Role of nano-SiO₂ in improving the microstructure and impermeability of concrete with different aggregate gradations

Permeability is a significant and key property of concrete, and aggregate gradation is one factor that can affect the properties of concrete. Therefore, the aim of this study is to explore the improvement characteristics of nano-SiO₂ on the microstructure and impermeability of concrete with different aggregate gradations. Two innovative test procedures have been applied in this research to obtain the parameters related to permeability: water permeability and real-time monitoring of water sorptivity. In addition, kernel density estimation and step function fitting are used to statistically characterize and quantify the microstructure features of samples. The results reveal that different aggregate gradations induce diverse types of defects. When the Fuller exponent (q) ranges from approximately 0.4–1.0, the microstructure of concrete is the densest and the impermeability is the strongest, in the meantime, the roles of nano-SiO₂ become much clearer in weakening the connectivity of microdefects and improving the impermeability of concrete.