Composition and method of forming a composition.

Abstract

A composition and method of forming a composition which includes an inhibited calcium sulphate hemi-hydrate suspended in an aqueous form and at least one rheology modifier adapted to inhibit settling and compaction of the inhibited calcium sulphate hemi-hydrate.

Description

Composition and Method of Forming a Composition.Related Applications

[0001] This application claims priority from Australian provisional patent application no. 2024902107 filed on 8 July 2024, the contents of which are incorporated by reference.Technical Field

[0002] The invention relates to a composition and a method of forming a composition. In particular, the invention relates to a composition including calcium sulphate hemihydrate in an aqueous form which is treated to inhibit settling and compaction, and a method of forming such a composition.Background

[0003] Calcium sulphate (CaSC ) may be provided in different forms depending on its hydration, including calcium sulphate hemi-hydrate (CaSO^^FCO) commonly known as Plaster of Paris and calcium sulphate dihydrate (CaSO4-2H2) commonly known is Gypsum.

[0004] Such forms of calcium sulphate may be used in a variety of applications including a building, geotechnical and mining related applications. One specific application is the use of a calcium sulphate-based composition mixed with an activator to fill and stabilise underground strata. Such a composition may include calcium sulphate hemi-hydrate which is initially inhibited using a hydration inhibitor to remain in the hemi-hydrate form when in an aqueous form. An example of such a composition and method is disclosed in PCT / AU2023 / 050144 entitled “Composition, Method and System for Stabilising a Rock Mass”.

[0005] A problem with such a calcium sulphate-based composition is that the inhibited calcium sulphate hemi-hydrate may settle over time and become hard packed. Thesettling and packing can be exacerbated by the vibration of transportation which makes pre-mixing problematic.

[0006] Once hard packed, the calcium sulphate hemi-hydrate particles may be very difficult to re-disperse into the composition. A reason for this is that calcium sulphate, by nature is a long thin particle, typically needle-like or rod-like, often described acicular in shape. These particles hard pack when settled due to the shape. This results in a problem of less calcium sulphate hemi-hydrate dispersed in the composition which may affect the final blend when mixed with the activator.

[0007] The invention disclosed herein seeks to overcome one or more of the above identified problems or at least provide a useful alternative.Summary

[0008] In accordance with a first broad aspect there is provided, a composition including inhibited calcium sulphate hemi-hydrate so as to be suspended in an aqueous form and at least one rheology modifier adapted to inhibit settling and compaction of the inhibited calcium sulphate hemi-hydrate.

[0009] In accordance with a second broad aspect there is provided, a composition including inhibited calcium sulphate hemi-hydrate so as to be suspended in an aqueous form and at least one rheology modifier adapted to provide particle-to-particle interactions between particles of inhibited calcium sulphate hemi-hydrate so as to inhibit compaction of the inhibited calcium sulphate hemi-hydrate.

[0010] In an aspect, the particle-to-particle interactions are at least one of a hydrophobic interaction, electrostatic gelation, or interparticle bridging.

[0011] In another aspect, the at least one rheology modifier is a HEUR (PU-Based Associative Thickeners), a HASE (Alkali-Swellable Associative Emulsions), or a HMHEC (Hydrophobically Modified Cellulose Ethers) adapted to provide the hydrophobic interaction.

[0012] In yet another aspect, the at least one rheology modifier is an inorganic structured gel, a nanoclay dispersion, a fumed silica, or a HASE adapted to provide the electrostatic gelation.

[0013] In yet another aspect, the at least one rheology modifier is a HMHEC (Hydrophobically Modified Cellulose Ethers), an inorganic structured gel, or a fumed silica adapted to provide the interparticle bridging.

[0014] In yet another aspect, the composition further includes a pH modifier adapted to increase the pH of the composition.

[0015] In yet another aspect, the pH modifier is calcium hydroxide.

[0016] In yet another aspect, the at least one rheology modifier includes a non-ionic, solvent free, hydrophobically modified ethylene oxide urethane (HEUR) rheology modifier.

[0017] In yet another aspect, the mass of the HEUR is at least about 0.1% of the dry mass of the calcium sulphate hemi-hydrate.

[0018] In yet another aspect, the mass of the HEUR is at least about 0.3% of the dry mass of the calcium sulphate hemi-hydrate.

[0019] In yet another aspect, the mass of the HEUR is at least about between 0.3% and 0.5% of the dry mass of the calcium sulphate hemi-hydrate.

[0020] In yet another aspect, the mass of the HEUR is less than about 1% of the dry mass of the calcium sulphate hemi-hydrate.

[0021] In yet another aspect, the at least one rheology modifier further includes an acid containing, anionic, cross linked acrylic emulsion co-polymer.

[0022] In yet another aspect, the acid is adapted to thicken with increased pH.

[0023] In yet another aspect, the acid is at least about 0.1% of the dry mass of the calcium sulphate hemi-hydrate.

[0024] In yet another aspect, the acid is at least about 0.3% of the dry mass of the calcium sulphate hemi-hydrate.

[0025] In yet another aspect, the calcium sulphate hemi-hydrate is at least about 60% the composition by weight.

[0026] In yet another aspect, the calcium sulphate hemi-hydrate is between about 60% and 80% of the composition by weight.

[0027] In accordance with a third broad aspect there is provided, a composition including calcium sulphate hemi-hydrate suspended in an aqueous form, a rheology modifier mixture adapted to inhibit settling of the calcium sulphate hemi-hydrate and a pH additive adapted to increase the pH of the composition, wherein the rheology modifier mixture is adapted to thicken in response to the pH increase of the composition and decrease in response to a reduction in pH.

[0028] In accordance with a fourth broad aspect there is provided, a composition including gypsum suspended in an aqueous form, a rheology modifier mixture adapted to inhibit settling of associated calcium sulphate and a pH additive adapted to increase the pH of the composition, wherein the rheology modifier mixture is adapted to thicken in response to the pH increase of the composition and decrease in response to a reduction in pH.

[0029] In an aspect, the rheology modifier mixture is adapted to inhibit settling of the calcium sulphate hemi-hydrate by providing particle-to-particle interactions between particles of calcium sulphate.

[0030] In another aspect, the rheology modifier mixture is selected to provided particle- to-particle interactions by at least one of a hydrophobic interaction, electrostatic gelation, or interparticle bridging.

[0031] In yet another aspect, the rheology modifier mixture includes a non-ionic, solvent free, hydrophobically modified ethylene oxide urethane (HEUR) rheology modifier.

[0032] In yet another aspect, the rheology modifier mixture includes an acid containing, anionic, cross linked acrylic emulsion co-polymer.

[0033] In yet another aspect, the pH additive is pH modifier is calcium hydroxide.

[0034] In yet another aspect, the composition is adapted such that when mixed with an activator it becomes a settable medium.

[0035] In accordance with a fourth broad aspect there is provided, a method of forming a composition, the method including: Suspending inhibited calcium sulphate hemihydrate in an aqueous solution; and, Adding at least one least one rheology modifier adapted to inhibit settling of the calcium sulphate, the at least one least one rheology modifier being selected to provide particle-to-particle interactions between particles of the inhibited calcium sulphate hemi-hydrate.

[0036] In accordance with a fifth broad aspect there is provided, a method of forming a composition, the method including: Suspending inhibited calcium sulphate hemi- hydrate in an aqueous solution; Introducing at least one least one rheology modifier adapted to inhibit settling of the inhibited calcium sulphate hemi-hydrate and to particle-to-particle interactions between particles of the inhibited calcium sulphate hemi-hydrate to reduce compaction; and, Introducing a pH additive adapted to increase the pH of the composition.

[0037] In accordance with a fifth broad aspect there is provided, a composition including inhibited calcium sulphate hemi-hydrate so as to be suspended in an aqueous form and at least one rheology modifier adapted to provide particle-to-particle interactions between particles of inhibited calcium sulphate hemi-hydrate so as to inhibit compaction of the inhibited calcium sulphate hemi-hydrate, wherein the calcium sulphate hemi-hydrate is between about 60% and 80% of the composition by weight and wherein the wherein the rheology modifier mixture includes a non-ionic, solvent free, hydrophobically modified ethylene oxide urethane (HEUR) rheology modifier, the mass of the HEUR is at least about 0.3% of the dry mass of the calcium sulphate hemi- hydrate. The HEUR being separate to a inhibitor that may be a dispersant.Detailed Description

[0038] Referring to Tables 1 and 2 here are provided examples of a composition, specifically a calcium sulphate-based composition, that may be mixed in use with an activator such as aluminium sulphate to harden and fill holes or voids in a material such as rock strata or the like. The composition may be considered to be a Part A, and the activator may be considered a Part B, although more Parts may be used. The subject invention is focussed on Part A.

[0039] The composition is generally based on calcium sulphate, more specifically calcium sulphate hemi-hydrate (CaSO^'AJLO), which is suspended in water so as to be in a generally aqueous form. The calcium sulphate hemi-hydrate is inhibited or retarded using a hydration inhibitor so that it initially remains in the hemi-hydrate whilst in the aqueous suspension. The calcium sulphate hemi-hydrate is preferably the alpha type.

[0040] Typically, the calcium sulphate hemi-hydrate is at least about 60% of the composition by weight and may be between about 60% and 80% of the composition by weight. In this example, the calcium sulphate hemi-hydrate is about 70%. The water may be about 5% to 15% by weight and in this example is about 10% by weight. Other suitable ratios may be used to adjust the composition. Various types of retarders or hydration inhibitors may be used. However, in this example, a hydrophilic dispersant type inhibitor is used which is not stripped from the calcium sulphate hemi-hydrate until the activator is added.

[0041] The composition may be formulated, mixed, and stored in a container prior to use. The container may be transported to site and may be then agitated such as by a mixer, prior to use. The composition may include a first set of active ingredients to assist generally with its final use as an injectable settable filler and also may include a second set of stabilising rheology control ingredients to assist with its useability, specifically its medium to longer term stability, resistance settling and ease of resuspension of any settled calcium sulphate.

[0042] The first set of ingredients, as generally set out in Table 1 include a retarder or hydration inhibitor that may be, but not limited to, a dispersant added to the calcium sulphate hemi-hydrate to form a retarded mixture. This allow the initial calcium sulphate-based mixture to remain more stable and able to be pumped prior to mixing with the accelerant or activator that as noted above may be aluminium sulphate mixed with water.

[0001] The retarder or hydration inhibitor may be hydrophilic copolymer pigment dispersant such as, but not limited to, OROTAN™ 1288. It is noted that other suitable hydration inhibitors may also be used. OROTAN™ 1288 is an acid, specifically a polycarboxylic acid dispersant supplied at 45% solids in the sodium form. OROTAN™ 1288 may be about 0.1 to 2% by weight, and in this example is about 0.42% by weight. Generally, however, it may be less that about 1% by weight so that it can be adequality stripped on when the activator is added.

[0002] Further components of the first set of ingredients, contain polymers, in particular acrylic emulsion polymers, surfactants, dispersants, solvents and defoamer. These may be interchanged and used in different quantities to those specified in Tables 1 and 2 and the quantities specified in Tables 1 and 2 are provided for non-limiting example purposes only.

[0003] In this example, the polymer may be, but not limited to, PRIMAL™ AC-339 which is a hydrophobic acrylic polymer and the defoamer may be, but not limited to, Nopco NXZ™ which is a metallic soap type anti-foaming agent for latex and emulsion, especially for acrylic, vinyl acetate or vinyl acetate-acrylic emulsions. PRIMAL™ AC- 339 may be about 0% to 15% by weight and in this example is about 10% by weight.

[0004] The surfactant may be TritonTM X-40 which is 70% Active Octylphenol Ethoxylate in water and further a polymer such as Primal ECO-16™ may be included which is a binding or cross-linking polymer. A coalescent such as, but not limited to, Butyl Carbitol may also be included. As noted above, the dispersant may be dispersant may be OROTAN 1288™. The Primal ECO-16TM may be about 0% to 10% by weight, and in this example is about 5.5%. It is noted that the composition may include either ECO-16 or AC-339 or both as shown in the below example.

[0005] Further details in relation to the function of these first set of ingredients is disclosed in PCT / AU2023 / 050144 which is incorporated in its entirety by reference as such the first set of ingredients are not described in detail again here.Table 1 Example Composition Formulation Ranges (% weight where indicated)

[0043] Turning now to the second set of ingredients, it was found that examples of the composition with only the first set of ingredients may exhibit problems with at least the calcium sulphate hemi-hydrate settling and becoming compacted in the container during transport or extended periods of rest. As such, generally, the examples of the composition with only the first set of ingredients were provided in multiple parts and mixed on site or within a relatively short time frame prior to use to avoid such settling and compaction. However, a solution was required to allow the Part A to be formulated and mixed offsite without the calcium sulphate hemi-hydrate settling and becoming compacted.

[0044] To solve this problem, a second set of ingredients was developed including a rheology modifier mixture adapted to inhibit settling of the inhibited calcium sulphate hemi-hydrate and inhibit compaction. Generally, it has been found that a class ofrheology modifier mixtures that provide for particle-to-particle interaction between the calcium sulphate hemi-hydrate are suitable for this purpose.

[0045] The rheology modifier mixture may in some examples also include a pH additive adapted to increase the pH of the composition. In such examples, the rheology modifier mixture is adapted to thicken thereby increasing its viscosity in response to the pH increase of the composition and decrease in response to a reduction in pH.

[0046] In this example, the rheology modifier mixture includes a hydrophobically modified ethylene oxide urethane (HEUR) rheology modifier such as, but not limited to, ACRTSOL™ RM-12W and may also include an alkali-swellable emulsion (ASE) thickener such as, but not limited to, ACRTSOL™ ASE-60. The pH modifier, if used, may be calcium hydroxide or lime. Of course, other suitable rheology modifier mixtures may also be used. Both ACRTSOL™ ASE-60 and ACRTSOL™ RM-12W are commercially available from DOW™ Chemicals.

[0047] In more detail, the ACRTSOL™ ASE-60 is an alkali-swellable emulsion (ASE) thickener in the form of an acid containing, anionic, cross linked acrylic emulsion copolymer which thickens the composition when in alkaline conditions. The ASE thickener becomes a dispersant when the pH drops when the activator, aluminium sulphate, is added at the point of use which aids pumpability and therefore has a surprising advantage in this application.

[0048] In the provided example, the ASE thickener may be at least about 0.1%, and preferably at least about 0.3% of the dry mass of the calcium sulphate hemi-hydrate. The ASE thickener may be about 0 % to 1% and preferably also about 0.2% by weight of the composition. However, in some examples, the ASE thickener may be omitted, and it is not essential to all examples of the invention.

[0049] ACRTSOL™ RM-12W is a non-ionic, solvent free, hydrophobically modified ethylene oxide urethane (HEUR) rheology modifier which thickens the composition while retaining shear thinning behaviour. In the provided examples, the dry mass of the HEUR modifier may be at least about 0.1%, and preferably about at least 0.3% of the dry mass of the calcium sulphate. The HEUR modifier may be about 0.1% to 1% and preferably about 0.2% by weight of the composition.

[0050] It is noted that other forms of a rheology modifier, such as other types. Of HEUR rheology modifiers may be substituted and depending on formulation may have differing quantities as is further detailed below.

[0051] The lime, including the calcium hydroxide, increases alkalinity. In the provided examples, the pH is adjusted using the lime to be in the range of about pH 7-8 whereas without the lime the pH may in the range of about in the range of pH 6-7. The lime provided in this example may be about 0% to 1% by weight of the composition. However, the amount may be varied to achieve the desired pH. It is noted that whilst lime is preferable, it is not essential to all examples of the composition.

[0052] As noted above, when the pH is increased the ASE thickener in the form of ACRTSOL™ ASE-60 becomes a more effective thickener and the inhibitor in the form of OROTAN™ 1288 becomes a more effective dispersant. Accordingly, the pH modifier, in this example lime, is used to ensure that the ASE rheology modifier works effectively as it only works as a thickener in a basic environment. It is noted that the pH may affect the set-time and consequently the amount of activator required to set the composition. It is noted, again, that whilst an ASE thickener is preferable, it is not essential to all examples of the composition and may be omitted.Table 2: Example Composition Formulations (Parts by weight (g) or weight % where indicated)

[0053] The “Pass” or “Fail” indication in Table 2 above relates to whether or not the settled calcium sulphate hemi-hydrate, otherwise known as Gypsum when in its dihydrate form, is compacted at a bottom of a storage container and hard or not-possible redisperse after the formulated composition has been allowed to settle and rest for a period of time. In this example, the period of time was in the order of days-to-weeks and involved some vibration by test transportation. For the purposes of this example the “Pass” or “Fail” will be considered to be substantial resuspension by agitation i.e. mixing after about 7 days.

[0054] In relation to test compositions Mix 1 to Mix 4 and Mix 9, it was found that whilst there was an increased composition thickness towards bottom of container, the calcium sulphate hemi-hydrate easily redispersed by shearing. However, in relation to Mix 8 it was found that there was only a minor difference in thickness from top of the container to bottom of the container and the calcium sulphate hemi-hydrate was easily re-dispersed by shearing.

[0055] Accordingly, Mix 8 which include the rheology modifier mixture of the ASE in the form of ACRTSOL™ ASE-60 and the HEUR in the form of ACRTSOL™ RM-12W as well as the pH modifier in the form of lime was the most preferable. However, each of the “Pass” mixes were acceptable.

[0056] As an example, the Mix 8 composition may be a relatively high viscosity of 8,000 mPa s to 12,000 mPa s and preferable about 10,000 mPa s (millipascal-second) and when agitated such as a by a rheometer the viscosity may drop to a much lower value such as below 1,000 mPa s and closer to 500 mPa s. This is due to the shear thinning behaviour of the composition. Now, due to the rheology modifier mixture and specifically the HEUR, even after the 7 days of settling - the composition was able to be agitated to exhibit these properties because of the particle-to-particle interactions that resist or inhibit the compaction and hard binding of the calcium sulphate hemihydrate particles.

[0057] Other mixtures tested generally exhibit similar viscosity and shear thinning behaviours. However, not all mixtures were able to be resuspended and thus it has been determined that the ability to resist or inhibit the compaction and hard binding of the calcium sulphate hemi-hydrate particles was the most critical factor rather than, for example, the initial mixture have a relatively high viscosity.

[0058] It is noted that in Table 2 “Pass” composition did not need to include both of the ASE in the form of ACRTSOL™ ASE-60 and the HEUR in the form of ACRTSOL™ RM-12W and could include just the HUER in the form of ACRTSOL™ RM-12W.

[0059] It is understood this is because such HEUR rheology modifiers provide particle- to-particle interactions such as hydrophobic interactions which inhibit settling and compaction of the calcium sulphate hemi-hydrate whereas the ACRTSOL™ ASE-60 which is an ASE thickener which functions by water thickening without providing the same particle-to-particle interactions.

[0060] It is noted that whilst the lime and the ASE thickener in the form of ASE-60 serve to improve the composition, it is believed that a useful composition requires only the HEUR rheology modifiers in the form of RM-12W and HEUR can be used by itself without lime or the ASE to produce a useful mix. As such, in some examples the limeand ASE may be 0%. Accordingly, the lime and ASE are not regarded as essential for all examples of the composition.

[0061] In other examples, further and other types of rheology modifiers and rheology modifier mixtures may be used including other types HEUR / polyurethane (PU) rheology modifiers. Such rheology modifiers operate by creating particle interactions at the calcium sulphate hemi-hydrate to inhibit the hard packing, in this case by creating hydrophobic interactions.

[0062] Accordingly, still further types of the rheology modifiers may also be used that create particle-to-particle interacting, more specifically, interactions between the calcium sulphate hemi-hydrate to inhibit the hard packing. Such still further types of the rheology modifiers have been found to include: Hydrophobically modified cellulose ethers based - HMHEC (Hydrophobically Modified Hydroxyethyl Cellulose); Inorganic structured gels (Attapulgite or Smectite Clay); Fumed silica; HASE (Hydrophobically Modified Alkali-Swellable Emulsion), and Nano clay Dispersions (Synthetic Layered Silicates). Use of all such rheology modifiers is contemplated herein.

[0063] Advantageously, there has been described a composition and a method for forming the composition that enables the composition to be stabilised to inhibit settling in an aqueous form. Specifically, the composition uses a rheology modifier mixture, with one or more rheology modifiers, and a pH modifier to provide a stable composition which resists settling and promotes homogeneous distribution of the gypsum that has favourable resuspension characteristics.

[0064] Further, the rheology may be preferably pH controlled, so that at the point of application, the pH may be lowered to thin the composition such as by adding the aforesaid activator to aid pumpability. Likewise, should the composition need to be thickened, the pH may be increased.

[0065] This removes the need for combining the components of the composition near the application site. The increased transportation distance and time stability of the composition, allows fewer batching plants to be constructed as a single plant can service a larger geographical range.

[0066] Throughout this specification and the claims that follow the term “about” means within about 20% of the referenced value. To about 10% means between 8% and 12%.

[0067] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0068] The reference in this specification to any known matter or any prior publication is not, and should not be taken to be, an acknowledgment or admission or suggestion that the known matter or prior art publication forms part of the common general knowledge in the field to which this specification relates.

[0069] While specific examples of the invention have been described, it will be understood that the invention extends to alternative combinations of the features disclosed or evident from the disclosure provided herein.

[0070] Many and various modifications will be apparent to those skilled in the art without departing from the scope of the invention disclosed or evident from the disclosure provided herein.

Claims

The claims defining the Invention are as follows:

1. A composition including inhibited calcium sulphate hemi-hydrate so as to be suspended in an aqueous form and at least one rheology modifier adapted to inhibit settling and compaction of the inhibited calcium sulphate hemi-hydrate.

2. A composition including inhibited calcium sulphate hemi-hydrate so as to be suspended in an aqueous form and at least one rheology modifier adapted to provide particle-to-particle interactions between particles of inhibited calcium sulphate hemi-hydrate so as to inhibit compaction of the inhibited calcium sulphate hemi-hydrate.

3. The composition of claim 2, wherein the particle-to-particle interactions are at least one of a hydrophobic interaction, electrostatic gelation, or interparticle bridging.

4. The composition of claim 3, wherein the at least one rheology modifier is a HEUR (PU-Based Associative Thickeners), a HASE (Alkali-Swellable Associative Emulsions), or a HMHEC (Hydrophobically Modified Cellulose Ethers) adapted to provide the hydrophobic interaction.

5. The composition of claim 3, wherein the at least one rheology modifier is an inorganic structured gel, a nanoclay dispersion, a fumed silica, or a HASE adapted to provide the electrostatic gelation.

6. The composition of claim 3, wherein the at least one rheology modifier is a HMHEC (Hydrophobically Modified Cellulose Ethers), an inorganic structured gel, or a fumed silica adapted to provide the interparticle bridging.

7. The composition according to claim 1 or claim 2, wherein the composition further includes a pH modifier adapted to increase the pH of the composition.

8. The composition according to claim 7, wherein the pH modifier is calcium hydroxide.

9. The composition according to claim 1 or claim 2, wherein the at least one rheology modifier includes a non-ionic, solvent free, hydrophobically modified ethylene oxide urethane (HEUR) rheology modifier.

10. The composition according to claim 9, wherein the mass of the HEUR is at least about 0.1% of the dry mass of the calcium sulphate hemi-hydrate.

11. The composition according to claim 10, wherein the mass of the HEUR is at least about 0.3% of the dry mass of the calcium sulphate hemi-hydrate.

12. The composition according to claim 10 or claim 11, wherein the at least one rheology modifier further includes an acid containing, anionic, cross linked acrylic emulsion co-polymer.

13. The composition according to claim 12, wherein the acid is adapted to thicken with increased pH.

14. The composition according to claim 12 or claim 13, wherein the acid is at least about 0.1% of the dry mass of the calcium sulphate hemi-hydrate.

15. The composition according to claim 14, wherein the acid is at least about 0.3% of the dry mass of the calcium sulphate hemi-hydrate.

16. The composition according to any one of the previous claims, wherein the calcium sulphate hemi-hydrate is at least about 60% the composition by weight.

17. The composition according to claim 16, wherein the calcium sulphate hemi- hydrate is between about 60% and 80% of the composition by weight.

18. A composition including calcium sulphate hemi-hydrate suspended in an aqueous form, a rheology modifier mixture adapted to inhibit settling of the calcium sulphate hemi-hydrate and a pH additive adapted to increase the pH of the composition, wherein the rheology modifier mixture is adapted to thicken in response to the pH increase of the composition and decrease in response to a reduction in pH.

19. A composition including gypsum suspended in an aqueous form, a rheology modifier mixture adapted to inhibit settling of associated calcium sulphate and a pH additive adapted to increase the pH of the composition, wherein the rheology modifier mixture is adapted to thicken in response to the pH increase of the composition and decrease in response to a reduction in pH.

20. The composition according to claim 18 or claim 19, wherein the rheology modifier mixture is adapted to inhibit settling of the calcium sulphate hemihydrate by providing particle-to-particle interactions between particles of calcium sulphate.

21. The composition according to claim 20, wherein the rheology modifier mixture is selected to provided particle-to-particle interactions by at least one of a hydrophobic interaction, electrostatic gelation, or interparticle bridging.

22. The composition according to claim 18 or claim 19, wherein the rheology modifier mixture includes a non-ionic, solvent free, hydrophobically modified ethylene oxide urethane (HEUR) rheology modifier.

23. The composition according to claim 22, wherein the rheology modifier mixture includes an acid containing, anionic, cross linked acrylic emulsion co-polymer.

24. The composition according to claim 18 or claim 19, wherein the pH additive is pH modifier is calcium hydroxide.

25. The composition according to any of the previous claims, wherein the composition is adapted such that when mixed with an activator it becomes a settable medium.

26. A method of forming a composition, the method including: a. Suspending inhibited calcium sulphate hemi-hydrate in an aqueous solution; and, b. Adding at least one least one rheology modifier adapted to inhibit settling of the calcium sulphate, the at least one least one rheology modifier being selected to provide particle-to-particle interactions between particles of the inhibited calcium sulphate hemi-hydrate.

27. A method of forming a composition, the method including: a. Suspending inhibited calcium sulphate hemi-hydrate in an aqueous solution; b. Introducing at least one least one rheology modifier adapted to inhibit settling of the inhibited calcium sulphate hemi-hydrate and to particle- to-particle interactions between particles of the inhibited calcium sulphate hemi-hydrate to reduce compaction; and, c. Introducing a pH additive adapted to increase the pH of the composition.

28. A composition including inhibited calcium sulphate hemi-hydrate so as to be suspended in an aqueous form and at least one rheology modifier adapted to provide particle-to-particle interactions between particles of inhibited calcium sulphate hemi-hydrate so as to inhibit compaction of the inhibited calcium sulphate hemi-hydrate, wherein the calcium sulphate hemi-hydrate is between about 60% and 80% of the composition by weight and wherein the wherein the rheology modifier mixture includes a non-ionic, solvent free, hydrophobically modified ethylene oxide urethane (HEUR) rheology modifier, the mass of the HEUR is at least about 0.3% of the dry mass of the calcium sulphate hemi- hydrate.

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