Study on deterioration of concrete subjected to sulfate attack in cold regions and its countermeasures

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In this study, the deterioration of concrete structures exposed to sulfuric acid, sulfate, and chloride were researched. Additionally the patterns with the combined deterioration between these factors and freeze/thaw attack and its mechanism were investigated. From these experiments, the following conclusions were drawn.The testing results of soaking mortar and concrete specimens in sulfuric acid solution revealed that the deterioration of concrete is more accelerated with low water-cement ratio compared to high water-cement ratio. Further it was indicated that the deterioration rate of concrete by sulfuric acid was predicted as a function of water-cement ratio, sulfuric acid concentration, and the period of soaking in sulfuric acid.From the testing results with the combined deterioration between seawater and freeze/thaw attack, it was recognized that the influence of sodium chloride in seawater on the deterioration is remarkably more than that of magnesium sulfate and the deterioration pattern is mainly governed by scaling from the concrete surface. On the other hand, it was confirmed that the combined deterioration between sulfuric acid and freeze/thaw attack induces remarkable scaling and the mass loss caused by scaling increases as water-cement ratio and sulfuric acid concentration increase. Further it was shown that this type of combined deterioration could be evaluated by superimposing the deterioration curves by the sulfuric acid attack considering the scaling rate at low temperatures and freeze/thaw attack.Finally it was recognized that the internal evaluated strength distribution of concrete by needle penetration testing method includes much variation depending on the deterioration pattern and this testing method is not always suitable for evaluating concrete strength.