Durability Evaluation of Concrete Subject to the Attack of Corrosive Acidic Substances

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The purpose of this study is to comprehensively evaluate durability of concrete subject to the attack of both weak and strong acids. Corrosive weak acid includes carbon dioxide, while corrosive strong acid includes sulfuric acid of which typical deterioration is found in sewage and wastewater treatment plants. In this study, research on the effects of weak and strong acids on concrete deterioration was carried out.Regarding the research on the effect of weak acid on concrete deterioration, consideration of the rates of chemical reaction associated with carbonation of concrete was investigated. Using synthesized C-S-H, ettringite, monosulfate and Friedel's salt, simulation tests for carbonation of cement hydrates were carried out and a modeling for decomposition of C-S-H, ettringite, monosulfate and Friedel's salt due to carbonation was developed considering their rates of carbonation reaction. Compared with a current model, the proposed model showed better agreement with experimental results. The necessity of consideration of the rates of chemical reaction in modeling was suggested.Regarding the research on the effect of strong acid on concrete deterioration, the effects of pH, use of mineral admixtures and a flow of solution on deterioration of concrete were investigated. Cement paste and mortar specimens containing blast furnace slag, fly ash and silica fume were prepared and immersed in sulfuric acid solution at pH=1.0 and 2.0. Some of the specimens were immersed in flowing solution. A flow was generated by circulating the solution with a pump. As a result, erosion of specimens immersed in flowing sulfuric acid solution at pH=2.0 was accelerated compared with that immersed in static solution, while erosion of specimens immersed in static and flowing sulfuric acid solutions at pH=1.0 was almost the same. Therefore, a shearing force acting on the surface of a specimen could accelerate erosion due to sulfuric acid attack according to the value of pH.