Workability and Mechanical Properties of Tensile Strain–Hardening PVA Fiber-Reinforced Magnesium Phosphate Cement Composites

To solve the inherent brittleness of magnesium phosphate cement (MPC)-based composites, we incorporated polyvinyl alcohol (PVA) fibers to develop tensile strain hardening fiber reinforced magnesium phosphate cement composites (SHFRMC). The effects of fly ash (FA) content, PVA fiber volume fractions ($V_f$), the sand to binder mass ratio (S/B), and the water to solid mass ratio (W/S) on the workability, compressive strength, and tensile properties of the SHFRMC were studied. Lastly, the micromorphology of PVA fibers and their bonding with the matrix was examined by the optical microscope test. Generally, when the FA content is 30%, the SHFRMC can achieve relatively high strength and strain capacity while maintaining good workability; the SHFRMC can achieve relatively high workability, strength, and strain capacity when the $V_f$ is 1.8%; when the S/B is 0, the workability, strength, and strain capacity of the SHFRM are the highest; and when the W/S is 0.13 or 0.16, the SHFRMC can achieve relatively high strength and strain capacity while maintaining good workability. The results revealed that a trade-off was needed among the workability, compressive strength, direct tensile stress, and tensile strain. The optical microscopy test showed that PVA fiber connects well with the matrix and plays an important bridging role in the tensile process to bear stress and restrain crack development, resulting in multicracking.