Carbonation of magnesium oxysulfate cement and its influence on mechanical performance

Abstract

In order to popularize magnesium oxysulfate (MOS) cement in civil engineering, it is very necessary to investigate its carbonation related durability. It was found that carbonization can increase compressive and flexural strength of MOS cement to some extent and compressive strength of MOS cement increases gradually at first, then decreases during carbonation process. The displacement to ultimate compressive force of hardened MOS cement paste carbonated for 28 days is larger than that of non-carbonated one at the same age. Evaporable water testing and X-ray computed tomography (X-CT) were adopted to examine the porous structure of MOS cement paste with and without carbonation. It was found that carbonation refines the meso-pore (≧38 µm meters) volume ratio of hardened MOS cement with 0.5 water-to-cement ratio by about 17%. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were adopted to analyze the carbonation characteristics of MOS cement. The results indicate that magnesium hydroxide and some basic magnesium oxysulfate phase are obviously neutralized with carbon dioxide to form magnesium carbonate phases in the hardened MOS cement, which leads to the refined porous structures and corresponding increased toughness.