m
m
0 . 1
m
0.7
m
1
m
m
1 0
m
m
1 0 0
BS Sieve
Particle size (mm) Figure 3.1: Grading Curve of Combined Aggregates
(Grading Curve 2009)
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Table 3.1: Grading of Combined Aggregates
Sieve 19.00 mm 9.50 mm 4.75 mm 2.36 mm 1.18 mm 600 μm 300 μm 150 μm Ratio
20 mm 98.10 0.19 0.14 0.14 0.14 0.14 0.13 0.11 30
Aggregates 10 mm 7 mm 100.00 100.00 90.68 100.00 1.16 44.67 0.71 1.49 0.69 0.52 0.69 0.37 0.68 0.25 0.66 0.11 15 25
Fine 100.00 100.00 99.94 99.78 99.47 70.98 17.81 1.96 30
Combination
BS 882.92
99.43 68.66 41.37 30.46 30.12 21.53 5.55 0.75
95‐100 35‐55
10‐35 0‐8
3.4
Preliminary Laboratory Work
The aim of this research was to gain a knowledge and understanding of the effect of altering mix designs in a geopolymer concrete mix. Due to the lack of experience in any geopolymer concrete production by the author, it was suggested that to begin with, a standard geopolymer concrete mix using the established sodium hydroxide and sodium silicate alkaline solution would be made first to familiarize with the process and use a reference to other mixes. The first two mixes were undertaken at the beginning of June, 2009, with the use of the 70 litre capacity pan mixer (Figure 3.2) to produce approximately 65 litres (156 kilograms) of geopolymer concrete. Samples were placed in test specimens, 100mm x 200mm compression cylinders and 150mm x 300mm tensile cylinders, and cured under the ambient conditions after pouring. The preliminary laboratory works focused on the following main objectives: -
To familiarize with the making of fly ash based geopolymer concrete.
-
To develop an understanding of an appropriate mix procedure in the production of fly ash based geopolymer concrete.
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Mix Design Development of Geopolymer Concrete
To develop an understanding of appropriate mix proportioning in the production of fly ash based geopolymer concrete.
-
To observe the strength development of fly ash based geopolymer concrete under ambient curing conditions.
3.4.1
Mixing Procedure
The mixing procedure plays a vital role in the production of geopolymer concrete due to the unstable nature of some mixes. If constituents are added in the wrong order, it is possible that the concrete may flash set in the mixer, causing both a failed mix and a tough clean up. For this reason, a particular order was followed in the concrete mixing during this research. Cylinder moulds were first prepared for concrete pouring by coating them with mould release. For the use of geopolymer concrete, a product by the name of Valsof PE‐40 was used as the mould release, as the usual grease would not work the same as with cement based concretes. The alkaline solution consisting of sodium hydroxide and sodium silicate was combined at the beginning of the day when producing concrete. This came under recommendation in order to avoid the solution crystallizing over a long stationary period, an outcome that would deem the concrete mix design to differ if water was used to dissolve the solid again. The sodium hydroxide solution was added carefully to the second constituent and mixed thoroughly, before being sealed with lids prior to mixing time. The mixing procedure for geopolymer concrete was similar to that of conventional OPC concrete. All dry aggregates and fly ash were first added to the pan mixer and mixed for a few minutes to properly combine all sizes. After this dry mixing, the alkaline solution and any extra water was then added gradually and then mixed for a further three minutes, or, until an adequately combined mixture was formed. Darryl Hole
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At the conclusion of this wet mixing, any mix design additives such as silica fume or calcium hydroxide were added and again mixed thoroughly for approximately three to four minutes. This was carried out so that in the event of a rapid setting mix, it would be obvious that the final added constituent was the contributing factor. The produced geopolymer concrete differed physically to concrete made with ordinary Portland cement. Geopolymer concrete is very dark in colour (a dark brown appearance) and has an extremely ‘sticky’ feel to it. The placement of the concrete into cylinders therefore took longer than expected due to the difficulty of moving the concrete after mixing. Cylinders were filled to approximately half way before being vibrated for a few minutes or until no bubbles were being formed at the surface. The cylinders were then filled to the top and vibration started again, each mould being topped up as the vibration caused the elimination of any air voids. Only a small amount of time on the vibration table was given to those mixes with a high free water content as it was discovered that excessive movement of these mixes caused segregation of the aggregates and the top of the cylinders became more of a paste. Upon completion of the concrete placement, cylinders were moved from the table to an area in the labs for setting under ambient conditions, as seen in Figure 3.3 below.
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Figure 3.2: Pan Mixer Used for Production of Concrete
Figure 3.3: Setting of Wet Geopolymer Concrete
3.4.2
Mixture Proportions
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Hardjito and Rangan (2005) have stated that using a higher molarity of sodium hydroxide solution within the alkaline mix will yield a higher strength concrete. In their experimental results it was seen that, in otherwise similar mixes, using NaOH with concentration of 14M as opposed to 8M consistently yielded higher compressive strengths. Knowing this, when preparing the sodium hydroxide prior to producing the geopolymer concrete, solutions of 10M were prepared in anticipation of returning the highest possible compressive strength in the given situation. Mix One (poured in June, 2009) was proportioned in accordance to the research by Hardjito and Rangan (2006), with a 10M sodium hydroxide solution, aggregate content of 77%, sodium silicate to sodium hydroxide ratio of 2.5, and an alkaline liquid to fly ash ratio of 0.35. Water was added to the first mix produced in anticipation of yielding a workable mix that was easy to place, as the moisture content of the aggregate used was quite low. This mix was used as a datum for further mix designs, as the amount of water used, combined with the moisture content of the aggregate, would be used as a reference of the amount of water in future mixes. It was discovered for Mix One that 1.5 litres of water was required to be added to gain an adequate workability of the mix. A summary of this first produced mixes water content is found below in Table 3.2.
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Table 3.2: Free Water Content of Mixes One and Two
MIX ONE Aggregate
Water
Mass of
Water
Content (%)
Aggregate (kg)
Content (kg)
20mm
0.45
36
0.16
10mm
0.69
18
0.12
7mm
1.64
30
0.49
Sand
0.42
36
0.15
Added Water
1.5
Alkaline Solution
1.6
Total Free Water
Content (kg)
Content (%) f'cm.28 (MPa)
4.0
Total Free Water
2.6 30
Throughout the year, seven geopolymer concrete mix designs were produced in order to gain a relevant comparison in the effect of altering the concrete mix properties. The final mix designs, in terms of mass of material included per cubic metre of concrete produced, are found in Table 3.3 below. A summary of each mix design and its overall performance is also provided in Appendix A.
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Table 3.3: Mix Design Summary of Carried Out Research
Materials 20 mm 10 mm 7 mm Sand Fly Ash Sodium Silicate Sodium Hydroxide Silica Fume Calcium Hydroxide Extra Water TOTAL
MIX ONE MIX TWO MIX THREE MIX FOUR MIX FIVE MIX SIX MIX SEVEN kg/m3 kg kg/m3 kg kg/m3 kg kg/m3 kg kg/m3 kg kg/m3 kg kg/m3 kg 554 36 554 36 554 36 554 39 554 5.5 554 5.5 554 5.5 277 18 277 18 277 18 277 19 277 2.8 277 2.8 277 2.8 462 30 462 30 462 30 462 32 462 4.6 462 4.6 462 4.6 554 36 554 36 554 36 554 39 554 5.5 554 5.5 554 5.5 408 27 362 24 380 25 408 29 408 4.1 408 4.1 408 4.1 103 6.7 103 6.7 103 6.7 103 7.2 103 1.0 103 1.0 103 1.0 41 2.7 41 2.7 41 2.7 41 2.9 41 0.4 41 0.4 41 0.4 46 3.0 28 1.8 2.8 0.03 5.5 0.1 17 0.2 23 1.5 23 1.5 96 1.0 96 1.0 96 1.0 2423 157.5 2423 157.5 2400 156.0 2400 168.0 2499 25.0 2502 25.0 2513 25.1
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3.4.3
Mix Design Development of Geopolymer Concrete
Curing of Geopolymer Concrete
The geopolymer concrete specimens produced for this research were cured under ambient temperatures. Due to having no exposure to elevated temperatures under ambient conditions, the cylinders did not have to be wrapped in plastic to prevent excessive evaporation. Therefore, the specimens were left uncovered in the laboratory until set. The first mix made revealed that under ambient conditions; the geopolymer concrete did not set until 6 days after pouring. Therefore, the cylinders remained in their moulds for the first week of curing. This also meant that compressive testing was not carried out at 3 days after pouring as was first anticipated. The first compression tests were undertaken at 7 days after pouring, and therefore all cylinder moulds were released at this time. From this time onwards, specimens remained under the same ambient conditions, only with their full surface area exposed. The first two mixes were poured at the beginning of June, 2009. The outside temperature during this month in Perth, Western Australia, varied between 3°C and 26°C (Bureau of Meteorology 2009).
Figure 3.4: Ambient Curing of Geopolymer Concrete
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3.5
Mix Design Development of Geopolymer Concrete
Testing of Concrete Specimens
The compressive and tensile strength testing of the concrete cylinders was for majority of the mixes undertaken at 7, 14, 21 and 28 days after pouring. The testing was performed using a 300 ton capacity Controls MCC8 hydraulic testing machine in accordance to AS1012.10 – 2000 and AS1012.9‐2000 for tensile and compressive test respectively. Compressive strength was determined using three 100x200 mm concrete cylinders at all 4 testing days, while the indirect tensile tests we carried out on three 150x300 mm cylinders at 14 and 28 days after pouring. Due to the top surface condition of the compressive specimens, sulfur caps were made for the cylinders to ensure that the compression force is transferred equally across the top of the surface. Figure 3.5 shows the exposed surface of the concrete, with aggregate particles exposed making an uneven surface, and the sulfur cap used to produce the even surface for testing.
Figure 3.5: Rough Surface of Cured Geopolymer Cylinder
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4. EXPERIMENTAL RESULTS AND DISCUSSION
4.1
Introduction
Chapter 4 presents the experimental results obtained during the year, and the discussion regarding the relevance and significance of these findings. The concrete strengths discussed in this chapter correspond to the mean value of strength from three test specimens in a series. All significant observations and occurrences are also noted with the results of the relevant concrete mix. For individual cylinder data, details and strengths see Appendix B. In this chapter, the effects on the strength of fly ash based geopolymer concrete within the mix design and preparation are compared and discussed. The different parameters considered within this research include: 1. A standard geopolymer concrete reference mix (Mix One). 2. The effect of adding silica fume to aid the ambient curing properties of geopolymer concrete (Mix Two). 3. The effect of a high free water content on the strength of geopolymer concrete (Mix Four). 4. The effect of adding calcium hydroxide to aid ambient curing properties of geopolymer concrete (Mix Three, Mix Five, Mix Six and Mix Seven).
4.2
Experimental Results Overview
The experimental results throughout the research for each mix are used in comparison to Mix One, a conventional geopolymer concrete mix with no additives used in any attempt to enhance its performance. The initial aim for these mix designs was to consistently prepare concrete mixes that would yield a 28 day strength of at least 30 MPa, which is exactly what Mix One came out to be. Darryl Hole
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The further mix designs did not yield as positive results as what was initially expected. The addition of silica fume to the mix created an inordinate amount of silicon in the concrete which had drastic negative effects on the final strength, exhibiting a 28 day strength of 12.8 MPa. Mix Two however did set slightly quicker with the addition of silica fume than Mix One and could therefore in theory be used under low strength geopolymer concrete applications being set under ambient conditions. The effect of raising the free water content of the concrete mix yielded the result that was expected in Mix Four. In fact at the first testing at 7 days, it was predicted that the concrete had not properly set, given the extremely low strength of 2.5 MPa. This however was dispelled at the 28 day test with a final strength of only 10.8 MPa. It was therefore seen that by doubling the water content of the mix, the resulting final strength of the concrete is in effect one third of the reference Mix One. Because of the nature of by which the aggregates were stored outside during the winter months, all further mixes now exhibited extremely wet aggregates leading to a high free water content. Therefore Mix Four was now used as a reference mix as to match the free water content of all further mixes and comparing compressive and tensile strengths of the concrete. As previously explained, aggregates were not specifically prepared to simulate a large scale concrete production. Mix Three incorporated the use of calcium hydroxide (hydrated lime) in order to both quicken the curing time for the concrete and produce a higher final strength. Even with a moderately low amount of lime used (5% of the geopolymer, replacement of fly ash), the mix flash‐set in the pan mixer before being completely placed in the moulds. This mix design would therefore not be applicable in an industry operation where large quantities of material are produced. The unaffected cylinders were still tested and showed positive results for a mix with a high free water content with a final strength of 18.2 MPa, comparative to Mix Four’s reference strength of 10.8 MPa.
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To further the investigation into the use of calcium hydroxide in geopolymer concrete, a further three mixes were prepared with varying quantities of the product. This was carried out to investigate what composition of hydrated lime caused a geopolymer concrete mix to set too quickly to place. Mixes Five, Six and Seven were produced with an addition of 0.5%, 1% and 3% of the geopolymer paste respectively, this time however the calcium hydroxide was added to the concrete mix without replacement of the fly ash. Again the mix was produced with high water content in order to produce a relative comparison with Mix Three and Four. Despite all three setting noticeably quicker than the standard mix, Mixes Five, Six and Seven showed no significant increase in strength at 28 days of age. What was even more unexpected was that Mixes Five and Six were significantly lower than the reference. Of the three differing amounts of calcium hydroxide used, Mix Six which contained an addition of 3% of the geopolymer exhibited the highest compressive strength of 11.0 MPa, just slightly above the 10.8 MPa reference of Mix Four. The resulting compressive strengths as strength develops over the first 28 days from pouring can be seen in the below Figure 4.1. The indirect tensile strengths were also determined for Mixes One to Four. The 28 day tensile strength for the majority proved proportional to compressive strength results, with Mixes One and Three ending up the strongest with 2.7 and 2.2 MPa respectively. It was seen that the relationship between the compressive and indirect tensile strength was extremely similar to one proposed by Neville (2000) suggesting: Fct = 0.3 fcm⅔ A relationship determined by Lloyd and Rangan (2009) for geopolymer concrete was not adhered to primarily due to a contrast in curing conditions. Lloyd and Rangan developed this relationship using geopolymer concrete specimens cured in the steam room, where as the laboratory work for this report was based on ambient curing. The indirect tensile strength of Mixes One to Four is shown below in Figure 4.2. Darryl Hole
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Compressive Strength of Geopolymer Concrete (MPa) 35
30
Compressive Strength (MPa)
25
20 Mix One Mix Two 15
Mix Four Mix Three Mix Five
10
Mix Six Mix Seven 5
0 0
5
10
15
20
25
Age After Pouring (Days) Figure 4.1: Compressive Strength of all Carried Out Mixes
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Tensile Strength of Geopolymer Concrete (MPa)
3
Tensile Strength (MPa)
2.5
2
Mix One
1.5
Mix Two Mix Three Mix Four
1
0.5
0 0
5
10
15
20
25
Age After Pouring (Days) Figure 4.2: Indirect Tensile Strength of Mixes One to Four
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4.3
Mix Design Development of Geopolymer Concrete
Compressive Strength and Observations of Geopolymer Concrete Mixes
4.3.1
Initial Geopolymer Concrete Reference Mix
Table 4.1: Mix Design One
Materials 20 mm 10 mm 7 mm Sand Fly Ash Sodium Silicate Sodium Hydroxide Silica Fume Calcium Hydroxide Extra Water TOTAL
MIX ONE kg/m3 kg 554 36 277 18 462 30 554 36 408 27 103 6.7 41 2.7 23 1.5 2400 157.5
Mix one was prepared in anticipation of it being the ‘reference mix’ by which to compare other mixes made. This was seen as the standard geopolymer concrete mix and all further mix designs were based on this with variations in quantities of materials used and additives included. Mix One was prepared in early June 2009 at the immediate beginning of the laboratory work conducted for this report. Mix One exhibited a 28 day strength of exactly 30 MPa, coincidentally the benchmark strength upon which all further mixes were expected to exceed. The shape of the strength development curve, as shown in Figure 4.3 also indicates that given extra curing time under these ambient conditions, a higher strength could be attained. Of the three mixes made throughout the year which was at regular intervals, Mix One is the only one that shows a still developing strength curve and promises to provide worthwhile higher strengths at an age beyond that of 28 days. Darryl Hole
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Table 4.2: Compressive Strength of Mix One (MPa)
MIX ONE Age in Days 0 7 14 21 28
Compressive Standard Number of Strength (MPa) Deviation Samples 0.0 0.00 8.6 0.19 3 17 0.65 3 24 0.30 3 30 0.25 3
Compressive Strength of Geopolymer Concrete (MPa) 35
30
Compressive Strength (MPa)
25
20 Mix One Mix Two 15
Mix Four Mix Three
10
5
0 0
5
10
15
20
25
30
Age After Pouring (Days)
Figure 4.3: Compressive Strength of Mix One
It was also noticed that an efflorescence precipitate was formed on the outside of the cylinders on Mix One. The efflorescence was in the form of a white crystal, and was apparent at 14 days after pouring. The amount of efflorescence changed too as the
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age of the concrete lengthened, and by 28 days the specimens had a substantial coating of material on the outside. Temuujin, van Riessen and Williams (2009) discovered similar findings on ambient cured geopolymer paste samples when using additives to aid mechanical properties of the paste under ambient curing conditions. It was led to believe that the efflorescence formed was an indication of insufficient geopolymerisation or excess alkali. Further investigation into the materials showed that the efflorescence was composed of sodium, oxygen and phosphorus. XRF analysis also showed that the precipitate showed clear presence of sodium phosphate hydrate (Na3PO4.12H2O) in all samples ambient cured. Figures 4.4 and 4.5 below show the efflorescence forming on the outside of Mix One at 14 and 28 days respectively.
Figure 4.4: Efflorescence Formed on the Outside of Cylinders ‐ Mix One at 14 days
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Mix Design Development of Geopolymer Concrete
Figure 4.5: Efflorescence on the Outside of Cylinders ‐ Mix One at 28 days
4.3.2
The Use of Silica Fume to Aid Ambient Curing Table 4.3: Mix Designs One and Two
Materials 20 mm 10 mm 7 mm Sand Fly Ash Sodium Silicate Sodium Hydroxide Silica Fume Calcium Hydroxide Extra Water TOTAL
MIX ONE MIX TWO kg/m3 kg kg/m3 kg 554 36 554 36 277 18 277 18 462 30 462 30 554 36 554 36 408 27 362 24 103 6.7 103 6.7 41 2.7 41 2.7 46 3.0 23 1.5 23 1.5 2400 157.5 2400 157.5
Mix Two was based upon using Mix One with the addition of silica fume to the mix. Silica fume was substituted in for fly ash at a quantity of 8.3% of the geopolymer (no
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aggregate) based upon mix designs previously established in geopolymer pastes. Upon scaling up to a concrete by addition of aggregate, the silica fume content of the mix stood at 1.9% of the 65 litre concrete mix. Both Mix One and Mix Two were produced on the same day.
The silica fume was the final constituent added during the mixing process in the production of Mix Two. This was undertaken so that in the event that rapid setting occurred upon addition, it would be obvious that the silica fume was the cause and could be traced. This method of mixing was used consistently throughout the research. It was observed that upon ambient curing of the first two mixes made, Mix Two (silica fume included) experienced some expansion after 3 days above the top of the cylinder mould as seen in Figures 4.6 and 4.7. There was no expansion of Mix One which would suggest that this was purely an effect from the included silica fume. The expansion of these cylinders therefore required that these cylinders be cut down to size (approximately 200mm in length for compression specimens) in order for them to be tested upon an even top surface for equal distribution of force throughout the specimen. The expansion of Mix Two’s cylinders only occurred during the initial setting when the concrete was wet. This was apparent as after the concrete had dried and was subsequently removed from the moulds at 7 days, there was no change in diameter of the specimens. It was also apparent that at 3 days after pouring Mix Two had set slightly faster than Mix One, suggesting that the silica fume did increase the rate of curing by a small amount. Mix Two had completely set by 5 days old in comparison to Mix One being ready at 7 days. Mix Two also exhibited an amount of efflorescence on the outside of cylinders similar to Mix One, the amount present though was considerably less.
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Figure 4.6: Expansion of Mix Two (right) Relative to Mix One (left).
Figure 4.7: Expansion of Mix Two Cylinders
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Compressive Strength of Geopolymer Concrete (MPa) 35
30
Compressive Strength (MPa)
25
20 Mix One Mix Two 15
Mix Four Mix Three
10
5
0 0
5
10
15
20
25
30
Age After Pouring (Days)
Figure 4.8: Compressive Strength for Mixes One and Two
Table 4.4: Compressive Strength of Mix Two (MPa)
MIX TWO Age in Compressive Standard Number of Days Strength (MPa) Deviation Samples 0.0 0.00 0 1.9 0.09 3 7 7.0 0.14 3 14 10 0.11 3 21 13 1.3 3 28 It can be seen from the resulting compressive strengths in Table 4.4 that the addition of silica fume to the geopolymer mix had a negative effect on the strength. With just 1.91% of the concrete mix being silica fume substituted for fly ash, the final strength of the concrete mix more than halved. The 28 day strength of Mix Two peaked at only 13 MPa in comparison to Mix One’s 30 MPa with no silica fume. The strength development curve can be seen to have diminished after 14 days and have no significant growth after 28 days (Figure 4.8). Darryl Hole
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The difference in compressive strengths between Mix One and Two can be explained through the extra amount of silicon present in Mix Two. The inclusion of silica fume combined with the already present sodium silicate presented an abnormal amount of silicon in the mix. It would be seen that silica fume particles have not reacted within the microstructure of the geopolymer, and are present in the concrete, un‐reacted. The resulting compressive strength of Mix Two was unexpected, as it had set faster than Mix One and a higher strength was therefore predicted, particularly at 7 days after curing. This is in contrast to the findings of Barbuiya et al (2009) who discussed that upon the addition of silica fume to cement based concrete, the fine particles of the silica fume combine with the concrete transition structure. This is known as the ‘micro‐filler effect’ upon which the material’s structure is strengthened with the transitional bonds between particles. It was discovered that an addition of silica fume at a quantity of 5% of the concrete increased the strength by approximately 20%. It can therefore be seen that the addition of silica fume to geopolymer concrete at a quantity of 8.3% of the geopolymer poses a negative effect on the final strength. With this composition of silica fume replacing fly ash, the final strength is more than halved. Further to this, the concrete specimens experience a swelling above the top of the cylinder moulds, something that would not be suitable in an industrial concrete application.
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4.3.4
Mix Design Development of Geopolymer Concrete
The Effect of Free Water Content on the Strength of Geopolymer Concrete
Table 4.5: Mix Design Four
Materials 20 mm 10 mm 7 mm Sand Fly Ash Sodium Silicate Sodium Hydroxide Silica Fume Calcium Hydroxide Extra Water TOTAL
MIX FOUR kg/m3 kg 554 39 277 19 462 32 554 39 408 29 103 7.2 41 2.9 2400 168.0
An investigation into the effect of raising the free water content of a geopolymer concrete mix was carried out. This undertaken research was required to distinguish between the method of producing geopolymer paste and concrete. The included aggregate in the concrete holds water and therefore a workable concrete mix can be made without the addition of any extra water to the mix. Avoiding this condition can be achieved by preparing the aggregate in Saturated Surface Dry condition. This was not carried out in an attempt to keep the research relevant to large scale concrete production, in which it would not be efficient to prepare large quantities of aggregates to SSD. It is also a difficult stage to get to, as it is based on visual and touch parameters, however it can be complied with by Australian Standard 1141.5‐2000 and 1141.6.1‐2000. The concept of preparing aggregate to SSD is that the particles appear damp, but upon surface touching no moisture is felt and therefore would occur differently upon individual opinion. This condition is optimum for concrete preparation in order to yield aggregate that is holding enough moisture only to a point where it is not surface wet, and therefore not
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contributing any water to the mix. The moisture of these particles also prevents any of the added free water to the concrete mix being absorbed by the dry aggregate too. The water content of the mix is contributed to by the condition of the aggregate, any extra water added to the mix, and the water used in the alkaline solution. In Mixes One and Two, it was found that the free water content was approximately 4.0 litres over a 65 litre mix of concrete, including 1.5 litres of extra added water, producing a 2.6% free water content as seen in Table 4.6. By using aggregate that was not prepared in any situation obtaining it straight from the outside conditions under the rain, Mix Four’s water content was raised to 4.2% after calculating 6.5 litres of free water in the aggregate and alkaline solution as seen in Table 4.7. Prior to mixing, it was anticipated that the strength of this mix with the higher free water content would be lower than Mix One. This is the situation as seen in ordinary Portland cement concrete, as raising the water content lowers the ultimate strength. Table 4.6: Free Water Content of Mix One
MIX ONE Aggregate 20mm 10mm 7mm Sand
Water Mass of Water Content (%) Aggregate (kg) Content (kg) 0.45 36 0.16 0.69 18 0.12 1.64 30 0.49 0.42 36 0.15 Added Water 1.5 Alkaline Solution 1.6 Total Free Water Content (kg) Total Free Water Content (%) f'cm.28 (MPa)
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Table 4.7: Free Water Content of Mix Four
MIX FOUR Aggregate 20mm 10mm 7mm Sand
Water Mass of Water Content (%) Aggregate (kg) Content (kg) 1.25 36 0.45 1.50 18 0.27 4.14 30 1.24 8.17 36 2.94 Added Water 0 Alkaline Solution 1.6 Total Free Water Content (kg) 6.5 Total Free Water Content (%) 4.2 f'cm.28 (MPa) 11
Mix Four (investigating a mix with a higher water content) was designed exactly the same as Mix One poured earlier in the year. No preparation of the aggregates was carried out as these were obtained straight from the storage area, that was exposed to heavy rain that week, into sealed bins to retain the water content at that time. It was noticed that the water in the mix had an effect on the appearance of the geopolymer concrete. The concrete had an oily appearance with black portions spread throughout where the excess water was sitting in the mix. Figure 4.9 below shows an example of this on top of a poured cylinder during the placement. These black sections disappeared as the concrete set. This oily appearance was seen consistently over all further mixes produced with this high free water content throughout the year.
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Figure 4.9: Excess Water in Geopolymer Concrete
Obviously, when mixed the concrete was exceptionally easy to place with the high water content and the mix had a high slump value of over 250mm. Due to the high slump nature of this mix, only a light amount of vibration was applied to the cylinders to avoid segregation of the mix and letting all the aggregate fall to the bottom of the moulds and therefore producing more of a paste at the top of the cylinder. Understandably, Mix Four took quite some time to set. At 7 days old it was seen that the concrete still may not have set properly, as the strength at this time was even lower than expected, with a 2.5 MPa average in comparison to Mix One’s 8.6 MPa. Mix Four only had specimens taken for 7 and 28 days old in compression, and 28 days for tensile. Therefore, the strength development and rate of changes cannot be observed as closely over 28 days. The final strength of Mix Four did not get close at all to Mix One as seen in Figure 4.10. At 28 days the compressive strength of concrete reached 10.8 MPa (Table 4.8). It can
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therefore be seen that by increasing the free water content in a geopolymer mix to almost double, it effectively reduces the 28 day strength to a third of the original mix. Table 4.8: Compressive Strength of Mixes One and Four (MPa)
MIX FOUR Age in Compressive Standard Number of Days Strength (MPa) Deviation Samples 0.0 0.00 0 2.5 0.09 3 7 11 0.48 3 28
Compressive Strength of Geopolymer Concrete (MPa) 35
30
Compressive Strength (MPa)
25
20 Mix One Mix Two 15
Mix Four Mix Three
10
5
0 0
5
10
15
20
25
30
Age After Pouring (Days)
Figure 4.10: Compressive Strength of Mixes One and Four
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4.3.3
Mix Design Development of Geopolymer Concrete
The Use of Calcium Hydroxide to Aid Ambient Curing Table 4.9: Mix Design Three
Materials 20 mm 10 mm 7 mm Sand Fly Ash Sodium Silicate Sodium Hydroxide Silica Fume Calcium Hydroxide Extra Water TOTAL
MIX THREE kg/m3 kg 554 36 277 18 462 30 554 36 380 25 103 6.7 41 2.7 28 1.8 2400 156.0
Calcium hydroxide (hydrated lime) is used in common concrete applications to shorten the setting time under ambient conditions. Similar to Mix Two, calcium hydroxide was substituted into Mix Three for fly ash, at an amount of 5% of the geopolymer mix. This replacement of fly ash therefore worked out to 27.6 kg/m3 for the total concrete mix. Mix Three was poured at the end of July, 2009 with the intention of developing a faster setting ambient cured geopolymer concrete with a higher early strength. The calcium hydroxide was added to the concrete mix in much the same fashion as the silica fume in Mix Two, in that it was the final constituent included in the mixing procedure. Due to the high moisture content of the aggregates used, the concrete mix was extremely wet during mixing. At this point it would be thought that placement of the concrete would be easier than in previous experiments, although the final strength of the concrete would be lower. The slump recorded of this mix exceeded 250mm, similar to Mix Four. Upon addition of the calcium hydroxide to the mix and then mixing, it was seen that the concrete was bubbling furiously as the reaction between the chemicals in the fly Darryl Hole
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ash and the calcium hydroxide. At this point it was realized that something never experienced by the author was occurring so progress was made as quick as possible to place the concrete into the moulds. Approximately ten minutes into placement of the concrete in the moulds, rapid setting began to occur and placement of the mix became very difficult. Vibration of the cylinders did not have an effect on the form of the concrete, and air voids remained in some of the cylinders. Because the concrete was set on the day of casting, de‐ moulding of the cylinders was carried out at only two days of age. Upon removing the concrete from the moulds it was apparent that majority of the compression cylinders turned out fine for testing as usual. The tensile cylinders on the other hand, appeared to have a considerable amount of voids in them because of the fast setting concrete, however testing of these cylinders was still carried out in order to yield some data for this mix (Figure 4.12). Mix Three and Four were produced on the same day and therefore had the same relatively high free water content. Mix Four, as explained in the previous section of this report, is a standard geopolymer concrete mix investigating the effect of high water content. For this reason, Mix Three and all further mixes later on in the year were compared to Mix Four. The strength of Mix Three was consistently stronger than the reference mix throughout, and the rate of strength development was substantially larger up until 14 days of age. Eventually, though, the strength development of Mix Three tapered off and did not exhibit any rapid strength gain within 28 days. The final testing at 28 days showed a compressive strength of 18 MPa, comparative to Mix Four which exhibited a 28 day strength of 11 MPa as seen in Table 4.10 and Figure 4.11. Darryl Hole
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Table 4.10: Compressive Strength of Mix Three
MIX THREE Age in Compressive Standard Number of Days Strength (MPa) Deviation Samples 0.0 0.00 0 9.2 0.78 3 7 15 0.25 3 14 17 0.33 3 21 18 0.3 3 28
Compressive Strength of Geopolymer Concrete (MPa) 20
18
Compressive Strength (MPa)
16
14
12 Mix One
10
Mix Two Mix Four
8
Mix Three Mix Five
6
Mix Six 4
Mix Seven
2
0 0
5
10
15
20
25
30
Age After Pouring (Days)
Figure 4.11: Compressive Strength of Mixes Three and Four
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Figure 4.12 : Rapid Setting Effects and Efflorescence on Mix Three Cylinders
Figure 4.13: Cross Section of Small Cylinder ‐ Mix Three
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Figure 4.13 shows the cross section of a cylinder from Mix Three. The most obvious aspect is the shape of the top (right side of the image) where the concrete had set just as the cylinder had been filled up. The material at the top of these cylinders was flaky and brittle and so each affected cylinder had this surface condition trimmed off prior to testing. Another aspect of this cylinder is the amount of air voids seen throughout the section. Because Mix Three set whilst the cylinders were being vibrated all of the air voids were not able to be removed from the concrete. It should however be noted, that any results obtained from the testing of these specimens provide little use in further applications of geopolymer concrete mix design. It is recommended that the research in the addition of calcium hydroxide is continued with varying amounts added. On a larger scale in industry the time for placement of concrete would be much longer, and therefore setting would occur before all concrete is put into place. However, for the purpose of this research, the strength development is to be investigated into the addition of calcium hydroxide to geopolymer concrete, so testing of the cylinders continued. As seen in Figure 4.12 Mix Three also exhibited an amount of efflorescence on the outside of the cylinders. It was apparent at this stage that all geopolymer concrete samples cured under ambient conditions consistently exhibited this property. Approximately a week later, it was informed to the author of this report, that the Physics department at Curtin University had attempted to replicate the rapid setting nature of this mix by producing a geopolymer paste mix with the same proportions as Mix Three, albeit without the aggregate. The outcome, however, differed in that the mix did not rapid set whilst preparing and in fact took approximately 36 hours before it had properly set (M. Lee, personal communication August 26, 2009). To further the research into the effect of adding calcium hydroxide to geopolymer concrete, Mixes Five, Six and Seven were produced with varying amounts of the product added. The difference in this mix was the calcium hydroxide was added to a Darryl Hole
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set mix as an addition, not through substitution for fly ash. This was achieved by producing a replica of Mix Four (standard geopolymer concrete mix, with high water content, as was Mix Three) and adding the hydrated lime at a percentage by mass of the geopolymer paste in the concrete. Quantities of 0.5%, 1% and 3% of the geopolymer were added to the concrete mix respectively. Table 4.11 below shows the specific mix designs of these mixes. It can be seen that the total composition of Mixes Five to Seven exceed a composition of 2400 kg/m3 due to the extra water and calcium hydroxide added to the already complete concrete mix. The amount of water added was calculated in order to yield the same free water content as Mixes Three and Four. Table 4.11: Mix Designs Five, Six and Seven
Materials 20 mm 10 mm 7 mm Sand Fly Ash Sodium Silicate Sodium Hydroxide Silica Fume Calcium Hydroxide Extra Water TOTAL
MIX FIVE MIX SIX MIX SEVEN kg/m3 kg kg/m3 kg kg/m3 kg 554 5.5 554 5.5 554 5.5 277 2.8 277 2.8 277 2.8 462 4.6 462 4.6 462 4.6 554 5.5 554 5.5 554 5.5 408 4.1 408 4.1 408 4.1 103 1.0 103 1.0 103 1.0 41 0.4 41 0.4 41 0.4 2.8 0.03 5.5 0.1 17 0.2 96 1.0 96 1.0 96 1.0 2499 25.0 2502 25.0 2513 25.1
In order to avoid quick setting mixes hardening in the pan, the bulk standard mix design was produced and then the required amount for each sub‐mix (Mixes Five, Six and Seven) was placed onto an aggregate preparation tray. From here the varying amounts of calcium hydroxide was added and then mixed by hand into the concrete. This also allowed for a better feel of the workability of the mix, as any quick setting could be detected straight away. Mix Five (0.5% calcium hydroxide) presented no difference in workability or immediate setting time whilst mixing compared to Mix Four. In order to make the required amount of concrete for 6 compression cylinders (3 x 7 days, 3 x 28 days), only 29 grams of calcium hydroxide was added to 25 kilograms of concrete. In the time it took to mix
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in the calcium hydroxide and then transfer the concrete into the cylinders, Mix Five appeared to have no difference in workability relative to any standard geopolymer mix prepared earlier in the year. After 24 hours of curing it was apparent that Mix Five had still not set. Complete setting occurred by 5 days after pouring, very similar to a standard geopolymer concrete mix with no additives. Mix Six (1% calcium hydroxide) exhibited a slightly faster setting rate than Mix Five during the day. An amount of 58 grams of calcium hydroxide was added to the concrete mix and whilst there was no noticeable setting or difference in workability during placement, approximately two hours after producing the mix it was clear that it had begun setting. Figure 4.14 below shows the excess of Mix Six at two hours after mixing and partially set. At this point the concrete was beginning to harden on the top, however beneath the surface it was still very wet. By 3 days of curing Mix Six had completely set and was able to be removed from the moulds.
Figure 4.14: Mix Six at Two Hours after Pouring
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Mix Seven (3% calcium hydroxide) was the only mix prepared out of the last three which exhibited noticeable early setting properties during placement of the concrete. It was experienced that whilst combining the 173 grams of calcium hydroxide that the workability of the concrete changed almost instantly, however not enough to affect the placement. The mix felt heavier to move after mixing in the calcium hydroxide as it appeared the reaction between the chemicals in the concrete had occurred immediately. The rate of reaction was not as quick as Mix Three though, where the concrete set before all cylinders could be poured, and therefore the placement of Mix Seven went accordingly to plan. Again, the left over concrete from Mix Seven was kept to observe how long it took to set compared to Mix Six. After just one hour Mix Seven was significantly harder than Mixes Five and Six, and was obviously going to be completely set within hours. Figure 4.15 below shows the condition of the excess from Mixes Six and Seven after one hour of setting, and it can be seen that Mix Six is still completely wet where as Mix Seven is significantly further along in the setting process. After twelve hours of standing after pouring, Mix Seven had completely set and therefore the cylinders would have been able to be de‐moulded after 24 hours.
Figure 4.15: Mixes Seven (Left) and Six (Right) at One Hour after Pouring
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The relatively low final strength’s of Mixes Five, Six and Seven came as quite unexpected due to the setting times experienced by the three mixes. Though Mix Five set in the same amount of time as the reference mix, it was expected that a small amount of calcium hydroxide would have a compressive strength slightly higher, if not equal to the reference Mix Four. The faster setting nature of Mixes Six and Seven made for the prediction of higher compressive strengths in proportion to the amount of calcium hydroxide used. Despite this, the highest compressive strength experienced by these three mixes was 11.0 MPa, only slightly higher than the 10.8 MPa reference as seen below in Figure 4.16.
Compressive Strength of Geopolymer Concrete (MPa) 12
Compressive Strength (MPa)
10
8
Mix One
6
Mix Two Mix Four Mix Three
4
Mix Five Mix Six Mix Seven
2
0 0
5
10
15
20
25
30
Age After Pouring (Days)
Figure 4.16: Compressive Strength of Mixes Five, Six and Seven (MPa)
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Table 4.12: Compressive Strength of Mixes Five, Six and Seven (MPa)
Age in Days MIX FIVE MIX SIX MIX SEVEN
Compressive Strength (MPa)
7 28 7 28 7 28
3.2 7.4 3.6 8.0 5.1 11
Standard Deviation
Number of Samples
0.10 0.33 0.37 0.81 0.10 0.89
3 3 3 3 3 3
It can be seen from the results in Table 4.12 that the compressive strength of geopolymer concrete increases in proportion to the amount of calcium hydroxide used within the mix. Mix Seven with a 3% calcium hydroxide addition exhibited a slightly higher compressive strength than Mixes Five and Six. The difference though is seen at the 7 day strengths where any addition of calcium hydroxide to a geopolymer concrete mix increases the strength and rate of setting, making the mix applicable for use in industry applications where the concrete is cured without the use of steam rooms. Mix Seven appears to be a practical solution to developing a geopolymer concrete mix that sets within 24 hours without decreasing the final strength. The addition of calcium hydroxide at an amount of 3% of the geopolymer provides a concrete mix that will set efficiently without the need for a steam room, and provide a final strength to that of equal to a mix without any additives. If Mix Seven had achieved a final compressive strength substantially higher than the reference mix, it would be seen that this was the optimum arrangement for the inclusion of calcium hydroxide in geopolymer concrete. Another aspect of these three mixes that was noticed is how quickly the efflorescence began to appear after de‐moulding. Approximately 30 minutes after all cylinders were removed from their moulds, a small amount of efflorescence started to appear around the top of the cylinders below where any excess bits of concrete had been chipped off during handling. Figure 4.17below shows the first amounts of efflorescence appearing at half an hour after de‐moulding the cylinders at five days after casting.
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It was interesting to discover the substantial difference between a 3% addition of calcium hydroxide relative to the 5% replacement of fly ash as seen in Mix Three. Despite the fact that Mix Three was deemed a failure, the compressive strengths of the unaffected cylinders were still substantial. From this, it would be seen that incorporating a 3% replacement of fly ash with calcium hydroxide would produce a mix that sets within 12 hours and presents positive compressive and tensile strengths.
Figure 4.17: Efflorescence Beginning to Form after De‐moulding ‐ Mix Five
4.4
Indirect Tensile Strength of Geopolymer Concrete
The relationship between the compressive strength and indirect tensile strength of concrete is well known. Whilst not as heavily relied upon from the results point of view, the tensile strength of the tested specimens must also be analysed to gain a full perspective of the conclusions. The tensile strength of these specimens was tested in compliance with Australian Standard 1012.10‐2000.
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The indirect tensile tests were only carried out on Mix One to Four due to both material and time restraints. To undertake this, cylinders were produced using 150mm diameter by 300mm long moulds. The tensile splitting strength was determined in accordance with Australian Standards AS1012.10‐2000: Method of testing concrete – Determination of indirect tensile strength of concrete cylinders (Brasil or splitting test). From the determined splitting load P (kN), it is possible to determine the indirect tensile strength in MPa by the following equation:
T = 2000P / πLD
Where P = Splitting strength of cylinder in kN.
L = Length of cylinder in mm
D = Diameter of cylinder in mm.
T = Tensile Strength in MPa
For the most part the indirect tensile strength of the four mixes were proportional to the compressive strength, with Mix One and Three being the strongest easily (2.7 MPa and 2.2 MPa respectively), and Mix Two and Four trailing behind. Mix Four (2.0 MPa) in fact was quite a bit stronger in tension than Mix Two (1.5 MPa) in contrast to the compressive strength of these two mixes in which the two mixes were extremely similar, Mix Two being just slightly stronger as seen in Figure 4.18. Due to time and material restraints again, Mix Four only had tensile cylinders cast for one day of testing. For this reason, the tensile strength development shape of the mix cannot be viewed and therefore is shown on the below figure by just a marking at 28 days old. It can be seen that the magnitude of tensile strength of geopolymer concrete at early stages in the curing life is a fairly good indicator of its later strengths relative to other mix designs. The ranking of strongest to weakest mix at 14 days old is the same at 28 days after casting. This is in contrast to compressive strength, which can change order as age increases. This can be seen particularly in Figure 4.1 where the strength of Mix Darryl Hole
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Three was higher than Mix One at 7 days, but that soon changes as Mix Three tapers off very early.
Tensile Strength of Geopolymer Concrete (MPa)
3
Tensile Strength (MPa)
2.5
2
Mix One
1.5
Mix Two Mix Three Mix Four
1
0.5
0 0
5
10
15
20
25
30
Age After Pouring (Days)
Figure 4.18: Indirect Tensile Strength of Mixes One to Four
Table 4.13: Indirect Tensile Strength of Mixes One to Four
TENSILE STRENGTH Age Mix One Mix Two Mix Three Mix Four 2.0 0.95 1.6 14 days 2.7 1.5 2.2 2.0 28 days Lloyd and Rangan (2009) suggest that it is possible to draw a relationship between the tensile and compressive strengths of geopolymer concrete. Over a period from 2007 and 2008, a variety of mix designs were tested at Curtin University and had their results used to develop this association. It was discovered that over 41 tests, the
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relationship between the compressive and tensile strengths of geopolymer concrete was:
Fct = 0.6 ± 0.1√fcm
Neville (2000) suggested that a similar relationship can be drawn between the tensile and compressive strength of ordinary Portland cement based cements. This relationship was as follows:
Fct = 0.3 fcm⅔
These relationships were tested with the results obtained through the research for this report. The results are presented below in Table 4.14. Table 4.14: Relationship Between Compressive and Tensile Strength
Age (days) fcm MPa
MIX ONE MIX TWO MIX THREE MIX FOUR
14 28 14 28 14 28 28
17.3 30 7.0 12.8 14.9 18.2 10.8
fct MPa (Lloyd fct MPa and (Neville fct MPa Rangan 2000) 2009) 1.0 2.0 2 1.1 2.9 2.7 0.87 1.1 0.95 0.96 1.6 1.5 0.97 1.8 1.6 1.0 2.1 2.2 0.93 1.5 1.4
As can be seen, the estimation for the relationship between tensile and compressive strengths for the research carried out here is much suited towards Neville’s suggestion. The relationship that Lloyd and Rangan suggested did not present very similar findings to the present research, which is unexpected considering it has been specifically developed from geopolymer concrete specimens. A possible reason for this though is that it is stated in the report that all utilized concrete mixes were cured in the steam room under varying temperatures and regimes. Under the research carried
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out for this relationship, no such investigation was carried out with specimens cured under ambient conditions as in the research for this present report. At this stage with only four mix designs and 7 values tested, an initial estimation into the relationship between the compressive and tensile strengths of geopolymer concrete cured under ambient conditions would suggest that Neville’s suggestion is valid.
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5. SUMMARY AND CONCLUSIONS
5.1
Introduction
Chapter 5 presents a summary of the present study, the major conclusions from the conducted research. The main objective of this study was to further the past research carried out in geopolymer concrete mix design and develop a scaling up process of work carried out by the Physics Department at Curtin University, in which they produced geopolymer pastes that set quicker under ambient conditions. By adding aggregate to these mixes and therefore producing a geopolymer concrete, several mix designs were tested by introducing different additives to the concrete. The two processes differed by more than just adding aggregate, as it was discovered that the longer handling time of the concrete restricted the effectiveness in adding calcium hydroxide to geopolymer concrete. It was also apparent how much water is stored within the aggregate, as no extra water needed to be added to the mix at all, due to how wet the aggregate was in Mixes Three to Seven. In order to maintain a constant approach between each of the batches, mixing procedures, materials used and mix designs for the most part were kept constant.
5.2
Production of Geopolymer Concrete
5.2.1
Pre-production Issues
The most important work carried out before the mixing of the concrete was the preparation of the alkaline liquid. This liquid was a combination of a sodium hydroxide solution and sodium silicate. The sodium hydroxide solution was formed by dissolving pellets into distilled water under pre‐calculated proportions. Upon carrying out this
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dissolution it was seen that the reaction carried out was exothermic, and heat was generated as the solid dissolved. Sodium silicate was used as obtained through a local supplier. These two elements were combined at the beginning of the day of mixing and kept sealed until use. The sodium hydroxide solution though was able to be produced a few days prior to mixing so long as any precipitate formed in that standing time was re‐dissolved again before use. No super plasticisers were used in the laboratory work in this research. Aggregates were not prepared prior to use to provide a realistic comparison to that of a larger scale in industry. The water content of the aggregates were taken, though, and noted what effect this content had on the final results.
5.3
Results and Observations
5.3.1
The Use of Silica Fume to Aid Ambient Curing
The addition of silica fume to geopolymer concrete produced a faster setting mix; however it had a negative effect on the compressive and tensile strength. In this mix, silica fume was added at a quantity of 8.3% of the geopolymer paste as a replacement for fly ash. The 28 day compressive strength for Mix Two peaked at 12.8 MPa comparative to Mix One’s 30.0 MPa (Figure 4.8). The addition of this silica fume to the concrete mix also caused a swelling of the cylinder, resulting in a porous expansion above the top of the mould upon setting as seen in Figures 4.6 and 4.7. 5.3.2
The Effect of Free Water Content on Geopolymer Concrete
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The effect of raising the free water content in geopolymer concrete was similar to that of ordinary concrete, reducing its strength. This was confirmed in Mix Four, where by doubling the free water content of Mix One, the 28 day strength resulted in one third of it with 10.8 MPa (Figure 4.10). 5.3.3
The Use of Calcium Hydroxide to Aid Ambient Curing
The addition of calcium hydroxide within a geopolymer concrete mix causes the concrete mix to set quicker. In the research carried out, the use of calcium hydroxide did not improve the compressive strength of the concrete despite it setting quicker. It can be seen in Table 4.16 that increasing the amount of calcium hydroxide into a geopolymer concrete mix proportionally increases the compressive strength of the concrete mix. It was seen that an addition of 3% of the geopolymer of calcium hydroxide produced a concrete mix that set within 24 hours and exhibited a compressive strength extremely similar the standard reference mix (11.0 MPa). It was also seen that 0.5% and 1% of calcium hydroxide added in fact decreased the compressive strength of the mix (Figure 4.16). Upon replacement of 5% of fly ash with calcium hydroxide in a geopolymer mix, the concrete flash set at approximately 10 minutes into placing the concrete into moulds. It was also seen that the chemicals in the mix were furiously reacting after thorough mixing in of the calcium hydroxide. Though the strength of Mix Three (5% calcium hydroxide utilized) substantially higher than the reference strength, it was seen as a failed mix because of the rapid setting and therefore would not be applicable in large scale operations (Table 4.10). 5.3.4
Other Observations During Research
During this research, all ambient cured geopolymer concrete specimens developed a layer of efflorescence on the outside as seen in Figures 4.4 and 4.5. This efflorescence Darryl Hole
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is thought to be unreacted sodium hydroxide in a white crystalline form (Temuujin, van Riessen and Williams 2009). This however, did not occur in the experimental research carried out in the steam curing of geopolymer concrete specimens.
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6. RECOMMENDATIONS To further develop the application of geopolymer concrete for structural use, research needs to be continued in order to refine the knowledge attained on the properties of this material. The research carried out for this report extends to only a very limited scope of the variables that were suggested for investigation. Because of both material and time restraints, a number of variables were not tested, however the following points are recommendations to be investigated in further research on geopolymer concrete mix design. 1. As can be seen by the shape of Mix One’s strength vs. age graph in Figure 4.3, the strength development of geopolymer concrete extends for a period beyond 28 days. The next step would be to investigate the strength development of geopolymer concrete for long term periods after pouring. The comparison of the final strength of geopolymer concrete comparative to the strength development of OPC concrete would promote the use of it in long term applications. 2. Past research has shown that the addition of silica fume in concretes with fly ash aid the strength after ambient curing. Similar to the method carried out in this report for calcium hydroxide, it is worth investigating the optimum quantity of silica fume required in a geopolymer concrete mix that allows a quicker setting time and a higher early strength of the concrete. 3. Mix Three showed promising results with the addition of calcium hydroxide to the concrete, but unfortunately did not allow enough time to complete the pour before it set. A possible solution into this could be the use of super plasticiser in the mix. This will increase the setting time of the mix and therefore hopefully provide a delay prior to rapid setting occurring. The super plasticiser would be added, though, not as a final additive like the calcium
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hydroxide, but as part of the alkaline liquid prior to mixing with the dry materials. 4. Mix Four was used to investigate whether raising the free water content of a geopolymer concrete lowered the strength of the mix, as is the case with ordinary Portland cement based concrete. The free water content between the two compared mixes differed greatly, and therefore producing a mix with a water content between Mix One and Four would establish whether any type of linear relationship exists within this variable. 5. To follow on from Lloyd and Rangan’s (2009) research for the relationship between compressive and tensile strengths, further investigation into this relationship could be considered for ambient cured geopolymer concrete. An initial investigation into this has been carried out in this report, however only four mixes were tested for tensile strength due to material and time constraints. Lloyd and Rangan only developed this relationship for geopolymer concrete specimens under steam curing. 6. An initial aim for this thesis was to investigate the use of a bayer liquor residue to produce a geopolymer concrete mix, which was unfortunately not carried out due to time restraints. Bayer liquor is a waste material that is produced in the bauxite removal stage in the production of alumina. The Centre of Materials Research at Curtin has previously used this material to produce a geopolymer paste in small quantities. Scaling this exercise up to produce a concrete mix with the bayer would provide a largely sustainable option in using a concrete that is comprised of fly ash and bayer, two industrial waste products. 7. Further to this, once the transition of bayer liquor in a geopolymer paste to concrete has been made, the next step in a sustainability exercise would be to investigate what amount of the conventionally made alkaline solution can be directly replaced with the bayer. This would not only increase the sustainability Darryl Hole
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view of the concrete, in using large amounts of waste, but an economic benefit could be established in negating the need to dispose of this material. Elemental composition of the concrete obviously matters, but by progressively increasing the amount of bayer in the mix, which replaces the costly sodium hydroxide and sodium silicate, economic and environmental advantage could be had. 8. The effect of adding calcium hydroxide to a geopolymer concrete mix was investigated in Mixes Three, Five, Six and Seven. However, due to the conditions in which the aggregates were kept, each of these mixes ended up with a substantially high water content in order to keep a viable comparison. Mixes Three (5% calcium hydroxide) and Seven (3% calcium hydroxide) exhibited the largest compressive strength, yet was limited through the high water content. It is worth reproducing these mixes with a lower water content to investigate just how well this product works in geopolymer concrete.
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REFERENCES Ash Development Association of Australia. 2009. Coal Ash Matters May 2009. http://www.adaa.adn.au/docs/Coal_Ash_Matters_May_09 (accessed September 16, 2009). Barbhuiya, S. A., J. K. Gbagbo, M. I. Russell, and P. A. M. Basheer. 2009. Properties of fly ash concrete modified with hydrated lime and silica fume. Construction and Building Materials 23 (10): 3233‐3239. http://www.sciencedirect.com/science/article/B6V2G‐4WS85SX‐ 1/2/8b71b06e46b273e47193252653c20399 (accessed September 15, 2009). Bureau of Meteorology. 2009. Western Australian Weather and Warnings.
http://www.bom.gov.au/weather/wa/ (accessed August 3, 2009).
Cross, D., J. Stephens, and J. Vollmer. 2005. “Field trials of 100% fly ash concrete.”
Concrete International 27(9): 47‐51.
Damtoft, J. S., J. Lukasik, D. Herfort, D. Sorrentino, and E. M. Gartner. 2008. “Sustainable development and climate change initiatives.” Cement and Concrete Research 38 (2): 115‐127. http://www.sciencedirect.com/science/article/B6TWG‐4PYMWW3‐ 1/2/7d4ac12efd5dc1867c42d07ec788b970 (accessed March 28, 2009). Davidovits, J. 1999. “Chemistry of Geopolymer Systems, Teminology.” Geopolymer ’99
International Conference, France.
Grading Curve [Image]. 2009. http://www.episkeves.civil.upatras.gr/ (accessed
May 19, 2009).
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Hardjito, D. and B. V. Rangan. 2005 “Development and properties of low‐calcium fly
ash‐based geopolymer concrete.” Research Report GC1, Faculty of Engineering, Curtin University of Technology. http://www.geopolymer.org.
(accessed April 29, 2009).
Hardjito, D, S. E. Wallah, D. M. J. Sumajouw, B. V. Rangan. 2004. “On the Development of Fly Ash‐Based Geopolymer Concrete.” ACI Materials Journal 101‐M52. http://www.sciencedirect.com (accessed April 29, 2009).
Hendriks, C.A., E. Worrell, D. deJager, K. Block, and P. Riemer. 2003. “Emission reduction of greenhouse gases from the cement industry.” IEA Greenhouse gas R&D Programme. http://www.ieagreen.org.uk/prghgt42.htm (accessed April 11, 2009).
Huntzinger, D. N., and T. D. Eatmon. 2009. “A life‐cycle assessment of Portland cement manufacturing: comparing the traditional process with alternative technologies.” Journal of Cleaner Production 17 (7): 668‐675. http://www.sciencedirect.com/science/article/B6VFX‐4SWP1TT‐ 1/2/017ab91eca875d825dfb76028d85907f (accessed April 11, 2009). Johnson, G. 2007. “Geopolymer concrete and method of preparation and casting.” United States Patent Application Publication 0125272 A1. http://www.freepatentsonline.com/y2007/0125272.html (accessed April 8, 2009). Lloyd, N. and V. Rangan. 2009. “Geopolymer concrete: Sustainable cement‐less
concrete.”
Malhotra, V.M. 2002. “Introduction: Sustainable development and concrete
technology.” ACI Concrete International 24(7): 22.
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Mehta, P.K. 2001. “Reducing the Environmental Impact of Concrete.” Concrete
International 23(10): 61‐66.
Neville, A. M. 2000. Properties of Concrete. New York: John Wiley and Sons. Sofi, M, van Deventer, J.S.J., Mendis, P.A., Lukey, G.C. 2006. “Engineering properties of inorganic polymer concretes (IPCs).” Cement and Concrete Research 37 (2007) 251‐ 257. Science Direct. http://www.sciencedirect.com (accessed March 28, 2009). Standards Australia. 1999. “Method of testing concrete – Determination of the
Compressive strength of concrete specimens.” AS1012.9. Standards Australia
Online.http://www.saiglobal.com (accessed June 9, 2009).
Standards Australia. 2000. “Method for sampling and testing aggregates. Method 5:
Particle density and water absorption of fine aggregate.” AS1141.5. Standards
Australia Online. http://www.saiglobal.com (accessed May 28, 2009).
Standards Australia. 2000. “Method of testing concrete – Determination of indirect tensile strength of concrete cylinders (Brasil or splitting test).” AS1012.10. Standards Australia Online. http://www.saiglobal.com (accessed June 9, 2009). Temuujin, J., A. van Riessen, and R. Williams. 2009. Influence of calcium compounds on the mechanical properties of fly ash geopolymer pastes. Journal of Hazardous Materials 167 (1‐3): 82‐88. http://www.sciencedirect.com/science/article/B6TGF‐4VB01X1‐ 1/2/75cbb075d0800a72d9ad23f9672e7d82 (accessed September 15, 2009). Wallah, S. E. and B. V. Rangan. 2006. “Low Calcium Fly Ash‐Based Geopolymer Concrete: Long‐Term Properties.”Research Report GC2, Faculty of Engineering,
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Curtin University of Technology. http://www.geopolymer.org (accessed April 29, 2009).
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APPENDIX A Mix Design Details of Carried Out Geopolymer Concrete Mixes
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MIX ONE MIX TWO MIX THREE MIX FOUR MIX FIVE MIX SIX MIX SEVEN Materials kg/m3 kg kg/m3 kg kg/m3 kg kg/m3 kg kg/m3 kg kg/m3 kg kg/m3 kg 20 mm 554 36 554 36 554 36 554 39 554 5.5 554 5.5 554 5.5 10 mm 277 18 277 18 277 18 277 19 277 2.8 277 2.8 277 2.8 7 mm 462 30 462 30 462 30 462 32 462 4.6 462 4.6 462 4.6 Sand 554 36 554 36 554 36 554 39 554 5.5 554 5.5 554 5.5 Fly Ash 408 27 362 24 380 25 408 29 408 4.1 408 4.1 408 4.1 Sodium Silicate 103 6.7 103 6.7 103 6.7 103 7.2 103 1.0 103 1.0 103 1.0 Sodium Hydroxide 41 2.7 41 2.7 41 2.7 41 2.9 41 0.4 41 0.4 41 0.4 Silica Fume 46 3.0 Calcium Hydroxide 28 1.8 2.8 0.03 5.5 0.1 17 0.2 Extra Water 23 1.5 23 1.5 96 1.0 96 1.0 96 1.0 TOTAL 2423 157.5 2423 157.5 2400 156.0 2400 168.0 2499 25.0 2502 25.0 2513 25.1
Compressive Strength of Mix Designs (MPa) Age (days) 7 14 21 MIX ONE 8.6 17 24 MIX TWO 1.9 7 10 MIX THREE 9.2 15 17 MIX FOUR 2.5 MIX FIVE 3.2 MIX SIX 3.6 MIX SEVEN 5.1 -
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APPENDIX B Details of Geopolymer Concrete Cylinder Testing
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Mix One
Mix Design Development of Geopolymer Concrete
Standard geopolymer reference mix
COMPRESSION Mass (g) Length (mm Diam (mm) Area (mm2) Force (kN) Stress (Mpa) 7 day 9th June 2009 7 day - 1 3960 205.1 99.5 7776 68.7 8.835 7 day - 2 4044 205.3 100 7854 66.8 8.505 7 day - 3 3994 204.7 99.8 7823 65.6 8.386 Average 8.576 14 day 16th June 2009 14 day - 1 3972
205.6
99.6
7791
131.1
16.8
14 day - 2 14 day - 3
3968 3989
203.7 204.3
99.6 100.0
7791 7854
131 143.0 Average
16.8 18.2 17.3
21 day 23rd June 2009 21 day - 1 3947 21 day - 2 3936 21 day - 3 3962
198.4 203.8 205
100.4 99.5 100.1
7917 7776 7870
190.2 191.5 194.3 Average
24.0 24.6 24.7 24.4
28 day 30th June 2009 28 day - 1 3990 28 day - 2 3934 28 day - 3 3957
205.1 203.4 203.8
100.2 99.8 99.6
7885 7823 7791
234 236.9 233.3 Average
29.7 30.3 29.9 30.0
TENSION Mass (g) Length (mm Diam (mm) Area (mm2) Force (kN) Stress (Mpa) 14 day 16th June 2009 14 day - 1 13008 300.5 149.9 17648 141.2 2.0 14 day - 2 13061 300 149.8 17624 140.6 2.0 14 day - 3 13034 300 149.8 17624 137.9 2.0 Average 2.0 28 day 30th June 2009 28 day - 1 12916 28 day - 2 12957 28 day - 3 12977
Materials 20 mm 14 mm 7 mm Sand Fly Ash Sodium Silicate odium Hydroxide Extra Water Silica Fume
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kg/m3 554.4 277.2 462 554.4 408 103 41 23.1 0
301 300.5 300
MIX ONE kg 36.0 18.0 30.0 36.0 26.5 6.7 2.7 1.5 0.0
149.6 150.1 150.2
17577 17695 17719
182 194.4 191.8 Average
2.6 2.7 2.7 2.7
% 23.1 11.6 19.3 23.1 17.0 4.3 1.7 1.0 0.0
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Mix Two
Mix Design Development of Geopolymer Concrete
8.3% silica fume fly ash replacement, cut - poured 2nd June 2009
COMPRESSION Mass (g) Length (mm Diam (mm) Area (mm2) Force (kN) Stress (Mpa) 7 day 9th June 2009 7 day - 1 3816 203.7 100 7854 15.7 2.0 7 day - 2 3806 202.7 100.1 7870 15.9 2.0 7 day - 3 3771 202.7 99.7 7807 14.2 1.8 Average 1.9 14 day 16th June 2009 14 day - 1 3813 14 day - 2 3813 14 day - 3 3792
203.3 203.9 201.4
99.8 100 99.3
7823 7854 7744
53.5 56.5 54.4 Average
6.8 7.2 7.0 7.0
21 day 23rd June 2009 21 day - 1 3972 21 day - 2 3731 21 day - 3 3820
201.2 200.7 202.3
99.6 100.8 100.3
7791 7980 7901
79.4 80.5 81.9 Average
10.2 10.1 10.4 10.2
28 day 30th June 2009 28 day - 1 3771 28 day - 2 3880 28 day - 3 3820
202.4 202 202.1
100 100.7 100.4
7854 7964 7917
103.3 113.4 87.8 Average
13.2 14.2 11.1 12.8
TENSION Mass (g) Length (mm Diam (mm) Area (mm2) Force (kN) Stress (Mpa) 14 day 16th June 2009 14 day - 1 12977 306.5 149.9 17648 66.9 0.9 14 day - 2 12989 307 149.8 17624 69.3 1.0 14 day - 3 13048 308 150.2 17719 69.2 1.0 Average 0.9 28 day 30th June 2009 28 day - 1 12910 28 day - 2 13005 28 day - 3 12914
Materials 20 mm 14 mm 7 mm Sand Fly Ash Sodium Silicate odium Hydroxide Extra Water Silica Fume
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kg/m3 554.4 277.2 462.0 554.4 362.2 103.0 41.0 23.1 45.8
306 310 311
MIX TWO kg 36.0 18.0 30.0 36.0 23.5 6.7 2.7 1.5 3.0
149.7 150 149.7
17601 17671 17601
105.7 111.2 103.8 Average
1.5 1.5 1.4 1.5
% 23.1 11.6 19.3 23.1 15.1 4.3 1.7 1.0 1.9
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Mix Three
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5% calcium hydroxide, fly ash replacement - poured 27th July 2009
COMPRESSION Mass (g) Length (mm Diam (mm) Area (mm2) Force (kN) Stress (Mpa) 7 day 3rd August 2009 7 day - 1 3.832 200.2 100.1 7870 77.2 9.8 7 day - 2 3.906 204.2 99.9 7838 75.5 9.6 7 day - 3 3.784 200 99.7 7807 63.1 8.1 Average 9.2 14 day 10th August 2009 14 day - 1 3.770 14 day - 2 3.822 14 day - 3 3.772
201.1 201.2 200.2
100 99.9 100.0
7854 7838 7854
117.4 118.9 114.4 Average
14.9 15.2 14.6 14.9
21 day 17th August 2009 21 day - 1 3.771 21 day - 2 3.801 21 day - 3 3.531
198 201.6 188.2
99.9 100.3 99.4
7838 7901 7760
131.3 137.8 129.8 Average
16.8 17.4 16.7 17.0
28 day 24th August 2009 28 day - 1 3.697 28 day - 2 3.710 28 day - 3 3.815
196 199.8 205.5
99.7 99.6 99.6
7807 7791 7791
142.8 138.4 144.9 Average
18.3 17.8 18.6 18.2
TENSION Mass (g) Length (mm Diam (mm) Area (mm2) Force (kN) Stress (Mpa) 14 day 10th August 2009 14 day - 1 12.335 275 149.9 17648 111.4 1.7 14 day - 2 12.855 282 150.2 17719 101.9 1.5 14 day - 3 12.825 301 150.2 17719 113.5 1.6 Average 1.6 28 day 24th August 2009 28 day - 1 12.611 28 day - 2 12.841 28 day - 3 12.222
Materials 20 mm 14 mm 7 mm Sand Fly Ash Sodium Silicate odium Hydroxide alcium Hydroxide Extra Water
Darryl Hole
kg/m3 554.4 277.2 462 554.4 380.4 103 41 27.6 0
285 282 209
MIX THREE kg 36.0 18.0 30.0 36.0 24.7 6.7 2.7 1.8 0.0
149.5 149.4 149.8
17554 17530 17624
138.4 135.3 123.1 Average
2.1 2.0 2.5 2.2
% 23.1 11.6 19.3 23.1 15.9 4.3 1.7 1.2 0.0
84
Civil Engineering Project 461 & 462 Curtin University of Technology
Mix Four
Mix Design Development of Geopolymer Concrete
No Silica Fume, uncut, large water content - poured 6th August 2009
COMPRESSION Mass (g) Length (mm Diam 7 day 13th August 2009 7 day - 1 3.876 199.9 7 day - 2 3.832 201 7 day - 3 3.851 200.3
28 day 3rd September 2009 28 day - 1 3.726 28 day - 2 3.735 28 day - 3 3.792
(mm) Area (mm2) Force (kN)
Stress (Mpa)
100.4 100.3 100.7
7917 7901 7964
20.8 19.2 19.5 Average
2.6 2.4 2.4 2.5
98.5 99 99.9
7620 7698 7838
78.9 81.6 89.9 Average
10.4 10.6 11.5 10.8
198.4 199.4 199.7
TENSION 28 day 3rd 28 day - 1 28 day - 2 28 day - 3
Mass (g) Length (mm Diam September 2009 13 298.5 13 301 13 295
Materials 20 mm 14 mm 7 mm Sand Fly Ash Sodium Silicate odium Hydroxide Extra Water Silica Fume
kg/m3 554.4 277.2 462 554.4 408 103 41 0.0 0
MIX FOUR kg 38.8 19.4 32.3 38.8 28.6 7.2 2.9 0.0 0.0
(mm) Area (mm2) Force (kN) 149.8 148.9 150.3
17624 17413 17742
101.8 93.7 95.3 Average
Stress (Mpa) 1.4 1.3 1.4 1.4
% 23.1 11.6 19.3 23.1 17.0 4.3 1.7 0.0 0.0
Darryl Hole
85
Civil Engineering Project 461 & 462 Curtin University of Technology
Mix Five
Mix Design Development of Geopolymer Concrete
0.5% calcium hydroxide additive, poured 24th September 2009
COMPRESSION Mass (g) Length (mm Diam (mm) Area (mm2) Force (kN) Stress (Mpa) 7 day 13th August 2009 7 day - 1 3.759 201.0 99.3 7744 25.6 3.3 7 day - 2 3.703 199.0 99.6 7791 24.1 3.1 7 day - 3 3.753 200.0 100.0 7854 24.2 3.1 Average 3.2 28 day 3rd September 2009 28 day - 1 3.636 28 day - 2 3.669 28 day - 3 3.683
Materials 20 mm 14 mm 7 mm Sand Fly Ash Sodium Silicate Sodium Hydroxide Extra Water Calcium Hydroxide
kg/m3 554 277 462 554 408 103 41 96 2.76
199.2 199.2 199.8
MIX FIVE kg 5.5 2.8 4.6 5.5 4.1 1.0 0.41 1.0 0.03
99.0 100.1 99.1
7698 7870 7713
54.7 62.1 56.4 Average
7.1 7.9 7.3 7.4
% 22.1 11.2 18.4 22.1 16.4 4.0 1.6 4.0 0.1
Darryl Hole
86
Civil Engineering Project 461 & 462 Curtin University of Technology
Mix Six
Mix Design Development of Geopolymer Concrete
1% calcium hydroxide additive, poured 24th September 2009
COMPRESSION Mass (g) Length (mm Diam (mm) Area (mm2) Force (kN) Stress (Mpa) 7 day 13th August 2009 7 day - 1 3.755 201.0 99.6 7791 25.8 3.3 7 day - 2 3.775 200.0 99.3 7744 32.2 4.2 7 day - 3 3.783 200.0 99.7 7807 27.1 3.5 Average 3.6 28 day 3rd September 2009 28 day - 1 3.712 28 day - 2 3.704 28 day - 3 3.651
Materials 20 mm 14 mm 7 mm Sand Fly Ash Sodium Silicate Sodium Hydroxide Extra Water Calcium Hydroxide
kg/m3 554 277 462 554 408 103 41 96 5.5
201.5 200.2 199.7
MIX SIX kg 5.5 2.8 4.6 5.5 4.1 1.0 0.41 1.0 0.10
100.0 99.9 99.5
7854 7838 7776
71.4 60.5 55.7 Average
9.1 7.7 7.2 8.0
% 22.1 11.2 18.4 22.1 16.4 4.0 1.6 4.0 0.4
Darryl Hole
87
Civil Engineering Project 461 & 462 Curtin University of Technology
Mix Seven
Mix Design Development of Geopolymer Concrete
3% calcium hydroxide additive, poured 24th September 2009
COMPRESSION Mass (g) Length (mm Diam (mm) Area (mm2) Force (kN) Stress (Mpa) 7 day 13th August 2009 7 day - 1 3.753 200.2 100.1 7870 40.7 5.2 7 day - 2 3.783 201.4 99.6 7791 40.2 5.2 7 day - 3 3.761 201.2 100.2 7885 39.1 5.0 Average 5.1 28 day 3rd September 2009 28 day - 1 3.707 28 day - 2 3.732 28 day - 3 3.711
Materials 20 mm 14 mm 7 mm Sand Fly Ash Sodium Silicate Sodium Hydroxide Extra Water Calcium Hydroxide
Darryl Hole
kg/m3 554 277 462 554 408 103 41 96 17
200.3 202.9 200.5
MIX SEVEN kg 5.5 2.8 4.6 5.5 4.1 1.0 0.41 1.0 0.20
100.2 99.2 99.4
7885 7729 7760
94.4 75.8 86.1 Average
12.0 9.8 11.1 11.0
% 22.1 11.2 18.4 22.1 16.4 4.0 1.6 4.0 0.8
88
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