Study on the shear strength and damage constitutive model of the contact surface between PVA fiber-enhanced cement mortar and concrete

In this study, a polyvinyl alcohol (PVA) fiber-enhanced cement mortar (PFCM) with high workability, early strength, and high strength was developed. The influences of water content (w), strength, and surface roughness (Rd) of concrete on the shear strength of its contact surface with PFCM were experimentally investigated, followed by the establishment of damage constitutive model. The PFCM was found to be suitable for spraying and achieved a compressive strength of 102.8 MPa and a flexural strength of 19.6 MPa at 28 days. At 3-7 days, its compressive and flexural strengths reached about 79-80% and 83-90% of the 28-day strength, respectively. The shear load and fracture energy release rate of the PFCM and Concrete contact surfaces is between 6.13 kN and 12.09 kN and 1.13 J/m2 to 2.20 J/m2, respectively, both increasing with the increasing w, strength and Rd of concrete. The increased w of concrete from 0.0% to 5.5% could reduce the porosity and capillary pore content of PFCM by about 43% and 50.4%, respectively, and the increased Rd could enhance the interlocking effect between PFCM and concrete. The damage function proposed based on the Najar energy theory could reflect the evolution characteristics of shearing damage of PFCM and Concrete contact surface, and the damage constitutive model proposed by combining the Weibull statistical distribution function and Guo Zhenhai model could reflect the shear mechanical behavior of the PFCM and Concrete contact surface.