Mechanical Properties and Deformation Characteristics of Hybrid Fiber Strain Hardening Cementitious Composites Based on Digital Image Method

To reveal the law of influence of hybrid fibers on the mechanical properties and deformation behavior of strain hardening cementitious composites (SHCC), the tensile and compressive properties of basalt-polyvinyl alcohol(PVA) fiber strain hardening cementitious composites (SHCC) were investigated at a constant fiber content of 2% (in volume fraction), different content ratios of basalt fiber and PVA fiber (i.e., 3:1, 1:1 and 1:3), and different ratios of fly ash to cement (FA/C) (i.e., 1.2, 1.5 and 2.0). The direct tensile and compressive strengths of hybrid fiber SHCC with different fly ash contents were analyzed. The horizontal and vertical strain evolution and crack development of the sample during compression were discussed via digital image correlation (DIC). The results show that the compressive strength of the mixed fiber specimens is greater than that of the single fiber specimens, indicating that the hybrid fiber can effectively improve the compressive strength. At FA/C ratios of 1.2 and 1.5, the optical fiber type is B0.5P1.5 (i.e., the volume fraction of basalt fiber is 0.5% and PVA fiber is 1.5%). At a FA/C ratio of 2.0, the optical fiber type is B1P1. The optical fiber type is different for different fly ash admixtures, indicating that the fly ash admixture affects the optical fiber type. In the hybrid fiber specimens, basalt fibers mainly play a role in improving the strength, but it is not suitable for the ductility of the material. In contrast, incorporating PVA fibers can effectively enhance the material's ductility, the addition of hybrid fibers can enhance the mechanical properties. The DIC can effectively characterize the strain evolution and crack formation and propagation process of the material, thus providing an effective method for investigating the material damage and crack evolution in the loading process.