Relationship between the particle size and dosage of LDHs and concrete resistance against chloride ingress

The present study investigates the transport properties of cement mortar with Ca-Al-NO3 layered double hydroxides (LDHs). A co-precipitation method is applied to synthesize the Ca-Al-NO3 LDHs and the effect of the synthesis environment on the size and particle shape is studied. The synthesized Ca-Al-NO3 LDHs are analytically characterized by XRD, SEM and FTIR analyses. The relationships between the sizes and addition amount of Ca-Al-NO3 LDHs and the mechanical and transport properties of mortars are investigated. Rapid chloride migration (RCM) tests are performed to the cement mortars with Ca-Al-NO3 LDHs. The results show that permeability of the designed concrete decreased with the addition of Ca-Al-NO3 layered double hydroxides (LDHs). The decrease of chloride migration coefficients can be attributed to the enhanced barrier effect because of the increase of tortuosity. In long-term natural diffusion tests, LDHs present significantly enhanced barrier effect due to the combined chloride binding ability and improved tortuosity.