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

This paper presents a study on the carbonation reaction heat and products of tricalcium silicate (C(3)S) paste exposed to carbon dioxide (CO(2)) for rapid curing. Reaction heat was measured using a retrofitted micro-calorimeter. The highest heat flow of a C(3)S paste subject to carbonation curing was 200 times higher than that by hydration, and the cumulative heat released by carbonation was three times higher. The compressive strength of a C(3)S paste carbonated for 2 h and 24 h was 27.5 MPa and 62.9 MPa, respectively. The 24-h carbonation strength had exceeded the hydration strength at 28 days. The CO(2) uptake of a C(3)S paste carbonated for 2 h and 24 h was 17% and 26%, respectively. The X-ray diffraction (XRD), transmission electron microscope coupled with energy dispersive spectrometer (TEM-EDS), and (29)Si magic angle spinning–nuclear magnetic resonance ((29)Si MAS-NMR) results showed that the products of a carbonated C(3)S paste were amorphous silica (SiO(2)) and calcite crystal. There was no trace of calcium silicate hydrate (C–S–H) or other polymorphs of calcium carbonate (CaCO(3)) detected.