Influence of carbonation depth on concrete strength evaluation carried out using the SonReb method

The structural evaluation of existing concrete structures is becoming everyday more important for several reasons ranging from their seismic assessment to the presence of increased design loads, from the damage caused by fire to forensic investigations and so on. Whilst it is generally recognized that concrete coring provides the most reliable information on concrete strength, it should also be mentioned that this kind of test is responsible of slight damage to the structure and that it can be carried out only for structural elements with sufficient spacing between the reinforcing bars. Thus, it would be highly desirable to obtain reliable information by means of non-destructive techniques (NDT). One of the major drawbacks of the well-known combined method SonReb is the effect of the carbonation on the rebound number. In this paper two correction formulas for this index based on the thickness of the carbonated concrete cover and, to a smaller extent, on the strength of the concrete itself, are proposed. The formulas have been determined by means of finite elements modeling (FEM) of the impact between the plunger of a Schmidt hammer and the concrete surface. Results from FEM have shown a good agreement with experimental results. The proposed correction formulas can provide a more reliable concrete strength evaluation without significantly increasing the cost and the time for the experimental tests.