Improvement of water resistance in magnesia cements with renewable source silica

Abstract Due to growing consumption of Portland cement, the employment of Rice Husk Silica (RHS) was analyzed as eco-friendly material for improving the water resistance of Sorel cements, such as Magnesium Oxysulfate (MOS) cement and Magnesium Oxychloride (MOC) cement, which have incipient application in civil engineering, due to presence of soluble or expansible phases when exposed to humidity or water. In Brazil, an alternative process has been efficient in the RHS production with higher amorphicity and reactivity. Thereby, considering the action of RHS on soluble phases and Magnesium Silicate Hydrated (M-S-H) formation, composites were produced in this study replacing MgO mass with RHS to verify its influence on mechanical properties, water resistance, and microstructure of the magnesia cements. Thus, the composites produced were cured in air and warm water conditions. Mechanical tests at 28 days were associated to microscopy electronic images and X-ray diffractograms. Results indicated higher expansion and soluble phases for MOC than for MOS composites. Also, all composites based on MOS cement show better stability in water, especially when a higher amount of RHS was adopted. It is concluded that MOS cement technology associated to RHS addition is an effective, environmentally sound technology for alternative building materials production.