Experimental determination of crack-bridging constitutive relations of hybrid-fiber Strain-Hardening Cementitious Composites using digital image processing

Abstract

This study explored the potential benefits of employing hybrid polyvinyl alcohol (PVA)/steel fibers in Strain-Hardening Cementitious Composites (SHCCs) at the single-crack level. Due to the multiple-cracking nature of SHCCs with tight crack spacing, direct measurement of the crack-bridging constitutive relation for a single crack is challenging, as any reasonably sized physical gauge length would cover a number of subparallel cracks, therefore masks the true value of crack opening. In this study, a new test method using Digital Image Processing to capture the opening of a single crack in a double edge-notched specimen under tension was proposed. Compared to the commonly-used single-crack tension method, the proposed method obtained a more satisfactory crack-bridging relation for SHCCs. With the test results from the new method, it was found that hybrid-fiber SHCCs have the potential to show smaller crack widths than PVA-SHCCs, and the hybridization of PVA/steel fibers results in a positive synergetic effect at the single-crack level under uniaxial tension. In addition, the pseudo-strain-hardening indices were used to evaluate the potential of achieving tensile strain-hardening of hybrid-fiber SHCCs. The findings of this study can support future designs of SHCCs for the experimental determination and model calibration of the crack-bridging relations, and provide a better understanding of fiber hybridizations in SHCCs.