Comparative Study on the Carbonation-Activated Calcium Silicates as Sustainable Binders: Reactivity, Mechanical Performance, and Microstructure

Abstract

Calcium silicate minerals can react with CO2 to form calcium carbonate and have been proposed to be a sustainable binder as a potential CO2 sinker. In this study, the carbonation characteristics are comparatively assessed among calcium silicates having different calcium/silica (Ca/Si) ratios and polymorphs (CS, C3S2, γ-C2S, β-C2S, C3S). Calcium silicate compacts exposed to a 100% CO2 environment at a 0.4 MPa pressure were tested for carbonation temperature evolution, degree of carbonation (DOC), mechanical properties, and microstructural characterization. Results indicate γ-C2S is the most reactive, reaching a DOC of 50% in 24 h, followed by C3S2, CS, β-C2S, and C3S, which generally agrees with the pattern of the cumulative normalized temperature increase. Meanwhile, carbonated β-C2S compact attains the highest compressive strength of 80 MPa in 24 h, followed by γ-C2S, C3S2, and C3S, while CS only reaches 20 MPa. Calcite and aragonite are the preferable polymorphs of calcium carbonate in the carbonated C3S, γ-C2S, β-C2S, and C3S2, while only the carbonation of CS generates vaterite in addition to calcite and aragonite. The unreacted grains coated by a thin rim of calcium-modified silica gels are encapsulated by the continuous calcium carbonates, which composes the skeleton of the carbonated calcium silicates.

Screening Out Reactivity-Promoting Candidates for γ-Ca2SiO4 Carbonation by First-Principles Calculations

“…The details about the materials preparation and testing procedures can be attained by consulting our previous study (Mu et al, 2018(Mu et al, , 2019.…”

“…Besides, compared with the polymorph β-Ca 2 SiO 4 , γ-Ca 2 SiO 4 also showed much higher carbonation reactivity (Chang et al, 2016). Mu et al (2019) found that the γ-Ca 2 SiO 4 samples exposed to a 100% carbon dioxide environment under high pressure achieved mechanical properties in hours equivalent to that of the hydration product of a cement clinker hydrated for days, which provides a perspective of using carbonation-activated cementitious materials to reduce the dependence on alite-and belite-based cementitious materials. Theoretically, the use of γ-Ca 2 SiO 4 carbonation instead of cement clinker hydration not only reduces the carbon dioxide emissions from clinker production but also sequestrates the released carbon dioxide in a natural way, i.e., mineralization (Ashraf, 2016).…”

Effect of Extended Carbonation Curing on the Properties of γ-C2S Compacts and Its Implications on the Multi-Step Reaction Mechanism

“…1,5,9 The carbonated matrix is composed of continuous calcium carbonates encapsulating the isolated unreacted particles and the surrounding silica gels. 24,27 Mu et al assumed that the low porosity, abundant, and compact calcium carbonates are the essential traits of the high strength. 27 Depending on the distinguished physical and chemical properties required for different applications, the reaction pathway for the carbonation must be designed and optimized.…”

“…24,27 Mu et al assumed that the low porosity, abundant, and compact calcium carbonates are the essential traits of the high strength. 27 Depending on the distinguished physical and chemical properties required for different applications, the reaction pathway for the carbonation must be designed and optimized. Therefore, the reaction mechanism and kinetics are worth to be investigated.…”

Improvement of the Hydration Kinetics of High Ferrite Cement: Synergic Effect of Gypsum and C3S–C4AF Systems

“…Cement production is an extensive energy consumption and high CO 2 emission industry, which accounts for about 5% of CO 2 emission and 12–15% energy consumption. − Researchers have been working on new types of cementitious materials and low carbon materials to reduce their environmental impact. , A green energy-saving clinker containing lower C 3 S (≤50 wt %) content and higher C 4 AF (≥20 wt %) can calcinate at a lower sintering temperature in comparison with that of Portland cement, which is called high ferrite cement (HFC), and it can reduce effectively the energy consumption and emissions in clinker production, possessing a wide range of application prospects.…”