Investigation on the shear behavior of RC beams strengthened with BFRP grids and PCM

The shear behavior of ten reinforced concrete (RC) beams strengthened with basalt-fiber-reinforced polymer (BFRP) grids and polymer cement mortar (PCM) was experimentally assessed. Four key factors, namely the reinforcing and bonding materials, interface treatment, and preparation method of strengthening layer, were incorporated. The contribution of the grids to the shear capacity was predicted using four different calculation methods. The results revealed that the initial stiffness of the strengthened beams consistently exceeded that of the control beam. Grid-strengthened beams exhibited a significant enhancement in load capacity under normal operating conditions, ranging from 32 % to 48 %. Additional grids comprehensively improved the shear behavior of strengthened beams compared to PCM-only strengthening. Incorporating macro basalt fibers increased both the diagonal cracking load by 38 % and reduced the diagonal crack width by 46 %, while negligibly affecting the ultimate load. The utilization of interface agents CB-720 and HPM-J effectively prevented debonding failure at PCM interface, while interface agent CBSR exhibited potential in enhancing shear behavior during the cracking stage. Precast layers demonstrated similar strengthening effects as cast-in-place ones. ACI 549.4 R is recommended to predict the contribution of the BFRP grids to the shear capacity, while CAN/CSA S6-14 is recommended for considering grids and PCM.