Neutralization of Concrete under Weak Sulfuric Acid Environment
By Toshio Yonezawa, Yasunori Matsufuji, Shizuo Harada, Tomoyuki Koyama, Etsutaka Maeda and Kyoichi Tanaka
Concrete Research and Technology
Vol.20, No.3, Sep. 2009 (Issue 51)
- Synopsis:
- Concrete structures are vulnerable to such acid environments as hot springs, sea origin soils and sewage plants. It is normally difficult for concrete to resist acid effects under the environment of pH less than 3 to 4; other measures as coating are necessary. It is rather important to understand durability of concrete under weak acid environment of pH 4 to 5 where concrete structures are normally exposed to the acid effects without protective measures. The durability of concrete under the environment, however, has not been sufficiently clarified yet. In particular, long term exposure test has been rarely carried out. In this study characteristics of neutaralization of concrete were studied based on 15 years' exposure tests to soil of pH 4 to 5 and atmosphere of SO2 concentration of 5 to 40 ppm. It was shown that neutralization of concrete under the weak sulfuric acid environment is very different from ordinary carbonation; a dormant period of neutralization exists due to densified surface layer. The layer was shown to be formed by ettringite based on EPMA analysis, X-ray diffraction analysis and Vicker's hardness measurement. Finally neutralization rate equations for concrete under weak sulfuric acid environment are propoesed based on the above results.
- Keywords:
- sulfuric acid, weak acid environment, neutralization, ettringite, neutralization rate equation, durability design
