Corrosion Resistance and Physical-Mechanical Properties of Reinforced Mortars with and without Carbon Nanotubes

Following the evolution of currently enforced Performance Based Design standards of reinforced concrete (RC) structures for durability, the designer, rather than complying with given prescriptive limits, may instead specify a cementitious mix design that is proven to exhibit a code prescribed resistance level (class) to a given exposure environment. Such compliance will lead to the protection of the steel reinforcement from corrosion and the cementitious mortar from degradation, during the design lifespan of the structure, under aggressive environmental exposure conditions such as, marine or deicing salts and carbonation. In this context, the enhancement of the physical and durability properties of common cement-based mortars under chloride exposure are experimentally investigated herein. In particular, the experimental program reported herein aims to evaluate the influence of incorporating multi-walled carbon nanotubes on the physical and mechanical properties of reinforced mortars against chloride ions. Furthermore, the anticorrosion protection of cementitious composites prepared with nanomaterials at 0.2% w/w is further investigated, by comparing all test results against reference specimens prepared without any additive. Electrochemical (Half-cell potential, corrosion current) and mass loss of reinforcement steel measurements were performed, while the porosity, capillary absorption and flexural strength were measured to evaluate the mechanical and durability characteristics of the mortars, following a period of exposure of eleven months; SEM images coupled with EDX analysis were further recorded and used for microstructure observation. The test results indicate that the inclusion of the nanomaterials in the mix improved the durability of the mortar specimens, while the nano-modified composites exhibited higher chloride penetration resistance and flexural strength than the corresponding values of the reference mortars. The test results and the comparison between nanomodified and reference mortars showed that the use of CNTs as addition led to protection of steel reinforcing bars against pitting corrosion and a significant improvement in flexural strength and porosity of the mortars.