Possibilities of using alizarin and neutral red indicators to determine the neutralized layer of concrete in the field

Abstract

The article concerns with the prospects of using the phenolphthalein test solution in the practice of surveying concrete and reinforced concrete building structures in planta. The problem of the study is the limits of application of the phenolphthalein test solution on the pH level of the determined concrete (the indicator works only at 8≤rn≤10). There is a need of expanding the phenolphthalein test solution application. In order to determine the different pH zones of concrete we have to modernize the method by adding other indicators to phenolphthalein. The standard phenolphthalein test solution does not allow a high degree of accuracy in determining the most sensitive to carbonation boundary zones of concrete. We proposed to modernize the phenolphthalein sample solution by using additional acid-base indicators alizarin and neutral red. We presented the results of experiments on measuring the surface neutralized layer of concrete by alcoholic solutions of acid-base indicators alizarin and neutral red on different age and size concrete samples. As a result, one of the proposed indicators (neutral red) allows to expand the phenolphthalein test solution application. We compared the results obtained by the traditional and modified methods. According to it, the proposed modified method is more accurate one.