Geopolymer building materials

Abstract

A free-flowing solid activator for a geopolymer mortar or concrete comprises or consists of an alkali(ne) metal carbonate surface treated with a sub-stoichiometric amount of alkali(ne) metal hydroxide. In one embodiment a method for producing an activated fly ash comprises: a) spraying an aqueous alkali(ne) metal silicate onto the surface of a solid particulate fly ash; b) drying the spray-treated product of step a); c) optionally grinding the dried product of step b); and optionally, repeating the spray treatment process for the product of step b) or step c) by returning the product of step b) or step c) to step a).

Description

[0001] GEOPOLYMER BUILDING MATERIALS

[0002] Technical Field

[0003] The present disclosure relates to geopolymer mortars and geopolymer concretes.

[0004] Considering the high consumption of concrete and the increasing necessity for cement production, high attention to the environmental degradation effects of this substance is needed. These effects include 8% of CO2emission and the considerable consumption of energy such as electricity and fossil fuels. Hence the provision of alternative products in order to move towards sustainable development is essential. Therefore, the use of an eco- friendly concrete enables the reduction of consumption of ordinary Portland cement (OPC) with activated pozzolanic binders as a replacement, leading to lower emission of CO2in the atmosphere[5].

[0005] The current process towards Portland cement generates about 8% of the global CO2 emissions. Geopolymers form a lower carbon footprint alternative. They are made up from alumino-silicate materials like fly ash and blast furnace slag and alkali activators like NaOH and Na-silicate. There are many advantages to using geopolymer concretes (GPC), including improved strength and durability properties. High early age strength and ambient curing of GPC helps to reduce construction time. Moreover, when industrial byproducts such as fly ash and ground granulated blast-furnace slag (GGBS) are added to GPC, this leads to advantages such as reduced carbon dioxide emission, reuse of waste materials (that would otherwise end up in landfill), cost reduction, and reduced energy requirements for the extraction of raw materials. In view of the current push for improved environmental profiles across all areas of technology, it is unsurprising that there is an ever-increasing volume of activity in this technology area (e.g., US2022002196, EP1732861 , EP3080053, EP2853519, EP2502890, US8349071).

[0006] There are, however, challenges with GPC. A key challenge is the provision of GPC with a suitable pot life (i.e., a cure rate that is not so fast that handling by builders is difficult and not so slow that the build time becomes unreasonable) and high final hardness. Additionally, current GPC systems either require the end user (e.g., builders or operators) to handle caustic solutions (NaOH and / or Na-silicate solution), which is difficult and dangerous to do on a construction site, or require the use of pure powders of NaOH (prills), which are more difficult to produce (and are therefore more expensive than the solution, in addition to there being a limited production capacity for making those prills). As such, there remains a need for a “powder ready-mix” that does not require the use of NaOH “prills”, which only requires the end user to add water to produce the GPC, and which GPC has suitable pot life and high final hardness.

[0007] Description

[0008] The present inventors have now developed such a “powder ready-mix”. The key to success in that respect was found to reside in newly developed alkali activators used in the GPC mix. Specifically, the desired pot life and final hardness balance in the GPC was achieved by using a free-flowing solid activator containing an alkali(ne) metal carbonate surface treated with a sub-stoichiometric amount of alkali(ne) metal hydroxide. It was found that this activator could be dry-blended with the usual dry pre-mix components of GPC to form a powder mixture that only needed to be mixed with water to produce the GPC with the desired pot life and final hardness. Furthermore, the GPC properties could be enhanced by using a newly developed free-flowing activated fly ash comprising or consisting of fly ash surface treated with an alkali(ne) metal silicate. Again, this activated fly ash could be dry- blended with the above activator and / or other usual dry pre-mix components of GPC to form a powder mixture that only needed to be mixed with water to produce the GPC with the excellent pot life and final hardness.

[0009] As such, in a first aspect, the present disclosure relates to a free-flowing solid activator for a geopolymer mortar or concrete comprising or consisting of an alkali (ne) metal carbonate surface treated with a sub-stoichiometric amount (relative to the alkali(ne) metal carbonate) of alkali(ne) metal hydroxide. Without wishing to be bound by theory, it is thought that the surface treatment may give rise to a “core-shell” type arrangement, wherein the carbonate (core) is coated by the hydroxide (shell), with some reaction occurring between the hydroxide and carbonate at the interface. It is postulated that it may be this “core-shell” type arrangement that contributes to the observed improvements in GPC properties.

[0010] “Free-flowing solid” is a normal term of the art and has its ordinary meaning, i.e., a substance consisting of solid particles and which is, or is capable of being in, a flowing or running consistency at standard conditions (room temperature and normal humidity).

[0011] For the avoidance of doubt, “GPC” when used in connection with the present disclosure is shorthand to describe both geopolymer concretes and geopolymer mortars. The alkali(ne) metal carbonate is preferably calcium carbonate, magnesium carbonate, dolomite (MgCaCO3), or mixtures thereof. Most preferably, the alkali(ne) metal carbonate is calcium carbonate.

[0012] The alkali(ne) metal hydroxide is preferably magnesium hydroxide, calcium hydroxide, lithium hydroxide, potassium hydroxide, or sodium hydroxide. Most preferably, the alkali(ne) metal hydroxide is sodium hydroxide.

[0013] Preferably, the free-flowing solid activator comprises or consists of 55 to 90, preferably 60 to 85, more preferably 65 to 80 parts by weight of the alkali(ne) metal carbonate and 10 to 45, preferably 15 to 40, more preferably 20 to 35 parts by weight of the alkali(ne) metal hydroxide surface treatment.

[0014] The free-flowing solid activator is preferably a powder having a median particle size (Dv50) of less than 100 microns, more preferably less than 50 microns. It has been found that the finer particle size improves the distribution and homogeneity of the “powder ready-mix”. Median particle size (Dv50) is determined using laser diffraction and is defined as the maximum particle diameter below which 50% of the sample volume exists. Dv50 is a common way to characterize particulate materials, and the skilled person would be fully aware of how to measure that parameter.

[0015] The term “an alkali(ne) metal carbonate surface treated with a sub-stoichiometric amount (relative to the alkali(ne) metal carbonate) of an alkali(ne) metal hydroxide” has its literal meaning. For the avoidance of any doubt, it means a controlled amount of an aqueous solution of an alkali(ne) metal hydroxide has been applied in a controlled manner to the surface of a controlled amount of a solid alkali(ne) metal carbonate, and the resulting material has then been dried, thereby producing an alkali(ne) metal carbonate surface treated with a sub-stoichiometric amount (relative to the alkali(ne) metal carbonate) of an alkali(ne) metal hydroxide. As explained below, there are many well-known apparatuses commonly available that would be suitable for performing this surface treatment, the correct use of which for this purpose would be routine for a person skilled in the art. It should be understood that “surface treated” does not mean or extend to a dissolution step (i.e., “surface treated” does not mean or extend to the solid alkali(ne) metal carbonate being dissolved in an aqueous solution of the alkali(ne) metal hydroxide prior to removal of water by drying). In that respect, in a second aspect, the present disclosure relates to a method for producing a free-flowing activator as described above, the method comprising: a) contacting an amount of an aqueous solution of an alkali(ne) metal hydroxide with the surface of a dry particulate alkali(ne) metal carbonate, wherein the amount of the aqueous solution of the alkali(ne) metal hydroxide contacted with the surface of a dry particulate alkali(ne) metal carbonate is selected such that the molar ratio of carbonate to hydroxide in the final surface treated product is greater than 1 , b) drying the product of step a), c) optionally grinding the surface treated product of step b), and d) optionally, repeating the surface treatment process for the product of step b) or step c) by returning the product of step b) or step c) to step a).

[0016] Preferably, the amount of aqueous solution of an alkali(ne) metal hydroxide is selected such that the resulting free-flowing solid activator comprises or consists of 60 to 90 parts by weight of the alkali(ne) metal carbonate and 10 to 55 parts by weight of the alkali(ne) metal hydroxide surface treatment, preferably 15 to 40 parts and most preferably 20 to 35 parts.

[0017] The aqueous solution of an alkali(ne) metal hydroxide is preferably a 15-70% aqueous solution of the alkali(ne) metal hydroxide, more preferably about 50% (as is commercially available for NaOH). When required, the solution can be heated to reduce viscosity and facilitate contacting.

[0018] For the avoidance of doubt, the “dry particulate alkali(ne) metal carbonate” can contain water but only to such a level that the powder remains free flowing. For calcium carbonate this means it typically contains less than 0.5 wt.% water, preferably < 0.2 wt.%. The dry particulate alkali(ne) metal carbonate preferably has a particle size (Dv50) of less than 300 microns, more preferably less than 200 microns, most preferably less than 100 microns and may be as low less than 10 microns.

[0019] There are many well-known suitable solid-liquid contactors that would be suitable for performing step a), such as high shear solid-liquid mixers (such as the Schugi Flexomix, Eirich granulator / mixer or the Lodige CM), ploughshare mixers, drum mixers, and spray coaters. The surface treatment may be performed in such solid-liquid contactors as a batch process or as a continuous process. The preferred solid-liquid contactor is a spray coater. Thus, in a preferred embodiment, the surface treatment is a spray treatment, and the method comprises: a) spraying an aqueous solution of an alkali(ne) metal hydroxide onto the surface of a dry particulate alkali(ne) metal carbonate, b) drying the spray treated product of step a), and c) optionally grinding the dried product of step b). d) optionally, repeating the spray treatment process for the product of step b) or step c) by returning the product of step b) or step c) to step a).

[0020] For the method for surface treating the dry particulate alkali(ne) metal carbonate it is preferable in step a) for the solid-liquid contactor to be operated at high shear (e.g., > 2000 - 5000 rpm, dependent on size and type of mixer) and with a low residence time (e.g. < 2 - 30 seconds, dependent on size and type of mixer).

[0021] In step b), the surface treated alkali(ne) metal carbonate is dried (i.e., water is removed). Any suitable drying means may be used to dry the surface treated alkali(ne) metal carbonate, such as a fluidized bed, vacuum mixer / dryer, drum dryer, belt dryer, etc. Ideally and to avoid any uncontrolled aggregation, the drying step should be performed immediately (i.e., within less than 20 minutes, preferably within less than 10 minutes and most preferably directly feeding into the dryer) after the surface treatment step a).

[0022] As noted above, the free-flowing solid activator is preferably a powder having a median particle size (Dv50) of less than 100 microns, more preferably less than 50 microns. It has been found that the finer particle size improves the distribution and homogeneity of the “powder ready-mix”. As such, the dried surface treated alkali(ne) metal carbonate of step b) may be subjected to an optional grinding step to meet this particle size preference. Any suitable grinding means may be employed, such as ball milling, hammer mill, jet mill, etc. Alternatively, or in addition to the optional grinding step, the particulate material may be sorted, e.g., by sieving.

[0023] In a further optional step, the product of step b) or step c) may be subjected to one or more further surface treatment(s) to further increase the alkali(ne) metal hydroxide content of the free-flowing solid activator. As such, the surface treatment process may be repeated for the product of step b) or step c) by returning the product of step b) or step c) to step a) as long as the carbonate is not all reacted. As mentioned above, the GPC properties could be enhanced by using a newly developed free-flowing activated fly ash comprising or consisting of fly ash surface treated with an alkali(ne) metal silicate. Accordingly, in a third aspect, the present disclosure relates to a free-flowing activated fly ash for a geopolymer mortar or concrete comprising or consisting of fly ash surface treated with an alkali(ne) metal silicate.

[0024] The activated fly ash preferably comprises at least 8 wt.%, 10 wt.% alkali(ne) metal silicate, more preferably at least 15wt%, more preferably at least 20wt%, most preferably at least 25wt%.

[0025] The fly ash used in the preparation of the activated fly ash is preferably a class C fly ash or a class F fly ash, more preferably a class F fly ash, as determined in accordance with ASTM C618.

[0026] The alkali(ne) metal silicate is preferably sodium silicate, most preferably with a SiO2 / NaO2 molar ratio of between 1.7 - 2.3.

[0027] Preferably, the activated fly ash is a free-flowing powder, preferably a powder having a median particle size (Dv50) of less than 100 microns, more preferably less than 50 microns (Dv50 is explained above).

[0028] The term “fly ash surface treated with an alkali(ne) metal silicate” has its literal meaning. For the avoidance of any doubt, it means an aqueous alkali(ne) metal silicate has been applied to the surface of a particulate fly ash, and the resulting material has then been dried, thereby producing a particulate fly ash surface treated with an alkali(ne) metal silicate. The solidliquid contactors described above would be equally suitable for performing this surface treatment of the fly ash. Thus, in a fourth aspect, the present disclosure relates to a method for producing an activated fly ash as described above, the method comprising: a) contacting an aqueous alkali(ne) metal silicate with the surface of a solid particulate fly ash, b) drying the product of step a), c) optionally grinding the dried product of step b), d) optionally, repeating the surface treatment process for the product of step b) or step c) by returning the product of step b) or step c) to step a).

[0029] The preferred solid-liquid contactor is a spray coater. Thus, in a preferred embodiment, the surface treatment is a spray treatment, and the method comprises: a) spraying an aqueous alkali(ne) metal silicate onto the surface of a solid particulate fly ash, b) drying the spray treated product of step a), and c) optionally grinding the dried product of step b). d) optionally, repeating the spray treatment process for the product of step b) or step c) by returning the product of step b) or step c) to step a).

[0030] For the method for surface treating the solid particulate fly ash it is preferable in step a) for the solid-liquid contactor to be operated at a lower shear and with a longer residence time.

[0031] In step b), the surface treated fly ash is dried (i.e. , water is removed). Any suitable drying means may be used to dry the surface treated fly ash, such as a fluidized bed, vacuum mixer / dryer, drum dryer, belt dryer, etc.

[0032] As noted above, the activated fly ash is preferably a powder having a median particle size (Dv50) of less than 100 microns, more preferably less than 50 microns. As such, the dried surface treated fly ash of step b) may be subjected to an optional grinding step to meet this particle size preference. Any suitable grinding means may be employed, such as ball milling, hammer mill, jet mill, etc. Alternatively, or in addition to the optional grinding step, the particulate material may be sorted, e.g., by sieving.

[0033] In a further optional step, the product of step b) or step c) may be subjected to one or more further surface treatment(s) to further increase the alkali(ne) metal silicate content of the activated fly ash. As such, the surface treatment process may be repeated for the product of step b) or step c) by returning the product of step b) or step c) to step a).

[0034] The primary objective of the present disclosure was to provide a “powder ready-mix” that does not necessarily require the use of NaOH “prills”, which only requires the end user to add water to produce the GPC, and which GPC has suitable pot life and high final hardness.

[0035] Accordingly, in a fifth aspect, the present disclosure relates to a geopolymer mortar or concrete pre-mix composition comprising:

[0036] - a free-flowing solid activator as described above (first aspect), fly ash, and an alkali(ne) metal silicate; or

[0037] - a solid activator comprising an alkali(ne) metal hydroxide; and an activated fly ash as described above (third aspect); or - a free-flowing solid activator as described above (first aspect), and an activated fly ash as described above (third aspect).

[0038] This pre-mix composition needs only to be blended with at least one filler and / or functional additive to form a powder ready-mix that only needs to be mixed with an appropriate amount of water to prepare a geopolymer mortar or concrete. The powder ready-mix can be easily produced on-site, or it can be produced off-site and shipped as a “ready to use” composition.

[0039] Accordingly, in a sixth aspect, the present disclosure relates to a geopolymer mortar or concrete powder ready-mix composition comprising:

[0040] - a free-flowing solid activator as described above (first aspect), fly ash, an alkali(ne) metal silicate, and at least one filler and / or functional additive; or

[0041] - a free-flowing solid activator as described above (first aspect), an activated fly ash as described above (third aspect), and at least one filler and / or functional additive.

[0042] The skilled person would be more than capable of selecting at least one suitable filler and / or functional additive for use in the above powder ready-mix. Preferred fillers include, but are not limited to, sand and / or aggregate. Functional additives include, but are not limited to, (ground) granulated blast furnace slag, polymer beads, mineral powders, or vegetable fibers such as wood or coconut fibers.

[0043] Per the above, this powder ready-mix need only be mixed with water to produce the geopolymer mortar or concrete. Accordingly, in a seventh aspect, the present disclosure relates to a process for preparing a geopolymer mortar or concrete comprising mixing the powder ready-mix composition described above (sixth aspect) with water.

[0044] Preferably, the process comprises mixing about 100 parts by weight of the powder ready-mix composition with up to about 50 parts by weight water and more preferably about 15 to about 35 parts by weight water.

[0045] Finally, in an eighth aspect, the present disclosure relates to the geopolymer mortar or concrete obtainable by the process of the seventh aspect.

[0046] It is noted that various elements of the present invention, including, but not limited to, preferred ranges for the various parameters, can be combined unless they are mutually exclusive. Examples

[0047] The invention will be elucidated by the following examples without being limited thereto or thereby.

[0048] A. General Procedure - Preparation of Mortars

[0049] All solids were charged to a plastic container and thoroughly mixed. Water was then added and mixed with the solids until a smooth mortar was achieved.

[0050] B. General Procedure - Penetration Test

[0051] Mortars prepared in accordance with General Procedure A were scooped into 2 plastic trays (150 g each) and tapped to level the surface. The 2 plastic trays were left to set for 6 hours and 1 day, respectively. These mortars were then subjected to the following penetration test. The sample is put in the Stable Micro Systems Texture Analyser TA.XT2i equipped with a 50 kg load cell. The measuring tool is a stainless-steel hemisphere with 10 mm radius.

[0052] The penetration test is executed in the “Compression” test-mode. In the pre-test phase the hemisphere moves downward at 2.0 mm / s until it touches the sample surface and the force measured by the load cell exceeds the trigger value of 0.1 N. Then the test phase is entered, and the speed is reduced to 0.5 mm / s while the force needed to penetrate the mortar is continuously logged. The test phase is continued until the hemisphere has travelled 10 mm into the mortar. Then the hemisphere is retracted from the sample and moves to its startposition. From the logged data a plot is constructed which gives the exerted force as a function of time (or travelled distance) in the test phase. The maximum exerted force is determined.

[0053] C. General Procedure - Diametrical breaking strength

[0054] Mortars prepared in accordance with General Procedure A were used to prepare tablets (95 g each). The mortar was scooped into a plastic mold, tapped, and left to set. The tablet dimensions were 050 mm and H = 21 mm. After 24 hours, the mold was removed, and the tablet was left for further hardening. After 1 week, the diametrical breaking strength of the tablet was measured as follows.

[0055] The tablet is placed diametrically between 2 rigid plates. The lower plate is fixed and slightly curved to prevent the tablet from moving. The upper plate moves downward at a constant speed (0.1 mm / s). When the plate touches the curved surface of the tablet, a force is needed to maintain the downward movement and the tablet distorts. The force increases until the tablet breaks. The maximum force is read from the display and is called the diametrical breaking strength. Example 1 - Preparation of a free-flowing solid activator (CaCO3surface treated with NaOH) Apparatus

[0056] The free-flowing solid activator was prepared in a pilot unit comprising

[0057] • a holding tank for the dry particulate CaCO3,

[0058] • a temperature-controlled holding tank equipped with a feedpump for the 50%-NaOH aqueous solution,

[0059] • a Schugi Flexomix mixer (model FX-160) to spray treat the CaCO3with the NaOH, and

[0060] • a fluidized bed to dry the obtained wet agglomerate.

[0061] The dried agglomerate is subsequently ground on a Retsch cross-beater mill type SK-1 equipped with a 0.5 mm screen.

[0062] Method

[0063] The CaCO3was charged to the mixer from the holding tank at a rate of 450 kg / h, while simultaneously the 50%-NaOH was fed at 225 kg / h. The rotation speed of the mixer was adjusted to 4600 rpm to create optimal conditions for the best obtainable particle size and homogeneity. After leaving the mixer, the agglomerate was dried in the batch fluid bed. Temperature of the air supply was set at 180°C and drying was continued until the product temperature reached 83°C. Residual moisture was at 0.2%. The obtained dry agglomerate was ground to a fine powder with a d50 of 13.0 pm.

[0064] Example 2 - Preparation of an activated fly ash

[0065] Apparatus

[0066] Same as for Example 1 , except the cross-beater mill was equipped with a 0.2 mm screen. Method

[0067] The solid particulate fly ash was charged to the mixer from the holding tank at a rate of 400 kg / h, while simultaneously the aqueous sodium silicate (45% Na2SiO3) was fed at 140 kg / h. The rotation speed of the mixer was adjusted to 4600 rpm to create optimal conditions for the best obtainable particle size and homogeneity. After leaving the mixer, the agglomerate was collected in the fluid bed and fluidized for few minutes with air at 30°C. Then the air temperature was increased to 180°C and the agglomerate was dried. Residual moisture was at 1.3%. The obtained dry agglomerate was ground to a fine powder with a d50 of 12.4 pm. Example 3

[0068] The following examples compare the free-flowing solid activator (Ex. 3A) against similar activators known in the art (CEx.3B-3D). The mortars of Table 1 were prepared in accordance with General Procedure A. Table 1 . Component amounts are in grams.

[0069] 1Granulated blast-furnace slag

[0070] 2Dry activator NC12 (as disclosed in H.A. Abdel-Gawwad, S.A. Abo-EI-Enein, A novel method to produce dry geopolymer cement powder, HBRC Journal (2016) 12, 13-24) was prepared as follows: 83 g NaOH-10%(aq) was mixed with 41 .7 g CaCO3 powder. The resulting low viscous suspension was dried in an oven at 80°C. The dry cake was ground on the Fritsch mill using a 0.5 mm screen.

[0071] These mortars were then subjected to General Procedures B (Penetration Test) and C (Diametrical breaking strength). The results of the penetration test are set out in Bar Graph A, and the results of the diametrical breaking strength are set out in Table 2 below.

[0072] » 6 hours ^ I day

[0073] Bar Graph A

[0074] Table 2

[0075] It can be clearly seen from Bar Graph A that Example 3A had the best pot life (low setting after 6h) whilst also providing excellent final hardness (generally comparable with the Comparative Examples 3B and 3C which had a poorer pot life than Example 3A, and better final hardness than Comparative Example 3D). The results of diametrical breaking strength test showed that comparative Example 3D produced weak tablets, whereas the other Examples produced tablets with acceptable compression strength.

[0076] Example 4

[0077] Example 3 was repeated, except using fly ash and sodium silicate instead of the activated fly ash of Example 2. The mortars of Table 3 were prepared in accordance with General Procedure A.

[0078] ‘added as a powder

[0079] Table 3

[0080] These mortars were then subjected to General Procedures B (Penetration Test) and C (Diametrical breaking strength). The results of the penetration test are set out in Bar Graph 2, and the results of the diametrical breaking strength are set out in Table 4.

[0081]

[0082] Bar Graph 2

[0083] Table 4

[0084] Again, the best combination of good pot life and final hardness was observed when using the activator of Example 1 (Bar Geaph 2). Whilst there was an improvement in pot life for some of the other activators (Comparative Examples 4C and 4D) when the activated fly ash of Example 2 was not used, the compression strength was substantially reduced for all the Comparative Examples. Conversely, the compression strength was only slightly reduced when using the activator of Example 1 .

[0085] An unexpected observation was that the activated fly ash substantially improved the compression strength (diametrical breaking strength) of the geopolymer mortars produced using conventional components (i.e. , not using the activator of Example 1).

[0086] Example 5

[0087] The above examples indicated that the best overall results were obtained when combining the free-flowing solid activator (Example 1) with the activated fly ash (Example 2). To corroborate this finding, the following further mortars (Table 5) were prepared in accordance with General Procedure A and then subjected to General Procedures B (Penetration Test) and C (Diametrical breaking strength).

[0088] Table 5 The results of the penetration test are set out in Bar graph 3, and the results of the diametrical breaking strength are set out in Table 6.

[0089] Bar Graph 3

[0090] Table 6

[0091] These results confirmed that the best overall results were obtained when combining the free- flowing solid activator (Example 1) with the activated fly ash (Example 2). Whilst the free- flowing solid activator (Example 1) could produce a geopolymer mortar with excellent properties without the activated fly ash (Ex. 5C), the activated fly ash demonstrably improved the geopolymer mortar, most notably in terms of pot life (not too fast) and diametrical breaking strength.

[0092] These results also confirm the above observation for the activated fly ash - substantial improvement in the compression strength (diametrical breaking strength) of the geopolymer mortars produced by more conventional means (CEx. 5B vs CEx. 5D). Whilst the objective of the present disclosure was to provide geopolymer mortars with improved pot life and excellent one-day hardness, this nevertheless demonstrates the utility of the activated fly ash in other geopolymer mortar applications (e.g., rapid-set geopolymer mortars where increased compressive strength is advantageous).

[0093] In this specification, unless expressly otherwise indicated, the word ‘or’ is used in the sense of an operator that returns a true value when either or both of the stated conditions is met, as opposed to the operator ‘exclusive or’ which requires that only one of the conditions is met.

[0094] The word ‘comprising’ is used in the sense of ‘including’ rather than to mean ‘consisting of’. All prior teachings acknowledged above are hereby incorporated by reference. No acknowledgement of any prior published document herein should be taken to be an admission or representation that the teaching thereof was common general knowledge in Europe or elsewhere at the date hereof.

Claims

CLAIMS1 . A free-flowing solid activator for a geopolymer mortar or concrete comprising or consisting of an alkali(ne) metal carbonate surface treated with a sub-stoichiometric amount of alkali(ne) metal hydroxide.

2. The free-flowing solid activator of claim 1 , wherein the alkali(ne) metal carbonate is calcium carbonate, magnesium carbonate, dolomite (MgCaCO3), or mixtures thereof, preferably calcium carbonate.

3. The free-flowing solid activator of claims 1 or 2, wherein the alkali(ne) metal hydroxide is calcium hydroxide, potassium hydroxide, or sodium hydroxide, preferably sodium hydroxide.

4. The free-flowing solid activator of any one of claims 1 to 3, wherein the free- flowing solid activator comprises or consists of 60 to 90 parts by weight (pbw) of the alkali(ne) metal carbonate surface treated with 10 to 40 pbw of the alkali(ne) metal hydroxide.

5. The free-flowing solid activator of any one of claims 1 to 4, wherein the free- flowing solid activator is a powder, preferably having a Dv50 value of less than 100 microns, most preferably less than 50 micron.

6. A method for producing a free-flowing activator according to any one of claims 1 to 5, comprising: a) contacting an amount of an aqueous solution of an alkali(ne) metal hydroxide with the surface of a dry particulate alkali(ne) metal carbonate, wherein the amount of the aqueous solution of the alkali(ne) metal hydroxide contacted with the surface of a dry particulate alkali(ne) metal carbonate is selected such that the molar ratio of carbonate to hydroxide in the final surface treated product is greater than 1 , b) drying the product of step a), c) optionally grinding the dried product of step b), d) optionally, repeating the surface treatment process for the product of step b) or step c) by returning the product of step b) or step c) to step a).

7. A free-flowing activated fly ash for a geopolymer mortar or concrete comprising or consisting of fly ash surface treated with an alkali(ne) metal silicate.

8. The free-flowing activated fly ash of claim 7, wherein the activated fly ash comprises at least 8 wt.%, preferably at least 10 wt.% alkali(ne) metal silicate, more preferably at least 15wt%, most preferably at least 20wt%.

9. The activated fly ash of claims 7 or 8, wherein the fly ash is a class C fly ash or a class F fly ash, preferably a class F fly ash, as determined in accordance with ASTM C618.

10. The activated fly ash of any one of claims 7 to 9, wherein the alkali(ne) metal silicate is sodium silicate, most preferably with a SiO2 / NaO2 molar ratio of between 1 .7 - 2.3.11 . The activated fly ash of any one of claims 7 to 10, wherein the activated fly ash is a free-flowing powder, preferably having a Dv50 value of less than 100 microns, most preferably less than 50 microns.

12. A method for producing an activated fly ash according to any one of claims 7 to 11 , comprising: a) contacting an aqueous alkali(ne) metal silicate with the surface of a solid particulate fly ash , b) drying the product of step a), c) optionally grinding the dried product of step b), d) optionally, repeating the surface treatment process for the product of step b) or step c) by returning the product of step b) or step c) to step a).

13. A geopolymer mortar or concrete pre-mix composition comprising:- a free-flowing solid activator according to any one of claims 1 to 5, fly ash, and an alkali(ne) metal silicate; or- a solid activator comprising an alkali(ne) metal hydroxide; and an activated fly ash according to any one of claims 7 to 11 ; or- a free-flowing solid activator according to any one of claims 1 to 5, and an activated fly ash according to any one of claims 7 to 11 .

14. A geopolymer mortar or concrete powder ready-mix composition comprising a geopolymer mortar or concrete pre-mix composition according to claim 13 and at least one filler.

15. The geopolymer mortar or concrete powder ready-mix composition according to claim 14, wherein the at least one filler comprises or consists of sand and / or aggregate and / or granulated blast furnace slag.

16. A process for preparing a geopolymer mortar or concrete comprising mixing the geopolymer mortar or concrete powder ready-mix composition according to claims 14 or 15 with water.

17. A geopolymer mortar or concrete obtainable by the process of claim 16.

18. A method for producing an activated fly ash according to any one of claims 7 to 11 , comprising: a) spraying an aqueous alkali(ne) metal silicate onto the surface of a solid particulate fly ash; b) drying the product of step a); c) optionally grinding the dried product of step b); and d) optionally, repeating the surface treatment process for the product of step b) or step c) by returning the product of step b) or step c) to step a).

19. A method for producing an activated fly ash comprising: a) spraying an aqueous alkali(ne) metal silicate onto the surface of a solid particulate fly ash; b) drying the spray-treated product of step a); c) optionally grinding the dried product of step b); and d) optionally, repeating the spray treatment process for the product of step b) or step c) by returning the product of step b) or step c) to step a).

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