WO2023141670A1

WO2023141670A1 - Admixture for concrete

Info

Publication number: WO2023141670A1
Application number: PCT/AU2022/051523
Authority: WO
Inventors: Paul KIDD; Bruce Perry
Original assignee: Cement Australia Pty Ltd
Priority date: 2022-01-25
Filing date: 2022-12-16
Publication date: 2023-08-03

Abstract

The present disclosure relates to admixtures, such as powdered admixtures, for concrete comprising sulfate, formate, water reducer and supplementary cementitious material. Preferably the admixture also comprises calcium carbonate. The admixtures of the invention enable higher levels of supplementary cementitious material to be used in concrete to reduce net embodied carbon. The present disclosure also describes preparations of the admixtures and uses thereof.

Description

ADMIXTURE FOR CONCRETE

TECHNICAL FIELD

[0001] The present invention relates to admixtures for concrete, methods of preparation, and uses thereof. However, it will be appreciated that the invention is not limited to this particular field of use.

BACKGROUND OF THE INVENTION

[0002] The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of the common general knowledge in the field.

[0003] Concrete is the worlds most used building material and cement is an indispensable material required to produce concrete. Portland cement manufacturing is associated with significant CO2 emissions, and its manufacture is estimated to contribute about 6-8% of anthropogenic CO2 emissions. There is significant pressure to reduce the CO2 emissions associated with cement and concrete production and use. Concrete is a vital component in construction and is not likely to be replaced, and so it is necessary to consider how levels of embodied CO2 in concrete can be reduced.

[0004] In 2020, the Global Cement & Concrete Association (GCCA) released a Climate Ambition Statement which committed the industry to drive down the industry’s carbon footprint with a view to delivering society carbon neutral concrete by 2050. This would entail work across the entire value chain to deliver this aspiration in a circular economy, whole of life context. In overview, the GCCA 2050 Net Zero Roadmap sets out in detail how, in collaboration with built environment stakeholders and policymakers, they will fully decarbonise the cement and concrete industry and provide net zero concrete for the world. Further to this, in October 2021 the Decarbonisation Pathway for the Australian Cement and Concrete Industry was released and identifies the critical pathways required to drive lower CO2 emissions. The Decarbonisation Pathway towards carbon neutral cement and concrete will require conventional measures to be applied to the highest degree possible but also breakthrough technologies.

[0005] Portland cement is made from clinker (about 95 wt.%) and gypsum (about 5 wt.%).

Low clinker content in cement leads to lower CO2 emissions. Clinker in cement can also be replaced by Supplementary Cementitious Materials (SCMs), such as fly ash and slag to produce blended and composite cements. SCMs such as calcined clay and volcanic ash have also gained some prominence over recent years in low CO2 cement and concrete. It is generally understood that 0.818 tonnes of CO2 is produced per tonne of clinker (“Scope 1”), which equates to 0.774 tonnes CO2 produced per tonne of cement (Scope 1 and "Scope 2”), on the basis of 7.5 wt.% limestone, 5 wt.% gypsum and 87.5 wt.% clinker. Scope 1 greenhouse gas emissions are understood as the emissions released to the atmosphere as a direct result of an activity, or series of activities, at a facility level, and are sometimes referred to as direct emissions (process and thermal). Scope 2 (“indirect”) emissions derive from consumption of purchased electricity, heat or steam (e.g., the emissions associated with the electricity purchased to manufacture cement).

[0006] SCMs are understood as essentially waste-products or by-products of other manufacturing processes. The primary energy and emissions associated with the use of SCMs in concrete need to be considered from three areas: (i) allocation from the upstream manufacturing process, (ii) transportation, and (iii) further preparation (drying and grinding). The main SCMs in use today are fly ash and ground granulated blast furnace slag (GGBFS).

[0007] Fly ash (low calcium Class F) is a fine grey powder consisting mostly of spherical glassy particles that are produced as a by-product in coal fired power stations. Fly ash has pozzolanic properties, meaning that it reacts with lime to form cementitious compounds. A significant proportion of the fly ash presently produced in Australia is land-filled or used in mine voids. Fly ash is sometimes attributed a zero emission factor, however this conclusion is flawed because fly ash needs to be extracted from the power station precipitators or bag houses, classified according to fineness and loss on ignition (carbon content), and then stored and transported. Therefore, to take into account emissions across the supply chain, is it appropriate to consider that 0.027 tonnes of CO2 is produced per tonne of fly ash. In other words, each tonne of cement that could be replaced with fly ash represents a reduction of 0.747 tonnes of emitted CO₂.

[0008] GGBFS is formed when granulated blast furnace slag (GBFS) is further processed or ground using conventional cement clinker grinding technology. GGBFS is produced after molten slag has been quenched rapidly by passing it through a trough of high-pressure, high- volume water sprays, causing the heat energy contained in the molten slag to explode and instantly form GBFS. In contrast to fly ash, GGBFS requires granulation (by water), drying and then milling (before storage and transportation). Therefore, although slag is essentially a waste product, there are many competing demands for the slag that is currently produced and if not used in the production of concrete, would be taken up elsewhere. In view of this, it is appropriate to consider that 0.1430 tonne of CO2 is produced per tonne of GGBFS. In other words, each tonne of cement that could be replaced with GGBFS represents a reduction of 0.632 tonnes of emitted CO2.

[0009] The partial substitution of cement with SCMs is commonly practiced by the Australian concrete industry. The introduction of SCMs results in a reduction in the total content of clinker in the binder, which reduces the environmental impacts of concrete production. It is also widely accepted across the construction material industry that SCMs enhance the later age performance properties and durability aspects of concrete. Additionally, SCMs in concrete benefits the environment by avoiding the requirement for landfilling of them.

[0010] Relatively higher levels of SCM usage in concrete, however, has not been possible to date because of the negative impact on construction programs due to the significant reduction in early strength development of such mixes. For example, supplementary levels of fly ash are typically limited to around 25 wt.% of the total binder content because of retarded setting and early strength development. Similar issues exist for slag, although supplementary levels of 40- 50 wt.% are more common.

[0011] In view of these limitations, one or more preferred objects of the present invention are to enable higher levels of SCM usage in concrete to reduce net embodied carbon. Further preferred objects of the present invention provide significantly lower shrinkage and/or enhanced strength performance during the construction phase and beyond.

[0012] It is an object of the present invention to overcome or ameliorate one or more of the disadvantages of the prior art, or at least to provide a useful alternative.

SUMMARY OF INVENTION

[0013] The present inventors have now surprisingly found that an admixture for concrete comprising a sulfate of an alkali metal selected from sodium and potassium, a formate salt, and a water reducer facilitates or enables higher levels of cement replacement with SCM than would otherwise be possible for the same or substantially equivalent concrete properties at relatively lower SCM levels. It will be appreciated that higher levels of SCM usage provides concomitant reductions in embodied CO2.

[0014] In a first aspect, the present invention provides an admixture for concrete comprising: a sulfate of an alkali metal selected from sodium (Na) and potassium (K); a formate salt; and a water reducer.

In some preferred embodiments, the admixture comprises a defoamer.

[0015] In a second aspect, the present invention provides an admixture pre-blend comprising: the admixture according to the first aspect; and supplementary cementitious material (SCM).

[0016] In a third aspect, the present invention provides a mix design for concrete comprising the admixture of the first aspect.

[0017] In a fourth aspect, the present invention provides a use of the mix design according to the third aspect or the admixture according to the first aspect to prepare concrete, wherein the concrete comprises cementitious material comprising SCM and cement, and optionally aggregate.

[0018] In a related aspect, the present invention provides a concrete mixture comprising: an admixture for concrete comprising: a sulfate of an alkali metal selected from sodium (Na) and potassium (K); a formate salt; a water reducer; and cementitious material comprising SCM and cement; and optionally aggregate.

[0019] In a fifth aspect of the present invention, there is provided an admixture according to the first aspect in powder or dry form which is pre-blended with one or more SCMs before delivery to the concrete producer.

[0020] In a sixth aspect of the present invention, there is provided a powdered cement preblend comprising the admixture according to the first aspect, optionally further including a SCM.

[0021] Pre-blending of the admixture, preferably in a powdered form, into bulk SCM may be a preferable option where the aim is to improve the reactive efficiency of SCM before bulk dispatch to the concrete producer. This embodiment of the present invention may be advantageous for low efficiency SCM such as volcanic ash, calcined clays, reclaimed dam (pond) ash, and other natural and manufactured pozzolanic material.

[0022] Inter-grinding the admixture in the cement milling process, preferably in a powdered form, into bulk cementitious product may be a preferable option where the aim is to improve the overall reactive efficiency of both the cement and the admixture (by fineness reduction) before bulk dispatch to the concrete producer. This process may include co-grinding of SCM or solely SCM (GBFS). This embodiment of the present invention may be advantageous for improving efficiency of admixture as well as reducing blending costs.

Sulfate

[0023] In the present invention, sulfate is preferably of an alkali metal selected from sodium (Na) and potassium (K), with Na being the most preferred. Sodium sulfate is an inorganic compound with formula Na2SO4 as well as several related hydrates. All forms are white solids that are relatively soluble in water. The decahydrate is a major commodity chemical product.

[0024] In some embodiments of the present invention, the sulfate may be present in the range of 1-50 wt.%. For example, sulfate may be present in 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, or 50 wt.% or any range therein. Preferably, the sulfate is in the range of 20-25 wt.% of the solid components of the admixture.

[0025] Alternatively, the sulfate ion may be derived from anhydrite (CaSCU) which is a moderately soluble form of gypsum. Anhydrite is a white powder that is relatively soluble in water. It is preferable that the anhydrite is not “burnt”, which tends to transform it into the insoluble species. If anhydrite is substituted for sodium sulfate, it is preferable to do so on an approximate 1:1 basis. Preferably no more than 50 wt.% of the sodium sulfate is replaced because the anhydrite is significantly less soluble.

Formate

[0026] In the present invention, the formate salt is selected from calcium, sodium, and potassium, with Ca being the most preferred (Ca(HCOO)2). Calcium formate is a white or cream coloured powder and is soluble in water. In some embodiments of the present invention, formate may be present in the range of 1-50 wt.%. For example, formate may be present in 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, or 50 wt.% or any range therein. Preferably, formate is in the range of 20-30 wt.% of the solid components of the admixture. In other embodiments, the formate salt is an alkali metal or alkaline-earth metal formate. It has been surprisingly found that in at least some embodiments of the invention, the use of formate tends to control extraneous entrained air in concrete.

[0027] In some embodiments of the present invention, the addition of formate appears to be useful for concrete mixes at low temperature, and/or for inhibition of corrosion of metal reinforcement. In some further embodiments of the present invention, formate appears to be effective in the prevention of efflorescence. Calcium formate may also function as a fire retardant.

[0028] In some embodiments of the present invention, relatively lower levels of formate in the admixture may enhance early reactivity (compressive strength at less than 3 days) and/or reduce overall concrete shrinkage.

Calcium carbonate

[0029] The admixture of the present invention may also comprise calcium carbonate. Without wishing to be being bound by any theory, it is believed the calcium carbonate is an inert component that acts as a “carrier”, but has the advantage of aiding particle packing and seeding in the concrete matrix. Preferably, the calcium carbonate is in the form of fine limestone with a particle size less than 150 microns. In some embodiments of the present invention, the calcium carbonate is present in the range of 50-60 wt.%. In preferred embodiments, the calcium carbonate is in the range of 52-59 wt.% of the solid components of the admixture.

Water reducer

[0030] In the present invention, the water reducer is a high-range water reducer (also known as a superplasticiser) and is selected from the group consisting of polycarboxylate ether (PCE), sodium lignosulphonate, and sodium naphthalene sulphonate. Other water reducers will be known to the skilled person, such as sulfonated naphthalene formaldehyde condensate, sulfonated melamine formaldehyde condensate, and acetone formaldehyde condensate. Crosslinked melamine- or naphthalene-sulfonates, referred to as PMS (polymelamine sulfonate) and PNS (polynaphthalene sulfonate), respectively, are further examples. Preferred water reducers for use in the present invention are PCEs, which are free-flowing spray dried powders which are routinely used as a high range water reducer for cement-based materials. It is also an excellent dispersion plasticiser suitable for gypsum and other mineral materials.

[0031] In some embodiments of the present invention, the water reducer is present in about 0.001, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 3, 4, or 5 wt.% of the solid components of the admixture or any range therein.

[0032] In a preferred embodiment of the present invention, the superplasticiser comprises a defoamer, more preferably an inherent defoamer. Advantageously, the defoamer reduces concrete entrained air which in turn improves concrete strength through densification, and thereby at least partially overcomes a side-effect of using a water reducer, for example a PCE superplasticiser, in that it can tend to pull or draw an excess of air into the concrete slurry. In some further embodiments of the present invention, the defoamer works in conjunction with the formate additive to improve overall concrete density by removing extraneous entrained air in concrete.

Supplementary cementitious material

[0033] The term “supplementary cementitious material” or “SCM" as used herein is a material with which cement can be substituted or partially replaced.

[0034] In the present invention, SCM includes one or more of fly ash, GGBFS (slag), and silica fume. For example, the SCM may be selected from one or more of the following: fly ash, rice husk ash, silica fume, blast furnace slag, clay, calcined clay, metakaolin, zeolites, metastable inorganic oxides, ground glass, powdered inorganic oxides, gypsum, or dam ash (e.g., beneficiated dam ash, reclaimed dam (pond) ash). In some embodiments of the present invention, the slag may comprise silicates, oxides and other compounds of calcium, silicon, manganese, magnesium, iron, aluminium, manganese, titanium, sulfur, chromium and nickel.

[0035] In some embodiments of the present invention, the fly ash is compliant with Australian Standard AS3582.1 for SCMs for use with general purpose and blended cement. In some embodiments of the present invention, the slag is compliant with Australian Standard AS3582.2 for SCMs for use with Portland cement. In some embodiments of the present invention, Manufactured Pozzolans may be compliant with Australian Standard AS3582.4 for SCMs for use with Portland cement. These standards are used in Australia, but other equivalent national standards can be used as well. [0036] The admixture of the present invention facilitates or enables relatively high levels of replacement of cement with SCM, e.g., up to 85 wt.%. It will be appreciated that use of higher levels of SCM in concrete translates to advantageously lower embodied carbon.

[0037] In some embodiments of the present invention, the SCM to cement ratio (for example type GP cement) is in the range of 1:4 to 4:1, such as 1:3, 1:2, 1:1, 2:1, or 3:1.

[0038] In some embodiments of the present invention, the cement replacement with SCM is in the range of 15-85 wt.%, depending on the type of SCM.

[0039] In some embodiments of the present invention, the dosage rate of the admixture may be adjusted in the blending process to take into account the varying SCM ratios used in concrete. The skilled person would appreciate that the ratio of slag in a concrete mixture can be higher than that of fly ash. Therefore, higher dose rates may be required in fly ash to ensure that adequate admixture is introduced into concrete. For example, the admixture in fly ash may be 5% (w/w) of the fly ash but at 4% in GGBFS.

Pigments

[0040] The admixture of the present invention may also comprise a pigment. The pigment may be used in various embodiments of the present invention. For example, red and green oxides may be used to differentiate admixtures for low shrinkage/early reactivity and later reactivity, respectfully. The pigment may also give some indication when batching of the homogeneity of the concrete mix. Preferably, the pigment is used in low enough doses so that it does not affect the overall colour of the concrete.

[0041] In some embodiments of the present invention, the pigment may be present in about 0.001, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, or 2 wt.% of the solid components of the admixture, or any range therein. Preferably, the pigment is iron oxide based.

Concentrations of components

[0042] As discussed above, concrete is a construction material composed of cement (commonly Portland cement) as well as other cementitious or pozzolanic materials such as fly ash and slag, aggregate, water, and chemical admixtures. Typically, the level of aggregate is about 60-80 wt.% of the concrete. The aggregate may be a mixture of coarse aggregate (made of crushed rocks such as limestone, or granite) and fine aggregate (such as sand). The chemical admixture may comprise components such as water reducers, superplasticisers, air entraining agents, accelerators, retardants, dispersants, extenders, weighting agents, gels, defoamers, fluid loss additives etc, and which are preferably used at the manufacturer’s recommended concentration.

[0043] It will be appreciated that a retardant is an agent, preferably a chemical agent, used to increase the thickening time of cement slurries to enable proper placement. The retardant may be selected from a sugar, a phosphonate, organic acids or their salts, or a mixture thereof.

[0044] It will be appreciated that an accelerator makes concrete set faster by increasing the rate of hydration. At the same time, the accelerator promotes strength development. The accelerator may include nitrate, calcium chloride, calcium hydroxide, or calcium oxide.

[0045] The admixture of the present invention may be added to a concrete mix at a concentration of around 1-30 kg/m³, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30 kg/m³. The admixture may be added directly to the batching vessel in packaged lots or by a dedicated weigh-feeder from a dispatch silo or hopper.

[0046] It will be appreciated that the various components of the admixture of the present invention can be added individually to the concrete mix in a sequential manner, or can be added concurrently, or the admixture can be pre -prepared as a blend and that blend added directly to the concrete mix. In other embodiments, the admixture can be pre-blended with calcium carbonate carrier, and the combined carbonate/admixture blend can be added to the concrete mix. It will be appreciated that this last embodiment is advantageous in that there is more efficient and homogenous mixing of the admixture into the concrete mix compared to adding several kilograms of admixture (containing active ingredients only) to many tonnes of concrete mix.

[0047] In preferred embodiments of the present invention, the admixture is in a powdered or dry form. However, the admixture of the present invention may be provided in a solubilised form. For example, in water, in an emulsion, in a slurry, or in a paste, which is then added to the concrete mix. In this case, any additional water would be taken into account when calculating the required volume of water to be added to the concrete.

[0048] Further embodiments of the present invention include various ratios of sulfate to formate depending on the performance requirements of the concrete. For example, specific concrete mix designs may require 1-day strengths to be substantially unaffected with an increase of SCM from 20 wt.% to 40 wt.%, and may dictate that the mix design requires 28-day strengths to be consistent with the 20 wt.% SCM mix. It has been generally found in some embodiments of the invention that formate may act to promote later strength, and sulfate may act to promote early strength. It has also been surprisingly found that the admixture of the invention moves the strength profile on the age scale, rather than generating additional strength. In the prior art where higher early strength is promoted, this is typically to the detriment of later age strength. For example, use of SCM tends to promote higher strength at the expense of early strength. Surprisingly, the admixture of the invention seems to account for, or compensate for, the effect of SCM on early strength.

[0049] In some embodiments of the present invention, the ratio of sulfate to formate is in the range of about 9:1 to about 1:1. For example, the ratio of sulfate to formate may be about 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, or about 1:1. It would be understood that the relative amounts of sulfate to formate may also be expressed as a percentage.

[0050] In some embodiments of the present invention, the ratio of sulfate to formate is about 4:1.

[0051] In some embodiments of the present invention, the ratio of sulfate to formate is about 1:1.

Advantages of the admixture of the invention

[0052] The present invention provides one or more of the following advantages: increased levels of SCM in concrete, enhanced early reactivity in high SCM mixes, and/or lower drying shrinkage in concrete. Further advantages of the present invention are one or more of the following:

• provides a viable admixture to reduce the overall net embodied carbon in concrete;

• comprises a suite of chemicals and minerals that show an excellent working interrelationship when combined;

• works well in concrete with slag, fly ash and other pozzolanic material;

• is an excellent admixture for post-tensioned concrete requiring maturity testing;

• improves density of concrete to prevent carbonation at higher SCM levels;

• allows different modes of dosing at concrete batching plant; allows for different ratios of activators to meet differing concrete requirements; • may include calcium carbonate to assist in concrete particle packing;

• delivery to concrete plants in packages or bulk;

• ability to control early or later strength development;

• compliant to the Australian Standard for Concrete admixtures AS 1478;

• concrete producers have flexibility to remove other admixtures from concrete;

• reduces entrained air in concrete;

• reduces potential efflorescence on concrete surfaces;

• cost impact and potential savings, i.e., the ability to reduce total cementitious content; and/or

• improves the efficiency of low reactivity SCM.

[0053] Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the present invention.

[0054] In one aspect, the admixtures of the present invention facilitate or enable higher ratios of SCMs such as fly ash and or slag to be used in concrete mixes than would otherwise be possible and with the same or better mechanical and physical properties of the ultimate cured concrete at relatively lower concentrations of SCMs. Furthermore, the admixtures of the present invention may be used with alternative SCMs such as beneficiated dam ash and calcined clays. Ternary mix designs of up to 80 wt.% SCM have been shown herein to perform similarly to “normal” or standard mixes containing 50 wt.% replacement. Advantageously, higher SCM levels are commensurate with lower embodied carbon levels in concrete.

[0055] In some embodiments of the present invention, the admixture allows for cement replacement by SCM of about 15, 20, 25, 30, 35, 40, 45, 55, 65, 70, 75, 80, or 85 wt.%, which represents an increase in cement replacement by SCM of 5, 10, 15, 20, 25, 30, 40 or even 50% with the same or better mechanical and physical properties of the ultimate cured concrete at relatively lower concentrations of SCMs.

[0056] In some embodiments of the present invention, the admixture provides a reduction in the embodied carbon content of concrete of about 10, 15, 20, 25, 30, 35, 40, 45, or 50%. [0057] In another aspect, the admixtures of the present invention seem to “compensate” for the usual lower reactivity at early ages when using elevated SCM levels. The admixtures of the present invention surprisingly provide comparable early strengths when compared to 100% general purpose cement concrete mixes, and in some cases exhibit even better early strengths.

[0058] In some embodiments of the present invention, the admixture provides an early strength development in high SCM concrete of about 1, 2, 3, 4, or 5 days. In particular, the present invention provides “Equivalent Age Strength Performance” about 1, 2, 3, 4, 5, 6, 7 8, 9 or 10 days. The person skilled in the art will be familiar with such comparisons.

[0059] In another aspect of the present invention, the admixtures reduce overall shrinkage, thereby enabling concrete producers to compete in markets where ultra-low shrinkage is required. Ultra-low shrinkage concrete usually requires relatively expensive shrinkage reducing admixtures together with carefully selected aggregate, which usually prevent some concrete producers from entering that market.

[0060] Concrete drying shrinkage is an important property as excessive drying shrinkage can lead to cracking that is detrimental to performance, durability and/or appearance. Volume change due to drying shrinkage is typically reported using the term “microstrain”. In some embodiments, the admixture of the present invention provides a reduction in drying shrinkage of concrete compared to cured concrete without the admixture of about 35, 40, 45, 50, 55, 60, or 65%.

[0061] In another aspect, the admixtures according to the present invention facilitate improvement in SCM efficiency, which may in turn be dispatched as a bulk product. Concrete producers are able to receive bulk supply of SCM with the admixture already incorporated into the product thus removing the need for dosing the admixture at the concrete batching plant.

[0062] In an aspect, the present invention provides a method of reducing the embodied carbon content of concrete comprising using the admixture to prepare concrete.

[0063] In another aspect, the present invention provides a method of increasing the amount of SCM in concrete comprising using the admixture to prepare concrete.

[0064] In another aspect, the present invention provides a method of producing concrete comprising mixing the admixture with SCM and cement in the presence of water and optional aggregates.

[0065] In another aspect, the present invention provides a concrete prepared by mixing the admixture with SCM and cement in the presence of water and optional aggregates.

[0066] The present invention also compensates for the usual lower reactivity at early ages when using elevated SCM levels, as well as promoting expansion across all ages to reduce overall concrete drying shrinkage. Varying the ratios of the active components in the admixture give some flexibility in meeting the requirements of various concrete performance requirements, as discussed above.

BRIEF DESCRIPTION OF DRAWINGS

[0067] Preferred features, embodiments and variations of the present invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the present invention. The Detailed Description will make reference to a number of drawings as follows:

[0068] Figure 1 compares the compressive strength of concrete mix designs comprising the admixture and a binary blend of cement and fly ash (see Table 1), indicating that use of the admixture provides enhanced early compressive strength to offset higher levels of SCM, including at day 1 (see mix references 2, 4).

[0069] Figure 2 compares the drying shrinkage of concrete mix designs comprising the admixture and a binary blend of cement and fly ash (see Table 1), indicating that use of the admixture reduces drying shrinkage (see mix references 2, 4) compared to concrete which does not contain the admixture (see mix references 1, 3).

[0070] Figure 3 is an evaluation of the embodied carbon content of concrete mix designs comprising the admixture and a ternary blend of cement, fly ash, and slag (see Table 2). The figure demonstrates that use of the admixture allows the mix design to include a significant increase in SCM without significantly affecting performance (see mix reference 2). This in turn provides a reduction in embodied carbon content

[0071] Figure 4 compares the compressive strength of concrete mix designs comprising the admixture and a ternary blend of cement, fly ash, and slag (see Table 2), indicating that use of the admixture provides sufficient compressive strength across all ages even at relatively high SCM levels (see mix reference 2).

[0072] Figure 5 shows the compressive strength of concrete mix designs using different ratios of sulfate to formate (see Table 3). Mix reference 1 contains a 1:1 ratio of sulfate and formate. Mix references 2, 3, and 4 contain a 4:1 ratio of sulfate and formate.

[0073] Figure 6 shows the compressive strength of concrete mix designs using a relatively low water reducer dosage under accelerated curing and an elevated level of fly ash replacement of cement, (see Table 4). The figure indicates that use of the admixture provides high early strength without compromising later strength.

[0074] Figure 7 shows the compressive strength of concrete mix designs comprising the admixture and different types of SCM (see Table 5).

[0075] Figure 8 shows the early age compressive strength of concrete mix designs based on ternary cementitious blends of GP cement, fly ash and slag cured at low temperature (see Table 6).

[0076] Figure 9 shows the later age compressive strength of concrete mix designs based on ternary cementitious blends of GP cement, fly ash and slag cured under standard curing conditions (see Table 6).

[0077] Figure 10 shows the early age compressive strength of concrete mix designs based on binary fly ash cementitious blends cured at low temperature (see Table 7).

DEFINITIONS

[0078] In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the present invention only and is not intended to be limiting.

[0079] Unless the context clearly requires otherwise, throughout the description and the claims, the terms “comprise”, “'comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. For example, a composition, mixture, process or method that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, mixture, process or method.

[0080] The transitional phrase "consisting of’ excludes any element, step, or ingredient not specified. If in the claim, such would close the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.

[0081] The transitional phrase "consisting essentially of" is used to define a composition, process or method that includes materials, steps, features, components, or elements, in addition to those literally disclosed, provided that these additional materials, steps, features, components, or elements do not materially affect the basic and novel characteristic(s) of the claimed invention. The term "consisting essentially of" occupies a middle ground between "comprising" and "consisting of".

[0082] Where the applicant has defined an invention or a portion thereof with an open-ended term such as "comprising", it should be readily understood that (unless otherwise stated) the description should be interpreted to also describe such an invention using the terms "consisting essentially of" or "consisting of." In other words, with respect to the terms “comprising”, “consisting of’, and “consisting essentially of’, where one of these three terms is used herein, the presently disclosed and claimed subject matter may include the use of either of the other two terms. Thus, in some embodiments not otherwise explicitly recited, any instance of “comprising” may be replaced by “consisting of’ or, alternatively, by “consisting essentially of’. Also, the indefinite articles "a" and "an" preceding an element or component of the invention are intended to be non-restrictive regarding the number of instances (i.e., occurrences) of the element or component. Therefore "a" or "an" should be read to include one or at least one, and the singular word form of the element or component also includes the plural unless the number is obviously meant to be singular.

[0083] As used herein, with reference to numbers in a range of numerals, the terms "about," "approximately" and "substantially" are understood to refer to the range of -10% to +10% of the referenced number, preferably -5% to +5% of the referenced number, more preferably -1 % to + 1 % of the referenced number, most preferably -0 .1 % to +0 .1 % of the referenced number. Moreover, with reference to numerical ranges, these terms should be construed as providing support for a claim directed to any number or subset of numbers in that range. For example, a disclosure of from 1 to 10 should be construed as supporting a range of from 1 to 8, from 3 to 7, from 1 to 9, from 3.6 to 4.6, from 3.5 to 9.9, from 8 to 10, and so forth.

[0084] As used herein, wt.% refers to the weight of a particular component relative to total weight of the referenced composition.

[0085] The term "and/or" used in the context of "X and/or Y" should be interpreted as "X," or "Y," or "X and Y." Similarly, "at least one of X or Y" should be interpreted as "X," or "Y," or "both X and Y."

[0086] The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.

[0087] Where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term “about”. The examples are not intended to limit the scope of the invention. In what follows, or where otherwise indicated, “%” will mean “weight %” (wt%), “ratio” will mean “weight ratio” and “parts” will mean “weight parts”.

[0088] The complete disclosures of the patents, patent documents and publications cited herein are incorporated by reference in their entirety as if each were individually incorporated.

[0089] As used herein “GP”, “GP cement”, or “general purpose cement” means cement manufactured from Portland cement (i.e., clinker and gypsum), and mineral addition. Type General Purpose Cement is typically understood as the Australian Standard designation within Australian Standard 3972. Most other cement standards (including EN & ASTM) do not include a Type GP.

[0090] As used herein “fly ash”, “ash”, “Gladstone ash”, and “Melbourne ash” means fly ash.

[0091] As used herein “slag”, “Bulwer slag”, “granulated blast furnace slag”, “ground granulated blast furnace slag”, or “GGBFS” means ground slag.

[0092] The terms “cementitious replacement” or “cement replacement” refers to the amount of cement replaced with SCMs, such as fly ash, slag, amorphous silica (silica fume), and the like.

[0093] The terms “water/cement ratio” or “w/c ratio” refers to the ratio of total water in the concrete to the cement content.

[0094] The term “mix design” or “concrete mix design” refers to the composition of a concrete mixture.

[0095] The terms “binary” and “ternary” are concrete mixtures comprising two or three types of SCMs, respectively.

[0096] The term “total cementitious content” refers to the total of cement and SCM(s). In some embodiments of the present invention, the total cementitious content is expressed as kg/m³

[0097] The term “microstrain” or “m’ strain” refers to the drying shrinkage of concrete in parts per million (e.g. a change in length described as being 850 microstrain is 850 parts per million, which is equivalent to a change in length of 0.085% or 0.85 mm/m).

DETAILED DESCRIPTION OF INVENTION

[0098] The inventors have found that use of the admixture of the present invention in concrete provides significant increases in the strength of concrete at day 1 when using relatively high levels of cement replacement materials (i.e., SCM's). In the prior art, concrete producers have trialled the use of high levels of cement replacement materials, but the strength of the concrete at 1 day was prohibitively low. The use of the admixture of the present invention mitigates this issue of low strengths, even at day 1. Additionally, it has surprisingly been found that the use of the admixture of the present invention in concrete provides significant reductions in the drying shrinkage movements.

[0099] The following examples illustrate the compositions, methods, and results according to the disclosed subject matter. These examples are not intended to be inclusive of all aspects of the subject matter disclosed herein, but rather to illustrate representative methods and results.

[00100] To illustrate the effectiveness of preferred forms of the present invention, the admixtures of the present invention were added to a number of cement, fly ash and/or slag concrete mixes and the results tabulated in Tables 1 to 7 below. The tables show various addition rates of fly ash and slag. Additionally, the examples include control mixes using traditional admixtures for concrete.

[00102] Table 1. Laboratory concrete trial mix results; binary cement / fly ash

[00103] Table 1 shows the use of admixtures in binary fly ash cementitious blends, including the compressive strength (Figure 1) and drying shrinkage (Figure 2) of the resulting concrete. The table also demonstrates the reductions in embodied carbon according to the present invention.

[00104] Table 2. Laboratory concrete trial mix results; ternary cement / fly ash / slag

[00105] Table 2 demonstrates the use of admixtures in ternary cementitious blends, including the embodied carbon content (Figure 3) and compressive strength (Figure 4) of the resulting concrete.

[00106] Table 3. Laboratory concrete trial mix results; binary cement / fly ash binder using various different sulfate to formate ratios, and PCE dosages

[00107] Table 3 shows that the admixture of the present invention promotes high early strength in concrete (Figure 5). In some embodiments of the present invention, the admixture helps to eliminate the occurrence of a white deposit.

[00108] Table 4. Laboratory concrete trial mix results; binary cement / fly ash using no calcium carbonate

[00109] Table 4 shows that the admixture of the present invention provides high early strength without compromising later strength (Figure 6) using accelerated curing and an elevated level of fly ash replacement of cement.

[00110] Table 5. Laboratory concrete trial mix results; measurement of different ash materials

[00111] Table 5 demonstrates the use of admixtures according to the present invention with different SCM materials, in particular ash. The table shows that the admixture of the present invention allows reclaimed dam (pond) ash to be used, and provides sufficient compressive strength across different types of SCM (Figure 7).

[00112] Table 6. Laboratory concrete trial mix results; measurement of ternary cementitious concrete mixes using treated slag and un-treated slag

[00113] Table 6 demonstrates the use of admixture according to the present invention by treating the SCM - in this case slag - prior to the SCM being added to the concrete mix. “Ternary” cementitious blends refer to a combination of GP cement with two SCM’s; fly ash and slag. The treatment of the SCM with the admixture of the present invention (in this application called the “treatment chemical”) has demonstrated a significant increase in early strength development when cured at a low temperature (Figure 8) as well as a significant increase in later age strength development when cured under standard conditions (Figure 9). In addition to these strength benefits, the treatment of the slag with the admixture has also given rise to a significant reduction (30%) in the drying shrinkage of the concrete. [00114] Table 7. Laboratory concrete trial mix results; measurement of the impact on strength development cured at low temperatures

00115] Table 7 demonstrates the use of admixture according to the present invention with specific reference to the impact on the Equivalent Age of the concrete determined by the measurement of the strength development at low temperatures (Figure 10). The Equivalent Age of the concrete is a function of the temperature of the concrete during the curing period and is often expressed as the “maturity” of the concrete. The replacement of the conventional water reducing admixture with the admixture according to the present invention has resulted in a reduction (9%) in the Equivalent Age of the concrete at a compressive strength of 20 MPa. This is particularly impressive bearing in mind the higher level of replacement of GP cement with fly ash (35%) compared to the concrete containing the conventional water reducing admixture (20%). [00116] 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 particular features of any one of the various described examples may be provided in any combination in any of the other described examples. Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. It should be understood that this invention is not intended to be unduly limited by the illustrative embodiments and examples set forth herein and that such examples and embodiments are presented by way of example only with the scope of the invention intended to be limited only by the claims set forth herein as follows.

[00117] Other embodiments of the present invention as described herein are defined in the following paragraphs:

1. An admixture for concrete comprising: a sulfate of an alkali metal selected from sodium (Na) and potassium (K); a formate salt; and a water reducer, preferably comprising a defoamer.

2. The admixture according to paragraph 1, wherein the formate salt is selected from calcium, sodium, and potassium.

3. The admixture according to paragraph 1 or 2, wherein the water reducer is a high- range water reducer and is selected from the group consisting of polycarboxylate ether, sodium lignosulphonate, and sodium naphthalene sulphonate.

4. The admixture according to any one of paragraphs 1-3, further comprising calcium carbonate, which is preferably limestone.

5. The admixture according to paragraph 4, wherein the calcium carbonate is fine limestone with a particle size less than 150 pm.

6. The admixture according to paragraph 4 or 5, comprising 50-60 wt.% of calcium carbonate.

7. The admixture according to any one of paragraphs 1-6, comprising 20-25 wt.% of sodium sulfate. 8. The admixture according to any one of paragraphs 1-7, comprising 20-30 wt.% of formate.

9. The admixture according to any one of paragraphs 1-8, comprising 1-3 wt.% of the water reducer.

10. The admixture according to any one of paragraphs 1-9, wherein the sulfate to formate ratio is 4:1.

11. The admixture according to any one of paragraphs 1-10, wherein the sulfate is at least partially substituted with anhydrite (CaSC ).

12. The admixture according to any one of paragraphs 1-11, wherein the admixture further comprises a pigment.

13. The admixture according to any one of paragraphs 1-12, wherein the admixture is in powdered form or is dry.

14. An admixture pre-blend comprising: the admixture according to any one of paragraphs 1-13; and supplementary cementitious material (SCM).

15. The admixture pre-blend according to paragraph 14, wherein the SCM is selected from the group consisting of fly ash, slag (e.g., ground granulated blast-furnace slag; GGBFS), dam (pond) ash, silica fume, and calcined clay.

16. A mix design for concrete comprising the admixture of any one of paragraphs 1-13.

17. Use of the mix design according to paragraph 16 to prepare concrete wherein the concrete comprises cementitious material comprising SCM and cement; and optionally aggregate.

17. The use according to paragraph 16, wherein the concrete comprises about 0.8 to 1.4 wt.% of the admixture.

19. The use according to paragraph 17 or 18, wherein the SCM is selected from one or more of fly ash, slag (e.g., ground granulated blast-furnace slag; GGBFS), dam (pond) ash, silica fume, and calcined clay.

20. The use according to any one of paragraphs 17-19, wherein the SCM to cement ratio is in the range of 1 :4 to 4: 1.

21. The use according to any one of paragraphs 17-20, wherein the cement replacement by SCM is:

(i) up to about 25 wt.% fly ash;

(ii) up to about 50 wt.% fly ash;

(iii) up to about 40 wt.% slag;

(iv) up to about 70 wt.% slag;

(v) up to about 25 wt.% dam ash;

(vi) up to about 30 wt.% slag and 20 wt.% fly ash; or

(vii) up to about 40 wt.% slag and 40 wt.% fly ash.

22. The use according to any one of paragraphs 17-21, wherein the cement is greater than 20 wt.% and less than 65 wt.% Portland cement or clinker.

23. The use according to any one of paragraphs 17-22, wherein the concrete further comprises additives selected from the group consisting of accelerators, retarders, dispersants, extenders, weighting agents, gels, defoamers, and fluid loss additives.

24. The use according to paragraph 23, wherein the retardant is selected from a sugar, a phosphonate, organic acids or their salts, or a mixture thereof.

25. The use according to paragraph 23, wherein the accelerator includes calcium nitrate, calcium chloride, calcium hydroxide, or calcium oxide.

26. The use according to any one of paragraphs 17-25, wherein the aggregate is a coarse aggregate made of crushed rocks such as limestone or granite, and/or a fine aggregate such as sand.

27. The use according to any one of paragraphs 17-26, wherein the admixture provides a reduction in drying shrinkage of the concrete compared to cured concrete without the admixture.

28. The use according to paragraph 27, wherein the admixture provides a reduction in drying shrinkage of the concrete compared to cured concrete without the admixture of about 35, 40, 45, 50, 55, 60, or 65%.

29. The use according to any one of paragraphs 17-28, wherein the admixture provides an early strength development in high SCM concrete.

30. The use according to paragraph 29, wherein the admixture provides an early strength development in high SCM concrete of about 1, 2, 3, 4, or 5 days.

31. The use according to any one of paragraphs 17-30, wherein the admixture provides a reduction in the embodied carbon content.

32. The use according to paragraph 31, wherein the admixture provides a reduction in the embodied carbon content of about 10, 15, 20, 25, 30, 35, 40, 45, or 50%.

33. The use according to any one of paragraphs 17-32, wherein the admixture allows for an increase in cement replacement with SCM.

34. The use according to paragraph 33, wherein the admixture allows for cement replacement by SCM of about 15, 20, 25, 30, 35, 40, 45, 55, 65, 70, 75, 80, or 85 wt.%.

35. A concrete mixture comprising: an admixture for concrete comprising: a sulfate of an alkali metal selected from sodium (Na) and potassium (K); a formate salt; a water reducer; and cementitious material comprising SCM and cement; and optionally aggregate.

36. A powdered cement pre-blend comprising the admixture according to any one of paragraphs 1-13 optionally further including an SCM.

Claims

1. An admixture for concrete comprising: a sulfate of an alkali metal selected from sodium (Na) and potassium (K); a formate salt; and a water reducer.

2. The admixture according to claim 1, wherein the formate salt is selected from calcium, sodium, and potassium.

3. The admixture according to claim 1 or 2, wherein the water reducer is a high-range water reducer and is selected from the group consisting of polycarboxylate ether, sodium lignosulphonate, and sodium naphthalene sulphonate.

4. The admixture according to any one of claims 1-3, further comprising calcium carbonate, which is preferably limestone.

5. The admixture according to claim 4, wherein the calcium carbonate is fine limestone with a particle size less than 150 pm.

6. The admixture according to claim 4 or 5, comprising 50-60 wt.% of calcium carbonate.

7. The admixture according to any one of claims 1-6, comprising 20-25 wt.% of sodium sulfate.

8. The admixture according to any one of claims 1-7, comprising 20-30 wt.% of formate.

9. The admixture according to any one of claims 1-8, comprising 1-3 wt.% of the water reducer.

10. The admixture according to any one of claims 1-9, wherein the sulfate to formate ratio is 4:1.

11. The admixture according to any one of claims 1-10, wherein the sulfate is at least partially substituted with anhydrite (CaSCU).

12. The admixture according to any one of claims 1-11, wherein the admixture further comprises a pigment and/or a defoamer.

13. The admixture according to any one of claims 1-12, wherein the admixture is in powdered form or is dry.

14. An admixture pre-blend comprising: the admixture according to any one of claims 1-13; and supplementary cementitious material (SCM).

15. The admixture pre-blend according to claim 14, wherein the SCM is selected from the group consisting of fly ash, slag (e.g., ground granulated blast-furnace slag; GGBFS), dam (pond) ash, silica fume, and calcined clay.

16. A mix design for concrete comprising the admixture of any one of claims 1-13.

17. Use of the mix design according to claim 16 to prepare concrete wherein the concrete comprises cementitious material comprising SCM and cement; and optionally aggregate.

18. The use according to claim 16, wherein the concrete comprises about 0.8 to 1.4% of the admixture.

19. The use according to claim 17 or 18, wherein the SCM is selected from one or more of fly ash, slag (e.g., ground granulated blast-furnace slag; GGBFS), dam (pond) ash, silica fume, and calcined clay.

20. The use according to any one of claims 17-19, wherein the SCM to cement ratio is in the range of 1:4 to 4:1.

21. The use according to any one of claims 17-20, wherein the cement replacement by SCM is:

(i) up to about 25 wt.% fly ash;

(ii) up to about 50 wt.% fly ash;

(iii) up to about 40 wt.% slag;

(iv) up to about 70 wt.% slag;

(v) up to about 25 wt.% dam ash;

(vi) up to about 30 wt.% slag and 20 wt.% fly ash; or

(vii) up to about 40 wt.% slag and 40 wt.% fly ash.

22. The use according to any one of claims 17-21, wherein the cement is greater than 20 wt.% and less than 65 wt.% Portland cement or clinker.

23. The use according to any one of claims 17-22, wherein the concrete further comprises additives selected from the group consisting of accelerators, retarders, dispersants, extenders, weighting agents, gels, defoamers, and fluid loss additives.

24. The use according to claim 23, wherein the retardant is selected from a sugar, a phosphonate, organic acids or their salts, or a mixture thereof.

25. The use according to claim 23, wherein the accelerator includes calcium nitrate, calcium chloride, calcium hydroxide, or calcium oxide.

26. The use according to any one of claims 17-25, wherein the aggregate is a coarse aggregate made of crushed rocks such as limestone or granite, and/or a fine aggregate such as sand.

27. The use according to any one of claims 17-26, wherein the admixture provides a reduction in drying shrinkage of the concrete compared to cured concrete without the admixture.

28. The use according to claim 27, wherein the admixture provides a reduction in drying shrinkage of the concrete compared to cured concrete without the admixture of about 35, 40, 45, 50, 55, 60, or 65%.

29. The use according to any one of claims 17-28, wherein the admixture provides an early strength development in high SCM concrete.

30. The use according to claim 29, wherein the admixture provides an early strength development in high SCM concrete of about 1, 2, 3, 4, or 5 days.

31. The use according to any one of claims 17-30, wherein the admixture provides a reduction in the embodied carbon content.

32. The use according to claim 31, wherein the admixture provides a reduction in the embodied carbon content of about 10, 15, 20, 25, 30, 35, 40, 45, or 50%.

33. The use according to any one of claims 17-32, wherein the admixture allows for an increase in cement replacement with SCM.

34. The use according to claim 33, wherein the admixture allows for cement replacement by SCM of about 15, 20, 25, 30, 35, 40, 45, 55, 65, 70, 75, 80, or 85 wt.%.

36. A powdered cement pre-blend comprising the admixture according to any one of claims 1-13 optionally further including an SCM.