Effectiveness of coated carbon fibre cementitious matrix systems for flexural strengthening of concrete beams

Fibre reinforced cementitious matrix (FRCM) composites are suitable solutions for structural retrofitting of various materials due to their high strength-to-weight ratio and good compatibility. The mechanical performance of FRCM depends on the properties of the textile, of the mortar and the adherence between fibre and matrix and between matrix and substrate, thus requiring proper characterization of the interfacial behaviour. In this research, 16 concrete beams reinforced with 3 different single-layer and double-layer FRCM systems were subjected to three-point bending tests. The matrices were two enhanced mortars and a conventional mortar, and the textile was a bidirectional carbon grid. At the midspan, a 70 mm notch was performed and the internal rebars were disconnected, to isolate the performance of the FRCM. Strain was monitored during the test using Digital Image Correlation (DIC). Ultimate strength for beams with the same fibre volume varied by up to 60 % depending on the mortar, with a minimum ultimate load of twice that of the control beam. The beams with two textile layers had better performance, although the fibre exploitation ratio decreases with two layers. The ultimate strength of FRCM applied in beams is superior to that obtained in tensile tests for all the compared systems. • Three-point bending tests were conducted on FRCM-reinforced concrete beams. • Stress-strain curves of FRCM are similar in tensile tests to when applied to beams. • The fibre exploitation ratio is higher for single-layer reinforcements. • The best system in terms of ultimate load had 4.5 times that of the control beam.