Durability and microstructure of cementitious composites under the complex environment: Synergistic effects of nano-SiO2 and polyvinyl alcohol fiber

As the most commonly used construction material for marine buildings, cementitious composites are exposed to a complex environment of coupled action of relative humidity, temperature, and chloride salts erosion, which severely impacts the safety and longevity of marine buildings. The effect of nano-SiO2 dosage on the durability of polyvinyl alcohol fiber-reinforced cementitious composites (PVAF-RCC) for the preparation of marine buildings under the complex environment was investigated in this work. The complex environment with the temperature of 50 degrees C, relative humidity of 100%, and chloride salt concentration of 5% was simulated by the environment chamber. The cementitious composites exposed to the complex environment for 30 d were tested for antipermeability, anti-chloride ion penetration, frost resistance, and chloride salt erosion resistance. Furthermore, the pore characteristics of the cementitious composites and the micromorphology of nano-SiO2, matrix, and fibers were characterized and analyzed by the combination of scanning electron microscope and mercury intrusion porosimetry tests. Results revealed that the durability of cementitious composites improved initially and subsequently decreased with rising the dose of nano-SiO2 under the complex environment. PVAF-RCC consisting of 1.5% nano-SiO2 obtained the best durability. As the nano-SiO2 dosage increased, the total porosity and cumulative porosity of PVAF-RCC decreased first and subsequently increased. Nano-SiO2 refined and improved the pore structure of PVAF-RCC and the interface between matrix and PVA fibers through its filling effect and participation in the hydration reaction to generate C-S-H gels with filling effect to convert more harmful and harmful pores into less harmful or harmless pores, thus enhancing the compactness and durability of cementitious composites under the complex environment.