Indicator of carbonation front in concrete as substitute to phenolphthalein

Abstract

A method to substitute the recognized toxic phenolphthalein in mortars and concretes is proposed. It comprises putting a portland cement sample in contact with an innocuous solution, curcumin-based, which acts as an indicator yielding a red color in areas where there is alkaline reserve (pH ~ 12) and yellow in carbonate zones (pH $\leq$ 9).

Solutions containing curcumin extracted from commercial turmeric powder and from the rhizomes of the turmeric plant were prepared by using ethanol as a solvent. Subsequently it has been experienced with solutions in which curcumin has been used with a purity of over 95%.

The dissolution of curcumin can be used with the same reliability as phenolphthalein in the carbonation process with the advantage that it is safe and presents no health risks.