Cement compositions

Abstract

The present disclosure relates to blended cement compositions comprising a combination of Portland cement and calcined bentonite. The present disclosure further relates to methods of producing such cement compositions comprising calcining bentonite, and mixing the calcined bentonite with Portland cement, where the calcined bentonite has a similar particle size distribution to the Portland cement.

Description

"Cement Compositions"Technical Field

[0001] The present disclosure relates to blended cement compositions, and more particularly to cement compositions in which a portion of the clinker is replaced with supplementary cementitious material of lower carbon footprint. The present disclosure further relates to methods of producing such cement compositions.Background

[0002] Cement is the single most widely used construction material in the world, more than that of steel, wood, plastics, and aluminium combined. Typical cement formulations (most commonly based on ordinary Portland cement) are mixed with aggregate and water to form construction materials such as mortar or concrete. While heavily relied on in the construction industry due to its workability as a slurry, speed of setting, and strength once cured, cement products are also considered to be one of the most environmentally unfriendly products due to the volume of material used worldwide.

[0003] The main component in forming ordinary Portland cement (herein referred to as Portland cement) is limestone, along with other raw materials such as clay, sand, or shale and other sources of silica and alumina. The raw materials are heated (calcined) in a kiln at temperatures of l,400°C-l,500°C in order to produce clinker and to thermally decompose the limestone from calcium carbonate into calcium oxide (lime) and carbon dioxide. Carbon dioxide is released in a one-to-one ratio, that is for every tonne of Portland cement produced, 1 tonne of carbon dioxide is released. As a result, the cement industry is one of the main producers of carbon dioxide in the world, both directly from the chemical decomposition of limestone, and indirectly due to the energy requirements to produce the cement, in particular the use of energy sourced from fossil fuels. In view of this, there is a continued interest in investigating ways in which toprovide cementitious compositions having similar physical properties to traditional cement mixtures (i.e. Portland cement) with reduced carbon footprints.

[0004] A common approach for seeking to produce more environmentally friendly cement compositions is the partial replacement of Portland cement with supplementary cementitious materials (SCMs) having lower carbon dioxide emissions associated with them. The supplementary cementitious materials may be by-products from other industries, for example ground granulated blast furnace slag (GGBFS) or fly ash. Preferably, the supplementary cementitious materials are able to replace a significant amount of the Portland cement, while still maintaining the desired physical properties of the cement as well as meeting relevant constructions standards.

[0005] The current availability of some of the more commonly used supplementary cementitious materials, however, no longer aligns with the overall demand of cement. For instance, the GGBFS from steel manufacture is now almost fully utilized in cement at its current production and no significant surge in its availability is anticipated. The second most widely used supplementary cementitious material, fly ash, comes from coal combustion and is generally available in larger quantities than GGBFS. However, its composition and quality vary significantly depending upon source material, impurities, and particle size (fly ash and bottom ash). As such only one third of FA is of suitable quality for use in cements. Moreover, the availability of FA will further decrease due to the gradual phasing-out of coal-fired energy with the sustainable development approaches being adopted worldwide.Summary

[0006] According to a first aspect, there is provided a blended cement composition comprising:10-90% w / w ordinary Portland cement;10-60% w / w calcined - bentonite;0-15% w / w limestone;0-5% w / w gypsum; and0-20% w / w source of calcium.

[0007] According to a second aspect, there is provided a method of producing a blended cement composition according to the first aspect, the method comprising: drying bentonite; calcination of the dried bentonite; milling and / or sieving at least one of: the bentonite prior to drying, the dried bentonite prior to calcination, and / or the calcined bentonite; and mixing the calcined bentonite and ordinary Portland cement, wherein the milling and / or sieving conditions are selected to provide a particle size range of the calcined bentonite substantially similar to a particle size distribution of the Portland cement.Brief Description of Drawings

[0008] Embodiments of the present disclosure will now be described by way of example only with reference to the accompanying drawings in which:

[0009] Figure 1 shows an example particle size distribution comparison of Portland cement, gypsum, limestone, metakaolin, and calcined bentonite;

[0010] Figure 2 shows compressive strength comparative data for samples using calcined bentonite (CNB and CAB) and kaolin (MK) prepared at various calcinationtemperatures, where the Strength Activity Index values are relative to a pure Portland cement mix (100%); and

[0011] Figure 3 shows the 7- and 28-day cured compressive strength for various cement mixtures prepared with Portland cement (OPC), calcined bentonite (CNB) and metakaolin (MK).Description of Embodiments

[0012] The present disclosure describes the following various non-limiting embodiments, processes, methods compositions and / or articles.

[0013] In the following description, reference is made to the accompanying drawings which form a part hereof, and which is shown, by way of illustration, several embodiments. It is understood that other embodiments may be utilised and structural changes or adaptions to one or more methods or processes, may be made without departing from the scope of the present disclosure.GENERAL DEFINITIONS

[0014] With regards to the definitions provided herein, unless stated otherwise, or implicit from 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 shall include the singular.

[0015] All publications discussed and / or referenced herein are incorporated herein in their entirety.

[0016] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing acontext for the present disclosure. It 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 claim of this application.

[0017] Throughout this disclosure, unless specifically stated otherwise or the context requires otherwise, reference to a single step, composition of matter, group of steps or group of compositions of matter shall be taken to encompass one and a plurality (i.e., one or more) of those steps, compositions of matter, groups of steps or groups of compositions of matter. Thus, as used herein, the singular forms “a”, “an” and “the” include plural aspects unless the context clearly dictates otherwise. For example, reference to “a” includes a single as well as two or more; reference to “an” includes a single as well as two or more; reference to “the” includes a single as well as two or more and so forth.

[0018] Those skilled in the art will appreciate that the disclosure herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the disclosure includes all such variations and modifications. The disclosure also includes all of the examples, steps, features, methods, processes, and compositions, referred to or indicated in this specification, individually or collectively, and any and all combinations or any two or more of said steps or features.

[0019] The term “and / or”, e.g., “X and / or Y” shall be understood to mean either “X and Y” or “X or Y” and shall be taken to provide explicit support for both meanings or for either meaning.

[0020] Unless otherwise indicated, the terms “first,” “second,” etc. are used herein merely as labels, and are not intended to impose ordinal, positional, or hierarchical requirements on the items to which these terms refer. Moreover, reference to a “second” item does not require or preclude the existence of lower-numbered item (e.g., a “first” item) and / or a higher-numbered item (e.g., a “third” item).

[0021] As used herein, the phrase “at least one of’, when used with a list of items, means different combinations of one or more of the listed items may be used and onlyone of the items in the list may be needed. The item may be a particular object, thing, or category. In other words, “at least one of’ means any combination of items or number of items may be used from the list, but not all of the items in the list may be required. For example, “at least one of item A, item B, and item C” may mean item A; item A and item B; item A and item C; item B; item B and item C; or item A, item B and item C. In some cases, “at least one of item A, item B, and item C” may mean, for example and without limitation, two of item A, one of item B, and ten of item C; four of item B and seven of item C; or some other suitable combination.

[0022] As used herein, the term “about”, unless stated to the contrary, typically refers to a range of up to + / - 10% of the designated value, and includes smaller ranges therein, for example + / - 5% or + / - 1% of the designated value.

[0023] 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.

[0024] 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, 4.5, 4.75, and 5, 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.

[0025] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a statedelement, 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.

[0026] Throughout this specification, the term "consisting essentially of" is intended to exclude elements which would materially affect the properties of the claimed composition, method or process.

[0027] The terms "comprising", "comprise" and "comprises" herein are intended to be optionally substitutable with the terms "consisting essentially of", "consist essentially of", "consists essentially of", "consisting of", "consist of" and "consists of", respectively, in every instance.

[0028] Herein “weight %” may be abbreviated to as “wt%” or “wt.%”. The weight % may be w / w or w / v, unless specifically indicated or clear from context.CEMENT COMPOSITION

[0029] According to the present disclosure, there is provided a blended cement composition comprising:10-90% w / w ordinary Portland cement;10-55% w / w calcined bentonite;0-15% w / w limestone;0-5% w / w gypsum; and0-20% w / w source of calcium.

[0030] As used herein, “Portland cement” is used in reference to ordinary Portland cement unless otherwise indicated.

[0031] In some embodiments, the bentonite may comprise bentonite in magnesiumsodium bentonite form comprising <50% sodium. In other embodiments the bentonite may comprise magnesium- sodium bentonite form comprising <50% magnesium and >30% magnesium.

[0032] The source of calcium may be any suitable source, for example the source of calcium may be calcium hydroxide, calcium oxide or other inorganic calcium source. The addition of calcium hydroxide, calcium oxide or other calcium source to the mixture may also allow for a further reduction in the amount of Portland cement used in the cement composition.

[0033] The amounts of Portland cement, calcined bentonite, limestone and, optionally, gypsum and an additional source of calcium can be varied to provide the desired properties of the intended final product, for example concrete or mortar prepared from the cement mixture.

[0034] By way of non-limiting example, cement compositions according to the present disclosure may include the following proportions, where Portland cement is denoted OPC, calcined bentonite is denoted CB, limestone is denoted LS, gypsum (powdered pure or plasterboard waste) is denoted GY, and the source of calcium (e.g. calcium hydroxide or calcium oxide) is denoted CH:• 90 % OPC, 10 % CB, or• 80 % OPC, 20 % CB, or• 70 % OPC, 30 % CB, or• 55 % OPC, 30 % CB, 15 % LS, or50 % OPC, 30 % CB, 15 % LS, 5 % GY, or• 40 % OPC, 40 % CB, 15 % LS, 5 % GY, or• 35 % OPC, 40 % CB, 15 % LS, 5 % GY, 5 % CH, or• 22.5 % OPC, 50 % CB, 10 % LS, 5 % GY, 12.5% CH, or• 17.5 % OPC, 55 % CB, 10 % LS, 5 % GY, 12.5% CH, or• 10 % OPC, 60 % CB, 10 % LS, 5 % GY, 15 % CH.

[0035] In some embodiments, the amount of Portland cement in the cement composition may be less than about: 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, or 15%. In some embodiments, the amount of Portland cement in the cement composition may be about, or greater than about: 10%, 20%, 30%, 40%, 50%, 50%, 60%, 70%, or 80%. The amount of Portland cement may be in a range provided by any two of these upper and / or lower values.

[0036] In some embodiments, the amount of calcined bentonite in the cement composition may be about, or greater than about: 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% or 60%. In some embodiments, the amount of calcined bentonite in the cement composition may be less than about: 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, or 15%. The amount of calcined bentonite may be in a range provided by any two of these upper and / or lower values.

[0037] In some embodiments, the amount of limestone in the cement composition may be less than about: 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%. In some embodiments, the amount of limestone in the cement composition may be about, or greater than about: 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%. The amount of limestone may be in a range provided by any two of these upper and / or lower values.

[0038] The gypsum may comprise quarried mineral gypsum, recycled gypsum, or combinations thereof. In an embodiment, the recycled gypsum is recycled plasterboardwaste. It will be appreciated that using recycled gypsum such as plasterboard waste further bolsters the environmental sustainability credentials of cement compositions according to the present disclosure, as plasterboard is a major source of construction and demolition waste. Diversion of this resource can simultaneously reduce the need for quarrying gypsum and reduce the quantity of plasterboard waste sent to landfill.

[0039] In some embodiments, where included, the amount of gypsum in the cement composition may be less than about: 5%, 4%, 3%, 2% or 1%. In some embodiments, where included, the amount of gypsum in the cement composition may be about, or greater than about: 0%, 1%, 2%, 3%, 4%. Where included, the amount of gypsum may be in a range provided by any two of these upper and / or lower values.

[0040] In some embodiments, where included, the amount of the source of calcium in the cement composition may be less than about: 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2% or 1%. In some embodiments, where included, the amount of the source of calcium in the cement composition may be about, or greater than about: 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, or 19%. Where included, the amount of calcium may be in a range provided by any two of these upper and / or lower values.

[0041] In some embodiments, the calcined bentonite has a similar particle size distribution as the Portland cement used in the composition.

[0042] Commercial Portland cement may be expected to have a particle size in the range of from about 0.1 pm to about 75 pm, and a D50 in the range of from about 10 pm to about 25 pm. However, it will be appreciated that the Portland cement used in cement mixtures according to the present disclosure may have size ranges and D50 values outside this range.

[0043] In some embodiments, the calcined bentonite has a particle size distribution in the range of from about 0.01 pm to about 750 pm, for example from about 0.05 pm toabout 500 |am, or from about 0.1 |am to about 75 |am. The particle size distribution of the calcined bentonite may have a D50 in the range of from about 1 pm to about 75 pm, for example from about 5 pm to about 50 pm, or from about 10 pm to about 25 pm.

[0044] In some embodiments, the gypsum has a similar particle size distribution as the Portland cement used in the composition.

[0045] In some embodiments, the gypsum has a particle size distribution in the range of from about 0.01 pm to about 750 pm, for example from about 0.05 pm to about 500 pm, or from about 0.1 pm to about 75 pm. The particle size distribution of the gypsum may have a D50 in the range of from about 1 pm to about 75 pm, for example from about 5 pm to about 50 pm, or from about 10 pm to about 25 pm.

[0046] In some embodiments, the limestone has a similar particle size distribution as the Portland cement used in the composition.

[0047] In some embodiments, the limestone has a particle size distribution in the range of from about 0.01 pm to about 750 pm, for example from about 0.05 pm to about 500 pm, or from about 0.1 pm to about 75 pm. The particle size distribution of the limestone may have a D 50 in the range of from about 1 pm to about 75 pm, for example from about 5 pm to about 50 pm, or from about 10 pm to about 25 pm.

[0048] It will be appreciated that the concrete mixture according to the present disclosure may be used in the same manner as conventional Portland cement mixtures. That is, the cement mixture may be combined with fine and / or coarse aggregate, water and chemical admixtures in the conventional manner. The applications are not particularly limited and may include residential and non- structural applications, as well as pathways, municipal kerb and channel, footings, driveways, and any other application for which Portland cement mixtures would be used.METHOD OF PRODUCING A CEMENT COMPOSITION

[0049] According to the present disclosure, there is further provided a method of producing a blended cement composition according to the present disclosure, the method comprising: calcination of bentonite; and mixing the calcined bentonite and ordinary Portland cement

[0050] Calcination of the bentonite may comprise heating the bentonite to a calcination temperature of from about 500°C to about 800°C. Due to the lower calcination temperatures for the bentonite, the energy requirements for calcination are significantly lower than that required for the preparation of Portland cement. Similarly, the embodied carbon requirement for producing calcined bentonite is lower than for other supplementary cementitious materials such as kaolinite or halloysite (1: 1 layer silicates), with calcination temperatures as much as 200°C lower required for activation.

[0051] In some embodiments, the calcination temperature is about, or less than about: 800°C, 775°C, 750°C, 725°C, 700°C, 675°C, 650°C, 625°C, 600°C, 575°C, 550°C, or 525°C. In some embodiments, the calcination temperature is greater than about: 500°C, 525°C, 550°C, 575°C, 600°C, 625°C, 650°C, 675°C, 700°C, 725°C, 750°C, or 775°C. The calcination temperature may be provided in a range provided by any two of these upper and / or lower values. In some embodiments, the calcination temperature may be 600°C, 650°C, 700°C, 750°C, or 800°C.

[0052] It will be appreciated that the period of calcination may be varied depending on the calciner type and conditions used. In an embodiment, calcination of the bentonite is undertaken for 1 hour at the desired calcination temperature at a heating rate of 10°C / minute.

[0053] The method may further comprise drying the bentonite prior to calcination. For example, the bentonite may be oven dried at or slightly above the boiling point ofwater. Drying time may vary depending on the temperature at which drying is conducted, the initial moisture content of the bentonite, the particle size of the bentonite, and the desired moisture content of the dried bentonite. Drying may be undertaken by any suitable method for reducing the adsorbed water content of the bentonite, for example solar drying. In an embodiment, the bentonite is dried at about 105 °C for at least 8 hours.

[0054] Milling of the bentonite may be conducted after drying the bentonite and before calcination of the bentonite, and / or after calcination of the bentonite. Milling may be undertaken by any suitable method for reducing the particle size of the bentonite. In an embodiment, milling the bentonite, dried bentonite or calcined bentonite may be conducted using a ball mill.

[0055] The method may further comprise sieving of the bentonite, dried bentonite or calcined bentonite.

[0056] Preferably, the milling and / or sieving is conducted to provide calcined bentonite having a similar particle size distribution as the Portland cement used in the composition. In an embodiment, the calcined bentonite are milled and sieved to a particle size distribution in the range of from about 0.01 pm to about 750 pm, for example from about 0.05 pm to about 500 pm, or from about 0.1 pm to about 75 pm. The particle size distribution of the calcined bentonite may have a D50 in the range of from about 1 pm to about 75 pm, for example from about 5 pm to about 50 pm, or from about 10 pm to about 25 pm.

[0057] The gypsum and / or limestone used in the cement composition may similarly undergo similar milling and sieving as the calcined bentonite to achieve a similar particle size distribution as the Portland cement. In some embodiments, the gypsum and / or limestone are milled and sieved to a particle size distribution in the range of from about 0.01 pm to about 750 pm, for example from about 0.05 pm to about 500 pm, or from about 0.1 pm to about 75 pm. The particle size distribution of the gypsumand / or limestone may have a D50 In the range of from about 1 m to about 75 pm, for example from about 5 pm to about 50 pm, or from about 10 pm to about 25 pm.

[0058] The results presented demonstrate that blended cement compositions according to the present disclosure exhibit compressive strength comparable to that of Portland cement and superior strength to an equivalent kaolin-based blended cement compositions. The low-carbon calcined bentonite material is estimated to reduce the embodied carbon of the resulting cementitious mix by around 40 % for a mix replacing 50 % of the Portland cement, and up to 52 % for a mix containing 40 % calcined bentonite.EXAMPLES

[0059] As used in the following examples, “bentonite” is used in reference to magnesium-sodium bentonite unless otherwise indicated. As used in the following examples, “Portland cement” is used in reference to ordinary Portland cement unless otherwise indicated.

[0060] Calcined bentonite clay from two sources (CAB and CNB) were prepared by crushing the bentonite material into particles of less than 2.5 mm in diameter, and sieved through a 2.36 mm sieve. The crushed bentonite was distributed on a metal tray and oven dried at 105°C for 24 hours. The dried materials were then milled in a planetary ball mill for 5 hours at 4,5000 RPM in 15-minute grinding-rest cycles to produce finely-divided powders.

[0061] Calcined bentonite with differing calcination temperatures, ranging from 600°C-800°C, were then prepared by placing the ground, dried bentonite in a crucible in a furnace at the calcination temperature for 1 hour at a heating rate of 10°C / minute. Upon completion of the heating cycle, the calcined bentonite was allowed to cool naturally to room temperature within the furnace.

[0062] Metakaolin, which is a 1: 1 layer silicate with a ratio of silicon (Si) to aluminium (Al) of ~1:1 and commonly used as supplementary cementitious material, was selected for comparison with the performance of the calcined bentonite which is a 2: 1 layer silicate, which has a Si: Al ratio ~2: 1.

[0063] Limestone, gypsum and plasterboard waste were each milled individually in the same manner as the bentonite, and the metakaolin was prepared in a similar manner to the calcined bentonite. Milling conditions were selected to provide a particle size distribution of the materials as close to as the Portland cement as possible. Figure 1 presents a comparison of the cumulative particle size distributions for various materials after ball milling.

[0064] Cement paste mixes were prepared using a water to cementitious binder ratio of 0.45. The material was then mixed according to ASTM C305 - Standard Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars of Plastic Consistency - and cast into 50 mm cube moulds. The cubes were left undisturbed at 23 ± 2°C and covered with plastic wrap for 24 hours before demoulding and being placed in a lime- saturated curing bath at 23 ± 2 °C until testing (curing compliant with Australian Standard AS 1012.8.1 - Method for Making & Curing Concrete).

[0065] After 7- and 28 days’ curing, cubes in triplicate were removed from the curing tank, dimensions measured using a digital Vernier caliper (± 0.01 mm precision), weighed, and compression tested in a 1,500 kN compression machine per Australian Standard AS 1012.9 - Method for Testing Concrete Specimens.

[0066] A first set of cement paste mixes were fabricated from each bentonite source (CAB and CNB), with bentonite calcined at the following calcination temperatures: 600°C, 650°C, 700°C, 750°C and 800°C. Comparative samples were make using metakaolin calcined at the same temperatures. The first set of cement paste mixes were formed in the manner described above from a cement mixture comprising 80% Portland cement and 20% calcined bentonite (or metakaolin for the comparative examples).

[0067] Figure 2 demonstrates the results of the compressive strength testing for the first set of cements after 28 days’ curing. The results demonstrate that both forms of calcined bentonite - CAB and CNB - were able to achieve strength equal to that of Portland cement using a temperature lower than that used for the metakaolin (calcined kaolin, Mk). This result means that the calcination of the bentonite in this embodiment is more energy efficient than an equivalent kaolin.

[0068] A second set of cement paste mixes have been fabricated according to the following mix proportions, with the bentonite calcined at 750°C:• B-CNB: 55 % OPC, 30 % CB, 15% LS• B-CNB+G: 50 % OPC, 30 % CB, 15 % LS, 5 % GY (as gypsum)• B-CNB+PW: 50 % OPC, 30 % CB, 15 % LS, 5 % GY (as plasterboard waste)

[0069] As the Portland cement comprises a small percentage of gypsum, the quantity of gypsum added to each prepared composition was adjusted to account for the gypsum already present in the Portland cement.

[0070] Figure 3 presents a comparison of the compressive strengths for ordinary Portland cement (OPC) against 30% metakaolin (B-MK), B-CNB, B-MK with 5% gypsum (B-MK+G), B-CNB+G, B-MK with 5% gypsum from plasterboard waste (B- MK+PW) and B-CNB+PW. The results demonstrate superior 7-day and 28-day compressive strength performance in all bentonite-based mixes as described above when compared with equivalent kaolin-based mixes, as well as comparable strength performance compared with Portland cement in all bentonite-based mixes.

[0071] The results demonstrate that the 2: 1 layer silicates of calcined bentonite to be suitable for use as a supplementary cementitious material with improved performance over cement mixes made with 1 : 1 layer silicates of metakaolin. It is understood that due to the finer inherent crystallite size and particle size of the calcined bentonite, morechemical reactions can occur, providing greater overall strength development with early strength development.

[0072] 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.

Claims

CLAIMS:

1. A blended cement composition comprising:10-90% w / w ordinary Portland cement;10-60% w / w calcined bentonite;0-15% w / w limestone;0-5% w / w gypsum; and0-20% w / w source of calcium.

2. A cement composition according to claim 1, wherein the calcined bentonite is magnesium-sodium bentonite.

3. A cement composition according to claim 1 or claim 2, comprising 5-15% w / w limestone.

4. A cement composition according to any one of the preceding claims, wherein the calcined bentonite has a particle size distribution substantially similar to a particle size distribution of the Portland cement.

5. A cement composition according to claim 3, wherein the particle size distribution of the calcined bentonite has a D50 in the range of from 1 pm to 75 pm.

6. A cement composition according to claim 4, wherein the particle size distribution of the calcined bentonite has a D50 in the range of 5 pm to 50 pm.

7. A cement composition according to claim 5, wherein the particle size distribution of the calcined bentonite has a D50 in the range of 10 pm to 25 pm.

8. A cement composition according to any one of the preceding claims, wherein the calcined bentonite has a particle size range of from about 0.01 pm to about 750 pm.

9. A cement composition according to claim 8, wherein the calcined bentonite has a particle size range of from about 0.05 pm to about 500 pm.

10. A cement composition according to claim 8, wherein the calcined bentonite has a particle size range of from about 0.1 pm to about 75 pm.

11. A cement composition according to any one of the preceding claims, wherein the gypsum has a particle size distribution substantially similar to a particle size distribution of the Portland cement.

12. A cement composition according to claim 11, wherein the gypsum wherein the particle size distribution of the gypsum has a D50 in the range of 10 pm to 25 pm.

13. A cement composition according to any one of the preceding claims, wherein the calcined bentonite has a particle size range of from about 0.05 pm to about 500 pm.

14. A cement composition according to claim 13, wherein the calcined bentonite has a particle size range of from about 0.1 pm to about 75 pm.

15. A cement composition according to any one of the preceding claims, wherein the limestone has a particle size range of from about 0.01 pm to about 750 pm.

16. A cement composition according to any one of the preceding claims, wherein the cement composition comprises:• 90% w / w Portland cement, 10% w / w calcined bentonite, or• 80% w / w Portland cement, 20% w / w calcined bentonite, or70% w / w Portland cement, 30% w / w calcined bentonite, or• 55% w / w Portland cement, 30% w / w calcined bentonite, 15% w / w limestone, or• 50% w / w Portland cement, 30% w / w calcined bentonite, 15% w / w limestone, 5% w / w gypsum, or• 40% w / w Portland cement, 40% w / w calcined bentonite, 15% w / w limestone, 5% w / w gypsum, or• 35% w / w Portland cement, 40% w / w calcined bentonite, 15% w / w limestone, 5% w / w gypsum, 5% w / w source of calcium, or• 22.5% w / w Portland cement, 45% w / w calcined bentonite, 15% w / w limestone, 5% w / w gypsum, 12.5% w / w source of calcium, or• 17.5% w / w Portland cement, 50% w / w calcined bentonite, 15% w / w limestone, 5% w / w gypsum, 12.5% w / w source of calcium, or• 10% w / w Portland cement, 60% w / w calcined bentonite, 10% w / w limestone, 5% w / w gypsum, 15% w / w source of calcium.

17. A cement composition according to any one of the preceding claims, wherein the gypsum comprises: quarried mineral gypsum, recycled gypsum, or combinations thereof.

18. A cement composition according to claim 17, wherein the recycled gypsum comprises recycled plasterboard waste.

19. A cement composition according to any one of the preceding claims, wherein the source of calcium is selected from: calcium hydroxide, and calcium oxide.

20. A method of producing a blended cement composition according to any one of the preceding claims, the method comprising: drying bentonite; calcination of the dried bentonite; milling and / or sieving at least one of: the bentonite prior to drying, the dried bentonite prior to calcination, and / or the calcined bentonite; and mixing the calcined bentonite and ordinary Portland cement, wherein the milling and / or sieving conditions are selected to provide a particle size range of the calcined bentonite substantially similar to a particle size distribution of the Portland cement.

21. A method according to claim 20, wherein calcination of the dried bentonite comprises heating the dried bentonite to a calcination temperature of from 500°C to 800°C.

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