Process for recovering cement powder from waste concrete

Abstract

A process for recovering a cement powder (CP) from waste concrete, the process comprising: a) heat treating waste concrete at a temperature to obtain a thermally treated concrete; b) comminuting the thermally treated concrete to form a treated concrete mixture; and c) separating the treated concrete mixture into a fine particle fraction and a coarse particle fraction, wherein the fine particle fraction comprises the CP.

Description

Process for recovering cement powder from waste concrete Technical Field

[0001] The present disclosure generally relates to recovering material from waste concrete. In particular, the present disclosure relates to recovering cement powder (CP) from waste concrete which can be recycled and used as a supplementary cementitious material (SCM). The present disclosure also relates to methods and uses of the recovered CP, including in composite cements.Background

[0002] The building and construction sectors are responsible for more than one-third of global CO2 emissions. Concrete is relied on heavily by the construction sector as the most used human-made material and the production and use of concrete accounts for 8% of global CO2 emissions. In addition, construction and demolition waste is more than one third of all waste generated in Australia and is mostly composed of concrete. Therefore, it would be advantageous to develop the next generation of sustainable concrete that significantly improves sustainability and improves the circularity of concrete use in the economy.

[0003] Concrete is a construction material composed of a mixture of cement, water, aggregates (such as sand, gravel, or crushed stone), and sometimes admixtures to modify its properties. Cement acts as a binder that holds aggregates together when mixed with water, forming a paste that hardens over time through a chemical reaction called hydration.

[0004] Recycling of concrete derived from construction waste is an established practice. The challenge lies in the separation and recovery of CP from waste concrete and the use of CP as a SCM in new concrete. That is to develop methods or processes for the recycling concrete which restore, at least in part, the original properties of the components of concrete.

[0005] Thus, there is a need for cost-effective and / or environmentally friendly alternative to new cement which is efficacious and can go some way to alleviate the environmental impact of the use of new cement in the production of new concrete.

[0006] It will be understood that any prior art publications referred to herein do not constitute an admission that any of these documents form part of the common general knowledge in the art, in Australia or in any other country.Summary

[0007] The present inventors have developed a process to recover cement powder (CP) from waste concrete. According to some embodiments or examples described herein, it has been found that heating waste concrete prior to comminution and subsequent selective screening recovers CP that is of sufficient quantity such that it can be used to prepare a composite cement blend by replacing a portion of conventional cement (such as Portland cement), in some instances the replacement percentage can beas high as 40%. Despite the high replacement percentage the composite cement exhibits comparable strength characteristics to commercial cements, highlighting the recovered CP’s high performance properties as a supplementary cementitious material. The process can be also be industrially scaled, providing the construction industry with a viable process to repurpose waste concrete.

[0008] In one aspect, there is provided a process for recovering a cement powder (CP) from waste concrete, the process comprising: a) heat treating waste concrete at a temperature to obtain a thermally treated concrete; b) comminuting the thermally treated concrete to form a treated concrete mixture; and c) separating the treated concrete mixture into a fine particle fraction and a coarse particle fraction, wherein the fine particle fraction comprises the CP.

[0009] In one embodiment, the waste concrete has a D90 particle size (in mm) of less than about 500, 200, 100, 75, 50 or 40.

[0010] In one embodiment, prior to step a) the process further comprises contacting the waste concrete with water to increase the moisture content of the waste concrete. In one embodiment, the waste concrete is contacted with water for a period of time (in hours) of between about 12 to about 36.

[0011] In one embodiment, step c) comprises passing least a portion of the treated concrete mixture through one or more screening steps to obtain the fine particle fraction comprising the CP and the coarse particle fraction.

[0012] In one embodiment, separating the treated concrete mixture at step c) comprises screening at least a portion of the treated concrete mixture at a size (in mm) of about, or less than about 4, 3, 2, 1.5, 1, 0.1, or 0.075, to obtain the fine particle fraction comprising the CP.

[0013] In one embodiment, the fine particle fraction comprising the CP has a D90 particle size (in pm) of about, or less than about 2,000, 1,000, 750, 500, 250, 100, 90, 80, 75, 70, 65, 60, 55, or 50. In one embodiment, the fine particle fraction comprising the CP has a D50 particle size (in pm) of about, or less than about 1,000, 750, 500, 250, 100, 75, 50, 45, 40, 35, 30, 25 or 20.

[0014] In one embodiment, the heat treatment at step a) is performed at a heat treatment temperature of between about 300°C to about 700°C, between 400°C to about 700°C, between 450°C to about 650°C, or between about 550°C to about 650°C.

[0015] In one embodiment, the waste concrete is heated at step a) to the heat treatment temperature at a rate of between about 1 °C / min to about 20°C / min.

[0016] In one embodiment, the heat treatment at step a) is performed for between about 1 to about 3 hours.

[0017] In one embodiment, prior to step b) the process further comprises cooling the treated concrete mixture.

[0018] In one embodiment, the comminuting the thermally treated concrete at step b) comprises grinding the thermally treated concrete. In one embodiment, the grinding is performed in a ball mill. In one embodiment, the grinding is performed for a period of time (in minutes) of between about 0.1 to about 10, or between about 1 to about 3.

[0019] In one embodiment, the fine particle fraction comprising the CP has an aggregate contaminant in an amount of between about 0.1% w / w to about 40% w / w. In one embodiment, the fine particle fraction comprising the CP has a heat release at 7 days between about 200 (Joule / gram) to 500 (Joule / gram).

[0020] In one embodiment, the process further comprises mixing at least some of the fine particle fraction comprising the CP with cement to form a cement composite. In one embodiment, the composite cement comprises between about 5 to about 45 % w / w of the fine particle fraction comprising the CP.

[0021] In another aspect, there is provided a use of the fine particle fraction comprising the CP obtained from the process described above and herein to form a composite cement. In one embodiment, the composite cement comprises between about 5 to about 45 % w / w of the fine particle fraction comprising the CP.

[0022] In another aspect, there is provided a use of the composite cement described above and herein to prepare concrete.

[0023] In another aspect, there is provided a use of the fine particle fraction comprising the CP obtained from the process described above and herein to prepare concrete.

[0024] It will be appreciated that any one or more of the embodiments and examples described herein for the process may also apply to the uses, composite cements and / or concretes, and vice versa. Any embodiment herein shall be taken to apply mutatis mutandis to any other embodiment unless specifically stated. It will also be appreciated that other aspects, embodiments and examples of the processes, uses, composite cements and concretes are described herein.

[0025] All publications discussed and / or referenced herein are incorporated herein in their entirety.

[0026] 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.

[0027] 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, processes, uses andcompositions, 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.

[0028] It will also be appreciated that some features of the process, uses, composite cements and / or concretes identified in some aspects, embodiments or examples as described herein may not be required in all aspects, embodiments or examples as described herein, and this specification is to be read in this context. It will also be appreciated that in the various aspects, embodiments or examples, the order of the process or use steps may not be essential and may be varied. .Brief Description of Drawings

[0029] Embodiments of the present disclosure will be further described and illustrated, by way of example only, with reference to the accompanying drawings in which:Figures 1A-1C -The X-Ray Diffraction (XRD) diffractograms of A) ordinary Portland cement (OPC), B) RCP type 1 (RCP1) and C) RCP type 2 (RCP2);Figures 2A-2C - The crystalline / amorphous phase compositions of A) OPC, B) RCP1 and C) RCP2;Figure 3 - The particle size distribution of OPC, RCP1 and RCP2;Figure 4 - The cumulative heat release of OPC, RCP1 and RCP2;Figure 5 - The compressive strength of blended cement composite; and Figure 6 - The yield percentage of recovered of CP at various heat treatment temperatures and hydration conditions.Figure 7 - Ternary diagram of the chemical composition of CP obtained from waste concrete processing from the literature.Description of Embodiments

[0030] 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.General terms

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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 subcombination.

[0035] 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 or between 1 to 5 should be considered to have specifically disclosed subranges such as from or between 1 to 3, from or between 1 to 4, from or between 1 to 5, from or between 2 to 4, from or between 2 to 5, from or between 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.

[0036] 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.

[0037] 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.

[0038] The terms "composition" and “formulation” as used herein are intended to encompass a product comprising the specified ingredients in the specified amounts, aswell as any product which results, directly or indirectly, from combination of the specified ingredients in the specified amounts.Process

[0039] In one aspect of the present disclosure, there is provided a process for recovering concrete powder (CP) from waste concrete, the process comprising:a) heat treating waste concrete at a temperature to obtain a thermally treated concrete;b) comminuting the thermally treated concrete to form a treated concrete mixture; andc) separating the treated concrete mixture into a fine particle fraction and a coarse particle fraction,wherein the fine particle fraction comprises the CP.Heating

[0040] The process described herein comprises heat treating waste concrete to form a thermally treated concrete. Any suitable method known in the art can be used for the heat treatment of the waste concrete.

[0041] In some embodiments, the heat treatment at step a) is performed at a heat treatment temperature (in °C) of about, or greater than about: 300, 350, 400, 450, 500, 550, 600, 650, 700, or 750. In some embodiments, the heat treatment at step a) is performed at a heat treatment temperature (in °C) of less than about: 750, 700, 650, 600, 550, 500, 450, 400, 350, or 300. The heat treatment temperature may be in a range provided by any two or more of these upper and / or lower amounts. In some embodiments, the heat treatment at step a) is performed at a heat treatment temperature (in °C) of between about 300 to about 700, between about 400 to about 700, or between about 450 to about 650, or between about 550 to about 650.

[0042] The thermal treatment at least in part reverses cement hydration, obtaining dehydrated compounds with potential cementitious reactivity. According to some embodiments or examples described herein, the inventors have discovered that by controlling the thermal treatment temperature, key reactions, for example dehydration, dehydroxylation, and decarbonation, lead to the formation of highly reactive compounds in CP, which can be utilised as a cementitious material. The thermal treatment can also weaken the hardened cement paste and its bonding with aggregates in the waste concrete, thereby maximising the separation and recovery of cement powder from the waste concrete. Advantageously, the thermal treatment temperature required is typically lower than the temperature used in clinker production, making it a viable alternative for reducing carbon emissions in the cement industry. Additionally, the process can minimise the CO2 emission from the chemically decomposition of calcium carbonate as in the clinker production. Thus, the process described herein mayreduce carbon emissions providing a more environmentally sustainable source of cement.

[0043] In some embodiments, the waste concrete is heated at step a) for a period of time (hours) of about, or greater than about: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 13,3, 14, 15, 16, 17, 18, 19, or 20, 24 or 48. In some embodiments, the waste concrete is heated at step a) for a period of time (hours) of less than about: 48, 24, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1. The heat treatment time may be in a range provided by any two or more of these upper and / or lower amounts. In some embodiments, the waste concrete is heated at step a) for a period of time (hours) of between about 0.1 to about 48, between about 0.5 to about 12, between about 1 to about 3. In some embodiments, the waste concrete is heated at step a) for a period of time (hours) of about 2.

[0044] In some embodiments, the waste concrete is heated at step a) to the heat treatment temperature at a rate (°C / min) of about, or greater than about: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 13,3, 14, 15, 16, 17, 18, 19, or 20. In some embodiments, the waste concrete is heated at step a) to the heat treatment temperature at a rate (°C / min) of less than about: 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1. The heating rate may be in a range provided by any two or more of these upper and / or lower amounts. In some embodiments, the waste concrete is heated at step a) to the heat treatment temperature at a rate (°C / min) of between about 1 to about 20. In some embodiments, the waste concrete is heated at step a) to the heat treatment temperature at a rate (°C / min) of about 5.Comminution

[0045] The process described herein comprises comminuting the thermally treated concrete to form a treated concrete mixture. Any suitable method known in the art can be used to comminute the thermally treated concrete, including for example, crushing, grinding, cutting, or vibrating.

[0046] In some embodiments, the comminuting the thermally treated concrete at step b) is performed for a period of time (minutes) of about, or greater than about: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 13,3, 14, 15, 16, 17, 18, 19, or 20, 30, 40, 50, or 60. In some embodiments, the comminuting the thermally treated concrete at step b) is performed for a period of time (minutes) of less than about: 60, 50, 40, 30, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1. The comminution time may be in a range provided by any two or more of these upper and / or lower amounts. In some embodiments, the comminuting the thermally treated concrete at step b) is performed for a period of time (minutes) of between about 0.1 to about 60, between about 0.1 to about 10, between about 1 to about 3. In some embodiments, the comminuting the thermally treated concrete at step b) is performed for a period of time (minutes) of about 2.

[0047] In some embodiments, the comminuting the thermally treated concrete at step b) comprises grinding the thermally treated concrete. Any suitable device known in the art can be used for grinding the thermally treated concrete, including for example, autogenous mill, ball mill, high pressure grinding roll, pebble mill, rod mill, SAG mill, vertical shaft impactor mill, vertical roller mill, or other mechanical mills, or other types of mechanical grinding devices.

[0048] In some embodiments, the grinding is performed in a vertical roller mill or ball mill. In some embodiments, the grinding is performed in a ball mill.

[0049] In one embodiment, the grinding is performed using a ball bill. In some embodiments, ball milling the thermally treated concrete at step b) is performed at a speed (rpm) of about, or greater than about: 10, 20, 30, 40, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 700, 750, 800, 850, 900, 950 or 1000. In some embodiments, ball milling the thermally treated concrete at step b) is performed at a speed (rpm) of less than about: 1000, 950, 900, 850, 800, 750, 700, 650, 600, 550, 500, 450, 400, 350, 300, 250, 200, 150, 100, 50, 40, 30, 20, or 10. The ball milling speed may be in a range provided by any two or more of these upper and / or lower amounts. In some embodiments, ball milling the thermally treated concrete at step b) is performed at a speed (rpm) of between about 10 and about 1000, between about 50 and about 500, between about 100 and 500, or between about 200 and 300. In some embodiments, ball milling the thermally treated concrete at step b) is performed at a speed (rpm) of about 250.Separating step

[0050] The process described herein comprises separating the treated concrete mixture to obtain a fine particle fraction and a coarse particle fraction, wherein the fine particle fraction comprises the CP.

[0051] In some embodiments, the separating the treated concrete mixture to obtain a fine particle fraction and a coarse particle fraction of step c) comprises screening the treated concrete mixture.

[0052] In some embodiments, the separating the treated concrete mixture to obtain a fine particle fraction and a coarse particle fraction of step c) comprises passing at least a portion of the treated concrete mixture through one or more screening steps to obtain the fine particle fraction and the coarse particle fraction.

[0053] In some embodiments, the portion of the treated concrete mixture passing through the one or more screens comprises the fine particle fraction comprising the CP.

[0054] In some embodiments, the separating the treated concrete mixture to obtain a fine particle fraction and a coarse particle fraction of step c) comprises screening at least a portion of the treated concrete mixture at size (in mm) of about, or less than about 5, 4.75, 4.5, 4.25, 4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.15, 0.1, 0.09, 0.08, 0.075, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, or 0.01 to obtain the fine particle fractioncomprising the CP. The screening size may be in a range provided by any two of these amounts.

[0055] In some embodiments, the separating the treated concrete mixture to obtain a fine particle fraction and a coarse particle fraction of step c) comprises screening at least a portion of the treated concrete mixture at a size (in mm) of between about 0.01 to about 5, between about 0.01 to about 4, between about 0.01 to about 2, between about 0.01 to about 1.5, between about 0.01 to about 1, between about 0.01 to about 0.5, between about 0.01 to about 0.3, or between about 0.05 to about 0.2, or between about 0.075 to about 0.15 to obtain the fine particle fraction comprising the CP.

[0056] In some embodiments, the fine particle fraction comprising the CP has a D90 particle size (in pm) of about, or less than about: 2,000, 1,000, 750, 500, 250, 100, 90, 80, 75, 70, 65, 60, 55, 50, 20 or 10. The D90 particle size may be in a range provided by any two of these amounts, for example between about 10 to about 100.

[0057] In some embodiments, the fine fraction comprising the CP has a D50 particle size (in pm) of about, or less than about 1,000, 750, 500, 250, 100, 75, 50, 45, 40, 35, 30, 25, 20, 15, or 10. The D50 particle size (in pm) may be in a range provided by any two of these amounts, for example between about 10 to about 50.

[0058] In some embodiments, the fine fraction comprising the CP has a Dio particle size (in pm) of about, or less than about 500, 100, 50, 20, 15, 10, 5 or 1. The Dio particle size may be in a range provided by any two of these amounts, for example between about 1 to about 10.

[0059] The particle size can be measured by any suitable method, for example laser diffraction.

[0060] In some embodiments, the separating the treated concrete mixture to obtain a fine particle fraction and a coarse particle fraction of step c) comprises screening at least a portion of the treated concrete mixture at size (in mm) of about 0.150.

[0061] In some embodiments, the separating the treated concrete mixture to obtain a fine particle fraction and a coarse particle fraction of step c) comprises screening at least a portion of the treated concrete mixture at size (in mm) of about 0.075 to obtain the fine particle fraction comprising the CP.Multiple separating steps

[0062] In some embodiments, the classifying the treated concrete mixture to obtain a fine particle fraction and a coarse particle fraction of step c) comprises passing the treated concrete mixture through two or more screening steps. This may allow for the recovery of other supplementary aggregate fractions which may be used in construction.

[0063] In some embodiments, step c) comprises passing the treated concrete mixture through at least two screening steps, one of which screens at a smaller size (smaller screen) compared to the other (larger screen). It will be appreciated that the order ofscreening is not important, and merely provides various ways to recover the fine particle fraction comprising the CP. For example, if the treated concrete mixture is passed through the smaller screen first to obtain the fine particle fraction comprising the CP, the particles retained by the smaller screen can then subsequently be passed through the larger screen. Alternatively, if the treated concrete mixture is first passed through the larger screen, the particles passing through the larger screen can then be subsequently passed through the smaller screen to obtain the finer particle fraction comprising the CP.

[0064] In some embodiments, the treated concrete mixture may be passed through multiple screening steps, for example screens or sieves, of different sizes such that the fine particle fraction has well defined lower and / or upper particle size limits. The lower and upper particle size limits may be varied depending on the desired composition of the screened undersize fraction and the screened oversize fraction.

[0065] In some embodiments, the separating the treated concrete mixture to obtain a fine particle fraction and a coarse particle fraction of step c) further comprises separating the fine particle fraction into an undersize powder fraction comprising the CP and an intermediate fraction comprising an intermediate supplementary aggregate material.

[0066] In some embodiments, the separating the treated concrete mixture to obtain a fine particle fraction and a coarse particle fraction of step c) further comprises separating the coarse particle fraction into an intermediate fraction comprising an intermediate supplementary aggregate material and an oversize fraction comprising a larger supplementary aggregate material.

[0067] In some embodiments, the portion of the treated concrete mixture passing through the smaller screen comprises the fine particle fraction comprising the CP. In some embodiments, the portion of the treated concrete mixture not passing through the smaller screen comprises the coarse particle fraction.

[0068] In some embodiments, the portion of the treated concrete mixture passing through the larger screen but not the smaller screen comprises the oversize fraction comprising a larger supplementary aggregate material. In some embodiments, the portion of the treated concrete mixture passing through the larger screen but not passing through the smaller screen comprises the intermediate fraction comprising an intermediate supplementary aggregate material.

[0069] In some embodiments, the smaller screen has a size (in mm) of about, or less than about: 5, 4.75, 4.5, 4.25, 4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, or 0.01. The smaller screen size may be in a range provided by any two or more of these amounts. In some embodiments, the smaller screen has a size (in mm) of between about 0.01 to about 1.5, between about0.05 to about 0.5. In some embodiments, the smallest screen has a size (in mm) of about 0.075.

[0070] In some embodiments, the larger screen has a size (in mm) of about, or greater than about 1, 2, 3, 4, 4.25, 4.5, 4.75, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20. The larger screen may be in a range provided by any two of these amounts. In some embodiments, the larger screen has a size (in mm) of between about 1 to about 20, between about 2.5 to about 10, between about 4 to about 6. In some embodiments, the larger screen has a size (in mm) of about 4.75.Moisture content

[0071] The person skilled in the art will understand that, depending on the source, the waste concrete may contain an amount of moisture or free water (e.g. water not involved in the cement hydration reaction). According to some embodiments or examples described herein, the inventors of the present application have discovered that by increasing the moisture content in the waste concrete prior to the heat treatment this can provide for improved recovery of the CP in the fine particle fraction, which in some cases can be as high as up to 50%.

[0072] In some embodiments, prior to step a) the process further comprises contacting the waste concrete with water to increase the moisture content of the waste concrete. Such contact with water can be achieved by various techniques, including for example immersing the waste concrete in water. Following contact (e.g. immersion) with water, the concrete can be called hydrated waste concrete.

[0073] The moisture content of the hydrated waste concrete is the amount of free water in the hydrated waste concrete which can be removed by drying the hydrated waste concrete to obtain a dry waste concrete. In one embodiment, the hydrated waste concreate has a moisture content (in %w / w relative to the mass of dry waste concrete) of greater than 0 to about 100. In some embodiments, the hydrated waste concrete has a moisture content (in %w / w relative to the mass of dry waste concrete) of about, or at least about 1, 2, 3, 4, 5, 6, 7, 8, 9 10, 11, 12, 13, 14, 15, 20, 25, 30, 40, 50, 70, 90 or 95. The moisture content may be in a range provided by any two of these values. In some embodiments, the moisture content of the waste concrete after contacting with water (in %w / w relative to the mass of dry waste concrete) is between about 1 to about 95, between about 1 to about 50, between about 2 to about 25, or between about 2 to about 10. The moisture content can be measured by any suitable method, including for example ASTM C0566.

[0074] In some embodiments, the contacting the waste concrete with water is performed for a period of time (hours) sufficient to substantially saturate waste concrete. In this context, it will be understood that saturated waste concrete is waste concrete that has been exposed to a sufficient amount of water for a sufficient period oftime that if exposure to water is continued the moisture content of the waste concrete will not appreciably change.

[0075] In some embodiments, the contacting the waste concrete with water is performed for a period of time (hours) of about, or greater than about: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, 24, 30, 36, 42, or 48. In some embodiments, the contacting the waste concrete with water is performed for a period of time (hours) of less than about: 48, 42, 36, 30, 24, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1. The water contact time may be in a range provided by any two or more of these upper and / or lower amounts. In some embodiments, the contacting the waste concrete with water is performed for a period of time (hours) of between about 0.1 to about 48, between about 12 to about 36, between about 1 to about 3.

[0076] According to some aspects or embodiments, it has been discovered that that the yield percentage of intermediate fraction and fine fraction comprising the CP increases with the inclusion of a hydration step before heat treatment. In addition, according to some aspects or embodiments, that pre-soaking in water facilitates the removal of lightweight impurities and dust from the waste concrete. By removing fine dust particles and other lightweight impurities, the properties of the resulting CP may be enhanced, for example, by reducing the water demand for concrete incorporating the CP, improved strength and durability, and / or better handling characteristics.

[0077] In embodiments, the process does not comprise contacting the waste concrete, or a portion thereof, with an acidic solution. In embodiments, the process does not comprise contacting the waste concrete, or a portion thereof, with a solution having a pH of less than about: 6.5, 6, 5.5, or 5.

[0078] In embodiments, the process does not comprise contacting the waste concrete, or a portion thereof, with an basic solution. In embodiments, the process does not comprise contacting the waste concrete, or a portion thereof, with a solution having a pH of greater than about: 7.5, 8, 8.5, or 9.Waste concrete

[0079] The process of the present disclosure can be applied to waste concrete sourced from a variety of sources, included by not limited to concrete demolition waste, concrete residues generated during construction, waste produced from cleaning concreting equipment, or mixtures of two or more of these materials.

[0080] In some embodiments, the waste concrete is obtained from a crushed concrete demolition waste in which the impurities such as metal, wood, brick and plastic, has been substantially removed.

[0081] If the waste concrete does not possess the desired particle size, it can be easily adjusted with any suitable method known in the art such as crushing, sieving and classifying.

[0082] According to some embodiments or examples described herein, the inventors of the present disclosure have discovered that, although not critical, the size of the waste concrete may influence the quantity and / or quality of the fine particle fraction comprising the CP. In particular, the inventors have surprisingly discovered that larger feed materials can possess higher amounts of cement paste and thus can produce a higher quantity and / or quality of fine particle fraction comprising the CP.

[0083] In some embodiments, the waste concrete has a D90 particle size (in mm) of about, or less than about 500, 200, 100, 75, 50, 40, 30, 20 or 10. In some embodiments, the waste concrete has a D90 particle size (in mm) of greater than 10, 20, 30, 40, 50, 75, 100, 200 or 500. The D90 particle size (in mm) may be in a range provided by any two these amounts. In some embodiments, the waste concrete has a D90 particle size (in mm) of between about 40 to about 500.

[0084] In some embodiments, the waste concrete has a Dio particle size (in mm) of about, or less than about 50, 40, 30, 20, 10, 5, 4.75, 4.5, 4.25, 4, 3, 2, 1, or 0.1. In some embodiments, the waste concrete has a Dio particle size (in mm) is greater than about 0.1, 1, 2, 3, 4, 4.25, 4.5, 4.75, 5, 10, 20, 30, 40 or 50. The Dio particle size (in mm) may be in a range provided by any two these amounts.

[0085] In some embodiments, prior to step a), the process further comprises classifying a crude waste concrete to obtain the waste concrete. The classifying the crude waste concrete may be performed to obtain a waste concrete with a particle size distribution more suitable for use in the process described herein. For example, the classifying the crude waste concrete may be performed to obtain waste concrete with a relatively well defined minimum particle size and / or a maximum particle size.

[0086] In some embodiments, the classifying the crude waste concrete to obtain a classified crushed waste concrete comprises passing the crude waste concrete through a crude waste concrete screen. The crude waste concrete screen can be used to remove larger particles or smaller particles from the waste concrete. Two ore more crude waste concrete screening steps can also be used, for example to remove both smaller and larger particles from the waste concrete.

[0087] In one embodiment, the crude waste concrete screen is used to remove smaller particles from the waste concrete. In this embodiment, the crude waste concrete screen has a size (in mm) of about, or less than about: 50, 40, 30, 20, 10, 5, 4.75, 4.5, 4.25, 4, 3, 2, 1, or 0.1. The crude waste concrete screen size may be in a range provided by any two or more of these amounts, such as between about 0.1 to about 50.

[0088] In one embodiment, the crude waste concrete screen is used to remove large particles from the waste concrete. In this embodiment, the crude waste concrete screen has a size (in mm) of about, or greater than about: 10, 25, 50, 75, 100, 150, 200, or 500. The crude waste concrete screen size may be in a range provided by any two these amounts, such as between about 10 to about 500.

[0089] Whilst not required, the classifying the crude waste concrete may comprise passing the crude waste concrete through at least two screening steps, one of which screens at a smaller size (smaller crude waste concrete screen) compared to the other (larger crude waste concrete screen). It will be appreciated that the order of screening is not material to the present disclosure. For example, if the crude waste concrete is passed through the smaller crude waste concrete screen first, the particles retained by the smaller crude waste concrete screen can then subsequently be passed through the larger crude waste concrete screen. Alternatively, if the crude waste concrete is first passed through the larger crude waste concrete screen, particles passing through the larger screen can then be subsequently passed through the smaller crude waste concrete screen. The screen sizes for the smaller and / or larger crude waste concrete screen can be selected from those described above in relation to the screening to remove smaller and larger particles.Fine particle fraction comprising the CP

[0090] According to some embodiments or examples described herein, the fine particle fraction comprising the CP obtained by the process described herein demonstrates good performance properties.

[0091] In some embodiments, the reactivity of the fine particle fraction comprising the CP is about, or greater than about: 200, 250, 300, 350, 400, 450, or 500 (Joule / gram). In some embodiment, the reactivity of the fine particle fraction comprising the CP is less than about: 500, 450, 400, 350, 300, 250 or 200. The reactivity may be in a range provided by any two or more of these upper and / or lower amounts recited above. In some embodiments, the reactivity of the fine particle fraction comprising the C is between about 200 to about 500, or between about 300 to 400. The reactivity may be determined by the heat release at 7 days from a Rapid Reliable Relevant (R3) test, such as that outlined in Londono-Zuluaga et al, Mater Struct 55, 142 (2022).

[0092] In some embodiments, the fine particle fraction comprising the CP comprises aggregate contaminants, for example but not limited to quartz, calcite, anorthite, augite and other minerals. In some embodiments, the amount of aggregate contaminants in the fine particle fraction comprising the CP (in % w / w of the total weight of the fine particle fraction comprising the CP) is about, or less than about: 40, 35, 30, 25, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1. The amount of aggregate contaminants may be in a range provided by any two or more of these amounts. In some embodiments, the amount of aggregate contaminants in the fine particle fraction comprising the CP (in % w / w of the total weight of the fine particle fraction comprising the CP) is between about 0.1 and about 40. The amount of aggregate contaminant can be determined using X-ray diffraction and Rietveld analysis.

[0093] In some embodiments, the amount of CP in the fine particle fraction comprising the CP (in % w / w of the total weight of the fine particle fraction comprising the CP) is about, or greater than about: 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.5, or 99.9. The amount of CP in the fine particle fraction comprising the CP may be in a range provided by any two or more of these upper and / or lower amounts recited above. In some embodiments, the amount of CP in the fine particle fraction comprising the CP (in % w / w of the total weight of the fine particle fraction comprising the CP) is between about 60 to about 99.9 % w / w. The amount of CP in the fine fraction can be determined using X-ray diffraction and Rietveld analysis.

[0094] In some embodiments, the amount of CaO in the CP in the fine particle fraction comprising the CP (in % w / w of the oxide content of the CP) is about, or greater than about: 40, 45, 50, 55 60, 65, 70, 75, or 80. The amount of CaO in the CP in the fine particle fraction comprising the CP (in % w / w of the oxide content of the CP) may be in a range provided by any two or more of these upper and / or lower amounts recited above. In some embodiments, the amount of CaO in the CP in the fine particle fraction comprising the CP (in % w / w of the oxide content of the CP) is between about 40 to about 80, or between about 45 to about 65.

[0095] In some embodiments, the amount of SiOi in the CP in the fine particle fraction comprising the CP (in % w / w of the oxide content of the CP) is about, or greater than about: 15, 20, 25 30, 35, or 40. The amount of SiCh in the CP in the fine particle fraction comprising the CP (in % w / w of the oxide content of the CP) may be in a range provided by any two or more of these upper and / or lower amounts recited above. In some embodiments, the amount of SiCh in the CP in the fine particle fraction comprising the CP (in % w / w of the oxide content of the CP) is between about 15 to about 40, or between about 20 to about 35.

[0096] In some embodiments, the amount of AI2O3 in the CP in the fine particle fraction comprising the CP (in % w / w of the oxide content of the CP) is about, or greater than about: 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. The amount of AI2O3 in the CP in the fine particle fraction comprising the CP (in % w / w of the oxide content of the CP) may be in a range provided by any two or more of these upper and / or lower amounts recited above. In some embodiments, the amount of AI2O3 in the CP in the fine particle fraction comprising the CP (in % w / w of the oxide content of the CP) is between about 1 to about 10, or between about 4 to about 8.

[0097] In some embodiments, the amount of CaO in the CP (in % w / w of the oxide content of the CP) is between about 40 to about 80, the amount of SiO2 in the CP (in % w / w of the oxide content of the CP) is between about 15 to about 40, and / or the amount of AI2O3 in the CP (in % w / w of the oxide content of the CP) is between about 1 to about 10.

[0098] In some embodiments, the amount of CaO in the CP (in % w / w of the oxide content of the CP) is between about 45 to about 65, the amount of SiO2 in the CP (in %w / w of the oxide content of the CP) is between about 20 to about 35, and / or the amount of AI2O3 in the CP (in % w / w of the oxide content of the CP) is between about 4 to about 8.

[0099] The oxide composition in the CP may be determined X-Ray Fluorescence.

[0100] According to some embodiments or examples described herein, it has been found that it is possible to obtain a fine particle fraction comprising the CP such that the CP has a chemical composition that is closer to the chemical composition of virgin Portland cement that the current state of the art, see Figure 7.Composite cement

[0101] The fine particle fraction comprising the CP can be used as a supplementary cementitious material (SCM).

[0102] In some embodiments, the process further comprising mixing at least some of the fine particle fraction comprising the CP with cement to form a composite cement (e.g. a blended cement mixture).

[0103] In an aspect of the present disclosure, there is provided the use of the fine particle fraction comprising the CP obtained from the process described herein to form a composite cement.

[0104] In some embodiments, the amount of the fine particle fraction comprising the CP (in % w / w of the total weight of the composite cement) is about, or greater than about: 5, 10, 15, 20, 25, 30, 35, 40 or 45. In some embodiments, the amount of the fine particle fraction comprising the CP (in % w / w of the total weight of the composite cement) is less than about: 45, 40, 35, 30, 25, 20, 15, 10, or 5. The amount of the fine particle fraction in the cement composite may be in a range provided by any two or more of these upper and / or lower amounts. In some embodiments, the composite cement comprises between about 5% w / w to about 45% w / w of the fine particle fraction comprising the CP. In some embodiments, the amount of the fine particle fraction comprising the CP in the cement composite (in % w / w of the total weight of the composite cement) is between about 10 to about 45, between about 15 to about 45, between about 20 to about 45.

[0105] Any type of cement can be blended with the fine particle fraction comprising the CP to form the composite cement. These include, for example, ordinary Portland cement (OPC), Portland pozzolana cement (PCC), rapid-hardening cement, quicksetting cement, low-heat cement, sulfate -resisting cement, blast furnace slag cement, high-alumina cement, white cement, coloured cement, air-entraining cement, expansive cement, hydrographic cement and Portland-limestone cement. However, a preferred cement for blending with the fine particle fraction comprising the CP is OPC.

[0106] In some embodiments, the amount of the cement in the cement composite (in % w / w of the total weight of the composite cement) is about, or greater than about: 55, 60, 65, 70, 75, 80, 85, 90 or 95. In some embodiments, the amount of cement in thecement composite (in % w / w of the total weight of the composite cement) is less than about: 95, 90, 85, 80, 75, 70, 65, 60, or 55. The amount of cement in the cement composite may be in a range provided by any two or more of these upper and / or lower amounts. In some embodiments, the composite cement comprises between about 55% w / w to about 95% w / w of cement.

[0107] Whilst not required, the composite cement may further comprise other additives.

[0108] In an aspect of the present disclosure, there is provided the use of the composite cement as described here to prepare concrete.

[0109] In an aspect of the present disclosure, there is provided the use of the fine particle fraction comprising the CP obtained from the process described herein to prepare concrete.Additional construction materials

[0110] In an aspect of the present disclosure, there is provided an aggregate material for use in construction comprising at least a portion of the coarse fraction obtained from the process described herein.

[0111] In an aspect of the present disclosure, there is provided an aggregate material for use in construction comprising at least a portion of the intermediate supplementary aggregate material obtained from the process as described herein.

[0112] In an aspect of the present disclosure, there is provided an aggregate material for use in construction comprising the larger supplementary aggregate material obtained from the process as described herein.ExamplesCrude waste concrete

[0113] Crude waste concrete was obtained from the demolished pile caps in a residential apartment building project in Melbourne, Australia. The pile caps were composed of Grade 50 concrete, made using ordinary Portland cement (OPC), washed river sand as the fine aggregate, and crushed basalt as the coarse aggregate.

[0114] The crude waste concrete was screened to obtain waste concrete with a maximum and minimum size of approximately 100 mm and 20 mm, respectively. Separation and recovery of CP

[0115] Waste concrete was immersed with water for 24 hours to form a saturated waste concrete. The saturated waste concrete was heat treated in an electric muffle furnace at 600°C for 2 hours. The waste concrete was also heat treated at 400°C and 500°C to investigate the effect of heating temperature. After the heat treatment, the heat treated concrete was allowed to cool to ambient conditions. Finally, the cooled thermally treated concrete underwent mechanical grinding using a SQM-2L ball mill. Steel balls were added to the mill to enhance the separation of recycled concretepowder from the waste concrete. The milling process was conducted for 2 minutes at a speed of 250 revolutions per minute. Following the treatment process, the treated material was classified through sieving at 0.075 mm to obtain the fine particle fraction comprising the CP (denoted herein as RCP1). The effect of the particle size on the composition of the CP was also investigated. In addition to 0.075 mm sieve size, three different sieve sizes were used (0.15, 0.3 and 0.6 mmm) to obtain the fine fraction comprising the CP.

[0116] For further comparative analysis, another cement powder (denoted herein as RCP2) was obtained with the following steps without any hydration step or heat treatment: The crude concrete was screened to obtain waste concrete with a maximum and minimum size of approximately 100 mm and 20 mm, respectively; the waste concrete was underwent comminution using a Rocklabs BOYD jaw crusher to achieve a targeted size of 20 mm; the jaw-crushed material was classified through sieving at 0.075 mm to obtained RCP2.

[0117] The quantity of RCP1 and RCP2 recovered from 100 kg of the crushed concrete was 8.4 kg and 1.1 kg, respectively. This highlight the efficacy of the present process described herein in recovering the RCP from the waste concrete.Characterisations of the RCPs and cement composite

[0118] Laser diffraction analyser (Mastersizer 3000+) and BET method (BELSORP-mini-X) were utilised to measure the particle size distribution and specific surface area of the materials. X-Ray Diffraction or XRD (Bruker D8 Advance Powder Diffractometer) with Rietveld refinement and X-Ray Fluorescence or XRF (Bruker S2 Puma) were used to quantify the crystalline phases and oxide composition of the materials. Rapid Reliable Relevant (R3) test was conducted using a TAM Air isothermal calorimeter to determine the reactivity of the materials through the cumulative heat release at 7 days. OPC was used as benchmark. The results are presented in the figures below.

[0119] Table 1 shows the mix proportion of the blended cement composite made using RCP1 and RCP2 (denoted herein as RCP1-P, RCP2-P). Replacement percentages were 10%, 20%, 30% and 40% by mass. The water-to-binder ratio is kept constant as 0.45. A mix with 100% OPC was used as benchmark. For each composition, nine, 50 x 50 x 50mm cubes, were produced for compression tests at 3, 7 and 28 days. The results are presented in the figures below:Table 1: Mix proportion of blended cement composites.

[0120] The oxide composition of OPC, RCP1 and RCP2, as determined by XRF, is summarised in Table 2.Table 2. Oxide composition of raw materials determined by XRF.

[0121] As illustrated in Table 2, RCP2 possesses low CaO (31%) and high SiO2 (42%) contents. This is considerably distinct from the presence of these oxides in OPC and RCP1. The high SiO2 concentration is stemmed from the abrasion and grinding of sand and gravel in the waste concrete. Additionally, RCP2 contains higher amounts of AI2O3 (10.33%) and Fe20s (8.43%) compared to OPC and RCP1, which is consistent with the presence of minerals in the original basalt aggregates used in the waste concrete. It is clear that the RCP1 obtained from the invented process consists of high CaO (59.27%) followed by SiO2, A12O3, Fe2O3 and SO3, closely resembling the oxide composition of OPC. This similarity suggests that the invention process enables maximising the recovery of hardened cement paste and minimising the amount of aggregate contaminants.

[0122] The key oxide composition of CP obtained at different heat treatment temperatures (400,500, and 600 °C) for the samples determined by XRF is shown in Table 3. XRF results show that as the temperature increases, the amount of CaO in the CP increases while the amount of SiO2decreases.Table 3: Oxide composition of CP at different heat treatment temperatures as determined by XRF

[0123] Figures 1A to 1C presents the XRD diffractograms of OPC, RCP1, and RCP2. It is evident that the diffraction peaks associated with quartz and rock minerals are more intense in RCP2 than RCP1. The rock minerals primarily consist of anorthite and augite, aligning with the basalt aggregate used in the original concrete.

[0124] Figures 2A to 2C further reveals the phase compositions of OPC, RCP1 and RCP2 from the XRD and Rietveld analysis. The phase composition of OCP is similar to the data in prior arts with the presence of four main clinker phases (C3S, C2S, C3A and C4AF). Figure 2C affirms that RCP2 contains a substantial amount of quartz (SiO2) and basalt rock minerals, accounting for approximately 63% of its composition. These components are originated from sand and basalt aggregate in the waste concrete. In contrast, Figure 2B shows that RCP1 exhibits a lower aggregate contaminants of 23%, with the remaining 77% composed of cementitious material (including amorphous content). This suggests that the invention process resulted in a more pronounced recovery of cementitious compounds, a conclusion further supported by the aforementioned oxide composition results.

[0125] Moreover, the recovered clinker phases in RCP1 (29%) is found to be about five times higher than in RCP2 (6%). In RCP2, the clinker phases primarily originate from unhydrated cement in the waste concrete, whereas in RCP1, it mainly results from the decomposition of hydration products, including calcium silicate hydrate (C-S-H) and AFm phases, which transform into calcium silicate (C2S) and aluminates (C4AF) under the heating step. C2S is identified as the predominant dehydrated component, with its two forms, P-C2S and a'L-C2S, being present. Other clinker phases, including C3S and C3A, are largely derived from the unhydrated cement recovered from the waste concrete. RCP1 also consists of a significant fraction of amorphous content (24%) resulting from the formation of metastable phases (calcium silicates and aluminate phases) and partial dehydration of C-S-H. These amorphous phases are known to possess cementitious reactivity. In contrast, RCP2 only contains approximately 9% amorphous content (primarily amorphous C-S-H).

[0126] Table 4 presents the changes in oxide composition and aggregate mineral (contamination) of the CP obtained from four sieve sizes (0.075, 0.15, 0.3, 0.6 mm). The XRF results show that the chemical composition by mass of CP significantly changes when the particle size of CP is larger than 0.150 mm, with a significant reduction in CaO and an increase in SiOi- Further, XRD results show that the amount of aggregate contaminants in the CP exceed 40% by mass when the sieve size is larger than 0.3 mm.Table 4: Oxide composition of CP at with varying size sizes as determined by XRF

[0127] Figure 3 represents the particle size distribution of OPC, RCP-1 and RCP-2. OPC exhibits the finest particle size distribution, followed by RCP1 and RCP2. The [DIO, D50, D90] of OPC, RCP1 and RCP2 is [4.21,16.8, 40.1] pm, [4.16, 20.6, 57.0] pm and [5.49, 31.2, 75.6] pm, respectively. The specific surface area of OPC, RCP1 and RCP2 obtained from the BET method is 1.62 m2 / g, 13.52 m2 / g and 20.70 m2 / g, respectively. The results indicate that RCP1 possesses a smaller particle size than RCP2, aligning more closely with OPC, whilst both RCPs have a significantly higher specific surface area compared to OPC. This can be attributed to the porous nature of hydrated and dehydrated compounds founded in the RCPs.

[0128] Figure 4 presents the cumulative heat flow of OPC, RCP1 and RCP2 obtained from the R3 test. The results indicate that the cementitious reactivity of RCP1 is remarkably 3.5 times higher than that of RCP2. The heat release at 7 days of RCP1 (276.5 J / g), which is approximately 60% that of OPC, is within the range of common SCMs. The increase in the reactivity of RCP1 is ascribed to: i) the substantial amount of recovered cementitious compounds with high reactivity potential and the limited amount of aggregate contaminants (as showed in the XRF and XRD results); and ii) the higher specific surface area (as showed in the BET results). It is worth noting that the reactivity of RCP2 is much lower although it has the highest surface area. This is clearly due to the high amount of aggregate contaminants (inactive) found in RCP2.

[0129] Figure 5 depicts the compressive strength results of the blended cement composites (Table 1). The values at the top of columns indicate compressive strength at 28 days, while the values inside stacked columns indicate the 3-day strength and subsequent strength gain. RCP2-P showed significant strength reduction, particularly beyond the 20% replacement. The strength of RCP2-P40 (40% replacement) is 30 MPa (less than 50% of the control sample) and there is negligible strength development from 7 days to 28 days. This suggests that RCP2 primarily has a filler effect on the blended composite and its contribution to cementitious reaction is very minimal, a conclusion further supported by the aforementioned R3 results. The strength development of RCP1-P is nearly identical to that of the control sample at 10% replacement. For other replacement levels, the compressive strength development in RCP1-P samples is similar to that of the control sample up to 7 days (45-47 MPa for RCP1-P and 49 MPa for the control) but is slower from 7 days to 28 days. Notably, RCP1-P40 showed 80% strength improvement than RCP2-P40 and also achieved 75% of the 28 days compressive strength of the control sample.

[0130] The example and results demonstrate that the separation and recovery process described herein is beneficial in: i) maximising the recovery of recycled concrete powder from the waste concrete (8.4 kg of RCP1 is recovered from 100 kg of the wasteconcrete, compared to 1.1 kg of RCP2); and ii) improving the cementitious reactivity and ensuring the utilisation of obtained RCP as a SCM (demonstrated by the R3 results of RCP1 and RCP2 and the compressive strength results of blended cement composites).Treatment with and without pre-hydration step

[0131] A sample of waste concrete was immersed in water for 24 hours to reach a saturated state, aiming to assess the impact of water saturation on the process efficiency (referred to as W-TMT). Another sample of waste concrete was oven-dried at 105°C for 24 hours to examine the process under dry conditions (D-TMT). It was observed that pre-soaking in water facilitates the removal of lightweight impurities and dust from the waste concrete.

[0132] Samples of W-TMT and D-TMT were then heated in an electric muffle furnace to 400°C , 500°C and 600°C for 2 hours.

[0133] The thermally treated concrete was then subjected to underwent mechanical grinding to obtain a treated concrete mixture. This was executed using a SQM-2L large capacity grinding ball mill. The milling process was conducted for 2 minutes at a speed of 250 revolutions per minute, achieving a total of 500 revolutions. To enhance the grinding effectiveness, steel balls were utilised within the mill.

[0134] The treated concrete mixtures were then classified through sieving into three categories: coarse fraction (ranging from 20 mm to 4.75 mm), intermediate fraction (from 4.75 mm to 0.075 mm) and fine fraction comprising the CP (less than 0.075 mm in size).

[0135] To determine the most effective treatment conditions for the process described herein, including the optimum temperature and saturation state of waste concrete, the yield percentage of three categories of materials obtained: coarse fraction (ranging from 20 mm to 4.75 mm), intermediate fraction (from 4.75 mm to 0.075 mm), and fine fraction comprising the CP (less than 0.075 mm in size) are calculated as follows:where MFis the mass of treated material; Mxand Yxare the mass and yielding percentage of class X (coarse fraction, intermediate fraction fine fraction comprising the CP). The higher yield of fine fraction comprising the CP the more efficient the process.

[0136] Figure 6 shows that the yield percentages of the intermediate fraction and fine fraction comprising the CP increases with the method described herein compared with a conventional mechanical process, where waste concrete was subjected to a grinding step (e.g. ball milling) without any prior water or heat treatment steps.. Figure 6 shows that the yield percentage of intermediate fraction and fine fraction comprising the CPincreases with both temperature and with the inclusion of a hydration step before heat treatment.Hydration of waste concrete

[0137] The impact on the moisture content of the waste concrete due to contact with water was investigated with the results shown in Table 5. It can be seen that contacting the waste concrete with water for 1 hour doubles the moisture content with a further increase in moisture content at 2 hours contact. The moisture content then stabilises.Table 5: Moisture content of the waste concrete

[0138] 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 process for recovering a cement powder (CP) from waste concrete, the process comprising:a) heat treating waste concrete at a temperature to obtain a thermally treated concrete;b) comminuting the thermally treated concrete to form a treated concrete mixture; andc) separating the treated concrete mixture into a fine particle fraction and a coarse particle fraction,wherein the fine particle fraction comprises the CP.

2. The process of claim 1, wherein the waste concrete has a D90 particle size (in mm) of less than about 500, 200, 100, 75, 50 or 40.

3. The process of claim 2, wherein prior to step a) the process further comprises contacting the waste concrete with water to increase the moisture content of the waste concrete.

4. The process of claim 3, wherein the waste concrete is contacted with water for a period of time (in hours) of between about 12 to about 36, preferably about 24.

5. The process of any one of claims 1 to 4, wherein step c) comprises passing least a portion of the treated concrete mixture through one or more screening steps to obtain the fine particle fraction comprising the CP and the coarse particle fraction.

6. The process of any one of claims 1 to 5, wherein separating the treated concrete mixture at step c) comprises screening at least a portion of the treated concrete mixture at a size (in mm) of about, or less than about 4, 3, 2, 1.5, 1, 0.1, or 0.075, to obtain the fine particle fraction comprising the CP.

7. The process of any one of claims 1 to 6, wherein the fine particle fraction comprising the CP has a D90 particle size (in pm) of about, or less than about 2,000, 1,000, 750, 500, 250, 100, 90, 80, 75, 70, 65, 60, 55, or 50.

8. The process of any one of claims 1 to 7, wherein the fine particle fraction comprising the CP has a D50 particle size (in pm) of about, or less than about 1,000, 750, 500, 250, 100, 75, 50, 45, 40, 35, 30, 25 or 20.

9. The process of any one of claim 1 to 8, wherein the heat treatment at step a) is performed at a heat treatment temperature of between about 300°C to about 700°C, between 400°C to about 700°C, between 450°C to about 650°C, or between about 550°C to about 650°C.

10. The process of any one of claim 1 to 9, wherein the waste concrete is heated at step a) to the heat treatment temperature at a rate of between about l°C / min to about 20°C / min, preferably about 5°C / min.

11. The process of any one of claim 1 to 10, wherein the heat treatment at step a) is performed for between about 1 to about 3 hours, preferably about 2 hours.

12. The process of any one of claim 1 to 11, wherein prior to step b) the process further comprises cooling the treated concrete mixture.

13. The process of any one of claim 1 to 12, wherein comminuting the thermally treated concrete at step b) comprises grinding the thermally treated concrete.

14. The process of claim 13, wherein the grinding is performed in a ball mill.

15. The process of claim 13 or claim 14, wherein the grinding is performed for a period of time (in minutes) of between about 0.1 to about 10, or between about 1 to about 3.

16. The process of claims 1 to 15, wherein the fine particle fraction comprising the CP has an aggregate contaminant in an amount of between about 0.1% w / w to about 40% w / w.

17. The process of claims 1 to 16, wherein the fine particle fraction comprising the CP has a heat release at 7 days between about 200 (Joule / gram) to 500 (Joule / gram).

18. The process of any one of claims 1 to 17, further comprising mixing at least some of the fine particle fraction comprising the CP with cement to form a cement composite.

19. The process of claim 18, wherein the composite cement comprises between about 5 to about 45 % w / w of the fine particle fraction comprising the CP.

20. Use of the fine particle fraction comprising the CP obtained from the process of any one of claims 1 to 17 to form a composite cement.

21. The use of claim 20, wherein the composite cement comprises between about 5 to about 45 % w / w of the fine particle fraction comprising the CP.

22. Use of the composite cement of claim 20 and claim 21 to prepare concrete.

23. Use of the fine particle fraction comprising the CP obtained from the process of any one of claims 1 to 17 to prepare concrete.

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