Cement mixtures

Abstract

The present disclosure relates to blended cement mixtures comprising a cement composition comprising a combination of Portland cement and reactive calcined gravel wash fines. The present disclosure further relates to methods of producing such cement mixtures comprising calcining gravel wash fines, and mixing the calcined gravel wash fines with Portland cement.

Description

"Cement Mixtures"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 (referred to herein as Portland cement) is limestone, along with other raw materials such as shales, clays 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 this process also thermally decomposes the limestone from calcium carbonate into calcium oxide (quicklime) 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 investigatingways in which to provide 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 of the present disclosure, there is provided a blended cement mixture comprising: a cement composition comprising:10-90% w / w ordinary Portland cement;10-75% w / w reactive calcined gravel wash fines, and0-15% w / w source of calcium.

[0007] According to a second aspect of the present disclosure, there is provided a method of producing a blended cement mixture according to the first aspect, the method comprising: calcination of gravel wash fines; sieving and milling the calcined gravel wash fines, wherein the calcined gravel wash fines comprise: reactive calcined gravel wash fines; and inert calcined gravel wash fines, mixing the calcined gravel wash fines and ordinary 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 compressive strength data for various blended cement mortars prepared with a first GWF calcined at 600°C;

[0010] Figure 2 shows compressive strength data for various blended cement mortars prepared with the first GWF calcined at 700°C;

[0011] Figure 3 shows compressive strength data for various blended cement mortars prepared with a second GWF calcined at 600°C;

[0012] Figure 4 shows compressive strength data for various blended cement mortars prepared with the second GWF calcined at 700°C;

[0013] Figure 5 shows diameter of flow and quantity of superplasticizer data for blended cement mortars with 10-40% replacement with the first GWF; and

[0014] Figure 6 shows diameter of flow and quantity of superplasticizer data for blended cement mortars with 10-40% replacement with the first GWF.Description of Embodiments

[0015] The present disclosure describes the following various non-limiting embodiments, processes, methods compositions and / or articles.

[0016] 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

[0017] 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.

[0018] All publications discussed and / or referenced herein are incorporated herein in their entirety.

[0019] 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 a context 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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).

[0024] 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 only one 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 A, item B, and item C; item B; item B and item C or 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0029] 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.

[0030] 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.

[0031] 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 MIXTURE

[0032] According to the present disclosure, there is provided a blended cement mixture comprising: a cement composition comprising:10-90% w / w ordinary Portland cement;10-75% w / w reactive calcined gravel wash fines, and0-15% w / w source of calcium.

[0033] As used herein, “Portland cement” is used in reference to ordinary Portland cement unless otherwise indicated.

[0034] Gravel wash fines are fines produced during aggregate processing. Gravel wash fines are typically used for landscaping or as a sub-base for pipes. Gravel wash fines have been found to have up to 80-85% less embodied carbon than an equivalent amount of cement clinker.

[0035] Calcination of gravel wash fines produces calcined gravel wash fines that comprise a mixture of reactive calcined gravel wash fines and inert calcined gravel wash fines. The relative amounts of reactive and inert calcined gravel wash fines will depend on a number of factors such as the sources gravel wash fines and the calcination conditions. Reactive calcined gravel wash fines typically that dominate the <2 pm particle size range of the calcined gravel wash fines.

[0036] Thus, the blended cement mixture according to the present disclosure will further comprise inert calcined. However, in preparing the cement composition, it is the relative weight of the reactive calcined gravel wash fines that is used to determine the amounts of the Portland cement, reactive calcined gravel wash fines and, optionally, the amount of the source of calcium, for example limestone, calcium hydroxide, calcium oxide or other calcium sources, in the cement composition.

[0037] The source of calcium may be any suitable source, for example the source of calcium may be limestone, calcium hydroxide, calcium oxide or other calcium sources. The addition of limestone, 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.

[0038] The amounts of Portland cement, reactive calcined gravel wash fines and, optionally, limestone, calcium hydroxide, calcium oxide or other calcium source can be varied to provide the desired properties of the intended final product, for example concrete or mortar prepared from the cement mixture.

[0039] By way of non-limiting example, cement compositions according to the present disclosure may include the following proportions, where Portland cement isdenoted OPC, reactive calcined gravel wash fines denoted CGF, and limestone, calcium hydroxide, calcium oxide or other calcium source denoted CH:• 90 % OPC, 10 % CGF, or• 80 % OPC, 20 % CGF, or• 70 % OPC, 30 % CGF, or• 60 % OPC, 40 % CGF, or• 55 % OPC, 40% CGF, 5 % CH, or• 45 % OPC, 50 % CGF, 5 % CH, or• 32.5% OPC, 60 % CGF, 7.5 % CH, or• 20 % OPC, 70 % CGF, 10 % CH, or• 10 % OPC, 75 % CGF, 15 % CH.

[0040] 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.

[0041] In some embodiments, the amount of reactive calcined gravel wash fines in the cement composition may be about, or greater than about: 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%. In some embodiments, the amount of reactive calcined gravel wash fines in the cement composition may be less than about: 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15% or 10%.The amount of reactive calcined gravel wash fines may be in a range provided by any two of these upper and / or lower values.

[0042] The binder content of the mixture is the sum of the Portland cement and the reactive calcined gravel wash fines composition. In some embodiments, the binder content may be about, or greater than 80%, 85%, 90% or 95%. In some embodiments, the binder content may be about, or less than, 100%, 90%, or 85%.

[0043] In some embodiments, where included, the amount of the source of calcium in the cement composition may be less than about: 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% or 14%. Where included, the amount of calcium may be in a range provided by any two of these upper and / or lower values.

[0044] Advantageously, the inert calcined gravel wash fines provide a filler effect and can act also as a fine aggregate in concretes or mortars made from the cement mixture. This further supports the sustainability of the cement compositions of the present disclosure by reducing aggregate needed and, therefore, the associated aggregate production requirements.

[0045] Preferably, the reactive calcined gravel wash fines have a similar particle size distribution to the Portland cement used in the mixture. In an example, the reactive calcined gravel wash fines have particle size distribution in the range of from about 0.1 pm to about 75 pm.

[0046] The cement mixture may comprise one or more additives, for example polycarboxylate-based superplasticizer. Additives such as superplasticizer may be added in an amount required to maintain similar fluid properties of the slurry to a corresponding Portland cement only composition. In an embodiment, additives such assuperplasticizer may be added in an amount of up to 1.5% w / w of the binder content of the mixture.

[0047] 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 MIXTURE

[0048] According to the present disclosure, there is further provided a method of producing a blended cement mixture as disclosed herein, the method comprising: calcination of gravel wash fines; milling the calcined gravel wash fines; sieving the milled calcined gravel wash fines to produce calcined gravel wash fines, the calcined gravel wash fines comprising: reactive calcined gravel wash fines; and inert calcined gravel wash fines, mixing the calcined gravel wash fines with ordinary Portland cement.

[0049] Calcination of the gravel wash fines may comprise heating the gravel wash fines to a calcination temperature of from about 500°C to about 800°C. In contrast to the preparation of Portland cement, calcination of the gravel wash fines in this temperature range does not release any carbon dioxide as part of the calcination. Inaddition, due to the lower calcination temperatures for gravel wash fines, the energy requirements for calcination are significantly lower than that required for the preparation of Portland cement.

[0050] 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 or 700°C.

[0051] By effectively replacing a portion of the Portland cement with calcined gravel wash fines, a reduction in embodied carbon dioxide can be achieved. By way of example, the estimated embodied carbon dioxide reduction, calculated based on the heat capacity of typical materials, for varying degrees of cement replacement and for calcination temperatures of 600°C and 700°C, respectively, is shown in the following table:

[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 gravel wash fines is undertaken at a heating rate of 10°C / minute with a 2 hour retention time at the selected calcination temperature.

[0053] Milling of the calcined gravel wash fines may be any suitable method for reducing the particle size of the calcined gravel wash fines. In an embodiment, milling the calcined gravel wash fines is conducted using a ball mill.

[0054] Preferably, the milling is conducted on material pre-sieved to provide calcined gravel wash fines having a similar particle size distribution as the Portland cement used in the mixture. In an embodiment, the calcined gravel wash fines are milled and sieved to a particle size distribution in the range of from about 0.1 pm to about 75 pm.

[0055] Determination of the amounts of inert calcined gravel wash fines in the calcined gravel wash fines may be determined, for example, using Quantitative X-Ray Diffraction (QXRD) analysis. Alternatively, the inert gravel wash fines content may be estimated using fines content determination by sieving or by sedimentation methods. A person skilled in the art will appreciate how these determinations are made.

[0056] Determination of the amount of inert calcined gravel wash fines, and by extension the determination of the reactive calcined gravel wash fines, allows for a calculation on the amount of calcined gravel wash fines to use in the mixture to achieve the desired amount of reactive calcined gravel wash fines in the cement composition. Additionally, determination of the amount of inert calcined gravel wash fines allows for adjustments in the amount of fine aggregate added to form the concrete or mortar using the cement mixture.

[0057] Cement compositions prepared according to the present disclosure have been found to produce cement mortars that maintain an equivalent, or even exceed, compressive strengths even with up to half of the Portland cement replaced with reactive calcined gravel wash fines.EXAMPLES

[0058] As used in the following examples, “Portland cement” is used in reference to ordinary Portland cement unless otherwise indicated.

[0059] Calcined gravel wash fines (CGF) from two sources (FinesA and FinesB) were prepared by placing gravel wash fines material in a crucible in a furnace at 600°C or 700°C for 2 hours at a heating rate of 10°C / minute. Upon completion of the heating cycle, the CGF was allowed to cool naturally to room temperature within the furnace.

[0060] Once cooled, the CGF was then milled in a planetary ball mill for 3-5 hours at 3,000 - 4,500 RPM in 15-minute grinding-rest cycles and sieved through a 75pm sieve and mixed with ordinary Portland cement (OPC) in the following weight ratios, where the mass of CGF is the mass of active material in the calcined gravel wash fines, to form a calcined gravel wash fines cement (CGFC) dry powder mixture.:• Control: 100% OPC• Fines A / B_10: 90% OPC, 10% CGF• Fines A / B_20: 80% OPC, 20% CGF• Fines A / B_30: 70% OPC, 30% CGF• Fines A / B_40: 60% OPC, 40% CGF

[0061] Mortar mixes were prepared using a water to cementitious binder ratio of 0.48, and a sand (fine aggregate) to binder ratio of 2. As shown in Figures 5 and 6, a commercially-available polycarboxylate-based superplasticiser was also used at dosages up to 1.1% w / w (by weight of cementitious binder) to provide comparable mortar workability across all mixes. 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).

[0062] After 7- and 28 days’ curing, cubes in triplicate were removed from the curing tank, dimensions measured using a digital Vernier calliper (± 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.

[0063] Figures 1 and 2 demonstrate the results of compressive strength testing for mortar prepared from FinesA calcined at 600°C and 700°C, respectively. Similarly, Figures 3 and 4 demonstrate the results of compressive strength testing for mortar prepared from FinesB calcined at 600°C and 700°C, respectively.

[0064] The results of the compressive strength testing clearly show that the substitution of a portion of the OPC with CGF enhances or maintains the compressive strength of the cement mortar at 7 or 28 days. In particular, Figures 1-4 show that up to 40% replacement of the OPC binder with CGF enhances the compressive strength of the mortar for the early strength measured at 7 days, while longer curing to 28 days results in mortar with a comparable compressive strength to that of the OPC (control) mortar.

[0065] Additionally, it can be seen from Figures 1-4 that calcining the GWF at the lower temperature of 600°C (and therefore requiring lower energy consumption for preparation) provided mortars of comparable compressive strength to those prepared from GWF calcined at 700°C.

[0066] 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 mixture comprising: a cement composition comprising:10-90% w / w ordinary Portland cement;10-75% w / w reactive calcined gravel wash fines, and0-15% w / w source of calcium.

2. A cement mixture according to claim 1, wherein the cement mixture comprises gravel wash fines in the form of inert calcined gravel wash fines and the reactive calcined gravel wash fines.

3. A cement mixture according to claim 2, wherein the calcined gravel wash fines have a particle size distribution substantially similar to a particle size distribution of the Portland cement.

4. A cement mixture according to claim 2 or claim 3, wherein the calcined gravel wash fines have a particle size distribution of from about 0.1 pm to about 75 pm.

5. A cement mixture according to any one of the preceding claims, wherein the cement composition comprises 10-50% w / w Portland cement.

6. A cement mixture according to any one of claims 1 to 4, wherein the cement composition comprises:• 90% w / w Portland cement, 10% w / w reactive calcined gravel wash fines, or80% w / w Portland cement, 20% w / w reactive calcined gravel wash fines, or• 70% w / w Portland cement, 30% w / w reactive calcined gravel wash fines, or• 60% w / w Portland cement, 40% w / w reactive calcined gravel wash fines, or• 55% w / w Portland cement, 40% w / w reactive calcined gravel wash fines,5% w / w source of calcium, or• 45% w / w Portland cement, 50% w / w reactive calcined gravel wash fines, 5% w / w source of calcium, or• 32.5% w / w Portland cement, 60% w / w reactive calcined gravel wash fines, 7.5% w / w source of calcium, or• 20% w / w Portland cement, 70% w / w reactive calcined gravel wash fines, 10% w / w source of calcium, or• 10% w / w Portland cement, 75% w / w reactive calcined gravel wash fines, 15% w / w source of calcium.

7. A cement mixture according to any one of the preceding claims, wherein the source of calcium is selected from: limestone, calcium hydroxide, calcium oxide or combinations thereof.

8. A cement mixture according to any one of the preceding claims, further comprising one or more additives.

9. A cement mixture according to any one of the preceding claims, further comprising a superplasticizer.

10. A cement mixture according to claim 9, wherein a binder content of the mixture is a sum of the Portland cement and the reactive calcined gravel wash finescomposition, and wherein the mixture comprises up to around 1.5% w / w of the binder content of the mixture.

11. A method of producing a cement mixture according to any one of the preceding claims, the method comprising: calcination of gravel wash fines; sieving and milling the calcined gravel wash fines, wherein the calcined gravel wash fines comprise: reactive calcined gravel wash fines; and inert calcined gravel wash fines, mixing the calcined gravel wash fines and Portland cement.

12. A method according to claim 11, wherein mixing the calcined gravel wash fines and Portland cement further comprises mixing a source of calcium.

13. A method according to claim 12, wherein the source of calcium is selected from limestone, calcium hydroxide, calcium oxide, or combinations thereof.

14. A method according to any one of claims 11 to 13, wherein calcination of gravel wash fines comprises heating the gravel wash fines to a calcination temperature of from 500°C to 800°C.

15. A method according to claim 14, wherein calcination of gravel wash fines comprises heating the gravel wash fines to a calcination temperature of from 600°C to 700°C.

16. A method according to any one of claims 11 to 15, wherein the sieving and milling is controlled to produce calcined gravel wash fines having a particle size distribution substantially similar to a particle size distribution of the Portland cement.

17. A method according to any one of claims 11 to 16, wherein the sieving and milling is controlled to produce calcined gravel wash fines having a particle size distribution of from about 0.1 pm to about 75 pm18. A method according to any one of claims 11 to 17, further comprising determining the amount of inert calcined gravel wash fines in the calcined gravel wash fines.

19. A method according to claim 18, wherein the amount of inert calcined gravel wash fines in the calcined gravel wash fines is determined using Quantitative X-Ray Diffraction (QXRD) analysis, sieving or sedimentation.

20. A construction material formed from mixing a cement mixture according to the any one of claims 1 to 10 with water and aggregate, and allowing the mixture to cure.

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