Moisture transport and steel rebar corrosion in repair composites incorporating Nano-Fibrillated Cellulose (NFC)

Abstract

Repair of deteriorating concrete infrastructure remains a major challenge. The concern is that current repair materials are not able to prevent premature failure after a repair has been performed. Thus, an engineered repair mortar that can enhance the durability of repaired composites by mitigating moisture transport and its debilitating influence on deterioration mechanisms such as steel rebar corrosion would be highly coveted. In this study, the influence of reinforcing a repair mortar with 0.1% by volume of Nano-Fibrillated Cellulose (NFC) on the capillary water transport in monolithic and composite specimens was investigated. Micro Computed Tomography (CT) imaging was also utilized in evaluating the microstructure of sorptivity test specimens. Thereafter, the influence of repair mortars on the corrosion behavior of deformed steel rebar was investigated via natural and accelerated tests. In these tests, concrete substrates had an embedded rebar in it, and repair mortars were applied on the top creating a composite specimen with a repair interface. Some of the parameters measured were surface resistivity, half-cell potential, overlay delamination time, residual rebar pullout load and rebar corrosion degree.Sorptivity tests indicated that the NFC is indeed capable of refining the pore structure through internal curing and thus reducing the capillary uptake of water. Moreover, the tendency of the NFC to entrap micro voids, especially near the repair interface, thereby indirectly reducing moisture transport and saturation of composite specimens was confirmed by CT imaging. Natural and accelerated corrosion test results demonstrated that NFC addition inhibited rebar corrosion as indicated by reduced rebar corrosion degree and delayed delamination of the repair overlay. The NFC also provided superior surface resistivity and a higher rebar pullout load capacity after corrosion.