Characteristic microstructural phase evolution and the compressive strength development mechanisms of tricalcium silicate pastes under various initial carbonation curing environments

The effects of various initial carbonation curing environments on the phase evolution and resulting mechanical characteristics of tricalcium silicate paste were studied. For the analyses of the reaction products and microstructure, synchrotron X-ray diffraction, thermogravimetry, Fourier transform-infrared spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy and high-resolution X-ray computed tomography were utilized. C₃S cured under carbonation environment pressurized by 0.1 MPa showed excellent mechanical properties owing to the highest degree of reaction and homogeneous generation of CaCO₃ with low-Ca/Si calcium silicate hydrates, resulting in a dense matrix with refined pore structure. C₃S paste treated under other carbonation conditions underwent deteriorative microstructural phase transitions, including void evolution by decalcification of C–S–H and an inhomogeneous composition of crystalline phases, resulting in inferior properties.