Applications of polycarboxylate polymers to enhance the performance of carbon dioxide-cured cementitious composites

Abstract

Disclosed are compositions containing carbonation-cured cementitious materials and a polyanionic polymer, and methods of making thereof. The carbonation-cured cementitious materials contain calcium silicates and the polyanionic polymer can constitute between about 0.01 wt.% and about 10 wt.% of the compositions, or between about 0.01 wt.% and about 10 wt.% of the calcium silicates. Containing the disclosed compositions have (i) increased compressive strength, (ii) increased flexural strength, (iii) increased carbon dioxide sequestration capabilities, (iv) increased calcite content, (v) reduced total pore area, or a combination of (i)-(v) when compared to a composition made from similar materials that are not carbonation-cured and / or not supplemented with the polyanionic polymer.

Description

[0001] APPLICATIONS OF POLYCARBOXYLATE POLYMERS TO ENHANCE THE PERFORMANCE OF CARBON DIOXIDE-CURED CEMENTITIOUS COMPOSITES

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of and priority to U.S. Provisional Application No. 63 / 553,820 filed February 15, 2024, which is incorporated herein by reference in its entirety.

[0004] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0005] This invention was made with government support under 2028462 awarded by National Science Foundation. The government has certain rights in the invention.

[0006] FIELD OF THE INVENTION

[0007] This invention is generally in the field of compositions and methods for increasing strength and / or carbon dioxide sequestration capabilities of composites made from cement-based materials.

[0008] BACKGROUND OF THE INVENTION

[0009] Concrete or cement-based composites are responsible for up to 9% of global man-made CO2 emissions. Production of ordinary Portland cement (OPC) is also one of the most energy- intensive manufacturing processes. The conventional cement industry is responsible for 5-8 % of global CO2 emissions to the environment. Utilization of alternative cementitious materials instead of OPC may allow mankind to achieve a lower CO2 footprint from concrete and other cement-based composites.

[0010] Carbonation-cured (or CO2 -cured) calcium silicate is one such alternative cementitious material. The hardening process of this type of cementitious material involves the reaction of calcium silicates with CO2 in the presence of moisture (addressed as ‘carbonation or CO2 curing’). The carbonation reaction products of calcium silicates are CaCCh and Ca modified silica gel (Ca / Si atomic ratio ~ 0.4), which act as the binding phases and provide strength to the hardened matrix.

[0011] Previous studies have shown that the mechanical performances of these carbonated cement composites are significantly influenced by the crystalline properties of CaCOs. In the case of calcium silicate-containing cementitious materials, the primary polymorphs of CaCOs formed during the carbonation include calcite, aragonite, vaterite, and amorphous calcium carbonate (ACC). Formation of these polymorphs of CaCOs ideally should follow the Ostwald's process; that is, the least stable polymorph ACC is the first to nucleate, which then crystallizes to form vaterite or aragonite (also metastable), and finally, forms calcite — the most stable polymorph. Nevertheless, this conversion route of CaCC polymorphs in carbonated cement composites is affected by several factors including relative humidity, CO2 concentration, pH, silica content, and magnesium content. Because of these factors, it is difficult to control the relative proportions of the different CaCO i polymorphs formed in the carbonated composites. Further, the intrinsic properties of these CaCCh polymorphs are significantly different. As an example, the stiffness of vaterite, aragonite, and calcite are 39.13 GPa, 67 GPa, and 72.83 GPa, respectively (data not available for ACC). The variation in the relative proportions of different CaCCC polymorphs along with their various intrinsic characteristics often results in significant variability in the mechanical performance of carbonated cement composites.

[0012] Other studies have utilized amino acids, other biomolecules, and polymers to modify CaCCh polymorphs or modify the viscosities of cementitious materials. However, the effectiveness of such organic molecules on the carbonation behavior of a calcium silicate (e.g., Y-C2S) have not been explored yet.

[0013] Considering these knowledge gaps, there remains a need to develop the ability to control the CaCCh polymorph formation and stabilization in carbonated cement composites, so as to facilitate microstructure-based design improvements of this sustainable cementitious system.

[0014] Therefore, it is an object of the present invention to provide methods for controlling the CaCCh polymorph formation and stabilization in carbonation-cured cementitious materials.

[0015] It is also an object of the present invention to provide compositions with improved compressive strength, increased flexural strength, and / or increased carbon dioxide sequestration capabilities.

[0016] SUMMARY OF THE INVENTION

[0017] Disclosed are compositions containing carbonation-cured cementitious materials and a polyanionic polymer. The disclosed compositions are provided in solid form, such as a powder. Preferably, the cured cementitious materials (e.g., carbonation-cured cementitious materials) contain calcium silicates with less than 60 wt.% tricalcium silicate (e.g., C3S or alite) and less than 60 wt.% calcium oxide. The polyanionic polymer can constitute between about 0.01 wt.% and about 10 wt.% of the compositions, or between about 0.01 wt.% and about 10 wt.% of the calcium silicates. The polyanionic polymer has a molecular weight (e.g., weight- average molecular weight or number- average molecular weight) between about 2 kDa and about 250 kDa, such as 2 kDa, 5 kDa, or 240 kDa. Preferably, the polyanionic polymer contains poly acrylic acids and / or anionic poly acrylates. The results demonstrate that materials containing the disclosed compositions have (i) increased compressive strength, (ii) increased flexural strength, (iii) increased carbon dioxide sequestration capabilities, (iv) increased calcite content, (v) reduced total pore area, or a combination of (i)-(v) when compared to a composition made from similar materials that are not carbonation-cured and / or not supplemented with the polyanionic polymer. Accordingly, the disclosed compositions contain effective amounts of the polyanionic polymer to impart one or more of these properties to the compositions. Examples of end-products that can be produced using the disclosed compositions, by mixing the compositions with water / liquids include, but not limited to, bridge girders, beams, blocks, hardscape components such as pavers, edging blocks, stepping stones, etc.

[0018] Also described are methods of making the disclosed compositions. The disclosed compositions are prepared by adding a polyanionic polymer, preferably polyacrylic acids and / or anionic polyacrylates, to a calcium silicate-containing cementitious material prior to carbonation and subjecting the formed mixture to carbonation. Preferably, the polyanionic polymer is added in an effective amount to provide one or more of the above listed properties ((i)-(iv)) to a material containing the composition. The methods involve the steps of (i) mixing a polyanionic polymer with water and powder calcium silicate-based cement, to form a mixture, (ii) compacting the mixture in a desired shape, (iii) exposing the mixture to carbon dioxide, water (such as in moisture form), or both during or after the mixing step, and (iv) allowing the mixture to cure in a chamber having a relative humidity of about 50% to 90% and a carbon dioxide concentration of more than 2%. The curing occurs at a temperature between about 20 °C and about 50 °C, such as 25 °C, 27 °C, or 50 °C. Further non-limiting details on how to make the disclosed compositions are provided in the Examples section below.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is bar graph showing particle size distribution of the synthesized y-CFS.

[0021] FIG. 2 is a non-limiting schematic diagram showing steps of sample preparation.

[0022] FIGs. 3A-3C are line graphs (FIGs. 3A and 3B) and a column graph (FIG. 3C) showing thermogravimetric analysis of 7 days carbonated Y-C2S paste samples: 2.5% batches (FIG. 3A), 5% batches (FIG. 3B), and comparison of CaCCh contents formation among the batches (FIG. 3C).

[0023] FIGs. 4A and 4B are line graphs of X-ray diffraction pattern of a y-C -S paste, 2.5% batch (FIG. 4A) and 5% batch (FIG. 4B). (1 : y-C S, 2: Calcite, 3: Aragonite, and 4: Vaterite).

[0024] FIGs. 5A -5D are line graphs showing FTIR spectra of 7 days carbonated biomimetic molecules modified y-C2S paste samples: 2.5% batch at 700-750 cm1(FIG. 5A); 5% batch at 700-750 cm’1(FIG. 5B); 2.5% batch at 1400 cm’1(FIG. 5C); 5% batch at 1400 cm’1(FIG. 5D). FIGs. 6A-6D are scanning electron microscopy images showing the morphology of the calcium carbonate polymorphs in control (FIG. 6A), 2.5% LAsp (FIG. 6B), 2.5% LGlu (FIG. 6D), and 2.5% PAA (FIG. 6D) samples. The scale bar represents 1 pm.

[0025] FIGs. 7A-7D are scanning electron microscopy (SEM) images showing the morphology of the calcium carbonate polymorphs in control (FIG. 7A), 5% LAsp (FIG. 7B), 5% LGlu (FIG. 7C), and 5% PAA (FIG. 7D), samples. The scale bar represents 1 pm.

[0026] FIGs. 8A-8D are line graphs showing the effects of biomimetic molecules on pore size distribution of 7 days carbonated y-CLS paste samples.

[0027] FIGs. 9A-9D are line graphs (FIGs. 9A and 9B) and column graphs (FIGs. 9C and 9D) showing pore size distribution 2.5% batch (FIG. 9A) and 5% batch (FIG. 9B); specific surface area 2.5% batch (FIG. 9C) and 5% batch (FIG. 9D).

[0028] FIGs. 10A and 10B are line graphs showing percent frequency versus elastic modulus 2.5% batches (FIG. 10A) and 5% batches (FIG. 10B).

[0029] FIGs. 11A and 11B are bar graphs showing compressive strength (FIG. 11A) and flexural strength (FIG. 11B) of samples cured at room temperature and after 7 days of carbonation period.

[0030] FIGs. 12A and 12B are bar graphs showing compressive strength (FIG. 12A) and flexural strength (FIG. 12B) of samples cured at 50 °C and after 7 days of carbonation period.

[0031] FIGs. 13A and 13B are line graphs showing the percent increase of strength after applying temperature curing: compressive strength (FIG. 13A) and flexural strength (FIG. 13B).

[0032] FIG. 14A is a bar graph showing particle size distribution of synthesized P-C2S. FIG. 14B is a line XRD plot of synthesized P-CrS (1 : P-C2S peak, 2: y-CrS peak)

[0033] FIG. 15 is a non-limiting schematic showing the test samples preparations containing P- C2S and the corresponding experimental methods.

[0034] FIGs. 16A and 16B are line graphs showing a sample in situ ATR FTIR measurement data showing time dependent phase alternations during carbonation curing of P-C2S (FIG. 16A) and normalized intensity of the peak around 1400cm1representing the carbonate formation with time (FIG. 16B).

[0035] FIG. 17 shows SEM images of the evolution of the reaction products of Control samples, MW 2000, MW 5000, and MW 240000 over the first 24 hours. The scale bar represents 1 pm.

[0036] FIGs. 18A-18D are SEM images showing the microstructure of carbonated P-C2S containing PAA MW 240000 after 6 hours (FIG. 18A), 24 hours (FIG. 18B), 7 days (FIG. 18C), and microstructure of carbonated P-C2S containing PAA MW 5000 after 3 days (FIG. 18D). The scale bar represents 1 pm. FIG. 19 depicts SEM images showing the morphology of reaction products after 3 days and 7 days of reaction of different samples. The scale bar represents 1 pm.

[0037] FIGs. 20A-20D are column graphs showing particle size of the carbonate phases as determined by analysis of the SEM secondary image.

[0038] FIGs. 21A-21C are a line graph (FIG. 21A) and bar graphs (FIGs. 21B and 21C) showing thermogravimetric analysis of 3 days and 7 days carbonated P-C2S samples: representative TGA-DTG plot (FIG. 21A); percent CaCOs formation of different batches after 3 days carbonation (FIG. 21B); and percent CaCOs formation of different batches after 7 days carbonation (FIG. 21C).

[0039] FIGs. 22A-22F are line graphs showing X-ray diffraction patterns of the P-C2S paste samples at 3 days and 7 days (different dosages; 1: P-C2S, 2: calcite, 3: vaterite).

[0040] FIGs. 23A and 23B are line graphs showing calcite crystal sizes in the carbonated P-C2S samples with various dosages of PAA: 3-days carbonation curing (FIG. 23A) and 7-days carbonation curing (FIG. 23B).

[0041] FIGs. 24A and 24B are line graphs showing the effects of biomimetic molecules on pore size distribution of 7 days carbonated P-C2S paste samples of 1 % dosage batch.

[0042] FIG. 25 is a line graph showing the effects of biomimetic molecules on the nanomechanical properties of carbonated P-C2S composites with and without PAA additions.

[0043] FIGs. 26A and 26B are column graphs showing compressive strength properties after 3 days (FIG. 26A) and 7 days (FIG. 26B) carbonation period (27°C cured batches).

[0044] FIGs. 27A and 27B are column graphs showing flexural strength properties after 3 days (FIG. 27A) and 7 days (FIG. 27B) carbonation period (27°C cured batches).

[0045] FIGs. 28A and 28B are column graphs showing compressive strength properties 1 % dosage - 50°C cured batches after 3 days (FIG. 28A) and 7 days (FIG. 28B) carbonation duration.

[0046] FIGs. 29A and 29B are column graphs showing flexural strength properties 1 % dosage - 50°C cured batches after 3 days (FIG. 29A) and 7 days (FIG. 29B) carbonation duration.

[0047] FIG. 30 is a non-limiting schematic showing the mechanisms by which polyacrylic acid affects the carbonated calcium silicate composites.

[0048] DETAILED DESCRIPTION OF THE INVENTION

[0049] I. Definitions

[0050] “Carbonation or CO2 curing,” and related terms such as “carbonation-cured,” “CO2- cured,” as used herein refers to hardening process of this type of cementitious materials such as calcium silicate mineral material involving the reaction of calcium silicates with CO2 in the presence of moisture.

[0051] “Cementitious material” refers to a building material that may be mixed with water (or other liquids) to form a plastic paste. Aggregates may then be added, such as cement, mortar, and limes. In other words, cementitious materials are one of the key ingredients in a concrete mixture. There are two types of cementitious materials: hydraulic cement and supplementary cementitious materials (SCMs). Hydraulic cements set and harden by reacting chemically with water. During the reaction, which is called hydration, heat is given off as the water-cement paste hardens and binds the aggregate particles together. Portland cement is the most common hydraulic cement. SCMs are used in conjunction with Portland cement in concrete mixtures to improve the workability of fresh concrete and reduce thermal cracking in massive structures by reducing heat of hydration.

[0052] “Flexural strength” as used herein refers to the stress in a material just before it yields in a flexure test.

[0053] “Polyanionic polymer” refers to a polymer in which at least two repeat units each contain a negative charge or chemical moiety that can dissociate in ionizing solvents e.g., water), yielding a charged polymeric chain with negatively charged units. Examples of polyanionic polymers include those in which the negative charge or the chemical moiety that can dissociate in ionizing solvents is in the side chains of at least one of the at least two repeat units.

[0054] “Sulfated polymer” refers to a polyanionic polymer containing covalently bonded sulfate groups.

[0055] “Sulfonated polymer” refers to a polyanionic polymer containing covalently bonded sulfonate groups.

[0056] “Phosphorylated polymer” refers to a polyanionic polymer containing covalently bonded phosphate groups.

[0057] “Phosphonated polymer” refers to a polyanionic polymer containing covalently bonded phosphonate groups. IL Compositions

[0058] The disclosed compositions contain cementitious materials, preferably, cured cementitious materials and a polyanionic polymer. Most preferably, the disclosed compositions contain carbonation-cured cementitious materials and a polyanionic polymer. Preferably, the cured cementitious materials (e. ., carbonation-cured cementitious materials) contain calcium silicates. The results demonstrate that composites containing the disclosed compositions have (i) increased compressive strength, (ii) increased flexural strength, (iii) increased carbon dioxide sequestration capabilities, (iv) increased calcite content, (v) reduced total pore area, or a combination of (i)-(v) when compared to a composition made from similar materials that are not carbonation-cured and / or not supplemented with the polyanionic polymer. Accordingly, the disclosed compositions contain effective amounts of the polyanionic polymer to impart one or more of these properties to the compositions. Without wishing to be bound by theory, it is believed that during the curing process, the polyanionic polymer adsorbs on calcium silicate particles in a paste containing these components. Once the carbonation-curing comments, newly formed calcium carbonate particles preferentially deposit on the polyanionic polymers optionally in a network configuration. As a result, the added polyanionic polymer provides new surface areas for calcium carbonate particles to nucleate and, therefore, accelerates the carbonation reaction, which can be observed from in situ Fourier Transform Infra-red spectroscopy.

[0059] The compositions can be used for cement and cementitious composite manufacturing. A cement is a binder, a substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixed with fine aggregate produces mortar for masonry, or with sand and gravel, produces concrete. Binders are substances which are used to bind inorganic and organic particles and fibers to form strong, hard and / or flexible components. This is generally due to chemical reactions which take place when the binder is heated, mixed with water and / or other materials, or just exposed to air. Cementing materials that are widely used for construction are materials that exhibit characteristic properties of setting and hardening when mixed to a paste with water. There are four main groups of binders: mineral binders, bituminous binders, natural binders, and synthetic binders. Cements used in construction are usually inorganic, often lime or calcium silicate based, which can be characterized as non- hydraulic, semi-hydraulic, or hydraulic respectively, depending on the ability of the cement to set in the presence of water.

[0060] A. Polyanionic polymers

[0061] The disclosed compositions most preferably contain a carbonation-cured cementitious material and a polyanionic polymer. The polyanionic polymer can be a polyanionic heteropolymer, containing two or more different anionic constitutional repeating units, or can be a poly anionic homopolymer, containing a single anionic constitutional repeating unit. Although preferred, clearly not every monomer / repeat unit need be negatively charged as long as there is sufficient negative charge for the polyanionic polymer to have a plurality of charges. The polyanionic polymer can be a chemical polymer and can contain anionic constitutional repeating units obtained from: acrylic acid, methacrylic acid, maleic acid, fumaric acid, ethylsulphonic acid, vinylsulphonic acid, vinylsulphonic acid, styrenesulphonic acid, vinylphenylsulphuric acid, 2-methacryloyloxyethane sulphonic acid, 3-methacryloyloxy-2- hydroxypropanesulphonic acid, 3-methacryl amido-3 -methylbutanoic acid, acrylamidomethylpropanesulfonic acid, vinylphosphoric acid, 4-vinylbenzoic acid, 3-vinyl oxypropane- 1 -sulphonic acid, N-vinylsuccinimidic acid, and salts of the foregoing. Alternatively, the polyanionic polymer can be a sulfated oligosaccharide, a sulfated polysaccharide, a phosphorylated oligosaccharide, or a phosphorylated polysaccharide.

[0062] In some forms, the polyanionic polymer contains a polycarboxylate polymer, polyphosphate polymer, phosphorylated polymer, phosphonated polymer, sulfated polymer, sulfonated polymer, co-polymers thereof, or blends thereof. In some forms, the polyanionic polymer contains a polycarboxylate polymer. Examples of suitable polyanionic polymers that can be included in the disclosed compositions include, but are not limited to, polyacrylic acids, poly(methacrylic acids), anionic polyacrylates, anionic poly(methacrylates), poly(maleic acids), anionic poly(maleates), poly(glutamic acids), poly(aspartic acids), anionic poly(glutamates), anionic poly (aspartates), poly(fumaric acids), anionic poly(fumarates), poly(itaconic acids), anionic poly(itaconates), alginates, polystyrene sulfonates, sulfated polysaccharides, phosphorylated polysaccharides, co-polymers thereof, or blends thereof. In preferred forms, the polyanionic polymer contains polyacrylic acids, poly acrylates, co-polymers thereof, or blends thereof. In further preferred forms, the polyanionic polymers are as described above, except that they contain a carbon-carbon backbone.

[0063] In some forms, the compositions contain between about 0.01 wt.% and about 30 wt.%, about 0.01 wt.% and about 25 wt.%, about 0.01 wt.% and about 20 wt.%, about 0.01 wt.% and about 15 wt.%, about 0.01 wt.% and about 10 wt.%, about 0.01 wt.% and about 5 wt.%, about 0.1 wt.% and about 30 wt.%, about 0.1 wt.% and about 25 wt.%, about 0.1 wt.% and about 20 wt.%, about 0.1 wt.% and about 15 wt.%, about 0.1 wt.% and about 10 wt.%, about 0.1 wt.% and about 5 wt.%, such as 0.1 wt.%, 0.5 wt.%, 1 wt.%, 2.5 wt.%, or 5 wt.% of the polyanionic polymer.

[0064] In some forms, the compositions are as described above, except that they contain between about 0.1 wt.% and about 30 wt.%, about 0.1 wt.% and about 25 wt.%, about 0.1 wt.% and about 20 wt.%, about 0.1 wt.% and about 15 wt.%, about 0.1 wt.% and about 10 wt.%, about 0.1 wt.% and about 5 wt.%, such as 0.1 wt.%, 0.5 wt.%, 1 wt.%, 2.5 wt.%, or 5 wt.% of the polyanionic polymer. In some forms, the compositions are as described above, except that they contain between about 0.1 wt.% and about 10 wt.%, about 0.1 wt.% and about 5 wt.%, such as 0.1 wt.%, 0.5 wt.%, 1 wt.%, 2.5 wt.%, or 5 wt.% of the polyanionic polymer. As polymers are complex populations of molecules of potentially different lengths, the molecular weight can be stated as a number average molecular weight (Mn) or a weight-average molecular weight (Mw). Preferably the polydispersity (a measure of homogeneity) of the polyanionic polymer is less than 3. In some forms, the molecular weight (e.g., Mn or Mw) of the polyanionic polymer is between about 1 kDa and about 500 kDa, about 1 kDa and about 400 kDa, about 1 kDa and about 300 kDa, about 1 kDa and about 250 kDa, about 1.5 kDa and about 500 kDa, about 1.5 kDa and about 400 kDa, about 1.5 kDa and about 300 kDa, about 1.5 kDa and about 250 kDa, about 2 kDa and about 500 kDa, about 2 kDa and about 400 kDa, about 2 kDa and about 300 kDa, or about 2 kDa and about 250 kDa.

[0065] In some forms, compositions are as described above, except that the molecular weight (e.g., Mn or Mw) of the polyanionic polymer is between about 2 kDa and about 500 kDa, about 2 kDa and about 400 kDa, about 2 kDa and about 300 kDa, or about 2 kDa and about 250 kDa.

[0066] In some forms, compositions are as described above, except that the molecular weight (e.g. , Mn or Mw) of the polyanionic polymer is between about 2 kDa and about 250 kDa, such as 2 kDa, 5 kDa, or 240 kDa.

[0067] In some forms, the compositions are as described above, except that the compositions contain calcium silicates, such that the polyanionic polymer is between about 0.01 wt.% and about 30 wt.%, about 0.01 wt.% and about 25 wt.%, about 0.01 wt.% and about 20 wt.%, about 0.01 wt.% and about 15 wt.%, about 0.01 wt.% and about 10 wt.%, about 0.01 wt.% and about 5 wt.%, about 0.1 wt.% and about 30 wt.%, about 0.1 wt.% and about 25 wt.%, about 0.1 wt.% and about 20 wt.%, about 0.1 wt.% and about 15 wt.%, about 0.1 wt.% and about 10 wt.%, about 0.1 wt.% and about 5 wt.%, such as 0.1 wt.%, 0.5 wt.%, 1 wt.%, 2.5 wt.%, or 5 wt.% of the calcium silicates.

[0068] B. Cementitious materials

[0069] The disclosed compositions contain a cured cementitious material (e.g., carbonation- cured cementitious material) containing calcium silicates. The calcium silicates include, but are not limited to belite, rankinite, wollastonite, tricalcium silicate (C3S), P-dicalcium silicate (P- C2S), y-dicalcium silicate (y-C2S), tricalcium disilicate (C3S2), monocalcium silicate (CS), amorphous calcium silicate, calcium aluminosilicate, or a combination thereof. In some forms, compositions are as described above, except that the calcium silicates are selected from belite, rankinite, wollastonite, P-dicalcium silicate (P-C2S), y-dicalcium silicate (y-CzS), or a combination thereof. Tricalcium silicate (C3S), -dicalcium silicate ( / 3 -C2S), y -dicalcium silicate ( y -C2S), tricalcium disilicate (C3S2) and monocalcium silicate (CS) can react with CO2 and form strong monolithic matrices. Wollastonite is naturally occurring low-lime calcium silicate (CaO.SiCh) mineral with a substantially lower carbon footprint compared to the ordinary Portland cement (OPC). Thus, in a preferred embodiment, the binder material is calcium silicate mineral containing material such as wollastonite, -C2S, y -C2S, etc. Wollastonite is a group of inosilicate minerals, with a formula, CaSiOs that may include small amounts of magnesium, manganese, and iron substituting for calcium. A valuable industrial mineral, wollastonite is white, gray, or pale green in color. It occurs as rare, tabular crystals or massive, coarse-bladed, foliated, or fibrous masses. Its crystals are usually triclinic, although its structure has seven variants, one of which is monoclinic. These variations are, however, indistinguishable in hand specimens. Wollastonite forms as a result of the contact metamorphism of limestones and in igneous rocks that are contaminated by carbon-rich inclusions. It can be accompanied by other calcium containing silicates, such as diopside, tremolite, epidote, and grossular garnet. Wollastonite also appears in regionally metamorphosed rocks in schists, slates, and phyllites. It forms when impure limestone or dolomite is subjected to high temperature and pressure, which sometimes occurs in the presence of silica-bearing fluids as in skarns or in contact with metamorphic rocks.

[0070] The disclosed compositions can be distinguished from other commonly known cementitious materials in that they contain less than 60 wt.%, less than 55 wt.%, less than 50 wt.%, less than 45 wt.%, less than 40 wt.%, less than 35 wt.%, less than 30 wt.%, less than 25 wt.%, less than 20 wt.%, less than 15 wt.%, less than 10 wt.%, or less than 5 wt.% tricalcium silicates, such as between 0.01 wt.% and 60 wt.% tricalcium silicates (such as C3S), as determined using an analytical method such as thermogravimetric analysis. The disclosed compositions can be further distinguished from other commonly known cementitious materials in that the contain low-lime calcium silicates, such that the compositions contain less than 60 wt.%, less than 55 wt.%, less than 50 wt.%, less than 45 wt.%, less than 40 wt.%, less than 35 wt.%, less than 30 wt.%, less than 25 wt.%, less than 20 wt.%, less than 15 wt.%, less than 10 wt.%, less than 5 wt.%, less than 3 wt.% calcium oxides, such as between 0.01 wt.% and 60 wt.% calcium oxides, as determined using an analytical method such as thermogravimetric analysis.

[0071] The disclosed compositions can be provided in solid form, such as a powder.

[0072] III. Methods of Making and Reagents therefor

[0073] Also described are methods of making the disclosed compositions. The disclosed compositions are prepared by supplementing a calcium silicate-containing cementitious material with one or more polyanionic polymers prior to carbonation, and subjecting the polyanionic polymer supplemented calcium silicate-containing cementitious material to carbonation. Making the disclosed compositions involves at least the step of mixing a calcium silicate- containing material with a polyanionic polymer disclosed herein to produce a mixture optionally in the presence of carbon dioxide, water (such as in moisture form), or both. Preferably, the calcium silicate-containing material is in a pulverized form prior to or during the mixing process. Preferably, during or after the mixing process, the mixture is exposed to carbon dioxide, water (such as in moisture form), or both.

[0074] Preferably, the calcium silicate-containing material is formed by sintering a first mixture containing calcium carbonate, silica, and optionally water (such as in moisture form). The sintering can be performed at a temperature between about 800 °C and about 1800 °C or between about 1000 °C and about 1800 °C, such as 800 °C, 1000 °C, 1200 °C, 1400 °C, 1600 °C, or 1800 °C.

[0075] The polyanionic polymer can be a chemical polymer and can contain anionic constitutional repeating units obtained from: acrylic acid, methacrylic acid, maleic acid, fumaric acid, ethylsulphonic acid, vinylsulphonic acid, vinylsulphonic acid, styrenesulphonic acid, vinylphenylsulphuric acid, 2-methacryloyloxyethane sulphonic acid, 3-methacryloyloxy-2- hydroxypropanesulphonic acid, 3-methacryl amido-3 -methylbutanoic acid, acrylamidomethylpropanesulfonic acid, vinylphosphoric acid, 4-vinylbenzoic acid, 3-vinyl oxypropane- 1 -sulphonic acid, N-vinylsuccinimidic acid, and salts of the foregoing. Alternatively, the polyanionic polymer can be a sulfated oligosaccharide, a sulfated polysaccharide, a phosphorylated oligosaccharide, or a phosphorylated polysaccharide.

[0076] In some forms, the polyanionic polymer contains a polycarboxylate polymer, polyphosphate polymer, phosphorylated polymer, phosphonated polymer, sulfated polymer, sulfonated polymer, co-polymers thereof, or blends thereof. In some forms, the polyanionic polymer contains a polycarboxylate polymer. Examples of suitable polyanionic polymers that can be included in the disclosed compositions include, but are not limited to, polyacrylic acids, poly(methacrylic acids), anionic polyacrylates, anionic poly(methacrylates), poly(maleic acids), anionic poly(maleates), poly(glutamic acids), poly(aspartic acids), anionic poly(glutamates), anionic poly (aspartates), poly(fumaric acids), anionic poly(fumarates), poly(itaconic acids), anionic poly(itaconates), alginates, polystyrene sulfonates, sulfated polysaccharides, phosphorylated polysaccharides, co-polymers thereof, or blends thereof. In preferred forms, the polyanionic polymer contains polyacrylic acids, poly acrylates, co-polymers thereof, or blends thereof. In further preferred forms, the polyanionic polymers are as described above, except that they contain a carbon-carbon backbone. The methods also involve a curing step, in which he mixture is allowed to cure at a temperature between about 20 °C and about 75 °C, about 20 °C and about 70 °C, about 20 °C and about 65 °C, about 20 °C and about 60 °C, about 20 °C and about 55 °C, about 20 °C and about 50 °C, about 25 °C and about 75 °C, about 25 °C and about 70 °C, about 25 °C and about 65 °C, about 25 °C and about 60 °C, about 25 °C and about 55 °C, or about 25 °C and about 50 °C, such as 25 °C, 27 °C, or 50 °C. The curing step can also involve allowing the mixture to cure in a period between 1 hour and 10 days, 1 hour and 7 days, 5 hours and 10 days, 5 hours and 7 days, 1 day and 10 days, 1 day and 7 days, 3 days and 10 days, or 3 days and 7 days. Preferably exposing the mixture to water (e.g., in the form of moisture), carbon dioxide, or both, occurs in a chamber having:

[0077] (al) a relative humidity between about 50% and about 90%, about 50% and about 85%, about 50% and about 80%, about 60% and about 90%, about 60% and about 85%, about 60% and about 80%, about 70% and about 90%, about 70% and about 85%, about 70% and about 80%,

[0078] (a2) a carbon dioxide concentration at least 2%, such as between about 2% and about 40%, about 2% and about 35%, about 2% and about 30%, about 2% and about 25%, about 2% and about 20%, between about 5% and about 40%, about 5% and about 35%, about 5% and about 30%, about 5% and about 25%, about 5% and about 20%, about 10% and about 40%, about 10% and about 35%, about 10% and about 30%, about 10% and about 25%, about 10% and about 20%, about 15% and about 40%, about 15% and about 35%, about 15% and about 30%, about 15% and about 25%, about 15% and about 20%, or

[0079] (a3) a combination of (al) and (a2).

[0080] Without wishing to be bound by theory, it is believed that during the curing process, the polyanionic polymer adsorbs on calcium silicate particles in a paste containing these components. Once the carbonation-curing comments, newly formed calcium carbonate particles preferentially deposit on the polyanionic polymers optionally in a network configuration. As a result, the added polyanionic polymer provides new surface areas for calcium carbonate particles to nucleate and, therefore, accelerates the carbonation reaction, which can be observed from in situ Fourier Transform Infra-red spectroscopy.

[0081] Examples of end-products that can be produced using the disclosed compositions, by mixing the compositions with water / liquids include, but not limited to, bridge girders, beams, blocks, hardscape components such as pavers, edging blocks, stepping stones, etc.

[0082] Further non-limiting details on how to make the disclosed compositions are provided in the Examples section below. IV. Methods of Using

[0083] The data in the application show that materials made from the compositions disclosed herein have (i) increased compressive strength, (ii) increased flexural strength, (iii) increased carbon dioxide sequestration capabilities, (iv) increased calcite content, (v) reduced total pore area, or a combination of (i)-(v) when compared to a composition made from similar materials that are not carbonation-cured and / or not supplemented with the poly anionic polymer. Accordingly, the disclosed compositions contain effective amounts of the polyanionic polymer to impart one or more of these properties to the compositions, and can be utilized in the construction industry, particularly in settings aiming for a greener and more sustainable cementconcrete construction industry.

[0084] The methods, compounds, and compositions herein described are further illustrated in the following examples, which are provided by way of illustration and are not intended to be limiting. It will be appreciated that variations in proportions and alternatives in elements of the components shown will be apparent to those skilled in the art and are within the scope of disclosed forms. All parts or amounts, unless otherwise specified, are by weight. Use of the term "about" is intended to describe values either above or below the stated value in a range of approx. + / - 10%. Examples of values within this range are + / - 1%, + / - 2%, + / - 3%, + / - 4%, + / - 5%, + / - 6%, + / - 7%, + / - 8%, + / - 9%, and + / - 10%.

[0085] Examples

[0086] Example 1: Enhancing the Properties of Carbonation Cured Gamma Dicalcium Silicates (Y-C2S) using Biomimetic Molecules

[0087] In recent times, there has been a growing call for the development of alternative and eco- friendly binder systems, and this demand has been prompted by the significant carbon footprint associated with conventional Portland cement (OPC)

[0001] — [6]. A recent inclusion among these alternative cementitious systems is the carbonation-activated low-lime calcium silicate binder. [7], [8]. Notably, these low-lime phases, which have been historically disregarded in OPC due to their hydraulic limitations, exhibit a remarkable surge in reactivity when exposed to CO2 [9]—

[0011] . Capitalizing on the potential of these calcium silicates provides an exceptional chance to tackle the carbon footprint of cement production. By reducing temperature requirements and clinker production, these materials offer promising solutions for more sustainable cement manufacturing. [7], [8],

[0012] ,

[0013] .

[0088] Among the calcium silicates, dicalcium silicate (C2S) can potentially lower the energy needed for cement manufacturing by 0.29 to 0.42 GJ / ton of clinker when employed as the principal cement constituent (for example, belite-based binders)

[0013] —

[0016] . Even though Portland cement largely contains P-C2S, in recent studies, y-CzS has received attention for several reasons. The Y-C2S crystal stands out as the most stable among the five polymorphs of dicalcium silicates, exhibiting minimal hydraulic activity at room temperature

[0017] ,

[0018] , While Y-C2S is less active than b-C2S

[0014] ,

[0019] , its unique ability to generate fine powders during production, aptly termed the 'dusting' effect, remarkably diminishes grinding energy requirements, setting it apart from traditional C3S

[0014] ,

[0019] . Y-C2S has been identified as an eco-friendly construction material with exceptional CCh-absorption abilities

[0020] . Carbonation activated Y-C2S blended cementitious composites have shown potential to produce carbon negative concrete

[0021] —

[0023] . Moreover, research indicates that wollastonite (CS) and rankinite (C3S2) behave similarly as that of Y-C2S when exposed to carbonation curing owing to the traditional non-hydraulic behavior [7], [9],

[0010] . Therefore, knowledge of y-CTS’s carbonation reactivity can give direction for activation of low-carbon calcium silicate-based cementitious materials.

[0089] Most of the previous studies on carbonated Y-C2S samples were performed after preparing the specimens under molding pressure and high temperature curing

[0024] —

[0027] . These applied pressure and elevated temperature enabled the non-hydraulic Y-C2S samples to achieve a very strength when cured under 99% CO2 carbonation concentration. However, it is also understandable that the application of such pressure and temperature during the production process increases the overall carbon footprint of the composites. Therefore, any potential pathway to enhance the mechanical performance of Y-C2S samples carbonated at room temperature can further reduce the energy consumption and the associated carbon footprint of such composites.

[0090] The mechanical performance of carbonated cement composites shows considerable variation due to the presence of different CaCCh polymorphs [7],

[0010] . Among the different CaCOs polymorphs, amorphous calcium carbonate (ACC) first forms inside capillary pores, and later, it converts to metastable phases - vaterite or aragonite due to nucleation, growth, and transition which eventually ends up forming the stable calcite

[0028] ,

[0029] . This metastable calcium carbonate polymorphs’ formation is responsible for improved mechanical strengths

[0030] ,

[0031] . Hence, controlling these polymorphs’ formation is important to achieve better carbonated cementitious properties, but it is challenging to control these polymorph formations which depend on factors like humidity, temperature, CO2 concentrations, water contents etc.

[0031] —

[0034] . Apart from fine-tuning these parameters, a variety of organic molecules can be used to control the polymorph formation in carbonated cementitious composites. Researchers utilized amino acids and other biomolecules - ovalbumin, lysozyme, and bovine serum albumin (BSA) to modify CaCOs polymorphs

[0030] ,

[0035] —

[0038] . Ovalbumin and lysozyme had been used to modify the CaCC morphology

[0036] . BSA was incorporated into CaCCh which was synthesized using the gas-diffused method and, the formation of CaCCh with hierarchical structures were observed

[0037] , Several amino acids have been successfully incorporated to improve the performances of carbonated wollastonite composites by Khan et al.

[0039] . Later, the effects of proteins with different molecular structures were investigated in carbonated wollastonite composites by Baffoe and Ghahremaninezhad

[0033] . In addition to amino acids, polyacrylic acid can be a reasonable alternative since it also showed the potential to control the crystallization of CaCCL

[0040] . These biomimetic molecules develop organic-inorganic composites in cementitious matrixes which play an important role in obtaining remarkable mechanical properties

[0030] ,

[0033] . However, the effectiveness of such organic molecules on the carbonation behavior of y-CzS have not been explored yet.

[0091] Considering these knowledge gaps, interest was triggered to explore and enhance the properties of carbonation activated y-CzS based cementitious materials with the addition of biomimetic molecules. Therefore, for this study, two amino acids - L-aspartic acid (LAsp)and L- glutamic acid (LGlu) were chosen along with polyacrylic acid (PAA) to observe their ability to enhance the nano and micro-structural properties of carbonated y-CzS composites. The hypothesis is these biomimetic molecules can alter the CaCO, polymorphs formation which will eventually enhance the micro and nano-mechanical performance of the carbonated y-CzS composites. For this, micro to nano structural analyses were performed on carbonated y-CzS composites to verify the hypothesis. The effects of the biomimetic molecules on compressive and flexural strengths of y-CzS pastes carbonated at 25°C and 50°C were evaluated to understand the effectiveness of this approach at different temperatures. In this study, the vision is to investigate the potential of biomimetic molecules in low calcium cementitious composites, aiming for a greener and more sustainable cement-concrete construction industry. Materials and methods i. Raw materials

[0092] Various techniques exist for the synthesis of pure calcium silicate phases.

[0041] —

[0043] . Most of these methods involve employing the technique of sintering a stoichiometric mixture of lime and silica. In this study, CaCOs (>99% purity) and fumed silica (>99% purity) were used to synthesize y-CzS. As mentioned earlier, L-aspartic acid (C4H7NO4; MW 133.10 and high purity grade), L-glutamic acid (C5H9NO4; MW 147.13 and high purity grade) and polyacrylic acid (50 wt% solution in water, approximate MW 5000) were used as the biomimetic molecules. The molecular structures of L-aspartic acid, L-glutamic acid, and polyacrylic acid are shown below from left to right. All these raw materials and biomimetic molecules were purchased through

[0093] VWR. ii. Sample preparation

[0094] A uniform mixture of CaCCh and fumed silica was prepared with a molar ratio of 2: 1. To facilitate the mixing process, water-to-binder (w / b) ratio was maintained at 0.65. The resulting paste mixture was then placed in a high-temperature furnace resistant crucible and sintered at 1400°C for 4 hours. Afterward, it was allowed to cool down slowly within the furnace to room temperature, ensuring the stabilization of Y-C2S.

[0095] The sintered products were then ground and sieved through a mesh #200 (74 pm). To optimize the chemical reaction between available lime and silica, the resulting powder was subjected to two additional firing cycles. X-ray diffraction (XRD) analysis was performed after each sintering cycle to verify the absence of any free lime contents.

[0096] Furthermore, thermogravimetric analysis (TGA) was utilized to monitor the free lime content of the synthesized y-CFS, ensuring it remained below 3%. These steps were undertaken to synthesize and verify the desired properties of Y-C2S for potential applications.

[0097] The particle size distribution of the synthesized Y-C2S is shown in FIG. 1, which was determined using a commercially available laser particle size analyzer.

[0098] Two types of samples were prepared for carbonation curing: (i) thin disc from paste samples (~5 mm thick and 20 mm Dia) and (ii) compacted paste cube and beam samples. First type of samples was used to monitor the CaCCh polymorph formation and evolution along with nanomechanical properties during the carbonation period. The second category was prepared for mechanical strength and pore size distribution analysis. For preparing the paste samples, dry biomimetic molecules were first mixed with water at 2.5% and 5% concentration (by weight percentage of Y-C2S). The control batch contained no biomimetic molecules. Y-C2S powder was then mixed using a high shear mixer (at 350 rpm for 2 min). The water to binder (w / b) ratio was maintained as 0.40 throughout the experimental process. Then the paste samples were used to prepare beam and cubes samples (the cube-shaped samples measured 25 mm x 25 mm x 25 mm, while the beam-shaped samples were 40 mm x 20 mm x 15 mm) using silicon molds. The samples were compacted by hand tamping and no external pressure was applied. The samples with the molds were then placed inside a commercially available carbonation chamber setting the relative humidity at 80% and CO2 concentration at 20%. The samples were demolded after 24 hours and placed back in the carbonation chamber. Separate set of samples were carbonated at 25 °C and 50°C to evaluate the effect of temperatures. FIG. 2 shows a schematic diagram of the sample preparation of each experiment. Hi. Test methods

[0099] 1. X-ray diffraction (XRD)

[0100] Samples of carbonated paste were gathered after 7 days and subsequently ground to prepare them for X-ray diffraction (XRD) analysis. These powdered samples were loaded into a Bruker D500 spectrometer, where a Cu Ka radiation (40 kV, 30 mA) was employed. The diffraction patterns were then recorded in the 20 range of 10° to 60° with a step size of 0.03 (20) per second.

[0101] Phase identification through X-ray diffraction (XRD) was carried out using commercially available software known as "Match! Phase Analysis using Powder Diffraction." The PDF card numbers used for reference were as follows: PDF #96-900-0967 for calcite, PDF #96-901-3802 for aragonite, PDF #96-150-8972 for vaterite, and PDF #96-154-6026 for Y-C2S.

[0102] 2. Scanning electron microscopy (SEM)

[0103] The microstructures of the carbonated Y-C2S pastes were analyzed using the Hitachi S4800 II FE-SEM. Operating in high- vacuum mode, the instrument employed a 30-kV accelerated voltage and maintained a working distance of approximately 11 mm. Before capturing the SEM images, the cement paste sample was coated with Gold (Au)-Platinum (Pt). The analysis utilized the powder form of the paste samples.

[0104] 3. Fourier transform infrared spectroscopy (FTIR) Fourier-Transformed Infrared (FTIR) spectra of the ground paste sample were obtained using the Attenuated Total Reflection (ATR) mode, employing a resolution of 4 cm'1and conducting 32 scans for each sample. The signal to noise ratio was maintained below 3:1. The FTIR test was performed on carbonated samples collected after 7 days.

[0105] 4. Thermogravimetric analysis (TGA)

[0106] The TGA experiment of the paste sample was conducted using a commercially available instrument (TA instrument, TGA 550). The paste samples, which had been stored in a vacuum desiccator, were used for this test. To prepare the samples, they were ground with a mortar pestle until a fine powder was obtained. Around 25-30 mg of the powdered sample, passing through a #200 sieve, was loaded into a platinum pan. The pan was subjected to an isothermal condition at 25°C for 5 minutes before gradually increasing the chamber temperature to 980°C at a rate of 15°C per minute. To ensure an inert environment, nitrogen gas was purged during the process.

[0107] To validate the consistency of carbonation across samples, the TGA test was initially performed with three replicate samples. The results showed a deviation of less than 2% by weight of total carbonated samples, indicating good reproducibility. Consequently, for the remaining batches, TGA was performed with only one sample due to the low level of deviation. 5. Mercury intrusion porosimeter (MIP)

[0108] The Micrometrics Instrument Corporation AutoPore IV 9500 V2.03.01 was utilized to conduct Mercury intrusion porosimeter (MIP) experiments on cementitious composites. This technique is employed to determine the structure of meso-porous (pore radius 2~50 nm) and macro-porous (> 50 nm) materials. The MIP test was carried out on three sets of samples: the control batch, and paste samples with 2.5% and 5% dosages, all subjected to carbonation curing for 7 days. The sample size was standardized to 15 x 15 x 15 mm.

[0109] In the MIP experiment, mercury was used with a surface tension of 0.485 N / m and an average contact angle of 130° with the pore wall. The maximum pressure applied was 413 MPa, allowing the examination of pores with a diameter as small as 3.02 nm. This analysis helps in characterizing the pore structures of the cementitious composites in different dosage conditions after the carbonation curing period.

[0110] 6. Dynamic vapor sorption test (DVS)

[0111] To obtain the moisture desorption isotherm of carbonated paste samples, the commercially available DVS equipment (TA instrument, Q5000) was employed. Prior to testing, the samples were immersed in DI water for 6 hours to ensure complete saturation. About 4-5 mg of the saturated sample was loaded into a quartz pan.

[0112] The desorption isotherm was obtained by first equilibrating the sample at 97.5% relative humidity (RH) for 5760 seconds. Subsequently, the RH was gradually reduced in steps of 5-10% to achieve desorption. At each RH level, mass equilibrium was considered reached when the sample's mass fluctuation remained below 0.001% for 15 minutes. The entire experiment was conducted at a constant temperature of 23 °C, and nitrogen gas was consistently purged during the process to maintain a stable environment.

[0113] DVS is the favored method for assessing meso and gel pore structures in cementitious phases, as opposed to mercury intrusion porosimetry (MIP)

[0044] , When compared to water sorption, the nitrogen sorption technique significantly underestimates the surface area of cementitious matrix. This article utilized the BET method to determine the surface area (SBET) of carbonated composites.

[0045] and pore size distribution was determined based on the BJH model

[0046] . The calculation of the BET and BJH methods can be found elsewhere

[0047] ,

[0048] .

[0114] 7. Nanoindentation

[0115] For the nanoindentation tests, a Hysitron Triboindenter UB1 system (Hysitron Inc., Minneapolis, USA) equipped with a Berkovich diamond indenter probe was utilized. To ensure accurate measurements, the tip area function was calibrated using multiple indents with varying contact depths on a standard fused quartz sample. The surface roughness was evaluated using the Berkovich tip, and in all instances, it was found to be below 80 nm over an area of 60 pm x 60 pm. This level of surface quality was deemed suitable for conducting nanoindentation tests.

[0116] For grid nanoindentation, 7 days carbonated samples were specifically chosen. The load function adopted a three-segment approach: (i) a 5-second loading process from zero to maximum load, (ii) a 5-second hold at the maximum load, and (iii) a 5-second unloading from maximum to zero load. To accurately determine the mechanical properties of individual microscopic phases, it was essential to ensure that the depth of indentations remained considerably smaller than the characteristic size of each microscopic phase (indentation depth « characteristic size of each microscopic phase)

[0049] . Therefore, for this study using the SNI technique, a maximum force of 2000 pN was selected. As a result, the average indentation depth within a 30 pm x 30 pm area ranged from approximately 100-300 nm.

[0117] 8. Compressive and flexural strength testing

[0118] To measure the compressive strength, a Gilson compressive strength testing machine was employed, applying a loading rate of 450 N / s. On the other hand, the flexural strength, determined through the 3 -point bending test, was measured using a laboratory-made micromechanical tester with a displacement rate of 1 mm / min.

[0119] After 7 days of carbonation curing, the compressive and flexural strength of paste samples were evaluated. The cube-shaped samples measured 25 mm x 25 mm x 25 mm, while the beam-shaped samples were 40 mm x 20 mm x 15 mm.

[0120] To observe the effects of high temperature curing, another set of samples were prepared for both compressive and flexural strength testing and kept inside the carbonation chamber at 50°C for 7 days (maintaining the same other parameters; 20% CO2 concentration, 80% RH). Results i. Effects on the carbonation extent and CO2 sequestration

[0121] FIGs. 3A and 3B illustrate the thermogravimetric analysis (TGA and DTG) graphs of 7 days carbonated samples. The observed mass losses in the temperature range of 5OO-8OO°C for the 7 days cured paste samples can be attributed to the decomposition of CaCO; phases

[0014] . The occurrence of multiple DTG peaks within this temperature range is associated with the decomposition of various polymorphs of CaCCL

[0039] ,

[0047] ,

[0050] . The TGA results were utilized to determine the total CaCCL content that underwent decomposition within the temperature range of 500-800°C (FIG. 3C).

[0122] It was observed that with the increase of the dosage in LAsp batches, the CaCOs contents decreased. This observation matches with previous findings on the role of LAsp in carbonated wollastonite composites

[0039] . For LGlu batches, the observation was opposite to that of LAsp. Increasing the dosage of LGlu increased carbonate formation, and therefore, the degree of carbonation. In PAA modified batches, 2.5% batch showed the highest amount of CaCOs contents. Accordingly, while the addition of LAsp reduced the CO2 sequestration capacity of y- C2S, the other two molecules increased the sequestration capacity relative to control. The CO2 stored in the carbonated composite increased by nearly 46% due to the addition of 5% LGlu and by around 110% due to the addition of 2.5% PAA, indicating the effectiveness of these molecules to enhance carbon sequestration capacity of the composites. ii. Effects of molecules on the CaCCh polymorphs: Observations from XRD, FTIR and SEM

[0123] FIGs. 4A and 4B show the XRD patterns of the 7-day carbonated y-C2S paste samples. The XRD pattern of the synthesized Y-C2S matched with previously published literature

[0014] ,

[0051] . Both the y-C2S and the calcite peak were identified at a very close range (~ 29° 2q). From FIG. 4A, it is observed that 2.5% PAA modified y-C2S batch showed the highest calcite peak (~ 29° 2q). Nevertheless, 2.5% PAA modified batch showed the formation of aragonite and vaterite as well. The other 2.5% biomimetic molecule modified batches showed comparatively less prominent calcite peak formation. However, all the 2.5% batches showed metastable CaCOs polymorphs (vaterite and aragonite) formation.

[0124] From FIG. 4B, it can be observed that calcite peak (around 29.6°) got reduced for the 5% molecule containing batches. With the increase of the dosage, the y-CsS peak intensity decreased as well. Other metastable CaCOs polymorphs peak was also observed in the 5% batches, but those were not prominent. Aragonite formation was also observed in the control batch.

[0125] Apart from the XRD patterns, the formation of carbonate polymorphs in the modified y- C2S samples was also investigated using FTIR spectra (FIGs. 5A-5D). FTIR peaks due to the asymmetric stretching (ns) and in-plane bending vibration (114) of COs2’, located at around 1450 cm1and 712 cm1, respectively, were used for this study. The peak due to the in-plane bending vibration (n4) of CO32" (after background removal) was used to distinguish the carbonate polymorphs. Noteworthy, the peak at around 1450 cm’1(corresponding to asymmetric stretching (ns) of CO32) is often used to identify the presence of vaterite / ACC in the carbonated composite in literature

[0039] . However, the peak at 1450 cm’1is generally overlapped by the presence of all carbonate polymorphs. The peaks in the 690 cm’1to 755 cm’1range shows clearly distinguishable peaks for different carbonate polymorphs

[0052] . They are at 700 cm’1for aragonite, at 712 cm'1for calcite and at 746 cm'1for vaterite (all these bands are due to the inplane bending vibration (m))

[0053] —

[0058] . Important to note, ACC formation does not show any peak in this wavenumber range, and therefore, allowing clear distinction between vaterite and ACC.

[0126] From the observation, both the 2.5% and 5% PAA and LGlu modified Y-C2S carbonated paste samples showed calcite peak at 712 cm1. A small aragonite peak was identified in the control and 2.5% PAA containing batches. The 2.5% LAsp batch showed low intensity calcite and vaterite peaks. However, at 5% LAsp dosage, the calcite peak disappeared and the intensity of vaterite peak was significantly reduced. Regardless, the FTIR peak at around 1400 cm'1confirms the formation of carbonates in this 5% LAsp samples. Therefore, the combined observations from both asymmetric stretching (nr) and in-plane bending vibration (114) of CO32'. are indicative that primarily ACC formed in this 5%LAsp sample.

[0127] The morphology of the Y-C2S paste samples prepared with and without different dosages of different biomimetic molecules was evaluated using SEM. The control sample exhibited calcite crystals with sharp rhombohedral edges (FIG. 6A). The 2.5% LAsp (FIG. 6B) and 2.5% PAA (FIG. 6D) contained spherical ACC and vaterite phases. In 2.5% LAsp sample, the ACC spheres were larger in diameter (200 nm, 20-point average with a standard deviation of 38 nm) and agglomerated together, whereas in 2.5% PAA, the crystal sizes were smaller (60 nm, 20- point average with a standard deviation of 17 nm), and spheres were agglomerated. It was interesting to note that both 2.5% and 5% LGlu (FIG. 6C and FIG. 7C, respectively) samples contained vaterite with different crystal sizes. A relatively larger crystal of calcite with rounded edges compared to the control sample was observed in 5% dosages of LAsp and PAA (FIG. 7B and FIG. 7D, respectively). In the 5% LAsp sample, there were no individual crystals of calcium carbonate observed throughout the sample. However, it appeared that the carbonate phases were covered with extra deposition, as presented in FIG. 7B. Vaterite was observed in both 5% LGlu and 5% PAA batches.

[0128] Hi. Effects on the micro and nanoscale pore size distribution

[0129] Table 1: Effects on the pore structure (7 days carbonated samples) obtained by mercury intrusion porosimeter (MIP)

[0130] Pore size distributions of the 7 days carbonated 7-C2S paste samples as obtained using MIP are presented in FIGs. 8A-8D and the quantitative comparison due to the addition of the biomimetic molecules on the pore structure is given in Table 2.

[0131] Table 2: Statistical (t-test) analysis results (p-values) of compressive and flexural strength at both room and elevated temperature

[0132] *Note: Bold fonts represent (p-values>0.05) that the data are not statistically significant

[0133] Compared to the control batch, the addition of 2.5% LGlu increased the total porosity by 19% and reduced the critical pore diameter. The addition of 2.5% PAA and 2.5% LAsp reduced the total porosity by 23% and 5%, respectively compared to the control batch. Therefore, the addition of these molecules enabled the formation of a denser microstructure. The addition of 5% LAsp showed nearly the same total porosity as compared to the control batch, however with a significant increase in the large porosity. Such formation of large porosity is due to the reduced degree of carbonation (as observed from TGA) after the addition of 5% LAsp. The 5% LGlu containing batch showed a reduced porosity compared to the control batch. The addition of 5% PAA resulted in an increase of the total porosity without altering the critical pore size compared to the control batch. The pore size distribution as obtained from MIP matches well with the observations from TGA. Specifically, at 2.5% dosage, PAA showed the highest degree of carbonation and the lowest total porosity. In the case of 5% dosage, LGlu showed the highest carbonate formation and the lowest total porosity. DVS is commonly regarded as a more appropriate method for characterizing and analyzing meso-scale and gel pore structures in cementitious materials that contain CSH or Ca- modified silica gels. In this aspect, it proves to be more efficient compared to MIP or nitrogen sorption procedures

[0047] . The nano pore size distributions of the carbonated Y-C2S composites with and without the biomimetic molecules are shown in FIGs. 9A-9D. From these graphs, three major peak locations were noticed. They are at 5 A, 8 A and 11.5 A. The peak location at 11.5 A is the corresponding peak due to the porosity of the interlayers in calcium silicate hydrates (CSH) or Ca-modified silica gel structures

[0053] . After the addition of the biomimetic molecules, no peak shift occurred which indicates the biomimetic molecules do not affect the silicate structure. However, addition of these biomimetic molecules resulted in reduced interlayer porosity indicating lower amount of CSH / Ca-modified silica gel formation. The specific surface area is correlated with the quantity of water-accessible fine pores

[0048] . The specific surface area (SBET) of completely hydrated cement paste typically falls within the range of 100-200 m2 / g

[0059] . Carbonated calcium silicates are known to have lower SBET compared to hydrated cement paste

[0060] . As observed from FIGs. 9C and 9D, the addition of biomimetic molecules decreased the specific surface area of the carbonated matrices compared to the control batch. In a past study

[0060] , it was reported that the formation of metastable carbonates shows a lower surface area compared to the matrix primarily containing calcite. This is because the stabilization of typical metastable carbonates (vaterite and ACC) often occurs due to the coating of the particle by silica gel or the biomimetic molecules. Such a process makes the surface area of the metastable carbonated inaccessible by water molecule and therefore, shows a lower surface area measurement. Accordingly, the reduced surface area in the cases of LGlu and PAA containing batches can be attributed to the formation (and stabilization) of typical metastable carbonates and agglomeration of carbonate particles as observed in the SEM. In the case of LAsp containing batch, the reduced surface area can be attributed to the similar agglomeration of the phases along with reduced degree of carbonation as observed from the TGA. iv. Effects on Nanomechanical properties

[0134] Grid nano-indentation technique was applied to each sample over two 60 mm x 60 mm sections, with a total of 200 indentations. FIGs. 10A and 10B show the elastic modulus (GPa) frequency distribution for the control and biomimetic molecules-modified Y-C2S paste samples after 7 days of carbonation period. As reported in earlier literature, the elastic moduli of Ca- modified silica gel and CaCOs found in carbonated cured cementitious composites are approximately 32-42 GPa and 54-79 GPa, respectively [7],

[0047] ,

[0061] —

[0063] . Furthermore, the composite phase formed by the mixture of carbonated calcium silicates, consisting of CaCCh and Ca- modified silica gel, exhibits a mean elastic modulus of approximately 40 GPa

[0062] . It is worth noting that the elastic modulus of CaCCh varies significantly due to the formation of different polymorphs. Specifically, the elastic moduli are as follows: 39 GPa for aragonite, 67 GPa for vaterite, and 72 GPa for calcite

[0064] . The elastic modulus of ACC has not been determined yet. Additionally, distinguishing between vaterite and the composite phase is challenging since they share identical elastic moduli.

[0135] From FIG. IDA, it can be observed that the control batch contains tentatively two peaks: one at around 22 GPa, corresponding to HD C-S-H or Ca-modified silica gel and another around 30 GPa, which can be attributed to the carbonate phases with and without mixing with the gel. The batch containing 2.5% LAsp exhibited a distinct peak at approximately 30 GPa in the elastic modulus, suggesting the presence of a single hybrid phase instead of two separate microstructural phases. The mean modulus due to the addition of 2.5% LAsp was increased by 8.5%. In the case of 2.5% LGlu containing batch, two peaks corresponding to the gel and carbonate phases are clearly visible. However, the elastic modulus corresponding to the carbonate phase (~ 40 GPa) was higher in this batch compared to that of the control batch. The mean modulus of the 2.5% LGlu containing batch was 3.5% higher than the control batch. The frequency distribution plot for 2.5% PAA containing batch was similar to that of the 2.5% LAsp batch, as this sample also showed a single peak instead of separate carbonate and gel phases. Therefore, the addition of 2.5% PAA also led to the formation of hybrid phase, i.e., mixture of silica gel and different CaCOs polymorphs. All of the molecules at 5% dosage showed an increase in the elastic modulus compared to the control batch. Specifically, the highest mean modulus was obtained for the batch containing 5% LGlu batch. This study confirms that all of the molecules can effectively enhance the nanomechanical properties of the carbonated y-CzS composites. v. Effects on compressive and flexural strengths

[0136] FIGs. 11A and 11B exhibit the compressive and flexural strength properties of the 7 days carbonated y-C?S paste samples with and without the addition of biomimetic molecules. FIG. 11A shows that 2.5% PAA and 5% LAsp modified y-CzS paste samples resulted in 61% and 52% higher than the control batch, respectively. Not only these two batches, but all other biomimetic molecules also modified batches increased the compressive strength as well. FIG. 11B shows the flexural strength properties of the 7 days carbonated paste samples. Both 2.5% and 5% dosage increased the flexural strength in the carbonated cementitious system. The flexural strength of the beam samples increased by 54% by the addition of 5% LGlu and 5% LAsp. Even though LAsp modified batch did not show significant CaCCL polymorphs formation in the microstructure, it enhanced the strength properties because of the adhesion characteristics of aspartic acid

[0065] —

[0067] . vi. Effects of temperature on strength properties

[0137] Another set of samples were cured at elevated temperature (50°C) to observe the effect of temperature curing on the samples. It was observed that elevated temperature enhanced strength gain for both compressive and flexural strength to a great extent. From FIG. 12A, the results revealed a substantial improvement in strength with increasing temperature. Of particular interest is the effect of different additives, specifically 5% LGlu and 2.5% LGlu, on the strength gain compared to the control batch.

[0138] When exposed to elevated temperature curing, 5% LGlu demonstrated the most significant strength enhancement, exhibiting a remarkable 100% increase in strength compared to the control batch. Additionally, 2.5% LGlu exhibited a substantial improvement, with a 69% increase in strength.

[0139] Conversely, the LAsp batches did not exhibit any noticeable improvement in strength when subjected to elevated temperature curing. This suggests that the efficacy of LAsp diminishes under high-temperature curing conditions. In contrast, the PAA-induced batches displayed a similar percentage increase in compressive strength compared to the batches cured at ambient temperature, indicating that the effects of PAA are consistent regardless of curing temperature.

[0140] The influence of temperature (50°C) curing on the flexural strength properties of the biomimetic molecules-induced batches is depicted in FIG. 12B. It was evident that the batches subjected to high-temperature curing exhibited improved flexural strength when compared to their counterparts cured at ambient temperature.

[0141] Among all the batches, the 2.5% LGlu modified batch demonstrated the most significant increase in flexural strength, registering 126.5% improvement compared to the control batch. Similarly, the 5% LGlu induced batch exhibited a noteworthy increase of 104.5% in flexural strength. Interestingly, the PAA modified batches, in contrast to previous observations, displayed a higher increase in strength when exposed to elevated temperature curing, with increments of 53.5% and 64.5% compared to the control batch. Furthermore, the 5% LAsp modified batch also showed a notable improvement in flexural strength, achieving a 73.5% increase.

[0142] These findings underscore the positive impact of high- temperature curing on the flexural strength properties of the biomimetic molecules-induced batches, with specific additives such as LGlu, PAA, and LAsp contributing significantly to these enhancements. FIGs. 13A and 13B are showcasing the percent increase of the strength compared to the room temperature cured batches. FIG. 13A shows that 2.5% LGlu batches improved both compressive strength and flexural strength properties to the maximum. For compressive strength, the percent increase is almost same for the 2.5% and 5% batches. However, for the flexural strength (FIG. 13B), 2.5% dosage batches enhanced the strength maximum compared to the 5% induced batches.

[0143] This study showed that the selected biomimetic molecules can affect the amounts and polymorphs of the carbonates form in the carbonated 7-C2S composites. However, effects of these molecules are substantially different due to their different characteristics including surface charge and chain lengths. The observed role of LAsp on carbonated y-CzS composites is similar to those observed in the case of carbonated wollastonite

[0039] . Specifically, with the increasing amounts of LAsp, an increase in the mechanical performance was observed, even though the degree of carbonation was reduced. The negatively charged LAsp forms complex phases with Ca2+surface sites of CaCOs and subsequently, stabilizes typical metastable polymorphs of CaCCL, including vaterite and ACC, which cause the strength enhancement due to the addition of this molecule

[0039] . However, due to the same mechanism, LAsp can also form complex with the Ca2+surface sites of Y-C2S and therefore, reduced the reacting surface area resulting in a reduced degree of carbonation. While LGlu is also negatively charged as that of LAsp, the effects of LGlu on the carbonated y-CiS composites were different. The increased dosage of LGlu enhanced the mechanical performance as well as the degree of carbonation of the composites, and therefore making LGlu a more effective admixture for y-C2S compared to the LAsp. Without wishing to be bound by theory, it is believed that such differences in the roles of LAsp and LGlu are due to their different chain length and solubility.

[0144] (a) (b) (c)

[0145] Molecular structure of (a) L-aspartic acid, (b) L-glutamic acid and (c) polyacrylic acid

[0146] The solubilities of LGlu and LAsp are 8.6g / L and 4.5g / L in water at room temperature. It is also believed that a higher solubility limit is likely to make LGlu more effective in controlling the carbonate polymorphs.

[0147] The role of PAA in carbonated composite is different than that of the LGlu and LAsp. Worthy to note, PAA is also negatively charged molecule and a very well-known viscosity modifying admixture for Portland cementitious materials

[0068] ,

[0069] . In the case of Portland cement paste, the negatively charged PAA can be adsorbed on the surface of cement particles, which stabilizes the particles in water and therefore, improves the workability of the mixture

[0068] ,

[0069] . PAA is also well-known for its ability to alter the CaCCh crystallization pathway

[0070] ,

[0148]

[0071] . PAA can enable forming CaCCL with variable crystal shapes, sizes, and polymorphs (vaterite, aragonite, ACC) depending on the dosage, molecular weight, and temperature

[0070] —

[0149]

[0072] . At 2.5% dosage, PAA increased the compressive strength of the composite by 61% and COr sequestration capacity by nearly 110%. Unlike LAsp and LGlu, the addition of 2.5% PAA enabled the stabilization of aragonite (observation from FTIR and XRD). Accordingly, the enhanced role of PAA compared to the LAsp and LGlu was attributed to its ability to stabilize aragonite. However, with an increased dosage (5%) of PAA, the strength and CO2 sequestration capacity were reduced compared to the 2.5% dosage (remained higher than the control and similar to 5% LGlu). This performance reduction at high dosage of PAA was attributed to the excessive adsorption of this molecule on y-CiS surface.

[0150] Moreover, strength results findings underscore the importance of temperature in the curing process and highlight the varying responses of different additives to elevated temperature conditions. The data demonstrate that LGlu additives can significantly enhance strength under such conditions, while LAsp’s effectiveness diminishes, and PAA maintains its consistent performance across curing temperatures. These results offer valuable insights into optimizing the curing process for enhanced material properties. Table 2 summarizes the p- values from the level of statistical significance. Statistical significance is often quantified by the p-value, represented as p. A small p-value, typically less than or equal to 0.05, indicates strong evidence against the null hypothesis and allows for its rejection. In the analysis, the compressive strength and flexural strength results were compared to those of the control batch, with the test conducted at a 95% confidence level. When p-values below 0.05 were obtained, it indicated a statistically significant difference between the two groups of samples, while p-values exceeding 0.05 suggested the absence of statistical significance between the groups. At room temperature, 5% LAsp and 5% PAA modified batches exhibited statistical significance in both compressive and flexural strength. When the biomimetic molecules modified batches were cured at 50°C, all batches containing 2.5% and 5% dosages demonstrated statistical significance in both compressive and flexural strength properties. Among the batches, both the 2.5% and 5% LGlu batches showed significant improvement in strength enhancement at high temperature curing condition, Table 2.

[0151] In sum, a variety of organic molecules have been used in the past to mimic the biomineralization process of stabilization of CaCCh polymorphs in carbonation cured calcium silicates

[0039] ,

[0073] . The past evaluated molecules include L-Aspartic, L-Serine, L-Arginine, polydopamine, and cellulose

[0039] ,

[0073] . The application of all of these molecules resulted in improved mechanical performances of the carbonated composites but reduced the CO2 sequestration in those composites

[0039] ,

[0073] . One of the most interesting observations of the presented study is that both LGlu and PAA were able to enhance the mechanical performance of the composites while also increasing the amounts of CO2 sequestered in the carbonated Y-C2S composites.

[0152] In conclusion: i. From XRD, Y-C2S formation is verified with prominent peaks. The XRD results also confirmed the calcite and other calcium carbonate phases formation. It indicates the proper laboratory synthesis of the Y-C2S materials. ii. FTIR in the 700 cm'1wavenumber range showed that LAsp batches showed delayed calcium carbonate formation. Therefore, it can be said that the degree of reaction was lower for LAsp dosages. iii. TGA results showed that PAA and LGlu had a higher amount of calcium carbonate formation compared to the control batch. Addition of biomimetic molecules accelerated the degree of reaction. iv. All the batches showed lower nano-porosity compared to the control batch which resulted in higher compressive strength. Among the batches, both 5% LAsp and 5% PAA batches showed an increase of compressive strength by around 50%. 2.5% PAA increased the strength by around 60%. v. From nanoindentation results, 5% LAsp and 5% LGlu showed improved modulus of elasticity. However, all the 2.5% batches showed higher mean modulus of elasticity compared to the control batch. vi. 2.5% PAA produced the highest amount of calcium carbonate contents and resulted in the highest compressive strengths at room temperature. vii. At a curing temperature of 50°C, both 2.5% and 5% LGlu demonstrated substantial enhancements in both compressive and flexural strength. Specifically, the addition of 2.5% LGlu resulted in a 69% increase in compressive strength and a remarkable 126.5% improvement in flexural strength. Similarly, the incorporation of 5% LGlu led to a doubling of compressive strength (100%) and a notable increase of 104.5% in flexural strength.

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[0065] R. L. Willett, K. W. Baldwin, K. W. West, and L. N. Pfeiffer, “Differential adhesion of amino acids to inorganic surfaces,” Proc Natl Acad Sci USA, vol. 102, no. 22, 2005, doi: 10.1073 / pnas.0408565102.

[0220]

[0066] O. Schussler et al., “Use of arginine-glycine-aspartic acid adhesion peptides coupled with a new collagen scaffold to engineer a myocardium-like tissue graft,” Nat Clin Pract Cardiovasc Med, vol. 6, no. 3, 2009, doi: 10.1038 / ncpcardiol451.

[0221]

[0067] J. J. Hwang and S. I. Stupp, “Poly(amino acid) bioadhesives for tissue repair,” J Biomater Sci Polym Ed, vol. 11, no. 10, 2000, doi: 10.1163 / 156856200743553.

[0222]

[0068] B. Ma, Y. Peng, H. Tan, Z. Lv, and X. Deng, “Effect of polyacrylic acid on rheology of cement paste plasticized by polycarboxylate superplasticizer,” Materials, vol. 11, no. 7, Jun. 2018, doi: 10.3390 / mal 1071081.

[0223]

[0069] Y. Guo et al. , “Effect of polyacrylic acid emulsion on fluidity of cement paste,” Colloids Surf A Physicochem Eng Asp, vol. 535, pp. 139-148, Dec. 2017, doi: 10.1016 / j.colsurfa.2017.09.039.

[0224]

[0070] S. Ouhenia, D. Chateigner, M. A. Belkhir, E. Guilmeau, and C. Krauss, “Synthesis of calcium carbonate polymorphs in the presence of poly aery lie acid,” J Cry st Growth, vol. 310, no. 11, pp. 2832-2841, May 2008, doi: 10.1016 / j.jcrysgro.2008.02.006.

[0225]

[0071] H. Watamura, Y. Sonobe, and I. Hirasawa, “Polyacrylic Acid-Assisted Crystallization Phenomena of Carbonate Crystals,” Chern Eng Technol, vol. 37, no. 8, pp. 1422-1426, 2014, doi: 10.1002 / ceat.201400017.

[0226]

[0072] S. C. Huang, K. Naka, and Y. Chujo, “Effect of molecular weights of poly(acrylic acid) on crystallization of calcium carbonate by the delayed addition method,” Polym J, vol. 40, no. 2, 2008, doi: 10.1295 / polymj.PJ2007162.

[0227]

[0073] R. I. Khan, M. I. Haque, W. Ashraf, S. Shah, and N. Saleh, “Role of biopolymers in enhancing multiscale characteristics of carbonation-cured cementitious composites,” Cem Concr Compos, vol. 134, Nov. 2022, doi: 10.1016 / j.cemconcomp.2022. 104766. Example 2: Role of polyacrylic acid with different molecular weights on the performance of CO2-cured beta-dicalcium silicate (P-C2S)

[0228] In recent years, the imperative need for environmentally sustainable construction practices has intensified, driven by growing concerns over the substantial carbon footprint associated with ordinary portland cement (OPC). As a pivotal component of concrete, OPC holds the distinction of being the second most utilized substance worldwide, just after water [1]. The staggering statistics from 2015, with a total cement mass of 4.6 billion tons and a per capita average of 626 kg, resulting in the production of 2.1-2.3 m3of cement-based materials, underscore the scale of its impact [2]. The production of OPC is further compounded by its significant contribution to global CO2 emissions, accounting for 7%-10% of anthropogenic CO2 emissions and 2%-3% of energy consumption [1], [3], [4]. Projections indicate a 50% increase in cement production by 2050, with an additional 85-105 Gt of CO2 emissions anticipated [3].

[0229] The primary source of CO2 emissions in OPC production stems from the calcination of limestone as well as energy-derived CO2 from fuel consumption during feed heating [5]. Consequently, the quest for sustainable alternatives has driven the development of various low carbon footprint cementitious systems. A few of these systems utilize low-lime calcium silicates (e.g., wollastonite, rankinite, belite, etc.), which exhibit remarkable reactivity in the presence of CO2 [6], [7], [8]. Utilizing these low-lime calcium silicates offers a promising solution to reducing the carbon footprint associated with cement production, primarily by decreasing the demand for limestone and the temperature requirements for clinker production 191.

[0230] In this context, it is paramount to recognize that C2S, constituting approximately 15 wt% of cement clinker, is integral to the long-term properties of cement

[0010] . Traditionally, C3S, accounting for about 65 wt% of cement clinker, has been favored over C2S for its rapid hydration and early strength development [6],

[0011] . However, C2S has the potential to reduce limestone consumption, save energy, and mitigate CO2 emissions. Enhancing the early strength development of C2S has led to the exploration of carbonation curing, which accelerates mineral transitions in C2S and sequestrates CO2 into chemically stable carbonates for extended periods

[0231]

[0012] .

[0232] A pivotal distinction arises from the various polymorphs that C2S can adopt, including a, aH', aL', f>, and y, each influenced by chemical impurities and cooling transition temperatures

[0233]

[0013] . a and a' tend to transform to phase at 675°C-750°C, then transform to y phase at a lower temperature

[0014] ,

[0015] . Among these, -C2S emerges as the principal mineral component of Portland cement, reacting with water to contribute to medium and long-term strength development. Both -C2S and y-C2S have demonstrated their ability to sequester CO2 and generate CaCOs and silica gel phases, thereby contributing to early strength development

[0012] ,

[0016] ,

[0017] . The distinction between the carbonation properties of P-C2S and y-CbS has been subject to rigorous investigation

[0018] , underscoring the potential for optimizing their performance by understanding and controlling the associated variables

[0017] ,

[0019] ,

[0020] .

[0234] A goal of this work is to identify new additives that can be used to enhance the performance of such carbonated calcium silicate composites. The mechanical properties of carbonated cement composites are significantly influenced by the formation of different CaCOs polymorphs. Among these, amorphous calcium carbonate (ACC) serves as the precursor, transitioning into metastable phases such as vaterite or aragonite before ultimately stabilizing as calcite

[0021] ,

[0022] . These metastable phases play a pivotal role in enhancing mechanical strengths, making the controlled regulation of polymorph formation a very important factor in achieving improved carbonated cementitious properties. Yet, this control is inherently challenging due to a multitude of variables, including humidity, temperature, CO2 concentrations, water content, and more

[0023] ,

[0024] ,

[0025] ,

[0026] . Apart from the precise calibration of these parameters, organic molecules have shown promise in influencing polymorph formation in carbonated cementitious composites. While previous research has explored the use of amino acids for this purpose

[0027] , polyacrylic acid (PAA) presents a viable alternative, given its demonstrated capacity to influence the crystallization of CaCOs

[0028] ,

[0029] . Molecular dynamics simulation showed the formation of Ca-0 and hydrogen bonds between CaCOs and PAA, which favor the adsorption of PAA on CaCOs particles

[0030] . Due to the affinity of CaCOs for PAA, such polymers, with or without further modifications, can be used to control the polymorph crystallization and growth rates of CaCOs

[0029] ,

[0031] . The superior bonding between CaCOs and PAA has been exploited to develop a variety of composites, including thin films

[0032] and hydrogels

[0033] .

[0235] The inclusion of PAA in cement paste has primarily aimed to enhance fluidity

[0034] ,

[0035] , with limited studies delving into its potential for CO2 cured composites. Crucially, PAA is available in a wide range of molecular weights (MW), and the selection of MW can significantly impact biomimetic mineralization processes

[0036] ,

[0037] . Notably, a study by Haque et al. introducing 1-aspartic acid, 1-glutamic acid, and polyacrylic acid into y-CsS, highlighted the substantial role of polyacrylic acid (PAA) with a molecular weight of 5000 (MW 5000) in enhancing carbonation properties under high-temperature conditions. However, this research spotlighted the influence of temperature, particularly relevant to y-CaS's non-hydraulic nature. Given that P-C2S possesses greater hydraulic properties than Y-C2S, it becomes imperative to investigate the effects of incorporating various molecular weights of polyacrylic acid to enhance the carbonation properties of P-C2S. This study, therefore, aims to elucidate the specific influence of different MWs of PAA on enhancing the carbonation properties of P-C2S, ultimately paving the way for more efficient and cost-effective construction materials while addressing significant environmental concerns.

[0236] Materials and methods i. Raw materials

[0237] Numerous methodologies are available to produce pure calcium silicate phases

[0038] ,

[0039] ,

[0040] . Most of these approaches entail the utilization of sintering to process a precise mixture of lime and silica. In this work, CaCCh with a purity exceeding 99% was employed and fumed silica with a purity exceeding 99% to create P-C2S. To make P-C2S formation stable, 0.3 wt.% boron was incorporated as dopant by the addition of boric acid (H3BO3)

[0041] ,

[0042] ,

[0043] ,

[0044] . Three different molecular weights (MW) of polyacrylic acid (PAA) were employed, specifically polyacrylic acid with MW 2000 (in a 63 wt% aqueous solution), polyacrylic acid with MW 5000 (in a 50 wt% aqueous solution), and polyacrylic acid with MW 240000 (in a 25 wt% aqueous solution). All these raw materials and biomimetic compounds were procured from VWR. ii. Sample preparation

[0238] A homogeneous blend of CaCCh and fumed silica was prepared with a molar ratio of 2:1. 0.3% (by wt percent of the CaCOs and silica contents) boron dopant was added in the form of boric acid. To aid the mixing process, the water-to-binder (w / b) ratio was maintained at 0.50. The resulting paste mixture was utilized to create l-inch cube specimens using a silicone mold, which were placed in a 40°C oven for a duration of 6 hours for a partial drying of these samples. Subsequently, these cube specimens were placed inside a high-temperature furnace and heated at a rate of 4.5°C per min. The cubes were sintered at 1400°C for a duration of 4 hours and finally, brought back to room temperature slowly. The sintered products were cubes with clinker-like hardness, which were then pulverized using a ball mill. These processes were repeated three times to ensure the formation of high purity P-C2S. The final product was sieved using a #200 mesh (74 pm opening) to ensure fine particle size distribution. X-ray diffraction (XRD) analysis was conducted after each sintering cycle to confirm the absence of any residual free lime components.

[0239] The particle size distribution and the X-ray diffraction results of the synthesized p-CzS is shown in FIGs. 14A and 14B. The XRD pattern of the synthesized -C2S matches with previous studies

[0016] ,

[0018] ,

[0045] .

[0240] Three categories of samples were fabricated for the purpose of carbonation curing: (i) paste samples were prepared by mixing powdered -C2S with water at a water-to-binder ratio of 0.4. The control batch did not contain any PAA. Additional batches with 0.1% by weight of PAA with different molecular weights were prepared to evaluate their role in carbonation kinetics. The paste samples were exposed to 99% CO2 purging for 15 hours while their infrared (IR) spectra were collected at 3.75-minute intervals, (ii) Thin plates were cut from P-C2S solid cubes (after sintering and before grinding) with around 5 mm in thickness and 20 mm in diameter. These samples were utilized to track the formation and evolution of CaCCh polymorphs on solid P-C2S plates. These plates were fully submerged in water containing various dosages of PAA for approximately 1 minute. The plates were then taken out of the solution and immediately placed in a carbonation chamber with conditions set at 80% relative humidity and 20% CO2 concentration. The plates were taken out of the chamber at frequent intervals, and the growth of CaCCh was monitored on these plates. Several plates were prepared for each batch and a new plate was used every time for the measurement. Paste cubes and beam samples were prepared by mixing p-CAS powder with water using a high-shear mixer at 350 rpm for 2 minutes. The water-to-binder ratio was maintained at 0.40 throughout the experimental process. The control batch did not contain any biomimetic molecules. The modified batches contained PAA at dosages 0.5%, 1%, and 2.5% by weight of P-C2S. PAA was first mixed with water, and the solution was used to prepare the paste samples. The paste mixtures were compacted into cube and beam molds, and subsequently, the compacted samples were placed inside a commercially available carbonation chamber with a set relative humidity of 80% and CO2 concentration of 20%. Samples were cured at two different temperatures: 27°C and 50°C. These samples were prepared for the analysis of mechanical strength, microstructural evolution, and pore size distribution. The overall sample preparation steps with experimental setups are shown in FIG. 15.

[0241] Hi. Test methods

[0242] 1. Thermogravimetric analysis (TGA)

[0243] The thermal gravimetric analysis (TGA) on the paste sample was carried out using a commercially available TGA 550 instrument from TA Instruments. To prepare test samples, carbonated pastes were manually ground with a mortar and pestle until a fine powder was achieved. Approximately 30-35 mg of the powdered material, having passed through a #200 sieve, was loaded into a platinum pan. The pan was then subjected to an isothermal condition at 25 °C for 5 minutes before gradually increasing the chamber temperature to 980°C at a rate of 15 °C per minute. To maintain an inert atmosphere, nitrogen gas was purged throughout the procedure.

[0244] To confirm the uniformity of carbonation among the samples, the TGA test was initially conducted using three replicate samples. The results exhibited a variation of less than 2% in terms of total carbonation, indicating acceptable reproducibility. Consequently, for the subsequent batches, TGA was carried out using a single sample due to the low level of variability.

[0245] 2. Scanning electron microscopy (SEM)

[0246] The microstructures of the carbonated P-C2S pastes were examined using a Hitachi S4800 II FE-SEM. This instrument operated in a high-vacuum mode, applying a 30-kV accelerated voltage and maintaining a working distance of roughly 11 mm. Prior to acquiring SEM images, the cement paste sample was coated with a layer of Gold (Au) and Platinum (Pt).

[0247] 3. Fourier transform infrared spectroscopy (FTIR)

[0248] Fourier-Transform Infrared (FTIR) spectra of the powdered paste sample were acquired utilizing the Attenuated Total Reflection (ATR) mode, with a resolution of 4 cm1, and involving 32 scans for each individual sample. The signal-to-noise ratio was held below 3: 1. The FTIR analysis was conducted on the carbonated samples obtained after 3 days and 7 days.

[0249] To perform the in-situ FTIR, first the background spectrum was collected using a I pL water drop in CO2 atmosphere. The samples were taken in powder form. Around 15 mg samples were taken. 1 pL water was put on top of the powder sample before starting the test. CO2 gas purging commenced immediately upon the placement of the paste sample onto the ATR tip. A total of 280 spectra was collected maintaining a time interval of 3.75 mins between two spectra. 99% CO2 gas purging was maintained.

[0250] 4. X-ray diffraction (XRD)

[0251] Samples of carbonated paste collected after 7 days were subsequently milled in preparation for X-ray diffraction (XRD) analysis. These powdered samples were loaded into a Bruker D8 spectrometer, utilizing Cu Kot radiation (40 kV, 40 mA). The diffraction patterns were then recorded within a 20 range of 10° to 60°, with a step size of 0.03 (20) per second.

[0252] For phase identification through X-ray diffraction (XRD), a commercially available software known as "Match! Phase Analysis using Powder Diffraction" was employed. The reference PDF card numbers utilized were as follows: PDF #96-900-0967 for calcite, PDF #96- 901 -3802 for aragonite, PDF #96-150-8972 for vaterite, and PDF #96-154-6026 for Y-C2S. For, P-C2S, previously published

[0018] ,

[0045] literature was used.

[0253] 5. Mercury intrusion porosimeter (MIP)

[0254] The Micrometrics Instrument Corporation AutoPore IV 9500 V2.03.01 apparatus was employed for conducting Mercury intrusion porosimeter (MIP) experiments on cementitious composites. This technique is utilized for assessing the architecture of both meso-porous materials (pore radius 2~50 nm) and macro-porous materials (> 50 nm). The MIP test was performed on three distinct sets of samples: the control batch and paste samples with 2.5% and 5% dosages, all subjected to 7 days of carbonation curing. The sample dimensions were standardized to l5 x l5 x l5 mm.

[0255] In the MIP experiment, mercury was used with a surface tension of 0.485 N / m and an average contact angle of 130° with respect to the pore wall. The maximum applied pressure reached 413 MPa, enabling the investigation of pores with diameters as small as 3.02 nm. This analysis aids in characterizing the pore structures of the cementitious composites under varying dosage conditions following the carbonation curing period.

[0256] 6. Nanoindentation

[0257] For the nanoindentation tests, a Hysitron Triboindenter UB1 system (Hysitron Inc., Minneapolis, USA) equipped with a Berkovich diamond indenter probe was utilized. To ensure accurate measurements, the tip area function was calibrated using multiple indents with varying contact depths on a standard fused quartz sample. The surface roughness was evaluated using the Berkovich tip, and in all instances, it was found to be below 80 nm over an area of 60 pm x 60 pm. This level of surface quality was deemed suitable for conducting nanoindentation tests.

[0258] For grid nanoindentation, 7 days carbonated samples were specifically chosen. The load function adopted a three-segment approach: (i) a 5-second loading process from zero to maximum load, (ii) a 5-second hold at the maximum load, and (iii) a 5-second unloading from maximum to zero load. For this study using the SNI technique, a maximum force of 2000 pN was selected. As a result, the average indentation depth within a 30 pm x 30 pm area ranged from approximately 100-300 nm.

[0259] 7. Compressive and flexural strength testing

[0260] The measurement of compressive strength was conducted using a Gilson compressive strength testing machine, with a loading rate of 450 N / s. On the other hand, flexural strength, determined through the 3-point bending test, was assessed using a custom-made micromechanical tester with a displacement rate of 0.1 mm / min.

[0261] After 3 days and 7 days of carbonation curing, the compressive and flexural strength of paste samples were examined. The cube-shaped samples had dimensions of 25 mm x 25 mm x 25 mm, while the beam-shaped samples measured 40 mm x 20 mm x 15 mm.

[0262] Results i. Early age carbonation characteristics

[0263] 1. Carbonate precipitation kinetics

[0264] The role of PAA on the carbonate precipitation kinetics during the CO2 curing of P-C2S was monitored using in-situ ATR FTIR. FIG. 16A shows a sample of in-situ ATR FTIR data obtained during the carbonation of P-C2S. The FTIR spectra were collected at 3.75-minute intervals for up to 15 hours. The anti-symmetric stretching (V3) band of silicate species (Q°) present in P-C2S appeared at around 840 cm'1and 890 cm1. The absorbance at 1600 cm'1corresponds to the O-H bond of water present in the paste samples. The polymerized silica gel shows peaks at around 1100 cm'1and 1200 cm'1corresponding to the anti-symmetric stretching (V3) band of Q3(- Si* - (O-Si)s) and Q4(Si* - (O-Si)4) silicate species, respectively. The presence of Q3and Q4silicate species indicates the formation of a three-dimensional silicate network. The vibrational spectra of carbonate ions show four types of intramolecular modes that can be assigned to anti-symmetric stretching (V3), symmetric stretching (v , out-of-plane bending (V2), and in-plane bending (V4)

[0046] . In contrast to the predicted values based on an isolated carbonate ion (1436 cm1, 1380 cm'1[V3], 1064 cm'1[vi], 880 cm'1[V2] and 684 cm'1[1 / 4]), the band positions vary depending on different chemical environments due to the decrease in symmetry in the carbonate ions. The carbonate V3 band absorbance shows the primary peak at the same wavenumber for calcite, vaterite, and ACC, even though peak splitting may occur.

[0265] As observed from FIG. 16A, the initial spectra showed the presence of only P-C2S and water by the peaks at around 840 cm1, 890 cm'1and 1600 cm1. With increasing duration, the absorbance peaks associated with both water and P-C2S molecules were reduced along with increased absorbance corresponding to polymerized silica gel and calcium carbonates, indicating the gradual progress of the carbonation reaction. The formation of polymerized silica gel was apparent due to the intensity increase of the peaks at around 1100 cm'1and 1200 cm1. For these carbonated samples, the V3 band absorbance of carbonate bond is located at around 1400 cm'1showing a relatively narrow peak. With the increasing carbonation duration, the absorbance of this band continues to increase, indicating the precipitation of calcium carbonates.

[0266] Considering the 1 / 3 absorbance of the carbonate bond remains at around 1400 cm1, irrespective of the carbonate polymorph variations, the normalized intensity of this peak is used to monitor the total carbonation precipitation kinetics in the samples. FIG. 16B shows the normalized intensity of this peak with carbonation duration for P-C2S prepared with and without PAA. As observed from this figure, for all the samples, the intensity reached the plateau within 850 minutes, indicating the maximum carbonation was achieved within this duration. Such rapid carbonation is expected due to the use of 99.9% pure CO2 purging and small sample amounts (~ 15 mg, no compaction) used for this experiment. Interesting to note that the carbonate precipitation started earlier for all PAA-containing samples compared to the control sample. Specifically, for the sample containing 1% of 240000 MW PAA, the carbonate precipitation was initiated at around 50 minutes and completed within 150 minutes. The samples containing 1% of 2000 MW PAA and 1% of 5000 MW PAA showed the same trend and for both samples, the carbonate precipitation was initiated at around 60 minutes. On the other hand, for the control batch, the carbonated precipitation started at around 75 minutes, and around 90% of precipitation was completed by 150 minutes. These findings show that the addition of PAA accelerated the carbonate formation during the carbonation curing of P-C2S. A higher molecular weight (MW) of PAA shows a more prominent acceleration of carbonation.

[0267] 2. Carbonate particle evolution

[0268] FIG. 17 shows the evolution of the reaction products of different batches (1% dosage) in early age curing periods (Ih, 3h, 6h and 24h). After an hour of carbonation, amorphous calcium carbonates (ACC) formed in the control sample. The size of the ACC crystals was approximately 200 nm. After 3 hours, they became agglomerated, which eventually rearranged and formed calcite after 6 hours. The coexistence of ACC and calcites is evident from FIG. 17. After 24 hours, scattered precipitation of calcites is observed. The average size of the calcite crystals was around 600 nm after 6 hours, which increased up to 1.5 pm (approximately) after 24 hours. With the addition of PAA of MW 2000, no significant change in the reaction product morphology was observed up to the first 3 hours. Some ACC was observed after 6 hours of reaction with an average size of around 530 nm, which became agglomerated after 24 hours of reaction. In the MW 5000 sample, after one hour of exposure, well-formed ACC with an average size of 570 nm were observed, which became agglomerated with time.

[0269] A similar trend was observed in the MW 240000 sample. However, the agglomeration was prominent after the first hour of exposure in the latter specimens. Interesting to note, in these samples, the agglomerations of ACC formed a grid-like pattern after 6 hours as shown FIG. 18A. Such grid-like formation of calcium carbonate persisted until 7 days of carbonation curing (FIG. 18B). These images indicate that the PAA with MW 240000 formed a three- dimensional polymer network within the paste matrix and calcium carbonate deposited on the polymer chains caused the deposition of carbonate in network pattern. Such carbonate networks were not present in MW 2000 and MW 5000 samples. However, in MW 5000, broken polymer fiber network was found indicating the reduced stability of such network at low molecular weights of the polymer (FIG. 18D).

[0270] After 3 days and 7 days of exposure, all the samples showed well-formed calcite crystals (FIG. 19). The calcite crystals of control samples and MW 2000 were similar, whereas the samples containing higher molecular weights (MW 5000 and MW 240000) showed well-formed calcites with a subtle boundary, which possibly resulted from the polyacrylic acid. For the control sample, after 3 days of carbonation, the crystal size of the calcites was 0.93 m with a standard deviation of 0.20 |im which increased to 1.36 |im with a standard deviation of 0.57 |im after 7 days of carbonation. MW 240000 sample showed the largest calcite crystals. After 3 days of carbonation, the crystal size of the calcites was 4.56 pm with a standard deviation of 2.31 pm, which increased to 4.63 pm with a standard deviation of 1.2 pm after 7 days of carbonation for MW 240000 samples. All of the crystal size is an average of 30 data points where the SEM images were analyzed with ImageJ software.

[0271] FIGs. 20A-20D show particle size of the carbonate phases as determined by analysis of the SEM secondary image. ii. Reaction product formation and CO2 sequestration

[0272] In FIG. 21A, a representative TGA-DTG plot of a carbonated sample after 7 days of carbonation is depicted. Similarly, all samples underwent testing and analysis after both 3 days and 7 days of carbonation. The mass losses observed in the temperature range of 500°C-800°C can be ascribed to the decomposition of CaCOa phases

[0047] . The presence of multiple DTG peaks within this temperature range was a result of the decomposition of various polymorphs of CaCOs

[0048] ,

[0049] ,

[0050] . These findings were further corroborated by SEM and XRD results. The unreacted PAA is expected to decompose at around 250°C

[0051] , which was not observed in these samples. The thermogravimetric analysis results were analyzed to obtain the total CaCO contents (%) (FIG. 21B and FIG. 21C).

[0273] It was observed that as the molecular weight increased, the CaCCh content also increased for all dosages. The overall formation of carbonate was greater at 7 days compared to 3 days, which can be attributed to the extended reaction time. Among the molecular weight groups, the batch with MW 240000 exhibited the highest total carbonate formation within the system. Additionally, in the lower molecular weight group, the 1% dosage resulted in the highest CaCOs formation. In the MW 240000 group, the 2.5% dosage led to the highest CaCCh formation. The composite with 1% MW 240000 PAA was found to contain 55% by weight CaCCE formation after 7 days of curing, which is 120% more than those observed for the control batch (25% CaCOr formation). Therefore, the addition of this molecule enhanced the carbon sequestration capacity by 120%. Interestingly, considering the balanced equation of carbonation reaction of a dicalcium silicate paste with 0.4 water to binder ratio, the maximum amount of CaCCh that can be formed is around 61% (assuming no moisture loss). Accordingly, the formation of 55% CaCOs in the carbonated sample containing 1% MW 240000 PAA indicates that nearly 90% of the P-C2S reacted within the 7 days of carbonation curing, whereas less than 50% reaction was completed after 7 days of carbonation. In short, the use of PAA, especially with a high molecular weight (e.g., 240000), significantly increased the CO2 sequestration capacity of P-C2S and thus also enhanced the efficiency of binder use.

[0274] Hi. Crystalline microstructural phase alterations

[0275] The X-ray diffraction results presented in FIGs. 22A-22F provide valuable insights into the carbonation process. In the context of the 3-day carbonation batches, a notable observation was the increased intensity of the major calcite peak (around 29° 20) in all the PAA-doped batches compared to the control batch (without PAA). Within the MW 2000 batch, both the 1% and 2.5% modifications exhibited the highest intensity of the calcite peak. Similarly, in the MW 5000 and MW 240000 batches, all modified batches (0.5%, 1%, and 2.5%) displayed enhanced calcite formation when compared to the control batch. It's important to note that in the MW 5000 and MW 240000 batches, small vaterite formations were also observed alongside calcite.

[0276] Another intriguing observation was the reduction in the P-C2S peak as the molecular weight increased. Specifically, for the control batch, the intensity of the P-C2S remained the highest even after 7 days of carbonation, and therefore, corroborating the finding of TGA that less than 50% of the reaction was completed. On the MW 240000 batches, both at 3 days and 7 days, the P-C2S peak notably decreased (approximately 32° 20) with the simultaneous increase in calcite peak intensity. This indicates that higher molecular weights accelerated and enhanced calcite formation compared to other batches. This finding aligns well with the insights gained from the previously conducted thermogravimetric analysis.

[0277] These X-ray diffraction results were further analyzed to determine the effects of PAA on the calcite crystal sizes using the Scherrer equation (FIGs. 23A and 23B). After 3 days of carbonation, the average calcite crystal size in the control batch was around 75 nm. The addition of PAA reduces the calcite crystal sizes for all the molecular weights. Furthermore, an increase in the molecular weight of PAA resulted in the further reduction of calcite crystal size. The average calcite crystal size was increased after the 7 days carbonation compared to the 3 days carbonation. For both PAA with MW 2000 and MW 5000, the smallest calcite crystal size was achieved at 0.5% dosages and then the sizes increased with increasing dosage. However, for PAA MW 240000, a linear trend was achieved where increasing dosage of PAA resulted in the smaller calcite crystals. iv. Effects of PAA on the pore size distribution

[0278] The initial findings, where the 1% dosage batch displayed the most favorable performance by forming calcite after 7 days, prompted further exploration into the effects of porosity (FIGs. 24A and 24B). In comparison to the control batch, it was observed that the 1% dosage of MW 2000 exhibited an increased critical pore diameter, leading to a higher overall porosity. In contrast, both the 1% dosage of MW 5000 and MW 240000 batches demonstrated a reduction in the critical diameter, resulting in a decreased total porosity. This decline in porosity can be attributed to the higher degree of carbonation, as indicated by the TGA analysis. The reduction in total porosity amounted to approximately 27 % and 44% for the MW 5000 and MW 240000 batches, respectively. These findings were further substantiated by the pore size distribution data obtained from MIP, which aligns with the observations from the TGA analysis. The denser microstructure resulting from these changes is anticipated to lead to improved strength performance. v. Effects of PAA on the nanomechanical properties

[0279] Grid nanoindentation technique was applied to each sample over two 60 pm x 60 pm sections, with a total of 200 indentations. FIG. 25 shows the elastic modulus (GPa) frequency distribution for the control and PAA containing P-C2S paste samples after 7 days of carbonation curing. The control batch showed the presence of three major phases with mean modulus of around 24 GPa, 31 GPa, and 40 GPa. Based on the previous studies of carbonated calcium silicates [ref-gamma c2s], the phase with 24 GPa and 40 GPa moduli are assigned to silica gel (also addressed as Ca-modified silica gel) and calcium carbonate, respectively. The microstructural phase with 31 GPa is assigned to the composite phase formed due to the mixing of silica gel and calcium carbonate. Data points showing more than 60GPa are attributed to the unreacted P-C2S grains. Noteworthy, these values are lesser than those observed for the carbonated wollastonite composites

[0052] , Such difference is expected as the modulus varies depending on the experimental setup (maximum load, loading rate), calcium carbonate polymorph and the bound water content of the silica-rich gel phase

[0053] . With the addition of PAA 2000 MW, there was no change on the above specified phase; however, a low modulus phase (-19 GPa) appeared in this composite. This low modulus phase is due to the increased porosity of the matrix as observed from the MIP data. Interestingly, with the addition of either 5000 MW or 240000 MW, new phase with a higher modulus appeared. In the case of the composite containing 1 % PAA 500MW, this new phase showed a modulus of around 45 GPa, whereas; for the 240000 MW batch, one peak appeared at around 45 GPa and another around 50 GPa. These new phases were assigned to the composite phase formed due to the binding of PAA on the calcium carbonate particles. Due to the formation of these high moduli phases, the mean modulus of composite containing 240000 MW PAA was around 10% higher than that of the control batch (34.8 GPa vs. 31.5 GPa). vi. Macroscale performance evaluation

[0280] The role PAA on the compressive and flexural strengths of the P-C2S composites were evaluated for two carbonation curing temperatures: 27 °C and 50°C. In both scenarios, the CO2 concentration and relative humidity were maintained at 20% and 80%, respectively. In FIGs. 26A and 26B, show the compressive strength results following 3 days and 7 days of carbonation at 27 °C. The addition of the PAA at all MW and dosages was observed to increase the compressive strength of the composites. In the case of low dosage batches with low molecular weight, a slight enhancement in strength was observed, with the most substantial improvement reaching up to 24% in the 0.5% dosage of the MW 5000 batch. As the dosage and molecular weight increased, the performance exhibited a significant boost. This enhancement can be attributed to the reduction in porosity and the densification of the microstructure within the samples.

[0281] Notably, among the various batches, the 1% dosage batch demonstrated the most significant improvement following the addition of PAA. Furthermore, with an increase in the molecular weight in the 1% dosage batches, the strength further improved. Specifically, after 7 days of carbonation, increases of 72%, 99%, and 106% in compressive strength compared to the control batch were observed due to the addition of 1% MW 2000, MW 5000, and MW 240000 PAA, respectively.

[0282] These findings underscore the remarkable impact of PAA doping, dosage levels, and molecular weight on the compressive strength of the specimens. The reductions in porosity and the enhancement of microstructural density contribute to the substantial improvements in strength, as evidenced by the substantial percentage increases observed across different molecular weight variations.

[0283] FIGs. 27A and 27B depict the flexural strength properties of the samples cured at room temperature. Mirroring the trends observed in compression strength properties, improvements in flexural strength properties were also evident. Specifically, an increase in the dosage from 0.5% to 1% resulted in a significant enhancement in performance. However, a 2.5% dosage did not yield better results than the 1% batch, indicating that 1% dosage was optimal for flexural strength.

[0284] Both at the 3-day and 7-day marks, the 1 % batch consistently showcased superior performance of carbonated P-C2S samples. The 1% dosage of MW 5000 exhibited a remarkable 130% improvement after 3 days and an even more impressive 156% increase after 7 days. Similarly, the 1% dosage of Mw 240000 displayed a notable 142% increment after 3 days, which further escalated to a substantial 169% improvement after 7 days. It is important to highlight that the higher molecular weight of the PAA batches corresponds to longer chain lengths. This increased chain length contributed to an enhancement in tensile properties, which, in turn, translated into improved flexural properties. Therefore, the superior flexural properties observed can be attributed to the influence of PAA molecular weight on the molecular structure and, subsequently, on the mechanical properties.

[0285] Given the notable performance of the 1% dosage batch in terms of both compressive and flexural strength properties, additional investigations with this dosage were conducted to explore the impact of temperature curing on the PAA-modified P-C2S system.

[0286] FIGs. 28A and 28B show the compressive strength results for carbonated P-C2S subjected to elevated temperature (50°C) curing. Notably, the control batch exhibited a significant improvement of 50% and 40% after 3 days and 7 days of curing, respectively, in comparison to the 27°C temperature cured batches. Similarly, the 1% PAA-modified batches displayed improved performance. After 7 days of carbonation curing at 50°C, the compressive strengths were improved by 17.5%, 35%, and 72% compared to the control batch for the addition of 1% MW 2000, MW 5000, and MW 240000 PAA, respectively. It is important to highlight that, while improvements were evident, the percent increase in compressive strength properties was not markedly higher than that of the 27°C cured batches. However, P-C2S composite cured at 27°C with 1% PAA showed a higher compressive strength compared to the batch cured at 50°C without any additive. This finding indicates that for such calcium silicate binder, the addition of PAA is more effective than the high temperature curing.

[0287] FIGs. 29A and 29B show the flexural strength of P-C2S composites carbonated for 3 days and 7 days, respectively, at 50°C. Similar to the elevated temperature cured batches for PAA-doped compressive strength samples, the flexural strength showed improvements. With increasing MW, the % enhancement in the flexural strengths also increased. The most notable enhancement in flexural strength was observed in the 1 % MW 240000 batch which showed 171% and 114% higher flexural strength compared to the control batch after 3 days and 7 days, respectively, carbonation curing.

[0288] Comparing the strength data, it is evident that elevated temperature had a positive impact on the strength performance of PAA-modified P-C2S. Accordingly, PAA remains effective in enhancing the mechanical performance of the carbonated calcium silicate composites at both tested temperatures.

[0289] The experimental analyses conducted in this study demonstrate the remarkable performance of polyacrylic acid (PAA) with different molecular weights (MW 2000, MW 5000, and MW 240000) and varying dosages (0.5%, 1%, and 2.5%) when added to carbonation cured P-C2S composites. Specifically, only around 1% by weight PAA with molecular weight of 240000 enhanced the compressive strength, flexural strength, and the CO2 sequestration capacity of P-C2S by more than 100% compared to the control batch. Based on the experimental observations, the mechanism by which PAA influences the carbonated composites are shown in FIGs. 30A-30E.

[0290] Due to the negatively charged surface sites, PAA binds calcium carbonate particles. Molecular dynamics simulation showed the formation of Ca-0 and hydrogen bonds between CaCCh and PAA which favor the adsorption of PAA on CaCC particles

[0030] . Due to the affinity of CaCCh for PAA, such polymers with or without further modifications can be used to control the polymorph crystallization and growth rates of CaCCh

[0029] ,

[0031] . The negatively charged PAA can produce CaCCh with various crystal shapes, sizes, and polymorphs (such as vaterite, aragonite, ACC) depending on the dosage, molecular weight, and temperature

[0054] ,

[0055] ,

[0056] . The superior bonding between CaCCh and PAA has been exploited to develop a variety of composites, including thin films

[0032] and hydrogels

[0033] .

[0291] When mixed with cement paste, PAA also adsorbs cement particles and forms an intermolecular network structure, which led to the use of PAA as viscosity-enhancing admixtures

[0057] . Accordingly, it is believed that in the [i-ChS paste containing PAA, the polymers initially adsorb on the P-C2S particles. However, once the CO2 curing started, i.e., the carbonation reaction started, the newly formed calcium carbonate particles preferentially deposited on the PAA network. As a result, the added PAA provides new surface areas for CaCCh particles to nucleate and, therefore, accelerates the carbonation reaction (as observed from in-situ FTIR, FIGs. 16A and 16B). A higher molecular weight PAA has a longer chain length and thus provides more surface area for CaCCh nucleation. This mechanism is reflected by the more prominent acceleration of carbonation due to the addition of PAA with 240000 MW compared to that observed for 2000 or 5000 MW. From the early age SEM images, it is also apparent that PAA adsorbed on the amorphous calcium carbonate (ACC) particles and formed thin layers on it (FIG. 30C marked with arrow) forming a composite phase of ACC-PAA.

[0292] With continued carbonation, new ACC deposits on the previous layer of ACC-PAA. As a result, PAA acts like an adhesive between the ACC particles, essentially forming ACC-PAA- ACC particles or the so-called ‘organic-inorganic’ composites. The presence of such PAA layers in between multiple ACC particles was observed in the SEM images (FIG. 30D).

[0293] With extended carbonation, more and more CaCCh particles deposit on the PAA network resulting in the formation of a three-dimensional grid-like network composed of CaCCh-PA A composites (see FIG. 30E marked with arrows). In addition to the SEM images, the formation of new CaCCh-PA A composite phases in the presence of PAA was also observed in the nanoindentation test result. Noteworthy, the adsorption of PAA on the ACC did not prevent the conversion to calcite crystals (as observed in the XRD); however, it retarded the growth of the crystals. As a result, the addition of PAA was observed to reduce the size of the calcite crystals (FIGs. 23A and 23B) but promoted the formation of larger particles through the agglomeration of calcites as observed from the image analysis (see ). Formation of this well-organized three- dimensional network of PAA-CaCCh composite phase is the primary cause of enhanced compressive strength and flexural strength of the carbonated -CFS composites in the presence of PAA.

[0294] It was further observed that the higher amounts of P-C2S carbonated due to the addition of PAA compared to the control samples. Specifically, with the addition of 0.1 wt.% of PAA 240000 MW, nearly 90% of the P-C2S reacted within the 7 days. To explain this, and without wishing to be bound by theory, it is believed that in the control batch, silica gel forms the boundary layer (z'.e., decalcified region) of the partially reacted P-C2S, and calcium carbonate particles deposit on top of that as it is the only available surface area available for nucleation. Such reaction product deposition on the grain results in a slow reaction rate which requires diffusion through the product layers and reduces the availability of P-C2S for further reaction. On the other hand, in the PAA-containing batch, the CaCO-, deposits on the polymer network keep the P-C2S surface still available for reaction (diffusion of ions only through the silica gel boundary layers). Due to this higher available surface area for reaction as well as reaction product nucleation, the addition of PAA enabled achieving a higher degree of carbonation of P- C2S samples.

[0295] An important feature underlying the superior performance of PAA-modified P-C2S binders is the molecular weight of PAA. As the molecular weight of PAA increases, so does the chain length of the polymer. The longer chains in higher molecular weight PAA molecules enable stronger binding and bridging between the components of the matrix, resulting in increased cohesion and reduced porosity. Additionally, the longer PAA chains provide a greater number of binding sites for calcium ions in the system, facilitating the nucleation and growth of calcium carbonate phases. This phenomenon leads to enhanced crystal formation, as observed in the increased CaCCh content and the formation of well-defined calcite crystals in higher molecular weight PAA batches. Past studies also revealed less effectiveness of PAA with low molecular weight (e.g., 2000 MW) to form composites due to the high mobility of these polymers in water

[0058] . It should be noted that those composites are not the same as those described in the instant studies. The dosage of PAA also plays an important role in influencing the performance of the 0- C2S binder. The findings described herein consistently point to the 1 % dosage as that with the best results, both in terms of CaCCh content and the formation of crystalline phases. At this dosage, the PAA molecules are present in sufficient quantities to initiate and regulate the formation of CaCO * phases, while not overwhelming the system to the extent of excess porosity.

[0296] In summary, the outstanding performance of PAA in modifying P-C2S binders can be attributed to its molecular weight, dosage, and their interplay with the material's porosity and microstructure. PAA acts as a bridge between components, enhances nucleation and growth of calcium carbonate phases, and influences the formation of distinct carbonate polymorphs. These mechanisms collectively contribute to the remarkable improvements in the mechanical properties of the material, making PAA a promising additive for a wide range of applications in construction and materials science.

[0297] This study has yielded new insights into the performance of polyacrylic acid (PAA) with varying molecular weights (MW 2000, MW 5000, and MW 240000) and dosages (0.5%, 1%, and 2.5%) as an additive for carbonated calcium silicate composites. Several notable findings can be summarized: i. The addition of PAA accelerated the CaCCh precipitation during the carbonation of [l-CbS. PAA with 240000 MW showed the most acceleration of carbonate precipitation, whereas there was no significant difference between MW 2000 and MW 5000 in terms of their effects on early-age carbonation kinetics. ii. The PAA-added batches achieved a higher degree of carbonation, enabling enhanced CO2 sequestration and efficient use of P-C2S compared to the control. For example, the P-C2S samples containing 1% (by wt.) PAA with 240000 MW showed around 55% by weight CaCCh formation (i.e., 24.2% CO2 sequestration), which is 120% higher than the control batch and close to the theoretical maximum value of 60%. iii. PAA-modified P-C2S binders exhibit reduced porosity and denser microstructure, with the 1 % dosage of MW 5000 and MW 240000 batches demonstrating the most substantial reductions in porosity, contributing to improved strength properties. iv. The 1% dosage of PAA, particularly with higher molecular weights, displayed remarkable improvements in strength, with increases reaching up to 106% for compressive strength and 169% for flexural strength after 7 days of carbonation at 27°C. These enhancements are attributed to reduced porosity and denser microstructure. v. When cured at 50°C, the addition of 1% PAA showed a maximum 72% and

[0298] 114% increase in compressive and flexural strengths, respectively. Interesting to note, P-C2S carbonated at 27°C with 1% PAA (either molecular weight) showed higher compressive and flexural strengths compared to the samples carbonated at 50°C without any PAA. Therefore, the use of PAA can eliminate the need for high-temperature carbonation curing.

[0299] In conclusion, this study highlights the remarkable performance of PAA as a modifier in P-C2S binders, with the molecular weight of PAA, dosage, and carbonation duration playing pivotal roles in enhancing calcium carbonate formation and improving mechanical strength. These findings point to significant benefits for the application of PAA-modified P-C2S binders in construction and materials science, where enhanced strength properties and control over carbonate polymorphs are crucial for various applications.

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[0054] S. Ouhenia, D. Chateigner, M. A. Belkhir, E. Guilmeau, and C. Krauss, “Synthesis of calcium carbonate polymorphs in the presence of polyacrylic acid,” J Cry st Growth, vol. 310, no. 11, pp. 2832-2841, May 2008, doi: 10.1016 / j.jcrysgro.2008.02.006.

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[0056] S. C. Huang, K. Naka, and Y. Chujo, “Effect of molecular weights of poly(acrylic acid) on crystallization of calcium carbonate by the delayed addition method,” Polym J, vol. 40, no. 2, 2008, doi: 10.1295 / polymj.PJ2007162.

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[0366] Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.

Claims

We claim:

1. A composition comprising a carbonation-cured cementitious material and a polyanionic polymer.

2. The composition of claim 1, wherein the polyanionic polymer comprises a polycarboxylate polymer, polyphosphate polymer, phosphorylated polymer, phosphonated polymer, sulfated polymer, sulfonated polymer, co-polymers thereof, or blends thereof.

3. The composition of claim 1 or 2, wherein the poly anionic polymer comprises a polycarboxylate polymer.

4. The composition of any one of claims 1 to 3, wherein the polyanionic polymer comprises polyacrylic acids, poly(methacrylic acids), anionic poly acrylates, anionic poly(methacrylates), poly(maleic acids), anionic poly(maleates), polyfglutamic acids), poly(aspartic acids), anionic poly (glutamates), anionic poly(aspartates), poly(fumaric acids), anionic poly (fumarates), poly(itaconic acids), anionic poly(itaconates), alginates, polystyrene sulfonates, sulfated polysaccharides, phosphorylated polysaccharides, co-polymers thereof, or blends thereof.

5. The composition of any one of claims 1 to 4, wherein the polyanionic polymer comprises polyacrylic acids, polyacrylates, co-polymers thereof, or blends thereof.

6. The composition of any one of claims 1 to 5, wherein the polyanionic polymer comprises a carbon-carbon backbone.

7. The composition of any one of claims 1 to 6, comprising between about 0.01 wt.% and about 30 wt.%, about 0.01 wt.% and about 25 wt.%, about 0.01 wt.% and about 20 wt.%, about 0.01 wt.% and about 15 wt.%, about 0.01 wt.% and about 10 wt.%, about 0.01 wt.% and about 5 wt.%, about 0.1 wt.% and about 30 wt.%, about 0.1 wt.% and about 25 wt.%, about 0.1 wt.% and about 20 wt.%, about 0.1 wt.% and about 15 wt.%, about 0.1 wt.% and about 10 wt.%, about 0.1 wt.% and about 5 wt.%, such as 0.1 wt.%, 0.5 wt.%, 1 wt.%, 2.5 wt.%, or 5 wt.% of the polyanionic polymer.

8. The composition of any one of claims 1 to 7, comprising between about 0.1 wt.% and about 30 wt.%, about 0.1 wt.% and about 25 wt.%, about 0.1 wt.% and about 20 wt.%, about 0.1 wt.% and about 15 wt.%, about 0.1 wt.% and about 10 wt.%, about 0.1 wt.% and about 5 wt.%, such as 0.1 wt.%, 0.5 wt.%, 1 wt.%, 2.5 wt.%, or 5 wt.% of the polyanionic polymer.

9. The composition of any one of claims 1 to 8, comprising between about 0.1 wt.% and about 10 wt.%, about 0.1 wt.% and about 5 wt.%, such as 0.1 wt.%, 0.5 wt.%, 1 wt.%, 2.5 wt.%, or 5 wt.% of the poly anionic polymer.

10. The composition of any one of claims 1 to 9, wherein the molecular weight (e.g., weightaverage molecular weight) of the polyanionic polymer is between about 1 kDa and about 500kDa, about 1 kDa and about 400 kDa, about 1 kDa and about 300 kDa, about 1 kDa and about 250 kDa, about 1.5 kDa and about 500 kDa, about 1.5 kDa and about 400 kDa, about 1.5 kDa and about 300 kDa, about 1 .5 kDa and about 250 kDa, about 2 kDa and about 500 kDa, about 2 kDa and about 400 kDa, about 2 kDa and about 300 kDa, or about 2 kDa and about 250 kDa.

11. The composition of any one of claims 1 to 10, wherein the molecular weight (e.g., weight-average molecular weight) of the polyanionic polymer is between about 2 kDa and about 500 kDa, about 2 kDa and about 400 kDa, about 2 kDa and about 300 kDa, or about 2 kDa and about 250 kDa.

12. The composition of any one of claims 1 to 11, wherein the molecular weight (e.g., weight-average molecular weight) of the polyanionic polymer is between about 2 kDa and about 250 kDa, such as 2 kDa, 5 kDa, or 240 kDa.

13. The composition of any one of claims 1 to 12, wherein the carbonation-cured cementitious material comprises calcium silicates.

14. The composition of claim 13, wherein the polyanionic polymer is between about 0.01 wt.% and about 30 wt.%, about 0.01 wt.% and about 25 wt.%, about 0.01 wt.% and about 20 wt.%, about 0.01 wt.% and about 15 wt.%, about 0.01 wt.% and about 10 wt.%, about 0.01 wt.% and about 5 wt.%, about 0.1 wt.% and about 30 wt.%, about 0.1 wt.% and about 25 wt.%, about 0.1 wt.% and about 20 wt.%, about 0.1 wt.% and about 15 wt.%, about 0.1 wt.% and about 10 wt.%, about 0.1 wt.% and about 5 wt.%, such as 0.1 wt.%, 0.5 wt.%, 1 wt.%, 2.5 wt.%, or 5 wt.% of the calcium silicates.

15. The composition of any one of claims 1 to 14, wherein the carbonation-cured cementitious material comprises belite, rankinite, wollastonite, tricalcium silicate (C3S), - dicalcium silicate ( -C2S), y-dicalcium silicate (y-C2S), tricalcium disilicate (C3S2), monocalcium silicate (CS), amorphous calcium silicate, calcium aluminosilicate, or a combination thereof.

16. The composition of any one of claims 1 to 15, the carbonation-cured cementitious material comprises belite, rankinite, wollastonite, -dicalcium silicate ( -C2S), y-dicalcium silicate (y-C2S), or a combination thereof.

17. The composition of any one of claims 1 to 16, comprising less than 60 wt.%, less than 55 wt.%, less than 50 wt.%, less than 45 wt.%, less than 40 wt.%, less than 35 wt.%, less than 30 wt.%, less than 25 wt.%, less than 20 wt.%, less than 15 wt.%, less than 10 wt.%, or less than 5 wt.% tricalcium silicates, such as between 0.01 wt.% and 60 wt.% tricalcium silicates, as determined using an analytical method such as thermogravimetric analysis.

18. The composition of any one of claims 1 to 17, comprising less than 60 wt.%, less than 55 wt.%, less than 50 wt.%, less than 45 wt.%, less than 40 wt.%, less than 35 wt.%, less than 30 wt.%, less than 25 wt.%, less than 20 wt.%, less than 15 wt.%, less than 10 wt.%, less than 5 wt.%, less than 3 wt.% calcium oxides, such as between 0.01 wt.% and 60 wt.% calcium oxides, as determined using an analytical method such as thermogravimetric analysis.

19. The composition of any one of claims 1 to 18, wherein the composition is a hydraulic composition, a semi-hydraulic composition, or a non-hydraulic composition.

20. Carbonated composites made from the composition of any one of claims 1 to 19, wherein the composites have (i) increased compressive strength, (ii) increased flexural strength, (iii) increased carbon dioxide sequestration capabilities, (iv) increased calcite content, (v) reduced total pore area, or a combination of (i)-(v) when compared to a composition made from similar materials that are not carbonation-cured and / or not supplemented with the polyanionic polymer.

21. A method of making the composition of any one of claims 1 to 19, or the carbonated composite of claim 20, the method comprising (i) mixing a calcium silicate-containing material with the polyanionic polymer to produce a mixture optionally in the presence of carbon dioxide, water (such as in moisture form), or both.

22. The method of claim 21, wherein the calcium silicate-containing material is in a pulverized form.

23. The method of claim 21 or 22, further comprising exposing the mixture to carbon dioxide, water (such as in moisture form), or both, during or after the mixing.

24. The method of any one of claims 21 to 23, wherein the mixture is allowed to cure at a temperature between about 20 °C and about 75 °C, about 20 °C and about 70 °C, about 20 °C and about 65 °C, about 20 °C and about 60 °C, about 20 °C and about 55 °C, about 20 °C and about 50 °C, about 25 °C and about 75 °C, about 25 °C and about 70 °C, about 25 °C and about 65 °C, about 25 °C and about 60 °C, about 25 °C and about 55 °C, or about 25 °C and about 50 °C, such as 25 °C, 27 °C, or 50 °C.

25. The method of any one of claims 21 to 24, wherein the mixture is allowed to cure in a period between 1 hour and 10 days, 1 hour and 7 days, 5 hours and 10 days, 5 hours and 7 days, 1 day and 10 days, 1 day and 7 days, 3 days and 10 days, or 3 days and 7 days.

26. The method of any one of claims 23 to 25, wherein exposing occurs in a chamber having: (al) a relative humidity between about 50% and about 90%, about 50% and about 85%, about 50% and about 80%, about 60% and about 90%, about 60% and about 85%, about 60% and about 80%, about 70% and about 90%, about 70% and about 85%, about 70% and about 80%,(a2) a carbon dioxide concentration at least 2%, such as between about 2% and about40%, about 2% and about 35%, about 2% and about 30%, about 2% and about 25%, about 2% and about 20%, between about 5% and about 40%, about 5% and about 35%, about 5% and about 30%, about 5% and about 25%, about 5% and about 20%, about 10% and about 40%, about 10% and about 35%, about 10% and about 30%, about 10% and about 25%, about 10% and about 20%, about 15% and about 40%, about 15% and about 35%, about 15% and about 30%, about 15% and about 25%, about 15% and about 20%, or(a3) a combination of (al) and (a2).

27. The method of any one of claims 21 to 26, comprising, before step (i), sintering a first mixture comprising calcium carbonate, silica, and optionally water (such as in moisture form) to produce the calcium silicate.

28. The method of claim 27, wherein the sintering is performed at a temperature between about 800 °C and about 1800 °C or between about 1000 °C and about 1800 °C, such as 800 °C, 1000 °C, 1200 °C, 1400 °C, 1600 °C, or 1800 °C.

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