Carbonation behavior of hydraulic and non-hydraulic calcium silicates: potential of utilizing low-lime calcium silicates in cement-based materials

Abstract

This paper presents a study on the carbonation behaviors of hydraulic and nonhydraulic calcium silicate phases, including tricalcium silicate (3CaOÁSiO 2 or C 3 S), c-dicalcium silicate (c-2CaOÁSiO 2 or c-C 2 S), b-dicalcium silicate (b2CaOÁSiO 2 or b-C 2 S), rankinite (3CaOÁ2SiO 2 or C 3 S 2 ), and wollastonite (CaOÁSiO 2 or CS). These calcium silicate phases were subjected to carbonation reaction at different CO 2 concentration and temperatures. Thermogravimetric analysis (TGA) tests were performed to quantify the amounts of carbonates formed during the carbonation reactions, which were eventually used to monitor the degree of reactions of the calcium silicate phases. Both hydraulic and non-hydraulic calcium silicates demonstrated higher reaction rate in case of carbonation reaction than that of the hydration reaction. Under specific carbonation scenario, non-hydraulic low-lime calcium silicates such as c-C 2 S, C 3 S 2 and CS were found to achieve a reaction rate close to that of C 3 S. Fourier transformed infrared (FTIR) spectroscopy and scanning electron microscope (SEM) tests were performed to characterize the carbonation reaction products of the calcium silicate phases. The FTIR spectra during the early stage of carbonation reaction showed formation of calcium silicate hydrate (C-S-H) from C 3 S, c-C 2 S, b-C 2 S, and C 3 S 2 phases with a similar degree of polymerization as that of the C-S-H that forms during the hydration reaction of C 3 S. However, upon further exposure to CO 2 , these C-S-H phases decompose and eventually converted to calcium-modified (Ca-modified) silica gel phase with higher degree of silicate polymerization. Contradictorily, CS phase started forming Ca-modified silica gel phase even at the early stage of carbonation reaction. This paper also revealed the stoichiometry of the Ca-modified silica gel that formed during the carbonation reaction of the calcium silicate phases using the SEM/energy dispersive spectroscopy (EDS) and TGA results.

Early Age Carbonation Heat and Products of Tricalcium Silicate Paste Subject to Carbon Dioxide Curing

“…The silicate phases reported by other researchers, such as C–S–H [9,10,11], calcium silicate hydrocarbonate [12], or Ca-modified silica gel [14], were not found in this study. Figure 16 shows the molecular structure of C 3 S, C–S–H, amorphous SiO 2 , and different Q n in their structure.…”

“…Shtepenko et al [13] used 29 Si magic angle spinning–nuclear magnetic resonance ( 29 Si MAS-NMR), XRD and a scanning electron microscope coupled with an energy dispersive spectrometer (SEM-EDS) to analyze the carbonation of β-dicalcium silicate (β-C 2 S), and concluded that polymerized silica, calcite, and aragonite were the main products. Ashraf and Olek [14] believed that Ca-modified silica gel and CaCO 3 crystal were the main products of C 3 S carbonation. From the above studies, it was indicative that the carbonation products of C 3 S could be classified into two phases: silica phase and calcium carbonate phase.…”

Carbonate-bonded construction materials from alkaline residues

“…Chemicals such as NaOH can be added to accelerate and enhance the process even further [7]. Most recent research developments in producing CO 2 uptake cements depart from calcium (and magnesium)-rich materials and relate to 1) accelerated curing of concrete [8][9][10], 2) carbonation of brines [11][12][13], 3) carbonation of hydrated lime [14,15] and 4) carbonation of calcium silicates [16][17][18][19].…”

Effect of Solidification and Cooling Methods on the Efficacy of Slag as a Feedstock for CO₂ Mineralization

“…To quantitatively assess the importance of mineralogy in CO 2 mineralization, Bodor et al 20) and Ashraf and Olek 21) reacted synthetic minerals common to slag using autoclave reactors. These mild conditions are consistent with processes that may result in net CO 2 Table 1, indicate ~2 orders of magnitude variation in PL thickness between the minerals studied.…”

“…pres., 95% humidity, 20% CO2 § Data from Ashraf and Olek. 21) Experimental conditions: incubator reactor, 35°C, atm. pres., 94% humidity, 15% CO2 a: Tridymite; b: Cristobalite; c: Pseudowollastonite; d: Wollastonite; e: Calcite; f: Aragonite; g: Vaterite alization by less reactive species.…”