Ceramic composition, method for its preparation and use thereof

Abstract

A cementitious composition comprising a cement composition comprising ground granulated blast furnace slag (GGBS) and a finely divided ceramic obtained from waste ceramic items. The finely divided cer

Description

The present invention relates to a ceramic composition and a method for the preparation thereof. The present invention also relates to uses of the ceramic composition. It is estimated that between 75,000 and 150,000 tonnes of ceramic waste materials are disposed of each year in the United Kingdom alone. The ceramic waste material is generally disposed of by way of land fill, with a small portion of the waste being used in low grade applications, such as being blended with other materials for road making. This amount is a small fraction of the total amount of ceramic waste material produced globally each year. It would be a significant advantage if a use could be found for the ceramic waste material. Huseien, G.F., et al. conducted a series of studies: ‘Waste ceramic powder incorporated alkali activated mortars exposed to elevated Temperatures: Performance evaluation’, Construction and Building Materials, 2018, 187, pages 307 to 317; ‘Performance of sustainable alkali activated mortars containing solid waste ceramic powder’, Chemical Engineering Transactions, 2018, 63, pages 673 to 678; ‘Evaluation of alkali-activated mortars containing high volume waste ceramic powder and fly ash replacing GBFS’, Construction and Building Materials, 2019, 210, pages 78 to 92; ‘Properties of ceramic tile waste based alkali-activated mortars incorporating GBFS and fly ash’, Construction and Building Materials, 2019, 214, pages 355 to 368; ‘Effects of ceramic tile powder waste on properties of self-compacted alkali-activated concrete’, Construction and Building Materials, 2020, 236, page 117574. Huseien and colleagues investigated extensively the use of ceramic waste as slag substitute in alkali activated mixes. The impact of substituting high-volume waste ceramic powder (CP) into slag alone or in conjunction with fly ash in the manufacture of alkali activated mortars was explored by assessing the fresh (workability, setting time) and hardened properties of mortar mixes (compressive strength, flexural strength, and water absorption), at room temperature as well as after exposure to high temperatures. Results showed that, even if a linear strength reduction was observed by replacing slag with CP, substitution rates of 50 to 70% were able to deliver satisfactory compressive strength of about 50 MPa. Fresh properties (setting time and workability were also observed to be improved with CP substitution, as well as a range of durability properties such as resistance to acid and sulfate attack, freeze-thaw, wet-dry cycles. A final strength of 40 MPa was recorded for substitution rate of 70%. Reig, L, et al. conducted a series of studies: ‘Alkaline activation of ceramic waste materials’, Waste and Biomass Valorization, 2013, 4, pages 729 to 736; ‘Influence of the activator concentration and calcium hydroxide addition on the properties of alkali-activated porcelain stoneware’, Construction and Building Materials, 2014, 63, pages 214 to 222; and ‘Compressive strength and microstructure of alkali-activated mortars with high ceramic waste content’, Ceramics International, 43(16), 2017, pages 13622 to 13634. Reig and colleagues investigated the suitability of ceramic waste as an alkali activated precursor. The study involved both “red” ceramic (brick waste) and “white ceramic” (porcelain stoneware), with size D50 = 10 pm. Porcelain powder was substituted with 2% Ca(OH)2, activated with NaOH and sodium silicate solution, and cured at 65°. Up to 30 MPa were obtained with 100% porcelain powder. In a further study, improved strength >35MPa was obtained by tuning the Ca(OH)2 and activation parameters. The use of ceramic waste as binder as well as aggregate was then investigated, with compressive strength of an all-waste mortar achieving >50 MPa when cured at 65°C, and 10 MPa when cured at room temperature. The same research group recently published a literature review on reusing ceramic waste as a precursor in alkali activated cements. The results indicated that ceramic powder can be an effective precursor, although it might need additional sources of Ca to react at room temperature, otherwise heat curing is needed. This alternative reuse option helps reducing CO2 emissions, embodied energy, Portland cement consumption, and ceramic waste accumulation in landfills, contributing to sustainable development. El-Dieb, et al., ‘The use of ceramic waste powder (CWP) in making eco-friendly concretes’, Ceramic Materials: Synthesis, Characterization, Applications and Recycling, 2019, pages 1 to 35, investigated the impact of ceramic waste powder produced during final polishing process of ceramic tiles. The researchers investigated the use of the powder both in conventional Portland cement-based concrete as well as in alkali activated concrete production. For this latter work, an optimised mix proportion with NaOH and KOH as activator, 40% slag inclusion and 24-hour curing at 60°C was suggested to achieve compressive strength of about 40 MPa after 7 days (with 28-day strength in the same range). Hwang et al., ‘Development of high-strength alkali-activated pastes containing high volumes of waste brick and ceramic powders. Construction and Building Materials, 2019, 218, pages 519 to 529, investigated the potential use of waste ceramic and red clay brick powders in the production of alkali-activated cement. Whilst 100% ceramic powder did not set at room temperature, dosage of 60% in conjunction with a blend of slag and fly ash delivered satisfactory compressive strength, in excess of 55 MPa after 28 days when the slag was dosed at 30%. It was observed that brick powder was more reactive than ceramic powder. Rashad and Essa, ‘Effect of ceramic waste powder on alkali-activated slag pastes cured in hot weather after exposure to elevated temperature’, Cement and Concrete Composites, 2020, 111, page 103617, explored the incorporation of up to 50% of ceramic waste powder into alkali-activated slag pastes cured in hot weather and exposed to elevated temperatures. The research examined the effect of ceramic powder inclusion on workability, water absorption, and compressive strength, and analysed the results using microstructural techniques. The study found that the inclusion of ceramic powder had a negative effect on workability but a positive effect on water absorption and compressive strength (>45MPa at 28 days) before and after exposure to elevated temperatures. Pommer et al., ‘Alkali-activated waste ceramics: Importance of precursor particle size distribution’, Ceramics International, 2021, 47(22), pages 31574 to 31582, studied the impact of particle size distribution on the performance of waste red brick ceramic materials as geopolymer precursors, finding that removing particles retained on a 0.5 mm sieve improves the mechanical performance and geopolymerization rate. The presence of coarser particles in the precursor leads to increased porosity, resulting in lower thermal conductivity and faster moisture transport in the activated material. Strength up to 35 MPa were recorded at room temperature curing for samples produced with fine red brick powder precursor. Zhang, et al.: ‘Effect of waste ceramic powder on properties of alkali-activated blastfurnace slag paste and mortar’, Polymers, 2021, 13(16), page2817 and ‘Effect of waste ceramic powder on the properties of alkali-activated slag and fly ash pastes exposed to high temperature’, 2021, Polymers, 13(21), page 3797, investigated the use of waste ceramic tiles substituting slag in alkali activated materials. Experimental results with substitution rate in the range 0 - 30% showed that as the rate of replacement of ceramic powder increases, the fluidity of the paste slightly increases. The strength of the mortar sample decreases in the early period but no significant decrease is observed in the later period. The durability under sulfuric acid attack improves with an increase in WCP content. The diffusion coefficient of chloride ions increases, and the resistivity decreases with an increase in ceramic powder content. In another study, the researchers studied the impact of ceramic waste powder substituting slag in the range 0 - 20% on the performance of alkali-activated slag and fly ash blends when exposed to high temperature up to 900°C. Results suggested that ceramic powder inclusion increased the strength both at 45°C curing (reaching >80MPa for 20% substitution) as well as after exposure, with residual strength of about 30 MPa after 900°C. Awoyera, P.O., etal., ‘Characterization of ceramic waste aggregate concrete’, HBRC Journal (2016), propose the use of ceramic tiles as aggregate in concrete formulations. The ceramic tiles were sieved into fine and coarse aggregates in line with standards. Other materials used to form the concrete were gravel, river sand, cement and potable water. CN115490448 discloses crushing waste sintered ceramics to form a waste ceramic reclaimed sand. The sand is used to prepare concrete and mortar by using the waste ceramic reclaimed sand as all or part of fine aggregate. Steiner, L.R., et al., ‘Effectiveness of ceramic tile polishing residues as supplementary cementitious materials for cement mortars’, Sustainable Materials and Technologies, 4 (2015), pages 30 to 35 describe experiments to use the sludge produced by the polishing of ceramic tiles. Polishing residue was recovered from the sludge and tested for its ability to replace a portion of the cement used in mortar comprising cement, sand and water. The polishing residue had a Dsc of from 5 to 12 microns. The polishing residue was used to replace 0, 10, 20, 25, 30 and 40% of the cement on a weight basis. The results indicate that polishing residue may be used to replace a portion of the cement in mortar, with the compressive strength of the mortar varying with the amount of polishing residue replacement employed. The use of ceramic tile waste to replace Portland cement was also investigated by Mas, M.A., et al., ‘Ceramic tile waste as replacement material in Portland cement’, Advances in Cement Research, 2015, 00(00), pages 1 to 12. Wall, stoneware and porcelain stoneware tile waste was crushed to particles of less than 2 mm and then ground in a ball mill to produce particles having a mean diameter of about 17.25 microns, with a Dgo under 43 microns. The resulting material was used to replace Portland cement in amounts of 15, 25, 35 and 50% by weight in paste and mortar samples. The results showed that increasing the amount of cement replacement decreased the strength activity index of the mortars. Lasseuguette, E., et al., ‘Recycling ceramic waste to produce green concrete’, 1st International Conference on Construction Materials for Sustainable Future, 19 to 21 April 2017, Zadar, Croatia, investigated a cement mortar mix employing a 15% by weight replacement of cement with ground ceramic tiles. The ceramic material had a particle size ranging from about 0.4 to 200 microns. The mortar mix comprised water, sand, cement and ceramic replacement. The use of ceramic replacement reduced the compressive strength of the mortar, compared with a control, in which no replacement was employed. CN113233835A discloses a concrete composition comprising cement, natural coarse aggregate, recycled coarse aggregate, natural fine aggregate, recycled ceramic fine aggregate, water, a ceramic admixture and a polycarboxylic acid superplasticizer. More recently, CN116283158A discloses a concrete composition comprising a waste ceramic component, in particular perlite, as a replacement for a portion of the cement. There is a continuing need for an improved manner to dispose of ceramic waste materials, such as those generated on construction and demolition sites. It would be very advantageous if a use could be found for ceramic waste materials that has a reduced environmental impact. It would be particularly advantageous if a use for waste and recycled ceramic and porcelain tiles could be found. In a first aspect, the present invention provides a cementitious composition comprising a cement composition, the cement composition comprising: ground granulated blast furnace slag (GGBS); and a finely divided ceramic obtained from waste ceramic items. The cementitious composition comprises ground granulated blast furnace slag (GGBS). GGBS is obtained from the slag formed on molten iron in a blast furnace during iron and steel production. GGBS is obtained by quenching the molten iron slag in water or steam to produce a glassy, granular product that is then dried and ground into a fine powder. GGBS is available commercially and is known in the art. The main components of GGBS are CaO (typically 30 to 50%), SiOs (typically 28 to 38% by weight), AI2O3 (typically 8 to 24% by weight), MnO and MgO (typically 1 to 18% by weight). GGBS is designated in ASTM C 989 and is divided into three classifications based on its activity index. Grade 80 has a low activity index and is used primarily in mass structures because it generates less heat than portland cement (OPC). Grade 100 has a moderate activity index and is most similar to portland cement (OPC) with respect to cementitious behaviour. Grade 120 has a high activity index and is more cementitious than portland cement (OPC). The cement composition may employ any one or a mixture of two or more of the aforementioned grades of GGBS. The cementitious composition further comprises a finely divided ceramic material. Cementitious compositions comprising GGBS, either alone or in combination with other binder materials, are known in the art. As described hereinbelow, GGBS is used in AAB cementitious compositions. In the present invention, it may be considered that the finely divided ceramic material is being used as a replacement for a portion of the GGBS in the composition. The ceramic material is obtained from waste ceramic items. Suitable waste ceramic items as sources for this ceramic material are abundantly available and include items found in kitchens and bathrooms, such as toilets, urinals, sinks including both wall mounted and pedestal mounted, sink pedestals, b-days and bath tubs. In a preferred embodiment, the cement composition comprises finely divided ceramic material is derived from ceramic tiles. The ceramic items may be waste produced as part of the manufacturing process. Generally, these waste items are produced during the manufacturing process, for example after the ceramic items have been (ie. post-kiln). Generally, these items cannot be recycled within the manufacturing process and must be disposed of, for example by way of land-fill. Other sources of waste ceramic items are in the distribution, wholesale and retail chain, for example as a result of damage to items during transport or storage. An alternative source of the waste ceramic items is from the refitting of existing installations or as a result of demolition and construction. As noted above, in one preferred embodiment, the finely divided ceramic material is derived from waste ceramic tiles. Typical raw materials used in the production of ceramic tiles include clay, feldspar, pottery stone, silica sand and talc. Generally, the most important component of ceramic tile bodies is clay. Clay is a term for naturally occurring mineral aggregates consisting mainly of the hydrous silicate of alumina. Ceramic tiles in the UK are commonly composed of clays, silica (milled to a desired particle size) and limestone which are mixed together with water to produce a slurry, or "slip". The slip is then spray dried to produce a homogeneous, free flowing granulate. The tiles are formed in a press and then dried and fired in a kiln, with a typical firing cycle of around four days. The fired tiles, known as "bisque", are then ready for the glazing cycle. The glazed product can be fired in a kiln with cycles from 12 to 20 hours, or in a single layer roller kiln with cycles of 30 to 45 minutes. The resultant tiles comprise a tile body with a fired glaze coating, typically on a major surface and possibly one or more edge surfaces. The finely divided ceramic material may comprise one or a mixture of different ceramic materials. In one embodiment, the finely divided ceramic material consists essentially of or comprises porcelain. Porcelain is a ceramic material formed by heating raw materials, generally including kaolinite, in a kiln to temperatures between 1,200 and 1,400 °C. References herein to ‘ceramic material’ include references to materials that consist of or comprise porcelain, unless otherwise stated. The finely divided ceramic material may have any suitable particle size. For example, the finely divided ceramic material may have a Dso of from 1 micron, preferably from 2 microns, more preferably from 5 microns, still more preferably from 7.5 microns. The finely divided ceramic material may have a Dso of up to 50 microns, preferably up to 45 microns, more preferably up to 40 microns, still more preferably up to 35 microns, more preferably still up to 30 microns, for example up to 25 microns or up to 20 microns. A Dso of from 5 to 30 microns is suitable for many embodiments, preferably from 6 to 25 microns, more preferably from 8 to 22 microns, especially from 10 to 20 microns. The finely divided ceramic material may have a bi-modal size distribution, that is with two different size fractions. For example, the first fraction may have a Dso of from 0.01 micron, preferably from 0.02 microns, more preferably from 0.03 microns, still more preferably from 0.04 microns. The first fraction may have a Dso of up to 2 microns, preferably up to 1.5 microns, more preferably up to 1 micron, still more preferably up to 0.5 microns, more preferably still up to 0.3 microns, for example up to 0.2 microns or up to 0.1 microns. A Dso of from 5 to 30 microns is suitable for many embodiments, preferably from 0.01 to 0.1 microns, especially from 0.02 to 0.06 microns. For example, the second fraction may have a Dso of from 1 micron, preferably from 2 microns, more preferably from 5 microns, still more preferably from 7.5 microns. The second fraction may have a Dso of up to 50 microns, preferably up to 45 microns, more preferably up to 40 microns, still more preferably up to 35 microns, more preferably still up to 30 microns, for example up to 25 microns or up to 20 microns. A Dso of from 5 to 30 microns is suitable for many embodiments, preferably from 6 to 25 microns, more preferably from 8 to 22 microns, especially from 10 to 20 microns. As noted above, the finely divided ceramic material is derived from waste ceramic items. In a particularly preferred embodiment, the waste ceramic items are ceramic tiles. The finely divided ceramic material may be prepared from the waste ceramic items by any suitable process, for example crushing, grinding or milling or a combination of one or more techniques. Suitable equipment for preparing the finely divided ceramic material is known in the art and is commercially available. As described above, the cement composition comprises a combination of GGBS and the finely divided ceramic material. The amounts of the GGBS and finely divided ceramic material may be any suitable amounts and the relative amounts of these components may be varied according to such factors as, for example, the end use of the composition and the required properties of the composition once cured, such as compressive strength. In one embodiment, the GGBS is present in the cement composition as the major component (that is greater than 50% by weight), with the finely divided ceramic material being present as the minor component (that is less than 50% by weight). In an alternative embodiment, the finely divided ceramic material is present in the cement composition as the major component (that is greater than 50% by weight), with the GGBS being present as the minor component (that is less than 50% by weight). The GGBS may be present in the cement composition in an amount of from 5% by weight, preferably from 10%, more preferably from 15%, still more preferably from 20%, more preferably still from 25%, especially from 30% by weight, more especially from 35%, still more especially from 40%, more especially still from 45%, in particular from 50%, more particularly from 55%, still more particularly from 60% by weight. The GGBS may be present in the cement composition in an amount of up to 98% by weight, preferably up to 95%, more preferably up to 90% by weight, still more preferably up to 85%, more preferably still up to 80%, especially up to 75%, more especially up to 70%, still more especially up to 65% by weight. In some embodiments, the GGBS is present in an amount of up to 55%, preferably up to 50%, more preferably up to 45% especially up to 40% by weight. In one embodiment, the cement composition comprises the GGBS in an amount of from 5 to 70% by weight, preferably from 10 to 60%, more preferably from 15 to 50%, still more preferably from 20 to 40% by weight. The GGBS and the finely divided ceramic material may be present in the cement composition in any suitable weight ratio. As noted above, in one preferred embodiment, GGBS is present in excess of the amount of the finely divided ceramic material. In an alternative embodiment, the finely divided ceramic material is present in excess of the amount of the GGBS. The weight ratio of GGBS and finely divided ceramic material in the cement composition may be from 10:1 to 1:10, preferably from 8:1 to 1:8, more preferably from 7:1 to 1:7, still more preferably from 6:1 to 1:6, more preferably still from 5:1 to 1:5. The weight ratio of GGBS and finely divided ceramic material in the cement composition may be from 2:1 to 1:10, preferably from 1:1 to 1:9, more preferably from 1:1 to 1:8, still more preferably form 1:1 to 1:7, more preferably still from 1:1 to 1:6, especially from 1:1.1 to 1:6, more especially from 1:1.2 to 1:6, still more especially from 1:1.3 to 1:6, for example 1:1.4 to 1:6. The weight ratio of GGBS and finely divided ceramic material in the cement composition may be from 1:1.2 to 1:6, still more preferably from 1:1.3 to 1:5.5, more preferably still from 1:1.4 to 1:5, especially from 2:3 to 1:4. In some embodiments, the weight ratio of the GGBS and the finely divided ceramic material is from 1:1.5 to 1:5. The cementitious composition may comprise one or more other binders in combination with GGBS. In such cases, the values indicated above for the amounts of GGBS present in the composition and the relative amounts of GGBS and finely divided ceramic material may be those for the total amount of GGBS and the one or more other binders. The cementitious composition of the present invention is preferably an alkali activated binder (AAB) cement, in which case the cementitious composition further comprises an activator. The activator is any compound or combination of compounds that activate the binder or precursor, in this case GGBS and the finely divided ceramic powder, comprising an alkali. The activator comprises one or more alkali compounds. Suitable alkali compounds include hydroxides, preferably alkali metal hydroxides or alkaline earth metal hydroxides. Alkali metal hydroxides are preferred, especially potassium and sodium hydroxides. The activator may comprise one or more hydroxides. Sodium hydroxide is particularly preferred for inclusion in the activator. Further alkali compounds that may be comprised in the activator are silicates. It is preferred that one or more silicates are used in combination with a hydroxide. Preferred silicates are alkali metal silicates and alkaline earth metal silicates. Alkali metal silicates are preferred, especially potassium and sodium silicates. The activator may comprise one or more silicates. Sodium silicate is particularly preferred for inclusion in the activator. In one preferred embodiment, the activator comprises a combination of a hydroxide and a silicate, preferably an alkali metal hydroxide and an alkali metal silicate, more preferably sodium hydroxide and sodium silicate. The activator may be present in the cementitious composition in any suitable amount to activate the binder. The activator may be present in an amount, based on the total weight of the binder, of from 10% by weight, preferably from 15%, more preferably from 20%, still more preferably from 25%, more preferably still from 30%, still more preferably from 40% by weight. The activator may be present in an amount, based on the total weight of the binder, of up to 80% by weight, preferably up to 70%, more preferably up to 65%, still more preferably up to 60%, more preferably still up to 55%, still more preferably up to 50% by weight. The activator may be present in an amount, based on the total weight of the binder, of from 10 to 80% by weight, preferably from 15 to 70%, more preferably from 20 to 70%, still more preferably from 25 to 65%, more preferably still from 30 to 60%, still more preferably from 40 to 55% by weight. In one preferred embodiment, the activator is present in an amount, based on the total weight of the binder, of from 40 to 55% by weight, preferably from 45 to 50% by weight, with 46 to 49% being particularly suitable, especially about 48% by weight. As noted above, in a preferred embodiment, the activator comprises a hydroxide and a silicate. The hydroxide and silicate may be present in any suitable amounts to activate the GGBS and finely divided ceramic material and any other binder that may be present. The hydroxide may be present in the activator in an amount, based on the weight of the activator, of from 10% by weight, preferably from 15%, more preferably from 20%, still more preferably from 25%, more preferably still from 30%, especially from 35% by weight. The hydroxide may be present in the activator in an amount, based on the weight of the activator, of up to 70% by weight, preferably up to 65%, more preferably up to 60%, still more preferably up to 55%, more preferably still up to 50%, especially up to 45% by weight. The hydroxide may be present in the activator in an amount, based on the weight of the activator, of from 10 to 70% by weight, preferably from 15 to 65%, more preferably from 20 to 60%, still more preferably from 25 to 55%, more preferably still from 30 to 50%, especially from 35 to 45% by weight, with an amount of from 40 to 45% by weight being preferred for many embodiments. The silicate may be present in the activator in an amount, based on the weight of the activator, of from 20% by weight, preferably from 30%, more preferably from 35%, still more preferably from 40%, more preferably still from 45%, especially from 50% by weight. The silicate may be present in the activator in an amount, based on the weight of the activator, of up to 90% by weight, preferably up to 85%, more preferably up to 80%, still more preferably up to 75%, more preferably still up to 70%, especially up to 65% by weight. The silicate may be present in the activator in an amount, based on the weight of the activator, of from 20 to 90% by weight, preferably from 25 to 85%, more preferably from 30 to 80%, still more preferably from 35 to 75%, more preferably still from 40 to 70%, especially from 45 to 65% by weight, with an amount of from 50 to 60% by weight being preferred for many embodiments. The weight ratio of the silicate and the hydroxide in the activator may be from 3:1 to 1:3, preferably from 2.5:1 to 1:2.5, more preferably from 2:1 to 1:2, still more preferably from 1.5:1 to 1:1.5. The silicate is preferably present in an amount in excess of the hydroxide, with the weight ratio of silicate and hydroxide being from 1.1:1 to 3:1, preferably from 1.2:1 to 2.5:1, more preferably from 1.25:1 to 2:1, still more preferably from 1.3:1 to 1.5:1, with a weight ratio in the range of about 1.4:1 being particularly preferred. In the AAB system, the alkali dosage (M+) is the mass ratio of metal oxide, such as sodium oxide (Na20), in the activating solution, that is the metal oxide, such as Na20, from the hydroxide, such as NaOH, plus the metal oxide, such as Na20, from the silicate, such as sodium silicate, to the dry mass of the binder, that is the total mass of GGBS and the finely divided ceramic material, together with any other binder or precursor present. M+ in % by weight is given by the following formula: M+ = metal oxide / (total mass of the binder). The value of M+ may be any suitable value, preferably from 3 to 15%, more preferably from 5 to 12%, still more preferably from 6 to 10%, especially from 7 to 8%, with a value of 7.5% being particularly suitable for many embodiments. The alkali modulus (AM) of the AAB system is the mass ratio of the metal oxide, such as Na2O, to SiO2 in the activator. In the case where the activator does not comprise a silicate, AM is °°. Preferably AM is in the range of from 0.1 to 5, more preferably from 0.2 to 4, still more preferably from 0.3 to 3, still more preferably from 0.4 to 2. A value of AM in the range of from 0.3 to 2 is particularly suitable for many embodiments, preferably from 0.4 to 1.7, still more preferably from 0.5 to 1.5. The cementitious composition finds advantageous use in a number of different ways. For example, the cementitious composition may be used to form a cement paste, a mortar or concrete. In a further aspect, the present invention provides a cementitious paste comprising a cementitious composition as hereinbefore described and water. Any suitable amount of water may be combined with the cementitious composition to form the paste and suitable amounts will be known to the skilled person. The amount of water that may be added to the cementitious composition to form the paste, based on the amount of the cementitious composition, may be from 1% by weight, preferably from 2%, more preferably from 3%, still more preferably from 4%, more preferably still from 5%, especially from 6%, more especially from 7%. The amount of water that may be added to the cementitious composition to form the paste, based on the amount of the cementitious composition, may be up to 30% by weight, preferably up to 25%, more preferably up to 20%, still more preferably up to 15%. Water in an amount, based on the amount of cementitous composition, may in many embodiments be from 3 to 20% by weight, preferably from 5 to 15%, more preferably from 6 to 12%, still more preferably from 8 to 10% by weight. The cementitious paste is allowed to cure after being applied or used. The paste may be allowed to cure at ambient temperatures, that is without the addition of heat from an external source. Alternatively, the paste may be cured at an elevated temperature, that is with heat added to the paste from an external source. It is an advantage of the paste that curing at ambient temperatures without the addition of heat from an external source is possible and the cured paste exhibiting a high compressive strength. The time required for the paste to cure may vary, for example depending upon the composition of the paste. The time required for the paste to fully cure may be from 5 days, for example 7 days, 10 days, 15 days, 20 days or longer. In many embodiments, the compressive strength of the paste will increase as the paste cures. For example, the compressive strength may increase for a period of 28 days or longer. In a further aspect, the present invention provides a cured cementitious paste prepared by combining the cementitious composition hereinbefore described with water and allowing the resulting mixture to cure. In a further aspect, the present invention provides a mortar composition comprising: an aggregate; and a cementitious composition as hereinbefore described. The mortar composition comprises an aggregate. The aggregate is typically a finely divided material. Sand is a particularly suitable aggregate for use in mortar compositions, as is well known in the art. The amount of aggregate present in the mortar composition may be any suitable amount, which may vary depending upon the use to be made of the mortar composition. The aggregate may be present in an amount, based on the amount of the mortar composition, of from 10% by weight, preferably from 15%, more preferably from 20%, still more preferably from 25%, more preferably still from 30%, especially from 35%, more especially from 40%, still more especially from 45% by weight. The aggregate may be present in an amount of up to 95% by weight, preferably up to 90%, more preferably up to 85%, still more preferably up to 80%. An amount of aggregate of from 10 to 90% by weight is suitable for many embodiments, preferably from 15 to 85%, more preferably from 20 to 80%, still more preferably from 30 to 80%, more preferably still from 40 to 80% by weight of the mortar composition. An amount of about 65% by weight is preferred for many embodiments. The amount of the cementitious composition present in the mortar composition may be any suitable amount, which may vary depending upon the use to be made of the mortar composition. The cementitious composition may be present in an amount, based on the amount of the mortar composition, of from 5% by weight, preferably from 7.5%, more preferably from 10%, still more preferably from 12.5%, more preferably still from 15%, especially from 17.5%, more especially from 20%, still more especially from 25% by weight. The cementitious composition may be present in an amount of up to 90% by weight, preferably up to 85%, more preferably up to 80%, still more preferably up to 75%, more preferably still up to 70%, especially up to 65%, more especially up to 60%, still more especially up to 55%, for example up to 50% by weight. An amount of cementitious composition of from 5 to 60% by weight is suitable for many embodiments, preferably from 20 to 50%, more preferably from 25 to 45%, still more preferably from 30 to 40% by weight of the mortar composition. An amount of about 35% by weight is preferred for many embodiments. The weight ratio of the aggregate to the cementitious composition in the mortar composition may be any suitable ratio, as determined, for example, by the intended use of the mortar composition. The weight ratio of the aggregate to the cementitious composition in the mortar composition may be from 10:1 to 1:10, preferably from 8:1 to 1:8, more preferably from 6:1 to 1:6. Preferably, the weight ratio of the aggregate to the cementitious composition in the mortar composition is from 10:1 to 1:2, more preferably from 8:1 to 1:1, still more preferably from 6:1 to 1:1, more preferably still from 4:1 to 1:1. A weight ratio of from 3:1 to 1:1 is suitable for many embodiments, more preferably from 2.5:1 to 1:1. In general, it is preferred that the aggregate is present in the mortar composition in excess of the amount of the cementitious composition. Examples of suitable weight ratios of aggregate and cementitious composition for particular end uses are as follows: Laying bricks: weight ratio of aggregate to cementitious composition of 4:1; Pointing: weight ratio of aggregate to cementitious composition of 3:1; External render: weight ratio of aggregate to cementitious composition of 3.5:1; Screed for flooring: weight ratio of aggregate to cementitious composition of 4:1; Application in chimneys: weight ratio of aggregate to cementitious composition of 5:1; Joints in paving: weight ratio of aggregate to cementitious composition of 3:1; and Construction of retaining walls: weight ratio of aggregate to cementitious composition of 3:1. In use, the mortar composition is combined with water and applied or used, after which the composition is allowed to cure. Any suitable amount of water may be combined with the mortar composition and suitable amounts will be known to the skilled person. Increasing the amount of water present can reduce the compressive strength of the final, cured composition. Reducing the amount of water, while still providing sufficient for complete curing of the composition, can increase the compressive strength of the final cured composition. These effects are known in the art. The amount of water that may be added to the mortar composition paste, based on the amount of the mortar composition, may be from 1% by weight, preferably from 1.5%, more preferably from 2%, still more preferably from 2.5%, more preferably still from 3%, especially from 3.5%. The amount of water that may be added to the mortar composition, based on the amount of the cement composition, may be up to 30% by weight, preferably up to 20%, more preferably up to 15%, still more preferably up to 10%, especially up to 5% by weight. Water in an amount, based on the amount of cement composition, may in many embodiments be from 1 to 25% by weight, preferably from 2 to 20%, more preferably from 2.5 to 15%, still more preferably from 3 to 10% by weight, with water in an amount of from 3 to 5% by weight being particularly suitable for many embodiments. The mortar composition may further comprise one or more components, for example a component to modify the physical properties of the composition. Such components are known in the art and their use is known to the skilled person. For example, the mortar composition may further comprise one or more plasticiser. Plasticisers provide the composition with an improved the flow characteristics and increased flexibility before the composition cures. Plasticisers can allow the amount of water employed to be reduced. This in turn can act to increase the compressive strength of the composition once cured and / or improve resistance to degradation, for example from freezing temperatures. Suitable plasticisers are commercially available and include lignosulfonates, sulfonated synthetic polymers (naphthalene, or melamine, formaldehyde condensates), and polycarboxylates-ether (PCE) synthetic polymers. The mortar composition is allowed to cure after being applied or used. The mortar composition may be allowed to cure at ambient temperatures, that is without the addition of heat from an external source. Alternatively, the mortar composition may be cured at an elevated temperature, that is with heat added to the mortar composition from an external source. It is an advantage of the mortar composition that curing at ambient temperatures without the addition of heat from an external source is possible and the cured mortar exhibiting a high compressive strength. The time required for the mortar composition to cure may vary, for example depending upon the composition of the mortar. The time required for the mortar composition to fully cure may be from 5 days, for example 7 days, 10 days, 15 days, 20 days or longer. In many embodiments, the compressive strength of the mortar composition will increase as the composition cures. For example, the compressive strength may increase for a period of 28 days or longer. In a further aspect, the present invention provides a cured mortar prepared by combining the mortar composition hereinbefore described with water and allowing the resulting mixture to cure. In a further aspect, the present invention provides a concrete composition comprising: an aggregate; and a cementitious composition as hereinbefore described. The concrete composition comprises an aggregate. The aggregate is typically a divided material. The aggregate may comprise two or more different aggregate components. For example, the aggregate may comprise a finely divided material, such as sand. The aggregate may comprise a coarse, granular material, such as a coarse sand, gravel or crushed rock. A mixture of two or more granular materials may be used. In one preferred embodiment, the aggregate comprises a finely divided material, preferably sand, and a coarse aggregate material, preferably gravel or crushed rock. The amount of aggregate present in the concrete composition may be any suitable amount, which may vary depending upon the use to be made of the concrete composition. The aggregate may be present in an amount of from 10% by weight, preferably from 20%, more preferably from 30%, still more preferably from 40%, more preferably still from 50%, especially from 55%, more especially from 60%, still more especially from 65% by weight. The aggregate may be present in an amount of up to 95% by weight, preferably up to 90%, more preferably up to 85%, still more preferably up to about 80%. An amount of aggregate of from 10 to 90% by weight is suitable for many embodiments, preferably from 20 to 85%, more preferably from 40 to 80% by weight of the concrete composition. An amount of from about 60 to 85% by weight is preferred for many embodiments, with an amount of from 75 to 85% by weight being particularly suitable for many embodiments. The amount of the cementitious composition present in the concrete composition may be any suitable amount, which may vary depending upon the use to be made of the concrete composition. The cementitious composition may be present in an amount of from 5% by weight, preferably from 7.5%, more preferably from 10%, still more preferably from 12.5%, more preferably still from 15%, especially from 17.5%. The cementitious composition may be present in an amount of up to 90% by weight, preferably up to 85%, more preferably up to 80%, still more preferably up to 75%, more preferably still up to 70%, especially up to 65%, more especially up to 60%, still more especially up to 55%, for example up to 50% by weight. An amount of cementitious composition of from 5 to 50% by weight is suitable for many embodiments, preferably from 10 to 40%, more preferably from 15 to 30%, still more preferably from 15 to 25% by weight of the concrete composition. An amount of about 20 to 25% by weight is preferred for many embodiments. The weight ratio of the aggregate to the cementitious composition in the concrete composition may be any suitable ratio, as determined, for example, by the intended use of the concrete composition. The weight ratio of the aggregate to the cementitious composition in the concrete composition may be from 10:1 to 1:10, preferably from 8:1 to 1:8, more preferably from 6:1 to 1:6. Preferably, the weight ratio of the aggregate to the cementitious composition in the concrete composition is from 10:1 to 1:2, more preferably from 10:1 to 1:1, still more preferably from 8:1 to 1:1, more preferably still from 6:1 to 1:1. A weight ratio of from 5:1 to 1:1 is suitable for many embodiments, especially a weight ratio of from 3:1 to 5:1. In general, it is preferred that the aggregate is present in the concrete composition in excess of the amount of the cementitious composition. Examples of suitable weight ratios of aggregate and cementitious composition for particular grades of concrete are as follows. The ratios indicated are the ratios of cementitious composition : fine aggregate (for example sand): coarse aggregate (for example gravel): M5 1:5:10; M7.5 1:4:8; M10 1:3:6; M15 1:2:4; M20 1:1.5:3; and M25 1:1:2. In use, the concrete composition is combined with water and applied or used, after which the composition is allowed to cure. Any suitable amount of water may be combined with the concrete composition and suitable amounts will be known to the skilled person. Increasing the amount of water present can reduce the compressive strength of the final, cured composition. Reducing the amount of water, while still providing sufficient for complete curing of the composition, can increase the compressive strength of the final cured composition. These effects are known in the art. The amount of water that may be added to the concrete composition paste, based on the amount of the concrete composition, may be from 1% by weight, preferably from 1.5%, more preferably from 2%, still more preferably from 2.5%. The amount of water that may be added to the concrete composition, based on the amount of the concrete composition, may be up to 20% by weight, preferably up to 15%, more preferably up to 10%, still more preferably up to 7.5%. Water in an amount, based on the amount of cement composition, may in many embodiments be from 1 to 20% by weight, preferably from 1.5 to 15%, more preferably from 2 to 10%, still more preferably from 2.5 to 8% by weight. Water in the amount of from 2.5 to 4% by weight is particularly suitable for many embodiments. The concrete composition may further comprise one or more components, for example a component to modify the physical properties of the composition. Such components are known in the art and their use is known to the skilled person. For example, the mortar composition may further comprise one or more plasticiser, as discussed above with respect to the mortar compositions. Other components that may be added, as known in the art, include corrosion inhibitors, colouring agents, agents for increasing (retarding) or decreasing (accelerating) the curing time, agents to promote air entrainment, and agents to reduce shrinking. The concrete composition is allowed to cure after being applied or used. The concrete composition may be allowed to cure at ambient temperatures, that is without the addition of heat from an external source. Alternatively, the concrete composition may be cured at an elevated temperature, that is with heat added to the composition from an external source. It is an advantage of the concrete composition that curing at ambient temperatures without the addition of heat from an external source is possible and the cured concrete exhibiting a high compressive strength. The time required for the composition to cure may vary, for example depending upon the composition of the concrete. The time required for the concrete composition to fully cure may be from 5 days, for example 7 days, 10 days, 15 days, 20 days or longer. In many embodiments, the compressive strength of the concrete composition will increase as the composition cures. For example, the compressive strength may increase for a period of 28 days or longer. In a further aspect, the present invention provides a cured concrete prepared by combining the concrete composition hereinbefore described with water and allowing the resulting mixture to cure. More generally, it has further been found that finely divided ceramic material may be activated by an alkali and employed as a binder or precursor in an AAB cementitious composition. For example, an AAB cementitious composition can be provided in which the binder or precursor that is activated consists essentially of finely divided ceramic material. Alternatively, the finely divided ceramic material may be employed with one or more further binders, such as GGBS, as discussed in detail above. Accordingly, in a further aspect, the present invention provides an AAB cementitious composition comprising: a finely divided ceramic material; and an activator. The AAB cementitious composition comprises a finely divided ceramic material. Details of the finely divided ceramic material are as discussed above. In one preferred embodiment, the finely divided ceramic material comprises a finely divided or powdered porcelain derived from waste ceramic tiles and / or another finely divided or powdered ceramic material derived from waste ceramic tiles. The amount of finely divided ceramic material in the AAB cementitious composition may be any suitable amount. The finely divided ceramic material may be present in an amount as discussed hereinbefore. In particular, the finely divided ceramic material may be present in the AAB cementitious composition in an amount of from 5% by weight, preferably from 10%, more preferably from 15%, still more preferably from 20%, more preferably still from 25%, especially from 30% by weight, more especially from 35%, still more especially from 40%, more especially still from 45%, particularly from 50% by weight. The finely divided ceramic material may be present in the AAB cementitious composition in an amount of up to 98% by weight, preferably up to 95%, more preferably up to 90%, still more preferably up to 85%, more preferably still up to 80% by weight. In some embodiments, the finely divided ceramic material is present in an amount of up to 90% by weight, preferably up to 85%, more preferably up to 80% especially up to 75% by weight. In one embodiment, the AAB cementitious composition comprises the finely divided ceramic material in an amount of from 20 to 95% by weight, preferably from 30 to 90%, more preferably from 40 to 85%, still more preferably from 50 to 80% by weight. In one embodiment, the AAB cementitious composition comprises the finely divided ceramic material in an amount of from 50 to 95% by weight, preferably from 55 to 90%, more preferably from 60 to 80% by weight. The finely divided ceramic material is a binder or precursor, that is activated by the activator, as described in more detail below. The finely divided ceramic material may be the sole binder or precursor present in the cementitious composition. Alternative, one or more other precursors or binders may be present, for example GGBS, as discussed in detail hereinbefore. The AAB cementitious composition further comprises an activator. The activator is an alkali and details of the activator are as described hereinbefore. In particular, the activator is any compound or combination of compounds that activate the binder or precursor, in this case the finely divided ceramic powder and any other binder present in the cementitious composition, such as GGBS, comprising an alkali. The activator comprises one or more alkali compounds. Suitable alkali compounds include hydroxides, preferably alkali metal hydroxides or alkaline earth metal hydroxides. Alkali metal hydroxides are preferred, especially potassium and sodium hydroxides. The activator may comprise one or more hydroxides. Sodium hydroxide is particularly preferred for inclusion in the activator. Further alkali compounds that may be comprised in the activator are silicates. It is preferred that one or more silicates are used in combination with a hydroxide. Preferred silicates are alkali metal silicates and alkaline earth metal silicates. Alkali metal silicates are preferred, especially potassium and sodium silicates. The activator may comprise one or more silicates. Sodium silicate is particularly preferred for inclusion in the activator. In one preferred embodiment, the activator consists essentially of a hydroxide, preferably an alkali metal hydroxide, more preferably sodium hydroxide. In one preferred embodiment, the activator comprises a combination of a hydroxide and a silicate, preferably an alkali metal hydroxide and an alkali metal silicate, more preferably sodium hydroxide and sodium silicate. The activator may be present in the AAB cementitious composition in any suitable amount to activate the finely divided ceramic material and any other binder present. The activator may be present in an amount, based on the total weight of the finely divided ceramic material and any other binder present, of from 10% by weight, preferably from 15%, more preferably from 20%, still more preferably from 25%, more preferably still from 30% by weight. The activator may be present in an amount, based on the total weight of the finely divided ceramic material and other binder material, of up to 80% by weight, preferably up to 70%, more preferably up to 65% by weight. The activator may be present in an amount, based on the total weight of the finely divided ceramic material and other binder material, of from 10 to 80% by weight, preferably from 15 to 75%, more preferably from 20 to 70%, still more preferably from 25 to 65% by weight. In one preferred embodiment, the activator is present in an amount, based on the total weight of the finely divided ceramic material and other binder, of from 25 to 70% by weight, preferably from 30 to 65% by weight, with 46 to 49% being particularly suitable, especially about 48% by weight for many embodiments. As noted above, in one preferred embodiment, the activator comprises a hydroxide and a silicate. The hydroxide and silicate may be present in any suitable amounts to activate the GGBS and finely divided ceramic material. The hydroxide may be present in the activator in an amount, based on the weight of the activator, of from 10% by weight, preferably from 15%, more preferably from 20%, still more preferably from 25%, more preferably still from 30%, especially from 35% by weight. The hydroxide may be present in the activator in an amount, based on the weight of the activator, of up to 70% by weight, preferably up to 65%, more preferably up to 60%, still more preferably up to 55%, more preferably still up to 50%, especially up to 45% by weight. The hydroxide may be present in the activator in an amount, based on the weight of the activator, of from 10 to 70% by weight, preferably from 15 to 65%, more preferably from 20 to 60%, still more preferably from 25 to 55%, more preferably still from 30 to 50%, especially from 35 to 45% by weight, with an amount of from 40 to 45% by weight being preferred for many embodiments. The silicate may be present in the activator in an amount, based on the weight of the activator, of from 20% by weight, preferably from 30%, more preferably from 35%, still more preferably from 40%, more preferably still from 45%, especially from 50% by weight. The silicate may be present in the activator in an amount, based on the weight of the activator, of up to 90% by weight, preferably up to 85%, more preferably up to 80%, still more preferably up to 75%, more preferably still up to 70%, especially up to 65% by weight. The silicate may be present in the activator in an amount, based on the weight of the activator, of from 20 to 90% by weight, preferably from 25 to 85%, more preferably from 30 to 80%, still more preferably from 35 to 75%, more preferably still from 40 to 70%, especially from 45 to 65% by weight, with an amount of from 50 to 60% by weight being preferred for many embodiments. The weight ratio of the silicate and the hydroxide in the activator may be from 3:1 to 1:3, preferably from 2.5:1 to 1:2.5, more preferably from 2:1 to 1:2, still more preferably from 1.5:1 to 1:1.5. The silicate is preferably present in an amount in excess of the hydroxide, with the weight ratio of silicate and hydroxide being from 1.1:1 to 3:1, preferably from 1.2:1 to 2.5:1, more preferably from 1.25:1 to 2:1, still more preferably from 1.3:1 to 1.5:1, with a weight ratio in the range of about 1.4:1 being particularly preferred. The value of M+ may be any suitable value, preferably from 3 to 15%, more preferably from 5 to 12%, still more preferably from 6 to 10%, especially from 7 to 8%, with a value of 7.5% being particularly suitable for many embodiments. In embodiments where the activator does not comprise a silicate, AM is 00. In another preferred embodiment, AM is in the range of from 0.1 to 5, more preferably from 0.2 to 4, still more preferably from 0.3 to 3, still more preferably from 0.4 to 2. A value of AM in the range of from 0.3 to 2 is particularly suitable for many embodiments, preferably from 0.4 to 1.7, still more preferably from 0.5 to 1.5. To be activated, the AAB cementitious composition must be combined with water. The amount of water employed will depend upon the particular use being made of the AAB cementitious composition. Typical amounts of water for different uses are described hereinbefore. In a further aspect, the present invention provides an AAB cementitious paste comprising an AAB cementitious composition as hereinbefore described and water. Further details of the AAB cementitious paste, its components and its use are as described above with respect to the previous aspects of the present invention. In a further aspect, the present invention provides an AAB mortar composition comprising: an aggregate; and an AAB cementitious composition as hereinbefore described. Further details of the AAB mortar composition, its components and its use are as described above with respect to the previous aspects of the present invention. In a further aspect, the present invention provides a concrete composition comprising: an aggregate; and a AAB cementitious composition as hereinbefore described. Further details of the AAB concrete composition, its components and its use are as described above with respect to the previous aspects of the present invention. Once combined with water, each of the AAB cementitious composition, AAB mortar composition and AAB concrete composition are cured. The compositions may be allowed to cure at ambient temperatures, that is without the addition of heat from an external source. Alternatively, the compositions may be cured at an elevated temperature, that is with heat added to the composition from an external source. It is an advantage of many of the compositions of the present invention that curing at ambient temperatures without the addition of heat from an external source is possible and the cured composition exhibits a high compressive strength. In embodiments in which the finely divided ceramic powder is the sole binder or precursor that is activated by the activator after the addition of water or the binder does not comprise another component that is rich in calcium (Ca) compounds, it may be necessary to cure the composition at an elevated temperature, that is apply heat from an external source to raise the temperature of the composition. If the temperature of the composition is to be raised during curing, the temperature is preferably raised to a temperature of from 30°C, for example from 40°C, or from 45°C, or from 50°C, or from 60°C. The temperature may be raised up to 90°C, for example up to 85°C, or up to 80°C, or up to 75°C. In a further aspect, the present invention provides a cured cementitious paste prepared by combining the AAB cementitious composition hereinbefore described with water and allowing the resulting mixture to cure. In a further aspect, the present invention provides a cured mortar composition prepared by combining the AAB mortar composition hereinbefore described with water and allowing the resulting mixture to cure. In a further aspect, the present invention provides a cured concrete prepared by combining the AAB concrete composition hereinbefore described with water and allowing the resulting mixture to cure. Embodiments of the present invention will now be described, for illustrative purposes only, by way of the following working examples. Percentages indicated are weight percent, unless otherwise stated. Reference will be made to the accompanying figures, in which: Figure 1 is an XRD diffractogram of GGBS, OPC and ceramic tile powders; Figure 2 is a graph of the FT-IR spectra of GGBS, OPC and ceramic tile powders; Figure 3 is a graph of the particle size distributions of a porcelain tile powder; Figure 4 is a graph of the particle size distribution of a ceramic tile powder; Figure 5 shows SEM micrographs of the porcelain and ceramic tile powders of Figures 3 and 4; Figure 6 is a graph showing the results of compressive strength tests for AAB mortars; Figure 7 is a graph showing the results of compressive tests for AAB concrete compositions; Figure 8 is an XRD diffractogram of cement pastes; Figure 9 is a graph of the FT-IR spectra of cement pastes; and Figure 10 shows SEM micrographs of cement pastes. EXAMPLES A range of experiments were conducted as described in detail below. Unused, new ceramic and porcelain tiles were supplied by Paignton Tile Company Ltd, labelled as non-marketable materials due to damages. References in these examples to ‘ceramic’ (CER) are to ceramic tile materials that do not contain porcelain. Porcelain is identified separately as POR. Powders were produced by pre-crushing the tiles in a drum cement mixer for one hour with metal weights, followed by sieving of the debris to 600 microns. The sieved powder was then ball milled for 10 minutes in a Retsch PM100 ball mill at 300 rpm. Ordinary Portland Cement (OPC) and Ground Granulated Blast-furnace Slag (GGBS) powders were supplied by Tarmac and Ecocem respectively and used as supplied. The oxide composition of the ceramic, porcelain and GGBS powders was obtained by X-ray Fluorescence Spectroscopy (XRF) using a Rigaku SuperMini 200 Wavelength Dispersive XRF spectrometer. The powders were dried overnight at 80°C then calcined at 1050°C for 1 hour. The calcined sample was fused with lithium borate flux using a Vulcan Automatic Fusion Machine to produce glass bead. Quantitative data was obtained using an empirical application calibrated with 52 certified reference materials. XRF results are shown in Table 1 below, along with the oxide composition of fly ash (sourced from Drax UK, reported for comparison purposes only). The (oxide) chemical composition of ceramic and porcelain was found to be broadly similar, apart from the CaO content, which was found to be >5% higher in ceramic than in porcelain. Other differences were measured in the range of about ±2%. A high similarity was also noted when comparing ceramics and porcelain compositions with that of a typical fly ash used in concrete industry, where the most notable differences observed were the presence of iron and the higher loss on ignition of fly ash, at the expenses of silicate content. Table 1. Oxide composition and loss on ignition (LOI) in %wt of ceramic, porcelain, and GGBS from XRF analysis. Oxide Ceramic Porcelain GGBS Na2O 1.14 3.92 0.26 MgO 0.67 0.72 7.89 AI2O3 16.45 18.18 11.15 SiO2 66.34 68.39 34.94 P2O5 0.15 0.16 0.03 SO3 0.03 <0.01 1.79 K2O 2.25 1.84 0.32 CaO 7.26 1.23 41.27 TiO2 0.67 0.63 0.81 Mn2O3 0.03 0.03 0.20 Fe2Os 1.93 1.73 0.45 ZnO 0.40 0.15 - SrO 0.02 0.04 - ZrO2 0.51 0.36 - BaO 0.12 0.14 0.10 LOI 0.6 0.9 0.9 The mineral composition of GGBS, OPC, and the tile powders (TP) was determined using x-ray diffraction (XRD), using a Bruker D8 Advance diffractometer with a CuK a, with a wavelength of 1.5418 A. The generator was adjusted to 40kV with a current of 40 mA and a goniometer speed of -0.04° 29 / s over the range 10-70°9. OPC was analysed by way of a comparison. The resulting XRD diffractograms are shown in Figure 1. The diffractograms show the vitreous nature of GGBS (entirely amorphous), and the expected peaks associated to the cement minerals in OPC (alite, belite, ferrite, gypsum, and aluminate species). The presence of amorphous materials in TP was suggested by the broad hump of the baseline in the range 20-30° 29, which appears more pronounced in porcelain than in ceramic. The mineral composition of TP was predominantly quartz and mullite, with some presence of plagioclase feldspar, anorthite, and almandine. Infrared spectroscopy characterisation of the tile powders and binders was obtained through Fourier Transform Infrared Spectroscopy in the Attenuated Total Reflectance mode (ATR-FTIR). The test was carried out using a JASCO 4100 series FTIR spectrometer performing 16 scans per measurement across the range of 400-4000 cm-1 with a resolution of 2.0 cm-1. The FTIR spectra are shown in Figure 2. Again, OPC was analysed by way of comparison. The interpretation of absorbance bands corresponding to vibrations of chemical bonds in specific compounds was performed based on available literature. The same equipment and settings were used to determine the infrared spectroscopy of the reaction products. Large peaks corresponding to Si-O-Si vibration could be observed in every material, shifted towards larger wavenumber for TP than for GGBS, confirming the more crystalline nature of the silicates. A strong presence of calcium-based species was observed for GGBS and OPC. The quartz distinctive peak was observed for the porcelain and ceramic powders. The grain size distribution of the tile powders (TP) was assessed using a Bettersizer S3 Plus device with water as a medium. The particle size distributions for porcelain tile powder and ceramic tile powder are shown in Figures 3 and 4 respectively. The size distribution for porcelain powder followed the expected trend, with a continuous and well-graded distribution, a D50 = 16 pm, and a large size D97 <70 pm, as shown in Figure 3. Unexpectedly, the ceramic powder showed a bi-modal distribution, with a substantial fraction (> 50%) of the powder having sub-micron size (D50 = 0.04 pm), whilst another fraction in the expected range centred around 15-20 pm, as shown in Figure 4. The test was repeated twice and gave very similar results. Visual appearance from SEM micrographs confirmed qualitatively the analysis, as shown in Figure 5. The sharp appearance of the surfaces of some of the powder grains indicates the vitreous (i.e., amorphous) nature of a fraction of the materials. Sodium hydroxide for the activation of AAB was produced by dissolving NaOH pellets in water obtaining to a 30% solution (SH) and a final solution density of 1.33 g / cm3. Sodium silicate solution (SS) was supplied by Fisher Chemical, with a density of 1.4 g / cm3 and an average composition of 12.8% wt.% Na2O, 25.5 wt.% SiO2, and 61.7 wt.% water. Aggregate (sand and 10mm gravel) was supplied by Bradfords. Example 1 Tile Powder in AAB mortar compositions Experiments were conducted to examine the use of the ceramic and porcelain tile powders (TP) as cementitious materials in alkali activated binders (AAB) cementitious compositions both with and without a binder, in particular ground granulated blast furnace slag (GGBS). In a first batch of experiments, a range of mortar mixes were prepared. The components used to prepare each of the mortar mixes are summarised in Table 2 below. Each mortar mix was formed from a mixture comprising sand, sodium silicate, sodium hydroxide and water. GGBS, Porcelein tile powder (POR) and ceramic tile powder (CER) were used in the amounts indicated in Table 2. Examples 1Ato 1E were conducted to assess the potential for ceramic TPs to be activated with no other precursors. The dosage parameters of alkali dosage (M+) and alkali modulus (AM) were used to determine the amount of sodium hydroxide and sodium silicate needed for the activation. M+ is the mass ratio of sodium oxide (Na2O) to the total mass of the precursor and AM is the mass ratio of Na20 to S1O2, as described by Rafeet, A., et al., ‘Effects of slag substitution on physical and mechanical properties of fly ashbased alkali activated binders (AABs)’, Cement and Concrete Research, 2019, 122, pages 118 to 135. M+ was selected to be equal to 7.5%, while AM was tested in the range of from 0.5 to 1.5. The water-to-solid ratio (w / s), that is, the mass ratio of water to the mass of binder including the solid chemicals S1O2 and Na2O was selected to be 0.37. The mortar composition of Example 1E was cured at room temperature. The compositions of Examples 1Ato 1D were cured in an oven at a temperature of 70°C. Examples 1F and 1G were conducted to assess the blend of ceramic TP and PPDQ UUdo. Alkali activation was conducted with sodium silicate and sodium hydroxide in the amounts indicated in Table 2, giving values of M+ of 7.5% and AM of 1. The water-to-solid ratio (w / s), that is, the mass ratio of water to the mass of binder including the solid chemicals SiO2 and Na20 was selected to be 0.37. The compositions of Examples 1F and 1G were cured at room temperature. Example 1H is a comparative example that did not employ either ceramic tile powder or porcelain tile powder. Examples 11 to 1N were conducted to assess the effect of porcelain and ceramic TPs used separately and blended with GGBS for producing a mortar. Alkali activation was conducted with sodium silicate and sodium hydroxide in the amounts indicated in Table 2, giving values of M+ of 7.5% and AM of 1. The compositions of Examples 11 to 1N were cured at room temperature. Examples 10 and 1P were conducted to assess the effects of combining porcelain and ceramic TPs with GGBS to produce a mortar. Alkali activation was conducted with sodium silicate and sodium hydroxide in the amounts indicated in Table 2, giving values of M+ of 7.5% and AM of 1. The water-to-solid ratio (w / s), that is, the mass ratio of water to the mass of binder including the solid chemicals SiO2 and Na20 was selected to be 0.4. The compositions of Examples 10 and 1P were cured at room temperature. Examples 1Q to 1S were conducted to assess the effects of combining porcelain and ceramic TPs with GGBS to produce a mortar. Alkali activation was conducted with sodium silicate and sodium hydroxide in the amounts indicated in Table 2, giving values of M+ of 7.5% and AM of 1. The water-to-solid ratio (w / s), that is, the mass ratio of water to the mass of binder including the solid chemicals SiO2 and Na2O was selected to be 0.39. The amount of water used included an allowance for absorption by the aggregate (sand). The compositions of Examples 1Q to 1S were cured at room temperature. Table 2. Example No. Tile Powder (TP) Fraction (wt%) GGBS (g) POR (g) CER (g) Sand (g) Sodium Silicate (g) Sodium Hydroxide (g) Water (g) 1A 100 0 0 500 1375 0 161 86 1B 100 0 0 500 1375 94 118 66 10 100 0 0 500 1375 142 97 56 1D 100 0 0 500 1375 283 32 26 1E 100 0 0 500 1375 142 97 56 1F 80 100 0 400 1375 142 97 56 1G 60 200 0 300 1375 142 97 56 1H 0 500 0 0 1375 142 97 73 11 60 200 300 0 1375 142 97 73 1J 70 150 350 0 1375 142 97 73 1K 80 100 400 0 1375 142 97 73 1L 60 200 0 300 1375 142 97 73 1M 70 150 0 350 1375 142 97 73 1N 80 100 0 400 1375 142 97 73 10 70 150 140 210 1375 142 97 73 1P 70 150 210 140 1375 142 97 73 1Q 65 175 162.5 162.5 1375 142 97 95 1R 70 150 175 175 1375 142 97 95 1S 75 150 187.5 187.5 1375 142 97 95 In a second batch of experiments, a range of concrete mixes were prepared. The components used to prepare each of the concrete mixes are summarised in Table 3 below. The composition of Example 1T comprised about 387 kg / m3 of binder, using 5 GGBS and 70% TPs with a porcelain:ceramic blend of 40 / 60 and a w / c = 0.4. The composition of Example 1U comprised about 356 kg / m3 of binder, using GGBS and 75% TPs with a porcelain:ceramic blend of 50 / 50 and a w / c = 0.4. The quantities indicated in Table 3 provided a 1 I mix of concrete, although the laboratory mix was dimensioned for 7 litres, in order to allow the production of io six 100 x 100 mm cubes and to perform a slump cone test on the fresh material. The quantity of water indicated in Table 3 refers to the total amount of water used in the mix, including the allowance for aggregate absorption (if foreseen). 5 Table 3. Example No. Tile Powder (TP) Fraction (wt%) GGBS (g) POR (g) CER (g) Sodium Hydroxide (g) Sodium Silicate (g) Sand (g) Gravel (g) Water (g) 1T 70 116 108.3 162.5 75 109.5 721 1111 71 1U 75 89 133.6 133.6 69 101 742 1144 84 The mortar and concrete samples of Examples 1Ato 1U were prepared and cast in accordance with BS EN 206, BS EN 12390-1, and BS EN 12390-2. The appropriate quantities of dry material were weighed and placed in a clean, dry bowl. The dry material was then mixed ensuring lumps had been broken up to achieve a uniform consistency. The liquid components were weighed and added to the mix. The liquid was added to the dry material as it was being mixed. Mortar mixes were prepared using a Quattro MXP004 planetary mixer. Concrete mixes were produced with a Creteangle PE / CL mixer. After mixing to a suitable texture the material was put into cube moulds: 50 mm cubes for mortar samples and 100 mm cube moulds for concrete. The moulds were clean and had a thin layer of lubricant applied to aid the process of demoulding. The filled moulds were vibrated on a Controls D0407B vibrating table to ensure the material filled the full volume of the mould. Once the samples had been suitably vibrated and flattened, these were wrapped in cling film. The samples of Examples 1Ato 1D were put in ovenat70°C. Samples for all other examples were left at room temperature. The samples were demoulded approximately 24 hours later and re-wrapped in cling film. The resulting samples were either returned to the oven (Examples 1Ato 1D) or kept at room temperature. In a third batch of experiments, a range of AAB pastes were prepared. The components used to prepare each of the concrete mixes are summarised in Table 4 below. Example 1V did not employ a tile powder and is a comparative example. Paste samples were mixed by hand from the components detailed in Table 4, cast into 4 cm3 silicon moulds and covered with cling film for 28 days curing at room temperature. Table 4 Example No. Tile Powder (TP) Fraction (wt%) GGBS (g) POR (g) CER (g) Sodium Hydroxide (g) Sodium Silicate (g) Water (ml) 1V 0 5 0 0 1 1.4 0.7 1W 60 2 3 0 1 1.4 0.7 1X 70 1.5 3.5 0 1 1.4 0.7 1Y 80 1 4 0 1 1.4 0.7 1Z 60 2 0 3 1 1.4 0.7 1AA 70 1.5 0 3.5 1 1.4 0.7 1BB 80 1 0 4 1 1.4 0.7 1CC 70 1.5 1.4 2.1 1 1.4 0.7 1DD 70 1.5 2.1 1.4 1 1.4 0.7 Example 2 Compressive Tests on AAB mortar compositions Samples of the OPC-based mortar compositions of Examples 1Ato 1S were allowed to cure and their compressive strength was tested. Compressive strength was tested on cubes of the mortar compositions at 1, 7 and 28 days in accordance with BS EN 12390-3 and BS EN 12390-4. The tests were conducted using a load-controlled press Controls MCC 8 Testing System with the machine set to a loading rate of 0.6 MPa / s. Two cubes were tested for each mix and each curing age. The results are shown in Figure 6. Referring to the results shown in Figure 6, the results of Examples 1Ato 1E showed that significant compressive strength can be obtained, with values of 20 MPa being obtained without the use of sodium silicate and greater than 30 MPa with the use of sodium silicate as a component of the alkali activator. The results of Examples 1F to 1N further show that a compressive strength in excess of 70 MPa could be achieved by samples with 40% GGBS in the precursor blend cured at room temperature, and strengths exceeding 45 MPa can be achieved with as little as 20% GGBS in the precursor blend. Referring to the results for Examples 10 and 1P, no difference can be seen between the two blends in terms of strength results after 7 days of curing. The final strength of samples mixed with higher proportion of ceramic TP was however higher than that of samples with a prevalence of porcelain. An average strength class of 40 MPa was obtained with 70% TPs in the mix. Blended TPs samples outperformed those with a similar substitution rate but with only one TP type in the mix. A higher water content resulted in a slight reduction in the final compressive strength of the cured mortars. Referring to Examples 1Q to 1S, samples with overall 70% TPs delivered compressive strengths of about 30 MPa, significantly higher than the strength obtained for 70% ceramic-only or porcelain-only compositions. Example 3 Flowability test on AAB mortar compositions Flow table tests were carried out on fresh mortar compositions of Examples 1J to 1M according to EN 1015-3:1999. The observed spread of the mortar compositions was about 95 mm on the table after 10 shocks. The inclusion of significant amounts of tile powder did not affect the flowability of the composition. Example 4 Compressive Tests on AAB concrete compositions Samples of the OPC-based concrete compositions of Examples 1T and 1U were allowed to cure and their compressive strength was tested. Compressive strength was tested on cubes of the concrete compositions at 1, 7 and 28 days in accordance with BS EN 12390-3 and BS EN 12390-4. The tests were conducted using a load-controlled press Controls MCC 8 Testing System with the machine set to a loading rate of 0.6 MPa / s. Two cubes were tested for each mix and each curing age. The results are shown in Figure 7. The samples of Example 1U exhibited a compressive strength slightly over 30 MPa at 28 days, and fast early strength development was seen (nearly 15 MPa after one day of curing). The composition of Example 1T had satisfactory slump falling in class S4. The compressive strength obtained from the mix exceeded 50 MPa, confirming the success of the use of TPs even at low GGBS amounts. Example 5 Slump Tests on OPC-based concrete compositions Samples of the OPC-based concrete compositions of Examples 1N to 1Q were tested to determine their tendency to slump. The slump tests were carried out on fresh concrete samples to determine the workability in accordance with BS EN 12350-2. The tests were carried out immediately after mixing. The compositions with reduced water (Example 1U) were rather stiff, and no slump fall was recorded. The compositions of Example 1T with standard water content exhibit satisfactory slump falling in class S4. Example 6 Characterisation of AAB cement pastes The properties of the cement pastes of Examples 1V to 1DD were analysed. In particular, the physical structure of the reacted pastes was analysed using x-ray diffraction. The analysis was conducted using a Bruker D8 Advance diffractometer with a CuK a, with a wavelength of 1.5418 A. The generator was adjusted to 40kV with a current of 40 mA and a goniometer speed of ~0.04° 20 / s over the range 1O-7O°0. Infrared spectroscopy characterisation of the cement pastes was obtained through Fourier Transform Infrared Spectroscopy in the Attenuated Total Reflectance mode (ATR-FTIR). The tests were carried out using a JASCO 4100 series FTIR spectrometer performing 16 scans per measurement across the range of 400-4000 cm-1 with a resolution of 2.0 cm-1. The cements pastes were further analysed using Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM / EDX). Figure 8 shows the XRD diffractograms for the cement pastes of Examples 1Vto 1DD. Referring to Figure 8, the diffractogram shows that no new crystalline reaction product (i.e., identified by newly identified peaks) was observed when using TPs in the composition. The main differences between pure GGBS and pastes with a combination of GGBS and TPs were the presence of quartz and the slight reduction and broadening of the peak attributed to the CASH gel (calcium-alumina-silicate-hydrated gel), highlighted in the figure. Comparing these results with the diffractogram of the raw TPs shown in Figure 2, it is observed that some of the peaks previously attributed to mullite (aluminosilicate miner) disappeared from the diffractograms, thus presumably consumed during the reaction. Figure 9 shows the FT-IR spectra obtained for the pastes of Examples 1V to 1DD. Referring to Figure 9, the broad hump centred at about 3500 cm’1 represents the extent of hydration of the samples. The hump is well developed in the sample of comparative Example 1V. The hump is less well developed in the other examples, indicating that the reactions do not mainly involve the hydration of species, but rather the creation of a “geopolymeric” gel (NASH-type gel). The peak associated with Si-0 vibrations for cured pastes was found at wavenumbers lower than 1000 cm-1, whereas the same peak for raw ceramic and porcelain powder was detected at higher wavenumbers, as shown in Figure 3. It is to be observed that in the spectrum of neat GGBS paste of Example 1V the shift was more pronounced, whereas for mixtures of GGBS and tile powders it is centred at about 1000 cm-1. Shifts of such peaks to a lower wavenumber are typically associated with a change of microstructure and formation of the amorphous reaction products, in which SiO4 units are partially replaced by tetrahedral AIO4 units. Figure 10 shows SEM images of the cement pastes of Examples 1V, 1Z, 1AAand 1BB. The scale of the images is in the range of from 50 to 100pm. The images in Figure 10 show overall homogeneous morphologies and elemental maps with expected distributions. The experimental results show the following: It is possible to use powder obtained from waste and recycled ceramic tiles, including porcelain tiles, as precursor in an AAB cementitious system. If cured in an oven at about 70 °C, compressive strengths from 20 MPa (mixes with no SS) to more than 30 MPa (mix with the highest SS content, AM = 0.5) can be obtained. When mixed with GGBS, tile powders are able to deliver significant strength with curing at room temperature with as little as 20% GGBS content. Higher strengths can be obtained with higher GGBS contents. A blend of 60% GGBS / 40% TPs, when using a single source of tile powder can produce increased compressive strength. Mixtures of ceramic / porcelain powders can provide compressive strengths in excess of 40 MPa with the tile powder being present in an amount of 65 to 70% of the total precursor mass. 75% TPs in combination with GGBS produces a mortar with compressive strength of about 30 MPa. AAB-based concrete strengths in excess of 50 MPa can be achieved. AAB concrete with GGBS and TPs, including up to 70 to 75% tile powder can deliver satisfactory compressive strengths, for example in the range of 30 to 50 MPa.

Claims

1. A cementitious composition comprising a cement composition, the cement composition comprising:ground granulated blast furnace slag (GGBS); anda finely divided ceramic obtained from waste ceramic items.

2. The cementitious composition according to claim 1, wherein the cement composition comprises finely divided ceramic material derived from ceramic tiles.

3. The cementitious composition according to either of claims 1 or 2, wherein the cement composition comprises finely divided porcelain material.

4. The cementitious composition according to any preceding claim, wherein the GGBS is Grade 80, Grade 100, Grade 120, or a mixture of two or more thereof.

5. The cementitious composition according to any preceding claim, wherein GGBS is present in the cement composition in an amount of from 5 to 70% by weight.

6. The cementitious composition according to any preceding claim, wherein the weight ratio of GGBS and finely divided ceramic material in the cement composition may be from 1:1.2 to 1:6.

7. The cementitious composition according to any preceding claim, further comprising an alkali activator.

8. The cementitious composition according to claim 7, wherein the alkali activator comprises a metal hydroxide and / or a metal silicate.

9. The cementitious composition according to either of claims 7 or 8, wherein the activator is present in an amount, based on the total weight of the binder, of from 30 to 60% by weight.

10. The cementitious composition according to any of claims 7 to 9, wherein the alkali dosage (M+) of the composition is from 3 to 15%.

11. The cementitious composition according to any of claims 7 to 10, wherein the alkali modulus (AM) is in the range of from 0.1 to 5.

12. The cementitious composition according to any preceding claim, wherein the finely divided ceramic material is present in an amount up to 30% by weight.

13. The cementitious composition according to any preceding claim, wherein the finely divided ceramic material has a Dso of up to 50 microns.

14. The cementitious composition according to any preceding claim, wherein the finely divided ceramic material has a bi-modal size distribution.

15. A cementitious paste comprising a cementitious composition according to any preceding claim and water.

16. A cured cementitious paste prepared by combining the cementitious composition according to any of claims 1 to 14 with water and allowing the resulting mixture to cure.

17. A mortar composition comprising:an aggregate; anda cementitious composition according to any of claims 1 to 14.

18. The mortar composition according to claim 17, wherein the weight ratio of the aggregate to the cementitious composition is from 8:1 to 1:

819. A cured mortar prepared by combining the mortar composition of either of claims 17 or 18 with water and allowing the resulting mixture to cure.

20. A concrete composition comprising:an aggregate; anda cementitious composition according to any of claims 1 to 14.

21. The concrete composition according to claim 20, wherein the weight ratio of the aggregate to the cementitious composition is from 8:1 to 1:8.

22. A cured concrete prepared by combining the concrete composition according to either of claims 20 or 21 with water and allowing the resulting mixture to cure.

23. An AAB cementitious composition comprising:a finely divided ceramic material; andan activator.

24. A cured cementitious composition prepared by combining the AAB cementitious composition according to claim 23 with water and allowing the resulting mixture to cure.

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