Axial Compressive Behavior of Predamaged Concrete Cylinders Retrofitted with CFRP Grid-Reinforced ECC

A fiber-reinforced polymer grid-reinforced engineered cementitious composite (FRPECC) is a promising strengthening composite that addresses the drawbacks of FRP and textile-reinforced mortar (TRM). The present study focused on the axial compressive behavior and constitutive models of predamaged concrete repaired with carbon FRP grid-reinforced ECC (CFRPECC). The test parameters included predamage level, grid number, and concrete strength. The test results indicated that compared with plain concrete, the peak stress (strength), strain at peak stress (peak strain), and energy dissipation capacities of CFRPECC-retrofitted predamaged concrete increased by 9%–82%, 28%–96%, and 60%–322%, respectively. The improvement increased with the number of CFRP grids and ECC thickness but decreased with concrete strength. On the other hand, the strength and elastic modulus of concrete after retrofitting degraded with an increase in the predamage level, especially when the concrete was severely damaged, while the peak strain and lateral rupture strain were barely influenced. When the predamage level increased, the enhancement of strength decreased from 41%–106% to 9%–60%. CFRPECC directly carried 11.0%–22.7% of the strength of the retrofitted concrete columns. The enhancements of strength and elastic modulus after retrofitting were mainly attributed to the confinement and axial stiffness of CFRPECC, respectively. Further, models for the strength, peak strain, and stress–strain relationship were developed for CFRPECC-retrofitted predamaged concrete. The applicability of the proposed models was verified by test results of the existing studies.