Image analysis for determination of cement content in concrete to improve accuracy of chloride analysis

The chloride content at the level of the reinforcement expressed as %Cl by weight of cement is an important parameter in condition assessment of reinforced concrete structures. Whereas standardized procedures are available to determine the chloride content in concrete powder, the cement content is assumed equal to the mix design or even as constant value. This work shows that the cement content in thin slices of 50 mm diameter concrete cores with maximal aggregate diameter 32 mm varies between 8.4% and 24.1% (bulk: 13.8%). A procedure based on colouring the cement paste, scanning the specimen surface, and image analysis allows the non-destructive determination of the cement content with good accuracy. It is concluded that a reliable determination of the chloride content in terms of %Cl by weight of cement requires the analysis of both the chloride and cement content in a concrete specimen.