Effect of nano silicon nitride on the microstructural characteristics and mechanical properties of ultra-high-performance steel fiber reinforced concrete

Abstract This study investigates the incorporation of an innovative nano-reinforcement, nano silicon nitride (NSIN), to enhance the workability and mechanical performance of ultra-high-performance fiber reinforced concrete. The addition of NSIN at dosages of 0.25, 0.5, 0.75, and 1.5 wt% of cement was analyzed to evaluate its impact on the distribution and interaction between steel fibers and the cementitious matrix. Experimental analyses, including thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and scanning electron microscopy (SEM), were conducted to establish a relationship between the microstructural modifications, fiber-matrix interactions, and the resulting mechanical behavior. The findings revealed that NSIN increased workability and extended setting time, enabling improved steel fiber dispersion and interaction with the matrix. This, in turn, reduced macroporosity around the fibers, enhancing the matrix integrity. TGA indicated a reduction in free calcium hydroxide, corroborating the observed strengthening of the matrix. Furthermore, the addition of 0.75 wt% NSIN yielded the optimal results, with a 17.3% improvement in compressive strength and a 66% increase in crack propagation resistance during the elastic phase. These results highlight the potential of NSIN as a nano-reinforcement to significantly improve the mechanical and microstructural properties of UHPFRC.