Toward Standardized pH Measurement for Hardened Cement-Based Materials: Influencing Factors and Measurement Guidelines.

The pH meter is a commonly used instrument in research and industries to test and monitor the pH of a process or material. However, its application in the concrete industry is not well explored. pH measurement for cement-based materials (CBMs) by using a pH meter is challenging because of these materials' high alkalinity, the fact that they do not exist as aqueous solutions, limited sample size availability, and susceptibility to carbonation. A pH electrode responds to hydrogen (H+) ions, but CBMs contain very few H+ ions because of their high alkalinity. As a result, accurate pH measurement in these materials requires a high-pH application electrode that is properly maintained to ensure reliable readings, especially for the comparing samples with small pH variation. The aim of this study is to propose guidelines and procedures for pH measurement of hardened CBMs that can be applied universally, reliably, and economically. The variables affecting the sample preparation and pH measurement stages in relation to sample processing, pH meter, and environmental factors are discussed. To accommodate different applications, this study proposes two pH measurement approaches: basic and comprehensive methods. The basic method reports the pH of the solution at the measured temperature and is suitable for the comparison of samples with a pH difference of more than 1. The comprehensive method eliminates the influence of solution temperature and generates a solution temperature-compensated pH (pHSTC) that represents pH at 25 °C. This method is suitable for the comparison of samples with a pH difference of less than 1 and for pH monitoring across different seasons. Test demonstrations using the developed methods is performed for validation purposes.