WO2017070748A1

WO2017070748A1 - Geopolymer composite and geopolymer matrix composition

Info

Publication number: WO2017070748A1
Application number: PCT/AU2016/051025
Authority: WO
Inventors: Behzad NEMATOLLAHI; Jay SANJAYAN
Original assignee: Swinburne University Of Technology
Priority date: 2015-10-29
Filing date: 2016-10-28
Publication date: 2017-05-04
Also published as: CN108698926A; AU2016347692A2; AU2016347692A1; AU2016347692A8; AU2016102403A4

Abstract

A dry-mix composition for forming an ambient temperature cured, strain hardening geopolymer composite (SHGC) is disclosed. The dry-mix composition consists of (a) aluminosilicate material that is rich in silica and alumina in an amorphous form and (b) an alkali activator powder. Furthermore, the dry-mix composition is selected to (i) enable the ambient temperature cured SHGC to be formed without addition of liquid activator and (ii) exhibit strain hardening behavior accompanied by multiple cracking behaviour. Also disclosed is An ambient temperature cured, strain hardened geopolymer composite (SHGC) formed by adding water and a method of forming an ambient temperature cured SHGC.

Description

TITLE OF THE INVENTION

GEOPOLYMER COMPOSITE AND GEOPOLYMER MATRIX

COMPOSITION

TECHNICAL FIELD

A geopolymer matrix composition and a geopolymer composite are disclosed. Also disclosed is a method of forming the geopolymer composite by utilising the geopolymer matrix composition.

BACKGROUND ART

A special class of high performance fiber reinforced cementitious composites (HPFRCCs) with advanced tensile ductility which is about 600 times the ductility of normal concrete in tension has been referred to engineered cementitious composites (ECCs). ECC is a micromechanics-based designed cementitious composite which utilizes a small amount of discontinues fibers (typically 2% or less by volume) and exhibits a tensile strain capacity of up to 6%. Sustainability performance has seldom been a concern in the development of HPFRCCs. High cement content is commonly found in the mixture design of several types of HPFRCCs, such as slurry infiltrated fiber concrete, ultra-high performance fiber reinforced concrete (UHPFRC) and ECC.

The manufacture of ordinary Portland cement (OPC) is one of the main contributors of global warming in the world. The cement industry is said to be responsible for almost 5% of total C0₂ emission in the world which is the main cause of global warming. The high cement content in typical ECC mixture design usually results in high autogenous shrinkage, heat of hydration, and cost. In addition, the associated increase in the C0₂ emission as well as the embodied energy apparently compromise the sustainability performance of the conventional ECC. Therefore, it is necessary to develop green ECCs with lower cement content; thereby, with lower global warming potential associated with the C0₂ emission of the cement production, which not only maintain the desirable tensile ductility properties of the conventional ECCs but also take into account the sustainability performance. One of the solutions to achieve this goal is to partially replace the cement in the typical ECC mix design by supplementary cementitious materials (SCMs) such as fly ash and slag. Within the last decade several efforts have been made to incorporate slag and high volume fly ash as partial replacement of OPC in the ECC mixture design to reduce the use of OPC; thereby, reducing the global warming potential associated with the C0₂ emission of the cement industry. However, a more sustainable approach to develop green ECCs is to completely replace the OPC binder in the ECC mixture design by an alternative cement-less binder such as geopolymer.

Geopolymer is an emerging cement-less binder purported to provide a promising sustainable alternative to OPC binder. Geopolymer is manufactured from materials of geological origin such as metakaolin or industrial by-products such as fly ash and slag which are rich in silica and alumina, activated with high alkaline activators. Synthesis of fly ash based geopolymer involves at least 80% less C0₂ emission and requires approximately 60% less energy compared to the production of OPC.

Recently, efforts have been made to develop a geopolymer-based ECC, known as strain hardening geopolymer composite (SHGC) where the OPC binder was completely substituted with fly ash-based geopolymer binder which exhibited strain hardening behavior under uni-axial tension. The developed fly ash-based SHGC possessed very high tensile ductility up to 4.3% on average. However, its low to moderate compressive and uni-axial tensile strengths in the range of 17.4-27.6 MPa and 2.9—3.4 MPa, respectively may apparently limit the widespread application of the developed SHGC in the construction industry. In addition, a highly corrosive sodium hydroxide (NaOH) solution composed of NaOH pellet (59% w/w) and tab water (41% w/w) resulting in a very high concentration of more than 14.0 M was used in the fly ash-based EGC composition which could also limit commercial and mass production of the developed SHGC in the construction industry due to the special safety

considerations required for handling large quantities of such user-hostile alkaline solutions.

More recent efforts have evaluated the effect of different activator combinations with relatively low concentration on the matrix and composite properties of the recently developed fly ash-based SHGC to improve its compressive and tensile strengths. The experimental results revealed that although the concentration of the NaOH solution was limited to 8.0 M to account for the safety considerations; however, the fly ash-based SHGC manufactured from the sodium-based (Na-based) activator combination composed of 8.0 M NaOH solution (28.6% w/w) and Na₂Si0₃ solution (71.4% w/w) with a Si0₂/Na₂0 ratio of 2.0 exhibited significantly enhanced compressive and ultimate tensile strengths with very high tensile ductility over 60 MPa, 4.7 MPa, and 4.3% on average, respectively.

The enhanced compressive and tensile strengths and the very high tensile ductility of the recently developed fly ash-based SHGC and the outstanding greenness potential of the geopolymer promote the application of the SHGC as a promising sustainable alternative to the conventional ECC. To make the most of the remarkable mechanical properties and the environmental advantages of the developed SHGC, its widespread and large scale structural applications in the construction industry should be really taken into consideration. However, there are two main obstacles that apparently hinder the widespread application of the developed fly ash-based SHGC in the construction industry compared to the conventional ECC.

The first obstacle is the use of corrosive and often viscose alkaline solutions to manufacture the geopolymer matrix. Conventionally, the geopolymer matrix is manufactured from a two-part mix, comprising of alkaline solutions and solid aluminosilicate precursors. These user-hostile activator solutions are frequently used to dissolve the aluminosilicate source materials and govern the mechanical properties of the geopolymer matrix such as its compressive strength. There are a number of drawbacks with regards to the two-part mix formulations used in manufacture of the "traditional" geopolymer matrix. The most important pitfall is that handling large quantities of highly corrosive and often viscous alkaline solutions would be difficult to be used for commercial and mass production of the geopolymer matrix; thereby, hinders the large-scale application of the developed fly ash-based SHGC. In addition, the rheology of the geopolymer matrix can be complex and difficult to control as a result of forming a sticky and thick paste, particularly in geopolymer matrices where the source of alkali is sodium. This is particularly problematic because the developed

SHGC is not self-compacting. The SHGC, therefore, requires considerable work to fill a given volume defined by, for example, formwork and reinforcement so that the cured product is substantially free of voids. Moreover, the geopolymer matrix is sensitive to the ratio of alkali to available silicate, which can be challenging to control in practice where waste materials are used as a silica source. Furthermore, as a result of movement of alkalis and water to the geopolymer surface during curing or in service there can be a 5 tendency toward efflorescence, and/or high permeability and water absorption, unless the water and alkali content of a geopolymer matrix are cautiously controlled.

The second hurdle towards the widespread and mass production of the developed SHGC is the necessity of heat curing which may limit the in-situ application of the developed fly ash-based SHGC in the construction industry,

l o The above references to the background art do not constitute an

admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art.

SUMMARY OF THE DISCLOSURE

15 The applicant has taken the aforementioned two main steps towards the large- scale application of the recently developed SHGC in the construction industry by developing an ambient temperature cured one-part "dry mix" geopolymer matrix composition compared to the "traditional" two-part geopolymer matrix composition. Specifically, the applicant has identified that a range of solid activators can be used in

2 o place of user-hostile activator solutions, which are highly corrosive and often viscous alkaline solutions. To eliminate the necessity of the heat curing, the applicant has also identified a range of aluminosilicate materials which can be used with the solid activators to manufacture an ambient temperature cured one-part "dry mix" geopolymer matrix composition similar to the conventional cement-based matrix compositions. This

25 has enabled the applicant to identify a range of ambient temperature cured one-part "dry mix" geopolymer matrix compositions that can be combined with reinforcing fibres to arrive at an ambient temperature cured one-part "dry mix" strain hardening geopolymer composite (hereafter called "ambient temperature cured SHGC") with suitable mechanical properties for use in the construction industry.

30 In a first aspect, there is disclosed a dry-mix geopolymer matrix composition for forming an ambient temperature cured geopolymer composite, the dry-mix composition consisting of: (a) aluminosilicate material that is rich in silica and alumina in an amorphous form; and

(b) an alkali activator powder; and

wherein the dry-mix composition is selected to (i) enable the ambient temperature

5 cured, strain-hardening geopolymer composite to be formed without addition of liquid activators and (ii) exhibit strain hardening behavior accompanied by multiple cracking behaviour.

The dry-mix composition is selected to enable the ambient temperature cured SHGC to be formed by addition of water only. Liquid activators are not added in the o process of forming the ambient temperature cured, strain hardened geopolymer

composite (SGHC). It is anticipated, however, that other materials may be added when the SHGC is prepared. For example in some cases (if needed) proper amount of high- range water-reducing admixture (HRWRA) and viscosity modifying admixture (VMA) may be used to achieve the proper rheology of the dry-mix composition to ensure

5 uniform fiber dispersion. Antifoaming agent may also be used to minimize the amount of air bubbles. It will be appreciated that forming the ambient temperature cured SHGC will include mixing the dry-mix composition with water in a mixer followed by adding the reinforcing fibers and casting the "fresh" composite in a mold or formwork before allowing it to cure. Accordingly, the phrase "formed by addition of water only" and o equivalent phrases used throughout this specification refer to water being the only

additional ingredient, other than materials for controlling rheology and foaming, that is combined with the dry-mix composition to form the ambient temperature cured geopolymer matrix. The phrase is not to be taken to exclude the further steps of mixing, casting and curing of the ambient temperature cured SHGC.

5 The aluminosilicate material may be an appropriate combination of materials selected from the group comprising: slag, low calcium (Class F) fly ash, calcium hydroxide (lime) and optionally other materials that are rich in silica and alumina in an amorphous form. Such other materials include naturally occurring materials such as metakaolin and industrial wastes such as sugarcane bagasse ash, rice husk ash, mine0 tailings, aluminum and grey cast iron slags.

The dry-mix geopolymer matrix composition may include fine silica sand. When incorporated in an appropriate amount into the dry-mix geopolymer matrix composition, the silica sand increases the elastic modulus of the ambient cured temperature one-part SHGC while maintaining its desirable strain hardening behavior. It will be appreciated that normal weight fine silica sand may be replaced by different fine light weight aggregates such as microscopic hollow ceramic spheres, fly ash

5 cenosphere, perlite and expanded recycled glass aggregate in a proper amount to reduce the density of the ambient temperature cured SHGC (i.e. to manufacture light weight ambient cured temperature one-part SHGC) while maintaining its desirable strain hardening behavior.

The alkali activator powder may be one or more materials selected from the o group comprising: sodium hydroxide, sodium silicate and sodium carbonate.

The sodium silicate may be one or more materials selected from the group comprising: anhydrous sodium metasilicate, penta sodium metasilicate and GD Grade sodium silicate.

The dry-mix geopolymer matrix composition may further include reinforcing5 fibres.

The reinforcing fibres may consist of one or more forms of fibre selected from the following group comprising: aromatic polyamide (i.e. aramid) fiber, high strength and high modulus polyethylene (PE) fiber, poly vinyl alcohol (PVA) fiber, Poly-p- phenylenebenzobisoxazole (PBO) fiber and high tenacity polypropylene (HTPP) fiber. o The reinforcing fibres may have a diameter in the range of 10 to 100 m.

However, the reinforcing fibres may have a diameter in the range of 30 to 60 m.

The reinforcing fibres may have a tensile strength at least 800 MPa and length in the range of 4 to 30 mm.

The reinforcing fibres may have a fiber modulus of elasticity in the range of 10 5 to 300 GPa. However, the fiber modulus of elasticity may be in in the range of 40 to 200 GPa.

The reinforcing fibres may have an interfacial chemical bond strength below 3.0

J/m 2. However, the interface chemical bonding may be below 1.5 J/m 2.

The reinforcing fibres may have an interfacial frictional bond strength in the0 range of 1.0 to 4.5 MPa. However, the interface frictional stress may be in the range of 2.5 to 3.5 MPa. The reinforcing fibres may have an interface slip hardening coefficient below 2.5. However, the interface slip hardening coefficient may be below 1.0.

Fibres are selected based on having properties that will achieve strain hardening and multiple cracking behaviors. In other words, depending on the geopolymer matrix composition, different fibers with different specifications (length, diameter, elastic modulus, tensile strength, etc.) and different fiber-matrix interfacial properties

(chemical bond strength, frictional bond strength and slip hardening coefficient) can be used based on micromechanics models. All these fiber and interface properties are determinable prior to forming a composite. The interfacial properties can be

characterized by single fiber pullout test and the fiber properties are usually found in specifications from fiber manufacturers.

Combinations of different types and/or different sizes of the reinforcing fibers may be used to manufacture hybrid fiber reinforced ambient temperature cured SHGC.

The strain hardening behaviour and the multiple cracking behaviour may be accompanied by tensile strain capacity in the range of 1 to 6%.

There is also disclosed, in a second aspect, an ambient temperature cured, strain hardened geopolymer composite (SHGC) formed by adding water to the dry-mix composition according to the first aspect and curing the SHGC at ambient temperature.

The ambient cured temperature SHGC is formed without adding liquid activator to the dry-mix composition according to the first aspect.

The ambient temperature cured SHGC may have a compressive strength in the range of 30 to 60 MPa.

In a third aspect, there is provided a method of forming an ambient temperature cured SHGC, the method including mixing the dry-mix composition according to the first aspect with water to form the SHGC with a generally uniform distribution of reinforcing fibres and curing the formed SHGC at ambient temperature.

The method may further include casting the mixed composition into a mold or formwork.

The method may involve not adding liquid activator, step of mixing the dry-mix composition with water may include mixing the dry-mix composition with water only.

The method may include mixing the dry-mix composition with water and other materials for controlling rheology and foaming of the composite prior to curing. BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the apparatus and method as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a graph showing the particle size distribution of fly ash and slag used as aluminosilicate material to form an ambient temperature cured SHGC in accordance with an embodiment of the invention.

Figure 2 is a graph showing tensile stress-strain response of three samples of ambient temperature cured SHGC formed in accordance with an embodiment of the invention.

Figure 3 is a photograph of multiple cracking behaviour on the surface of ambient temperature cured SHGC in accordance with an embodiment of the invention.

DESCRIPTION OF EMBODIMENT(S)

Embodiments of the present invention are illustrated through the following examples by referring to the accompanying description, Figures and tables. However, it is to be understood that limiting the description to the embodiments of the present invention through the examples and to the Figures and tables by no means is intended as limitations on the scope of the invention and is merely exemplary in nature to facilitate discussion of the present invention.

The applicant carried out significant laboratory test work to arrive at a series of compositions for SHGCs that can be ambient cured temperature and that can be formed by the addition of water only. It is anticipated that other ingredients may be added to the compositions, for example, fine silica sand, without affecting the capability of the SHGC compositions from being formed with water and from being ambient cured temperature. The following description, however, will focus on compositions for which water is the only additional ingredient required for forming the SHGC. The

compositions for forming the matrix of the SHGC are referred to as "one -part geopolymer matrix compositions" because the mixed dry materials basically form a "dry mix" composition. From the point of view of a construction worker, this means that they are only concerned with handling one ingredient (other than water) when preparing the SHGC. This is a significant advantage in practical terms on a construction site where the existing range of SHGCs would require construction workers to handle or be exposed to highly corrosive liquid activators which need to be used with a

5 corresponding set of dry ingredients.

In a general sense, the SHGCs consist of an aluminosilicate material, an alkali activator powder and reinforcing fibres as the dry ingredients. The aluminosilicate material and alkaline activator powder are pre-mixed and comprise the one-part geopolymer matrix composition, examples of which are presented in Table 1.

l o The aluminosilicate material may be an appropriate combination of slag, low calcium (Class F) fly ash and calcium hydroxide (lime). It will be appreciated, however, that other materials that are rich in silica and alumina in an amorphous form may be used as the aluminosilicate material. Such materials include naturally occurring materials such as metakaolin and industrial wastes such as sugarcane bagasse ash, rice

15 husk ash, mine tailings, aluminum and grey cast iron slags.

Table 1: Compositions of one-part geopolymer matrix

Mix Compositions Curing condition

number

1 Fly ash + Slag + NaOH + Na₂Si0₃-GD Ambient temperature cured

2 Fly ash + Ca(OH)₂ + NaOH + Na₂Si0₃-GD Ambient temperature cured

3 Fly ash + Ca(OH)₂ + Na₂Si0₃-GD Ambient temperature cured

4 Fly ash + Ca(OH)₂ + Na₂Si0₃-Anhydrous Ambient temperature cured

5 Fly ash + Ca(OH)₂ + Na₂Si0₃-Penta Ambient temperature cured

6 Fly ash + Slag + Na₂Si0₃-GD Ambient temperature cured

7 Fly ash + Slag + Na₂Si0₃-Anhydrous Ambient temperature cured

8 Fly ash + Slag + Na₂Si0₃-Penta Ambient temperature cured

9 Fly ash + Slag + Na₂C0₃ Ambient temperature cured

10 Fly ash + Slag + Na₂Si0₃-Anhydrous + Ambient temperature cured

Na₂C0₃ The alkali activator powder may be sodium hydroxide, sodium silicate and sodium carbonate or a combination of them. It will be appreciated that other solid activators may also be suitable. The sodium silicate may comprise anhydrous sodium metasilicate, penta sodium metasilicate, GD Grade sodium silicate or a combination of them. It will be appreciated that other grades of sodium silicate may also be suitable.

For the purpose of illustration and not limitation, the exemplary specifications of different grades of sodium silicate, available through Redox, Australia and PQ, Australia, which are used in the current disclosure are presented in Table 2.

Table 2: Exemplary specifications of different grades of sodium silicate

* Average wt. % reported by the supplier

Chemically bound water in the powder which is released when dissolved in water.

Generally speaking, addition of water to the one-part geopolymer matrix composition hydrates the alkali activator powder so that it becomes chemically active and acts on the aluminosilicate material to form the geopolymer matrix. The alkali activator is selected so that it does not react with the reinforcing fibres. Once the fresh SHGC is formed by mixing the ingredients together, it can be cured at ambient temperature. It will be appreciated that the fresh one-part SHGC can be subjected to heat curing (e.g. 60°C for 24 hours) to accelerate the curing procedure.

One exemplary low calcium (Class F) fly ash is Gladstone fly ash available through Gladstone power station in Queensland, Australia. One exemplary slag is a locally available ground granulated blast furnace slag (GGBFS) supplied by

Independent Cement Pty Ltd, Australia. The chemical composition and loss on ignition (LOI) of the fly ash and slag determined by X-ray Fluorescence (XRF) are presented in Table 3. The total does not sum up to 100% because of rounding-off of the percentages. The fly ash and slag axe used in the one-part geopolymer matrix compositions listed in Table 1.

Table 3: Exemplary chemical compositions of fly ash and slag determined by XRF

Loss on ignition

The particle size distribution of the fly ash and slag are determined by using a CILAS particle size analyzer model 1190 and the distributions are presented in Figure 1. The passing percentages of particle size distribution are summarized in Table 4. It is to be understood that the presented chemical composition and LOI of fly ash and slag are for illustration purposes only and by no means are intended to be limitative thereof.

Table 4: Particle size distribution of fly ash and slag

The passing percentage. Two different grades of calcium hydroxide (Ca(OH)₂), namely Supercalco 97 and Industrial grade are suitable for use in the mixes identified in Table 1. However, other grades may also be suitable. Supercalco 97 is a laboratory grade powder supplied 5 by Redox Australia, while the Industrial Grade is a hydrated lime powder commonly used in the construction industry supplied by Cement Australia.

The amount of alkaline activator powder used in the SHGC compositions may range from 1.5% to 16% of the combined mass of the aluminosilicate material depending on the alkaline activator powder used. For instance, if the slag content is less o than 50 wt% of the total aluminosilicate material, a higher amount of anhydrous sodium metasilicate powder (e.g. 12 wt.%) is needed. While the slag content is equal or greater than 50 wt.%, a lower amount of anhydrous sodium metasilicate powder (e.g. 8 wt.%) would be sufficient. While these dosages have been identified as the most suitable to promote acceptable setting times and desirable structural evolution in the developed5 geopolymer, it will be appreciated that higher or lower dosages will be appropriate depending on the materials in the one -part geopolymer matrix composition and the desired mechanical properties of the SHGC.

Optionally, an appropriate amount of fine silica sand can be incorporated into the one-part geopolymer matrix compositions to increase the elastic modulus of the o one-part SHGC while maintaining its desirable strain hardening behavior. It will be appreciated that normal weight fine silica sand may be replaced by different fine light weight aggregates such as microscopic hollow ceramic spheres, fly ash cenosphere, perlite and expanded recycled glass aggregate in a proper amount to reduce the density of the ambient temperature cured SHGC (i.e. to manufacture light weight ambient 5 temperature cured one -part SHGC) while maintaining its desirable strain hardening behavior.

A variety of commercially available polymeric fibres can be used in the SHGC. It will be appreciated that steel fibres may also be used. Without being limited to the following properties, suitable properties for the fibres may include, provided that they0 have the following properties: fibre strength at least 800 MPa, fibre diameter from 10 to 100 m, fibre modulus of elasticity from 10 to 300 GPa and, and fibre length from 4 to 30 mm. The fibres preferably also have the following interfacial bond properties: interfacial chemical bond strength below 3.0 J/m , interfacial frictional bond strength from 1.0 to 4.5 MPa, and interface slip hardening coefficient below 2.5 and more preferably below 1.0.

Examples of suitable reinforcing fibres include: high strength and high modulus polyethylene (PE), poly vinyl alcohol (PVA), Poly-p-phenylenebenzobisoxazole (PBO) and high tenacity polypropylene (HTPP) fibers. It will be appreciated that other fibers with suitable properties (e.g. steel fibres) may be used in place of the examples mentioned here. For the purpose of illustration and not limitation, the properties of an exemplary PVA fibre Kuralon^®, available through Kuraray Co. Ltd., Japan, which are used in the current disclosure are presented in Table 5. The PVA fibres are used in a volume fraction in the range of 1 to 3% and preferably about 2%.

Table 5: Exemplary properties of the PVA fibres

The cost of the engineered geopolymer composite will be heavily affected by the cost of the fibres. To be cost effective, the fibre volume fraction is limited to 2% or less by volume, but this is not a practical limit on the fibre content. The fibre content also depends on the fibre dispersion and workability limitations. It is necessary to ensure uniform fibre dispersion within the matrix in order to have good tensile performance (high tensile strain capacity). It should be noted that from the

micromechanical point of view there is a critical fiber volume fraction (V ) which the composite exhibits strain hardening behavior if the fibre content is equal or greater to the (V ). If the fiber content is less than the (V ), then the composite exhibits conventional strain softening behavior typically seen in conventional fiber reinforced concretes. The (l^^£* ) depends on the properties of the fibre, matrix and interfacial bond properties between the fibre and the matrix.

An example composition based on mix number 7 from Table 1 is set out below in Table 6. The mass ratios presented in this specific example promote desirable mechanical properties, moderate setting time and adequate rheology for uniform fiber dispersion. However, these are for illustration purposes only and by no means are intended to be limitative thereof. For example, the relative amounts of slag and fly ash may vary for a given mix from 10 mass% fly ash with 90mass% slag to 90 mass % fly ash with 10 mass % slag. Examples of the fly ash content include 89 mass%, 75 mass% and 50 mass%, with the balance being slag, a combination of slag and calcium hydroxide or a combination of slag with other aluminosilicate materials.

Table 6: Example composition based on mix no. 7 in Table 1

*Mass ratio relative to the combined mass of fly ash and slag.

1 Composed of the Anhydrous Grade sodium metasilicate powder. It ipplied by Redox, Australia and its specification is given in Table 2

Added to the fly ash, slag and solid activator.

The amount of water used in preparing the SHGC affects the workability, rheology and strength of the geopolymer matrix and the fiber-matrix interfacial properties. In general, similar to conventional cement based materials, the higher the water content, the higher will be the workability and the lower strength results. Also, a good level of workability and viscosity is required to ensure uniform fiber dispersion. The higher the slag content, the higher will be the water content required to achieve acceptable workability. The water content also depends on the fineness (surface area) of the aluminosilicate source materials. In general, water content may be greater than 30% of the combined mass of the aluminosilicate material to achieve good level of workability and fiber dispersion. But this is only an approximate limit.

Generally speaking, the SHGC is prepared by the steps of 1) mixing dry powders including fly ash, slag and solid activator in a Hobart mixer for approximately 3 minutes; 2) combining the mixed dry powders with tap water and continue mixing for about 8 minutes; 3) gradually adding the fibres such as PVA fibres into the fresh geopolymer matrix after it reaches a desired fresh state, in terms of rheology, and continue mixing to ensure generally uniform fiber dispersion.

To obtain a more homogenous fibre dispersion, the fibres can be dispersed into the geopolymer matrix at low water to geopolymer solids ratio and then the residual 5 amount of water is added. In another method, hydrophilic fibres can be presoaked in water before being dispersed into the fresh geopolymer matrix. Prior to mixing, the PVA fibre can be in random form or in bundled form (with a water-soluble binder), with the bundled form being preferred. It will be appreciated that in another method, the reinforcing fibres may be combined and mixed with the dry mix composition, wherein o water may be gradually added to manufacture the SHGC.

The fresh one -part geopolymer matrix and SHGC are cast into different molds and compacted using a vibrating table. For ambient curing, the specimens are cured in air at ambient temperature (23 °C + 3°C) for 24 hours. The hardened specimens are then removed from the molds and cured in water tank at a temperature of 23°C+3°C for 275 days after de-molding.

The ambient cured temperature specimens are tested 28 days after casting.

Compression tests are conducted to evaluate the compressive strength of the ambient cured temperature geopolymer matrix and composite. The loading rate is 20 MPa+2 per minute and only the peak loads are recorded. At least three matrix specimens and three o composite specimens are cast into standard 50 mm plastic cube molds and compacted using a vibrating table. At the testing day the cube specimens are weighed to determine the density of the matrix and composite specimens.

Three-point bending tests on single edge notched beam specimens with a fixed span to depth (1/d) ratio equal to 4 and an initial notch depth to beam depth (a/d) ratio 5 equal to 0.5 were conducted to evaluate the matrix fracture properties including elastic modulus (E_m), fracture toughness (K_m) and crack tip toughness (J_t ) of the

manufactured ambient temperature cured SHGC. At least four matrix prisms with the dimensions of 60 mmx60 mmx280 mm are cast and compacted using a vibrating table.

The displacement control rate is 0.18 mm/min so that the maximum load for any

0 specimen is achieved within the first 30-60 s. The E_m and K_m are calculated according to the formulas given in effective crack model (ECM). Single-fiber pullout test was performed to determine the fiber-matrix interfacial properties, comprising chemical bond strength (Gd), fnctional bond strength ( o), and slip-hardening coefficient ( ). Specimen preparation, test configuration, data processing, and calculation of interfacial parameters can be found in the literature.

Uni-axial tension tests were conducted to evaluate the behavior of the developed ambient temperature cured SHGC under tension. At least three rectangular coupon specimens with the dimensions of 200 mmX75 mmX 10 mm were prepared. All coupon specimens were tested in uni-axial tension under displacement control with a displacement rate of 0.25 mm/min using MTS testing machine with hydraulic wedge grips.

Test results are summarized in Table 7, including density, compressive strength, matrix fracture properties comprising matrix fracture toughness, elastic modulus and crack tip toughness, and uni-axial tensile performance including first crack strength, ultimate tensile strength and tensile strain capacity. Exemplary tensile stress versus strain curves and typical multiple cracking pattern of the ambient temperature cured SHGC are presented in Figures 2 and 3, respectively. As shown in these figures, the manufactured ambient temperature cured SHGC exhibits clear strain hardening behavior accompanied by multiple cracking behaviour with very high tensile strain capacity of 4.2% on average which is several hundred times that of normal cement or geopolymer concrete.

Table 7: Test results for ambient cured one-part SHGC composition in Table 6

Ultimate tensile strength, a_c ; (MPa) 4.6+0.26

Tensile strain capacity, ¾ ; (%) 4.2+0.71

It is to be understood that any reference to information being "traditional" or "known" does not constitute an admission that the information forms a part of the common general knowledge in the art, in Australia or any other country.

Claims

1. A dry-mix composition for forming an ambient temperature cured, strain hardening geopolymer composite (SHGC), the dry-mix composition consisting of:

5 (a) aluminosilicate material that is rich in silica and alumina in an amorphous form; and

(b) an alkali activator powder;

wherein the dry-mix composition is selected to (i) enable the ambient temperature cured SHGC to be formed without addition of liquid activator and (ii) exhibit strain hardening o behavior accompanied by multiple cracking behaviour.

2. The dry-mix composition defined in claim 1, wherein the aluminosilicate material is an appropriate combination of materials selected from the group comprising: slag, low calcium (Class F) fly ash and calcium hydroxide (lime).

5

3. The dry-mix composition defined in claim 1 or claim 2, wherein the dry-mix geopolymer composition includes fine silica sand.

4. The dry-mix composition defined in claim 1 or claim 2, wherein the dry-mix o geopolymer composition further includes fine light-weight aggregates to reduce the density of the geopolymer composite.

5. The dry-mix composition defined in claim 4, wherein the fine light-weight aggregate comprise one or more aggregates selected from the group comprising:

5 microscopic hollow ceramic spheres, fly ash cenosphere, perlite and expanded recycled glass aggregate.

6. The dry-mix composition defined in any one of the preceding claims, wherein the alkali activator powder is one or more materials selected from the group

0 comprising: sodium hydroxide, sodium silicate and sodium carbonate.

7. The dry-mix composition defined in claim 6, wherein the sodium silicate may be one or more materials selected from the group comprising: anhydrous sodium metasilicate, penta sodium metasilicate and GD Grade sodium silicate.

5 8. The dry-mix composition defined in any one of the preceding claims, wherein the composition further includes reinforcing fibres consisting of one or more forms of fibre selected from the following group comprising: aromatic polyamide (i.e. aramid) fiber, high strength and high modulus polyethylene (PE) fiber, poly vinyl alcohol (PVA) fiber, Poly-p-phenylenebenzobisoxazole (PBO) fiber, steel fibers and high o tenacity polypropylene (HTPP) fiber.

9. The dry-mix composition defined in any one of the preceding claims, wherein the reinforcing fibres have a tensile strength at least 800 MPa, and length in the range of 4 to 30 mm.

5

10. The dry-mix composition defined in any one of the preceding claims, wherein the reinforcing fibres have an interfacial chemical bond strength below 3.0 J/m .

11. The dry-mix composition defined in any one of the preceding claims, wherein 0 the reinforcing fibres have an interfacial fnctional bond strength in the range of 1.0 to

4.5 MPa.

12. The dry-mix composition defined in any one of the preceding claims, wherein the reinforcing fibres may have an interface slip hardening coefficient below 2.5 and 5 more preferably below 1.0.

13. The dry-mix composition defined in any one of the preceding claims, wherein the reinforcing fibres have a fibre modulus of elasticity in the range of 10 to 300 GPa. 0

14. The dry-mix composition defined in any one of the preceding claims, wherein the reinforcing fibres have a diameter in the range of 10 to 100 m.

15. The dry-mix composition defined in any one of the preceding claims, wherein the strain hardening behaviour and the multiple cracking behaviour is accompanied by tensile strain capacity in the range of 1 to 6%.

5 16. An ambient temperature cured, strain hardening geopolymer composite (SHGC) formed by adding water to the dry-mix composition defined in any one of claims 1 to 15 and curing the SHGC at ambient temperature.

17. The ambient temperature cured SHGC defined in claim 16, wherein the

o composite is formed without adding liquid activator to the dry-mix composition.

18. The ambient temperature cured SHGC defined in claim 16 or claim 17, wherein the ambient temperature cured SHGC has a compressive strength in the range of 30 to 60 MPa.

5

19. The ambient temperature cured SHGC defined in any one of claims 16 to 18, wherein the composite exhibits strain hardening behavior accompanied by multiple cracking behaviour. 0

20. The ambient temperature cured SHGC defined in any one of claims 16 to 19, wherein the strain hardening behaviour and the multiple cracking behaviour is accompanied by tensile strain capacity in the range of 1 to 6%.

21. A method of forming an ambient temperature cured SHGC, the method

5 including mixing the dry-mix composition according to any one of claims 1 to 15 with water to form a generally uniform distribution of reinforcing fibres and curing the fresh SHGC at ambient temperature.

22. The method defined in claim 21, wherein the method further includes casting 0 the mixed composition into a mold or formwork.

23. The method defined in claim 21 or claim 22, wherein the method involves not adding liquid activator.