Alkali-Activated Material

Abstract

A geopolymeric composition for forming an alkali-activated concrete material, the geopolymeric composition comprising metakaolin (MK), a source of calcium oxide and a source of aluminosilicate other than metakaolin (MK). A method for forming an alkali-activated concrete material and the use of such an alkali-activated concrete material are also described.

Claims

2. A composition for forming an alkali-activated concrete material, the composition comprising a geopolymeric composition, water and an aggregate, wherein the geopolymeric composition comprises metakaolin (MK), a source of calcium oxide and a source of aluminosilicate other than metakaolin (MK).

3. A method of forming an alkali-activated concrete material, the method comprising: (1) mixing a geopolymeric composition, water and an aggregate to obtain a concrete mix; and (2) curing the concrete mix obtained in step (1); wherein the geopolymeric composition comprises metakaolin (MK), a source of calcium oxide and a source of aluminosilicate other than metakaolin (MK).

4. A method according to claim 3, wherein step (2) comprises curing the concrete mix in the presence of air and/or water.

5. A method according to claim 4, wherein the concrete mix is cured in air at a temperature of from 18 to 25 C.

6. A method according to claim 4, wherein the concrete mix is cured in water at a temperature of from 18 to 25 C.

7. A method according to claim 4, wherein the concrete mix is cured in water at a temperature of from 30 C. to 90 C., preferably about 50 C.

8. A composition according to claim 2, wherein the aggregate comprises sand, gravel, limestone, sandstone, chalk, soil or combinations thereof, preferably sand.

9. A composition according to claim 1, wherein the geopolymeric composition comprises from 25 wt % to 35 wt % of metakaolin (MK).

10. A composition according to claim 1, wherein the source of calcium oxide is bypass dust (BPD), suitably wherein geopolymeric composition comprises from 25 wt % to 35 wt % of bypass dust (BPD).

11. A composition according to claim 1, wherein the source of aluminosilicate other than metakaolin (MK) is natural pozzolan (NP), suitably wherein the geopolymeric composition comprises from 30 wt % to 50 wt % of natural pozzolan (NP).

12. A composition according to claim 1, wherein the metakaolin (MK) comprises from 45 to 60 wt % silicon dioxide and/or from 30 to 50 wt % aluminium oxide.

13. A composition according to claim 10 wherein the bypass dust (BPD) comprises from 15 to 30 wt % silicon dioxide and/or from 40 to 65 wt % calcium oxide.

14. A composition according to claim 11, wherein the natural pozzolan (NP) comprises from 35 to 55 wt % silicon dioxide and/or from 20 to 40 wt % aluminium oxide.

15. A hybrid binder composition comprising a geopolymeric composition according to claim 1 and cement, preferably OPC.

16. A method according to claim 3, further comprising the step of forming the concrete mix into a concrete structure.

17. An alkali-activated concrete material obtained or obtainable by the method of claim 3.

18. A concrete structure obtained or obtainable by the method of claim 16.

19. An alkali-activated concrete material derived from a geopolymeric composition, water and an aggregate, wherein the geopolymeric composition comprises metakaolin (MK), a source of calcium oxide and a source of aluminosilicate other than metakaolin (MK); wherein the alkali-activated concrete material has a compressive strength of at least 10 M Pa as measured by compression testing.

20. A concrete structure formed from an alkali-activated concrete material according to claim 19.

21. Use of an alkali-activated concrete material according to claim 19 in construction.

22. Use of a concrete structure according to claim 20 in construction.

Description

[0179] For a better understanding of the invention, and to show how exemplary embodiments of the same may be carried into effect, reference will be made, by way of example only, to the accompanying diagrammatic Figures, in which:

[0180] FIG. 1 shows powder X-Ray Diffraction (XRD) data collected for MK, BPD and NP.

[0181] FIG. 2 shows the particle size distribution (PSD) of sand used for making mortar with a geopolymeric composition of the present invention.

[0182] FIG. 3 shows the compressive strength of mortar prepared from a geopolymeric composition of the present invention and comparison with mortar prepared from conventional cement.

[0183] FIG. 4 shows the compressive strength of hybrid mortar prepared using different amounts of the geopolymeric composition of the present invention under various curing conditions and comparison with mortar prepared from conventional cement.

EXAMPLES

[0184] The invention will now be described with reference to the following non-limiting examples.

Example 1: Preparation of an Alkali-Activated Material

[0185] Geopolymeric compositions were prepared comprising MIK, NP and BPD. The chemical composition of each of MK, NP and BPD are illustrated in Table 1.

TABLE-US-00001 TABLE 1 Composition of MK, NP and BPD Com- ponents (wt. %) SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO Na.sub.2O K.sub.2O MgO TiO.sub.2 MK 55 40 1.4 0.15 0.4 0.4 0.95 1.7 NP 46.6 30.4 3.8 4.5 3.9 6 4.2 0.6 BPD 20.7 1.0 1.7 53.0 2.1 5.0 1.2 0.3

[0186] Geopolymeric compositions were prepared with the amounts of each of the MK, NP and BPD set out in Table 2.

TABLE-US-00002 TABLE 2 Geopolymeric Composition Mix ID Geopolymeric Composition Content Inventive Example 1 35 wt % MK; 35 wt % BPD and 30 wt % NP (AAC1) Comparative Example 1 50 wt % BPD and 50 wt % NP (AAC2) Comparative Example 2 50 wt % BPD and 50 wt % MK (AAC3) Comparative Example 3 100 wt % Cement (OPC)

[0187] The elemental composition of raw materials was determined using a Shimadzu EDX 720 and energy dispersive X-ray fluorescence (EDXRF) spectrometer.

[0188] The XRD measurements were carried out using a Rigaku mini-flex diffractometer (mini-flex goniometer), with Cuk X-ray radiation (30 kV voltage and 15 mA current at scanning speed of 2.0 deg./min in continuous scan mode) and scanning range (2) of 5-60.

[0189] The XRD data for each of MK, BPD and NP is shown in FIG. 1.

[0190] The geopolymeric compositions according to Table 2 were mixed with kiln dried sand with a particle size distribution (PSD) shown in FIG. 2 and a specific gravity of 2.62 (measured by Quantachrome gas expansion multi-pycnometer purged with helium gas) with a weight ratio of geopolymeric composition:sand of 1:2 and a water:geopolymeric composition weight ratio of 0.45:1 to produce a mortar.

[0191] The mortars were mixed using a Hobart mixer and poured into steel prism moulds (each mould having dimensions of 40 mm40 mm160 mm).

[0192] The mortars were demoulded after 24 hours and cured in water for 1 day at 50 C. and then cured in room temperature (20 C.) water. The compressive strength was measured according to the BS 196-1. The test was carried out using a Control Automax 5 compression tester, with a load rate of 0.4 MPa/s. The resulting compressive strength and its comparison against conventional cement (OPC) are shown in FIG. 3. The comparative examples 2 and 3 (AAC2 & AAC3) showed no strength and are therefore not shown in FIG. 3.

Example 2: Hybrid Binder Compositions

[0193] Hybrid binder compositions were prepared according to Table 3. The geopolymeric compositions were mixed with kiln dried sand with a particle size distribution (PSD) shown in FIG. 2 and a specific gravity of 2.62 with a mixing weight ratio of binder:sand of 1:2 and water:binder of 1:0.55 to produce a mortar. The mortars were mixed using a Hobart mixer and poured into steel prism moulds (each mould having dimensions of 40 mm40 mm160 mm).

[0194] The mortars were demoulded after 24 hours and cured as also shown in Table 3.

TABLE-US-00003 TABLE 3 Mix ID Hybrid Binder Composition Content Curing method Inventive 50 wt % geopolymeric composition (35 Room temperature air curing Example 2 wt % MK + 35 wt % BPD + 30 wt % NP) + Room temperature water (0.5 Hb1) 50 wt % OPC curing 3 days 50 C. water and room temperature water curing Inventive 75 wt % geopolymeric composition (35 Room temperature air curing Example 3 wt % MK + 35 wt % BPD + 30 wt % NP) + (0.75 Hb1) 25 wt % OPC Comparative 100 wt % cement Room temperature water Example 3 curing (OPC)

[0195] The resulting compressive strength of the inventive examples and a comparison against conventional cement (OPC) is shown in FIG. 4.

[0196] FIG. 4 shows a comparison of the compressive strength of hybrid binders in comparison to the conventional OPC (Comparative Example 3). The mortar comprising 50 wt % OPC and 50 wt % alkali-activated material (0.5Hb1) showed comparable compressive strength to OPC mortar with a compressive strength of 35 MPa after curing in air for 28 days, The mortar comprising 25 wt % OPC and 75 wt % alkali-activated material (0.75Hb1) in the hybrid binder achieved a compressive strength of 30 MPa, following air curing.

[0197] Therefore, use of a hybrid binder comprising both OPC and the geopolymeric composition means that water and hot water curing is not necessary, which reduces the energy cost of the process.

[0198] Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

[0199] Throughout this specification, the term comprising or comprises means including the component(s) specified but not to the exclusion of the presence of other components. The term consisting essentially of or consists essentially of means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention. Typically, when referring to compositions, a composition consisting essentially of a set of components will comprise less than 5% by weight, typically less than 3% by weight, more typically less than 1% by weight of non-specified components.

[0200] For the avoidance of doubt, wherein amounts of components in a composition are described in wt %, this means the weight percentage of the specified component in relation to the whole composition referred to. For example, wherein the BPD comprises 35 wt % to 65 wt % calcium oxide means that 35 wt % to 65 wt % of the BPD is provided by calcium oxide.

[0201] The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each aspect or exemplary embodiment of the invention as set out herein are also to be read as applicable to any other aspect or exemplary embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each exemplary embodiment of the invention as interchangeable and combinable between different exemplary embodiments.

[0202] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0203] All of the features disclosed in this specification (including any accompanying claims, and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0204] Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0205] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.