Effects of filler carbonates on magnesium-oxide based pastes

Abstract

In this study, the influence of mineral admixtures on magnesium oxysulfate (MOS) pastes was investigated, specially the replacement of MgO by carbonates and their effects on hydration kinetics, microstructure and mechanical properties. In this way, Thermal analyses (TG/dTG), Scanning Electron Microscopy (SEM) and Calorimetry were applied. Further investigation has been conducted to verify the compressive and flexural strength of these matrices. Results indicate that carbonate powders allow decreasing the molar ratio (MgO/MgSO4) and can also control the amount of water available in the hydration process. Lower MgO replacement and higher H2O/MgSO4 molar ratio provided better flexural strength results than the compressive strength. Furthermore, carbonate replacement reduces hydration temperature and accelerate the hydration process, affecting the 5-phase formation and mechanical properties, especially in some pastes with higher MgO replacement and higher molar ratio H2O/MgSO4 molar ratio. Therefore, despite being considered an inert mixture, carbonate fillers can act in the hydration process.