Strengthening fire damaged light weight high strength reinforced concrete beams through BFRP grid and ECC jackets

The development of the rehabilitation techniques for post-fire deteriorated lightweight reinforced concrete beams (LWC) has been significantly advanced through the incorporation of a composite reinforcement material comprised of Basalt fiber reinforced polymer (BFRP) grid and Engineered Cementitious Composite (ECC).This progress is attributed to the impressive mechanical properties of BFRP grid and the self-healing capabilities of ECC.This article presents an experimental study aimed at strengthening deteriorated reinforced lightweight high-strength concrete beams that have been exposed to high temperatures. The study introduces the performance of a retrofitting technique that combines a basalt fiber-reinforced polymer (BFRP) grid with Engineered Cementitious Composites (ECC) to create a composite reinforcement layer (CRL), known as a u- shaped jacket to increase and re-store the capacity and strength of fire-damaged beams. The study involved fourteen reinforced lightweight concrete beams(LWC), including both control (undamaged) and damaged beams, which were exposed to fire for different durations (30 and 60 min with three-faced fire exposure (bottom and two sides). The specimens that were strengthened by the proposed U-shape jacket method were subjected to two point loading test in the lab, and the results showed that the repaired LWC beams demonstrated an improved and increased maximum load-bearing capacity, ductility, and stiffness when compared to fire-damaged LWC beams. Therefore, the performance of the BFRP grid and ECC jacket repair method was thoroughly discussed in terms of maximum load-bearing capacity, displacements, ductility, and stiffness. The retrofitting composite material (U-shape jacket) enhances, restores the shear strength and transforms the failure pattern from shear to pure flexural crack behavior after repair. The study observed flexural cracks behavior in the BFRP grid-ECC composite layer and rupture of the BFRP grid for the retroffited LWC beams with no debonding of the BFRP grid and ECC layer. Subsequently, the proposed repair technique provides a viable strengthening solution by combining the exceptional mechanical properties of BFRP with the ductility and self-healing capabilities of ECC.