Classifications

• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B14/00—Use of inorganic materials as fillers, e.g. pigments, for mortars, concrete or artificial stone; Treatment of inorganic materials specially adapted to enhance their filling properties in mortars, concrete or artificial stone
  • C04B14/02—Granular materials, e.g. microballoons
  • C04B14/04—Silica-rich materials; Silicates
  • C04B14/06—Quartz; Sand
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
  • C04B28/14—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing calcium sulfate cements
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B7/00—Hydraulic cements
  • C04B7/14—Cements containing slag
  • C04B7/147—Metallurgical slag
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B7/00—Hydraulic cements
  • C04B7/32—Aluminous cements
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B7/00—Hydraulic cements
  • C04B7/32—Aluminous cements
  • C04B7/323—Calcium aluminosulfate cements, e.g. cements hydrating into ettringite
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B7/00—Hydraulic cements
  • C04B7/36—Manufacture of hydraulic cements in general
  • C04B7/364—Avoiding environmental pollution during cement-manufacturing
  • C04B7/367—Avoiding or minimising carbon dioxide emissions

Definitions

• the present invention relates to method for the production of a hydraulic binder.
• the present invention relates to a hydraulic binder produced through an improved cement hydration mechanism.
• Portland cement is the most common type of hydraulic binder in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout.
• the widespread use of Portland cement is due, at least in part, to the low cost and ready availability of the materials from which it is manufactured.
• An essential step in the Portland cement utilisation process is a hydration step.
• Portland cement powder is dissolved in water to produce hydration products in the form of calcium hydroxide (CH) and calcium silicate hydrate (CSH) at a pH of approximately 13.5.
• CSH calcium hydroxide
• CSH calcium silicate hydrate
• This reaction with carbon dioxides and salts has the effect of destabilising the hydration products, such that the CSH and CH are no longer environmentally stable.
• hydrated Portland cement can suffer from significant reductions in its performance (due to decomposition) over a relatively short period of time.
• Embodiments of the present invention provide a method for the production of a hydraulic binder, 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.
• a method for the production of a hydraulic binder comprising: introducing a source of aluminium to a body of water to produce aluminium hydroxide; introducing an ion source, in the form of a slag, to the body of water, the source configured to release a plurality of ions into the body of water; introducing a counterion source to the body of water, the counterion source configured to release a plurality of counterions into the body of water; converting at least a portion of the aluminium hydroxide at least a portion of the plurality of counterions and/or at least a portion of the plurality of ions to a crystalline AFt phase; and converting at least a portion of the crystalline AFt phase using at least a portion of the plurality of ions to a crystalline AFm phase, wherein the crystalline AFm phase and/or the crystalline AFt phase forms the hydraulic binder.
• AFt phase is an abbreviation for “alumina, ferric oxide, tri-counterion” or (AI2O3 - Fe2Os - tri).
• the term represents a group of calcium sulfoaluminate hydrates.
• AFt phases have the general formula [Ca6(AI,Fe)(OH)6 , 12H2O]2*X3*nH2O where X represents a charged anion (X in this case denoting sulfate).
• Ettringite is a common member of the AFt group and is the name of the mineralogical supergroup to which all AFt’s belong.
• AFm phase is an abbreviation for "alumina, ferric oxide, mono-counterion” or (AI2O3 - Fe2Os - mono). It represents another group of calcium aluminate hydrates with general formula [Ca2(AI,Fe)(OH)6]2*X*nH2O where X represents a lone charged anion. X may be one of many anions, with common anions including hydroxyl, sulfate and carbonate.
• the source of aluminium may be of any suitable form.
• the source of aluminium may comprise a single material, or may comprise two or more materials.
• the source of aluminium may be an inorganic material.
• 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.
• the aluminium may introduce aluminium cations into the body of water.
• a source of calcium may also be introduced to the body of water.
• the source of calcium may be of any suitable form.
• the source of calcium may comprise a single material, or may comprise two or more materials.
• the source of aluminium may be an inorganic material.
• 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, acetates or the like, or any suitable combination thereof.
• the calcium may introduce calcium cations into the body of water.
• the depletion of the pore solution calcium may drive the dissolution of the pozzolan materials.
• the depletion of the solution at a relatively low pH draws ions from the raw materials introduced to the body of water.
• the source of aluminium and the source of calcium may comprise different compounds.
• the source of aluminium and the source of calcium may be the same compound.
• 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.
• an ion source in the form of a slag, is introduced to the body of water.
• the slag may comprise a slag produced from a steel manufacturing process, such as slag produced in a basic oxygen furnace (BOF).
• BOF basic oxygen furnace
• the slag may be a steel slag.
• the slag may undergo a size reduction process prior to being introduced to the body of water.
• Any suitable size reduction technique may be used, such as, but not limited to, crushing, grinding or the like.
• the slag may be reduced to any suitable particle size.
• 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.
• the slag may be combined with a calcium sulphoaluminate cement or a calcium aluminate cement prior to being introduced to the body of water.
• 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 body of water.
• the slag may be combined with the calcium sulphoaluminate cement or the calcium aluminate cement in any suitable proportions.
• the proportion of the 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%.
• the ion source may comprise a source of aluminium ions. More preferably, the ion source may comprise a source of aluminium and calcium ions. Still more preferably, the ion source may comprise a source of aluminium, calcium and silicon ions. It is envisaged, however, that the slag may constitute a source of ions of a number of other elements, such as, but not limited to, gallium, manganese, tungsten, cadmium, chromium, strontium, cobalt, lead, nickel, barium, titanium, molybdenum, vanadium, selenium, arsenic, iodine, bromine, boron, chlorine and the like.
• the slag does not constitute a traditional cementitious agent, but is instead a “mineable” resource, in that ions from the slag may be recovered for use in the method of the present invention. It is envisaged that the ions of the other elements may be utilised in the method of the present invention to aid in the formation of the AFt phase.
• the ions of the other elements would not typically be utilised, as they either do not normally occur in the body of water at the onset of hydration, and/or are supressed by their rate of reaction or excluded by more reactive/ dominant ions.
• introducing these ions into the body of water before the usual hydration reactions occur results in the reactivity of the phase and the particle size has a relatively low effect on the hydration rate compared to processes using Portland cement.
• slags such as steel slag are classed as having low reactivity.
• the reactions occurring in the method of the present invention are typically fast (and certainly faster than those in the hydration of Portland cement) even when the slag is not ground to a relatively small particle size.
• the present invention may comprise a sequence of reactions, in which one or more products from a previous reaction may be utilised.
• the sequence of reactions may comprise a stepwise sequence of reactions.
• 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.
• phases of the ion source that may have low reactivity may be effectively mined from the ion source to produce solute for the formation of other members of a solid solution series.
• a silicate counter ion may be extracted from a C2S phase before normal hydration occurs, trapping atmospheric carbon dioxide as a counterion during the formation of the more stable but slower forming C6ASSC solid solution member, as opposed to the more rapidly formed three sulphate - aluminium solid solution member of an ettringite (C6ASSS) series which decomposes to calcium carbonate, aluminium hydroxide and calcium sulphate in the presence of atmospheric carbon dioxide.
• C6ASSS ettringite
• the counterion source may be of any suitable form and may release counterions into the body of water in any suitable manner, such as by dissolving in the body of water.
• the counterion source may comprise one or more water-soluble inorganic compounds.
• the counterions may be released into the body of 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.
• 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).
• the desired counterions may comprise sodium, potassium, calcium, iron, aluminium, copper, nickel, strontium, chromium, zinc ions or the like, or any suitable combination thereof.
• the counterion source may comprise a source of calcium ions.
• a stoichiometric excess of calcium ions may be provided in order to drive the formation of the crystalline AFt phase.
• the negative counterions provided by the counterion source may be of any suitable form, and it will be understood that the negative counterions may vary depending on the nature of the positive counterions, the nature of the source of aluminium (and the source of calcium, if present) and so on.
• the negative counterions may comprise carbonate anions, chloride anions, oxide anions, sulfate anions, hydroxide anions and so on, or any suitable combination thereof.
• the body of water may be of any suitable type, and it will be understood that the size and nature of the body of water will depend on the quantity of the crystalline AFt phase to be produced.
• the body of water comprises a pool, vat, tank, pond, reservoir or the like.
• the water in the body of water may be of any suitable form, it is preferred that, prior to the method of the present invention, the water may be relatively free from ions. In some embodiments of the invention, however, the water may include a quantity of the counterions. While the water may be of any suitable pH, it is preferred that the water may be of a relatively neutral pH, or a slightly basic pH (i.e. , a pH of between 7 and approximately 9).
• one or more reactants may be added to the body of water.
• the one or more reactants may be of any suitable form, and those skilled in the art will understand that the addition of the one or more reactants (as well as the quantity of the one or more reactants used) will be dependent on the nature and composition of the other components of the method and so on.
• the one or more reactants may comprise one or more of a plasticiser, a retarder and an accelerator. Any suitable substance may be used as the plasticiser, retarder and accelerator.
• the plasticiser may comprise calcium naphthalenesulphonate.
• the retarder may comprise an acid, and in particular citric acid.
• the accelerator may comprise lithium carbonate and, in particular, relatively fine lithium carbonate.
• the aluminium hydroxide produced from the source of aluminium may be produced in any suitable manner.
• the aluminium hydroxide may be produced as a precipitate.
• the aluminium hydroxide may be precipitated as aluminium hydroxide gel.
• the aluminium hydroxide that is formed precipitates out of solution as an amorphous semi soluble polymer, which then combines with calcium to form a hydrated ion pair. The formation of this ion pair is the reason for the growth of the AFt phase as an elongate, acicular crystal.
• the base of the AFt crystal there is a catalyst which is insoluble and provides a charged surface on which the AFt is co-ordinated. Further calcium aluminium ion pairs are inserted at the base of the crystal, effectively pushing up or growing the crystal from the base.
• Any suitable reaction may be used to precipitate aluminium hydroxide from solution.
• a specific example of an aluminium hydroxide precipitation reaction (involving aluminium chloride, sodium carbonate and water) is set out below:
• the conversion of aluminium cations to aluminium hydroxide gel is a relatively fast process.
• the precipitation of aluminium hydroxide gel occurs at a pH of approximately 8.
• At least a portion of the aluminium hydroxide, at least a portion of the ions and at least a portion of the plurality of counterions are converted to a crystalline AFt phase.
• the at least a portion of the aluminium hydroxide, the at least a portion of the ions and the at least a portion of the plurality of counterions may be converted to any suitable crystalline AFt phase, although in a preferred embodiment of the invention, the at least a portion of the aluminium hydroxide, the at least a portion of the ions and the at least a portion of the plurality of counterions may be converted to ettringite.
• the compound may be of the general form: (CaO)6(Al2O3)(SO3)3'32H 2 O or
• the aluminium hydroxide, the at least a portion of the ions and the at least a portion of the plurality of counterions may be converted to the crystalline AFt phase using any suitable technique.
• the aluminium hydroxide, the at least a portion of the ions and the at least a portion of the plurality of counterions are converted to the crystalline AFt phase via a hydration mechanism.
• the crystalline AFt phase may absorb a relatively large amount of water from the body of water such that the crystalline AFt phase has a relatively high water content.
• the crystalline AFt phase may have any suitable crystalline structure.
• the crystalline AFt phase may have a triclinic, monoclinic, orthorhombic, tetragonal, trigonal, hexagonal or cubic crystalline structure, or any suitable combination thereof.
• the crystalline AFt phase may have a relatively elongate (or acicular) morphology.
• the crystalline AFt phase has a relatively high water content.
• the conversion of the crystalline AFt phase to the crystalline AFm phase may be driven, at least in part, by the dehydration of the body of water during the formation of the crystalline AFt phase. More specifically, as water is consumed during the formation of the crystalline AFt phase, a reduction in the available water then assists in the conversion of the crystalline AFt phase to the crystalline AFm phase.
• the conversion of the crystalline AFt phase to the crystalline AFm phase is performed in the presence of the ion source.
• the ion source may be provided in order to drive the formation of the crystalline AFt phase and/or the crystalline AFm phase.
• the crystalline AFm phase may be of any suitable form.
• the crystalline AFm phase may comprise a combination of mono carbonate, mono sulphate and gehlenite hydrate (C2ASH8).
• the crystalline AFt phase may be a rapidly forming, thermodynamically-unstable crystalline hydrate.
• the crystalline AFt phase may include an elongated morphology and may have a high water content.
• the crystalline AFt phase may form a dispersed non-contiguous support structure that, preferably, defines the initial dimensions of the cement product and, in particular, the cement product once set.
• the crystalline AFt phase may form a frame structure or scaffold where the crystalline AFm phase may form.
• the formation of the crystalline AFt phase may consume large quantities of water.
• the hydration of the crystalline AFt phase assists in the conversion of at least a portion of the crystalline AFt phase by dehydrating unbound pore water to a point where the unavailability of water in the body of water slows or ceases the formation of the crystalline AFt phase, such that the reaction changes to the formation of the crystalline AFm phase.
• the mechanism of the formation of the crystalline AFm phase may include the sequential replacement of elements within the crystalline AFt phase and/or the counterions.
• the formation of the crystalline AFm phase may occur within the frame structure or scaffold of the crystalline AFt phase. It is envisaged that developing a contiguous crystalline matrix within the AFt frame structure places the AFt frame structure under dehydrating conditions. In turn, this may destabilise the AFt frame structure causing the AFt crystals to decompose to their base raw materials, freeing them for their consumption by the ongoing AFm hydration process.
• the crystalline AFm phase may have any suitable crystalline structure.
• the crystalline AFm phase may have a triclinic, monoclinic, orthorhombic, tetragonal, trigonal, hexagonal or cubic crystalline structure, or any suitable combination thereof.
• the present invention uses the AFt-AFm transition system to effectively mine the components of the hydration mixture (i.e., the body of water and the ion sources located therein) allowing the use of non-reactive materials to form hydrates having rapid strength gains which are also stable in the environment.
• the hydraulic binder comprises the crystalline AFm phase and/or the crystalline AFt phase.
• the hydraulic binder may comprise both the crystalline AFm phase and the crystalline AFt phase.
• the hydraulic binder may comprise the crystalline AFm phase only.
• the AFt phase and the AFm phase may comprise only a single crystalline form of AFt and AFm.
• the AFt phase and/or the AFm phase may comprise a plurality of crystalline forms of AFt and AFm. It will be understood that the different crystalline forms of the AFt and AFm phases may be of a different crystalline structure, different chemical composition and/or different stoichiometry to one another.
• the hydraulic binder may further comprise one or more anhydrite deposits. More specifically, the hydraulic binder may further comprise one or more botryoidal anhydrite deposits.
• the invention resides broadly in a hydraulic binder when formed bv the method of the first aspect.
• the present invention does not require the materials used to be cementitious or hydraulic. Instead, the present invention only requires a mechanism for the formation of AFt hydrates, and particularly AFt hydrate crystals, and that the materials used are at least somewhat soluble.
• the present invention provides further advantages in that the initial pH of the invention is reduced in comparison to conventional methods, and that environmental substances (such as carbon dioxide, salt and the like) that are attracted to the method of the present invention may be consumed as counterions rather than causing decomposition or degradation or the hydration products.
• environmental substances such as carbon dioxide, salt and the like
• the rate at which the strength of the hydraulic binder of the present invention is achieved is rapid in comparison to Portland cement.
• the rapid pace of the reactions to form the hydraulic binder means that at least 25% of the total 28 day strength of concrete formed using the hydraulic binder may be achieved in less than approximately 4 hours from the initial set, with between 60% and 70% of the total 28 day strength achieved within 24 hours.
• a further hydration burst may occur at between 7 and 14 days from the initial set. It is envisaged that the further hydration burst may be associated with silicates in the hydraulic binder.
• the 28 day strength of hydraulic binders prepared according to the method of the present invention are considerable higher (approximately 2 - 2.5 times higher) than the 28 day strength of conventional concrete formed using Portland cement.
• the hydraulic binder of the present invention achieves a high proportion of its total 28 day strength within a short period of time means that the hydraulic binder may also be used in applications where traditional cements have needed to be allowed to set and cure for a longer period of time before use. For instance, in the 3D printing of structures (such as houses and the like), a first layer of traditional cement product would be printed and then allowed to cure for a relatively lengthy period of time in order to achieve a sufficient proportion of the total 28 day strength before a second layer could be printed on top of the first layer.
• the rapid setting and curing of the hydraulic binder of the present invention means that a second layer may be printed on top of a first layer a relatively short period of time after a first layer is printed.
• the overall speed of construction is increased, decreasing the time taken to construct a structure in comparison to conventional cement products.
• Steel slag S500 was of a controlled composition taken from the top of the molten steel within a crucible.
• Steel slag S502 was the remainder of the slag formed, containing material which had been ejected from the crucible during steel manufacture. It contained a high proportion of steel particles and iron oxide.
• a grout containing each of the slags was formed, along with a control grout in which no slag was present (i.e., a conventional CSA cement grout).
• the grouts were of the compositions shown in Table 1.
• Each grout was then processed (with the slag grout being processed according to the method of the present invention) in order to produce a hydraulic binder that was subsequently air cured.
• the compressive strengths of the hydraulic binders were tested over a period of 28 days.
• the results set out in Table 2 illustrate that the hydraulic binders produced according to the method of the present invention (i.e. , those produced from slag) were both of significantly higher compressive strength to a conventional Portland cement hydraulic binder.
• initial hydration produced AFt hydrates based on a calcium-aluminium backbone with sulphate as the counterion.
• Ettringite formation rapidly depleted the pore solution of both ions and water content, driving the AFt phase to scavenge ions from other sources (including the ion source, or slag).
• a proportion of the crystalline AFt phase (in the form of ettringite) formed contained counterions other than sulphate and formed the more stable AFt solid solution end members such as woodfordite.
• Figure 1 illustrates a method for the production of a hydraulic binder according to an embodiment of the present invention.
• Figure 2 illustrates a schematic representation of a method for the production of a hydraulic binder according to an embodiment of the present invention.
• Figure 1 illustrates a method 10 for the production of a hydraulic binder according to an embodiment of the present invention.
• a source of aluminium 11 is introduced to a body of water 12.
• the source of aluminium 11 is also a source of calcium and may comprise any suitable soluble aluminium calcium inorganic compound.
• the source of aluminium 11 comprises a calcium suphoaluminate.
• the dissociation of the inorganic compound comprising the source of aluminium 11 in the body of water generates a reaction between the aluminium ions and the water that results in the formation of aluminium hydroxide gel 13.
• the aluminium hydroxide gel 13 is produced at a pH of approximately 8, which is a considerably less alkaline pH than those experienced in the generation of CSH gel in the conventional Portland cement hydration process.
• a counterion source 14 is also introduced to the body of water 12.
• the counterion source 14 is a soluble inorganic calcium compound, such as calcium nitrate, calcium sulfate, calcium acetate, calcium hydroxide, calcium chloride, calcium bromide or calcium iodide, or any combination thereof.
• the dissociation of the inorganic compound of the counterion source 14 introduces calcium cations and anions into the body of water 12.
• At least a portion of the aluminium hydroxide gel 13, at least a portion of the counterions produced from the counterion source 14, and at least a portion of the ions produced from the ion source 16 are subsequently converted to a crystalline AFt phase.
• the crystalline AFt phase is in the form of the AFt phase of ettringite 15.
• the ettringite is of the composition (CaO)3(Al2O3)(CaSO4)3-32H 2 O.
• the AFt phase of ettringite 15 is formed from the aluminium hydroxide gel 11 , the ions from the ion source 16 and the counterions from the counterion source 14 hydrate via a hydration mechanism. It is envisaged that the crystalline AFt phase may absorb a large amount of water from the body of water 12 such that the crystalline AFt phase 15 has a high water content.
• the AFt phase of ettringite 15 will have an elongate, or acicular, crystal structure.
• Ions and, in particular, calcium, aluminium and silicon ions
• the slag used as the ion source 16 is effectively a “mineable” resource as certain components of the slag may be extracted for use in the method of the present invention.
• Environmental agents such as carbon dioxide 17, are typically considered to be detrimental in the conventional Portland cement hydration process.
• atmospheric carbon dioxide 17 may provide ions for use in the conversion of the aluminium hydroxide 13 to the AFt phase of ettringite 15.
• the AFm phase may at least partially comprise gehlenite hydrate having the formula C2ASH8.
• the mechanism of the formation of the crystalline AFm phase 18 includes the sequential replacement of elements within the crystalline AFt phase 15 and/or the counterions 14 and/or the ions 16.
• the formation of the crystalline AFm phase 18 occurs within the frame structure or scaffold of the crystalline AFt phase 15. Developing a contiguous crystalline matrix within the AFt frame structure places the AFt frame structure under dehydrating conditions. In turn, this destabilises the AFt frame structure causing the AFt crystals 15 to decompose to their base raw materials, freeing them for their consumption by the ongoing AFm hydration process.
• the AFm crystals 18 are, advantageously, environmentally stable, meaning that carbon dioxide 17 and salts 19 that are attracted to the hydration process do not react with the AFm crystals 18, and therefore no decomposition or degradation of the AFm crystals 18 occurs (unlike in the Portland cement hydration process).
• the crystal structure of the AFm phase 18 means that shrinkage of the AFm crystals 18 is reduced or eliminated, thereby providing a dimensionally stable product.
• the method 10 of the present invention relatively fast in comparison to the conventional Portland cement hydration process, but the strength of the hydraulic binder (the AFm crystals 18 and/or residual AFt crystals 15) develops much faster than conventional Portland cements.
• the compressive strength of a hydraulic binder produced according to the method of the present invention is greater than that of conventional hydraulic binders produced using Portland cement.
• the 28 day compressive strength of hydraulic binders produced according to the method of the present invention is 2 - 2.5 times higher than the 28 day compressive strength of conventional hydraulic binders produced using Portland cement.
• FIG. 2 illustrates a schematic representation of a method 10 for the production of a hydraulic binder 20 according to an embodiment of the present invention.
• counterions 14 produced from the counterion source and ions produced from the slag 16 react with aluminium hydroxide gel 13 formed in the body of water 12 to form the crystalline AFt phase 15.
• reaction time represented by arrow 21
• the conversion of the counterions 14 produced from the counterion source, the ions produced from the slag 16 and the aluminium hydroxide gel 13 continues.
• This reaction corresponds to a decrease in free water (represented by arrow 22) within the system, which in turn drives the conversion of the crystalline AFt phase 15 to a crystalline AFm 18 phase.
• the conversion of the crystalline AFt phase 15 to the crystalline AFm 18 phase is also driven by ions obtained from the slag 16 as well as carbon dioxide (such as atmospheric carbon dioxide).
• the hydraulic binder 20 comprises a plurality of forms of the crystalline AFm phase 18. It is envisaged that the hydraulic binder 20 may comprise the most chemically stable forms of AFm.
• the hydraulic binder 20 also comprises a chemically stable form of the AFt phase 20a as well as one of more deposits of botryoidal anhydrite 20b.

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• 2023
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