Resistance of the composite cementitious system of ordinary Portland/calcium sulfoaluminate cement to sulfuric acid attack

•Sulfuric acid resistance of OPC-CSA composites was studied.•The degradation mechanism of OPC-CSA composites was analyzed.•OPC-CSA composites exhibit the potential resistance to sulfuric acid attack. The sulfuric acid resistance of the composite cementitious system of ordinary Portland cement (OPC)/calcium sulfoaluminate (CSA) cement is presented in this paper. Specimens were exposed to sulfuric acid solution for 70 days, and deterioration was evaluated in terms of visual appearance, mass change, and compressive strength loss. The microstructure was analyzed using X-ray diffraction (XRD) and scanning election microscopy coupled with energy dispersive spectrometry (SEM/DES). The results indicate that OPC-CSA composites have the potential to improve the corrosion resistance of the cement matrix to sulfuric acid. Moreover, the results demonstrated that the deterioration mechanism of composites exposed to sulfuric acid was based on a combination of shrinkage and expansion caused by simultaneous leaching of main elements and gypsum deposition and growth. The SEM/EDS observation showed that the composites enhanced resistance to sulfuric acid attack by reducing the penetration depth of harmful ions.