One-Year Sulfate Attack on Various Types of Fine Grained Concrete

Abstract

Concrete shows extensive degradation when exposed to the external sulfate attack, characterized by ingress of sulfate ions from surrounding medium. This process leads to gradual pH decrease, to expansion, cracking, spalling of concrete, and finally to the complete disintegration of the material. Sulfate attack becomes a major destructor in sewage collection systems where the concrete sewer pipes are exposed to sulfates from wastewater as well as from biogenic activity of bacteria. This paper is focused on the sulfate attack on fine grained concrete where the effect of 0.5% sulfuric acid, simulating biogenic sulfuric acid corrosion, 5% sodium sulfate solution and solution simulating sewage water on various types of concrete has been investigated. The concrete specimens were characterized after exposition to corroding media by their mechanical parameters, microstructure and in the case of H2SO4 as the most aggressive corroding solution, the mineralogical composition was also determined by XRD analysis. It was found that the exposition to Na2SO4 solution twofold improved flexural strengths of concrete mixes based on Portland and sulfate-resisting cements. Contrary, the exposition to H2SO4 solution significantly decreased compressive strengths of all types of concrete.