Effect of carbonation on the chloride diffusion of mortar specimens exposed to cyclic wetting and drying

Carbonation and chloride ingress are the two main causes of corrosion in reinforced concrete structures. Despite the combined action of these mechanisms being a reality, there is little research on the effect of carbonation on the chloride diffusion in concrete. This work intends to study the influence of carbonation on chloride diffusion of mortar specimens. Cubic mortar specimens were cast with 0.55 of water-cement ratio. After curing, the specimens were subjected to 56 days of wetting and drying cycles. Half the samples were immersed for a day in a 3.5% NaCl solution and then placed for 6 days in a carbonation chamber (4% CO₂); the other half were also kept a day in 3.5% NaCl, but after were kept during 6 days in laboratory environment. Afterwards, the depth of chlorides and CO₂ penetration was evaluated. Complementary tests were also carried out, such as rapid chloride migration coefficient and water capillary absorption. The results show that carbonation has a direct influence on chloride penetration, decreasing it. The noncarbonated samples showed a profile with higher amount of chloride than carbonated ones. This fact can be related to the refinement of the mortar pores caused by carbonation and observed in water absorption tests.