Long-Term Chloride Accumulation on Concrete Surface in Marine Atmosphere Zone—Modelling the Influence of Exposure Time and Chloride Availability in Atmosphere

Abstract

Surface chloride concentration (Cs) is a key parameter used to feed models adopted to simulate chloride penetration into concrete and evaluate the initial period of corrosion. Although there are several models that have been proposed for the representation of Cs behaviour in the marine atmosphere zone, such models are still scarce. In this context, we analysed the behaviour of surface chloride concentration in concrete specimens exposed over 12.5 years in a marine atmosphere zone in the northeast of Brazil. The experimental work was carried out in two steps: environmental characterization, which was undertaken for temperature, relative humidity, rainfall, wind characteristics and sea-salt data; and chloride concentration measurements for the concrete surface considering three different concrete mixtures with w/b ratios of 0.65, 0.57 and 0.50. The results showed that the Cs increase over time followed three stages: a first short stage characterised by an initial dispersion, followed by an increase period and then a final period of stabilisation, which was not fully reached in the present study. This behaviour can be represented by a power function or a sigmoidal function, with a better fit with the latter. Chloride concentration in the atmosphere plays an important role in Cs behaviour. Higher availability of chlorides means higher Cs values. The relationship between Cs and the rate of chloride deposition on a wet candle was analysed and the function Cs=C0+kcs·(Dac)n was the one that best fit the experimental data.

Keywords

• concrete
• corrosion
• marine atmosphere zone
• surface chloride concentration