*Article* **Study of the Interfacial Bond Behavior between CFRP Grid–PCM Reinforcing Layer and Concrete via a Simplified Mechanical Model**

**Huijuan Dai 1, Bo Wang 2,\*, Jiawei Zhang 2, Junlei Zhang <sup>3</sup> and Kimitaka Uji <sup>3</sup>**


**Abstract:** This paper presents the results of pull-out tests conducted to investigate the interfacial bond behavior between a carbon-fiber-reinforced polymer (CFRP) grid–polymer cement mortar (PCM) reinforcing layer and existing concrete, and proposes a simplified mechanical model to further study the interface bond mechanism. Four specimens composed of a CFRP grid, PCM, and concrete were tested. The influence of the type of CFRP grid and the grid interval on the interface bond behavior was discussed. The failure patterns, maximum tensile loads, and CFRP grid strains were obtained. The change process of interface bond stress was investigated based on the grid strain analysis. In addition, the simplified mechanical model and finite element model (FEM) were emphatically established, and the adaptability of the simplified mechanical model was validated through the comparative analysis between the FEM results and the test results. The research results indicate that a CFRP grid with a larger cross-sectional area and smaller grid interval could effectively improve the interface bond behavior. The tensile stress was gradually transferred from the loaded edge to the free edge in the CFRP grid. The interface bond behavior was mainly dependent on the anchorage action of the CFRP grid in the PCM, and the bond action between the PCM and the concrete. The FEM results were consistent with the test results, and the simplified mechanical model with nonlinear springs could well describe the interface bond mechanism between the CFRP grid–PCM reinforcing layer and concrete.

**Keywords:** CFRP grid; PCM; interface; mechanical model; pull-out test; finite element analysis
