The Effect of Water/Cement Ratio on the Sulfate Corrosion of Fine Grained Concrete

Abstract

Sulfate corrosion is one of the major threats for durability of concrete constructions and it becomes a major destructor in sewage collection systems where concrete sewer pipes are exposed to sulfates from waste water as well as from biogenic activity of bacteria. The second type of corrosion is termed microbiologically induced concrete corrosion (MICC) and during this process the pH of the surface of concrete sewer pipes is reduced and it may lead to steel depassivation and results in the corrosion of this steel reinforcement. This paper is focused on the sulfate attack on fine grained concrete where the effect of 0.5% sulfuric acid emulating MICC and also effect of solution simulating sewage water on the concrete samples with three different water/cement ratios (w/c = 0.4, 0.45 and 0.5) have been investigated. After 1, 3 and 6 months of the corrosive treatment the content of sulfate ions and pH values in several layers of specimens were determined. It was found that the sulfate ions penetrate into concrete to maximum depth of 20 mm and the pH of the aqueous leaches of particular layers of the samples was reduced to 11.92 at the most. Thus, the conditions for the depassivation of reinforcement were not met.