Using thymolphthalein for accelerated carbonation testing of high volume fly ash cementitious blends

Abstract

Phenolphthalein is the most common pH indicator used to measure the carbonation depth of cementitious materials. It is simple and quick to use, but according to some authors, is not an appropriate tool. Moreover, this substance is in the candidate list as a substance of very high concern by European Chemicals Agency. This article discusses the use of thymolphthalein rather than phenolphthalein. Accelerated carbonation tests were performed on cement mortars and high volume fly ash mortars. Once this kind of mixtures has low carbonation resistance additional alkalinity was provided by adding hydrated lime during its fresh mixture, and by curing the samples immersed in a calcium hydroxide solution. The results showed that the best indicator was the thymolphthalein, mainly for blends with lower carbonation depth. It was also checked that adding alkalinity can be useful for increasing the carbonation resistance.