Effect of modified nano-SiO2 on properties and microstructure of the high-performance cementitious composites

•Nano-SiO2 was modified with silane coupling agents KH550 to resolve the agglomeration problem of nano-SiO2.•The influences of modified nano-SiO2 on the service performances such as workability, mechanical properties, shrinkage, and durability of HPCC were comprehensively investigated.•The hydration process, hydration products and microstructure of HPCC were investigated via different characterization methods. The effect of modified nano-SiO2 (MNS) on the performance of high-performance cementitious composites (HPCC) was investigated and the underlying mechanism was revealed by various microscopic analysis and testing methods. Results indicated that the fluidity of HPCC initially increased and then decreased with the increase of MNS content. Meanwhile, The HPCC with 0.8% MNS exhibited a 25% increase in compressive strength at the curing age of 3 days, while the HPCC with 0.8% nano-SiO2 showed a 10% increase. Compared with the reference mixture, the durability and autogenous shrinkage of HPCC with MNS were significantly improved, the chloride diffusion coefficient of HPCC with 0.8% MNS decreased by 25.9%. Furthermore, the quantitative analysis results of hydration process and hydration products show that the inclusion of nano-materials accelerated the hydration rate of cementitious composites, resulting in increased cumulative heat release. HPCC with MNS exhibited a higher generation of amorphous phases and greater consumption of calcium hydroxide compared with reference mixture. Moreover, the addition of MNS effectively refined the pore size of HPCC and converted some harmful pores into less harmful or harmless pores, enhancing the microstructure of HPCC with MNS and improving the interface transition zone. This optimization was mainly attributed to the effect of filling, nucleation of crystal and pozzolanic reactive of nano-materials, which further benefit from the good dispersion of MNS, resulting in excellent mechanical properties and durability of HPCC.