Behaviour of concrete under severe environment: effect of carbonation on the chloride diffusion coefficient from non-steady-state migration test

Abstract

To ensure the durability of concrete structures it is necessary to understand its behaviour in the presence of aggressive agents. Carbonation and chloride ingress are the two main causes of degradation in reinforced concrete. The combination of these factors can create a very harsh environment for concrete structures. Given the importance of chloride migration coefficient for areas such as service life prediction, this work intends to study the influence of carbonation on the chloride migration coefficient of ordinary Portland cement (OPC) concrete. Concrete specimens were cast with different water-cement ratios: 0.4, 0.5 and 0.6. After 90 days of curing, half of samples were subjected to carbonation chamber (4% CO2, 20 ºC and 55% RH) for 6 months. The other half was protected with plastic sheet during the same period. Non-steady-state migration test was performed in specimens with and without exposure to carbon dioxide environment. The results show that, for these conditions, the carbonation has a direct influence on chloride diffusion coefficient, increasing it. The carbonated samples studied showed a chloride migration coefficient up to 130% higher than noncarbonated ones. This fact can be related to the reduce in chloride binding capacity caused by carbonation front.