A graphical method for assessing the concrete strength class in existing RC structures

This paper aims to provide the reader a simple graphical method for the estimation of the concrete strength class (CSC) in existing reinforced concrete structures, which may be adopted even using limited concrete core drillings (less than three per test region) when compared to actual practice (European standards). The method is based on a combined probabilistic/empirical model for material properties of in situ concrete compressive strength and age-hardening effects. Assumptions are according to Eurocodes. The procedure has been subjected to a rigorous validation process. The principle of this approach is to use two graphs to mimic the role that in situ compressive strength test results play in determining the CSC of existing structures at the ages of the core drilling and of the construction time (28 days). Basis for the method are few considerations on: (a) age of concrete; (b) exposure environment; and (c) type of cement. Information from the two graphs is combined allowing valid and reliable estimates to be drawn. The proposed method is intended to be used as a clear alternative to classic methodologies and will be useful for professionals working in the field of structural rehabilitation. It reduces invasiveness, time expenditure and labour cost while maintaining high accuracy in estimations. Furthermore, it provides extra information about the concrete strength development that may be used to explore alternative scenarios in safety analyses.