Multiscale investigation on tensile properties of ultra-high performance concrete with silane coupling agent modified steel fibers

Ultra-high performance concrete (UHPC) is a new generation of cementitious composites that exhibit excellent compressive strength and durability. However, the poor bonding between steel fiber and UHPC matrix usually results in insufficient tensile properties and limits its application. Here, the surface of steel fibers is modified with silane coupling agent (SCA) to enhance fiber/matrix bond. The macroscale workability, flexural and tensile properties of UHPC are investigated. It has been found that SCA modifications contribute to strength enhancement and cracking behavior improvement of UHPC, and its energy absorption capacity increases 13.8%. The microscale characterizations of fiber/matrix interface are conducted through scanning electron microscopy, energy dispersive spectrometer and Fourier transform infrared spectroscopy. The mechanisms behind the enhancement have been revealed and classified into mechanical friction, chemical bonding and physical adhesion. This work provides a green and effective approach for promoting tensile properties and an in-depth understanding of SCA modification mechanisms.