Graphene oxide–silica nanocomposites reinforced mortars: Mechanical properties, permeability and microstructure

•0.05 wt% GO-nanoSiO2 improves the mechanical properties and chloride penetration resistance of mortar most effectively.•GO-nanoSiO2 reduces the total porosity of mortar and optimizes the pore structure.•GO-nanoSiO2 decreases the porosity and Ca(OH)2 enrichment in ITZ between aggregate and matrix and makes the microstructure of ITZ more uniform. The purpose of this work is to study the effect of graphene oxide-silica nanocomposites on the mechanical properties, transport properties and microstructure of mortar, to reveal the working mechanism of GO-nanoSiO2 to improve the properties of mortar, so as to fully understand the mechanical and physical behavior of GO-nanoSiO2 reinforced mortar. The macroscopic test results showed that adding 0.05 wt% GO could improve the compressive strength, fracture toughness and chloride penetration resistance of mortar most effectively. The compressive strength, initial fracture toughness and unstable fracture toughness increased by 15.1%, 92.2%, and 64.7%, and the non-steady state chloride migration coefficients decreased by 49.6%. The microstructure of mortar was studied by MIP, SEM and multifractal analysis. The results showed that the addition of GO-nanoSiO2 reduces the total porosity and optimizes the pore structure of mortar, resulting in the reduction of large pores, the improvement of the homogeneity of pore distribution, and the formation of pores with poor pore connectivity, which is conducive to improving the impermeability of mortar. In the interface transition zone between aggregate and matrix, the addition of GO-nanoSiO2 decreases the porosity and Ca(OH)2 enrichment. The decrease of ITZ porosity and the presence of GO-nanoSiO2 nanosheets in ITZ can inhibit the crack propagation, thus contributing to the improvement of macroscopic fracture properties of mortar.