A simplified approach for the evaluation of old concrete strength

To design retrofit and/or conservation of existing reinforced concrete structures, the assessment of concrete strength is generally required. The current methodologies consist of destructive tests (DT), based on uniaxial compression tests performed on concrete cores extracted from a structure, and/or non-destructive tests (NDT), in which the strength of concrete is indirectly estimated by measuring other physical properties (like the ultrasonic pulse velocity). Nevertheless, in several situations (like, e.g., the seismic vulnerability assessment of long-term service structures), the traditional DT and NDT cannot be used. Hence, a new simplified approach is introduced and described in this paper. It can be applied to structures located in a precise geographical area, where the average strength of concrete (and the relative percentiles) is a function of the year of construction. Such relationship is summarized by the so-called “strength curves”, statistically computed from a huge database stored in the Department of Structural and Geotechnical Engineering of Politecnico di Torino (Italy). Referring to a concrete dam built during the 1950s, the strength predicted by these curves is in good agreements with the measurements of DT.