Durability and Interfacial Properties of Concrete with Nanosilica-Modified Mortar Cover

Durability is a major concern with concrete structures. The ion transport properties of concrete cover can greatly influence the durability of concrete structures since most of the deterioration starts from the surface. The study described here focused on improvement of the durability of conventional concrete (CC) by covering it with nanosilica-modified mortar cover (NMMC). NMMC was designed according to the Dinger-Funk particle-packing model. The results revealed that mortar with low porosity and high strength could be produced by utilizing this particle-packing model, and that the durability of CC could be greatly improved when it was covered with NMMC: the chloride diffusion coefficient decreased by 95.12% and the Coulomb electric flux decreased by 97.02%. The NMMC also increased the freeze-thaw resistance of CC: the mass loss of CC+NMMC was only 1.72% after 300 rapid freeze-thaw cycles. Further, NMMC can significantly improve the carbonation resistance of CC. Almost no carbonation was observed after CC+NMMC was put into a chamber for carbonation for 28 days. The NMMC and CC had comparable drying shrinkage. Through fluidity adjustment and roughing of the NMMC surface, the bonding strength between NMMC and CC reached 5.4 MPa. Scanning electron micrography (SEM) showed a compact bonding between NMMC and CC.