Effect of Cement Type on the Concrete Resistance to Chloride Penetration over Time

To predict the reinforcement corrosion, it is usually considered that the chloride diffusion coefficient decreases with time due to the refinement of the pore structure and this phenomenon is usually called “concrete ageing”. The predictions of the service life, carried out for instance through the Model Code for Service Life Design, proposed by the fib in 2006, are significantly affected by the ageing factor that has been identified to mainly depend on cement type. In the literature several methods have been proposed to consider the ageing in transport parameters, as concrete bulk diffusion tests or electrical resistivity tests. In this paper the ageing factor was evaluated on concretes made with three different types of cement (Ordinary Portland cement, Portland-Limestone cement and Pozzolanic cement) and two water/cement ratios (0.45 and 0.55) through the pure diffusion immersion test, performed after different exposure times (from 32 to 540 days) and the rapid chloride migration test, performed after different curing times (from 7 to 540 days in moist curing regime). The ageing factors obtained from the two different tests were comparable. Considering Portland and Portland-Limestone cement, and by averaging results obtained for the two water/cement ratios, values between 0.3 and 0.4 were obtained. Conversely, for concrete made with pozzolanic cement significantly higher values were evaluated.