Retrofitting of severely damaged RC beams using novel bio-composite-based mat-matrix system

Due to the rapid urbanization and boom in the infrastructure sector, the frequency of repair and retrofitting in major structures has significantly increased in recent times. Hence, it is essential to adopt a repair/retrofit strategy that not only improves the load-carrying capacity but is also ductile, durable, and cost-effective. In this study, efforts are put forth to develop a novel bio-composite-based mat-matrix strengthening system for restoring the overall performance of severely damaged reinforced concrete (RC) beams. In total, eight full-scale RC beams of span 2.2 m were tested under two different shear span (a v ) to effective depth (d) ratios of 5.0 and 3.9 to understand the efficiency of proposed strengthening schemes under flexure and shear load combinations. The initial loading of RC beams (i.e. damage phase) showed intense opening of tension cracks in the constant moment zone and crushing at the compression face of the beam. After failure, all the beams were surface prepared and retrofitted with the novel bio-composite mat-matrix system using different combinations of bi-directional flax/ hemp fiber mat and discrete flax/hemp fiber based UHTCC matrix. The parameters investigated include (i) type of bio-fiber mat, (ii) type of discrete bio-fiber in UHTCC matrix, and (iii) shear span (a v ) to effective depth (d) ratio. Results revealed that the proposed composite system was able to completely restore the overall performance of severely damaged RC beams at low a v /d ratios. However, in the case of beams with flexure-dominant failure (high a v /d), the strengthening system was able to restore about 90% of the ultimate load.