Improved pozzolans for clinker substitution and methods of manufacture

Abstract

A flowable, low-emissions pozzolan powder comprising a substantially fused composite of constituent particles, wherein the constituent particles comprise: a low-emissions active calcined clay; a low-emissions active calcined carbonate with a surface area exceeding 45 m2 / g and a mean pore size greater than about 100 nm; and a carbonate extender; wherein the pozzolan powder has a particle size of about 50 microns, and wherein the hydration reactivity of the pozzolan powder is adjustable by particle engineering to match the hydration rate of Ordinary Portland Cement (OPC).

Description

IMPROVED POZZOLANS FOR CLINKER SUBSTITUTION ANDMETHODS OF MANUFACTURETECHNICAL FIELD

[0001] The present inventions disclosed herein relate broadly to pozzolan powders and a means of manufacture of such powders from minerals. The disclosures herein describe low CO2 emissions intensity and low energy intensity manufactured pozzolan powders. Ordinary Portland Cement clinker (OPC) powder generally has a high CO2 emissions intensity (hereafter called emissions intensity), in the range of 840 and 1040 kg CO2 per tonne. The powders disclosed herein may be used as Substitute Clinker Material (SCMs) for OPC powders used in mortars, cement and concrete structures to mitigate climate change, by reducing the need to use OPC clinker for manufacture of mortar, concrete and cement products.

[0002] When such a pozzolan powder is blended with powdered OPC powder, along with other powder additives such as retarders, accelerants and flow aids, and mixed with water, sand or aggregates to make a make a mortar, cement or concrete paste, the set product has substantially the same desirable attributes, such as strength and durability, as similar products manufactured from OPC with existing pozzolan powders, such as slag and fly ash. The higher the substitution of OPC in the blend by a low-emissions pozzolan, the lower the emissions intensity of the cement or concrete product. Such pozzolan powders disclosed herein are Substitute Clinker Materials (SCMs) by virtue of the reduction of the emission intensity of such set products.

[0003] Most pozzolan powders are industrial wastes, such as fly ash and slag, and do not generally produce strong cements without OPC because of inherent kinetic and composition constraints, and the extent of substitution of these in OPC products has been limited.

[0004] The manufactured pozzolan powders disclosed herein may produce sufficiently strong products without OPC for some industrial uses.

[0005] The manufacturing of the constituent powders of the pozzolan described herein uses one or more powdered processed minerals as constituents, and in the preferred pozzolan, these are generally available near cement factories. The manufacturing process of these constituents, generally by calcination of one or more of the minerals, uses low emissions processes at an industrial scale. The pozzolan powder is formed by fusing the minerals by grinding the constituents of the pozzolan, blending the ground constituents, and making a flowable compounded powder by a fusion process. The meaning of a flowable fused compound material pozzolan in this disclosure means that the constituent particles of the pozzolan are substantially adhered during production by the fusion process, which generally improves the performance of the products compared with uncompounded constituents, but also simplifies the blending process of the OPC with the pozzolan. Such compounding manufactures a pozzolan that can replace waste pozzolans, to generate improved construction products.

[0006] The CO2 emissions intensity of OPC itself will likely be reduced progressively by processes such as cement fines recycling and CO2 capture processes, such as oxyfuel combustion, end-of-pipe capture, and direct separation technology. The low energy intensity of the pozzolan powders disclosed herein are such that their use as SCMs with such low emissions intensity OPC, provide a path to net zero cement and concrete products.

[0007] Additionally, the blend of OPC and the pozzolans described herein may be used to as the basis for new mortar, cement and concrete formulations such as applications, such as self-healing Engineered Cementitious Composite (ECC) materials, that may, for example, limit the corrosion of OPC based concrete in sea water.BACKGROUND

[0008] There is a need for a process to reduce CO2 emissions from OPC based concrete and cement to mitigate climate change. OPC cement is currently responsible for about6% or more of mankind’s CO2 emissions, and there is a need to substantially reduce these emissions to meet targets to limit the impact of climate change.

[0009] The manufacture of low emissions OPC is a challenge because the CO2 released from limestone, CaCCh, to make lime, CaO, during calcination of cement raw meals is unavoidable, so that CO2 sequestration or re-use is required to mitigate climate change impact. The development of low emissions OPC is being progressed using oxyfuel combustion, end-of-pipe capture, and direct separation technology. Direct separation was disclosed by Sceats et. al. in PCT / AU214 / 001054 “Process and Apparatus for Manufacture of Portland Cement” .

[0010] Combined together, PCT / AU214 / 001054, direct separation to reduce emissions of OPC and the use of indirectly heated reactors to make low emissions pozzolans described in this disclosure to substitute OPC may provide a route to zero emissions cement and concrete products.

[0011] Lime is the active ingredient of OPC through its reaction with silica during clinker formation to form belite CaSi2O4 and alite CaSnO?. In making clinker, CO2 is also emitted from the use of carbon-based fuels for both the calcination and clinkering steps. The clinker is ground to make OPC powder as the primary constituent for most cements and concrete. In an OPC based cement, mixing of OPC powder with water forms a paste in which the water reacts with the belite and alite in the OPC powder to form Portlandite, Ca(OH)2 which then reacts with the silicates to form a strong binding cementitious network of calcium silicates hydrates as the paste sets. The water added is sufficient to hydrate all the belite and alite, and to provide the water for workability of the paste, with the overall water demand depending on the application. The desirable outcome is to use the lowest water content because excess water lowers the strength. This may be partially offset by the use of superplasticisers. Pozzolans that are in used in cement, like fly ash and slag also hydrate and are consumed as the paste sets. In sum, it is highly desirable that the belite and alite in OPC powder are completely hydrated during the setting process, usually over about 28 days. It is highly desirable that any excess of Portlandite formed during hydration is small, typically less than 1% of the total calcium in theclinker. An object of the present invention may be to disclose a new pozzolan that may be used with OPC to give a cement or concrete with comparable strength as OPC and existing pozzolans to reduce the emissions intensity of such OPC -based products.

[0012] Based on current manufacturing approaches, the emissions intensity of OPC is typically between 840 and 1040 kg per tonne. The manufacture of low emissions OPC powder is a substantial technical challenge because of the large amounts of CO2 emitted and to reach net zero emissions in an integrated calcination and clinkering process. There is a need to reduce both the emissions of CO2 during production of OPC, and to reduce the use of OPC through SCMs, and also to reduce the emissions from production of SCMs.[ OO13]In Europe and USA, new building codes incorporate the use of 50% OPC into standards. Many SCM materials described in the prior art cannot meet these codes, while meeting other standards required for strength and durability. In most cases, the materials, such as LC3described by Scrivener et.al. in “Calcined clay limestone cements (LC3)” in Cement and Concrete Research”, 114, 49-56 (2018). LC3cannot be blended in a cement batching plant. The reason being that to achieve the required properties, the OPC is ground with the SCM materials. A batching plant is not configured for grinding, based on economies of scale and current practice. An object of the present invention may be to describe a new low emissions intensity pozzolan that is an SCM that can be used to make low emissions products by blending with OPC and other materials that can meet and preferably exceed standards based on LC3.

[0014] A pozzolan such as fly ash waste from coal fired power stations or slag waste from steel and aluminium manufacturing are typically used in many cement formulations. A pozzolan is typically a fine powder of siliceous or aluminous materials, which when hydrated, to form a paste may produce a settable binder, without OPC. Such a pozzolan forms additional silicates, aluminium silicates and calcium aluminium silicates binders, depending on composition, to add strength, decrease permeability, and to improve other characteristics of the product, such durability. In most cases, the pozzolan itself, when tested using standard methods, makes cements with little strength because thecompositions to make a strong cement are rarely met, or because the kinetics of hydration and binding do not meet the needs for strength, or chemical constituents are insufficient. An object of the present invention may be to describe a new low emissions pozzolan that can be used to make high strength cementitious binders, with or without OPC for mortars, cements and concretes for different applications.

[0015] The amount of pozzolan fly ash from coal fired power plants in the future is expected to be reduced as renewable power is generated from sources such as solar and wind. Also, pozzolan slags from the production of steel and lime plants is often restricted by availability and proximity. Thus manufactured pozzolans are likely to be required. There is a need for new low emissions intensity pozzolans to replace both fly ash and slag, and which are SCMs, using materials which are commonly available to OPC manufacturers. An object of the present invention may be to describe a new low emissions pozzolan to replace fly ash and slags used as pozzolans in cements and concrete, and preferably those which use materials available to OPC manufacturers.

[0016] Ground limestone fines are commonly used as an extender, up to about 8-13% for high strength OPC cements and concrete. Extenders were first described by Borghom et. al, in “Cement Composition” EP 0 640 062 Bl (1993) in which OPC is mixed with ground calcium carbonate, or magnesium carbonate, or calcium-magnesium carbonates, and mixtures thereof to make a strong cement. It is believed that the limestone reacts with alite during the hydration process. An object of the present invention may be to describe a pozzolan that may incorporate such extenders.

[0017] Vicedo et.al. in EP 2239 239A1 (2010) teaches that an ideal synthesised pozzolan should be textured, meaning that all the active constituents for a pozzolan cement should be incorporated in the pozzolan material and preferably distributed uniformly within the pozzolan. According to Vicedo, when such a pozzolan is mixed with ground OPC clinker, the rates of formation of binders around the pozzolan can then be controlled by the chemical and physical compositions of the Pozzolan, typically through the control of particle size and other additives that can accelerate or decelerate the reaction. Vicedo teaches that Roman cement is such a pozzolan containing lime as the active ingredient, soPortlandite is quickly generated within such a particle as it is hydrated and the materials in the hydrated pozzolan are then consumed by cementitious reactions. In many cases, traditional pozzolans such as fly ash and slag also have such a distributed texture, but are often impervious and tend to hydrate slowly. In sum, Vicedo teaches that the strongest cement formed from several cementitious constituents is created when the rates of hydration in each constituent are similarly fast, and the rates of formation of the cementitious binders are similar over the entire setting time, say 28 days, of the cement. There are additives that can be added to any pozzolan constituent to control the rate of generation of the cementitious binders around and within each of the constituent particles, such as the pozzolan and OPC particles. An object of the present invention may be to disclose a new pozzolan that obeys the rules disclosed by Vicedo to achieve high strength materials.

[0018] The Vicedo rule of controlling the reaction rates by the initial formulation’s reactivity and particle sizes is, in practice, often restrictive if the diffusion of materials between setting particles is linked to hydration. Thus, such processes with a pozzolan and OPC blend may become coupled. Lloyd et. al. in AU 201736546 and references therein teach that improved control of the processes with OPC and a pozzolan slag can be made by mixing a water-soluble accelerator, such as sodium or potassium sulphate to the setting paste, with a delay of up to 60 minutes from the blending process, to accelerate the slow initial processes of the pozzolan slag activation. The delay is long enough for the initial steps of forming a binder the OPC material, with its retarder, are sufficiently complete. The teaching of Lloyd et. al. may provide a general means of control of the intermediate stages of the slowest reactions to better meet the net design rules of Vicedo. The agitation of the setting paste is such that a soluble accelerator is uniformly mixed, but such a delay may be designed to have significant impact on one component to give the desired setting time.

[0019] Calcined clay is a well-known pozzolan. Sabir, et al. in “Metakaolin and calcined clays as pozzolans for concrete: a review.” Cement & Concrete Composites, (2001), vol. 23, 441-454 reviewed the prior arts at that time. Hertfort et.al in US 9,212,092 (2015)describe mixing calcined clay with limestone extender to give a settable paste. The limits of substitution as described by Schulze et.al in “Suitability of natural calcined clays as supplementary cementitious material”. Cem. Concr. Compos. 2019, 9, 92. For later reference to the disclosures herein, the mixing described in Hertfort et. al. and Shultz et. al. does not involve fusion of the calcined clay and the extender, but rather a powder mixture is formed by blending.

[0020] There has been considerable research and development of calcined clay-based cements and pozzolans for SCM materials, and such work has been reviewed by Roman et al in “Calcined Clay as Supplementary Cementitious Material”, Materials 2020, 13(21), 4734 and Khandelwal et.al “Evaluation of pozzolanic activity, heterogeneous nucleation, and microstructure of cement composites with modified bentonite clays”. Constr. Build. Mater. 2022, 323, 126617. An object of the present invention may be to disclose a low-emissions, pozzolan based on calcined clay as a constituent with a high OPC replacement capability.

[0021] A major challenge of using calcined clays as a pozzolan SCM is that the intrinsic slow rate of hydration of the calcined clay, and high demand for excess water for a paste associated with fine porous particles adds to water demand, which reduces the 28-day strength. Hence the use of calcined clay as a pozzolan, and as an SCM has been limited in practice. In calcined-clay based SCMs, it is known that a constituent from the hydrating OPC, namely Portlandite Ca(OH)2, bleeds into the calcined clay and induces the hydration and stimulate calcium-silicate-aluminate -hydrate binders around the calcined clay particles to supplement the calcium-silicate -hydrate binders being formed around the hydrated OPC particles. The need for OPC to provide the Portlandite to metakaolin is an inherent limit to the substitution of OPC in many calcined clay SCM materials, because the matching the rates of binder formation in and around the OPC and SCM, are complicated through the need of Portlandite to exchange between particles to enable a preferably uniform network of calcium-alumino-silicates which sets at about the same rate in and between all particles of the formulation. This is further compounded by the need to minimise the water demand of the mixture, to maintain strength of the set cement,because calcined clay has a high water-demand for workability. Simply, a calcined clay based pozzolan does not obey the desirable design rules of Vicedo. In sum, the challenge for calcined clay as a pozzolan has been to provide a formulation with a low water demand, a similar hydration rate to OPC, and a similar setting rate of the cementitious binder. An object of the present invention may be to disclose a low emissions pozzolan based on calcined clay that forms a strong homogeneous binder with OPC.

[0022] An invention of an SCM has been the use of vaterite in US 8,114,214 B2, Vaterite is unstable crystal from of CaCCh which forms a SCM self-healing matrix that sets when hydrated with considerable strength.

[0023] A benefit of pozzolans and extenders is that they both reduce the emissions intensity of the cement in the concrete by reducing the mass of OPC. Formulation of OPC with existing pozzolans and extenders is now a routine part of current cement blends, and these have been blends have been optimised. There is a need for new low emissions pozzolans, as SCMs, to further reduce the OPC in cement and concrete formulations. An object of the present invention may be to disclose a low emissions pozzolan that may set within a mixture with OPC powder and which obeys the Vicedo strategy for each component, and which may be assisted by using the strategy taught by Lloyd et. al.

[0024] The production of limestone and clay are known arts, typically using rotary kilns, fluidised beds and shaft reactors. These use combustion processes, and the products have a high emissions intensity. The use of indirectly heated reactors to make low emissions calcined materials are described in the patent of Sceats in PCT WO2022 / 115897 “Processes and Methods for the Calcination of Minerals” and references therein.Specifically, the use for the calcination of limestone and of clay is referenced. Garces- Vargas et.al in “The challenge of grinding ternary blends containing calcined clays and limestone”, Minerals 2022, 12, 1170, disclose a pozzolan derived from co-grinding limestone and calcined clay. However, that work describes challenges in co-grinding minerals. They used grinding aids such as aliphatic amines (triethylenetetramine (TETA)) and tetraethylenepentamine (TEPA)) and alcoholamines (diethanolamine) to inhibit agglomeration during grinding. That work showed the benefits of the setting performanceof pastes when the pozzolan powder was formed by co-grinding of soft limestone and soft calcined clay, with a mixing aid. An object of the present invention may be to disclose a process for manufacturing a low-emissions pozzolan that limits the need for grinding aids.

[0025] Dolomites, magnesitic limestone and magnesite are generally wastes from limestone mines for cement because the dead burned high density MgO from clinkering of these materials expands slowly in a cement paste, and cracks appear in concrete with magnesium oxide MgO exceeding about 5% by weight in the OPC. Harrison in US 2005 / 0103235 discloses that reactive MgO does not expand. Sceats et. al. in PCT AU2006-001573 describe a reactive powder material, semi-dolime MgO.CaCOs made from dolomite and discloses its use as a binder in building materials. Vlasopoulos et a. in W02009 / 156740 describe a powder based on a blend of MgO and MgCOa as a binder for cement materials. Nevertheless, any magnesium materials in a cement are not currently preferred because the magnesium content is often used as a proxy for cement cracking failure in OPC cements and concretes because unreactive MgO is produced in clinker, expands slowly and cracks concrete. An object of the present invention may be to disclose a new pozzolan that may use of reactive magnesium-based materials as a constituent.

[0026] In the manufacture of concrete, generally a batching plant is used to blend the constituents, such as those described above, with water, sand or aggregates, and retarders or accelerants to make a settable concrete paste which generally transported to a construction site for setting in a structure. Blending in such a plant excludes grinding. A characteristic of a batching plant is the use of silos where the control of the flows of powders is used to form a blend flowable powders, and then to manufacture of a paste for a particular application. An object of the present invention may be to disclose a low emissions flowable pozzolan that can be blended with OPC for use in a batching plant.

[0027] It is well established that a pozzolan comprising calcined clay and lime hydrates quickly and the lime provides the calcium for making calcium-aluminium silicate binders. This is a long-established art from Roman cement as a pozzolan and obeys theVicedo rule. A feature of Roman cement is that its corrosion in sea water was very low compared to OPC based cements, and there has been intense speculation of the mechanism. More generally, this the low tensile strength of OPC based cements and concretes is such that structures are prone to developing cracks, typically less than about 100 pm, that lead to corrosion, for example by ingress of sea water and destruction from seismic events.

[0028] There has been a recently a rapid development of ECC formulations that can seal such cracks as they form which inhibit fracture growth, including those formed during seismic events. The availability in the set material of mobile water is a of ECC formulations is a common feature. Most formulations are generally expensive, requiring polymer additives, capsules, thin polymer or steel fibres. There is a need for a low cost, minerals-based ECC formulation. An object of the present invention may be to disclose an ECC composite of a low emissions pozzolan and OPC.

[0029] Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the fieldSUMMARY

[0030] PROBLEMS TO BE SOLVED

[0031] The problems arise from one or more of the limitations of manufactured pozzolan powders, such as:- a. using high emissions intensity processes. b. having a low intrinsic 28-day strength and long-term durability for mortars, cements and concretes (as made without OPC)) d. having a limited ability of the existing pozzolan to replace OPC as an SCM with at least a 50% OPC replacement.e. avoiding the complexity of co-grinding of SCM materials and OPC to make pastes that set to meet high strength cements and concretes. f. avoiding the inability of manufactured SCMs materials to be used for blending with ground OPC in cement batching plants to enable the production of cement and concrete paste formulations for different applications that require range of blends, including with other powders. g. avoiding, in a blend with OPC, fracturing and corrosion over a long period of time.

[0032] The invention described herein may address at least one of the aforementioned problems.

[0033] MEANS FOR SOLVING THE PROBLEM

[0034] A first aspect of the present invention may relate to a flowable, low-emissions pozzolan powder comprising: a substantially fused composite of constituent particles, wherein the constituent particles comprise: a low-emissions active calcined clay; a low- emissions active calcined carbonate with a surface area exceeding 45 m2 / g and a mean pore size greater than about 100 nm; and a carbonate extender; wherein the pozzolan powder has a particle size of about 50 microns, and wherein the hydration reactivity of the pozzolan powder is adjustable by particle engineering to match the hydration rate of Ordinary Portland Cement (OPC).

[0035] Preferably, the constituent particles further comprise: powder based retardants and accelerators for controlling the formation of cementitious materials when the pozzolan powder is combined with ground OPC, sand, aggregates, and water.

[0036] Preferably, the fusion process comprises: co-grinding the constituent particles to reduce particle size to below approximately 50 microns; mechano-fusing the co-groundconstituent particles to form a homogenous mixture, wherein the homogenous mixture forms a cementitious material when combined with OPC and water.

[0037] Preferably, when blended with the OPC and water, forms a settable hydrated paste, in which the strength of the set product is adjustable by changing the ratio of the mixture of the pozzolan powder to OPC, wherein the minimum strength of the set cementitious product is at least 35 MPa.

[0038] Preferably, the fusion process provides intraparticle voids of about 13%, wherein when blended with OPC, sand and aggregates, and hydrated to form a cementitious material with crack self-healing properties.

[0039] Preferably, when a soluble accelerator or retarder is added to the cementitious material, the soluble accelerator controls the rate of setting of the cementitious material to set the product with the strength at least 35 MPa, and with a higher mass fraction of pozzolan 40% or greater.

[0040] Preferably, the low-emissions active calcined clay contains at least 50% of metakaolin and less than 1% of mullite.

[0041] Preferably, low CO2 emissions of the low-emissions active calcined clay or the low-emissions active calcined carbonate are produced using a calcination process which uses heat from a low emission intensity fuel.

[0042] Preferably, the low emission intensity fuel is one selected from the group of: biomass, refused derived fuels, renewable electrical power, waste heat from a cement plant or another industrial process.

[0043] Preferably, the activity of the low emissions active calcined clay is produced from input clay powder being ground to a mean particle size of less than about 50 microns; and wherein the calciner used is indirectly heated, and wherein the residence time of the clay powder being calcined is less than about 30 seconds.

[0044] Preferably, the low emissions calcined carbonate constituent is produced by the calcination of a mixture of mineral limestone, magnesite or dolomite; and wherein the degree of calcination is measured by the loss in weight in excess of 95%.

[0045] Preferably, the mixture of mineral limestone, magnesite or dolomite; comprises marl.

[0046] Preferably, the calcined carbonate constituent uses a calcination process which uses heat from a low emission intensity fuel. More preferably, the low emission intensity fuel is one selected from the group of: renewable electrical power, waste heat from a cement plant or another industrial process; and wherein the CO2 emissions from the calcination process is captured.

[0047] Preferably, the activity of the low emissions calcined carbonate constituent is achieved by the following steps of: controlling the sintering of the calcined carbonate powder; grinding the constituent to a mean particle size of less than about 200 microns; using an indirectly heated calciner, and wherein the residence time of the calcined powder is less than 30 seconds; grinding the low emissions calcined carbonate product to about 50 microns or less.

[0048] Preferably, the low-emissions active calcined clay, low emissions calcined carbonate constituent or the carbonate extender are produced by the partial calcination of any mixture of the mineral limestone, magnesite or dolomite.

[0049] A second aspect of the present invention may relate to a flowable low emissions pozzolan powder comprising a substantially fused composite of constituent particles which provide a chemical composition of binder constituents comprising at a low emissions active calcined clay, a low emissions intensity active calcined carbonate each with a surface area greater than 45 m2 / g and a mean pore size greater that about 100 nm set by the respective calcination conditions such as particle size, residence time and steam sintering, and a carbonate extender, with the hydration rate of the constituents of the pozzolan powder set to match that of OPC by control of theparticle sizes of all constituents selected by purity, mineralogy and griding, of about 50pm size. Other constituents may be powder based retardants and accelerators, which control the formation of the cementitious materials when the pozzolan is mixed with ground OPC, sand, aggregates, sand and water.

[0050] Preferably, the means of fusion to make a flowable composite pozzolan powder of the constituent powders may be through a process of co-grinding the pozzolan powder constituents to reduce the particle size to below about 50 , with grinding aids if required, and preferably using mechano-fusion to provide a high degree of homogeneity of the constituents such that the cementitious materials formed when the pozzolan is mixed with OPC and water, exhibits the high rate of temperature increase from exothermic hydration, with the high rate being a characteristic of a material with a uniform reaction rate compared to a material with non-unform hydration rate.

[0051] Preferably, when blended with sand and mixed with water in a to form a hydrated paste which sets to give a cement with a strength of at least 18 MPa in 28 days, and more preferably a strength of more than 30 MPa in 28 days by variation of the constituents, and the means of grinding and fusing; such that at that at least before 28 days the binder constituents of the pozzolan powder have been substantially consumed and the excess of any oxide / or hydroxide is less than about 1%.

[0052] Preferably, when blended with a powder of Ordinary Portland Cement, and mixed with water without accelerators or retarders to form a hydrated paste which sets to give a cement or concrete with a strength of at least 35 MPa in 28 days, and more preferably a strength of more than 40 MPa in 28 days by optimisation of the ratio of the mixture of pozzolan to Ordinary Portland Cement such that within 28 days at least 97% of the hydrated pozzolan powder and the hydrated OPC powder have been incorporated into cementitious networks.

[0053] Preferably, through the fusion process, it provides sufficient intraparticle voids of about 13% so that, when blended with OPC, sand and aggregates, and hydrated to form of form a paste, such voids are filled with water to initiate self-healing of cracks that may otherwise form over time in the application of the set product.

[0054] Preferably, a soluble accelerator or retarder is added to the paste within about 60 minutes of formation of the paste in which the selection of the accelerator is to control the rate of setting is of the paste to deliver the similar or improved outcomes, with desirably a higher mass fraction of pozzolan not less than 40%.

[0055] Preferably, the desired low emissions active calcined clay constituent contains at least 50% of metakaolin, and preferably more than 80%; and most preferably 99% and less than 1% of mullite.

[0056] Preferably, the active calcined clay constituent is low CO2 emissions by virtue of using a calcination process which uses heat from a low emission intensity fuel, including biomass, refused derived fuels or renewable electrical power, or uses waste heat from, say a cement plant or another industrial process.

[0057] Preferably, low emissions calcined clay constituent is active by virtue of the input clay powder has been ground to a mean particle size of less than about 50 microns; and the calciner is preferably indirectly heated; and the residence time of the powder in the calciner is less than about 30 seconds.

[0058] Preferably, the low emissions calcined carbonate constituent is produced by the calcination of a mixture of the mineral limestone, magnesite or dolomite, and may also contain impurities that are desirably in the form of a marl; and where the degree of calcination measured by the loss in weight is desirably in excess of 95%.

[0059] Preferably, the calcined carbonate constituent is low emissions by virtue of using a calcination process which uses heat from a low emission intensity fuel, including renewable electrical power, or waste heat from, say a cement plant oranother industrial process; and the process CO2 emissions are not substantially emitted into air and any fuel CO2 emissions, if any, are also preferably not emitted into the air.

[0060] Preferably, the activity of the low emissions calcined carbonate constituent is achieved by controlling the sintering of the calcined carbonate powder; griding the constituent to a mean particle size of less than about 200 microns; the calciner is indirectly heated; and the residence time of the powder is less than 30 seconds; and the low emissions active calcined product is then ground to about 50 microns or less.

[0061] Preferably, the carbonate is any mixture of the mineral limestone, magnesite or dolomite, and may also contain impurities that are desirably in the form of a marl; and which is ground to about 50 microns or less.

[0062] Preferably, the low emissions calcined carbonate constituent and the extender constituent are produced together by the partial calcination of any mixture of the mineral limestone, magnesite or dolomite, and may also contain impurities that are desirably in the form of a marl.

[0063] Preferably, the low emissions active calcined clay, the low emissions calcined carbonate constituent and the extender constituent are produced together by the partial calcination of any mixture of clay, the mineral limestone, magnesite or dolomite, and may also contain impurities that are desirably in the form of a marl.

[0064] Preferably, the carbonate extender is any mixture of limestone, magnesite or dolomite, and may also contain impurities that are desirably in the form of a marl.

[0065] Preferably, the carbonate extender and calcined carbonate are produced in a low emissions by partly calcining a powder carbonate mineral, or a mixture of carbonate minerals to an extent to achieve (a) the desired mass ratio of the uncalcined material as the extender to the calcined material; and (b) the reactivity of thepozzolan to hydration is controlled by either sintering of the materials or the fusion process to preferably match hydration that of OPC.

[0066] Preferably, the flowable low emissions pozzolan power is a manufactured material with cementitious constituents.

[0067] Preferably, that flowability properties are similar to concrete and does not require excessive water demand or superplasticizers to control flow properties.

[0068] Preferably, that this pozzolan powder is produced with at least more than 20% less CO2 emissions than traditional manufactured pozzolans.

[0069] Preferably, that is capable of OPC clinker replacement for the same performance properties as that of blended cements.

[0070] Preferably, set to match means that the calcination process is controlled to produce material with similar hydration characteristics of OPC cement.

[0071] Preferably, the fused composite of the three listed constituents is ready made for use in concrete batching plants.

[0072] Preferably, the reactivity matching OPC is the combination of the mineral components being calcined in a controlled methodology or process, and the subsequent optimization process through milling or blending of the finished product.

[0073] In a third aspect of the present disclosure, the means of making low emissions, low energy intensity calcined powder constituents of pozzolans using indirect heating of the constituents.

[0074] In a fourth aspect of the present invention, the means of fusing the constituents to make a composite, flowable pozzolan.

[0075] In a fifth aspect of the present invention, the means of optimising the composite pozzolan composition to make mortars, cements and concretes from a paste that sets to high strength durable products (without OPC).

[0076] In a sixth aspect of the present invention, the means of optimizing a blend of the pozzolan and OPC and other constituents to make mortars, cements and concrete from a paste that sets to high strength durable products with a high OPC replacement, preferably greater than 50%.

[0077] In seventh aspect, a formulation for a pozzolan that when blended with OPC that makes a paste which sets which, after setting, is significantly resistant to fracturing and corrosion as an effective ECC.BRIEF DESCRIPTION OF THE FIGURES

[0078] Embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:

[0079] Figure 1 illustrates a schematic of an indirectly heated calciner as an embodiment of the first aspect for one of more of the constituents of the pozzolan.

[0080] Figure 2 illustrates a schematic of a two segment indirectly heated calciner in which a powder is formed of a mixture of calcined clay, lime, and limestone is produced.

[0081] Figure 3 illustrates a schematic of a process flow for making a flowable pozzolan composite, as an embodiment of the second aspect.

[0082] Figure 4 illustrates a schematic of a process flow of cement batching plant in which the OPC, the pozzolan and other constituents are blended with other powder constituents, sand and other aggregates and water to form a setting paste, as an embodiment of the fourth aspect.DESCRIPTION OF THE INVENTION

[0083] Preferred embodiments of the invention will now be described by reference to the accompanying drawings and non-limiting examples.

[0084] Figure 1 describes an example embodiment in which indirectly heated reactor system in which a powder 101 to be calcined, such as a clay mineral or a carbonate mineral in the, is transformed into a pozzolan constituent. An optional gas input stream 103 may be injected into the reactor generally with the intent of controlling the reaction rate, the sintering of the calcined product and energy consumption, and the exhaust process gas steam 104 contains the gas from the relevant calcination reaction such as steam or CO2 considered below. A preferred gas input of limestone calcination may be steam, which may be sourced from the clay calcination reactor, which not only lowers the temperature required for calcination bit also can be used to control the reactivity of the calcined carbonate. The powder 101 is injected into a hopper 105 and fed by a rotary valve 106 into the reactor tube 107. The reactor tube is heated externally by a hot gas, typically from combustion and if so, from a low CO2 emissions fuel, or electric power, and if so by renewable power or from a hot waste gas stream from another industrial process. The calcined power to be used in the pozzolan is collected in a hopper 109 and ejected from the system 110. Particles entrained in the process gas are ejected by a cyclone or filter 111 and reinjected as a powder stream 112. The desirable low energy density of the powdered product is achieved by preheating the input powder 101, generally by capturing heat from the process gas stream 104 and the product gas stream 102 using one of a number of processes in the literature. The desirable low CO2 emissions intensity is achieved by extracting CO2 from the process gas steam 104 using one of a number of processes described in the literature, as and if required. The calcined powder may be sintered, as required, to lower the hydration reaction of the product in the final pozzolan product disclosed herein. Such sintering may occur in the reactor as described, or the reactor bed, or an process outside the reactor (not shown).

[0085] Figure 2 describes an example embodiment of a two-segment calcination process using indirectly heated reactor segments. A limestone powder 201 is calcined in a first indirectly heated reactor segment 202 and a clay powder 203 is calcined in a second indirectly heated reactor segment 204 to give the lime-limestone calcined clay (L2C2) product 205, with a pure CO2 gas steam 206 exhausted from the first segment and a steam stream 207 exhausted from the second reactor segment. The heat in the product stream 205 and the CO2 steam 206 and the steam stream 207 is recuperated (no shown) and used to preheat the limestone and clay steams 201 and 203. In detail, the ground limestone 201, preferably preheated, in hopper 208 is injected into the indirect heated steel reactor tube segment 202 by a rotary valve 209 and the energy from the furnace 210 is heats the limestone so that calcination of the limestone occurs at about 1 bar gas pressure as the particles fall through the reactor to the collector cone 211 where a bed if formed. The degree of calcination is controlled by the furnace settings and the bed residence time, which also impacts on the sintering of lime to achieve the desired reactivity of the pozzolan product. Alternatively, the sintering may be carried out in a separate process outside the reactor (not shown). The rising pure CO2 from calcination is exhausted from the reactor by a fan (not shown) and the fines 212 are separated by a filter 213 to give a gas stream 217 of CO2 at about 1 bar pressure. The calcination of clay 203 occurs in the second indirectly heated reactor segment. The ground clay from hopper 214 is transferred by a transport system 215-216 into the steel reactor segment 204 where it is mixed with the hot partially calcined limestone 217 injected through the rotary valve 218. The additional heat for clay calcination is provided from the furnace 219. The temperature in this segment is kept sufficiently low that the calcined clay may be sintered with in the reactor system, although the general requirement is for a high reactivity of the calcined clay. A small flow of a reducing gas 220, such a syngas, is injected into the base of this segment so that the oxidation of any iron in the reactor is suppressed so the colour of the material meets industry requirements. The falling powder is collected in bed 221 and in ejected from the reactor by the rotary valve 222 to give the pozzolan powder product 205. The rising gas in this reactor segment is primarily steam, and fines are 223 are reinjected into the bed 211 using a filter 224and the steam 207 is exhausted from the reactor. The steam output 207, or a slipstream thereof, may be injected into the carbonate reactor 202 for the benefit of lowering the reaction temperature and to control sintering, so as to control the hydration rate of the pozzolan product. The steam injection should preferably be limited because the steam in the exhaust 206 would be condensed in compression system for carbon capture and storage.

[0086] Figure 3 illustrates a schematic of a process flow for making a flowable pozzolan composite as an embodiment of the second aspect. In this embodiment the powders that constitute the pozzolan are a calcined clay powder 301 and a partially calcined limestone powder 302. The process for making these powders may be different and not optimum for making the pozzolan composite, so, if required the powders are further ground individually in mills 304 and 305, to a size desirable for the fusion process. The mills may be ball mills, Raymond mills or other mills most appropriate for the material. The fusion process is carried out in a system 308 and if required, a flow aid 309 may be added so that the composite pozzolan powder 310 is flowable. The preferable fusion system is a mechano-fusion machine such a produced by Hosakawa in Japan https: / / www.hosokawamicron.co.ip / en / product / machines / detail / 214.html. This machine also acts as a co-grinder of the particles. The intermixing of the materials may impact on the hydration rate of the compounded product.

[0087] Figure 4 is an example embodiment of a process flow of material in a cement batching plant in which OPC powder 401, the composite pozzolan powder 402 and another powder constituent 403 such as gypsum are conveyed and blended to a powder 404 and injected into a blender 405. Aggregate 406 and sand 407 are added into the blender which produces a paste 410 in which the constituents are reacting. A soluble accelerant retarder solution or superplasticizer 411 may be added after the materials are blended. The output of the batching plant 412 is carried from the blending plant, such as a cement truck for delivery at a site at which the setting paste is introduced into the structure in which the setting is completed to a requiredstrength. The hydration rate of the blend will impact on the heat release rate of the powder, which may be controlled by the calcination and fusion processes as described in the previous figures.

[0088] A traditional OPC Clinker plant is a large-scale production process, typically producing about 6000 tpd of ground OPC. The low-cost product is achieved through economies of scale, and the common availability of limestone, silica and amounts of aluminium and iron minerals that enable the formation of ground clinker, OPC, at low cost. These plants are large point sources of CO2 emissions from the unavoidable process CO2 from calcining limestone and the use of carbon-based fuels. The development of low emissions ACM’s, to reach a target of 50% OPC reduction has been developed by the industry to reduce the emissions intensity of cement and concrete to mitigate climate change.

[0089] A successful approach to development of ACM-OPC is LC3 (lime-calcined claycement). For example a typical composition of LC3 has 15% lime, 30% calcined clay, 50% OPC, with 5% gypsum. This sets with comparable strength and durability as OPC. The challenge of this approach is that the production of lime emits CO2 and the emissions intensity of lime is about 785kg CO2 / tonne, so that at face value the emissions intensity is about 630 kg / tonne when the emissions intensity of OPC is taken to be 940 kg / tonne.

[0090] The primary issue of LC3 is that it is essential to co-grind all the powders, which means that the ability of a cement and concrete maker to blend the mixtures at a batching plant for different applications is lost. The flexibility of blending an extender like limestone, and a retarder like gypsum, at a batching plant to meet applications is therefore lost because of the need for co-grinding.

[0091] The prior art of Sceats et. al. teaches that indirect heating of limestone or raw cement meal in a reactor produces a pure gas stream of process CO2, enabling direct capture of this CO2 for CCSU emissions reduction as illustrated in Figure 1. Such a reactor can be used to make the calcined oxides, CaO, CaO.MgO, or MgO.CaCCh orMgO or mixtures thereof, and the calcined clay in which case the exhaust gas is steam. That is, a pair of such reactors may be used as illustrated in Figure 3.

[0092] It is a feature of indirectly heated reactors described above can calcine particles with a size of preferably less than about 200 microns within a residence time of less than about 60 seconds primarily set by the reartor height and the process gas flows within the reactor, with control of the temperature of the reactor walls to preferably less that about 1050°C to control calcination of the particles and sintering of the products. The particle size is determined by pre-grinding the input powders and the sintering of the products are determined by the residence time in the reactor, and post-processing time in heat exchangers and gas compostions in these systems.

[0093] The preferable clay should be preferably dominated by kaolinite based on the prior arts of clay calcination and pozzolan reactivity. However the use of reactive lime and fusion is such that a wider range of clays can be used such as clays in the smectite, illite and chlorite groups, and mixtures therof.

[0094] It may be said that the CO2 emissions capture in the lime calcination is inconsistent with minimising the OPC. However, the total CO2 emissions intensity of a product is dominated by the total CaO in the powders, and an easy capture of this CO2 emitted during pozzolan production leads to a lower emissions intensity of the product. As CO2 is captured in OPC production over time, the emissions intensity will be further lowered.

[0095] It is noted that the MgO containing materials come from dolomite and magnesite minerals, which are generally waste materials at or near limestone mines. The prior art teaches that these materials are reactive due to the short residence time in the rector, and as a result the particles do not swell during hydration, so that the material will not fracture setting concrete or cement.

[0096] The two dedicated calciners of Figure 1 or the one dual segment reactor of Figure2 may be used for calcination of the pozzolan constituents. In addition, one single reactorof Figure 1 may be used to calcine a mix of clay and an carbonate, albeit with controls such as the temperature profile of the external heater, and / or the grind sizes of particles, and / or the reactor length, and / or the residence tome in the bed as variables to control the degree of calcination of the carbonate and the clay, and the activity of each from reactor sintering. It is noted that the presence of steam for the calcination of carbonates will have an impact of reducing the reaction temperature by lowing the partial pressure of CO2, and also impact on the reactivity of the limestone by the known fast sintering of limestone.

[0097] The options used in calcination described above will impact on the grinding and fusion processes used to make a composite pozzolan. The approach of Figure 3 of each material being separately calcined provides the simplest scheme because the particle size for the calcination of each can be optimised. The options of co-calcination described above requires specification of the input particles sizes of the carbonate and the clay inputs. The fusion system described in Figure 3 can operate as a grinder and a fusion system with the appropriate controls. Any binding of particles in the reactors from particles agglomeration due to high temperature reactions will promote the fusion of the particles, and if that process if effective, there may be no need for the mechanofusion step.

[0098] There are other means of fusing particles such as moisture, liquid additives and additives like bentonite which are known arts. The preferred approach of using mechanofusion is that the processes of breaking up and reforming particles leads ultimately to the development of pozzolans which have a uniform distribution of chemical constituents, which is the ideal outcome for reaction uniformity.

[0099] The grinding of dry clays generally gives small particles of less than 20 microns size as the 1: 1 or 1:2 layers of the clays, under pressure, shatter. The grinding of limestones is energy intensive, and a preferred approach is to grind the limestone particles to less than about 200 microns for calcination in an indirectly heated reactor, and then grind the partly calcined limestone to about 20 microns for injection into the fusion system. The fusion system can be designed to produce an output which produces the pozzolan at less than, or greater than 20 microns. If the OPC powder is about 35 microns,neglecting agglomerates, then the pozzolan size should be lower and set to give the highest packing density so that, the water demand, after hydration is as low as possible. The proposed approach of mechanofusion provides the necessary control for powder packing.

[0100] The invention of this disclosure is exemplified by the separating the production of a pozzolan composite of low emissions lime, limestone and calcined clay (called herein L2C2), with its own accelerator / retardant, so that blending with OPC (called C for a naming convention) and a retarder in a batching plant may be used to make cement / concrete paste for different applications (say L2C3). In this example, the pozzolan by itself form a strong binder and the strength of the blend with OPC allows a higher replacement of OPC than 50%. A process improvement is that the lime / limestone ratio can be controlled by the degree of calcination of an input of limestone in a reactor, to make a product, in this example of Figure 2.

[0101] The example pozzolan L2C2is essentially a low emissions Roman Cement formulation of lime, limestone and calcined clay made in reactor systems described above. The pozzolan L2C2may be formulated with OPC to be an ECC by setting with sufficient mobile water, which is initially absorbed within the pozzolan as a design feature, so as to not impact on workability required for strong setting, so that the water can migrate to heal small cracks that emerge to extend the lifetime of the structure. Such an approach can lower the corrosion rate of the structure in salt water, or mitigate failure in seismic events, and enhance durability of structures. The design feature is enabled by manufacture of porous constituents using the calcination processes described above; and the using the know arts to increase porosity of particles if required; controlling the grind sizes of these constituents; controlling the fusion processes to provide inter-constituent pores that weakly absorb the required water to provide mobility required for an ECC composite with OPC.

[0102] The indirectly heat calciners describe above may make pozzolans with a porosity of about 30-40% by minimising the residence time in the reactor to about 60 seconds or less to inhibit both pore size reduction and particle size reduction fromsintering. The sintering can be controlled to give a pore size distribution, say between 0.1 to 0.5 microns to provides the fast transport of water through the particle while not sintering to an extent that the particles swell to crack the setting pozzolan-OPC mix. During production of the pozzolan, steam may be used as a catalyst to aid the control of the desired degree of sintering along with the temperature of residence time in the reactor, reactor segments or heat exchangers. In certain embodiments the reactor temperature and residence time of particles is set a need to inhibit phase changes of the product which generally adversely result in a loss of porosity, slow swelling wit rehydration, and in certain cases a loss of pozzolanic activity. For example, it has been found that for calcined clays that the formation of mullite can be supressed completely by the control features of indirtectly heated reactors.

[0103] In sum, the invention disclosed herein are based on the observation that fast hydration of OPC and the pozzolan powders allows the formation of calcium-silicate- aluminate-carbonate -hydrate binding networks to consume the input powders during setting to form stronger materials that bind to the sand and aggregates to give a strong durable network. The kinetics of binder formation can be controlled by accelerators / retardant so that, ideally those reaction rates in the OPC are closely matched to those in the pozzolan itself, on the basis that the mixture rates differences are minor.

[0104] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms, in keeping with the broad principles and the spirit of the invention described herein.

[0105] The present invention and the described preferred embodiments specifically include at least one feature that is industrial applicable.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A flowable, low-emissions pozzolan powder comprising: a substantially fused composite of constituent particles, wherein the constituent particles comprise: a low-emissions active calcined clay; a low-emissions active calcined carbonate with a surface area exceeding 45 m2 / g and a mean pore size greater than about 100 nm; and a carbonate extender; wherein the pozzolan powder has a particle size of about 50 microns, and wherein the hydration reactivity of the pozzolan powder is adjustable by particle engineering to match the hydration rate of Ordinary Portland Cement (OPC).

2. The flowable, low-emissions pozzolan powder according to claim 1, wherein the constituent particles further comprise: powder based retardants and accelerators for controlling the formation of cementitious materials when the pozzolan powder is combined with ground OPC, sand, aggregates, and water.

3. The flowable, low-emissions pozzolan powder according to any one of claims 1 to 2, wherein the fusion process comprises: co-grinding the constituent particles to reduce particle size to below approximately 50 microns; mechano-fusing the co-ground constituent particles to form a homogenous mixture, wherein the homogenous mixture forms a cementitious material when combined with OPC and water.

4. The flowable, low-emissions pozzolan powder according to claim 3, wherein when blended with the OPC and water, forms a settable hydrated paste, in which the strength of the set product is adjustable by changing the ratio of the mixture of the pozzolan powder to OPC, wherein the minimum strength of the set cementitious product is at least 35 MPa.

5. The flowable, low-emissions pozzolan powder according to any one of claims 3 to 4, wherein the fusion process provides intraparticle voids of about 13%, wherein when blended with OPC, sand and aggregates, and hydrated to form a cementitious material with crack self-healing properties.

6. The flowable, low-emissions pozzolan powder according to any one of claims 3 to 5, wherein when a soluble accelerator or retarder is added to the cementitious material, the soluble accelerator controls the rate of setting of the cementitious material to set the product with the strength at least 35 MPa, and with a higher mass fraction of pozzolan 40% or greater.

7. The flowable, low-emissions pozzolan powder according to any one of claims 3 to 6, wherein the low-emissions active calcined clay contains at least 50% of metakaolin and less than 1% of mullite.

8. The flowable, low-emissions pozzolan powder according to any one of claims 3 to 7, wherein low CO2 emissions of the low-emissions active calcined clay or the low- emissions active calcined carbonate are produced using a calcination process which uses heat from a low emission intensity fuel.

9. The flowable, low-emissions pozzolan powder according to claim 8, wherein the low emission intensity fuel is one selected from the group of: biomass, refused derived fuels, renewable electrical power, waste heat from a cement plant or another industrial process.

10. The flowable, low-emissions pozzolan powder according to any one of claims 3 to 9, wherein the activity of the low emissions active calcined clay is produced from input clay powder being ground to a mean particle size of less than about 50 microns; and wherein the calciner used is indirectly heated, and wherein the residence time of the clay powder being calcined is less than about 30 seconds.

11. The flowable, low-emissions pozzolan powder according to any one of claims 3 to 10, wherein the low emissions calcined carbonate constituent is produced by the calcination of a mixture of mineral limestone, magnesite or dolomite; and wherein the degree of calcination is measured by the loss in weight in excess of 95%.

12. The flowable, low-emissions pozzolan powder according to claim 11, wherein the mixture of mineral limestone, magnesite or dolomite; comprises marl.

13. The flowable, low-emissions pozzolan powder according to any one of claims 11 to12, wherein the calcined carbonate constituent uses a calcination process which uses heat from a low emission intensity fuel.

14. The flowable, low-emissions pozzolan powder according claim 13, wherein the low emission intensity fuel is one selected from the group of: renewable electrical power, waste heat from a cement plant or another industrial process; and wherein the CO2 emissions from the calcination process is captured15. The flowable, low-emissions pozzolan powder according to any one of claims 11 to13, wherein the activity of the low emissions calcined carbonate constituent is achieved by the following steps of: controlling the sintering of the calcined carbonate powder; grinding the constituent to a mean particle size of less than about 200 microns; using an indirectly heated calciner, and wherein the residence time of the calcined powder is less than 30 seconds; grinding the low emissions calcined carbonate product to about 50 microns or less.

16. The flowable, low-emissions pozzolan powder according to claim 1, wherein the low- emissions active calcined clay, low emissions calcined carbonate constituent or thecarbonate extender are produced by the partial calcination of any mixture of the mineral limestone, magnesite or dolomite.

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