Impermeability, Strength and Microstructure of Concrete Modified by Nano-Silica and Expansive Agent

The impermeability of concrete is very important to its durability and service life, which could be affected by nanomaterial and mineral admixture additions. This paper tends to enhance the impermeability, strength, and microstructure of concrete using nano-silica (NS) and U-type expansive agent (UEA). The slump flow, compressive strength, chloride ion resistance, water penetration and absorption, hydration, and microstructure of concrete are investigated under different NS and UEA contents. The results indicate that an appropriate NS content of 2% contributes to dense pore structure and the generation of more hydration product for impermeability-enhanced concrete, which results in a compressive strength of 43.53 MPa and chloride ion and water penetration resistance improvements of 21% and 35%, respectively. The slump flow and compressive strength of concrete decrease slightly in the presence of UEA utilization, while the chloride ion and water penetration resistances are firstly enhanced and then weakened with the increase in UEA contents. In the case of 9% UEA, the concrete achieves a compressive strength of 31.54 MPa, a chloride ion penetration coefficient of 9.34 × 10−12 m2/s, and a relative permeability coefficient of 2.56 cm/s.