A Study on Flexural Enhancement in Beam Strengthened with CFRP Plate and Toughened Mussel Epoxy as Bonding Agent

Abstract

Structural concrete beams in old and historic buildings are not designed to resist increasing applied loads. Therefore, flexural beam strengthening is mandatory. Fibre Reinforced Polymer (FRP) is used as a reinforcing material to increase its flexural loading resistance. In structural retrofitting, carbon fibre reinforced polymer (CFRP) plates, composed of carbon fibres bonded with epoxy resin, have grown in popularity. However, the inherent brittleness and low shear strength of neat epoxy resin require modification with fillers such as micro-silica and zirconia. As a sustainable alternative, mussel powder, which is rich in calcium carbonate (CaCO?) compound, acts as a rigid bio-filler, enhancing the toughness, bonding strength, and impact resistance of pure epoxy resin. This study incorporates 7.5% volume fraction of mussel powder into epoxy resin, an optimized percentage reported in previous findings?. The selection of a 7.5% composition was justified as it demonstrated improved mechanical performance without significantly compromising the workability of the resin?. The research investigates the influence of varying CFRP plate lengths (ranging from 50 mm to 250 mm) bonded with 7.5% Toughened Mussel Epoxy (TME) by volume fraction on the flexural strength of plain concrete beams. Four-point bending tests were conducted to record failure modes, load-displacement behavior, and ultimate load capacities. Results indicate that longer CFRP plates enhance load-carrying capacity, with 200 mm CFRP length exhibiting an optimal balance between material efficiency and structural performance, leading to a 26% increase in strength compared to unstrengthened beams?. Failure modes varied with CFRP length; shorter plates primarily exhibited shear failure, while longer plates (i.e., CFRP length more than 200 mm) displayed delamination failure. The study concludes that using a 200 mm CFRP plate with TME provides a significant improvement in flexural strength, offering a cost-effective and environmentally friendly alternative to conventional strengthening techniques .