A Study on Evaluation Method of pH in Concrete Applying Multiple Indicators

Phenolphthalein method is utilized as the general diagnosis method on neutralization of concrete. However, this method cannot satisfy to indicate the soundness of reinforced concrete. In this research, the applicability of phenolphthalein method to the specific evaluation and prediction of neutralization was evaluated through the analytical and the experimental method. As a result, analytical estimation using image processing on pH distribution of cement hydrates was possible by multiple indicators: two concentrations of phenolphthalein solution and 0.4 % concentration of tropaeolin O solution. It was also clarified that visual inspection method using two types of indicator (1.0 % concentration of phenolphthalein solution and 0.4 % concentration of tropaeolin O solution) can give sufficient and accurate information about the relationship between the discolored pH and its depth from surface of concrete. Finally, new evaluation method was proposed for specific evaluation on neutralization of concrete considering the remaining neutralization time.