Method of improving the strength of a product comprising cementitious material containing ordinary portland cement

Abstract

A method of improving the strength of a product comprising cementitious material comprising ordinary Portland cement (OPC) may comprise preparing an admixture comprising an amine component and a solve

Description

The present invention relates to a method of improving the strength of a product comprising cementitious material containing ordinary Portland cement, preferably by the use of an admixture comprising an alkanolamine. An admixture for improving the strength of a product comprising cementitious material containing ordinary Portland cement is also provided. Amine groups react with carbon dioxide in an equilibrium state to form either an ammonium carbonate salt or an ammonium carbamate salt, depending on the process characteristics used. Alkanolamines, that is, organic compounds having both a hydroxyl group and an amine group on an alkane backbone, react to form alkanolammonium carbonate or alkanolammonium carbamate, referred to as a urethane. It is known to use alkanolamines as accelerants in the curing process of cementitious materials. One example of such an arrangement is disclosed in EP1727775A1. The purpose of the accelerant is to substantially reduce the set time by rapid desorption of the carbon dioxide from the urethane compounds. Rapid curing of the cementitious material does reduce the time taken to manufacture the final product, typically concrete products. It may be desirable, however, to improve the strength of the products produced from cementitious materials by slowing the curing process, since a slower sequestration of carbon dioxide may result in strength improvements in the final product. An example of rapid curing from CO2 derived species is disclosed in US5624493A, where specifically ammonium carbonate is used to facilitate the dissolution and reaction of CO2 in a wet cementitious material slurry, which is then left to harden. It is an object of the present invention to provide an improved method of enhancing the strength of products comprising cementitious material. According to a first aspect of the invention, there is provided a method of improving the strength of a product comprising cementitious material containing ordinary Portland cement, the method comprising the steps of: a] preparing an admixture comprising an amine component and a solvent; b] loading the admixture with carbon dioxide by delivering gaseous carbon dioxide to the admixture for a duration; wherein a water content of the admixture does not exceed 60wt.%; and c] introducing the admixture into a cementitious material in an amount of 0.1wt.% to 5.0wt.% with respect to a weight of ordinary Portland cement in the cementitious material for enhancing the strength of the subsequent product. Amine based species are known in the art to act as curing accelerants for cementitious materials, usually in the formation of concrete products. However, strength improvements in the concrete products have not been demonstrated. In the present invention, it can be shown that by promoting the formation of a urethane or carbamate species under loading with carbon dioxide to form an admixture which can be subsequently added into a cementitious material will lead to specific strength improvements in the final product. This is achieved by careful control over the water content of the admixture in particular since a higher water content will promote the preferential formation of carbonate species instead. Carbamate species are not immediately available to the cementitious material, which prevents excess carbon dioxide from hindering the production of calcium-silicate-hydrate and portlandite by calcium sequestration. By use of an admixture, and specifically an end-of-production-line admixture, the present invention is quite distinct from existing accelerant based alkanolamine technologies in the art which contaminate or otherwise adulterate grinding facilities and mid-stage production lines. Optionally, the amine component may be an alkanolamine. Preferably, the amine component may be selected from a group comprising: monoethanolamine; diethanolamine; triethanolamine; 2-aminomethylpropanol; diglycolamine; methyldiethanolamine; branched polyethylenimine; or combinations thereof. The urethane-based carbon dioxide transfer agents resulting from the alkanolamine compounds yield a modular carbon dioxide sequestration reaction sequence which become mechanical property enhancement agents for cementitious materials. The amine component may be provided in an amount in the range 30wt.% to 80wt.% of the admixture. Optionally, the amine component may be provided in an amount of at least 60 mol% of the admixture. A reasonably large proportion of amine component is required in the admixture in order to produce sufficient carbamate for sequestration into the cementitious material. Optionally, the solvent may comprise an aqueous solvent. In one arrangement, the solvent may comprise a non-aqueous solvent. In one preferable embodiment, the solvent may comprise both an aqueous solvent and a non-aqueous solvent. Optionally, the solvent may comprise a 4:3 ratio of non-aqueous solvent to water. Various solvents can be considered for the delivery of the amine component. It is notable that carbamate formation can be promoted without necessarily eliminating water entirely. There merely needs to be a sufficient shift towards carbamate production. Preferably, during step b], the complete delivery of carbon dioxide may occur over a duration of at least 24h, and more preferably of at least 120h. In order for sufficient carbamate species to be produced in the admixture, a relatively long duration of carbon dioxide loading becomes necessary, else the free amine concentration in the admixture is relatively high and can alter the pH of the admixture in a deleterious fashion. The method may further comprise a step, prior to step c], of drying the admixture. Said drying may be performed by vacuum drying. Drying of the admixture can assist with reduction of the water concentration therein to preferentially form the carbamate species rather than the carbonate species. In an alternative arrangement, the admixture may not be dried prior to step c]. It may be that, where the admixture has been prepared to limit the water content, for example, where a two-phase solvent is used, or a high amine concentration is used, then further drying may not be required. At least one process characteristic may be controlled so that a ratio of free carbonate to free carbamate is less than 5 mol% once added to the cementitious material. At least one process characteristic may be controlled so that a free amine content is within a range of 3% to 20% of the weight of the admixture prior to step c]. At least one process characteristic may be controlled so that a water content of the admixture does not exceed 60wt.% prior to step c]. At least one process characteristic may be controlled so that a molar ratio of carbonate is less than 5% prior to step c]. Optionally, the at least one process characteristic may comprise one or more of: pH; water content; and amine content. The control of the process characteristics is important to ensure that the slow sequestration of carbon dioxide occurs in the cementitious material, and this is achieved by preferential carbamate speciation. According to a second aspect of the invention, there is provided an admixture for improving the strength of a product comprising cementitious material containing ordinary Portland cement, the admixture comprising: an amine component loaded with carbon dioxide by delivering gaseous carbon dioxide to the admixture for a duration; and a solvent; the admixture having a water content that does not exceed 60wt.%. The provision of an admixture which can be introduced into the cementitious material as an end-of-production-line admixture, leads to less contamination of the processing equipment for the cementitious material compared with introduction of alkanolamines prior to grinding, for instance. According to a third aspect of the invention, there is provided a method of improving the strength of a product comprising cementitious material containing ordinary Portland cement, the method comprising the step of: adding an alkanolamine into a cementitious material in an amount of 0.1wt.% to 5.0wt.% with respect to a weight of ordinary Portland cement, a strength of a subsequent product being enhanced via carbon dioxide release during setting or curing of the cementitious material. Whilst an admixture is preferred, it may be possible to utilise the teachings of the present invention in a direct additive process of an alkanolamine into a cementitious material, and still achieve the same preferential carbamate speciation. The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows respectively, clockwise from top left, graphs of the carbon dioxide loading based on gravimetric data over time, carbamate content as mole fraction of the admixture over time, free amine content of the admixture over time, and carbonate content as mole fraction of the admixture over time, for three different admixture preparations; and Figure 2 shows 13C NMR spectroscopic data indicating the measurements of free amine and carbamate species in the admixture over time. The present invention will now be described with reference to the following examples in particular. Examples Example 1 (Formulation HJ400_1) An admixture was prepared comprising 30wt.% monoethanolamine in a solvent comprising a 3:4 ratio of water to isopropanol. The admixture was loaded with carbon dioxide by passing a stream of pure carbon dioxide at a rate of 200 cubic centimetres per minute for 120 hours at 25°C. The admixture was then dried for 3 hours at a pressure of 50 mbar at 40°C. Analysis of the admixture following drying showed that there was 18.17wt.% free monoethanolamine, a water content of 20.98wt.%, a carbon dioxide capacity of 16.1wt.%, and zero mol.% of the carbonate product. The admixture was then added to various cementitious materials, specifically, 100% cement (referred to here as CEM 1), 65% cement and 35% another material, here either fly ash or milled lime (referred to here as CEM2), and around 50% cement, and the rest another material, here ground granulated blast-furnace slag (referred to here as CEM3). The exact percentages of the materials in CEM2 and CEM3 can vary in practice, and therefore the indicators used are for reference only in the examples below to distinguish 5 between the various cementitious materials. Table 1 Admixt ure to cement ratio % Free MEA / wt.% Water content / wt.% CO2 capacity / wt. % Carbonate content / mol% Binder CP Compressive strength / MPa (% increase over reference) 1 day 7 day 28 day 0.5 18.17 20.98 16.1 0 CEM 1 9.4 9.5 11.0 CEM 3 (GGBS) 8.8 9.1 12.1 CEM 2 (Milled lime) 7.1 10.2 13.5 CEM 2 (Fly Ash) 8.9 8.8 11.6 1 18.17 20.98 16.1 0 CEM 1 7.6 11.9 16.5 CEM 3 (GGBS) 6.8 12.3 17.6 CEM 2 (Milled lime) 5.9 11.7 19.4 CEM 2 (Fly Ash) 7.5 10.9 21.6 1.5 18.17 20.98 16.1 0 CEM 1 6.0 13.6 17 CEM 3 (GGBS) 5.8 11.7 19.2 CEM 2 (Milled lime) 4.6 10.8 20.9 CEM 2 (Fly Ash) 9.4 12.2 23.4 Table 1 shows the increased strength of the concrete product produced after 1 day, 7 days and 28 days from addition of the admixture to the various cementitious materials over time. The plasticity, durability, and pH of the concrete exhibited very limited 10 changes. Example 2 (Formulation HJ400_2) An admixture was prepared comprising 80wt.% monoethanolamine in a solvent comprising a 3:4 ratio of water to isopropanol. The admixture was loaded with carbon dioxide by passing a stream of pure carbon dioxide at a rate of 200 cubic centimetres per minute for 120 hours at 25°C. The admixture was then dried for 3 hours at a pressure of 50 mbar at 40°C. Analysis of the admixture following drying showed that there was 11.36wt.% free 5 monoethanolamine, a water content of 18.96wt.%, a carbon dioxide capacity of 18.5wt.%, and zero mol.% of the carbonate product. The admixture was then added to various cementitious materials, specifically, 100% cement (referred to here as CEM 1), 65% cement and 35% another material, here either fly ash or milled lime (referred to here as CEM2), and around 50% cement, and the rest 10 another material, here ground granulated blast-furnace slag (referred to here as CEM3). The exact percentages of the materials in CEM2 and CEM3 can vary in practice, and therefore the indicators used are for reference only in the examples below to distinguish between the various cementitious materials. Table 2 Admixt ure to cement ratio % Free MEA / wt.% Water content / wt.% CO2 capacity / wt. % Carbonate content / mol% Binder CP Compressive strength / MPa (% increase over reference) 1 day 7 day 28 day 0.5 11.36 18.96 18.5 0 CEM 1 5.4 11.4 12.7 CEM 3 (GGBS) 7.2 11.1 13.6 CEM 2 (Milled lime) 6.1 10.7 12.9 CEM 2 (Fly Ash) 8.4 11 13.1 1 11.36 18.96 18.5 0 CEM 1 5.6 14.2 16.5 CEM 3 (GGBS) 4.7 13.9 15.9 CEM 2 (Milled lime) 6.1 14.1 16.7 CEM 2 (Fly Ash) 6.2 14.8 19.7 1.5 11.36 18.96 18.5 0 CEM 1 7.2 15.9 21.0 CEM 3 (GGBS) 6.3 14.8 21.6 CEM 2 (Milled lime) 7.8 14.6 20.8 CEM 2 (Fly Ash) 7.2 15.9 21.0 Table 2 shows the increased strength of the concrete product produced after 1 day, 7 days and 28 days from addition of the admixture to the various cementitious materials over time. The plasticity, durability, and pH of the concrete exhibited very limited changes. 5 Example 3 (Formulation HJ400_3) An admixture was prepared comprising 30wt.% monoethanolamine in a solvent comprising a 3:4 ratio of water to isopropanol. The admixture was loaded with carbon dioxide by passing a stream of pure carbon dioxide at a rate of 1000 cubic centimetres per minute for 120 hours at 25°C. 10 The admixture was then dried for 3 hours at a pressure of 50 mbar at 40°C. Analysis of the admixture following drying showed that there was 4.66wt.% free monoethanolamine, a water content of 16.77wt.%, a carbon dioxide capacity of 20.8wt.%, and zero mol.% of the carbonate product. The admixture was then added to various cementitious materials, specifically, 100% 15 cement (referred to here as CEM 1), 65% cement and 35% another material, here either fly ash or milled lime (referred to here as CEM2), and around 50% cement, and the rest another material, here ground granulated blast-furnace slag (referred to here as CEM3). The exact percentages of the materials in CEM2 and CEM3 can vary in practice, and therefore the indicators used are for reference only in the examples below to distinguish 20 between the various cementitious materials. Table 3 Admixt ure to cement ratio % Free MEA / wt.% Water content / wt.% CO2 capacity / wt. % Carbonate content / mol% Binder CP Compressive strength / MPa (% increase over reference) 1 day 7 day 28 day 0.5 4.66 16.77 22.8 0 CEM 1 18.3 10.6 14.6 CEM 3 (GGBS) 16.6 11.5 15.2 CEM 2 (Milled lime) 16.8 12.6 15.6 CEM 2 (Fly Ash) 16.9 12.9 15.1 1 4.66 16.77 22.8 0 CEM 1 11.6 10.2 16.9 CEM 3 (GGBS) 10.1 9.7 17.0 CEM 2 (Milled lime) 11.4 10.1 16.8 CEM 2 (Fly Ash) 10.4 9.3 15.8 1.5 4.66 16.77 22.8 0 CEM 1 6.9 7.1 15.2 CEM 3 (GGBS) 6.3 7.4 14.6 CEM 2 (Milled lime) 7.1 8.2 16.1 CEM 2 (Fly Ash) 8.5 9.2 17.3 Table 3 shows the increased strength of the concrete product produced after 1 day, 7 days and 28 days from addition of the admixture to the various cementitious materials over time. The plasticity, durability, and pH of the concrete exhibited very limited changes. 5 Example 4 (Formulation HJ400_4) An admixture was prepared comprising 30wt.% monoethanolamine in a solvent comprising a 3:4 ratio of water to isopropanol. The admixture was loaded with carbon dioxide by passing a stream of pure carbon dioxide at a rate of 1000 cubic centimetres per minute for 120 hours at 25°C. 10 The admixture was then dried for 2 hours at a pressure of 50 mbarat 40°C, i.e., with less drying time than in Example 3. Analysis of the admixture following drying showed that there was 4.53wt.% free monoethanolamine, a water content of 17.75wt.%, a carbon dioxide capacity of 20.6wt.%, and zero mol.% of the carbonate product. 15 The admixture was then added to various cementitious materials, specifically, 100% cement (referred to here as CEM 1), 65% cement and 35% another material, here either fly ash or milled lime (referred to here as CEM2), and around 50% cement, and the rest another material, here ground granulated blast-furnace slag (referred to here as CEM3). The exact percentages of the materials in CEM2 and CEM3 can vary in practice, and therefore the indicators used are for reference only in the examples below to distinguish between the various cementitious materials. Table 4 Admixt ure to cement ratio % Free MEA / wt.% Water content / wt.% CO2 capacity / wt. % Carbonate content / mol% Binder CP Compressive strength / MPa (% increase over reference) 1 day 7 day 28 day 0.5 4.53 17.75 22.6 0 CEM 1 15.2 12.5 19.8 CEM 3 (GGBS) 15.7 11.9 20.1 CEM 2 (Milled lime) 15.3 11.4 19.6 CEM 2 (Fly Ash) 14.9 10.6 17.8 1 4.53 17.75 22.6 0 CEM 1 10.1 8.6 18.6 CEM 3 (GGBS) 10.4 8.3 19.1 CEM 2 (Milled lime) 9.6 6.9 16.8 CEM 2 (Fly Ash) 9.1 8.2 17.1 1.5 4.53 17.75 22.6 0 CEM 1 7.8 6.2 16.9 CEM 3 (GGBS) 8.2 7.1 18.6 CEM 2 (Milled lime) 6.7 6.8 19.3 CEM 2 (Fly Ash) 7.4 6.9 18.6 Table 4 shows the increased strength of the concrete product produced after 1 day, 7 5 days and 28 days from addition of the admixture to the various cementitious materials over time. The plasticity, durability, and pH of the concrete exhibited very limited changes. Example 5 (Formulation HJ400_5) An admixture was prepared comprising 80wt.% monoethanolamine in pure water. The 10 admixture was loaded with carbon dioxide by passing a stream of pure carbon dioxide at a rate of 1000 cubic centimetres per minute for 180 hours at 25°C. The admixture was then dried for 3 hours at a pressure of 50 mbar at 40°C. Analysis of the admixture following drying showed that there was 8.35wt.% free monoethanolamine, a water content of 16.03wt.%, a carbon dioxide capacity of 20.0wt.%, and zero mol.% of the carbonate product. The admixture was then added to various cementitious materials, specifically, 100% 5 cement (referred to here as CEM 1), 65% cement and 35% another material, here either fly ash or milled lime (referred to here as CEM2), and around 50% cement, and the rest another material, here ground granulated blast-furnace slag (referred to here as CEM3). The exact percentages of the materials in CEM2 and CEM3 can vary in practice, and therefore the indicators used are for reference only in the examples below to distinguish 10 between the various cementitious materials. Table 5 Admixt ure to cement ratio % Free MEA / wt.% Water content / wt.% CO2 capacity / wt. % Carbonate content / mol% Binder CP Compressive strength / MPa (% increase over reference) 1 day 7 day 28 day 0.5 8.35 16.03 20 0 CEM 1 4.1 8.5 10.6 CEM 3 (GGBS) 6.3 9.1 11.2 CEM 2 (Milled lime) 6.4 8.6 11.5 CEM 2 (Fly Ash) 8.2 9.1 12.9 1 8.35 16.03 20 0 CEM 1 8.5 10.6 16.2 CEM 3 (GGBS) 7.9 11.2 16.9 CEM 2 (Milled lime) 8.3 11.7 17.1 CEM 2 (Fly Ash) 7.8 9.8 16.8 1.5 8.35 16.03 20 0 CEM 1 5.2 6.8 10.7 CEM 3 (GGBS) 6.1 9.6 12.4 CEM 2 (Milled lime) 7.2 10.2 13.1 CEM 2 (Fly Ash) 6.9 9.6 12.7 Table 5 shows the increased strength of the concrete product produced after 1 day, 7 days and 28 days from addition of the admixture to the various cementitious materials over time. The plasticity, durability, and pH of the concrete exhibited very limited changes. Example 6 (Formulation HJ400_6) An admixture was prepared comprising 80wt.% monoethanolamine in pure water. The 5 admixture was loaded with carbon dioxide by passing a stream of pure carbon dioxide at a rate of 1000 cubic centimetres per minute for 180 hours at 25°C. No drying step was performed. Analysis of the admixture showed that there was 6.65wt.% free monoethanolamine, a water content of 20.89wt.%, a carbon dioxide capacity of 19.2wt.%, and 1,6mol.% of the 10 carbonate product. The admixture was then added to various cementitious materials, specifically, 100% cement (referred to here as CEM 1), 65% cement and 35% another material, here either fly ash or milled lime (referred to here as CEM2), and around 50% cement, and the rest another material, here ground granulated blast-furnace slag (referred to here as CEM3). 15 The exact percentages of the materials in CEM2 and CEM3 can vary in practice, and therefore the indicators used are for reference only in the examples below to distinguish between the various cementitious materials. Table 6 Admixt ure to cement ratio % Free MEA / wt.% Water content / wt.% CO2 capacity / wt. % Carbonate content / mol% Binder CP Compressive strength / MPa (% increase over reference) 1 day 7 day 28 day 0.5 6.65 20.89 19.2 1.6 CEM 1 8.6 10.7 15.2 CEM 3 (GGBS) 7.9 10.2 14.9 CEM 2 (Milled lime) 8.1 11.1 15.7 CEM 2 (Fly Ash) 9.2 12.7 16.5 1 6.65 20.89 19.2 1.6 CEM 1 5.3 8.8 17.2 CEM 3 (GGBS) 6.6 9.2 14.9 CEM 2 (Milled lime) 5.9 8.9 15.2 CEM 2 (Fly Ash) 7.1 9.3 14.3 1.5 6.65 20.89 19.2 1.6 CEM 1 3.7 5.7 11.2 CEM 3 (GGBS) 4.3 5.2 9.7 CEM 2 (Milled lime) 5.2 6.5 10.6 CEM 2 (Fly Ash) 4.7 5.1 9.9 Table 6 shows the increased strength of the concrete product produced after 1 day, 7 days and 28 days from addition of the admixture to the various cementitious materials over time. The plasticity, durability, and pH of the concrete exhibited very limited changes. 5 Example 7 (Formulation HJ400_7) An admixture was prepared comprising 50wt.% monoethanolamine in pure water. The admixture was loaded with carbon dioxide by passing a stream of pure carbon dioxide at a rate of 1000 cubic centimetres per minute for 180 hours at 25°C. No drying step was performed. 10 Analysis of the admixture following drying showed that there was 3.91wt.% free monoethanolamine, a water content of 51,2wt.%, a carbon dioxide capacity of 20.1 wt.%, and 17.4mol.% of the carbonate product. The admixture was then added to various cementitious materials, specifically, 100% cement (referred to here as CEM 1), 65% cement and 35% another material, here either 15 fly ash or milled lime (referred to here as CEM2), and around 50% cement, and the rest another material, here ground granulated blast-furnace slag (referred to here as CEM3). The exact percentages of the materials in CEM2 and CEM3 can vary in practice, and therefore the indicators used are for reference only in the examples below to distinguish between the various cementitious materials. 20 Table 7 Admixt ure to cement ratio % Free MEA / wt.% Water content / wt.% CO2 capacity / wt. % Carbonate content / mol% Binder CP Compressive strength / MPa (% increase over reference) 1 day 7 day 28 day 0.5 3.91 51.2 20.1 17.4 CEM 1 2.0 3.2 4.2 CEM 3 (GGBS) 3.6 3.8 4 CEM 2 (Milled lime) 2.7 4.2 5.1 CEM 2 (Fly Ash) 2.2 3.6 4.9 1 3.91 51.2 20.1 17.4 CEM 1 3.5 4.5 6.2 CEM 3 (GGBS) 1.6 3.9 4.8 CEM 2 (Milled lime) 1.9 3.3 5.4 CEM 2 (Fly Ash) 2.7 3.9 5.3 1.5 3.91 51.2 20.1 17.4 CEM 1 0.8 1.2 3.1 CEM 3 (GGBS) -0.3 1.6 2.7 CEM 2 (Milled lime) 1.6 2.9 4.8 CEM 2 (Fly Ash) 1.2 3.1 4.7 Table 7 shows the increased strength of the concrete product produced after 1 day, 7 days and 28 days from addition of the admixture to the various cementitious materials over time. The plasticity, durability, and pH of the concrete exhibited very limited changes. 5 Example 8 (Formulation HJ400_8) An admixture was prepared comprising 30wt.% monoethanolamine in pure water. The admixture was loaded with carbon dioxide by passing a stream of pure carbon dioxide at a rate of 1000 cubic centimetres per minute for 180 hours at 25°C. No drying step was performed. 10 Analysis of the admixture following drying showed that there was 2.23wt.% free monoethanolamine, a water content of 68.5wt.%, a carbon dioxide capacity of 23.2wt.%, and 42.6mol.% of the carbonate product. The admixture was then added to various cementitious materials, specifically, 100% cement (referred to here as CEM 1), 65% cement and 35% another material, here either 15 fly ash or milled lime (referred to here as CEM2), and around 50% cement, and the rest another material, here ground granulated blast-furnace slag (referred to here as CEM3). The exact percentages of the materials in CEM2 and CEM3 can vary in practice, and therefore the indicators used are for reference only in the examples below to distinguish between the various cementitious materials. 5 Table 8 Admixt ure to cement ratio % Free MEA / wt.% Water content / wt.% CO2 capacity / wt. % Carbonate content / mol% Binder CP Compressive strength / MPa (% increase over reference) 1 day 7 day 28 day 0.5 2.23 68.5 20.2 42.6 CEM 1 -0.8 0.1 1.3 CEM 3 (GGBS) -1.7 -0.2 0.2 CEM 2 (Milled lime) 0.2 0.6 0.8 CEM 2 (Fly Ash) 0.4 0.5 1.1 1 2.23 68.5 20.2 42.6 CEM 1 -2.9 0.3 1.7 CEM 3 (GGBS) -2.2 -0.6 0.3 CEM 2 (Milled lime) -3.2 -1.3 0.7 CEM 2 (Fly Ash) -2.7 -1.9 -0.7 1.5 2.23 68.5 20.2 42.6 CEM 1 -5.6 -1.3 -0.2 CEM 3 (GGBS) -4.4 -3.1 -1.8 CEM 2 (Milled lime) -3.4 -2.2 -1.2 CEM 2 (Fly Ash) -4.9 -1.8 -0.6 Table 8 shows the increased strength of the concrete product produced after 1 day, 7 days and 28 days from addition of the admixture to the various cementitious materials over time. The plasticity, durability, and pH of the concrete exhibited very limited changes. 10 Example 9 (HJ400_9) An admixture was prepared comprising 30wt.% monoethanolamine in a solvent comprising a 3:4 ratio of water to isopropanol. The admixture was loaded with carbon dioxide by passing a stream of pure carbon dioxide at a rate of 1000 cubic centimetres per minute for 120 hours at 25°C. The admixture was then dried for 3 hours at a pressure of 50 mbar at 40°C, before being re-diluted so as to have an approximate water content of around 40wt.%. 5 Analysis of the admixture following drying showed that there was 6.84wt.% free monoethanolamine, a water content of 42.0wt.%, a carbon dioxide capacity of 20.4wt.%, and 0.5mol.% of the carbonate product. The admixture was then added to various cementitious materials, specifically, 100% cement (referred to here as CEM 1), 65% cement and 35% another material, here either 10 fly ash or milled lime (referred to here as CEM2), and around 50% cement, and the rest another material, here ground granulated blast-furnace slag (referred to here as CEM3). The exact percentages of the materials in CEM2 and CEM3 can vary in practice, and therefore the indicators used are for reference only in the examples below to distinguish between the various cementitious materials. 15 Table 9 Admixt ure to cement ratio % Free MEA / wt.% Water content / wt.% CO2 capacity / wt. % Carbonate content / mol% Binder CP Compressive strength / MPa (% increase over reference) 1 day 7 day 28 day 0.5 6.84 42 20.4 0.5 CEM 1 4.7 5.2 6.7 CEM 3 (GGBS) 2.8 3.9 6.1 CEM 2 (Milled lime) 3.1 4.2 6.9 CEM 2 (Fly Ash) 1.2 3.1 4.9 1 6.84 42 20.4 0.5 CEM 1 3.4 4.70 6.9 CEM 3 (GGBS) 2.9 4.2 7 CEM 2 (Milled lime) 2.5 3.8 6.4 CEM 2 (Fly Ash) 4.6 5.3 7.4 1.5 6.84 42 20.4 0.5 CEM 1 1.6 1.90 2.4 CEM 3 (GGBS) 2.8 3.9 6.1 CEM 2 (Milled lime) 3.1 4.2 6.9 CEM 2 (Fly Ash) 1.2 3.1 4.9 Table 9 shows the increased strength of the concrete product produced after 1 day, 7 days and 28 days from addition of the admixture to the various cementitious materials over time. The plasticity, durability, and pH of the concrete exhibited very limited changes. 5 Example 10 (Formulation HJ400_10) An admixture was prepared comprising 30wt.% monoethanolamine in a solvent comprising a 3:4 ratio of water to isopropanol. The admixture was loaded with carbon dioxide by passing a stream of pure carbon dioxide at a rate of 1000 cubic centimetres per minute for 120 hours at 25°C. 10 The admixture was then dried for 3 hours at a pressure of 50 mbar at 40°C, before being re-diluted so as to have an approximate water content of around 60wt.%. Analysis of the admixture following drying showed that there was 3.84wt.% free monoethanolamine, a water content of 56.0wt.%, a carbon dioxide capacity of 16.5wt.%, and 10.2mol.% of the carbonate product. 15 The admixture was then added to various cementitious materials, specifically, 100% cement (referred to here as CEM 1), 65% cement and 35% another material, here either fly ash or milled lime (referred to here as CEM2), and around 50% cement, and the rest another material, here ground granulated blast-furnace slag (referred to here as CEM3). The exact percentages of the materials in CEM2 and CEM3 can vary in practice, and 20 therefore the indicators used are for reference only in the examples below to distinguish between the various cementitious materials. Table 10 Admixt ureto cement ratio % Free MEA / wt.% Water content / wt.% CO2 capacity / wt. % Carbonate content / mol% Binder CP Compressive strength / MPa (% increase over reference) 1 day 7 day 28 day 0.5 3.84 56 16.5 10.2 CEM 1 1.9 3.6 5.1 CEM 3 (GGBS) 3.3 4.2 5.1 CEM 2 (Milled lime) 2.9 5.1 5.9 CEM 2 (Fly Ash) 1.7 4.1 4.3 1 3.84 56 16.5 10.2 CEM 1 1.1 3.2 4.1 CEM 3 (GGBS) 1.4 3.3 4.1 CEM 2 (Milled lime) 1.7 2.9 4.1 CEM 2 (Fly Ash) 1.6 2.2 3.2 1.5 3.84 56 16.5 10.2 CEM 1 -0.3 1.0 2.2 CEM 3 (GGBS) -1.2 0.7 1.2 CEM 2 (Milled lime) -0.3 1.2 2.2 CEM 2 (Fly Ash) -0.9 1.7 2.5 Table 10 shows the increased strength of the concrete product produced after 1 day, 7 days and 28 days from addition of the admixture to the various cementitious materials over time. The plasticity, durability, and pH of the concrete exhibited very limited changes. 5 Example 11 (HJ401_1) An admixture was prepared comprising 30wt.% branched polyethylenimine in a solvent comprising a 3:4 ratio of water to isopropanol. The admixture was loaded with carbon dioxide by passing a stream of pure carbon dioxide at a rate of 200 cubic centimetres per minute for 120 hours at 25°C. 10 The admixture was then dried for 3 hours at a pressure of 50 mbar at 40°C. The admixture was then added to various cementitious materials, specifically, 100% cement (referred to here as CEM 1), 65% cement and 35% another material, here either fly ash or milled lime (referred to here as CEM2), and around 50% cement, and the rest another material, here ground granulated blast-furnace slag (referred to here as CEM3). 15 The exact percentages of the materials in CEM2 and CEM3 can vary in practice, and therefore the indicators used are for reference only in the examples below to distinguish between the various cementitious materials. Table 11 Admixt ure to cement ratio % Binder CP Compressive strength / MPa (% increase over reference) 1 day 7 day 28 day 0.5 CEM 1 -16.7 -0.1 3.2 CEM 3 (GGBS) -12.4 1.0 4.3 CEM 2 (Milled lime) -11.8 0.2 2.2 CEM 2 (Fly Ash) -12.8 0.8 5.1 Table 11 shows the increased strength of the concrete product produced after 1 day, 7 days and 28 days from addition of the admixture to the various cementitious materials over time. The plasticity, durability, and pH of the concrete exhibited very limited 5 changes. Example 12 (HJ402_1) An admixture was prepared comprising 30wt.% 2-aminomethylpropanol in a solvent comprising a 3:4 ratio of water to isopropanol. The admixture was loaded with carbon dioxide by passing a stream of pure carbon dioxide at a rate of 200 cubic centimetres 10 per minute for 120 hours at 25°C. The admixture was then dried for 3 hours at a pressure of 50 mbar at 40°C. The admixture was then added to various cementitious materials, specifically, 100% cement (referred to here as CEM 1), 65% cement and 35% another material, here either fly ash or milled lime (referred to here as CEM2), and around 50% cement, and the rest 15 another material, here ground granulated blast-furnace slag (referred to here as CEM3). The exact percentages of the materials in CEM2 and CEM3 can vary in practice, and therefore the indicators used are for reference only in the examples below to distinguish between the various cementitious materials. Table 12 Admixt ure to cement ratio % Binder CP Compressive strength / MPa (% increase over reference) 1 day 7 day 28 day 0.5 CEM 1 2.5 8.6 5.4 CEM 3 (GGBS) 1.0 4.5 2.0 CEM 2 (Milled lime) 1.4 8.4 3.8 CEM 2 (Fly Ash) 0.1 2.4 1.2 Table 12 shows the increased strength of the concrete product produced after 1 day, 7 days and 28 days from addition of the admixture to the various cementitious materials over time. The plasticity, durability, and pH of the concrete exhibited very limited changes. Conclusions It is clear from the examples that carrier formulations, that is, the binder plus admixture, yield strength enhancements of cement paste in the region of 5-15 % after 1 day of curing, and 8-12 % after 7 days curing where incorporated in 0.5 wt.% quantities to the cement slurry prior to casting. A desirable carrier formulation involves the use of isopropanol controlled free-amine removal, higher quantities if delivery of carbon dioxide and subsequent drying for three hours at reduced pressure (HJ400_3, HJ400_4), with both carriers exhibiting comparable results over all curing durations, alongside optimal carbon dioxide delivery extents. Controlling free carbonate to carbamate ratio to below 5 mol% produces highly desirable performance in the resultant product due the as detailed availability of CO2 at initial periods to the system, as evidenced by the significantly reduced performance of carriers HJ400_7 and HJ400_8. In comparison with carriers with both similar water content and free amine quantity, the relative performance is considerably worse. An increased free-amine content (HJ400_1, HJ400_2), achieved through a reduced carbon dioxide delivery manifold, gives a product with reduced performance particularly in early age strength in comparison to the optimal system (HJ400_4, HJ400_4). Water content also results in a significant reduction in carrier performance over 1 day, but also over longer term curing conditions, as a result of the less amount of viable carrier delivered to the system. Conclusions which can be drawn are that preferred process characteristics include: • Free amine content tolerance in the admixture in a range of 3-20wt.%, with a preferred quantity within the range of 3-8 wt.%; • CO2 capacities and delivery extents in the range of 10wt.% to 30wt.% in the admixture, preferably greater than 15wt.%, and more preferably greater than 20wt.%; • A water content below 60wt.% in the admixture, which appears to be crucial to creating a working admixture, and more preferably less than 20wt.%; and • A molar ratio of the carbonate species in the admixture of less than 5.0%, and more preferably less than 2.0%. Without wishing to be bound by theory, it is anticipated that the processes which dictate the performance of the admixture are as follows: • Free amine content The concentration of free amine (directly proportional to the carbon dioxide capacity and speciation of the amine-CO2 content) in the as-produced carrier material is important to the function and durability of the admixture owing to its effect on the material pH, as well as its impact on cement paste. Increasing free-amine content will significantly raise the pH of the stored sample, which avoids pre-cement hydrolysis. Given the Pka of the protonated amine (~9.5), buffering the system at a pH centred around 9.5 will reduce the rate of carbon dioxide loss prior to introduction into cementitious materials, allowing the admixture to be stored for longer periods. Furthermore, the free amine demonstrates moderate long-term enhancement of cementitious materials with regards to mediating mineral-phase speciation. Free amine content in the admixture can be controlled relatively easily by modifying the carbon dioxide loading time. As can be seen in Figure 1(c), as more carbon dioxide is loaded, the free amine wt.% decreases. The rate at which this plateaus depends on the concentration of the amine in the first instance. Monoethanolamine was used in the examples provided. Free amine can also be controlled by the use of the specific solvent in question. A protic, water-soluble solvent, such as isopropanol, can cause a reduction in free amine content when compared with a pure water equivalent. This will result in phase separation as the amine separates out with the isopropanol. A 4:3 ratio of isopropanol to water has been determined to be quite effective, but similar results can be achieved by the use of any appropriate two-phase solvent where the amine preferentially separates into one of the layers. • Carbon dioxide transfer Carbon dioxide transfer occurs via the mechanism of precipitation and development of nanoscale calcium carbonate species which both accelerate the formation and increase the packing density of calcium-silicate-hydrate nanocrystalline gel structures, and furthermore by increasing overall cementitious binder density through the precipitation of calcium carbonates within the pore-volume of cementitious materials. The carbon dioxide transfer is therefore directly related to the carbon dioxide capacity of the carrier. The temporarily stable CO2-carrier conjugate will degrade over time in alkaline environments such as those of cementitious materials. These time periods depend on the available concentration of OH' ions available, in the order of 24-200h for complete hydrolysis. The quantity of nanoscale calcium carbonate deposits and densification due to precipitation is directly proportional to the extent of carbonation extent, and thus the CO2 content of the carrier invention is directly related both the chemical and physical effect on cementitious materials. Carbon dioxide loading can be altered by increasing the volumetric flow of carbon dioxide to the admixture. Modifying the gas temperature may also affect this loading capacity. • Speciation of the amine-CO2 conjugate The chemistry of the amine-CO2 conjugate is of important to the action of the carrier within cementitious materials. The interaction of amines with carbon dioxide is highly dependent on a variety of factors. Depending on the availability of water and the amine concentration, amines will either form an ammonium carbonate salt or ammonium carbamate salt, as indicated below. The specific chemistries of the two amine-carbamate species with regards to their interaction with a high-pH aqueous environment is explained by the nature of the interactions between the nitrogen of the amine moiety and the central carbon of the carbon dioxide species. In the ammonium carbonate salt, it is the electrostatic interaction of the two associated species (ammonium and carbonate, shown as bicarbonate in the reaction diagram above) in a dynamic manner with other cations which retains carbon dioxide. In the presence of other cations (such as Ca2+ in cement, present in extremely high concentrations), the carbon dioxide (as carbonate or bicarbonate) is immediately available owing to the high solubility of ammonium carbonates in water. Due to the very low solubility of CaCOs in high-pH environments, the equilibrium will shift to immediately consume the available carbonate added to the system, immediately precipitating calcium carbonate. Where the second species, an ammonium carbamate, is formed, the interaction between the amine nitrogen and central carbon atom in carbon dioxide is covalent in nature. Carbamates are particularly stable in high pH environments owing to the resonance stabilisation of the formed carbonyl species, greatly reducing the electrophilicity of the carbonyl carbon and reducing the propensity for hydrolysis via OH- nucleophilic substitution. As such, the hydrolysis of carbamates occurs through protonation of the carbonyl species, which in strongly disfavoured in high pH environments. The present invention works very well when the balance towards the carbamate species is promoted. • Water content The final major compositional factor of the admixture is its water content. The water content of the admixture arises from the aqueous synthetic process. Increased water content directly affects factors free amine content, amine-CO2 conjugate speciation, and carbon dioxide capacity, as it can both drive the hydrolysis of carbamate species which yields either carbonate species or carbon dioxide release to the environment prior to the carriers use. Furthermore, higher water content reduces the quantity of the actual carrier introduced to the cementitious system by dilution. Where required, water content can be varied by post-synthesis solvent removal processes, and in particular, via drying under vacuum. The admixture is tolerant of reduced pressure evaporation. This is employed to achieve water contents in a desired range, evaluated according to standardised Karl-Fisher titrations and NMR spectroscopy. Free amine and carbamate content can be evaluated according to 13C NMR, as shown in Figure 2. The speciation of carbonate and carbamate is determined from 13C NMR spectroscopy. Through analysis (taking the 80 wt.% monoethanolamine, HJ400_6, as an example, with some values shifting slightly depending on concentration) of the NMR spectra: the ammonium carbamate material methylene resonances (shifting from 61.86 - 65.52 ppm and 44.26 to 45.59 ppm), the free amine methylene resonances (62.85 and 43.62 ppm) and the carbonate / bicarbonate (162.51, identical due to rapid exchange), and carbamate (164.16 ppm) quaternary carbon environments can be quantified. By way of evaluating total carbon dioxide uptake, simple gravimetry can be employed in order to evaluate the mass of carbon dioxide taken up by the system. Through varying the monoethanolamine ratio, it is possible to directly elicit control over the carbon dioxide loading kinetics and speciation, with 80 wt.% monoethanolamine exhibiting almost no carbonate formed after 180 minutes of the reaction, as shown in Figure 2. By effective quantification through this technique, the free amine and carbamate / carbonate ratios can be effectively calculated. These are further reinforced by standardised titration methodologies to evaluate the total amine and total carbon dioxide content. It is anticipated that examples of viable amines which are suitable for producing the desirable carbamate or urethane species include, but are not limited to a group comprising: monoethanolamine; diethanolamine; triethanolamine; 2- aminomethylpropanol; diglycolamine; methyldiethanolamine; or combinations thereof. Whilst the present invention has been demonstrated as functioning in the form of an admixture in solution, which is loaded with carbon dioxide, it may be equally feasible to provide an alkanolamine or similar amine directly into a cementitious material, controlling the process conditions within the cementitious material mixture, and then loading carbon dioxide during the curing process. It is therefore possible to prepare an admixture for a cementitious material before curing into a product, typically a concrete product, which makes use of a carbon dioxide loaded amine to produce slow carbon dioxide sequestration into the cementitious material, and thereby improving the strength of the product over a long period of time compared with a product formed without such an admixture. This is believed to be achieved by the preferential formation of carbamate or urethane species from the amine, rather than the more usual high carbonate speciation which occurs in amine-based accelerant admixtures known in the art. The words ‘comprises / comprising’ and the words ‘having / including’ when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps, or components, but do not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention as defined herein.

Claims

1. A method of improving the strength of a product comprising cementitious material containing ordinary Portland cement, the method comprising the steps of:a] preparing an admixture comprising an amine component and a solvent;b] loading the admixture with carbon dioxide by delivering gaseous carbon dioxide to the admixture for a duration; wherein a water content of the admixture does not exceed 60wt.%; andc] introducing the admixture into a cementitious material in an amount of 0.1wt.% to 5.0wt.% with respect to a weight of ordinary Portland cement in the cementitious material for enhancing the strength of the subsequent product.

2. A method as claimed in claim 1, wherein the amine component is an alkanolamine.

3. A method as claimed in claim 2, wherein the amine component is selected from a group comprising: monoethanolamine; diethanolamine; triethanolamine; 2-aminomethylpropanol; diglycolamine; methyldiethanolamine; branched polyethylenimine; or combinations thereof.

4. A method as claimed in any one of the preceding claims, wherein the amine component is provided in an amount in the range 30wt.% to 80wt.% of the admixture.

5. A method as claimed in any one of the preceding claims, wherein the amine component is provided in an amount of at least 60 mol% of the admixture.

6. A method as claimed in any one of the preceding claims, wherein the solventcomprises an aqueous solvent.

7. A method as claimed in any one of the preceding claims, wherein the solventcomprises a non-aqueous solvent.

8. A method as claimed in any one of the preceding claims, wherein the solventcomprises both an aqueous solvent and a non-aqueous solvent.

9. A method as claimed in claim 8, wherein the solvent comprises a 4:3 ratio of nonaqueous solvent to water.

10. A method as claimed in any one of the preceding claims, wherein, during step b], the complete delivery of carbon dioxide occurs over a duration of at least 24h.

11. A method as claimed in claim 10, wherein, during step b], the complete delivery of carbon dioxide occurs over a duration of at least 120h.

12. A method as claimed in any one of the preceding claims, further comprising a step, prior to step c], of drying the admixture.

13. A method as claimed in claim 11, wherein the drying is performed by vacuum drying.

14. A method as claimed in anyone claims 1 to 10, wherein the admixture is not dried prior to step c],15. A method as claimed in any one of the preceding claims, wherein at least one process characteristic is controlled so that a ratio of free carbonate to free carbamate is less than 5 mol% once added to the cementitious material.

16. A method as claimed in any one of the preceding claims, wherein at least one process characteristic is controlled so that a free amine content is within a range of 3% to 20% of the weight of the admixture prior to step c],17. A method as claimed in any one of the preceding claims, wherein at least one process characteristic is controlled so that a water content of the admixture does not exceed 60wt.% prior to step c],18. A method as claimed in any one of the preceding claims, wherein at least one process characteristic is controlled so that a molar ratio of carbonate is less than 5% prior to step c],19. A method as claimed in any one of claims 14 to 17, wherein the at least one process characteristic comprises one or more of: pH; water content; and amine content.

20. An admixture for improving the strength of a product comprising cementitious material containing ordinary Portland cement, the admixture comprising:an amine component loaded with carbon dioxide by delivering gaseous 5 carbon dioxide to the admixture for a duration; anda solvent;the admixture having a water content that does not exceed 60wt.%.

21. A method of improving the strength of a product comprising cementitious material 10 containing ordinary Portland cement, the method comprising the step of:adding an alkanolamine into a cementitious material in an amount of 0.1wt.% to 5.0wt.% with respect to a weight of ordinary Portland cement, a strength of a subsequent product being enhanced via carbon dioxide release 15 during setting or curing of the cementitious material.s