Bond strength and flexural performance of repair composites incorporating nanofibrillated cellulose (NFC) modified mortar

This study investigates the influence of Plain and 0.1% NanoFibrillated Cellulose (NFC) modified repair mortar mixtures on the bond strength and flexural performance of composite and monolithic beam specimens. First, the effect of the NFC on the slant shear and flexural bond strength of repair mortar overlays was assessed. Thereafter, repair mortar thicknesses ranging from 25 to 50 mm were overlaid on concrete substrates, and flexural strength and toughness of specimens were evaluated. Furthermore, the effect of hybrid combination of the NFC and steel macro fiber on the flexural toughness and strain evolution of monolithic Fiber Reinforced Concrete (FRC and FRC + 0.1% NFC) beams were also evaluated. Test results showed that the NFC enhanced the slant shear and flexural bond strengths of repair mortar by about 35% and 43%, respectively. Flexural strength capacity of composite beams generally increased as the repair mortar thickness was raised from 25 to 50 mm. Relative to the single-layer FRC beam, concrete substrate overlaid with 50 mm thick Plain + 0.1% NFC mortar showed about 56% increase in flexural strength. However, a post-crack toughness superior to that of the single-layer FRC beam was only achieved using 25–35 mm thick Plain + 0.1% NFC repair mortar as overlays. Furthermore, with the combination of NFC and steel fiber as discrete reinforcements in FRC, the bending strength, static modulus and toughness of beams were also enhanced.