Contribution of fiber-matrix interface enhancement on flexural properties of Ultra-high-performance concrete

Herein, the effect of steel fiber-matrix interface reinforcement on the macromechanical properties of ultra--high-performance concrete (UHPC) is studied. Two types of nano-SiO2-coated steel fibers are prepared using the sol-gel method. Single-fiber pull-out tests are conducted, and flexural and compression tests of UHPC with fiber contents of 1 vol%, 2 vol%, and 3 vol% are performed. The results reveal that the enhancement of inter-facial adhesion significantly influences the macromechanical properties of UHPC. However, the granular nano-SiO2 on the surface of the modified steel fibers increases the roughness of the steel fiber and reduces the fluidity of fresh UHPC mixture. Analysis of the images of crack section reveals that appropriate vibration can reduce the influence of the steel fiber surface roughness on the distribution of fibers in UHPC. A flexural load-deflection response model for UHPC that considers steel fiber-matrix interface bond strength and fiber orientation is established.