A curable cementitious composition

Abstract

The invention provides a curable cementitious composition comprising: a hydraulic cementitious binder; fine aggregate; coffee grounds biochar; and water.

Description

[0001] A curable cementitious composition

[0002] Technical Field

[0003]

[0001] The invention relates to a curable cementitious composition comprising a hydraulic cementitious binder, fine aggregate, coffee grounds biochar and water. The invention also relates to a cured cementitious composite, a dry particulate cementitious composition for combining with water and optionally aggregate to produce a curable cementitious composition, a method of producing a curable cementitious composition and to use of coffee grounds biochar as an additive to a curable cementitious composition.

[0004] Background of Invention

[0005] [2] The disposal of organic waste such as food and beverage waste poses a major environmental challenge as it generates methane gas which is 21 times worse than carbon dioxide in its global warming potential. In addition, the decomposition process emits several other greenhouse gases like carbon dioxide, nitrous oxide and ammonia. Spent coffee grounds make up a significant proportion of the total organic waste going to landfills. Australia alone generates around 75,000 tonnes of ground coffee waste every year, a significant proportion of which is directly deposited into landfills. Therefore, there is an urgent need for recycling solutions that can help divert spent coffee grounds from landfills into commercial applications.

[0006] [3] One proposal for beneficial utilisation of organic waste materials is to incorporate the waste or a derivative thereof into cementitious composites like concrete. Thus, biochar obtained by pyrolysis of waste biomass has been applied as a partial replacement for cement in mortar and concrete compositions. Some biochars, like rice husk biochar, bamboo leaf biochar and sugarcane bagasse biochar, have cementitious properties because of the presence of amorphous silica which is pozzolanic in nature. Wood waste biochar is believed to enhance cement curing by chemical acceleration of the cement hydration reaction.

[0007] [4] Much of the work on biochar replacement of cement has focused on wood waste biochar and high pyrolysis temperatures of greater than 500°C. The biochar in many studies is finely ground after pyrolysis to match the morphology of the cement that is being replaced in the cementitious composition.

[0008] [5] For example, it has been shown that addition of modest amounts of wood waste biochar can improve the compressive strength of concrete, but that high pyrolysis temperatures (such as 700°C) and thus highly carbonised biochar products are needed to obtain substantial enhancements. Various studies with low temperature pyrolysis (e.g. 300°C) of wood or food waste have found that incorporation of the resultant biochars provides limited or even negative impacts on concrete properties.

[0009] [6] The apparent need to use high pyrolysis temperatures and further processing steps such as grinding may limit the opportunities for the concrete industry to utilise organic waste materials in a cost and energy efficient manner.

[0010] [7] There is therefore an ongoing need for curable cementitious compositions, suitable for producing concrete or other cementitious composite building materials, which at least partially address one or more of the above-mentioned short-comings or provide a useful alternative.

[0011] [8] A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that the document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

[0012] Summary of Invention

[0013] [9] The inventors have surprisingly found that addition of coffee grounds biochar, produced by pyrolysis of spent coffee grounds, to a curable cementitious composition can enhance the compressive strength of the resultant cured cementitious composite, e.g. concrete. Increases to the 28-day compressive strength of up to about 30% have been experimentally demonstrated. This approach beneficially utilises a waste material which is currently discarded with negative environmental impacts and permanently sequesters carbon in the composite material. Moreover, the porous biochar particles as produced in pyrolysis have properties making them a suitable volume-for-volume replacement of a portion of the fine aggregate in the cementitious composite, significantly reducing the demand for quarried fine aggregate such as sand.

[0010] Advantageously, there is no need for high pyrolysis temperatures, a high degree of biochar carbonisation or post-pyrolysis comminution to provide desirable enhancement of cementitious composite properties. Superior outcomes have been obtained with unground biochars produced at pyrolysis temperatures below 500°C, such as 350°C. At such temperatures, incomplete pyrolysis produces a biochar composition having a comparatively low carbon content relative to fully pyrolyzed high temperature biochars, and a porous yet mechanically robust particulate morphology. Without wishing to be limited by any theory, it is proposed that these properties may allow the hydraulic cementitious binder to infiltrate the porous biochar particles, provide internal curing by delayed water release during curing and thus produce a well- integrated composite structure with excellent mechanical properties. The low temperature pyrolysis and omission of a grinding step also mitigates the energy intensity and process complexity of producing a suitable biochar additive.

[0014]

[0011] In accordance with a first aspect the invention provides a curable cementitious composition, comprising: a hydraulic cementitious binder; fine aggregate; coffee grounds biochar; and water.

[0015]

[0012] In some embodiments, the coffee grounds biochar has a carbon content of between 55 and 70 wt.%. In some embodiments, the coffee grounds biochar has a carbon content of between 60 and 65 wt.%.

[0016]

[0013] In some embodiments, the coffee grounds biochar is a partial pyrolysis product of coffee grounds, preferably spent coffee grounds.

[0017]

[0014] In some embodiments, the coffee grounds biochar is produced by pyrolysis of coffee grounds, preferably spent coffee grounds, to a maximum temperature of between 250°C and 450°C, for example between 275°C and 425°C. In some embodiments, the coffee grounds biochar is produced by pyrolysis of coffee grounds, preferably spent coffee grounds, to a maximum temperature of between 300°C and 400°C.

[0018]

[0015] In some embodiments, the coffee grounds biochar is not comminuted after pyrolysis.

[0016] In some embodiments, the coffee grounds biochar in the curable cementitious composition has a D50 particle size of between 150 and 300 pm, such as between 200 and 250 pm.

[0019]

[0017] In some embodiments, the coffee grounds biochar is present in the curable cementitious composition in an amount of between 1 wt.% and 7 wt.%, expressed as wt.% of the hydraulic cementitious binder. In some embodiments, the coffee grounds biochar is present in the curable cementitious composition in an amount of between 1 .4 wt.% and 5 wt.%, such as between 2.5 wt.% and 4.5 wt.%, expressed as wt.% of the hydraulic cementitious binder.

[0020]

[0018] In some embodiments, the coffee grounds biochar is present in an amount of between 5 vol.% and 20 vol.%, expressed as vol.% of the fine aggregate. In some embodiments, the coffee grounds biochar is present in an amount of between 9 vol.% and 17 vol.%, expressed as vol.% of the fine aggregate.

[0021]

[0019] In some embodiments, the coffee grounds biochar is present in the curable cementitious composition in an amount of between 5 kg / m3and 20 kg / m3, such as between 10 kg / m3and 17 kg / m3, based on the volume of the curable cementitious composition.

[0022]

[0020] In some embodiments, the curable cementitious composition develops a compressive strength of at least 1 10%, such as at least 120%, relative to a control curable cementitious composition, when determined at 28 days curing according to AS1012.8.1 and AS1012.9 (2014), wherein the control curable cementitious composition has the same composition as the curable cementitious composition but with the coffee grounds biochar substituted by an additional amount of fine aggregate of equal volume to the coffee grounds biochar.

[0023]

[0021] In some embodiments, the curable cementitious composition develops a compressive strength of at least 25 MPa, such as above 27 MPa, when determined at 28 days curing according to AS1012.8.1 and AS1012.9 (2014).

[0024]

[0022] In some embodiments, the hydraulic cementitious binder comprises portland cement. In some embodiments, the hydraulic cementitious binder is ordinary portland cement (OPC).

[0023] In some embodiments, the hydraulic cementitious binder is present in an amount of between 250 kg / m3and 450 kg / m3, such as between 300 kg / m3and 400 kg / m3, based on the volume of the curable cementitious composition.

[0025]

[0024] In some embodiments, the curable cementitious composition further comprises coarse aggregate.

[0026]

[0025] In some embodiments, the coarse aggregate is present in an amount of between 800 kg / m3and 1200 kg / m3, such as between 900 kg / m3and 1100 kg / m3, based on the volume of the curable cementitious composition.

[0027]

[0026] In some embodiments, the fine aggregate is present in an amount of between 550 kg / m3and 950 kg / m3, such as between 600 kg / m3and 900 kg / m3, based on the volume of the curable cementitious composition.

[0028]

[0027] In accordance with a second aspect the invention provides a cured cementitious composite, produced by curing the curable cementitious composition of any embodiment of the first aspect.

[0029]

[0028] In accordance with a third aspect, the invention provides a cured cementitious composite comprising: a hardened matrix comprising a hydraulic cementitious binder; fine aggregate; and coffee grounds biochar.

[0030]

[0029] In some embodiments, the coffee grounds biochar has a carbon content of between 55 and 70 wt.%. In some embodiments, the coffee grounds biochar has a carbon content of between 60 and 65 wt.%.

[0031]

[0030] In some embodiments, the coffee grounds biochar is a partial pyrolysis product of spent coffee grounds.

[0032]

[0031] In some embodiments, the coffee grounds biochar is produced by pyrolysis of spent coffee grounds to a maximum temperature of between 250°C and 450°C, for example between 275°C and 425°C. In some embodiments, the coffee grounds biochar is produced by pyrolysis of spent coffee grounds to a maximum temperature of between 300°C and 400°C.

[0032] In some embodiments, the coffee grounds biochar has a D50 particle size of between 150 and 300 pm, such as between 200 and 250 pm.

[0033]

[0033] In some embodiments, the coffee grounds biochar is present in the cured cementitious composite in an amount of between 1 wt.% and 7 wt.%, expressed as wt.% of the hydraulic cementitious binder. In some embodiments, the coffee grounds biochar is present in the cured cementitious composite in an amount of between 1.4 wt.% and 5 wt.%, such as between 2.5 wt.% and 4.5 wt.%, expressed as wt.% of the hydraulic cementitious binder.

[0034]

[0034] In some embodiments, the coffee grounds biochar is present in the cured cementitious composite in an amount of between 5 kg / m3and 20 kg / m3, such as between 10 kg / m3and 17 kg / m3, based on the volume of the cured cementitious composite.

[0035]

[0035] In some embodiments, the coffee grounds biochar is present in an amount of between 5 vol.% and 20 vol.%, expressed as vol.% of the fine aggregate. In some embodiments, the coffee grounds biochar is present in an amount of between 9 vol.% and 17 vol.%, expressed as vol.% of the fine aggregate.

[0036]

[0036] In some embodiments, the hydraulic cementitious binder comprises portland cement. In some embodiments, the hydraulic cementitious binder is ordinary portland cement (OPC).

[0037]

[0037] In some embodiments, the cured cementitious composite further comprises coarse aggregate.

[0038]

[0038] In some embodiments, the coarse aggregate is present in an amount of between 800 kg / m3and 1200 kg / m3, such as between 900 kg / m3and 1100 kg / m3, based on the volume of the cured cementitious composite.

[0039]

[0039] In some embodiments, the fine aggregate is present in an amount of between 550 kg / m3to 950 kg / m3, such as between 600 kg / m3and 900 kg / m3, based on the volume of the cured cementitious composite.

[0040]

[0040] In accordance with a fourth aspect, the invention provides a dry particulate cementitious composition for combining with water and optionally aggregate to produce a curable cementitious composition, the dry particulate cementitious composition comprising: a hydraulic cementitious binder and coffee grounds biochar.

[0041]

[0041] The hydraulic cementitious binder, coffee grounds biochar and any fine aggregate present in dry particulate cementitious composition may generally be as disclosed herein in the context of the first embodiment.

[0042]

[0042] In accordance with a fifth aspect, the invention provides a method of producing a curable cementitious composition according to any embodiment of the first aspect, the method comprising: pyrolyzing coffee grounds, preferably spent coffee grounds, to produce coffee grounds biochar; and combining the coffee grounds biochar with at least hydraulic cementitious binder, fine aggregate and water to produce a curable cementitious composition.

[0043]

[0043] In some embodiments, the coffee grounds biochar is produced by partial pyrolysis of the spent coffee grounds.

[0044]

[0044] In some embodiments, the spent coffee grounds is pyrolyzed to a maximum temperature of between 250°C and 450°C. In some embodiments, the spent coffee grounds is pyrolyzed to a maximum temperature of between 300°C and 400°C.

[0045]

[0045] In some embodiments, the coffee grounds biochar is not comminuted after pyrolysis.

[0046]

[0046] In accordance with a sixth aspect, the invention provides use of coffee grounds biochar as an additive to a curable cementitious composition.

[0047]

[0047] Where the terms “comprise”, “comprises” and “comprising” are used in the specification (including the claims) they are to be interpreted as specifying the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof.

[0048]

[0048] Further aspects of the invention appear below in the detailed description of the invention.

[0049] Brief Description of Drawings

[0049] Embodiments of the invention will herein be illustrated by way of example only with reference to the accompanying drawings in which:

[0050]

[0050] Figure 1 is a thermogravimetric analysis and differential thermogravimetry mass loss curves of Ordinary Portland Cement (OPC) used in methods according to Example 3.

[0051]

[0051] Figure 2 shows thermogravimetric analysis and differential thermogravimetry mass loss curves of spent coffee grounds (SCG) used in methods according to Example 3.

[0052]

[0052] Figure 3 is an X-Ray diffraction patterns of SCG discussed in Example 3.

[0053]

[0053] Figure 4 is an X-Ray diffraction patterns of coffee grounds biochar produced at 350°C (350CBC) discussed in Example 3.

[0054]

[0054] Figure 5 is an X-Ray diffraction patterns of coffee grounds biochar produced at 500°C (500CBC) used in methods discussed in Example 3.

[0055]

[0055] Figure 6 illustrates scanning electron microscopy images of SCG discussed in Example 3.

[0056]

[0056] Figure 7 illustrates scanning electron microscopy of 350CBC discussed in Example 3.

[0057]

[0057] Figure 8 illustrates scanning electron microscopy images of 500CBC used in methods discussed in Example 3.

[0058]

[0058] Figure 9 is an X-Ray diffraction pattern of cement paste containing different replacement levels of SCG produced in Example 6.

[0059]

[0059] Figure 10 is an X-Ray diffraction pattern of cement paste containing different replacement levels of 350CBC produced in Example 6.

[0060]

[0060] Figure 11 is an X-Ray diffraction pattern of cement paste containing different replacement levels of 500CBC produced in Example 6.

[0061] Figure 12 shows scanning electron microscopy images of 350CBC concrete samples, produced according to embodiments of the invention in Example 5 and discussed in Example 7.

[0061]

[0062] Figure 13 depicts scanning electron microscopy images 500CBC concrete samples, produced according to embodiments of the invention in Example 5 and discussed in Example 7.

[0062]

[0063] Figure 14 is a graph of the compressive strength of concrete samples, produced in Example 5, as a function of the level of replacement of fine aggregate by SCG, as discussed in Example 8.

[0063]

[0064] Figure 15 is a graph of the compressive strength of concrete samples, produced in Example 5, as a function of the level of replacement of fine aggregate by 350CBC, as discussed in Example 8.

[0064]

[0065] Figure 16 is a graph of the compressive strength of concrete samples, produced in Example 5, as a function of the level of replacement of fine aggregate by 500CBC, as discussed in Example 8.

[0065] Detailed Description

[0066] Curable cementitious composition

[0067]

[0066] The present invention relates to a curable cementitious composition. The curable cementitious composition comprises a hydraulic cementitious binder, fine aggregate, coffee grounds biochar and water. In some embodiments, the curable cementitious composition further comprises coarse aggregate.

[0068]

[0067] As used herein, a curable cementitious composition refers to a composition which has the capacity to cure and thus form a hardened cementitious composite such as concrete or mortar, but which has not yet hardened. The curable cementitious composition is thus still a paste or flowable slurry which can be worked, cast or poured into a desired configuration for hardening. Suitably, the curable cementitious composition may be a curable mortar or concrete composition. In some embodiments, it is a curable concrete composition and thus includes coarse aggregate. Hydraulic cementitious binder

[0069]

[0068] The curable cementitious composition comprises a hydraulic cementitious binder. As used herein, a hydraulic cementitious binder refers to a cement that sets and hardens by chemical reaction with water, i.e. hydration. In a cementitious composite such as mortar or concrete, the hydraulic cementitious binder thus forms a hardened matrix upon curing which binds to and encapsulates the aggregate.

[0070]

[0069] In principle, the hydraulic cementitious binder may be any known type of hydraulic cement, such as portland cement or blended hydraulic cements (e.g. General Blended Cement). Blended hydraulic cements may include blends of portland cement clinker and other components such as blast furnace slag, fly ash, limestone, silica fume, or raw or calcined natural pozzolans. In some embodiments, the hydraulic cementitious binder comprises portland cement, for example a portland cement as defined in ASTM C150-07. For example, the hydraulic cementitious binder may be ordinary portland cement (OPC).

[0071]

[0070] The hydraulic cementitious binder may be present in any amount, relative to the other components and particularly water, to form a cured cementitious composite with acceptable mechanical properties. In some embodiments, the hydraulic cementitious binder is present in an amount of between 250 kg / m3and 450 kg / m3, such as between 300 kg / m3and 400 kg / m3, or about 350 kg / m3, based on the volume of the curable cementitious composition.

[0072] Aggregate

[0073]

[0071] The curable cementitious composition comprises at least fine aggregate and may also comprise coarse aggregate. Mortars typically contain only fine aggregate whereas concretes comprise both fine aggregate and coarse aggregate. The fine aggregate may comprise sand or crushed stone. The coarse aggregate may be gravel or crushed stone of the required particle size.

[0074]

[0072] As defined by Australian Standard AS 2758.0-2009, fine aggregate has a maximum particle size of less than 4.75 mm and coarse aggregate has a particle size of more than 4.75 mm. In some embodiments, the fine aggregate used in the curable cementitious composition has a D50 particle size of between 200 and 600 pm, such as between 250 and 500 pm. The D50 particle size for fine aggregate may be as determined by laser diffraction particle size analysis, e.g. as performed with a Malvern Mastersizer 3000 particle size analyser. In some embodiments, the coarse aggregate used in the curable cementitious composition has a D50 particle size of between 3500 and 10000 pm, such as between 4750 and 8000 pm. The D50 particle size for coarse aggregate may be as determined by sieve analysis.

[0075]

[0073] In some embodiments, the fine aggregate is present in an amount of between 550 kg / m3and 950 kg / m3, such as between 600 kg / m3and 900 kg / m3, based on the volume of the curable cementitious composition. In some embodiments, coarse aggregate is present in an amount of between 800 kg / m3and 1200 kg / m3, such as between 900 kg / m3and 1 100 kg / m3, based on the volume of the curable cementitious composition.

[0076] Coffee grounds biochar

[0077]

[0074] The curable cementitious composition comprises coffee grounds biochar. As used herein, coffee grounds biochar refers to biochar produced by pyrolysis of coffee grounds, typically spent coffee grounds (also known as used coffee grounds) which is a waste product of coffee brewing. Coffee grounds comprise polysaccharides, such as hemicellulose and cellulose, proteins and lignins. When coffee grounds are subjected to pyrolysis, these organic materials thermally decompose in a low oxygen environment (to avoid combustion reactions), causing volatiles to be driven off and producing a carbonised biochar product. The biochar properties, such as the carbon content, porosity and mechanical strength (fragility), may be dependent on the rate of heating and particularly the maximum heat of pyrolysis, since the different components may have different susceptibilities to thermal decomposition (hemicellulose > cellulose > lignin).

[0078]

[0075] In some embodiments, the coffee grounds biochar has a carbon content of above 55%, such as between 55 and 70 wt.%, for example between 60 and 65 wt.%. By contrast, spent coffee grounds (after drying at 60°C to constant weight) may have a carbon content of about 50%. Excessive carbonisation, for example to a carbon content of above 75 wt.%, or above 70 wt.%, may render the biochar too fragile to form a robust composite or to adequately provide water for internal curing.

[0076] In some embodiments, the coffee grounds biochar is a partial pyrolysis product of coffee grounds. By this it is meant that pyrolysis is conducted to a maximum temperature and for a limited pyrolysis time whereby thermal decomposition and mass loss from the coffee grounds is still substantially incomplete. When a thermogravimetric analysis (TGA) of spent coffee grounds is conducted at a heating rate of 10°C / min, mass loss commences at about 135°C and ends at about 575°C, with most of the mass loss occurring between 300°C and 500°C. Decomposition of hemicellulose and part of the cellulose is believed to occur below 350°C, with further cellulose decomposition and partial lignin decomposition occurring above 350°C.

[0079]

[0077] In some embodiments, the coffee grounds biochar is a partial pyrolysis product of coffee grounds wherein no more than 70 wt%, such as no more than 60%, of the initial dry mass of spent coffee grounds (i.e. the mass after drying to constant mass at 60°C) has been lost.

[0080]

[0078] In some embodiments, the coffee grounds biochar is produced by pyrolysis of coffee grounds to a maximum temperature of between 250°C and 450°C, or between 275°C and 425°C, such as between 300°C and 400°C, or between 320°C and 380°C, for example about 350°C. Such temperatures can be expected to produce a partial pyrolysis product with a suitable degree of carbonisation, as disclosed herein. The pyrolysis method may comprise heating the coffee grounds to a specified maximum temperature or temperature range followed by a hold at this maximum temperature or temperature range until substantially constant mass, or to no detectable emission of volatiles.

[0081]

[0079] As a result of the thermal decomposition, coffee grounds biochar is typically porous, i.e. the biochar particles are porous particles containing an interconnected network of pores. Porosity is considered desirable as water may be retained in and gradually released from the pores during curing of the cementitious composition. However, excessive porosity caused by high temperature pyrolysis causing a high degree of mass loss is believed to be undesirable due to the mechanical fragility of the porous skeleton causing cracking of the biochar particles, failure of the biochar-binder interface upon curing and / or inadequate ability of the biochar to provide sustained water release for internal curing. In some embodiments, the porosity is between 30 and 60%, such as about 40%. Here, the porosity refers to the fraction of the total particle volume taken up by pores.

[0082]

[0080] The coffee grounds biochar may have a suitable particle size to allow it to act as a volume-for-volume replacement of fine aggregate. In some embodiments, the coffee grounds biochar has a D50 particle size of between 150 and 300 pm, such as between 200 and 250 pm.

[0083]

[0081] Due to the natural particle size ranges of typical spent coffee grounds starting materials, and because the coffee grounds biochar is envisaged as a replacement for part of the fine aggregate content in the curable cementitious composition, there is generally no need to comminute the coffee grounds biochar. In some embodiments, therefore, the coffee grounds biochar is not comminuted between pyrolysis and blending into the curable cementitious composition.

[0084]

[0082] The coffee grounds biochar may be present in the curable cementitious composition in any suitable amount provided that the properties of the resultant cured cementitious composite meet the required specifications. Higher amounts may be desirable due to one or more of (i) improved mechanical properties (e.g. compressive strength) of the composite, (ii) light-weighting of the cementitious composite due to the low density of the biochar, (iii) reduced requirement for fine aggregate, (iv) increased utilisation of spent coffee grounds waste product, and (v) increased carbon sequestration in the cementitious composite. However, excessive levels of coffee grounds biochar may adversely affect the mechanical properties.

[0085]

[0083] In some embodiments, the coffee grounds biochar is present in the curable cementitious composition in an amount of between 1 wt.% and 7 wt.%, such as between 1 .4 wt.% and 5 wt.%, for example between 2.5 wt.% and 4.5 wt.%, expressed as wt.% of the hydraulic cementitious binder.

[0086]

[0084] In some embodiments, the coffee grounds biochar is present in the curable cementitious composition in an amount of between 5 kg / m3and 20 kg / m3, such as between 10 kg / m3and 17 kg / m3, based on the volume of the curable cementitious composition.

[0085] In some embodiments, the coffee grounds biochar is present in an amount of between 5 vol.% and 20 vol.%, such as between 9 vol.% and 17 vol.%, expressed as vol.% of the fine aggregate.

[0087] Cure properties of the curable cementitious composition

[0088]

[0086] The coffee grounds biochar when used in appropriate amounts may impart one or more desirable mechanical properties to the cured cementitious composite produced from the curable cementitious composition, or at least not unacceptably degrade the mechanical properties in view of other advantages gained from the biochar additive.

[0089]

[0087] In some embodiments, the coffee grounds biochar may improve the compressive strength of the cured cementitious composite, particularly after complete hardening e.g. as measured after 28 days curing. This improvement may be quantified by comparison to a control composition lacking the coffee grounds biochar but including an equivalent volume of fine aggregate.

[0090]

[0088] Thus, in some embodiments, the curable cementitious composition develops a compressive strength of at least 1 10%, or at least 120%, such as about 130%, relative to a control curable cementitious composition, when determined at 28 days curing according to AS1012.8.1 and AS1012.9 (2014). The control curable cementitious composition has the same composition as the curable cementitious composition but with the coffee grounds biochar substituted by an additional amount of fine aggregate of equal volume to the coffee grounds biochar.

[0091]

[0089] In some embodiments, the cured cementitious composite comprising coffee grounds biochar may have a desired absolute compressive strength after complete hardening e.g. as measured after 28 days curing. It will be appreciated that the compressive strength of any particular embodiment will depend on many variables including the nature and amounts of the hydraulic cementitious binder and aggregate. Nevertheless, in some embodiments such as some OPC concrete embodiments the curable cementitious composition develops a compressive strength of at least 25 MPa, such as above 27 MPa, when determined at 28 days curing according to AS1012.8.1 and AS1012.9 (2014). Preparation of the curable cementitious composition

[0092]

[0090] The curable cementitious composition can typically be prepared by conventional means and apparatus, for example as used to prepare curable mortar or cement compositions. The preparation may be conducted in a concrete mixer, typically at room temperature. For example, the hydraulic cementitious binder may be mixed with water to desirable homogeneity, the coffee grounds biochar may be added and mixed to evenly distribute it through the cementitious slurry, and finally the aggregate can be mixed into the composition. Alternatively, all of the dry components can be premixed and then combined with water.

[0093] Cured cementitious composite

[0094]

[0091] The present invention further relates to a cured cementitious composite comprising a hardened matrix comprising a hydraulic cementitious binder; fine aggregate; and coffee grounds biochar. In some embodiments, the cured cementitious composite further comprises coarse aggregate. In some embodiments, the cured cementitious composite concrete is concrete or mortar, for example within a building or other infrastructure.

[0095]

[0092] It will be appreciated that cured cementitious composite is typically produced by curing the curable cementitious composition as disclosed herein. The hydraulic cementitious binder, fine aggregate, coarse aggregate and coffee grounds biochar are thus generally as already described herein.

[0096]

[0093] In some embodiments, the coffee grounds biochar is present in the cured cementitious composite in an amount of between 1 wt.% and 7 wt.%, such as between 1 .4 wt.% and 5 wt.%, for example between 2.5 wt.% and 4.5 wt.%, expressed as wt.% of the hydraulic cementitious binder.

[0097]

[0094] In some embodiments, the coffee grounds biochar is present in the cured cementitious composite in an amount of between 5 kg / m3and 20 kg / m3, such as between 10 kg / m3and 17 kg / m3, based on the volume of the cured cementitious composite.

[0095] In some embodiments, the coffee grounds biochar is present in an amount of between 5 vol.% and 20 vol.%, or between 9 vol.% and 17 vol.%, expressed as vol.% of the fine aggregate.

[0098]

[0096] In some embodiments, the fine aggregate is present in an amount of between 550 kg / m3to 950 kg / m3, such as between 600 kg / m3and 900 kg / m3, based on the volume of the cured cementitious composite.

[0099]

[0097] In some embodiments, coarse aggregate is present in an amount of between 800 kg / m3and 1200 kg / m3, such as between 900 kg / m3and 1 100 kg / m3, based on the volume of the cured cementitious composite.

[0100] Dry particulate cementitious composition

[0101]

[0098] The present invention further relates to a dry particulate cementitious composition for combining with water (and optionally also aggregate) to produce a curable cementitious composition. The dry particulate cementitious composition comprises a hydraulic cementitious binder and coffee grounds biochar.

[0102]

[0099] It will be appreciated that the hydraulic cementitious binder and coffee grounds biochar are generally as already described herein.

[0103]

[0100] The dry particulate cementitious composition may be formulated such that only water is needed to produce a curable cementitious composition suitable for working, casting or pouring into a desired configuration for hardening. Thus, for example, the dry particulate cementitious composition may comprise fine aggregate in the required proportion, and optionally any other dry additives required in the final curable composition. Alternatively, further components such as fine and / or coarse aggregate may be combined with the dry particulate cementitious composition and water when the curable cementitious composition is prepared for use.

[0104] Method of producing a curable cementitious composition

[0105]

[0101] The invention further relates to a method of producing a curable cementitious composition according to any of the embodiments disclosed herein. The method comprises pyrolyzing coffee grounds to produce coffee grounds biochar, and combining the coffee grounds biochar with at least hydraulic cementitious binder, fine aggregate and water to produce a curable cementitious composition.

[0106]

[0102] The coffee grounds used in the method are typically spent coffee grounds which may be collected from various domestic and commercial sources, such as cafes. Optionally, the spent coffee grounds are dried before use in the method. Alternatively, drying can be done in a low temperature early stage of the pyrolysis process, for example a drying step at 1 10-1 10°C before further heating to pyrolyze the material.

[0107]

[0103] The coffee grounds are then pyrolyzed to produce biochar. The coffee grounds are thus subjected to a heat treatment in a low-oxygen environment sufficient to thermally decompose the coffee grounds, driving off volatiles and producing a biochar product. The pyrolysis may be conducted in any suitable reactor, such as a fixed bed or fluidised bed reactor. It is not required in all scenarios that oxygen is rigorously excluded, but the presence of oxygen gas during pyrolysis should be sufficiently low that pyrolytic reactions predominate over combustion. Preferably, pyrolysis is conducted in the presence of an inert gas or under a vacuum. Preferably, the oxygen concentration in the gas atmosphere in pyrolysis is below 0.1 %.

[0108]

[0104] Preferably, the coffee grounds biochar is produced by partial pyrolysis of the spent coffee grounds. By this it is meant that the pyrolysis is conducted to a maximum temperature and for a limited pyrolysis time whereby thermal decomposition and mass loss from the coffee grounds is still substantially incomplete. In some embodiments, no more than 70 wt%, such as no more than 60%, of the initial dry mass of the coffee grounds (i.e. after drying to constant mass at 60°C) is lost in the pyrolysis. By contrast, TGA experiments have shown that pyrolysis to higher temperatures such as 600°C or above may cause the loss of more than 80% of the initial dry mass of the coffee grounds.

[0109]

[0105] In some embodiments, the spent coffee grounds is pyrolyzed to a maximum temperature of between 250°C and 450°C, or between 275°C and 425°C, such as between 300°C and 400°C, or between 320°C and 380°C, for example about 350°C. The pyrolysis method may comprise heating the coffee grounds to a specified maximum temperature or temperature range followed by a hold at this maximum temperature or temperature range until substantially constant mass, or to no detectable emission of volatiles.

[0110]

[0106] In some embodiments, the coffee grounds biochar has a carbon content of above 55%, such as between 55 and 70 wt.%, for example between 60 and 65 wt.%. By contrast, the coffee grounds (after drying at 60°C to constant weight) may have a carbon content of less than 55%, such as about 50%.

[0111]

[0107] The resultant coffee grounds biochar is typically porous, i.e. the biochar particles are porous particles containing an interconnected network of pores. In some embodiments, the porosity is between 30 and 60%, such as about 40%. Here, the porosity refers to the fraction of the total particle volume taken up by pores. In some embodiments, the coffee grounds biochar has a D50 particle size of between 150 and 300 pm, such as between 200 and 250 pm.

[0112]

[0108] After the coffee grounds biochar is produced in the pyrolysis reaction, it is cooled and may be stored until use. In some embodiments, the coffee grounds biochar is not comminuted after pyrolysis.

[0113]

[0109] The coffee grounds biochar is then combined with hydraulic cementitious binder, fine aggregate and water to produce a curable cementitious composition. Optionally, coarse aggregate is added as well. It will be appreciated that the hydraulic cementitious binder, fine aggregate, coarse aggregate are generally as already described herein.

[0114]

[0110] The curable cementitious composition can typically be prepared by conventional means and apparatus, for example as used to prepare curable mortar or cement compositions. The preparation may be conducted in a concrete mixer, typically at room temperature. For example, the hydraulic cementitious binder may be mixed with water to desirable homogeneity, the coffee grounds biochar may be added and mixed to evenly distribute it through the cementitious slurry, and finally the aggregate can be mixed into the composition. Alternatively, all of the dry components can be premixed and then combined with water.

[0115] EXAMPLES

[0111] The present invention is described with reference to the following examples. It is to be understood that the examples are illustrative of and not limiting to the invention described herein.

[0116] Materials

[0117]

[0112] Eureka Ordinary Portland cement (OPC), coarse aggregate (CA) and fine aggregate (FA) were sourced in Melbourne, Australia. Spent coffee grounds (SCG) were collected from various local cafes in Melbourne and dried in an oven for 48 hours at 60°C until no further loss in moisture was observed (complete drying) before using it in its raw form in concrete or for preparing biochar.

[0118] Example 1. Leaching test for SCG

[0119]

[0113] A leaching test was conducted on SCG to detect leaching of organic compounds that may influence the hydration reaction of cement particles. A small amount of SCG was soaked in water in a test tube for 5 minutes with continuous shaking to provide a high shear mixing as provided to the concrete mix. The colour of the water changed to brown due to the leaching of organic compounds from the SCG.

[0120] Example 2. Preparation of coffee grounds biochar (CBC)

[0121]

[0114] Coffee grounds biochar (CBC) was prepared by the following methodology. The SCG was filled into aluminium trays and an aluminium foil was wrapped tight on top of the tray to seal the aluminium tray from all sides. Small micro holes were pierced into the aluminium foil at random locations to allow for the escape of gases during the thermal decomposition of SCG. The SCG were pyrolyzed at 350°C and 500°C temperatures for 2 hours each at a heating rate of 10°C / minute in a furnace. The tight packing and containment (apart from the microholes to allow pyrolysis gas escape) of SCG ensures that the thermal decomposition reactions occur under pyrolytic (low- oxygen) conditions. The furnace was allowed to cool down before the residual biochar was removed. The SCG biochar produced at 350°C is identified herein as 350CBC, and that produced at 500°C is identified herein as 500CBC.

[0122] Example 3. Characterisation of material properties

[0115] The material properties of the coffee grounds biochar produced in Example 2, along with the starting materials OPC, SCG, CA and FA were assessed.

[0123]

[0116] Thermogravimetric analysis (TGA) of OPC and SCG was carried out in an N2 environment at N2 flow rate of 20 mL / min. Figures 1 and 2 show the TGA and differential thermogravimetry (DTG) mass loss curves of OPC and SCG respectively. The TGA analysis of OPC shows the presence of gypsum, bassanite, calcium hydroxide (CH) and calcium carbonate (CC). The concentration of CH was 1.15% and that of CC was 7.85%.

[0124]

[0117] The TGA mass loss of SCG (Figure 2) starts at about 135°C and ends at about 575°C temperature. The early stages of pyrolysis, in the 200 - 350°C temperature range, is primarily associated with the decomposition of hemicellulose and some initial cellulose degradation. It is characterized by significant mass loss due to the breakdown of these polysaccharides. The later stages of pyrolysis, in the 350 - 525 °C temperature range, involves further decomposition of cellulose and the beginning of lignin degradation. It is the stage with the highest percentage of mass loss, indicating the substantial breakdown of organic material. After the complete thermal decomposition of coffee grounds, the residual inorganic material is about 16.4% of the original mass of the dried coffee grounds.

[0125]

[0118] Particle size distribution (PSD) analysis of OPC, SCG, 350CBC, 500CBC and sand was undertaken using the Malvern particle size analyser “Malvern Mastersizer 3000”, and that of CA was carried out using the sieve analysis. The results are shown in Table 2.

[0126] Table 2. Particle size distributions of OPC, CBC, FA and CA

[0127]

[0119] Carbon, Hydrogen, Nitrogen and Sulfur (CHNS) analysis of SCG, 350CBC and 500CBC was carried out using a CHNS analyser and the results are illustrated in Table 3.

[0128] Table 3. CHNS analysis of SCG, 350CBC and 500CBC samples

[0129]

[0120] The elemental composition of SCG, 350CBC and 500CBC were determined by X-Ray Fluorescence (XRF) spectroscopy, and the results are shown in Table 4.

[0130] Table 4. Elemental composition of SCG, 350CBC and 500CBC

[0131]

[0121] The mineralogical composition of SCG, 350CBC and 500CBC was characterised by X-Ray Diffraction spectroscopy. The XRD analysis of the samples was carried out using the solvent exchange method. The XRD data were collected between 5° and 70° 2theta using a step size of 0.1 ° and a count time of 0.5 seconds per step. Figures 3 to 5 shows the different mineralogical compositions of SCG, 350CBC and 500CBC samples respectively. The XRD pattern shown in Figure 3 indicate that SCG shows amorphous broad humps centred around 20° and 38° 2theta locations. These amorphous humps are more likely from the organic phases present in the SCG. These amorphous humps shift to higher 2theta angles (i.e. 25° and 45° 2theta) due to the thermal decomposition of organic compounds into residual carbon as shown in Figures 4 and 5.

[0132]

[0122] Figures 6, 7 and 8 shows the surface microstructure characteristics of SCG, 350CBC and 500CBC biochar particles respectively, as determined by scanning electron microscopy (SEM), at 250x magnification. The coffee ground particle (SCG) shows solid microstructure but little to no porosity. Thermal decomposition of coffee grounds due to pyrolysis created a porous structure within the particles that increased with the increase in pyrolysis temperature (Figures 7 and 8). Based on the SEM analysis and also X-Ray Micro-CT analysis, it was estimated that the 350CBC and 500CBC biochars had porosity of 40% and 65% respectively.

[0133] Example 4. Concrete mix design

[0134]

[0123] Eleven mix designs were utilised to compare the effects of SCG in the forms of untreated SCG, 350CBC and 500CBC on the mechanical and microstructural behaviour of concrete. Four were produced with regular SCG, four with 350CBC, and a further three with 500CBC. The untreated SCG and biochars were incorporated at varying percentages to act as a substitute for FA. Plain concrete samples with no additions of SCG, 350CBC or 500CBC served as control samples. Table 5 details all the mix proportions utilised throughout the experiments. Table 5. Concrete mix designs

[0135] Example 5. Preparation of concrete mix for compressive strength testing

[0136]

[0124] The concrete mix specimens as detailed in Example 4 were prepared for compressive strength test in accordance with AS1012.8.1 (Australian Standard “Method for making and curing concrete - compression and indirect tensile test specimens”, 2014). Moulds were utilised for compressive strength testing at sizes 75 mm depth x 150 mm height. For casting purposes, a cement paste was formed in the concrete mixer by combining cementitious materials and water to decrease the formation of lumps throughout the mixing process. After the cement paste was formed, SCG, 350CBC or 500CBC was separately added to the mixer to allow for a better distribution of materials. Finally, FA and CA were added into the mix and mixed for 3 minutes to allow for a uniform distribution of materials.

[0137]

[0125] The fresh concrete was poured into the lubricated moulds and vibrated to remove any air pockets. The samples were cured at room temperature for 24 hours, demoulded and cured in a water tank at approximately 22°C until the time of testing. The samples were ground flat at the top to eliminate rough surface that can potentially create stress concentration points prior to carrying out the compressive strength tests.

[0138] Example 6. Mineralogical compositions of cement paste samples

[0139]

[0126] Mineralogical compositions of the cured cement samples according to the compositions detailed in Table 5 (Example 4) were characterised by X-Ray Diffraction spectroscopy (XRD). In order to ascertain the effect of SCG, 350CBC and 500CBC on the hydration reaction of cement, the inert FA and CA were not incorporated into the cement paste samples. The hardened samples were crushed into fine powder before carrying out the XRD analysis.

[0140]

[0127] Figure 9 shows the XRD analysis of cement paste samples containing different concentrations of SCG. Figure 9 indicates that the portlandite (Ca(OH)2) content (reflection “P”) decreased considerably with the addition of 5% of SCG (SCG5). With further increase in the concentration of SCG, there is a drastic further reduction in the portlandite content to negligible content. This is followed by an increase in the ettringite (“E”), calcite (“C”), alite (“A”) and larnite (“L”) phases. The increase in alite and larnite phases with the increase in SCG content shows that the addition of SCG significantly hampers the hydration reaction of calcium silicate phases. The organic compounds leached by the SCG, are most likely instrumental in hindering the hydration reaction of cement particles. Moreover, calcium carbonate takes part in the hydration reaction to produce hemi-carboaluminate, mono-carboaluminate and other carbonate phases. With the hindering of the hydration of cement particles, the calcium carbonate present in OPC stays unreacted; therefore, this content increases with the increase in SCG concentration. Interestingly, Figure 9 further depicts that the ettringite peaks show an increase in intensity with the increase in SCG, indicating that the reaction of calcium aluminate and gypsum phases is promoted by SCG.

[0141]

[0128] Figure 10 illustrates the XRD diffractograms of hydrated cement paste samples containing different percentages of 350CBC. Figure 10 shows that the peak intensities of alite and larnite phases show significant reduction compared to that of the SCG samples (as in Figure 9). This indicates that the thermal decomposition of the organic compounds due to the pyrolysis process is highly beneficial in negating the negative effects of SCG in concrete. Figure 10 further shows that the portlandite peak intensity shows only a small reduction with the addition of 350CBC, which progressively reduces with the increase in 350CBC content. The remaining peaks do not show any noticeable differences. Given that XRD works on a volume basis, the overall volume of the finely ground samples of hydrated cement paste containing different concentrations of 350CBC will have a lower concentration of OPC content with the progressive increase in 350CBC. The reduction in the XRD peak intensities of portlandite is most likely due to the reduction in the overall OPC content in the cement paste samples modified with 350CBC. Since the XRF and XRD analyses of 350CBC (see Example 3) do not show the presence of any amorphous silica or aluminosilicates, there is no potential for the reduction of portlandite due to the pozzolanic reaction. This indicates that the addition of 350CBC does not have any adverse influence on the chemical changes within the cement microstructure.

[0142]

[0129] Figure 11 depicts the XRD diffractograms of hydrated cement paste containing different percentages of 500CBC. Similar to 350CBC, Figure 1 1 indicates a small reduction in the portlandite peak intensities that progressively decreases with the increase in 500CBC content. This is most likely because of the overall reduction in the OPC content with the increase in the proportion of 500CBC. The remaining peaks, like that of ettringite, hemi-carboaluminate, mono-carboaluminate, calcite, alite and larnite, did not show any noticeable differences. This indicates that the different pyrolyzing temperature temperatures (350°C and 500°C) of SCG do not have any adverse effect on the chemical reaction of cement particles.

[0143] Example 7. Microstructure properties and bond performance of concrete mix samples

[0144]

[0130] Microstructure properties and bond performance of the concrete mix samples produced in Example 5 were characterised by scanning electron microscopy (SEM), at 250x magnification.

[0145]

[0131] The concrete sample containing SCG had very low strength, due to which grinding and polishing were not possible for the preparation of samples for SEM analysis.

[0132] Figure 12 shows the SEM images of concrete samples containing 350CBC. The SEM images show that the 350CBC particles have seamless bond performance with the cement matrix. It was also noted that the cement paste has penetrated the porous biochar material, allowing for strength development across 350CBC. No evidence of concrete microcracking can be seen. It is proposed that the water absorbed by the biochar contributes to the internal curing of cementitious materials once the relative internal humidity begins to drop.

[0146]

[0133] Figure 13 depicts the SEM images of concrete samples containing 500CBC. It is evident that the porosity of the biochar is significantly higher than the 300CBC sample. The SEM images illustrate that the bond performance between the 500CBC particles and the cement matrix is excellent. However, compared to the 350CBC concrete samples (see Figure 12), 500CBC shows highly porous biochar with extensive micro-cracking within both the concrete microstructure and the biochar particles. Microcracking within the biochar particles clearly shows the fragile nature of its skeleton structure after significant thermal decomposition at 500 °C temperature. It is proposed that the micro-cracking observed in concrete is due to a lack of sufficient internal curing provided by the water from the excessively porous 500CBC biochar.

[0147] Example 8. Mechanical testing of concrete mix samples

[0148]

[0134] The compressive strength of the concrete mix samples produced in Example 5 were further assessed in accordance with AS 1012.9 (Australian Standard, “Compressive strength tests - concrete, mortar and grout specimens”, 2014). According to the size of the compressive strength samples, a loading rate of 88 kN per minute was applied.

[0149]

[0135] Figure 14 details the compressive strength results at 7 and 28 days of concrete mix samples containing different concentrations of SCG incorporated as a replacement of FA by volume. Figure 14 indicates that the compressive strength of concrete decreases with the increase in the percentage of SCG.

[0150]

[0136] Figure 15 shows the compressive strength results of 350CBC blended concrete samples. The compressive strength of 350CBC blended concrete samples at 28 days increases with the increase in 350CBC content of up to a sand (FA) replacement level of 15 volume %. The compressive strength of 350CBC15 concrete sample was 29.6 MPa compared to 22.9 MPa of the control sample at 28 days, providing about 30% increase in compressive strength. With a further increase in the replacement level to 20%, the compressive strength began to decrease. However, even at a replacement level of 20%, the compressive strength results are similar to the control sample, while providing the advantage of addition sequestration of biochar, significant replacement of FA, and reduced density.

[0151]

[0137] Figure 16 illustrates the compressive strength results of 500CBC blended concrete samples. As depicted in Figure 16, across both 7-day and 28-day outcomes, a decreasing trend can be observed forming throughout all replacement levels compared to the control sample. At its lowest point, 500CBC15 denotes a decrease in strength of 34.5%. Given the decreasing trend in compressive strength results from 0 to 15% replacement levels, the sample of 500CBC20 was not prepared and tested.

[0152]

[0138] Without wishing to be limited by any theory, it is proposed that the low temperature incomplete pyrolysis process producing the 350CBC biochar provides an optimum porosity and robustness of the biochar skeleton. The porous wall structures can thus withstand the water pressure inside and outside of the pores. When concrete hardens, the internal relative humidity decreases, creating demand for water. If the biochar pore structure remains intact the internal capillary pressure can help in delivering water to the concrete. However, in case of 500CBC the pore wall structures become extremely fragile because of extensive decomposition under high temperatures. The wall structures may collapse under pressure and cannot sustain capillary pressure to deliver water for the internal curing of concrete. The extensive cement and biochar microcracking observed in the 500CBC concrete samples may also contribute to the observed decrease in compressive strength.

[0153] Example 9. Comparison of coffee and wood biochars

[0154]

[0139] The effects of different types of organic waste biochars, derived from coffee and wood, on the compressive strength of Portland cement-based concrete mixes were compared as a function of pyrolysis temperature and amount of biochar added. The change in compressive strength compared to a control sample with 0% replacement level was noted for each type of biochar and the representative concrete mixes are given in Table 6. Table 6 indicates that coffee grounds biochar at a pyrolysis temperature of 350°C provided the highest increase in compressive strength (about 30%). Wood biochar performed poorly when produced at a pyrolysis temperature of 300°C, and seemed to require pyrolysis temperatures of above 500°C for effective enhancement of concrete compressive strength.

[0155] Table 6. Increase in compressive strength of concrete samples with organic waste biochars aSource: Souradeep Gupta, PhD thesis, “Biochar enhanced concrete for better performance and more effective bio-based self-healing”, National University of Singapore, 2018bSource: Roychand et al, Construction and Building Materials 379 (2023) 131221

[0156]

[0140] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

Claims

Claims1 . A curable cementitious composition comprising: a hydraulic cementitious binder; fine aggregate; coffee grounds biochar; and water.

2. The curable cementitious composition of claim 1 , wherein the coffee grounds biochar has a carbon content of between 55 and 70 wt.%.

3. The curable cementitious composition of claim 1 , wherein the coffee grounds biochar has a carbon content of between 60 and 65 wt.%.

4. The curable cementitious composition of any one of claims 1 -3, wherein the coffee grounds biochar is a partial pyrolysis product of coffee grounds.

5. The curable cementitious composition of any one of claims 1 to 4, wherein the coffee grounds biochar is produced by pyrolysis of coffee grounds to a maximum temperature of between 250°C and 450°C.

6. The curable cementitious composition of any one of claims 1 to 4, wherein the coffee grounds biochar is produced by pyrolysis of coffee grounds to a maximum temperature of between 300°C and 400°C.

7. The curable cementitious composition of any one of claims 1 to 6, wherein the coffee grounds biochar is not comminuted after pyrolysis.

8. The curable cementitious composition of any one of claims 1 to 7, wherein the coffee grounds biochar in the curable cementitious composition has a D50 particle size of between 150 and 300 pm.

9. The curable cementitious composition of any one of claims 1 to 8, wherein the coffee grounds biochar is present in the curable cementitious composition in an amount of between 1 wt.% and 7 wt.%, expressed as wt.% of the hydraulic cementitious binder.

10. The curable cementitious composition of any one of claims 1 to 8, wherein the coffee grounds biochar is present in the curable cementitious composition in an amount of between 2.5 wt.% and 4.5 wt.%, expressed as wt.% of the hydraulic cementitious binder.11 . The curable cementitious composition of any one of claims 1 to 10, wherein the coffee grounds biochar is present in the curable cementitious composition in an amount of between 5 kg / m3and 20 kg / m3, based on the volume of the curable cementitious composition.

12. The curable cementitious composition of any one of claims 1 to 11 , wherein the curable cementitious composition develops a compressive strength of at least 110% relative to a control curable cementitious composition, when determined at 28 days curing according to AS1012.8.1 and AS1012.9 (2014), wherein the control curable cementitious composition has the same composition as the curable cementitious composition but with the coffee grounds biochar substituted by an additional amount of fine aggregate of equal volume to the coffee grounds biochar.

13. The curable cementitious composition of any one of claims 1 to 12, wherein the curable cementitious composition develops a compressive strength of at least 25 MPa when determined at 28 days curing according to AS1012.8.1 and AS1012.9 (2014).

14. The curable cementitious composition of any one of claims 1 to 13, wherein the hydraulic cementitious binder comprises portland cement.

15. The curable cementitious composition of any one of claims 1 to 14, wherein the hydraulic cementitious binder is present in an amount of between 250 kg / m3and 450 kg / m3based on the volume of the curable cementitious composition.

16. The curable cementitious composition of any one of claims 1 to 15, further comprising coarse aggregate.

17. The curable cementitious composition of any one of claims 1 to 16, wherein the fine aggregate is present in an amount of between 550 kg / m3and 950 kg / m3based on the volume of the curable cementitious composition.

18. A cured cementitious composite, produced by curing the curable cementitious composition of any one of claims 1 to 17.

19. A cured cementitious composite comprising: a hardened matrix comprising a hydraulic cementitious binder; fine aggregate; and coffee grounds biochar.

20. The cured cementitious composite of claim 19, wherein the coffee grounds biochar has a carbon content of between 55 and 70 wt.%.21 . The cured cementitious composite of claim 19, wherein the coffee grounds biochar has a carbon content of between 60 and 65 wt.%.

22. The cured cementitious composite of any one of claims 19 to 21 , wherein the coffee grounds biochar is a partial pyrolysis product of spent coffee grounds.

23. The cured cementitious composite of any one of claims 19 to 22, wherein the coffee grounds biochar is produced by pyrolysis of spent coffee grounds to a maximum temperature of between 250°C and 450°C.

24. The cured cementitious composite of any one of claims 19 to 23, wherein the coffee grounds biochar has a D50 particle size of between 150 and 300 pm.

25. The cured cementitious composite of any one of claims 19 to 24, wherein the coffee grounds biochar is present in the cured cementitious composite in anamount of between 1 wt.% and 7 wt.%, expressed as wt.% of the hydraulic cementitious binder.

26. The cured cementitious composite of any one of claims 19 to 25, wherein the coffee grounds biochar is present in the cured cementitious composite in an amount of between 2.5 wt.% and 4.5 wt.%, expressed as wt.% of the hydraulic cementitious binder.

27. The cured cementitious composite of any one of claims 19 to 26, wherein the coffee grounds biochar is present in the cured cementitious composite in an amount of between 5 kg / m3and 20 kg / m3, based on the volume of the cured cementitious composite.

28. The cured cementitious composite of any one of claims 19 to 27, wherein the hydraulic cementitious binder comprises portland cement.

29. The cured cementitious composite of any one of claims 19 to 28, further comprising coarse aggregate.

30. The cured cementitious composite of any one of claims 19 to 29, wherein the fine aggregate is present in an amount of between 550 kg / m3to 950 kg / m3, based on the volume of the cured cementitious composite.31 . A dry particulate cementitious composition for combining with water and optionally aggregate to produce a curable cementitious composition, the dry particulate cementitious composition comprising a hydraulic cementitious binder and coffee grounds biochar.

32. A method of producing a curable cementitious composition according to any one of claims 1 to 18, the method comprising: pyrolyzing coffee grounds to produce coffee grounds biochar; and combining the coffee grounds biochar with at least hydraulic cementitious binder, fine aggregate and water to produce a curable cementitious composition.

33. The method according to claim 32, wherein the coffee grounds biochar is produced by partial pyrolysis of the spent coffee grounds.

34. The method according to claim 32 or claim 33, wherein the spent coffee grounds is pyrolyzed to a maximum temperature of between 250°C and 450°C.

35. The method according to claim 32 or claim 33, wherein the spent coffee grounds is pyrolyzed to a maximum temperature of between 300°C and 400°C.

36. The method according to any one of claims 32 to 35, wherein the coffee grounds biochar is not comminuted after pyrolysis.

37. Use of coffee grounds biochar as an additive to a curable cementitious composition.

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