A method for the formation of a hydration product

Abstract

A method for the formation of a hydration product, the method comprising the steps of: Combining one or more ion sources, at least one of the one or more ion sources being in the form of steel slag, with a source of aluminium in the presence of water and gypsum to form the hydration product; and wherein the method is performed in the absence of Portland cement, alkaline activators and alkaline hydraulic supplementary cement mixtures.

Description

A METHOD FOR THE FORMATION OF A HYDRATION PRODUCTTECHNICAL FIELD

[0001] The present invention relates to a method for the formation of a hydration product. The present invention also relates to a method for the formation of a construction material containing gypsum using the hydration product, the method for the formation of the hydration product requiring fewer processing steps than conventional processes.BACKGROUND

[0002] Plasterboard (also referred to as drywall, sheet rock and gyprock) is a panel made of gypsum, with or without additives, typically extruded between thick sheets of facer and backer paper. Plasterboard is used extensively in the construction industry around the world, with 8.4 billion square metres of plasterboard sold worldwide in 2020.

[0003] However, the production of plasterboard is a complicated and energy-intensive process, requiring the heating of gypsum to drive off water to form a hemihydrate, followed by rehydration of the hemihydrate to reform the gypsum in the form of plaster. The plaster is mixed with fibre (typically paper and / or glass fibre), plasticizer, foaming agent, finely ground gypsum crystal or potassium sulphate to act as an accelerator, EDTA, starch or other chelate as a retarder, and various additives that may increase mildew and fire resistance, lower water absorption (wax emulsion or silanes), or reduce creep (tartaric or boric acid).

[0004] The panel is then formed by sandwiching a core of the wet mixture between two sheets of heavy paper or fiberglass mats. When the core sets, it is dried in large drying chambers, and the panel becomes rigid and strong enough for use as a building material.

[0005] The drying of the wet panel is highly energy-intensive, requiring between 1 .85 and 2.63 GJ of energy to dry 93m2of plasterboard, meaning that an energy input of approximately 5.41 GJ per 93m2of plasterboard is required for the entire conventional plasterboard production process. Thus, not only is the process for the manufacture of conventional plasterboard relatively long (both in terms of time taken and the number of steps required), but it also involves high costs, in terms of the equipment required, operating costs and the footprint required for housing plasterboard manufacturing equipment. Further, the production of plasterboard is detrimental to the environment, with each sheet of plasterboard causing the emission of the equivalent of 12kg of CO2 over its lifespan, while decomposing plasterboard can emit hydrogen sulfide, which can cause ground pollution and damage to ecosystems.

[0006] Thus, there would be an advantage if it were possible to provide an alternativeproduct to conventional plasterboard that not only reduced the environmental impacts of plasterboard, but was faster and less expensive to manufacture, both in terms of equipment required and operating costs.

[0007] The production of conventional plasterboard entails the use of a binder formed primarily from gypsum, although some alternative products rely on the use of Portland cement in their manufacture. However, the production and use of Portland cement involves a number of drawbacks, including that, during manufacture of a hydraulic binder using Portland cement, carbon dioxide and salts can react with the binder, reducing the environmental stability of the binder and reducing its performance over a relatively short period of time. Further, the production of Portland cement itself is not environmentally-friendly, with the production of each tonne of Portland cement clinker generates an average of 843kg of carbon dioxide.

[0008] One attempt to mitigate the environmental impacts of Portland cement use is disclosed in PCT patent application no. W02024036360 A1 which provides a hydraulic binder that operates in the absence of Portland cement through a primarily AFt transition system to effectively mine the components of a hydration mixture and convert the AFt to other AFt minerals. This method still requires standard steps such as size reduction and additives such as plasticisers, retarders, and / or accelerators.

[0009] In light of the foregoing, there would also be an advantage if it were possible to provide a hydraulic binder or grout for use in the production of an alternative plasterboard product that avoided the use of Portland cement and avoided the drawbacks (such as high energy usage and carbon dioxide emissions) associated therewith.

[0010] It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.SUMMARY OF INVENTION

[0011] Embodiments of the present invention provide a method for the formation of a hydration product, which may at least partially address one or more of the problems or deficiencies mentioned above or which may provide the public with a useful or commercial choice.

[0012] In a first aspect, the invention resides broadly in a method for the formation of a hydration product, the method comprising the steps of:Combining one or more ion sources, at least one of the one or more ion sources beingin the form of steel slag, with a source of aluminium in the presence of water and gypsum to form the hydration product; and wherein the method is performed in the absence of Portland cement, alkaline activators and alkaline hydraulic supplementary cement mixtures.

[0013] The gypsum may be present in any suitable manner. For instance, the gypsum may be present in the slag. In other embodiments, the gypsum may be present in the source of aluminium. In further embodiments, an ion source containing gypsum may be combined with the slag, the source of aluminium and the water. Thus, in this embodiment of the invention, two ion sources may be combined with the source of aluminium in the presence of water to form the hydration product. In this embodiment, a first ion source may be the slag, while a second ion source may be of any suitable form. Preferably, however, the second ion source may be a source of calcium ions. In a particular embodiment, the second ion source may comprise calcium sulphate.

[0014] In still further embodiments, gypsum may be added during the combining of the components of the hydration product.

[0015] In a preferred embodiment of the invention, the hydration product may be combined with one or more gases and / or one or more vapours to form a foamed hydration product. In an alternative embodiment of the invention, the hydration product may be combined with a source of gypsum in the presence of one or more gases and / or one or more vapours to form a foamed hydration product. The foamed hydration product may be of any suitable form. For instance, the foamed hydration product may be a mixture of gas and liquid, or a mixture of solids, gas and liquid. In a particular embodiment, the foamed hydration product may comprise a gel.

[0016] It will be understood that the term “hydration product" as used herein is defining a product that is the result of chemical action and / or interaction that results from a hydration process. Specifically, this term is applied to describe the hydration of a binder. It will be further understood that the hydration product may be provided in any suitable physical state such as, but not limited to, a crystalline form.

[0017] The terms “binder" and “hydraulic binder” are used throughout to describe a material that functions as a physical joiner between component materials. A binder may be used as a strengthening additive in a hydration product, as it hardens with the addition of water. More generally, the binder is any component that acts to hold or draw other materials together eithermechanically or chemically.

[0018] It will be understood that the term “hydration matrix” as used herein is intended to refer to a product resulting from a hydration reaction between a binder and water, such as a cement grout. The hydration matrix may be of any suitable form, such as, but not limited to, a crystalline form, a gel, a foam, a solid mass or the like.

[0019] Preferably, the hydration product formed by the combination of the at least one ion source and the source of aluminium in the presence of water may be a crystalline hydration product. The crystalline hydration product may provide a microstructure (such as a gel microstructure) for the formation of a hydration matrix when a cementitious phase is hydrated and accompanied by crystal growth. Preferably, the hydration product is present during the formation of the hydration matrix. The hydration matrix may comprise any suitable material, although in some embodiments of the invention, the hydration matrix may comprise a mechanical space filler.

[0020] The term “filler”, “mechanical space filler”, and “space filling matrix” are used herein to describe a component in a matrix that functions to occupy space. The filler may modify the flow and physical properties of the matrix as a whole. For example, air may be considered a type of filler, as it reduces the density of a matrix. As such, air would provide an increase in volume and reduction in physical strength. A filler may be inert or reactive.

[0021] The crystalline hydration product may provide a microstructure for the formation of the hydration matrix. The hydration product may form in voids provided by the hydration matrix, and it is envisaged that the ions present and the volume of water present may impact the formation, composition, and / or morphology of crystal growth within the hydration matrix.

[0022] In some embodiments of the invention, the hydration matrix may comprise a mechanical space filler. It will be understood that this may be advantageous as a mechanical space filler may also provide supplementary ions within voids of the hydration matrix, thus providing localised crystal formation and / or a denser binding material for the formation of a hydration matrix. In a preferred embodiment of the invention, the mechanical space filler may be formed by and / or from a gypsum containing material. Such material may include, but is not limited to, raw gypsum, gypsum in its mineral form (CaSO4.2H2O), material containing gypsum and one or more other minerals and / or phosphogypsum.

[0023] The source of aluminium may be of any suitable form. For instance, the source of aluminium may comprise a single material, or may comprise two or more materials. Preferably, the source of aluminium may be an inorganic material. More preferably, the source of aluminiummay comprise one or more water soluble ionic compounds. The source of aluminium may comprise one or more silicates, oxides, sulphates, sulfides (or other soluble sulphur-containing compounds), hydroxides, carbonates, chlorides or the like, or any suitable combination thereof. Thus, it is envisaged that the aluminium may generate aluminium cations in the presence of the water.

[0024] In some embodiments of the invention, a source of calcium may also be used in the formation of the hydration product. The source of calcium may be of any suitable form. For instance, the source of calcium may comprise a single material, or may comprise two or more materials. Preferably, the source of calcium may be an inorganic material. More preferably, the source of calcium may comprise one or more water soluble ionic compounds. The source of calcium may comprise one or more silicates, oxides, sulphates, sulfides (or other soluble sulphur-containing compounds), hydroxides, bromides, iodides, chlorides, nitrates, acetates or the like, or any suitable combination thereof. Thus, it is envisaged that the source of calcium may generate calcium cations into the presence of the water.

[0025] In some embodiments of the invention, the source of aluminium and the source of calcium may comprise different compounds. Alternatively, the source of aluminium and the source of calcium may be the same compound. In this embodiment, the compound may be of any suitable type, such as, but not limited to, an aluminium calcium silicate, an aluminium calcium oxide, an aluminium calcium halide, an aluminium calcium hydroxide, an aluminium calcium chloride, an aluminium calcium sulfide, an aluminium calcium sulphate or the like, or any suitable combination thereof.

[0026] As previously stated, at least one ion source is in the form of a steel slag. The steel slag may be of any suitable form, although in some embodiments, the steel slag may be produced in an electric arc furnace, a basic oxygen furnace (BOF), and so on.

[0027] In some embodiments of the invention, the steel slag may at least partially comprise gypsum. In these embodiments, it is envisaged that the gypsum present in the slag may act as the source of at least a portion of the ions. Gypsum may be present in any suitable form and any suitable quantity within the slag. For instance, gypsum may be present as raw gypsum, gypsum in its mineral form (CaSO4.2H2O), material containing gypsum and one or more other minerals and / or phosphogypsum. In alternative embodiments, a gypsum containing material may be added to the method. The gypsum containing material may be added at any suitable stage of the method. For instance, the gypsum containing material may be added when the slag, the source of aluminium and water are combined. Alternatively, the gypsum containing material may be added in the presence of the one or more gases and / or the one or more vapoursto form the foamed hydration product.

[0028] In some embodiments, the slag may contain gypsum, and an additional gypsum containing material may be added to the method.

[0029] In some embodiments of the invention, the steel slag may undergo a size reduction process prior to being combined with the source of aluminium and the water. Any suitable size reduction technique may be used, such as, but not limited to, crushing, grinding or the like.

[0030] The slag may be reduced to any suitable particle size. For instance, the average particle size of the slag following the size reduction process may be less than 100mm. In other embodiments of the invention, the average particle size of the slag following the size reduction process may be less than 50mm. In other embodiments of the invention, the average particle size of the slag following the size reduction process may be less than 10mm.

[0031] In some embodiments of the invention, a relatively large quantity of coarse steel slag may be added to increase the quantity of ions made available for the formation of the hydration product. The steel slag may at least partially dissolve or dissociate to provide excess ions for crystallisation and a mechanical space filler within the hydration matrix of the hydration product. Advantageously, this may reduce or eliminate the requirement to add that additional materials to provide a mechanical space filler.

[0032] It is envisaged that at least a portion of the aluminium source and at least a portion of the ions from the ion source and / or the gypsum containing material may be converted to a crystalline phase. In some embodiments of the invention, the ions provided from the ion source and / or the gypsum containing material may allow the formation of the mineral ettringite and / or AFt members of the ettringite Super Group. The at least a portion of the aluminium source and at least a portion of the ions from the ion source and / or the gypsum containing material may be converted into a crystalline phase via a hydration mechanism. It is envisaged the crystalline phase may absorb water, such that the hydration matrix may form at least a portion of the hydration product.

[0033] The term “pore solution” as used herein refers to the free, non-chemically bound water within a cement mixture. The pore solution is typically located within the hydration matrix, and preferably outside chemically bound water in a crystal matrix. As such, it is envisaged that the pore solution volume may be inversely proportional to the degree of hydration. It will be further understood that the pore solution may provide a least a portion of the water used in the formation of the hydration product.

[0034] It is envisaged that a pore solution may form within the hydration matrix. It is envisaged that, during the formation of the hydration product, ions in the pore solution may be depleted. In particular, it is envisaged that the depletion of ions in the pore solution may drive the dissolution of soluble materials in the ion source and / or the gypsum containing material. Specifically, the depletion of the pore solution may draw ions from the ion source and / or the gypsum containing material which were not preferentially soluble. This action negates the solubility restrictions enforced by the solubility product of the ions derived from the ion source.

[0035] It will be understood that the amount of gypsum present will affect the formation of the hydration product, in terms of the rate of formation of the hydration product, the composition of the hydration product and / or the mechanical and chemical properties of the hydration product. Specifically, the concentration of gypsum will be related to the rate of dissolution. As such, if the slag contains no or relatively small quantities of gypsum, adding the gypsum containing material in stoichiometric excess may provide sufficient material to form the hydration product, and generate the mechanical space filler.

[0036] In some embodiments of the invention, a relatively large quantity of gypsum may be added to increase the quantity of ions made available for the formation of the hydration product. It is envisaged that excess ions generated from the gypsum containing material may at least partially dissolve to form ions for crystallisation as well as a mechanical space filler within the hydration matrix of the hydration product. This has the advantage that additional materials need not be added to provide a mechanical space filler, and the slag and / or the gypsum containing material may be used as a source for a plurality of components in the formation of a hydration product.

[0037] Dimensional change within two different materials with different coefficients of expansion may produce internal stress within a contiguous matrix. This may induce a separation from between the two materials forming microcracks and a separation between components within the matrix producing failure pathways. Binders which have a similar coefficient of thermal expansion have fewer microcracks, and therefore have a more competent matrix. Advantageously, excess slag and / or gypsum may provide a filler that is chemically reactive and bound to the matrix materials. This provides a filler with a comparable coefficient of expansion that results in an increase in the overall strength of the of the material when compared to use of an additional filler that lacks chemical interaction.

[0038] In a particular embodiment of the invention, the source of aluminium and / or the source of calcium may comprise a calcium sulphoaluminate (CSA) cement, a calcium sulphoaluminate belite (SAB) cement or a calcium aluminate (CA) cement, or a combinationthereof.

[0039] The steel slag may be combined with the calcium sulphoaluminate cement or the calcium aluminate cement in any suitable proportions. For instance, the proportion of the steel slag in the combined slag and calcium sulphoaluminate cement or calcium aluminate cement may be between 1wt% and 99wt%. More preferably, the proportion of the slag in the combined slag and calcium sulphoaluminate cement or calcium aluminate cement may be between 10wt% and 90wt%. More preferably, the proportion of the slag in the combined slag and calcium sulphoaluminate cement or calcium aluminate cement may be between 25wt% and 75wt%.

[0040] It will be understood that slags such as steel slag are classed as having low reactivity and, in particular, low hydraulic reactivity. However, the reactions occurring in the method of the present invention are typically fast (and considerably faster than those that occur during the hydration of Portland cement) even when the slag is not ground to a relatively small particle size.

[0041] In particular, it is envisaged that the present invention may comprise a sequence of reactions, in which one or more products from a previous reaction may be utilised. Thus, in some embodiments, the sequence of reactions may comprise a stepwise sequence of reactions.

[0042] The sequence of reactions may drive (or be manipulated to drive) a process in which less favourable ions (in terms of their reactivity or crystal-forming properties) may be released or scavenged from the ion source when the body of water becomes low in soluble ions. Thus, phases of the ion source that may have low solubility may be effectively mined from the ion source to produce solute for the formation of other members of a solid solution series.

[0043] In some embodiments, a source of counterions may be combined with the slag, the source of aluminium ions and the water to form the hydration product. Any suitable source of counterions may be used, and the counterion source may release counterions in any suitable manner, such as by dissolving or dissociating in the presence of the water. Preferably, however, the counterion source may comprise one or more water-soluble inorganic compounds. In this embodiment, the counterions may be released into the water by dissociation of the water-soluble inorganic compounds. It will be understood that the exact nature of the counterion source will depend on the counterions that are to be released into the body of water. For instance, if the desired positive counterions comprise sodium, the counterion source may comprise a water- soluble sodium compound (such as a sodium chloride, sodium oxide, sodium sulfate, sodium carbonate, sodium hydroxide or the like, or any suitable combination thereof). In some embodiments, the desired counterions may comprise sodium, potassium, calcium, iron, aluminium, copper, nickel, strontium, chromium, zinc ions or the like, or any suitable combination thereof. In a most preferred embodiment, the counterion source may comprise a source ofcalcium ions. In a specific embodiment of the invention, the counterion source may comprise calcium carbonate (for instance, in the form of limestone). In a preferred embodiment of the invention, a stoichiometric excess of calcium ions may be provided in order to drive the mechanism for the formation of the hydration product.

[0044] As previously stated, gypsum may be added to the hydration product in the presence of one or more gases and / or one or more vapours to form a foamed hydration product. The gypsum may be of any suitable form. It should be noted that, in some publications, the term gypsum is incorrectly and inaccurately used to describe any substance largely composed of calcium sulphate, including but not limited to, the gypsum hemihydrate (CaSC .O.SFW), alpha and beta anhydrites (anhydrous CaSC ), and calcium sulphate dihydrate (CaSO4.2H2O). However, it will be understood that use of the term gypsum in the present application refers only (and technically correctly) to the mineral having the chemical composition CaSC>4.2H2O.

[0045] In some embodiments, the gypsum may be raw gypsum. It will be understood that the term “raw gypsum” is intended to refer to gypsum that has not been chemically treated or artificially heated and has natural origins such as, but not limited to, evaporite deposition or volcanic outgassing. Thus, raw gypsum is gypsum that has not been heated or otherwise chemically treated prior to its use in the method of the present invention.

[0046] In some embodiments of the invention, at least a portion of the gypsum may comprise phosphogypsum.

[0047] In some embodiments of the invention, at least a portion of the gypsum may act as a diluent, and in particular a reactive diluent. It will be understood that the reactive diluent may provide two roles in the mechanism for the formation of a hydration product. Specifically, the reactive diluent may act as both a dilute solution and an active reagent.

[0048] The reactive diluent may comprise at least a portion of the gypsum. It is envisaged that, in this embodiment of the invention, the at least a portion of the gypsum has a solubility product that facilitates hydration.

[0049] In some embodiments, the gypsum comprising the reactive diluent may be a waste product stream containing anhydrous calcium sulphates. The waste product stream may be of any suitable composition, and may be procured from any suitable source. For instance, the waste product stream may comprise fluorogypsum or may be in the form of flue gas desulphurised gypsum. It is envisaged that the gypsum in these forms may have greater solubilities at relatively low temperatures than other forms of gypsum and may therefore function effectively as a reactive diluent.

[0050] Conventionally, gypsum is considered a poor hydration reactant for a reactive diluent. To overcome this limitation, the present invention uses the depletion of the pore solution (and, particularly, the scavenging of ions therefrom) to prevent the solubility product of the gypsum from limiting dissolution, and therefore facilitates continuous dissolution of gypsum.

[0051] It will be further understood that the source of gypsum may determine, at least in part, the solubility of the reactive diluent. This is because gypsum obtained from different mineral deposits and / or suppliers may have slightly different chemical and / or physical properties to one another. Thus, the source of gypsum may also determine, at least in part, the mechanism for the formation of a hydration product. In some embodiments of the invention, the depletion of ions in the pore solution provides sufficient solubility of the source of gypsum to provide a reactive diluent for the mechanism for the formation of a hydration product.

[0052] It is envisaged that the gypsum may undergo a size reduction process prior to its use in the method of the present invention. In particular, it is envisaged that the gypsum may undergo a milling process prior to its use in the method of the present invention. However, it is envisaged that the size reduction process may be undertaken within the gypsum supply chain. Thus, it is envisaged that the gypsum used in the present invention may be obtained in a form that is ready for immediate use in the method without requiring further size reduction.

[0053] In some embodiments, the gypsum may be subjected to a classification process before further use in the formation of a hydration product. Any suitable classification process may be used, although in a preferred embodiment of the invention, the classification process may involve separating the gypsum on the basis of particle size. In this embodiment of the invention, the classification process may comprise a screening process. In a particular embodiment, the starting material may be introduced to a rotary screen to separate relatively small particles from relatively large particles before the gypsum is combined with the hydration product.

[0054] It will be understood that in some embodiments of the invention, the gypsum will not require a classification process prior to its use in the present method.

[0055] While it is envisaged that commercially available gypsum will typically be of a particle size that can be used in the present invention without requiring additional size reduction, if the only gypsum that is commercially available is of a relatively large particle size, a size reduction process could be used.

[0056] It is envisaged that when the gypsum functions as both the ion source and the mechanical space filler for the hydration matrix, no classification process will be required.Furthermore, in some embodiments of the invention, it is envisaged that the classification process may be used to recombine one or more screened particle sizes to form an ideal mixture.

[0057] The combination of the steel slag and the source of aluminium may be performed prior to the addition of the gypsum to form the hydration product. Alternatively, the combination of the slag, the source of aluminium and the gypsum may be performed substantially simultaneously.

[0058] The combination of the steel slag and the source of aluminium may be performed in any suitable vessel. For instance, the combination of the slag and the source of aluminium may be performed in a mixing tank, reactor vessel or the like. Water may be added to the vessel with the slag and the source of aluminium, or the slag and the source of aluminium may be combined prior to the addition of the water.

[0059] Gypsum may be combined with the hydration product in any suitable vessel. For instance, the slag, the source of aluminium and the gypsum may all be added to the same mixing tank, reactor vessel or the like for combination.

[0060] The gypsum used in the present invention may be obtained from two or more more different origins. Further, the gypsum may be a mixture of different particle sizes. For instance, gypsum particles having a first particle size may be combined with gypsum particles of the same particle size from another source, or with gypsum particles of a different particle size from the same source or from a different source.

[0061] The mixing of different gypsum particles may occur at the start of the method of the present invention, or may occur after a process step and / or a period of time.

[0062] The gypsum may be added to the hydration product in any suitable quantity. In a preferred embodiment, the ratio of gypsum to slag in the hydration product may be between approximately 1 :5 and 5: 1. More preferably, the ratio of gypsum to slag in the hydration product may be between approximately 1 :4 and 4:1. Still more preferably, the ratio of gypsum to slag in the hydration product may be between approximately 1 :3 and 3: 1. Yet more preferably, the ratio of gypsum to slag in the hydration product may be between approximately 1 :2 and 2:1. Most preferably, the ratio of gypsum to slag in the hydration product may be approximately 1 :1.

[0063] In one embodiment of the invention the hydration product and gypsum may be separately combined with water and left for a period of time before further processing occurs. In some embodiments of the invention, the period of time may be between one and twenty days. In other embodiments of the invention, the period of time may be relatively insignificant and thehydration product in water and the gypsum in water may be immediately combined. It will be understood that the period of time may depend on commercial requirements. However, it will also be understood that allowing the hydration product and gypsum to be separately combined with water and left for a period of time does not have a detrimental effect on the properties of the final product.

[0064] The combination of the hydration product in water and the gypsum in water may occur using any suitable means. For example, the grout in water and the gypsum in water may be combined using gravitational flow, mechanical mixing, and / or via a transfer mechanism.

[0065] The transfer mechanism may be of any suitable type. In a preferred embodiment, the transfer mechanism may be a pumping mechanism. The pumping mechanism may be of any suitable form, such as one or more pumps. In a preferred embodiment of the invention, the hydration product may be combined with the gypsum in a pump. Any suitable pump may be used, although in a preferred embodiment of the invention, the pump may be a positive displacement pump. Any suitable type of positive displacement pump may be used, although in a specific embodiment of the invention, the positive displacement pump may comprise a progressive cavity pump.

[0066] As previously stated, the gypsum may be combined with the hydration product in the presence of one or more gases and / or one or more vapours. In some embodiments of the invention, the one or more gases and / or one or more vapours may be any suitable gas, but in particular a gas containing nitrogen. Preferably, the one or more gases and / or one or more vapours may be air. In alternative embodiments of the invention, the one or more gases and / or one or more vapours may comprise a mixture of air and steam.

[0067] As previously stated, the gypsum is combined with the hydration product in the presence of one or more gases and / or one or more vapours. The addition of one or more gases and / or one or more vapours may be achieved in any suitable manner. For instance, the one or more gases and / or one or more vapours may be injected or blown into the vessel. Alternatively, the one or more gases and / or one or more vapours may be drawn into the vessel, such as via a Venturi or the like.

[0068] In a particular embodiment of the invention, it is envisaged that the hydration product and the gypsum may be introduced to the pump at a rate that is less than that required to fill the pump. In this way, the one or more gases and / or one or more vapours may be drawn into the pump with the hydration product and the gypsum.

[0069] It is envisaged that the introduction of the one or more gases and / or one or morevapours may result in the formation of a foamed hydration product.

[0070] In a preferred embodiment, a source of calcium sulphate is introduced to the source of aluminium and the ion source in the pump at a rate that draws the one or more gases and / or the one or more vapours into the pump, wherein drawing the one or more gases and / or the one or more vapours into the pump generates the foamed hydration product.

[0071] Preferably, the formation of the foamed hydration product results in the removal of the water (as free water) from the foamed hydration product, and instead the water may be stored in the matrix of the foamed hydration product as hydrate species form. In this way, the hydration product may effectively dehydrate (or dry) through the use of free water to form hydrate reaction products. Thus, it is envisaged that the foamed hydration product may dry and harden under ambient conditions (i.e., without requiring external heating, such as in an oven or kiln).

[0072] The term “dehydration” and its variants are used herein to describe the reduction of water via a chemical reaction or chemical change process. By way of example, the dehydration of the hydration product may involve a chemical change process of gypsum (CaSO4.2H2O) to an anhydrite (CaSC ). However, it will be appreciated that the process represents a reduction in the presence of free water in the hydration product.

[0073] As previously stated, the present invention is performed in the absence of Portland cement, alkaline activators and alkaline supplementary hydraulic cement mixtures. The present invention may also be performed in the absence of any other material that functions as a replacement for Portland cement. The term supplementary hydraulic cement mixture refers to soluble siliceous, aluminosiliceous or calcium aluminosiliceous powders used as partial replacements of clinker in cements, or as partial replacements of Portland cement in concrete mixtures.

[0074] The drawbacks associated with the use of Portland cement, alkaline activators and alkaline supplementary hydraulic cement mixtures have been discussed elsewhere in the present specification, and it will be understood that the applicant considers the use or presence of Portland cement, alkaline activators and alkaline supplementary hydraulic cement mixtures in the present method to be not just undesirable, but detrimental to the efficiency and effectiveness of the invention. Specifically, any hydration product that may be produced by the method of the present invention that uses Portland cement, alkaline activators and alkaline supplementary hydraulic cement mixtures, or in which these materials are present, will not have the advantageous properties of the present invention, including the reduction in CO2 generation, improved mechanical strength of the hydration product, decreased production time, decreased time to reach final strength and so on.

[0075] In some embodiments of the invention, the method may be conducted in the absence of acids or pH activators having a relatively low pH.

[0076] The foamed hydration product may be discharged from the pump for use or for further processing. It is envisaged that the foamed hydration product may be used for any suitable purpose. For instance, the foamed hydration product may be used as a construction material. The construction material may be of any suitable form, and may include a settable material (such as a cement, binder, filler or the like). Alternatively, the foamed hydration product may be used to form a construction product.

[0077] In other embodiments of the invention, the foamed hydration product may be subject to one or more treatment steps in order to form a construction product. The one or more treatment steps may be of any suitable form. However, in a preferred embodiment of the invention, the foamed hydration product may be cast (for instance, in a mould) in order to form a construction product. The construction product formed in this manner may be of any suitable size, shape or configuration, and may comprise a building element (such as a building block, brick, panel, board or the like).

[0078] In other embodiments, the foamed hydration product may be subject to a forming process (such as rolling, extrusion, pultrusion or the like) in order to form a construction product.

[0079] Preferably, the foamed hydration product may be used in the formation of a construction product in the form of a panel or board. The panel or board may be used for any suitable purpose. For instance, the panel or board may be used as a structural element (such as for a wall, ceiling, fence or the like). Alternatively, the panel or board may be used as cladding or sheeting material. In some embodiments of the invention, the construction product may be used as a replacement for, or alternative to, conventional plasterboard or cement sheeting.

[0080] In this embodiment, it is envisaged that the foamed hydration product may be cast or rolled into an elongate panel shape. Preferably, the elongate panel shape comprises a first face and a second face on an opposed side thereof. Sheet material may be added to the first face and / or the second face. The sheet material may be of any suitable form, and may comprise paper, cardboard, plastic or the like. Thus, in this embodiment, it is envisaged that the foamed hydration product may form the core of the construction product.

[0081] The construction product may be cut to any suitable shape or size, and it will be understood that the size to which the construction product is cut will be dependent on the purpose for which it is to used.

[0082] The applicant has found that the construction product of the present invention has numerous advantages over conventional plasterboard or cement sheeting. Specifically, the construction product of the present invention is substantially waterproof or at least has water- resistant properties, making it suitable for use outdoors. Further, the construction product of the present invention has relatively high heat- and fire-resistant properties. Thus, when used in the construction of a building, the construction product provides the building with improved fire- resistant properties in comparison to conventional plasterboard or cement sheeting. In addition, the construction product may be used in the construction of firebreak walls, for instance in areas experiencing significant bushfire risks.

[0083] The present invention provides an alternative mechanism to form a foamed hydration product from various starting materials. To overcome the deficiencies of the current hydration mechanisms, a low solubility sulphate source may act as a counterion source in hydration process. As such, this allows for previously underutilised and / or burdensome waste products to be incorporated into a commercially viable product in an environmentally friendly manner. Thus, it should be well understood that the present invention describes a method which may be used to produce a range of materials from various waste products and / or resources. As an example of a preferred embodiment of the invention, a method for the production of a construction product that provides an alternative to conventional plasterboard or cement sheeting has been described.

[0084] In a second aspect, the invention resides broadly in a method for the production of a construction product comprising:Introducing a material containing gypsum to a mixing process in the presence of steel slag, a source of aluminium, and water;Introducing one or more gases and / or one or more vapours to the mixing process to form a foamed hydration product, wherein the formation of the foamed hydration product is performed in the absence of Portland cement, alkaline activators and alkaline supplementary hydraulic cement mixtures;At least partially dehydrating the foamed hydration product under ambient conditions through the formation of hydrates to form a dehydrated hydration product; andForming the construction product from the dehydrated hydration product.

[0085] The material containing gypsum may be of any suitable form. For instance, gypsum may be present as raw gypsum, gypsum in its mineral form (CaSO4.2H2O), material containinggypsum and / or one or more other minerals.

[0086] In some embodiments, the material containing gypsum may comprise phosphogypsum. In a preferred embodiment the phosphogypsum may be a calcium sulphate dihydrate (CaSO4.2H2O) waste product from the manufacture of fertiliser.

[0087] Phosphogypsum is a hazardous by-product of the phosphate industry that is challenging to safely dispose of or store. Processing phosphogypsum according to the present invention provides an avenue to utilise a raw waste product for economic return and environmental benefit.

[0088] It is envisaged that the material containing gypsum may undergo a size reduction process prior to its use in the method of the present invention. In particular, it is envisaged that the material containing gypsum may undergo a milling process prior to its use in the method of the present invention. However, it is envisaged that the size reduction process may be undertaken within the gypsum supply chain. Thus, it is envisaged that the material containing gypsum used in the present invention may be obtained in a form that is ready for immediate use in the method without requiring further size reduction.

[0089] In some embodiments, the material containing gypsum may be subjected to a classification process before being introduced to the mixing process. Any suitable classification process may be used, although in a preferred embodiment of the invention, the classification process may involve separating the material containing gypsum on the basis of particle size, density or the like. In a preferred embodiment of the invention, the classification process may comprise a screening process. In a particular embodiment, the material containing gypsum may be introduced to a rotary screen to separate larger particles before the material containing gypsum is introduced to the mixing process.

[0090] Preferably, the particle size of the material containing gypsum used in the present method is between 2000pm and 5pm. More preferably the particle size is less than 500pm.

[0091] In a preferred embodiment, no pretreatment of the material containing gypsum may occur prior to use in the method of the present invention. This is a significant advantage over conventional plasterboard manufacturing processes, which require both grinding and calcination of gypsum. Thus, the present invention significantly reduces energy and infrastructure expenditure in comparison to conventional plasterboard manufacturing processes.

[0092] It is envisaged, however, that while commercially available material containing gypsum will typically be of a particle size that can be used in the present invention withoutrequiring additional size reduction, it is envisaged that, if the only material containing gypsum that is commercially available is of a relatively large particle size, a size reduction process could be used.

[0093] The mixing process may be performed in any suitable vessel. Preferably, however, the mixing process may be performed in a mixing vessel, or agitated vessel. The vessel may be of any suitable size, shape or configuration, and may comprise a tank, vat, reactor or the like. In some embodiments, the vessel may be substantially circular in shape to facilitate circulation of the materials therewithin.

[0094] As previously stated, the vessel may be agitated. Agitation of the vessel may be achieved using any suitable technique, such as one or more impellers, recirculating pumps or the like, or any suitable combination thereof.

[0095] The vessel may be an open vessel or a closed vessel. However, in a preferred embodiment of the invention, the vessel may be an open vessel to facilitate the formation of foam.

[0096] The vessel may be of any suitable volume, and it will be understood that the exact volume of the vessel may be dependent on the desired throughput for the method and the availability of the materials used in the method. Thus, the volume of the vessel may vary depending on these factors, or may be scaled upwardly or downwardly according to the availability of the materials and so on.

[0097] As previously stated, steel slag is present in the mixing process. In a specific embodiment, the steel slag may be produced in a steel manufacturing process, such as steel slag produced in an electric arc furnace and / or a basic oxygen furnace (BOF).

[0098] In some embodiments of the invention, the gypsum may provide both a source of ions and a mechanical space filler within the hydration matrix.

[0099] In some embodiments of the invention, botryoidal anhydrite may be present in the foamed hydration product. The botryoidal anhydrite may originate in any suitable component of the foamed hydration product. However, in a preferred embodiment, the botryoidal anhydrite may be present as a result of a transition between different forms of minerals in the formation of the hydration product. Preferably, the botryoidal anhydrate forms part of the hydration matrix. Preferably, the botryoidal anhydrate is substantially excluded from further transitions due to the lack of pore water (as a result of to dehydration) and relative mineral stabilities.

[0100] In some embodiments of the invention, the slag may undergo a size reductionprocess prior to being introduced to the vessel. Any suitable size reduction technique may be used, such as, but not limited to, crushing, grinding or the like.

[0101] The steel slag may be reduced to any suitable particle size. For instance, the average particle size of the slag following the size reduction process may be less than 5000 pm. In other embodiments of the invention, the average particle size of the slag following the size reduction process may be less than 500pm. In other embodiments of the invention, the average particle size of the slag following the size reduction process may be less than 50pm.

[0102] Preferably, the slag may be combined with a calcium sulphoaluminate cement or a calcium aluminate cement prior to being introduced to the reaction vessel. The calcium sulphoaluminate cement or a calcium aluminate cement may comprise the source of aluminium, or may be introduced to the mixing process as an additional component.

[0103] The slag may be subject to a size reduction process prior to being combined with the calcium sulphoaluminate cement or the calcium aluminate cement prior to being introduced to the reaction vessel.

[0104] The slag may be combined with the calcium sulphoaluminate cement or the calcium aluminate cement in any suitable proportions. For instance, the proportion of the slag in the combined slag and calcium sulphoaluminate cement or calcium aluminate cement may be between 0% and 90%.

[0105] The slag may be combined with the material containing gypsum in any suitable proportions. For instance, the ratio of the slag to the material containing gypsum in the mixing process may be between approximately 1 :10 and 10:1. More preferably, the ratio of the slag to the material containing gypsum in the mixing process may be between approximately 1 :5 and 5:1. Still more preferably, the ratio of the slag to the material containing gypsum in the mixing process may be between approximately 1:2.5 and 2.5:1. Most preferably, the ratio of the slag to the material containing gypsum in the mixing process may be approximately 1 :1.

[0106] In some embodiments of the invention, one or more additional components may be introduced to the mixing process. Any suitable additional components may be introduced, such as, but not limited to, an alkaline material. In some embodiments of the invention, the alkaline material may comprise a carbonate anion source. In a specific embodiment, the alkaline material may comprise limestone.

[0107] In some embodiments of the invention, the one or more additional components may comprise an admixture. In some embodiments of the invention, the admixture may comprise amaterial to enhance one or more characteristics (such as strength, durability etc.) of the hydration product. In a specific embodiment, the admixture may comprise one or more of the following: calcium carbonate, aluminium hydroxide, silica, ash, magnesium hydroxide, and the like.

[0108] In some embodiments of the invention, the one or more additional components may comprise a calcium sulphoaluminate (CSA) source. In some embodiments of the invention, the CSA source may comprise a CSA containing a proportion of belite within the clinker. In a specific embodiment, the CSA source may comprise a CSA clinker derived from ye’elimite.

[0109] The source of aluminium may be of any suitable form. For instance, the source of aluminium may comprise a single material, or may comprise two or more materials. Preferably, the source of aluminium may be an inorganic material. More preferably, the source of aluminium may comprise one or more water soluble ionic compounds. The source of aluminium may comprise one or more silicates, oxides, sulphates, sulfides (or other soluble sulphur-containing compounds), hydroxides, carbonates, chlorides or the like, or any suitable combination thereof. Thus, it is envisaged that the aluminium may generate aluminium cations in the presence of the water.

[0110] In some embodiments of the invention the material containing gypsum, the slag and the source of aluminium may be combined with one or more additional components to form a mixture. The material containing gypsum, the slag, the source of aluminium and the one or more additional components may be combined using any suitable device. In some embodiments, the material containing gypsum, the slag, the source of aluminium and the one more additional components may be combined in a mixing vessel, a pump, and so on to form the mixture. In a preferred embodiment of the invention, the mixture may be combined in a progressive cavity stator pump.

[0111] In some embodiments of the invention the mixture may be combined with a controlled volume of water such that the rate of addition of the water may be less than the rate required to refill the pump.

[0112] By controlling the volume of water available to the mixture, one or more gases and / or one or more vapours may be introduced to the mixture, thereby forming a foamed hydration product. In some embodiments, the degree of aeration may be modified to modify the structural properties of the foamed hydration product.

[0113] As previously stated, the foamed hydration product may be at least partially dehydrated. It will be understood that the term “dehydrating” refers to the removal of water fromthe foamed hydration product. The removal of water may be achieved using any suitable technique, such as evaporation of water from the foamed hydration product. More preferably, at least a portion of the water in the foamed hydration product may be dehydrated through the formation of hydrates. Thus, rather than losing hydrogen and oxygen atoms being removed from the foamed hydration product, the removal of water (as free water) from the foamed hydration product may be in the form of storing water in the matrix of the foamed hydration product as hydrate species form. In this way, the foamed hydration product may effectively dry (or dehydrate) through the use of free water in the mixture to form hydrate reaction products. Thus, it is envisaged that the foamed hydration product may dry and harden without requiring an external heating source (such as in an oven, kiln, furnace, or even sunlight).

[0114] It is envisaged that the dehydration of the foamed hydration product through the formation of hydrates may occur relatively quickly. For example, it is envisaged that the dehydration of the foamed hydration product may take no more than 30 minutes. More preferably, the dehydration of the foamed hydration product may take no more than 20 minutes. Yet more preferably, the dehydration of the foamed hydration product may take no more than 10 minutes. Thus, the dehydration of the foamed hydration product through the formation of hydrates occurs significantly faster than the drying of conventional plasterboard, and requires significantly less energy to achieve.

[0115] Specifically, it is envisaged that the dehydrating of the foamed hydration product may be performed at ambient conditions. It will be understood that the term “ambient conditions” refers generally to room temperature and atmospheric pressure. More specifically, the term “ambient conditions” is intended to mean that no artificial external heat source (such as a kiln, oven, furnace, heat lamps or the like) is used to achieve the dehydrating of the foamed hydration product.

[0116] Any suitable portion of water in the foamed hydration product may be removed though the dehydrating process. In a preferred embodiment of the invention, at least 50% of the water in the foamed hydration product may be removed though the dehydrating process. More preferably, at least 60% of the water in the foamed hydration product may be removed though the dehydrating process. More preferably, at least 70% of the water in the foamed hydration product may be removed though the dehydrating process. More preferably, at least 80% of the water in the foamed hydration product may be removed though the dehydrating process. More preferably, at least 90% of the water in the foamed hydration product may be removed though the dehydrating process.

[0117] This represents a significant advantage over the prior art in which energy-intensivesources of heat (such as ovens or kilns) are required to dewater the product. The ability to at least partially dewater the foamed hydration product at ambient conditions reflects a significant saving (both in equipment and operational costs) over conventional process requiring the provision of an artificial external heat source. In addition, the continued process of hydrate formation within the foamed hydration product represents a reduction in CO2 emissions in comparison to conventional processes.

[0118] The dehydrating of the foamed hydration product may be conducted for any suitable period of time. In a preferred embodiment of the invention, however, the dehydrating of the foamed hydration product may be a relatively short process. In some embodiments, the dehydrating of the foamed hydration product may occur in the time taken between the formation of the foamed hydration product and conveying the foamed hydration product to the step of forming the construction product from the dehydrated hydration product.

[0119] As previously stated, the method comprises the step of forming the construction product from the dehydrated hydration product. Any suitable forming process may be used, such as, but not limited to, moulding, extrusion, pultrusion, casting, and the like, or any suitable combination thereof.

[0120] In a preferred embodiment, the construction product may be formed using a casting process. Any suitable casting process may be used, although in some embodiments the casting process may comprise strand casting. In a preferred embodiment, the foamed hydration product may undergo a continuous casting process.

[0121] In some embodiments of the invention, the construction product may comprise a board or panel. In particular, the construction product may be in the form of plasterboard, or a product of a similar nature. In these embodiments, the formation of the construction product may comprise more than the formation of the construction product from the foamed hydration product. For instance, one or more surface covering layers may be provided on the foamed hydration product to form the construction product.

[0122] In embodiments of the invention in which the construction product comprises a board or panel, one or more surface covering layers may be applied to an external surface of the construction product. The one or more surface covering layers may be of any suitable form, and may comprise a film, mesh or similar material. The surface covering layers may be in the form of a cementitious material, a polymeric material, a cellulosic material, a glass or fibreglass material or any suitable combination thereof. In a preferred embodiment, the one or more surface coating layers may comprise a cellulosic material in the form of paper, cardboard or the like. In a preferred embodiment, the cellulosic material may be applied to opposed faces of theconstruction product. Preferably, the application of the cellulosic material forms a construction product suitable for curing.

[0123] The formation of the construction product is advantageous in that it benefits the environment through the use of gypsum and slag, thereby reducing the amount of these materials sent to landfill.

[0124] Advantageously, the present invention does not require the materials into the mixing process to be soluble, finely ground, externally heated, or produce an insoluble final product, as required in the formation of conventional hydration products.

[0125] The present invention provides further advantages in that the materials introduced to the mixing process may be any low solubility sulphate source, such as mineral gypsum deposits, or phosphogypsum. In doing so, the present invention provides a useful commercial product and environmental benefits.

[0126] The hydration product or construction product of the present invention provide structural advantages in strength and density whilst also having low environmental impact and reduced energy consumption costs due to an absence of heat processing, calcination, and / or drying.

[0127] It will be understood that the hydration product may be formed in response to the volume of raw material provided and the concentration of the solution may not be impacted by the proportion of raw material present. This is due to the low solubility product of the raw material providing a rate of consumption greater than the available supply.

[0128] It will be understood that the rate of formation of the hydration product will only be limited by the solubility product of the ions required for the hydration process.

[0129] It will be understood that the term ettringite is used to refer to the mineral ettringite and not another AFt mineral or solid solution end member of the ettringite Super Group.

[0130] Ettringite mineral is often utilised in grouts that allow for bulk precipitation of the highly exothermic ettringite mineral hydration product. The ettringite mineral hydration product is a compressible solid formed rapidly after mixing. This process can lead to grout separation and cracking if the raw material is poorly selected and unable to adequately sequester the water present.

[0131] When a lower water ratio is used, the dehydration of the system forces rapid deposition of calcium aluminate monosulphate (SCaO A^Os CaSC ^FW) instead of the targetettringite mineral. This calcium aluminate monosulphate will convert to ettringite when exposed to environmental water, this causes expansive disruption and limits the industrial applicability of the grout.

[0132] While it is well known that the mineral ettringite may be used in the commercial formation of grouts, a multitude of minerals belonging to the ettringite super group may also be utilised through manipulating the presence of ions to preferentially form the less common super group minerals.

[0133] Notably, the stabilities of the other ettringite super group members may be superior for grout and / or plaster formation when compared to the mineral ettringite as they are environmentally stable and resist decomposition, thus eliminating expansive deformation. The grouts formed via this mechanism are mineralogically different to Portland cement in that the hydration products are substantially AFt end members and their solid solutions of the ettringite super group.

[0134] As the mechanism is dependent on the presence of ions, it will be understood that the composition of the minerals present will be variable and often hybrids of many different minerals as consequence of scavenging available ions from the pore solution.

[0135] It will be understood the scavenging of ions from the pore solution will be influenced by the limited solubility of the raw starting materials.

[0136] In some embodiments of the invention the solid solution end members of the ettringite super group will contain borate ions in their crystal structures. These minerals may include, but are not limited to, Charlesite, Hielscherite, Sturmanite, and / or Buryatite.

[0137] It will be understood that any mineral of the ettringite super group may be formed in the hydration process, but in a preferred embodiment of the invention the mineral formed will be of a similar space group to the ettringite mineral.

[0138] In some embodiments of the invention, the formation of a hydration product is used in the production of plasterboard.

[0139] In a third aspect, the invention resides broadly in a hydration product produced according to the method of the first aspect.

[0140] In a fourth aspect, the invention resides broadly in a construction product formed according to the method of the second aspect.

[0141] In a fifth aspect, the invention resides broadly in a foamed hydration product formed according to the method of the present invention.

[0142] In a sixth aspect the invention resides broadly in a hydraulic binder for use as a construction material, the hydraulic binder comprising:Between approximately 10 wt% and 70 wt% steel slag;Between approximately 1 wt% and 50 wt% of a calcium sulphoaluminate (CSA) cement, a calcium sulphoaluminate belite (SAB) cement and / or a calcium aluminate (CA) cement; andBetween approximately 10 wt% and 95 wt% gypsum;Wherein the hydraulic binder is produced in the absence of Portland cement, alkaline activators and alkaline supplementary hydraulic cement mixtures.

[0143] As stated, the hydraulic binder comprises between approximately 10 wt% and 70 wt% steel slag. More preferably, the hydraulic binder comprises between approximately 20 wt% and 60 wt% steel slag. More preferably, the hydraulic binder comprises between approximately 30 wt% and 50 wt% steel slag. Most preferably, the hydraulic binder comprises about 40 wt% steel slag.

[0144] As stated, the hydraulic binder comprises between approximately 1 wt% and 50 wt% of a calcium sulphoaluminate (CSA) cement, a calcium sulphoaluminate belite (SAB) cement and / or a calcium aluminate (CA) cement. More preferably, the hydraulic binder comprises between approximately 5 wt% and 35 wt% of a calcium sulphoaluminate (CSA) cement, a calcium sulphoaluminate belite (SAB) cement and / or a calcium aluminate (CA) cement. More preferably, the hydraulic binder comprises between approximately 10 wt% and 20 wt% of a calcium sulphoaluminate (CSA) cement, a calcium sulphoaluminate belite (SAB) cement and / or a calcium aluminate (CA) cement. Most preferably, the hydraulic binder comprises about 15 wt% of a calcium sulphoaluminate (CSA) cement, a calcium sulphoaluminate belite (SAB) cement and / or a calcium aluminate (CA) cement

[0145] As stated, the hydraulic binder comprises between approximately 10 wt% and 95 wt% gypsum. More preferably, the hydraulic binder comprises between approximately 20 wt% and 75 wt% gypsum. More preferably, the hydraulic binder comprises between approximately 30 wt% and 55 wt% gypsum. Most preferably, the hydraulic binder comprises about 45 wt% gypsum.

[0146] In a preferred embodiment, the hydraulic binder may be produced using the method of the first aspect of the invention.

[0147] Advantageously, unlike any other hydration product formation methods, the present method does not include a typical “drying” step when used for forming a construction material. This is due to “self-drying” provided by the continual formation of hydrates that dehydrates the material of any water that may be present.

[0148] Specifically, the formation of the hydration product according to the present methods results in the removal of the water (as free water) from the hydration product, and instead the water may be stored in the matrix of the hydration product as hydrate species form. In this way, the hydration product may effectively dry (or dehydrate) through the use of free water in the mixture to form hydrate reaction products. Thus, it is envisaged that the hydration product may dry and harden without requiring external heating, such as that provided by an oven or kiln, or from extensive evaporation time.

[0149] Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention.

[0150] The reference to any prior art in this specification is not, and should not be taken as an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge.BRIEF DESCRIPTION OF DRAWINGS

[0151] Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of Invention in any way. The Detailed Description will make reference to a number of drawings as follows:

[0152] Figure 1 illustrates a prior art method for the production of conventional plasterboard.

[0153] Figure 2 illustrates a method for the production of a construction product according to an embodiment of the present invention.

[0154] Figure 3 illustrates a comparison of the prior art method illustrated in Figure 1 with the method of the present invention illustrated in Figure 2.DETAILED DESCRIPTION

[0155] Figure 1 illustrates a prior art method 10 for the production of conventional plasterboard. It may be seen that the method 10 is very laborious, involving a large number of steps. In particular, the method 10 comprises two energy intensive processes 11, 12 that are essential for the production of conventional plasterboard.

[0156] The first of the energy intensive processes 11 involves the preparation of gypsum for use in the manufacturing process. In particular, quarried and milled gypsum must undergo a further size reduction process in the form of a grinding process 13. The ground gypsum is then calcined 14 and dehydrated 15 to form plaster. The plaster must then be ground 16 before it can be used to form the plasterboard.

[0157] Not only do these process steps (grinding, calcining and dehydrating) involve the use of large amounts of energy (which increases the cost of the process), they require a large process footprint and the use of specialised equipment. Furthermore, the step of calcining 14 the gypsum produces carbon dioxide 17 which is an environmental pollutant.

[0158] The second of the energy intensive processes 12 occurs when the wet plasterboard has been cast and cut to size. Wet plasterboard must then be dried 18 in drying ovens 19 to remove water 20 from the plasterboard. This has the effect of reducing the size of the plasterboard, making it difficult to ensure precise consistency of size and properties between plasterboard panels.

[0159] Figure 2 illustrates a method 21 for the production of a construction product according to an embodiment of the present invention.

[0160] In this embodiment, a source of gypsum 22 undergoes a particle size reduction process in the form of a grinding process 23. The grinding process 23 need not form part of the method, as the gypsum for the method may be obtained in ground form.

[0161] Gypsum 26 from the grinding process 23 is combined with BOF steel slag 24 and a source of aluminium 25 in the form of CSA. In the embodiment of the invention illustrated in Figure 2, both the slag 24 and the CSA 25 are combined with limestone. The limestone acts as a counterion source in the method, and in particular a source of calcium ions.

[0162] The slag 24, CSA 25 and gypsum 26 are combined in a mixing vessel 30 in the form of a pump. Gas in the form of air 27 and water 28 are also added to the mixing vessel 30 along with an admixture 29 of calcium carbonate, aluminium hydroxide, silica, ash and magnesium hydroxide.

[0163] In the embodiment of the invention illustrated in Figure 2, the mixing vessel 30 is aprogressive cavity stator pump. The mixing vessel 30 is operated so that the addition of the slag 24, gypsum 26 and CSA 25 is performed at a rate that induces the flow of air 28 and water 27 into the mixing vessel 30. By introducing air 28 into the mixing vessel, a foamed hydration product 31 is formed, the foamed hydration product 31 being in the form of a gel.

[0164] The foamed hydration product 31 that exits the mixing vessel 30 is transferred to a continuous casting process 32. The foamed hydration product 31 is cast onto a conveyor 33 in the form of a panel or board, and sheet material in the form of paper 34 is applied to opposed faces of the cast foamed hydration product 38.

[0165] While on the conveyor 33, the cast foamed hydration product 38 undergoes a dehydration process. Importantly, the dehydration process takes place under ambient conditions (i.e., room temperature and atmospheric pressure) meaning that no artificial heat source (such as drying ovens) is required to dehydrate the cast foamed hydration product 38.

[0166] More specifically, the dehydration of the cast foamed hydration product 38 is achieved through the conversion of water within the cast foamed hydration product 38 to hydrates. In this way, free water is removed from the cast foamed hydration product 38 by converting the hydrogen and oxygen atoms from the water into hydrates. Not only does this serve to at least partially dehydrate (dry) the cast foamed hydration product 38 without the need for an artificial heat source, but it also hardens the cast foamed hydration product 38, providing the cast foamed hydration product 38 with improved mechanical properties in a much shorter period of time than conventional plasterboard.

[0167] After the paper 34 is applied to the cast foamed hydration product 38, the cast foamed hydration product 38 is cut 35 to a desired size and then trimmed 36 to produce the construction product 37.

[0168] Figure 3 illustrates a comparison of the prior art method illustrated in Figure 1 with the method of the present invention illustrated in Figure 2. In this Figure, the steps of the method of Figure 1 are reproduced, with the steps eliminated by the present invention (as illustrated in Figure 2) marked with crosses.

[0169] In particular, it will be noted that the energy intensive processes 11 , 12 identified in Figure 1 have been entirely eliminated by the present invention. As previously stated, the energy intensive processes 11 , 12 of a conventional plasterboard manufacturing process represent significant costs, both in terms of energy costs associated with grinding, calcining and drying, but also requires the purchase and maintenance of a significant amount of specialised equipment (grinding mills, calcining kilns, drying ovens, etc.). Thus, by eliminating these processsteps, the present invention provides significant advantages over the prior art in terms of the cost of producing the construction product, as well as a reduction in the time taken to produce the construction product.

[0170] Further, the conventional plasterboard manufacturing process generates a significant quantity of carbon dioxide 17 through the calcining process. By eliminating the need to calcine the gypsum, the quantity of carbon dioxide produced by the present invention is significantly reduced in comparison to the conventional process.

[0171] Further, it will be noted that the conventional plasterboard manufacturing process requires a waiting time for the production of gel 39 in the cast plasterboard before it can be cut to size and dried. This means that longer conveyors are required, increasing the cost, time and overall footprint of the plasterboard manufacturing process.

[0172] By contrast, the present invention eliminates the requirement to wait for the formation of a gel in the cast foamed hydration product, meaning that the method of the present invention is faster than the conventional process.

[0173] In the present specification and claims (if any), the word ‘comprising’ and its derivatives including ‘comprises’ and ‘comprise’ include each of the stated integers but does not exclude the inclusion of one or more further integers.

[0174] Reference throughout this specification to ‘one embodiment’ or ‘an embodiment’ means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases ‘in one embodiment’ or ‘in an embodiment’ in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

[0175] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.

Claims

CLAIMS1. A method for the formation of a hydration product, the method comprising the steps of:Combining one or more ion sources, at least one of the one or more ion sources being in the form of steel slag, with a source of aluminium in the presence of water and gypsum to form the hydration product; and wherein the method is performed in the absence of Portland cement, alkaline activators and alkaline hydraulic supplementary cement mixtures.

2. The method of claim 1 wherein the hydration product is combined with one or more gases and / or one or more vapours to form a foamed hydration product.

3. The method of claim 1 or claim 2 wherein the gypsum is present in the steel lag and / or the source of aluminium.

4. The method according to any one of the preceding claims wherein the gypsum is present in a second ion source.

5. The method according to claim 4 wherein the second ion source comprises calcium sulphate.

6. The method according to claim 5 wherein the calcium sulphate acts as a mechanical space filler.

7. The method according to any one of the preceding claims wherein the hydration product is a crystalline hydration product.

8. The method according to claim 7 wherein the crystalline hydration product provides a microstructure for the formation of a hydration matrix.

9. The method according to claim 8 wherein the crystalline hydration product provides a microstructure for the formation of a hydration matrix when a cementitious phase is hydrated and accompanied by crystal growth.

10. The method according to any one of the preceding claims wherein the source of aluminium comprises a calcium sulphoaluminate (CSA) cement or a calcium aluminate cement.11 . The method according to any one of the preceding ciaims wherein combining the one or more ion sources and the source of aluminium in the presence of the water and gypsum generates a pore solution.

12. The method according to claim 11 wherein the pore solution is depleted of ions during the formation of the hydration product.

13. The method according to claim 12 wherein ions from the one or more ion sources and / or the source of aluminium replace depleted ions in the pore solution.

14. The method according to any of the preceding claims wherein the gypsum is in the form of one or more of raw gypsum, gypsum in its mineral form (CaSO4.2H2O), a material containing gypsum and one or more other minerals, and / or phosphogypsum.

15. The method according to any of the preceding claims wherein the steel slag undergoes a size reduction process prior to being combined with the source of aluminium and the water.

16. The method according to claim 15 wherein the size reduction process reduces the steel slag to a particle size of less than 10mm.

17. The method according to any of the preceding claims wherein the steel slag comprises between 25wt% and 75wt% of the steel slag and the source of aluminium when combined.

18. The method according to any of the preceding claims wherein the formation of a hydration product comprises a stepwise sequence of reactions.

19. The method according to any of the preceding claims wherein a source of counterions may be combined with the slag, the source of aluminium, the gypsum and the water to form the hydration product.

20. The method according to claim 19 wherein the source of counterions includes one or more water soluble inorganic cations.

21. The method according to claim 19 or claim 20 wherein the source of counterions generates a stoichiometric excess of calcium ions.

22. The method according to any of the preceding claims wherein the gypsum is obtained from two or more different origins and / or is a mixture of different particle sizes.

23. The method according to any of the preceding claims wherein the ratio of gypsum to steel slag in the hydration product is between 1 :2 and 2:1.

24. The method according to claim 2 wherein the one or more gases and / or the one or more vapours include nitrogen.

25. The method according to claim 2 wherein the one or more gases and / or the one or more vapours comprise air.

26. The method according to claim 25 wherein the one or more gases and / or the one or more vapours comprise air and steam.

27. The method according to claim 2 wherein the one or more ion sources and the source of aluminium in a pump at a rate that draws the one or more gases and / or the one or more vapours into the pump.

28. The method according to claim 27 wherein drawing the one or more gases and / or the one or more vapours into the pump generates the foamed hydration product.

29. The method according to claim 2 wherein the foamed hydration product undergoes a casting process.

30. The method according to claim 29 wherein the foamed hydration product undergoes a continuous casting process.

31. The method according to claim 29 or claim 30 wherein, during the casting process, a sheet material is added to a first face and / or an opposed second face of the foamed hydration product to form a construction product.

32. The method according to claim 31 wherein the construction product is in the form of a panel or board.

33. The method according to any one of claims 30 to 32 wherein the foamed hydration product dries and hardens under ambient conditions during the casting process.

34. The method according to any of claims 30 to 33 wherein hydrates continue to form in the foamed hydration product during the casting process.

35. A hydration product generated according to the method of claim 1.

36. A foamed hydration product generated according to the method of claim 2.

37. A method for the production of a construction product comprising:Introducing a material containing gypsum to a mixing process in the presence of steel slag, a source of aluminium, and water;Introducing one or more gases and / or one or more vapours to the mixing process to form a foamed hydration product, wherein the formation of the foamed hydration product is performed in the absence of Portland cement, alkaline activators and alkaline supplementary hydraulic cement mixtures;At least partially dehydrating the foamed hydration product under ambient conditions through the formation of hydrates to form a dehydrated hydration product; andForming the construction product from the dehydrated hydration product.

38. The method according to claim 37 wherein the construction product is formed by casting the foamed hydration product.

39. The method according to claim 37 or 38 wherein the construction product comprises a board or panel.

40. The method according to claim 39 wherein one or more surface coating layers are applied to an external surface of the construction product.41 . The method according to claim 40 wherein the one or more surface coating layers comprise a cellulosic material.

42. The method according to claim 40 or 41 wherein the one or more surface coating layers are applied to opposed faces of the construction product.

43. The method according to any one of claims 40 to 42 wherein the one or more surface coating layers comprise paper.

44. The method according to any one of claims 37 to 43 wherein the step of at least partially dehydrating the foamed hydration product under ambient conditions takes no more than 10 minutes.

45. A construction product formed according to the method of any one of claims 37 to 44.

46. A hydraulic binder for use as a construction material, the hydraulic binder comprising:Between approximately 10 wt% and 70 wt% steel slag;Between approximately 1 wt% and 50 wt% of a calcium sulphoaluminate (CSA) cement, a calcium sulphoaluminate belite (SAB) cement and / or a calcium aluminate (CA) cement; andBetween approximately 10 wt% and 95 wt% gypsum;Wherein the hydraulic binder is produced in the absence of Portland cement, alkaline activators and alkaline supplementary hydraulic cement mixtures.

47. The hydraulic binder according to claim 46 wherein the hydraulic binder comprises between approximately 30 wt% and 50 wt% of the steel slag, between approximately 10 wt% and 20 wt% of the calcium sulphoaluminate (CSA) cement, the calcium sulphoaluminate belite (SAB) cement and / or the calcium aluminate (CA) cement, and between approximately 30 wt% and 55 wt% gypsum.

48. The hydraulic binder according to claim 46 or claim 47 when produced according to the method of any one of claims 1 to 34.

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