WO2020097690A1

WO2020097690A1 - Geopolymer compositions

Info

Publication number: WO2020097690A1
Application number: PCT/AU2019/051259
Authority: WO
Inventors: David Preston Gregory
Original assignee: Canasia Australia Pty Ltd
Priority date: 2018-11-16
Filing date: 2019-11-15
Publication date: 2020-05-22
Also published as: AU2019379875A1; BR112021009563A2; EP3880628A1; EP3880628A4

Abstract

A geopolymer composition comprising the reaction product of a reaction mixture comprising 30-80% w/w aluminosilicate material, the aluminosilicate material having a combined Al2O3 and SiO2 content of from 15-90% w/w; 1-20% w/w Portland cement; 10-60% w/w water; and 1-10% w/w alkali metal silicate, wherein the Portland cement:alkali metal silicate ratio is in the range from about 0.1 to about 3.0.

Description

"Geopolymer compositions"

Technical Field

[0001] The present disclosure relates to concrete compositions and, more particularly, to geopolymer compositions and method for making same.

Background

[0002] Since their conception in 1994, geopolymers have been investigated and developed as an alternative to standard hydraulic cements such as Portland cement. Geopolymers provide many environmental advantages to traditional cements, for example having a smaller carbon footprint by producing approximately 0.25 tonnes of carbon dioxide per tonne of geopolymer produced where traditional cements produce up to 1 tonne of carbon dioxide per tonne of cement produced. In addition,

geopolymers may be formed from waste streams from industrial processes, such as fly ash or blast-furnace slag.

[0003] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims.

Summary

[0004] Disclosed herein are geopolymer compositions formed from aluminosilicate materials, Portland cement and an alkali metal silicate in a predetermined ratio with the Portland cement. It is an advantage of the geopolymer compositions disclosed herein that the ratio of Portland cement to alkali metal silicate can be selected to provided predetermined advantageous properties of the geopolymer composition. It is a further advantage of the geopolymer compositions disclosed herein that, upon addition of the alkali metal silicate to a slurry comprising an aluminosilicate material, Portland cement and water, a phase change occurs providing a low viscosity liquid mixture that is self compacting and self-levelling prior to the onset of setting of the geopolymer composition. In addition, a flowable slurry can be formed from the aluminosilicate material, Portland cement and water, which can then be activated as required by the addition of the alkali metal silicate to initiate the geopolymerisation reaction.

[0005] According to the present disclosure, there is provided a geopolymer composition comprising the reaction product of a reaction mixture comprising:

30-80% w/w aluminosilicate material, the aluminosilicate material having a combined AI2O3 and S1O2 content of from 15-90% w/w;

1-20% w/w Portland cement;

10-60% w/w water; and

1-10% w/w alkali metal silicate, wherein the Portland cement: alkali metal silicate ratio is in the range from about 0.1 to about 3.0.

[0006] The aluminosilicate material is not particularly limited and may be, for example, selected from the group consisting of: fly ash, metakaolin, blast furnace slag, perlite, red mud, ferronickel slag, volcanic ash, and combinations thereof.

[0007] Preferably, the aluminosilicate material comprises less than 10% w/w calcium oxide, more preferably less than 7% w/w calcium oxide. In some embodiments, the aluminosilicate material comprises Class F fly ash.

[0008] The alkali metal silicate may be selected from the group consisting of: lithium silicate, sodium silicate, potassium silicates, rubidium silicate, caesium silicate and combinations thereof. For example, the alkali metal silicate is sodium silicate or potassium silicate. The metal silicate may have a SiC>2% to M2O ratio in the range of from 1 to 3. [0009] The reaction mixture may further comprise aggregate. The aggregate may comprise a particles of any suitable size, for example from about 10 pm to about 150 mm. The aggregate may comprise coarse aggregate having a particle size, for example, of about 5 mm to about 40 mm and/or fine aggregate having particle size, for example, of about 40 pm to about 400 pm. In some embodiments, the fine aggregate comprises sand.

[0010] The reaction mixture may include further additives, such as fibres,

microspheres, foaming agents, surfactants, dispersants, retarders and rheology modifiers. In some embodiments, the reaction mixture includes fibres, for example cellulose fibres (e.g. rice husk), mineral fibres (e.g. basalt fibres, quartz fibres), glass fibres, carbon fibres, carbon nanotubes, and/or synthetic fibres (e.g. polypropylene fibres, poly amide fibres, poly (amide-hydrazide) fibres, polyacrylonitrile fibres, poly paraphenylene ter ephthal amide fibres). The type, quantities and physical properties of the fibres can be selected based on a number of desired parameters, including cost, and strength and flexibility of the final product.

[0011] The compressive strength of the geopolymer composition may be varied by varying the concentrations and/or ratios of the components in the reaction mixture. Preferably, the geopolymer composition has a 7 day compressive strength greater than 5 MPa, more preferably greater than 10 MPa, or greater than 15 MPa. Preferably, the geopolymer has a 28 day compressive strength of greater than 10 MPa, preferably greater than 15 MPa, or greater than 20 MPa.

[0012] The Portland cement: alkali metal silicate ratio may be selected to provide a geopolymer composition having certain predetermined properties. In some

embodiments, Portland cemenrialkali metal silicate ratio is selected to control the geopolymer composition set time.

[0013] The specific gravity of the geopolymer composition may be greater than 1.0, greater than 1.5, or greater than 2.0. [0014] According to the present disclosure, there is further provided a method of preparing a geopolymer composition disclosed herein, the method comprising: forming an aqueous slurry of the aluminosilicate material, Portland cement and water; adding the alkali metal silicate to the slurry to initiate a geopolymerisation reaction; and allowing the slurry to set.

[0015] The aqueous slurry may be mixed to form a substantially homogenous mixture.

[0016] After adding the alkali metal silicate to the slurry, the slurry may be formed into a predetermined shape prior to the slurry setting. In some embodiments, the slurry is formed into a brick shape, for example by moulding, extrusion, or any other suitable production method.

[0017] In some embodiments, the geopolymerisation reaction occurs at room temperature.

Definitions

[0018] With regards to the definitions provided herein, unless stated otherwise, or implicit from the context, the defined terms and phrases include the provided meanings. Unless explicitly stated otherwise, or apparent from context, the terms and phrases below do not exclude the meaning that the term or phrase has acquired by a person skilled in the relevant art. The definitions are provided to aid in describing particular embodiments, and are not intended to limit the claimed invention, because the scope of the invention is limited only by the claims. Furthermore, unless otherwise required by context, singular terms shall include pluralities and plural terms hall include the singular. [0019] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0020] It is to be appreciated that certain features that are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any sub combination.

[0021] Throughout the present specification, various aspects and components of the invention can be presented in a range format. The range format is included for convenience and should not be interpreted as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range, unless specifically indicated. For example, description of a range such as from 1 to 5 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 5, from 3 to 5 etc., as well as individual and partial numbers within the recited range, for example, 1, 2, 3, 4,

5, 5.5 and 6, unless where integers are required or implicit from context. This applies regardless of the breadth of the disclosed range. Where specific values are required, these will be indicated in the specification.

Description of Embodiments

[0022] With reference to the accompanying examples, there is provided a geopolymer composition comprising the reaction product of a reaction mixture comprising 30-80% w/w aluminosilicate material, the aluminosilicate material having a combined AI2O3 and S1O2 content of from 15-90% w/w, 1-20% w/w Portland cement, 10-60% w/w water, and 1-10% w/w alkali metal silicate, wherein the Portland cement: alkali metal silicate ratio is in the range from 0.1 to 3.0. [0023] There is further provided a method of preparing a geopolymer composition disclosed herein comprising forming an aqueous slurry comprising the aluminosilicate material, Portland cement and water, and allowing the slurry to set.

[0024] It has been surprisingly found that the properties of the geopolymer composition, including the set time upon initiation of the geopolymerisation reaction through introduction of the alkali metal silicate, and compressive strength of the geopolymer composition can be selectively varied by controlling the concentrations and, more particularly, the Portland cement: alkali metal silicate ratio of the reaction mixture.

[0025] Furthermore, it has been surprisingly found that the use of a combination of Portland cement and alkali metal silicate results in a phase change of the slurry upon addition of the alkali metal silicate, i.e. the initiation of the geopolymerisation reaction. This phase change results in a low viscosity liquid mixture that is self-compacting and self-levelling prior to the onset of setting of the geopolymer composition. This feature makes compositions according to the present disclosure particularly suited to forming moulded products, for example bricks and the like for the construction industry.

Furthermore, the set time of the geopolymer compositions can be varied to suit the geopolymer composition to the intended application of the geopolymer composition. For example, the Portland cement and alkali metal silicate can be selected so as to provide a quick set time for applications such as sprayed concrete applications, or to provide relatively slow set time for applications such as building subsidence repair requiring the injection of the geopolymer composition underground.

[0026] In cost sensitive applications, it is preferred to minimise the concentrations of the Portland cement and silicate, whilst maintaining compressive strength targets in the final product of greater than 2MPa non structural, 3MPa structural, and 8MPa structural below ground after 7 days.

[0027] The aluminosilicate material for use in geopolymer compositions according to the present disclosure may be any suitable aluminosilicate material, for example the aluminosilicate material may be selected from the group consisting of: fly ash, metakaolin, blast furnace slag, perlite, red mud, ferronickel slag, volcanic ash, and combinations thereof. It is preferable that the aluminosilicate material is an

aluminosilicate-containing waste product that can be recycled and avoid the

environmental and financial costs of disposal and storage of such waste products.

[0028] In an embodiment, the aluminosilicate material is fly ash. Fly ash is a by product of the burning of coal combustion, for example in power stations. Fly ash itself possesses little or no cementitious properties. Given the high levels of silicon dioxide (S1O2) and aluminium oxide (AI2O3) make fly ash a suitable precursor with which to form geopolymer materials.

[0029] Fly ashes are categorised into two classes: Class F fly ash and Class C fly ash. Among other differences, Class F fly ash contains less than 7% calcium oxide (CaO), significantly less than Class C fly ash which generally contains more than 20% CaO.

[0030] Geopolymer compositions according to the present disclosure may be formed from Class F fly ash, Class C fly ash or mixtures thereof, preferably from Class F fly ash.

[0031] Preferably, to better control set times and compressive strengths of the geopolymer compositions, the aluminosilicate material comprises less than 10% w/w calcium oxide, more preferably less than 7% w/w calcium oxide.

[0032] The reaction mixture further comprises water which can be combined with the aluminosilicate material and the Portland cement in order to form a slurry. Preferably, the amount of water added is just enough to form a workable slurry with good dispersion of the slurry components. It has been found that minimising the amount of water present in the reaction mixture helps to reduce shrinkage of the final geopolymer product. The amount of water required to form the slurry will be dependent on the water content of the other components of the reaction mixture, including the water content of the aluminosilicate material and the alkali metal silicate if added as an aqueous solution.

[0033] The formed slurry comprising the aluminosilicate material, Portland cement and water, as well as any optional additives such as aggregate, has been found to have a good stability. The slurry can be stored, handled and transported readily and can remain flowable until such time that the geopolymerisation reaction is initiated.

[0034] The alkali metal silicate acts to initiate a geopolymerisation reaction of the reaction mixture. The alkali metal silicate may be any suitable metal silicate, for example lithium silicate, sodium silicate, potassium silicate, rubidium silicate, caesium silicate, and combinations thereof. Typically, due to costs and availability, the metal silicate is potassium or sodium silicate.

[0035] The alkali metal silicate may be provided in anhydrous form, or may be provided in an aqueous solution to assist in dispersing the metal silicate through the reaction mixture. For the purposes of the present disclosure, where an aqueous solution has been used, the water content of the aqueous metal silicate solution forms part of the described water content of the reaction mixture.

[0036] In an embodiment, the alkali activator is a metal silicate having a Si02% to Micro ratio in the range of 1 to 3. The amount of alkali metal silicate in the reaction mixture will vary depending on a number of factors, including the type of metal silicate used, the Si02% to M₂0% ratio, the amount of Portland cement present in reaction mixture, as well as the desired properties of the geopolymer composition.

[0037] The reaction mixture may further include aggregate. The amount and size of aggregate added to the reaction mixture will vary depending on the properties of the aggregate such as density and particle size, as well as the desired properties of the final geopolymer product. For example, coarse aggregate having a particle size of greater than 5 mm may be added to increase compressive strength, and/or fine aggregate having a particle size of less than 5 mm may be added to reduce shrinkage. In an example, the amount of aggregate in the reaction mixture is in the range of 0-30%.

[0038] Alternatively or additionally, the reaction mixture may further include fibres. The amount of fibres added to the reaction mixture will vary depending on the type and properties of the fibre, such as length, diameter and strength, as well as the desired properties of the final geopolymer product, such as the desired flexural strength of the final product.

[0039] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

EXAMPLES

[0040] The present disclosure is now described further in the following non-limiting examples.

EXAMPLE GEOPOLYMER COMPOSITIONS

[0041] Geopolymer compositions were prepared in accordance with the present disclosure from various aluminosilicate materials. The AI2O3 and S1O2 content of the aluminosilicate materials used to form geopolymer compositions according to the present disclosure are summarised in the results tables below.

[0042] Geopolymer compositions were prepared by dry mixing the aluminosilicate material with Portland cement and, optionally, 5 mm and/or 10 mm aggregate. Water was then added to the dry mixture and thoroughly mixed to form a slurry.

[0043] To the slurry was added either sodium or potassium silicate in liquid form, and the mixture stirred briefly to aid distribution after which the mixture was left to set. Strength measurements were conducted at 7 days. A representative, non-exhaustive, summary of geopolymer compositions formed using this method, the specific gravity, and day 7 strength testing are summarised in Tables 1 and 2 below.

[0044] In preparing geopolymer compositions according to this method, it was observed that the addition of the metal silicate solution to the slurry led to an initial decrease in the viscosity of the slurry to form a“fluid phase” prior to the setting of the geopolymer composition. Moreover, as described in more detail below with regard to samples 18 to 20, the decrease in viscosity following the addition of the metal silicate solution was greater than would be achieved by adding the same amount of water despite the metal silicate solution being more viscous than water. This“fluid phase” promoted the self-compacting and self-levelling of the geopolymer composition, where the greater the decrease in viscosity typically providing geopolymer compositions with increased specific gravity and/or compressive strength. It was further observed that the “fluid phase” could be controlled by controlling the concentrations and ratios of the Portland cement and metal silicate.

[0045] In the examples shown in Table 1, the aluminosilicate material used to prepare samples 1, 2 and 3 had higher quantities of calcium compounds than the

aluminosilicate material used to prepare samples 4 and 5. Without wishing to be bound by theory, geopolymer compositions formed from aluminosilicate materials comprising higher quantities of calcium compounds had a tendency to set more quickly than geopolymer compositions formed from aluminosilicate materials comprising lower quantities of calcium compounds. In samples 1 to 5, this quicker set time was observed to reduce the development of compressive strength of the geopolymer composition, however this relationship between fast set times and lower compressive strengths was not the case for all tested aluminosilicate materials.

[0046] In addition to having lower quantities of calcium compounds, the

aluminosilicate material used to form samples 4 and 5 had a larger particle size than the aluminosilicate material used to form samples 1, 2 and 3. As can be seen from Table 1, less water was required to form the slurry of larger aluminosilicate material particle size samples 4 and 5 than for samples 1, 2 and 3.

Table 1: Geopolymer compositions

Table 2: Further example geopolymer compositions

EFFECT OF PORTLAND CEMENTrMETAL SILICATE RATIO

ON SET TIME

[0047] Geopolymer compositions were prepared in accordance with the present disclosure from various aluminosilicate materials in the manner described above for the samples in Tables 1 and 2. The Portland cementmetal silicate ratio of the

compositions was varied to assess the effect of the ratio on set times. A summary of geopolymer compositions formed using this method and the set times for the formed geopolymer compositions are summarised in Table 3 below.

[0048] As can be seen from Table 3 below, an increase in metal silicate concentration relative to the Portland cement concentration (i.e. a decrease in the Portland cement: metal silicate ratio) typically resulted in increased set times.

Table 3: Effect of Portland cementrmetal silicate ratio on set time

EFFECT OF SILICATE CONCENTRATION ON COMPRESSIVE STRENGTH

[0049] Geopolymer compositions were prepared in accordance with the present disclosure from an aluminosilicate material in the manner described above for the previous examples. The water and sodium silicate solution concentrations were varied to assess the effect of metal silicate concentration on the geopolymer composition. A summary of geopolymer compositions formed using this method and day 7 strength testing are summarised in Table 4 below.

Table 4: Effect of silicate concentration on compressive strength

* 44% w/w solids; Si02%/Na20% ratio 2.0 [0050] In preparing samples 18 to 20, it was observed that the specific gravity of the geopolymer composition increased with increasing sodium silicate concentration. Furthermore, it was observed that a lower viscosity“fluid phase” was achieved with a higher silicate level before setting, leading to a slower set time. This is an unexpected result as viscosity of liquid sodium silicate is higher than water, yet a greater viscosity decrease is observed on silicate addition than would be expected by standard water addition. This further suggests that the phase change, which provides the beneficial self-compacting and self-levelling properties of the geopolymer compositions according to the present disclosure, is linked to geopolymer formation.

Claims

CLAIMS:

1. A geopolymer composition comprising the reaction product of a reaction mixture comprising:

1-20% w/w Portland cement;

10-60% w/w water; and

2. A geopolymer composition according to claim 1, wherein the aluminosilicate material is selected from the group consisting of: fly ash, metakaolin, blast furnace slag, perlite, red mud, ferronickel slag, volcanic ash, and combinations thereof.

3. A geopolymer composition according to claim 1 or claim 2, wherein the aluminosilicate material comprises less than 10% w/w calcium oxide.

4. A geopolymer composition according to claim 3, wherein the aluminosilicate material comprises less than 7% w/w calcium oxide.

5. A geopolymer composition according to any one of the preceding claims, wherein the aluminosilicate comprises Class F fly ash.

6. A geopolymer according to any one of the preceding claims, wherein the alkali metal silicate has a SiC>2% to M20% ratio in the range of from 1 to 3.

7. A geopolymer composition according to claim 5 or claim 6, wherein the alkali metal silicate is selected from the group consisting of: lithium silicate, sodium silicate, potassium silicate, rubidium silicate, caesium silicate, and combinations thereof.

8. A geopolymer composition according to claim 7, wherein the metal silicate is sodium silicate or potassium silicate.

9. A geopolymer composition according to any one of the preceding claims, wherein the reaction mixture further comprises aggregate.

10. A geopolymer composition according to claim 9, wherein the aggregate comprises coarse aggregate having a particle size of from 5 mm to 40 mm.

11. A geopolymer according to claim 9 or claim 10, wherein the aggregate comprises fine aggregate having a particle size of from 40 pm to 400 pm.

12. A geopolymer according to claim 11, wherein the fine aggregate comprises sand.

13. A geopolymer composition according to any one of the preceding claims, wherein the geopolymer composition has a 7 day compressive strength greater than 15 MPa.

14. A geopolymer composition according to any one of the preceding claims, wherein the geopolymer composition has a 28 day compressive strength of greater than 20 MPa.

15. A geopolymer composition according to any one of the preceding claims, wherein the Portland cemenrialkali metal silicate ratio is selected to control the geopolymer composition set time.

16. A geopolymer composition according to any one of the preceding claims, wherein the geopolymer composition has a specific gravity of greater than 1.5.

17. A method of preparing a geopolymer composition according to any one of the preceding claims comprising: forming an aqueous slurry comprising the aluminosilicate material, Portland cement and water; adding the alkali metal silicate to the slurry to initiate a geopolymerisation reaction; and allowing the slurry to set.

18. A method according to claim 17, wherein the aqueous slurry is mixed to form a substantially homogenous mixture.

19. A method according to claim 17 or claim 18, wherein the geopolymerisation reaction occurs at room temperature.