AU2024227639A1

AU2024227639A1 - Methods for producing a low CO2 cement composition

Info

Publication number: AU2024227639A1
Application number: AU2024227639A
Authority: AU
Inventors: Louise Margaret Keyte; Redmond Richard Lloyd
Original assignee: Boral IP Holdings Australia Pty Ltd
Current assignee: Boral IP Holdings Australia Pty Ltd
Priority date: 2017-10-17
Filing date: 2024-10-25
Publication date: 2024-11-14

Abstract

The present disclosure relates to improved methods for producing a low CO 2 cement composition. Disclosed herein are methods for producing a cement composition comprising mixing reactants comprising a reactive powder, an activator, and a retardant in the presence of water, followed by the mixing of an accelerator into the reactants, and allowing the reactants to react to form the cement composition.

Description

METHODS FOR PRODUCING A LOW CO 2 CEMENT COMPOSITION

RELATED APPLICATIONS

This application is a divisional application of Australian Patent Application No. 2017436546, the entire contents of which is incorporated herein by reference.

FIELD

The present disclosure relates to methods of producing a low CO 2 cement composition.

BACKGROUND

Manufacture of portland cement contributes significantly to global CO2 emissions and is a major cost component of concrete. The manufacture and use of portland cement has been refined over time and thus there are few avenues remaining to increase efficiency and reduce carbon emissions in cement manufacture, and these are relatively expensive to implement (e.g. carbon capture and storage). Reducing the amount of portland cement used in concrete to achieve a given strength requirement is therefore highly desirable, as it will reduce carbon emissions and concrete cost.

Previous attempts to reduce carbon emissions included a ternary system of ordinary portland cement (OPC), ground granulated blast furnace slag (GGBFS) and an activator (e.g. sodium sulphate). This ternary system produced binders with superior performance to systems without activator when the mix design was optimized. See W02011/134025. The two main binder materials - OPC and GGBFS have different reaction potentials and therefore the required performance is usually not reached in a desirable timeframe for commercial application as the GGBFS is slower to react under normal hydration conditions. When the right concentration of sodium sulphate activator was employed, it acted on the GGBFS to increase reactivity, and overall the reaction potential of the system was significantly increased.

However, one of the drawbacks of this system is that the activator has a negative impact on the OPC, reducing its reaction potential. While overall the ternary system is superior to previous methods, ideally the activator would target the GGBFS only, resulting in still further increased performance.

The compositions and methods disclosed herein address these and other needs.

SUMMARY

Disclosed herein are improved methods for producing a low CO 2 cement composition. The inventors have found that if a conventional retardant is added to a ternary cement system (ordinary portland cement (OPC), slag, and activator) followed by the delayed addition of an accelerator, the impact of the activator on the OPC is significantly reduced, leading to improved performance and compressive strength of the cement composition.

In some aspects, disclosed herein is a method for producing a cement composition, comprising mixing reactants comprising a reactive powder, an activator, and a retardant in the presence of water, wherein the reactive powder comprises portland cement and/or portland cement clinker and slag; mixing an accelerator into the reactants, wherein the accelerator is added from 30 seconds to 60 minutes after the mixing of the reactive powder, activator, and retardant; and allowing the reactants to react to form the cement composition.

In some embodiments, the ratio of slag to portland cement and/or portland cement clinker is 1:3 to 9:1. In some embodiments, the ratio of slag to portland cement and/or portland cement clinker is 1:2 to 4:1. In some embodiments, the ratio of slag to portland cement and/or portland cement clinker is 1:2 to 2:1. In some embodiments, the ratio of slag to portland cement and/or portland cement clinker is 1:1 to 4:1.

In some embodiments, the portland cement and/or portland cement clinker is present in an amount of greater than 20 wt% and less than 65 wt% of the total amount of reactive powder. In some embodiments, the portland cement and/or portland cement clinker is present in an amount of greater than 30 wt% and less than 50 wt% of the total amount of reactive powder.

In some embodiments, the slag is present in an amount of 20 wt% to 90 wt% of the total amount of reactive powder. In some embodiments, the slag is present in an amount of 40 wt% to 80 wt% of the total amount of reactive powder. In some embodiments, the slag is present in an amount of 50 wt% to wt% of the total amount of reactive powder.

In some embodiments, the slag is granulated blast furnace slag. In some embodiments, the slag is steel slag. In some embodiments, the slag is granulated blast furnace slag in combination with steel slag. In some embodiments, the steel slag constitutes greater than 0 to 30 wt% of the total amount of reactive powder. In some embodiments, the steel slag constitutes greater than 0 to 20 wt% of the total amount of reactive powder.

In some embodiments, the slag comprises CaO and SiO 2 , and wherein the CaO/ SiO 2 wt ratio of the slag is in the range of 1.0 - 1.3.

In some embodiments, the activator is present in an amount of 1 - 6 wt%, based on the total amount of the cement composition. In some embodiments, the activator is present in an amount of 1.5 - 6 wt%, based on the total amount of the cement composition. In some embodiments, the activator includes sodium sulphate or potassium sulphate. In some embodiments, the activator includes sodium sulphate. In some embodiments, the activator includes potassium sulphate.

In some embodiments, the retardant is selected from a sugar, a phosphonate, organic acids or their salts, or a mixture thereof. In some embodiments, the retardant includes a sugar. In some embodiments, the retardant includes a commercially available retardant. In some embodiments, the retardant includes Sika Retarder N. In some embodiments, the retardant includes sodium citrate.

In some embodiments, the accelerator includes calcium nitrate, calcium chloride, calcium hydroxide, calcium oxide, or calcium formate. In some embodiments, the accelerator is the nitrate of an alkaline earth metal. In some embodiments, the accelerator is calcium nitrate.

In some embodiments, the accelerator includes a commercially available accelerator. In some embodiments, the accelerator includes Sika Rapid 4. In some embodiments, the accelerator is added in combination with sodium thiocyanate or triethanolamine.

In some embodiments, the accelerator is added 30 seconds to 60 minutes after the mixing of the reactive powder, activator, and retardant. In some embodiments, the accelerator is added 30 seconds to minutes after the mixing of the reactive powder, activator, and retardant. In some embodiments, the accelerator is added 30 seconds to 20 minutes after the mixing of the reactive powder, activator, and retardant. In some embodiments, the accelerator is added 30 seconds to 10 minutes after the mixing of the reactive powder, activator, and retardant. In some embodiments, the accelerator is added 30 seconds to 3 minutes after the mixing of the reactive powder, activator, and retardant. In some embodiments, the accelerator is added 1 minute to 15 minutes after the mixing of the reactive powder, activator, and retardant. In some embodiments, the accelerator is added 1 minute to 10 minutes after the mixing of the reactive powder, activator, and retardant. In some embodiments, the accelerator is added 1 minute to 5 minutes after the mixing of the reactive powder, activator, and retardant.

In some embodiments, the reactive powder further comprises calcium sulphate, any of the hydrated forms of calcium sulphate (e.g. gypsum, hemihydrate, anhydrite), or a combination thereof. In some embodiments, the calcium sulphate, any of the hydrated forms of calcium sulphate (e.g. gypsum, hemihydrate, anhydrite), or a combination thereof is present in an amount greater than zero to 10 wt% of the total amount of reactive powder. In some embodiments, the calcium sulphate, any of the hydrated forms of calcium sulphate (e.g. gypsum, hemihydrate, anhydrite), or a combination thereof is present in an amount greater than zero to 5 wt% of the total amount of reactive powder. In some embodiments, the calcium sulphate, any of the hydrated forms of calcium sulphate (e.g. gypsum, hemihydrate, anhydrite), or a combination thereof is present in an amount of 1 - 6 wt% of the total amount of reactive powder. In some embodiments, the calcium sulphate, any of the hydrated forms of calcium sulphate (e.g. gypsum, hemihydrate, anhydrite), or a combination thereof is present in an amount of 2 - 5 wt% of the total amount of reactive powder. In some embodiments, the reactive powder further comprises gypsum. In some embodiments, a cement composition is prepared according to the methods disclosed herein.

In some embodiments, provided herein is a method of making concrete according to the methods disclosed herein, further comprising mixing aggregate with the reactants. In some embodiments, the aggregate is in a range of 65 - 95 wt% of the concrete. In some embodiments, the aggregate is in a range of 65 - 85 wt% of the concrete. In some embodiments, provided herein is a method of making concrete according to the methods disclosed herein, further comprising mixing sand and/or aggregate with the reactants.

DETAILED DESCRIPTION

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. The term "comprising" and variations thereof as used herein is used synonymously with the term "including" and variations thereof and are open, non-limiting terms. Although the terms "comprising" and "including" have been used herein to describe various embodiments, the terms "consisting essentially of and "consisting of can be used in place of "comprising" and "including" to provide for more specific embodiments and are also disclosed. As used in this disclosure and in the appended claims, the singular forms "a", "an", "the", include plural referents unless the context clearly dictates otherwise.

In some aspects, disclosed herein is a method for producing a cement composition, comprising: mixing reactants comprising a reactive powder, an activator, and a retardant in the presence of water, wherein the reactive powder comprises portland cement and/or portland cement clinker and slag; mixing an accelerator into the reactants, wherein the accelerator is added from 30 seconds to 60 minutes after the mixing of the reactive powder, activator, and retardant; and allowing the reactants to react to form the cement composition.

As noted above, the reactive powder includes portland cement and/or portland cement clinker. Portland cement is "hydraulic cement" (cement that not only hardens by reacting with water but also forms a water-resistant product) produced by pulverizing clinkers which consist essentially of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulphate as an inter-ground addition. Portland cement clinker is a hydraulic material which generally consists of at least two-thirds by mass of calcium silicates (3CaO. SiO 2 and 2CaO. SiO 2 ), the remainder consisting of aluminum- and iron-containing clinker phases and other compounds. The magnesium content typically does not exceed 5.0% by mass. The major raw material for making the clinker is usually limestone (CaCO 3) mixed with a second material containing clay as source of alumino-silicate; aluminium oxide and iron oxide are present as a flux and contribute little to the strength. The production of portland cement clinker is associated with high-CO2 emissions. One way to reduce clinker content in cement and concrete is to replace clinker with supplementary cementitious materials (SCM), for example, slag such as ground, granulated blast-furnace slag (GGBFS).

In some embodiments, the portland cement and/or portland cement clinker is present in an amount of from 20 wt% to 65 wt% of the total amount of the reactive powder. In some embodiments, the portland cement and/or portland cement clinker can be present in an amount of from 25 wt% to 55 wt%, from 30 wt% to 50 wt%, or from 35 wt% to 45 wt% (e.g., 40 wt%) of the total amount of the reactive powder.

The reactive powder also includes slag. In some embodiments, the slag is present in an amount of 20 wt% to 90 wt% of the total amount of reactive powder. In some embodiments, the amount of slag in the reactive powder is from 40 wt% to 80 wt% of the total amount of the reactive powder. For example, the amount of slag in the cement composition can be 20-90 wt%, 30-90 wt%, 40-80 wt%, 40 wt%, 50-70 wt%, 40-60 wt%, or 50 - 60 wt%.

In some embodiments, the slag includes blast furnace slag, steel slag, or a mixture thereof. Blast furnace slag is a nonmetallic product produced during the production of iron. It consists primarily of silicates, aluminosilicates, and calcium-alumina-silicates. Granulated blast furnace slag (GBFS) is the result of cooling and solidifying the molten slag by rapid water quenching to a glassy state, where little or no crystallization occurs. This process results in the formation of sand sized fragments. The physical structure of the granulated slag depends on the chemical composition of the slag, its temperature at the time of water quenching, and the method of production. When crushed or mil led to very fine cement sized particles, ground granulated blast furnace slag (GGBFS) has cementitious properties.

In some embodiments, the slag includes steel slag. In some embodiments, the slag is granulated blast furnace slag in combination with steel slag. In some embodiments, the steel slag greater than 0 to wt% of the reactive powder. In some embodiments, the steel slag constitutes greater than 0 to 20 wt% of the reactive powder.

In some embodiments, the slag comprises CaO and SiO 2 In some embodiments, the slag comprises CaO and SiO2 , and wherein the CaO/ SiO2 wt ratio of the slag is less than or equal to 1.3. In some embodiments, the slag comprises CaO and SiO 2 , and wherein the CaO/ SiO 2 wt ratio

of the slag is in the range of 1.0 - 1.3. Generally, the lower the CaO/ SiO 2 wt ratio, the lower the reactivity of the slag.

In some embodiments, the slag has an A1 2 0 3 / SiO 2 wt ratio of 0.3-0.5. In some embodiments, the slag has a MgO/CaO wt ratio of 0.1-0.5.

In some embodiments, the reactive powder further comprises calcium sulphate, any of the hydrated forms of calcium sulphate (e.g. gypsum, hemihydrate, anhydrite), or a combination thereof.

In some embodiments, the calcium sulphate, any of the hydrated forms of calcium sulphate (e.g. gypsum, hemihydrate, anhydrite), or a combination thereof is present in an amount greater than zero to wt%. In some embodiments, the calcium sulphate, any of the hydrated forms of calcium sulphate (e.g. gypsum, hemihydrate, anhydrite), or a combination thereof is present in an amount greater than zero to 5 wt%. In some embodiments, the calcium sulphate, any of the hydrated forms of calcium sulphate (e.g. gypsum, hemihydrate, anhydrite), or a combination thereof is present in an amount of 1 6 wt%. In some embodiments, the calcium sulphate, any of the hydrated forms of calcium sulphate (e.g. gypsum, hemihydrate, anhydrite), or a combination thereof is present in an amount of 2 - 5 wt%. In some embodiments, the calcium sulphate, any of the hydrated forms of calcium sulphate (e.g. gypsum, hemihydrate, anhydrite), or a combination thereof is present in an amount of 1 - 3 wt%.

In some embodiments, the reactive powder further comprises gypsum. In some embodiments, the gypsum is present in an amount greater than 0 to 10 wt% based on the weight of the reactive powder. In some embodiments, the gypsum is present in an amount greater than 0 to 5 wt% based on the weight of the reactive powder. In some embodiments, the gypsum is present in an amount of 1 - 6 wt%, 2 - 5 wt%, or 1 - 3 wt% based on the weight of the reactive powder.

The methods disclosed herein include an activator. In some embodiments, the activator is sodium sulphate or potassium sulphate. In some embodiments, the activator is sodium sulphate. In some embodiments, the activator is potassium sulphate.

In some embodiments, the activator is present in an amount of 1.5 - 6 wt%, based on the total amount of the cement composition. In some embodiments, the activator is present in an amount of 1 6 wt%, based on the total amount of the cement composition. In some embodiments, the activator is present in an amount of 1 - 3 wt%, based on the total amount of the cement composition. In some embodiments, the activator is present in an amount of 0.5 - 6 wt%, based on the total amount of the cement composition. In some embodiments, the activator is present in an amount of 0.5 - 4 wt%, based on the total amount of the cement composition.

The methods disclosed herein include a retardant. In some embodiments, the retardant is selected from a sugar, a phosphonate, organic acids or their salts, or a mixture thereof In some embodiments, the retardant includes a sugar. In some embodiments, the retardant includes sodium citrate. In some embodiments, the retardant includes a commercially available retardant. In some embodiments, the retardant includes Sika Retarder N. Sika Retarder N is a proprietary retardant and is a liquid retardant containing selected carbohydrates. The rate of addition of Sika Retarder N is generally in the range of 200ml± 100ml per 100kg of cementitious materials. In some embodiments, Sika Retarder N can be used to retard the setting time of the concrete to allow concreting under conditions of high ambient temperatures and placing of mass concrete. In some embodiments, Sika Retarder N can be used for pumped, pre-stressed and structural concrete. The effect of Sika Retarder N depends on a number of factors such as cement type, ambient temperature and mix design. The dosage used can be determined by site or laboratory tests with the particular concrete mix design. The Sika line of proprietary retardants and are available from Sika Australia Pty. Ltd.

In some embodiments, the retardant includes SikaTard 930 or SikaTard 990. SikaTard 930 is a proprietary liquid solution of polycarbonate acid salts. SikaTard 930 is an admixture developed for the control of cement hydration. SikaTard 930 facilitates stabilization of concrete mixes for long periods without negatively influencing their quality. The rate of addition of SikaTard 930 is generally in the range of 200ml 100ml per 100kg of cementitious materials. Sikatard 990 is also a proprietary liquid solution of polycarbonate acid salts. The rate of addition of SikaTard 990 is generally in the range of 250-2000 mls/100 kg of cementitious materials.

The methods disclosed herein include an accelerator such as a liquid or solid accelerator. In some embodiments, the accelerator is a liquid accelerator. In some embodiments, the accelerator includes an alkaline earth metal. In some embodiments, the accelerator includes calcium nitrate, calcium chloride, calcium hydroxide, calcium oxide, or calcium formate.

In some embodiments, the accelerator is a nitrate of an alkaline earth metal. In some embodiments, the accelerator is calcium nitrate. In some embodiments, the accelerator is added in combination with a strength accelerator. In some embodiments, the strength accelerator is added in combination with a salt of thiocyanic acid. In some embodiments, the accelerator is added in combination with sodium thiocyanate or triethanolamine.

In some embodiments, the accelerator includes a commercially available accelerator. In some embodiments, the accelerator includes Sika Rapid 4. SikaRapid-4 is a set accelerator for concrete and mortar containing added chloride (1000ml contains approximately 86g Chloride ion). Dosage is generally 400ml - 2000ml/ 100 kg of total cementitious material. The exact dosage rate can be determined by site trials. The Sika line of proprietary accelerators are available from Sika Australia Pty. Ltd, and comprise a mixture of calcium nitrate and calcium chloride.

In some embodiments, the method disclosed herein includes mixing the reactive powder, the activator, and the retardant in the presence of water, such as in a cement mixer, and then later adding the accelerant. In some embodiments, the accelerator is added 30 seconds to 60 minutes after the mixing of the reactive powder, activator, and retardant. In some embodiments, the accelerator is added 1 minute to 60 minutes after the mixing of the reactive powder, activator, and retardant. In some embodiments, the accelerator is added 30 seconds to 30 minutes after the mixing of the reactive powder, activator, and retardant. In some embodiments, the accelerator is added 30 seconds to 20 minutes after the mixing of the reactive powder, activator, and retardant. In some embodiments, the accelerator is added 1 minute to 15 minutes after the mixing of the reactive powder, activator, and retardant. In some embodiments, the accelerator is added 1 minute to 10 minutes after the mixing of the reactive powder, activator, and retardant. In some embodiments, the accelerator is added 1 minute to 5 minutes after the mixing of the reactive powder, activator, and retardant.

In some embodiments, the accelerator is added at least 30 seconds (for example, at least 30 seconds, at least 1 minute, at least 2 minutes, at least 3 minutes, at least 4 minutes, at least 5 minutes, at least 6 minutes, at least 7 minutes, at least 8 minutes, at least 9 minutes, at least 10 minutes, at least 15 minutes, at least 20 minutes, at least 25 minutes, at least 30 minutes, at least 40 minutes, at least 50 minutes) after the mixing of the reactive powder, activator, and retardant.

In some embodiments, the accelerator is added less than 60 minutes (for example, less than 60 minutes, less than 50 minutes, less than 40 minutes, less than 30 minutes, less than 25 minutes, less than minutes, less than 15 minutes, less than 10 minutes, less than 5 minutes, or less than 1 minute) after the mixing of the reactive powder, activator, and retardant.

In some embodiments, the accelerator is added to the reactive powder, activator, and retardant after a suitable period of time to allow the ordinary portland cement (OPC) grains to adsorb the retardant.

In some embodiments, the addition of the retardant and the accelerator to the cement composition increases the compressive strength of the cement by at least 5% (for example, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 40%, at least 50%, at least %, at least 70%, at least 80%, at least 90%, at least 100%) for a given amount of cement in comparison to a cement composition lacking the retardant and the accelerator. In some embodiments, the compressive strength can be measured according to AS 1012.9:2014. This standard is used in Australia, but other national standards can be used as well. As a result, the use of the retardant and later added accelerator can produce concrete with much lower amounts of cement for a given strength grade.

In some embodiments, the cement composition is provided as a binder for aggregate and other materials to produce concrete. 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 (generally a coarse aggregate made of crushed rocks such as limestone, or granite, plus a fine aggregate such as sand), water, and chemical admixtures. In some embodiments, the cement composition further comprises aggregate. In some embodiments, the aggregate is present in an amount of 65 - 95 wt% of the concrete.

EXAMPLES

The following examples are set forth below to 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. These examples are not intended to exclude equivalents and variations of the present disclosure which are apparent to one skilled in the art. Parts and percentages are provided on a weight basis herein, unless indicated otherwise.

Example 1. Concrete cylinder results for low CO 2 cement compositions

Concrete cylinders were prepared for testing. The process included preparing a blend of ordinary portland cement (OPC), ground granulated blast furnace slag (GGBFS), and/or activator, to form the binder mixture. Aggregate was then added to the binder mixture to prepare a concrete precursor. The retardant was added to the initial water and mixed with the binder mixture until sufficient time had passed for the retardant to be adsorbed onto the cement grains. Then, a liquid accelerator was added with the finishing water. The concrete mixture was formed into cylinders for testing. As tested herein, the cylinders are 100 mm in diameter and 200 mm high.

In this example, various ternary mixtures (OPC, GGBFS, and/or sodium sulphate) were analyzed in combination with the addition of retardants, following by the delayed addition of an accelerator. In some experiments, gypsum was optionally added to the mixtures. The gypsum added in the milling process partially dehydrates, and thus the mixture comprises calcium sulphate, any of the hydrated forms of calcium sulphate (e.g. gypsum, hemihydrate, anhydrite), or a combination thereof.

The cement mixtures shown in Table 1 below (40% OPC with GGBFS replacement (gypsum/ sodium sulphate additions)) were tested in combination with Sika Retarder N as a retardant and/or Sika Rapid 4 as a liquid accelerator.

Table 1. Concrete cylinder results at 23 C for 40% OPC with GGBFS replacement

1 2 3 4 5 wt% OPC 100 40 40 40 40 GGBFS 57 57 57 57 Na2SO4 3 3 Gypsum 3 3

mL I 100kg binder Retarder 200 200 Accelerator 800 800

MPa 3 Day 31 19 27 25 33 7 Day 38 27 41 31 40 28 Day 47 37 57 38 47

As shown in Table 1, addition of the retardant (retarder) followed by the delayed addition of the accelerator resulted in significant improvements in cement compressive strength.

The cement mixtures shown in Table 2 below (50% OPC with GGBFS replacement (gypsum/ sodium sulphate additions)) were next tested using the same process and were tested in combination with Sika Retarder N as a retardant and/or Sika Rapid 4 as a liquid accelerator.

Table 2. Concrete cylinder results at 23 ° C for 50% OPC with GGBFS replacement

1 2 3 4 wt% OPC 100 50 50 50 GGBFS 47.5 47.5 47.5 Na2SO4 2.5 2.5 1.25 Gypsum 1.25

mL / 100kg binder Retarder 100 100 Accelerator 400 400

MPa 3 Day 27 24 27 25 7 Day 32 30 35 36 28 Day 41 35 45 45

As shown in Table 2, addition of the retardant followed by the delayed addition of the accelerator to the 50% OPC mix resulted in significant improvements in cement compressive strength.

The cement mixtures shown in Table 3 below (50% OPC with GGBFS replacement (gypsum /

sodium sulphate additions)) were also tested using the same process in combination with Sika Retarder N as a retardant and/or Sika Rapid 4 as a liquid accelerator.

Table 3: Concrete cylinder results at 23 0 C for 50% OPC with GGBFS replacement (retardant and/or accelerator)

1 2 3 4 5 6 wt% OPC too 100 50 50 50 50 GGBFS 47.5 47.5 47.5 47.5 Na2SO4 2.5 1.25 1.25 1.25 Gypsum 1.25 1.25 1.25

mL / 100kg binder Retarder 100 100 100 100 200 Accelerator 400 600

MPa 3 Day 31 31 27 24 27 29 7 Day 38 40 37 35 40 41 28 Day 47 51 48 46 51 53

As shown in Table 3, addition of the retardant followed by the delayed addition of the accelerator to the 50% OPC mix resulted in significant improvements in cement compressive strength.

The cement mixtures shown in Table 4 below (100% OPC) were tested in combination with Sika Retarder N as a retardant and/or Sika Rapid 4 as a liquid accelerator, along with the addition of a water reducer. In the example here, the water reducer used was Sika Plastiment 10, which comprises a combination of polycarboxylate ether and lignosulphonate water reducing agents.

Table 4. Concrete cylinder results at 23 ° C for 100% OPC

1 2 3 4 5 6 wt% OPC 100 100 100 100 100 100 GGBFS Na2SO4 Gypsum

mL /100kg binder Retarder 200 200 400 800 800 1600 Accelerator 800 1600 3200 Water reducer y y y y y y

MPa 3 Day 31 35 39 35 48 41 7 Day 41 43 49 43 53 53 28 Day 53 53 61 54 64 64

As shown in Table 4, addition of the retardant followed by the delayed addition of the accelerator to the 100% OPC mix resulted in significant improvements in cement compressive strength.

The cement mixtures shown in Table 5 below (50% OPC with GGBFS replacement (gypsum

/ sodium sulphate additions)) were also tested using a combination of Sika Retarder N as a retardant and/or Sika Rapid 4 as a liquid accelerator. The accelerator was added at various time points to examine the effect on cement compressive strength and initial set time.

Table 5. Concrete cylinder results at 23 0 C for 50% OPC with GGBFS replacement and various delay times

1 2 3 4 5 6 7 8 9 wt% OPC 50 50 50 50 50 50 50 50 50 GGBFS 47.5 47.5 47.5 47.5 47.5 47.5 47.5 47.5 47.5 Na2SO4 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Gypsum

mL / 100kg binder Retarder 200 200 200 200 200 200 200 200 0 Accelerator 0 800 800 800 800 800 800 800 800 Delay time (min) 0 0 0.5 1 2 6 10 30 0 MPa 3 Day 31 31 33 33 32 34 31 33 32 7 Day 39 40 42 42 41 43 41 42 41 28 Day 49 51 49 50 51 53 45 49 47

Initial Set (hours) 5.3 4.4 5.6 5.5 5.6 5.1 5.3 3.9 3.2

10 11 12 13 14 15 16 17 18 wt% OPC 50 50 50 50 50 50 50 50 50 GGBFS 47.5 47.5 47.5 47.5 47.5 47.5 47.5 47.5 47.5 Na2SO4 1,25 1.25 1,25 1.25 1.25 1.25 1.25 1.25 1.25 Gypsum 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25

mL / 100kg binder Retarder 200 200 200 200 200 200 200 200 0 Accelerator 0 800 800 800 800 800 800 800 800 Delay time (min) 0 0 0.5 1 2 6 10 30 0 MPa 3 Day 29 32 31 31 32 32 32 30 27 7 Day 39 40 41 42 41 42 41 42 36 28 Day 50 53 54 55 53 54 51 51 49

Initial Set (hours) 6.4 5.3 6.4 6.5 6.3 6.2 5.7 4.7 3.4

As shown in Table 5, addition of the retardant followed by the delayed addition of the accelerator to the 50% OPC mix resulted in significant improvements in cement compressive strength. The initial set time decreased at the later delayed time points for accelerator addition (for example, at minutes delay). These results demonstrate the importance of the delayed accelerator addition on strength and setting time.

The cement mixtures shown in Table 6 below (50% OPC with GGBFS replacement (sodium sulphate additions)) were also tested using the same process as above in combination with Sika Retarder N as a retardant and/or Sika Rapid 4 as a liquid accelerator, along with the addition of a water reducer. In the example here, the water reducer used was Sika Plastiment 10, which comprises a combination of polycarboxylate ether and lignosulphonate water reducing agents. The accelerator was added at various time points (6 and 60 minutes) to examine the effect on cement compressive strength and initial set time.

Table 6. Concrete cylinder results at 23 0 C for 50% OPC with GGBFS replacement and water reducer

1 2 3 4 wt% OPC 50 50 50 50 GGBFS 47.5 47.5 47.5 47.5 Na2SO4 2.5 2.5 2.5 2.5 Gypsum

mL 100kg binder Water Reducer 400 400 400 400 Retarder 200 400 200 400 Accelerator 1600 1600 Delay time (min) 6 60

3Day 33 36 37 43 7 Day 41 47 37 45 28 Day 52 58 49 55

Initial Set (hours) 5.3 6.3 5.3 6.6

As shown in Table 6, addition of the retardant followed by the delayed addition of the accelerator to the 50% OPC mix in the presence of a water reducer resulted in significant improvements in cement compressive strength. However, the initial set time actually increased, even with the addition of the accelerator, when the water reducer was present.

The methods of the appended claims are not limited in scope by the methods described herein, which are intended as illustrations of a few aspects of the claims and any methods that are functionally equivalent are intended to fall within the scope of the claims. Various modifications of the methods in addition to those shown and described herein are intended to fall within the scope of the appended claims. Further, while only certain method steps disclosed herein are specifically described, other combinations of method steps also are intended to fall within the scope of the appended claims, even if not specifically recited. Thus, a combination of steps, elements, components, or constituents may be explicitly mentioned herein; however, other combinations of steps, elements, components, and constituents are included, even though not explicitly stated.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavor to which this specification relates.

Claims

WHAT IS CLAIMED IS:

1. A method for producing a cement composition, comprising: mixing reactants comprising a reactive powder, an activator, and a retardant in the presence of water, wherein the reactive powder comprises: portland cement and/or portland cement clinker; and slag; mixing an accelerator into the reactants, wherein the accelerator is added from 30 seconds to minutes after the mixing of the reactive powder, activator, and retardant; and allowing the reactants to react to form the cement composition.

2. The method of claim 1, wherein the weight ratio of slag to portland cement and/or portland cement clinker is in the range of 1:3 to 9:1.

3. The method of claim 2, wherein the ratio of slag to portland cement and/or portland cement clinker is 1:2 to 4:1.

4. The method of claim 1, wherein the portland cement and/or portland cement clinker is present in an amount of from 20 wt% to 65 wt% of the total amount of reactive powder.

5. The method of claim 4, wherein the portland cement and/or portland cement clinker is present in an amount of from 30 wt% to 50 wt% of the total amount of reactive powder.

6. The method of any one of claims 1 to 4, wherein the slag is present in an amount of wt% to 90 wt% of the total amount of reactive powder.

7. The method of claim 6, wherein the slag is present in an amount of 50 wt% to 70 wt% of the total amount of reactive powder.

8. The method of any one of claims I to 7, wherein the slag is granulated blast furnace slag.

9. The method of any one of claims 1 to 7, wherein the slag is steel slag.

10. The method of any one of claims 1 to 9, wherein the slag is granulated blast furnace slag in combination with steel slag.

11. The method of claim 9 or 10, wherein the steel slag constitutes greater than 0 to 30 wt% of the total amount of reactive powder.

12. The method of claim 11, wherein the steel slag constitutes greater than 0 to 20 wt% of the total amount of reactive powder.

13. The method of any one of claims I to 12, wherein the slag comprises CaO and SiO 2

, and wherein the CaO/SiO 2 wt ratio of the slag is in the range of 1.0 - 1.3.

14. The method of any one of claims I to 13, wherein the activator is present in an amount of 1 - 6 wt%, based on the total amount of the cement composition.

15. The method of any one of claims I to 14, wherein the activator is sodium sulphate or potassium sulphate.

16. The method of any one of claims 1 to 15, wherein the retardant is selected from a sugar, a phosphonate, organic acids or their salts, or a mixture thereof.

17. The method of claim 16, wherein the retardant includes a sugar.

18. The method of claim 16 or 17, wherein the retardant includes Sika Retarder N.

19. The method of any one of claims 16 to 18, wherein the retardant includes sodium citrate.

20. The method of any one of claims 1 to 19, wherein the accelerator includes the nitrate of an alkaline earth metal.

21. The method of claim 20, wherein the accelerator includes calcium nitrate.

22. The method of any one of claims 1 to 19, wherein the accelerator includes calcium nitrate, calcium chloride, calcium hydroxide, calcium oxide, or calcium formate.

23. The method of any one of claims 1 to 19, wherein the accelerator includes Sika Rapid 4.

24. The method of any one of claims I to 23, wherein the accelerator is added in combination with sodium thiocyanate or triethanolamine.

25. The method of any one of claims I to 24, wherein the accelerator is added 30 seconds to 30 minutes after the mixing of the reactive powder, activator, and retardant.

26. The method of claim 25, wherein the accelerator is added 30 seconds to 20 minutes after the mixing of the reactive powder, activator, and retardant.

27. The method of claim 26, wherein the accelerator is added 1 minute to 15 minutes after the mixing of the reactive powder, activator, and retardant.

28. The method of claim 27, wherein the accelerator is added 1 minute to 10 minutes after the mixing of the reactive powder, activator, and retardant.

29. The method of claim 28, wherein the accelerator is added 1 minute to 5 minutes after the mixing of the reactive powder, activator, and retardant.

30. The method of any one of claims I to 29, wherein the reactive powder further comprises calcium sulphate, any of the hydrated forms of calcium sulphate, or a combination thereof.

31. The method of claim 30, wherein the calcium sulphate, any of the hydrated forms of calcium sulphate, or a combination thereof is present in an amount greater than 0 to 10 wt% of the total amount of reactive powder.

32. The method of claim 31, wherein the calcium sulphate, any of the hydrated forms of calcium sulphate, or a combination thereof is present in an amount greater than 0 to 5 wt% of the total amount of reactive powder.

33. The method of claim 30, wherein the calcium sulphate, any of the hydrated forms of calcium sulphate, or a combination thereof is present in an amount of 1 - 6 wt% of the total amount of reactive powder.

34. The method of claim 33, wherein the calcium sulphate, any of the hydrated forms of calcium sulphate, or a combination thereof is present in an amount of 2 - 5 wt% of the total amount of reactive powder.

35. The method of any one of claims 30 to 34, wherein the reactive powder comprises gypsum.

36. A cement composition prepared according to any one of claims I to 35.

37. A method of making concrete according to any one of claims I to 36, further comprising mixing aggregate with the reactants.

38. The method of claim 37, wherein the aggregate is in a range of 65 - 95 wt% of the concrete.