Quantitative analysis of steel fiber-matrix ITZ and multi-scale enhancement mechanism of SFRC

In this study, the enhancement mechanism of steel fiber reinforced cement-based composite was investigated by quantitative analysis of the fiber-matrix interfacial transition zone (ITZ) and the corresponding fiber pull-out behavior. Silica fume was selected as a typical mineral admixture with modification effects. The fiber-matrix ITZ microstructure was innovatively characterized by backscattered-electron image analysis, EDS map scanning mode combined with image analysis, and micro-hardness test. Pull-out tests were performed to determine the bond strength and pull-out energy, and the anchorage force and normalized slip-hardening shear stress during fiber pull-out were calculated. The macro mechanical performances were also analyzed and discussed. The results showed that although the improvement effect of silica fume was less significant in the ITZ than in the bulk paste, the gaps, defects, and aggregated calcium hydroxide around the fiber were improved effectively. The increased calcium silicate hydrate and contact area strengthened the bonding established between fiber and matrix, and the denser microstructure and harder matrix resulted in the enhanced anchorage force and slip-hardening effect. The flexural performance was improved by strengthening interfacial bond properties by silica fume, whereas silica fume increased the compressive strength through improving matrix microstructure.