The overall aim of this paper is to establish the process and amount of chlorides penetrating reinforced concrete elements when exposed to a salt-laden environment. For this purpose, a number of slabs were subjected to 70 cycles of wetting-drying regime with a 4% sodium chloride solution over a period of 2-3 years. To examine the direction of transportation of the chlorides, some of the slabs were partially coated with a surface coating system known to be highly resistant to chloride penetration. The amount and depth of penetration of chlorides in the coated and uncoated parts of the slab were then determined. The results show conclusively that, in large exposed areas of concrete, chlorides diffuse both in the direction of depth and in a direction lateral to the depth of the element. The amount of chlorides and the distance of their lateral diffusion depend on the water-to-cement (w/c) ratio of the concrete and the duration of exposure. Concrete mixes with a high w/c ratio (0.75) are highly conducive to this lateral diffusion of chlorides. Although concrete mixes of lower w/c ratios (0.45 and 0.60) are less conducive to lateral diffusion of chlorides, in practice, all concretes should be considered to be prone to chloride diffusion in both the direction of gravity and the lateral direction because of the effects of cracking. In unprotected concrete, reducing the w/c ratio from 0.60 to 0.45 is far more effective in decreasing chloride penetration than that achieved by reducing the w/c ratio from 0.75 to 0.60. The acrylic-based surface coating system is totally resistant to chloride penetration.Key words: chloride diffusion, concrete slabs, durability, water-to-cement ratio, surface coating, lateral diffusion.
Analysis Technique for Chloride Penetration using Double-layer and Time-Dependent Chloride Diffusion in Concrete
