Proposal of a digital image analysis method for determining the carbonated front in concretes

Abstract

Carbonation is one of the most common pathologies in concretes and the correct determination of the depth reached by this process is essential to predict the lifespan of a structure. The most common method for measuring carbonation is to spray a phenolphthalein solution onto the concrete and then measure the colorless area of the solution. Traditionally, such measurement is done manually through visual assessment. However, as this is a subjective assessment, this process is subject to errors. In order to minimize these errors, researchers have used image editing processes and measurements obtained with computerized tools. Even using these programs, the process still depends on the operator’s sensitivity and judgment to determine the areas affected by carbonation. This work proposes a digital analysis with the assignment of phenolphthalein turning pH values in order to obtain the carbonated front limit with greater precision and in a semi-quantitative way. For this, three admixtures of concrete with pozzolans (fly ash and rice husk ash) were analyzed in binary and ternary mixtures submitted to natural carbonation. The proposed method proved to be accurate and efficient as an aid in reading carbonated depths.