Comparison of methods to determine the carbonation depth in fly ash blended cement mortars

Abstract

Carbonation negatively affects the durability of steel-reinforced concrete structures by causing a decrease in pore solution pH, thus facilitating corrosion which eventually leads to cracking and spalling. Different analytical methods for assessing carbonation depth were compared on carbonated cement mortar samples, including blended samples in which up to 40% of the ordinary portland cement (OPC) were substituted for Type C coal fly ash (FA). The methods included the measurement of CaCO3 concentrations by FTIR, the dust digestion method which provided and apparent pH profile, the traditional phenolphthalein method, and computerized image-processing methods based on the use of different pH indicators (thymolphthalein, phenophthalein, and alizarin) or changes in mortar colour due to carbonation.