Method of producing a product formed from cementitious material

Abstract

A method of producing a product formed from cementitious material having an enhanced strength is provided. The method comprises the steps of providing a polymeric carbonate composition which is formed by sequestration of CO2 into an organic polymer, and mixing the polymeric carbonate composition with a freshly prepared cementitious material. The polymeric carbonate composition is provided in an amount of 0.2-10.00wt.% of the cementitious material. The cementitious material is then cured with aggregate material, wherein a duration of the curing step exceeds 24 hours by hydrolytic release of carbonate from the polymeric carbonate composition for slow release of CO2 into the product and improve strength.

Description

[0001] Method Of Producing A Product Formed from Cementitious Material

[0002] The present invention relates to a method of producing a product formed from cementitious material, such as concrete, mortar, cement paste, or grout, for example, having an enhanced strength due to carbonation, as well as a concrete product formed in accordance with the method.

[0003] In the literature there are disclosed processes of carbonating cementitious materials to achieve permanent sequestration of CO2 within the mineralogical make-up of longlifetime materials, using inorganic carbonate species. Cementitious materials, in this context, refer to materials derived from calcium silicate / aluminate-based binders, such as ordinary Portland cement (OPC).

[0004] CO2 sequestration within cementitious materials is chiefly undertaken through mineralisation, whereby the cementitious material comprising primarily of calcium silicates, aluminates and their respective hydration products, typically calcium silicate hydrate, calcium aluminate hydrate, or calcium hydroxide (C-S-H, C-A-H and CH respectively in cement chemist notation), provide a source of calcium able to yield stable calcium carbonates which remain throughout the lifetime of the material. In controlled environments and / or conditions, the carbonation of cementitious materials can be associated with an improvement of key properties of the respective material, predominantly compressive strength and durability, relating to reductions in the permeability of water, chloride or sulfate, for example.

[0005] Careful control over the extent and rate of carbonation of cementitious materials is required to prevent significant lowering of the overall pH of the cementitious materials, arising from the reaction of CO2with alkaline calcium-based materials within the material, as well as avoiding deleterious effects by interfering with the typical hydration mechanisms that are the direct cause of the development of compressive strength, which are correlated with the formation of calcium silicate or aluminate hydrate species, during curing. It is therefore important to avoid excessive carbonation throughout the course of the curing process to avoid the inhibition of hydrate development, or the decalcification of the relevant hydrated species. Excessive carbonation of cementitious materials at early stages during curing can promote adverse impacts upon the microstructure and mineralogical make-up, yielding poor compressive strength as a result. Consequently, if CO2sequestration within cementitious materials is to yield effective and usable materials, control over both the extent and rate of carbonation is vital.

[0006] Curing of cementitious materials derived from OPC within a CO2 rich atmosphere is well established in the literature, for example in CO2Sequestration in Concrete through Accelerated Carbonation Curing in a Flow-through Reactor, Ind. Eng. Chem. Res. 2010, 49, 3, 1143-1149 or Review on carbonation curing of cement-based materials, Journal of CO2 Utilization, Volume 21, 2017, Pages 119-131. This has been demonstrated to yield controllable carbonation development of cementitious materials such as concrete masonry units (CMlls), and associated improvements in thel ir compressive strengths and durability. Advantages with this approach include facile control over the extent and rate of carbonation. However, this approach is predominantly confined to materials with comparatively limited dimensions, such as CMlls, and resultant carbonation inhomogeneity using this approach is fundamentally linked to the limited diffusion of CO2 throughout the material pore structure, and dissolution of CO2 within the pore solution.

[0007] To overcome these limitations a CO2 source can be dispersed throughout the cementitious material by incorporating it within the slurry prior to casting and / or curing. Prior literature has investigated the applications of alkali metal carbonates, such as sodium carbonate, to provide a soluble and hence immediately available source of CO2 in the form of carbonate ions when incorporated into the high pH cement slurry before casting / curing. See, for example, Wang, Y et al. "Comparison of Effects of Sodium Bicarbonate and Sodium Carbonate on the Hydration and Properties of Portland Cement Paste" Materials (Basel) (2005) 28; 12(7): 1033. These alkali carbonates significantly accelerate the setting of concrete, resulting in drastically reduced initial and final setting times. Significant issues are encountered, however, with regards to inhibiting the development of compressive strength in cementitious materials containing alkali metal carbonates beyond a limited proportion. This is related to both the addition of alkali metal ions, which are associated with impeding the structural integrity of key mineral phases within cementitious materials, and the immediate availability of carbonate ions in the cementitious slurry. Therefore, it is fundamentally impossible to control the rate of CO2 delivery to cementitious materials using this methodology.

[0008] Examples of the use of degradable polymers such as polylactic acid (PLA) and poly(e- caprolactone) within cementitious materials can be found in for instance US2005 / 0205258A1 and US2006 / 0169454A1. Typically, these are used for their self- healing properties in subterranean usage, such as in oilwells. Such degradable materials are not derived from CO2, and therefore do not degrade to release a CC>2-derived carbonate species.

[0009] The application of polymeric carbonates within cementitious materials is largely limited to the incorporation of ‘non-aliphatic’ (for example bisphenol-A based) polycarbonate or polycarbonate waste as aggregate replacement, or as fibre-reinforcement to aid in the development of flexural strength. Examples of such arrangements are provided in EP1947069A1, US6669773B2, US2017 / 0088463A1 and US2017 / 0260093A1 . See also Woods, M.C.; Kulkarni, A.; Pearce, J.M. The Potential of Replacing Concrete with Sand and Recycled Polycarbonate Composites: Compressive Strength Testing. J. Compos. Sci. 2023, 7, 249., and Sathvik, S., Kumar, R., Ulloa, N. et al. Modelling the mechanical properties of concrete produced with polycarbonate waste ash by machine learning. Sci ep 14, 11552 (2024). There are few examples of the incorporation of aliphatic polycarbonates, including US2005 / 0205258A1 and CN108947393A; however, these are typically incorporated in mixtures far-removed from typical OPC cementitious materials, and incorporate quantities either in excess, i.e., as an aggregate, >10%, or far lower, i.e. , as a minor additive <0.2%, than would be suited to CO2 sequestration within cementitious materials.

[0010] The present invention seeks to improve the strength of concrete products by control of the availability of CO2 during the curing stage.

[0011] The same considerations apply for other cementitious materials as apply for concrete.

[0012] According to a first aspect of the invention, there is provided a method of producing a product formed from cementitious material having an enhanced strength due to carbonation, the method comprising the steps of: a] providing a polymeric carbonate composition which is formed by sequestration of CO2 into an organic polymer; b] mixing the polymeric carbonate composition with a freshly prepared cementitious material, wherein the polymeric carbonate composition is provided in an amount of 0.2-10.00wt.% of the cementitious material; and c] curing the cementitious material with aggregate material, wherein a duration of the curing step exceeds 24 hours, and more preferably exceeds 7 days, by hydrolytic release of carbonate from the polymeric carbonate composition. The present invention produces carbonate ions in cementitious conditions using a slow- release mode of action. It has been unexpectedly determined that overall strength of concrete or other cementitious products can be enhanced by slow release of carbonate into the mixture over an extended duration. This avoids the issues with curing accelerators which instantaneously release carbonate ions that can reduce the strength of the resultant material. Conversely, the use of polymeric carbonates which degrade over a period of many days has been shown to increase strength permanently.

[0013] The polymeric carbonate composition may preferably be an aliphatic carbonate composition. More preferably, this applies to any aliphatic carbonate having up to seven carbon atoms in the monomer unit, in addition to any applicable heteroatom content.

[0014] Preferably, the polymeric carbonate composition may comprise any of the following formulae: where either m or n = 0, or both are each > 1 ; or and where x > 2. Optionally, the polymeric carbonate composition is any of: polypropylene carbonate; polyethylene carbonate; polycyclohexene carbonate; polytrimethylene carbonate; copolymers thereof; or a combination thereof.

[0015] The polymeric carbonate composition may be a solid polymeric carbonate composition having a particle size in the range of 1 m to 2500pm.

[0016] Modification of particle size alters the rate of degradation of the polymeric carbonate composition. Tailoring the particle size can therefore allow optimisation of the overall increase in compressive strength when compared with ordinary Portland cement (OPC). Other factors that affect the rate of degradation include molecular weight, formulation, polymer chain end-capping groups, intrinsic viscosity and CO2 content.

[0017] The polymeric carbonate composition may be a solid polymeric carbonate composition having a particle size in the range of 10pm to 500pm, and more preferably in the range of 50pm to 250pm.

[0018] In one preferred embodiment, the polymeric carbonate composition may be provided in powder form.

[0019] In an alternative embodiment, the polymeric carbonate composition may be provided in fibre form.

[0020] The use of solid polymeric additions can be mixed into cement having a size similar to the grains in the cement mixture itself, and therefore may be more straightforward to disperse through a cement mixture.

[0021] In an alternative embodiment, the polymeric carbonate composition may be encapsulated or coated by a protective degradable layer. The encapsulation reduces the rate of polymeric decomposition and availability of the carbonate ions to carbonate cementitious materials. The encapsulation methods used may include but are not limited to spray drying, fluidised bed coating, pan coating, coacervation, extrusion, in-situ polymerisation, melt encapsulation, spray chilling / solidification and physical vapour decomposition, such as plasma and / or polymer evaporation.

[0022] The coatings include but are not limited to: poly(lactic acid) (PLA), polyglycolic acid (PGA), polycaprolactone (PCL), polyhydroxybutyrate (PHB), poly(lactic-co-glycolic acid) (PLGA), cellulose acetate (CA), hyaluronic acid (HA), poly(ethylene glycol) (PEG), polyanhydrides, chitosan, fluoropolymers, silicone polymers, cyclic polyolefins, polyarylene ethers, highly cross-linked polymers, phosphonated polymers and silane- based polymers.

[0023] Alternatively, the polymeric carbonate composition may be provided as a liquid solution or dispersion.

[0024] Liquid dispersions may advantageously be an easier way of storing and metering the polymeric carbonate composition for mixing into cement materials without adversely affecting the curing properties.

[0025] Optionally, the polymeric carbonate composition may have a molecular weight of between 0.1-1000kDa.

[0026] More preferably, the polymeric carbonate composition may have a molecular weight of between 1-500kDa.

[0027] During step c], the curing may occur in a chamber, bath, open conditions or any other standard curing techniques used by the concrete industry at 30- 90% relative humidity.

[0028] Preferably, during step c], the duration of the curing step may exceed 14 days.

[0029] Optionally, the cementitious material is a concrete binder mixture which may comprise any of: cement, limestone, supplementary cementitious material, sand, aggregate, water, and one or more admixtures.

[0030] Preferably, the polymeric carbonate composition may hydrolytically release carbonate during the curing step c] in an amount of between 20-60% by mass of sequestered carbon dioxide.

[0031] Advantageously, the polymeric carbonate composition may hydrolytically release carbonate during the first 8 hours of the curing step c] in an amount of not more than 10% by mass of sequestered carbon dioxide.

[0032] Advantageously, the polymeric carbonate composition may hydrolytically release carbonate during the first 24 hours of the curing step c] in an amount of not more than 5% by mass of sequestered carbon dioxide. Limited release of carbonate release during the initial stages of curing enables the slow strengthening process of the present invention to be achieved.

[0033] Optionally the polymeric carbonate composition may hydrolytically release carbonate during the first 7 days of the curing step c] in an amount of between 5-50% by mass of sequestered carbon dioxide.

[0034] Preferably, the polymeric carbonate composition may hydrolytically release carbonate during the first 28 days of the curing step c] in an amount of not more than 95% by mass of sequestered carbon dioxide.

[0035] During step c], decomposition conditions of the polymeric carbonate composition may be selected to achieve a preferred CO2 release rate.

[0036] Optionally, the decomposition conditions may include at least one of: temperature; humidity; particle size of the polymeric carbonate composition; hydrophobic content of the constituent monomers in the polymer.

[0037] Optionally, the predetermined amount of carbon dioxide may be up to 20% carbon dioxide relative to a weight of cement binder in the concrete-carrier mix within 24 to 1344 hours to increase the compressive strength of the concrete material by between 20 and 100%.

[0038] Optionally, the compressive strength of the concrete material is increased by between 20 and 100%.

[0039] Preferably, the predetermined amount of carbon dioxide may be 1 - 3% carbon dioxide relative to a weight of cement binder in the concrete-carrier mix within 24 to 1344 hours to increase the compressive strength of the concrete material by between 5 and 25%.

[0040] Optionally, the compressive strength of the concrete material is increased by between 5 and 25%.

[0041] Alternatively, a weight of binder in the concrete-carrier mix may be reduced by between 2 and 50% relative to a standard concrete mix.

[0042] Alternatively, a weight of binder in the concrete-carrier mix may be reduced by between 5 and 35% relative to a standard concrete mix. Alternatively, a weight of binder in the concrete-carrier mix may be reduced by between 5 and 20% relative to a standard concrete mix. A standard concrete mix would usually include binder, such as cement, in a weight of 10 to 20% of the weight of the concrete mix.

[0043] Optionally, the polymer degradation rate of the polymeric carbonate composition may be in the range of 0.043 to 0.1454 mmol / g / h based on measured carbonate release rate.

[0044] Optionally, the polymer degradation rate of the polymeric carbonate composition may be in the range of 0.0145 to 0.0582mmol / g / h based on measured carbonate release rate.

[0045] Preferably, the polymer degradation rate of the polymeric carbonate composition may be in the range of 0.0016 to 0.0290 mmol / g / h based on measured carbonate release rate.

[0046] Preferably, the polymer degradation rate of the polymeric carbonate composition may be in the range of 0.00016 to 0.0145 mmol / g / h based on measured carbonate release rate.

[0047] Optionally, a rate of carbon dioxide uptake in the concrete material may be less than 0.0014 mmol / g / h, by the weight of concrete reactive material agent from the binder of the concrete mix.

[0048] Preferably, the polymeric carbonate composition may be selected so as to release a predetermined amount of carbon dioxide, in the form of carbonate during the curing process over a predetermined time period, to thereby achieve a desired increase in compressive strength and / or carbonation of the concrete material.

[0049] Preferably, the predetermined amount of carbon dioxide may be a percentage by weight of carbon dioxide relative to a weight of cement in the concrete-carrier mix.

[0050] It is desirable to specifically modify the carrier being used, within the present invention, to achieve specific advantageous properties of the concrete that is subsequently formed.

[0051] The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

[0052] Figure 1 shows a graph identifying the degradation extent of various polymeric carbonate compositions of different particle size distribution ranges used in a method in accordance with the first aspect of the invention over seven days within simulated pore solutions, wherein the polymeric carbonate compositions have a molecular weight of 240kDa: circles with dotted line - polypropylene carbonate <63pm; diamonds with dashed line - polypropylene carbonate 63-125pm; squares with long dashes - polypropylene carbonate 250-500pm; triangles with solid line - polypropylene carbonate 1000pm ± 200pm; wherein the decomposition extent is equivalent to the release of CO2- originating carbonate within the alkaline solution, as evaluated by the total release of propylene glycol by1H NMR spectroscopy; particle sizing obtained by passing through sieve following milling, as determined by microscopy;

[0053] Figure 2 shows a graph comparing the degradation extents of various polymeric carbonate compositions used in a method in accordance with the first aspect of the invention over seven days within simulated pore solutions: circles with dotted line - polyethylene carbonate 1000pm; triangles with solid line polypropylene carbonate 1000pm; squares with dashed lines polypropylene carbonate / polycyclohexane carbonate 1000pm; diamonds with long dashed lines polycyclohexane carbonate 1000pm; wherein the decomposition extent is equivalent to the release of CO2- originating carbonate within the alkaline solution, as evaluated by the total release of the respective glycol by1H NMR spectroscopy; and

[0054] Figure 3 shows representative light micrographs of three polymer samples used in the experiments of Figure 1 , respectively polypropylene carbonate 250-500pm; polypropylene carbonate 63-125pm; and polypropylene carbonate <63pm, with the scale bar representing 100pm.

[0055] The present invention is directed towards the controlled, slow release of CO2 in a concrete mixture during the curing or setting process, so as to improve the strength of the finished concrete product by carbonation. Whilst reference is made to a concrete product, the disclosure applies equally to other products formed from cementitious materials.

[0056] This is achieved by the use of polymeric decomposition materials that degrade to release CC>2-originating carbonate for carbonation reactions. Polymeric carbonate compositions are used, preferably aliphatic polycarbonates, and more preferably having the following structures: where either m or n = 0, or both are each > 1 ; or where x > 2.

[0057] The polymers may be comprised of repeating units of a single or multiple monomeric species to form the carbonate. The polymer structures may be purely homo-polymeric (e.g., AAAAAA structure) or alternating (e.g., ABABAB) or block (e.g., AAAABBBB) copolymer.

[0058] Figure 1 shows an exemplary graph of decomposition rates over time for polypropylene carbonate compositions of different particle size ranges.

[0059] Such polymers may be produced through copolymerisation of CO2 with epoxide monomers such as ethylene oxide, propylene oxide, cyclohexene oxide. Alternatively, such polymers may be produced through the copolymerisation of CO2 with oxetane and / or its derivatives, to produce trimethylene-derived polycarbonate materials. Desirable features of the polymer include: water insolubility; one or combination thereof polymers and co-polymers where the polymer hydrolyses to release carbonate for the carbonation of the cementitious phase of concrete; measurable degradation in an alkaline environment such as cement over a period of 28 days, preferably of at least 20 wt%, to release carbonate ions and the respective diol; measurable degradation in an alkaline environment such as cement over a period of 24 hours of less than 10 wt%; particle size or fibre diameter in the range of 1 m to 2500pm, more preferably 1 pm to 1000pm, more preferably 10pm to 500pm, and most preferably 125pm to 250pm; and / or a molecular weight in the range of 0.1 kDa to 1000kDa, and more preferably 1kDa to 500kDa. The mode of release of carbonate ions is as illustrated below, with decomposition occurring in alkaline conditions. The liberated carbonate results in production of carbonated mineral phases within the cementitious material which persist throughout its lifetime and thus improve the strength of the concrete product formed. where m within the monomer unit = 2 or 3, n > 1

[0060] There is a relationship between hydrophobicity of the monomeric species and hydrolysis rates in alkaline environments. For instance, the hydrolysis rate of polypropylene carbonate is approximately three times slower in alkaline solution compared with polyethylene carbonate. This is demonstrated in Figure 2.

[0061] Different degradation rates are preferred for different cementitious materials, and therefore it is desirable to select the characteristics of the polymeric carbonate composition prior to use. For instance, different base monomers may be used to alter degradation rates, as may different particle or fibre sizes of the polymeric carbonate composition. For instance, carbonate release rates are tuned through the incorporation of other monomeric units into the polymeric structure, including C2-C8 cyclic and linear hydrocarbons and those containing other functional groups or by co-processing individual copolymers of the aliphatic carbonate family together through extrusion, blending or milling.

[0062] Figure 2 shows examples of how degradation rate can be altered by using different copolymers. Four copolymer carbonates are shown, indicating the rates of decomposition with respect to pure polypropylene carbonate.

[0063] Polyethlene carbonate (190 kDa) - solid black line, Polypropylene carbonate (240 kDa) - dotted black line, Polycyclohexene carbonate / polypropylene carbonate copolymer (210 kDa) - long dashed line, Polycyclohexene carbonate (162 kDa) - short dashed line. Different criteria may apply depending on whether the polymeric carbonate composition is provided in solid form, such as a powder or fibre, or whether it is provided as a liquid dispersion in a solvent such as a glycol solvent, including but not limited to propylene glycol, ethylene glycol, or polyethylene glycol.

[0064] Where powders or fibres are used, effective dispersal of the polymeric carbonate composition in ready-mix cement powder may be achievable by maintaining a particle size or particle diameter within the range of cement grain sizes, typically 1-100pm. Dispersal agents such as bentonite can be used to create a more stable mixture. Where liquid dispersions are used, the polymeric carbonate composition will immediately precipitate out of solution upon addition to cement, and therefore the liquid dispersion may be a more convenient means of storing the polymeric carbonate composition. Solutions of, for example, polypropylene carbonate can be used in cement without significant negative effect, in addition to superplasticisers such as polyethers, whilst still remaining insoluble or substantially insoluble in water.

[0065] Examples

[0066] Analysis of materials presented here was achieved through TGA-FTIR and FTIR spectroscopy (CO2 content) and gel-permeation-chromatography (GPC) to inspect molecular weight. Particle sizing was achieved through evaluation by microscopy. Simulated pore solution experiments were conducted in D2O, with the concentrations of specifically relevant ions (mM: Na+= 106; K+= 447; [OH]' = 470) achieved through the addition of NaOD, KOD and NaCI respectively (see “Influence of limestone on the hydration of Portland cements” Cement and Concrete Research (2008), vol. 38, 848- 860). Solutions were agitated once daily and stored at 20°C over the course of the degradation experiment.

[0067] Example 1

[0068] Polypropylene carbonate (Mn ~ 75kDa, Mw = 240kDa), produced via standard CO2 / propylene oxide copolymerisation, to produce particle size range of 1000 ± 200pm, as determined by microscopy and size exclusion separation, specifically via sieving.

[0069] Examples of standard CO2 / propylene oxide copolymerisation can be found in Evolution of Copolymers of Epoxides and CO2: Catalysts, Monomers, Architectures, and Applications, Guan-Wen Yang, Rui Xie, Yao-Yao Zhang, Cheng-Kai Xu, and Guang- Peng Wu, Chemical Reviews 2024 124 (21), 12305-12380.

[0070] The polypropylene carbonate sample was mixed with cement binder, having a water / cement ratio of 0.4:1 , in a ratio of 1 wt.% and was then cast and cured over the course of 28-days, yielding sample referenced CEM1+PPC1000.

[0071] Example 2

[0072] Polypropylene carbonate (Mn ~ 75kDa, Mw = 240kDa), produced via standard CO2 / propylene oxide copolymerisation, to produce particle size range of 250-500 pm, as determined by microscopy and size exclusion separation, specifically via sieving.

[0073] The polypropylene carbonate sample was mixed with cement binder, having a water / cement ratio of 0.4:1 , in a ratio of 1 wt.% and was then cast and cured over the course of 28-days, yielding sample referenced CEM1+PPC250-500.

[0074] Example 3

[0075] Polypropylene carbonate (Mn ~ 75kDa, Mw = 240kDa), produced via standard CO2 / propylene oxide copolymerisation, to produce particle size range of 63-125 pm, as determined by microscopy and size exclusion separation, specifically via sieving.

[0076] The polypropylene carbonate sample was mixed with cement binder, having a water / cement ratio of 0.4:1 , in a ratio of 1 wt.% and was then cast and cured over the course of 28-days, yielding sample referenced CEM1+PPC63-125.

[0077] Example 4

[0078] Polypropylene carbonate (Mn ~ 75kDa, Mw = 240kDa), produced via standard CO2 / propylene oxide copolymerisation, to produce particle size range of <63 pm, as determined by microscopy and size exclusion separation, specifically via sieving.

[0079] The polypropylene carbonate sample was mixed with cement binder, having a water / cement ratio of 0.4:1 , in a ratio of 1 wt.% and was then cast and cured over the course of 28-days, yielding sample referenced CEM1+PPC<63.

[0080] Example 5 Polyethylene carbonate (Mn ~ 72kDa, Mw = 190kDa), produced via standard CC>2 / ethylene oxide copolymerisation, to produce particle size range of 1000 (+ / - 200) pm, as determined by microscopy and size exclusion separation, specifically via sieving.

[0081] The polyethylene carbonate sample was mixed with cement binder, having a water / cement ratio of 0.4:1 , in a ratio of 1 wt% and was then cast and cured over the course of 28-days, yielding sample termed CEM1+PEC1000.

[0082] Example 6

[0083] Polycyclohexene / polypropylene carbonate copolymer (determined by TGA / FTIR as 49:51 mix, Mn ~ 78kDa, Mw = 210kDa), produced via standard CO2 / ethylene oxide copolymerisation, to produce particle size range of 1000 (+ / - 200) pm, as determined by microscopy and size exclusion separation, specifically via sieving.

[0084] The polypropylene carbonate sample was mixed with cement binder, having a water / cement ratio of 0.4:1 , in a ratio of 1 wt% and was then cast and cured over the course of 28-days, yielding sample termed CEM1+PPC / PCC1000.

[0085] Example 7

[0086] Polycyclohexene carbonate (Mn ~ 68kDa, Mw = 162kDa), produce via standard CC>2 / cyclohexene oxide copolymerisation, to produce particle size range of 1000 (+ / - 200) pm, as determined by microscopy and size exclusion separation, specifically via sieving.

[0087] The polypropylene carbonate sample was mixed with cement binder, having a water / cement ratio of 0.4:1 , in a ratio of 1 wt% and was then cast and cured over the course of 28-days, yielding sample termed CEM1+PCC1000.

[0088] A summary of the characteristics of the polymeric materials utilised within cement pastes in the contained examples is given in Table 1 , and the compressive strength test results of the cement paste-polycarbonate mixtures are presented in Table 2.

[0089] Table 1 : A summary of the characteristics of the degradable polycarbonate additives included. *Measured in simulated pore solutions over the course of 7-days.

[0090] Table 2: Compressive strength testing data for cement paste and polycarbonate samples, relative to reference.

[0091] Whilst the polymeric carbonate composition is described as being added in powder or solution forms to a cement mixture, it will be possible to deposit the polymeric carbonate composition onto a supplementary cementitious material, such as a pozzolan, which will allow for effective storage and delivery of the CO2 releasing agent.

[0092] It is therefore possible to provide a method of producing a concrete product having an enhanced strength due to carbonation is provided. The method comprises the steps of providing a polymeric carbonate composition and mixing the polymeric carbonate composition with a freshly prepared concrete binder mixture. The polymeric carbonate composition is provided in an amount of 0.2-10.00wt.% of the concrete binder mixture. The concrete binder mixture is then cured with aggregate material, wherein a duration of the curing step exceeds 7 days for slow release of CO2 into the concrete product and improve strength.

[0093] 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.

[0094] 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.

[0095] 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

Claims1. A method of producing a product formed from cementitious material having an enhanced strength, the method comprising the steps of: a] providing a polymeric carbonate composition which is formed by sequestration of CO2 into an organic polymer; b] mixing the polymeric carbonate composition with a freshly prepared cementitious material, wherein the polymeric carbonate composition is provided in an amount of 0.2-10.00wt.% of the cementitious material; and c] curing the cementitious material with aggregate material, wherein a duration of the curing step exceeds 24 hours by hydrolytic release of carbonate from the polymeric carbonate composition.

2. A method as claimed in claim 1, wherein the polymeric carbonate composition is an aliphatic carbonate composition.

3. A method as claimed in claim 1 or claim 2, wherein the polymeric carbonate composition has any of the following formulae:where either m or n = 0, or both are each > 1 ; or; orand where x > 2.

4. A method as claimed in any one of the preceding claims, wherein the polymeric carbonate composition is any of: polypropylene carbonate; polyethylene carbonate; polycyclohexene carbonate; polytrimethylene carbonate; copolymers thereof; or a combination thereof.

5. A method as claimed in any one of the preceding claims, wherein the polymeric carbonate composition is a solid polymeric carbonate composition having a particle size in the range of 1 pm to 2500pm.

6. A method as claimed in claim 5, wherein the polymeric carbonate composition is a solid polymeric carbonate composition having a particle size in the range of 20pm to 500pm.

7. A method as claimed in claim 6, wherein the polymeric carbonate composition is a solid polymeric carbonate composition having a particle size in the range of 50pm to 250pm.

8. A method as claimed in any one of claims 5 to 7, wherein the polymeric carbonate composition is provided in powder form.

9. A method as claimed in any one of claims 5 to 7, wherein the polymeric carbonate composition is provided in fibre form.

10. A method as claimed in any one of the preceding claims, wherein the polymeric carbonate composition is encapsulated or coated by a protective degradable layer.

11. A method as claimed in any one of claims 1 to 4, wherein the polymeric carbonate composition is provided as a liquid solution or dispersion.

12. A method as claimed in any one of the preceding claims, wherein the polymeric carbonate composition has a molecular weight of between 0.1-1000kDa.

13. A method as claimed in claim 11, wherein the polymeric carbonate composition has a molecular weight of between 1-500kDa.

14. A method as claimed in any one of the preceding claims, wherein during step c], the curing occurs in a chamber, bath, open conditions or any other standard curing techniques used by the concrete industry at 30-90% relative humidity.

15. A method as claimed in any one of the preceding claims, wherein during step c], the duration of the curing step exceeds 14 days.

16. A method as claimed in any one of the preceding claims, wherein the cementitious material is a concrete binder mixture which comprises any of: cement, supplementary cementitious material, limestone, sand, aggregate, water, and one or more admixtures.

17. A method as claimed in any one of the preceding claims, wherein the polymeric carbonate composition hydrolytically releases carbonate during the curing step c] in an amount of between 20-60% by mass of sequestered carbon dioxide.

18. A method as claimed in any one of the preceding claims, wherein the polymeric carbonate composition hydrolytically releases carbonate during the first 8 hours of the curing step c] in an amount of not more than 10% by mass of sequestered carbon dioxide.

19. A method as claimed in any one of the preceding claims, wherein the polymeric carbonate composition hydrolytically releases carbonate during the first 7 days of the curing step c] in an amount of between 5-50% by mass of sequestered carbon dioxide.

20. A method as claimed in any one of the preceding claims, wherein the polymeric carbonate composition hydrolytically releases carbonate during the first 28 days of the curing step c] in an amount of not more than 95% by mass of sequestered carbon dioxide.

21. A method as claimed in any one of the preceding claims, wherein during step c], decomposition conditions of the polymeric carbonate composition are selected to achieve a preferred curing condition.

22. A method as claimed in claim 21 , wherein the decomposition conditions include at least one of: temperature; humidity; particle size of the polymeric carbonate composition; hydrophobic content of the constituent monomers in the polymer.

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