Research on the influencing mechanism of nano-silica on concrete performances based on multi-scale experiments and micro-scale numerical simulation

In this study, multi-scale experiments and micro-scale numerical simulation were used to comprehensively analyze the influencing mechanism of nano-silica (NS) on the concrete performances. With the NS content increases, the results indicate that the concrete performances are improved first and then deteriorated, and the optimum NS content is 2%. By improving the physical and mechanical properties of cement paste and meliorating the interface transition zone (ITZ) structure, 2% NS increases the compressive strength of the concrete sample cured for 28 days by 23.04%. Meanwhile, it can be found that 2% NS makes the pore structure the most refined and maximizes the compactness of concrete through the nuclear magnetic resonance technology, making concrete the best resistance to chloride ion penetration. Through numerical simulation, it can be found that the concrete added with 2% NS has the better resistance to external force than the concrete without NS, and the reason for the improvement is that 2% NS enhances the mechanical properties of ITZ and mortar. Although 5% NS meliorates the ITZ structure, it deteriorates the physical and mechanical properties of cement paste, which makes the compressive strength of concrete sample cured for 28 days decrease by 7.91%.