Assessing carbonation depth using pH indicators: A comparison between phenolphthalein and thymolphthalein indicator

Carbonation in concrete reduces alkalinity and increases the risk of steel reinforcement corrosion in the presence of moisture. Carbonation depth measurement using pH indicator is a widely used and standardised approach for assessing the carbonation-affected region in concrete for concrete durability evaluation. This study compares the carbonation depth obtained using phenolphthalein and thymolphthalein indicators in cement mortars and concretes subjected to natural and accelerated carbonation in a widely used and standardised approach of assessing the carbonation-affected range in cement combinations with varying clinker contents. Results demonstrate that the use of 1% thymolphthalein indicator provides similar carbonation depth to 1% phenolphthalein solution, confirming its usage for carbonation depth measurement in laboratory evaluation and for condition assessment in the field structures subjected to ambient carbonation.