Application of the Sonreb method requires evaluation of local values ​​of ultrasonic speed V and of rebound index S, from which you can get an estimate of the strength of Rc concrete in site, using expressions like:

Rc = a⋅Sb⋅Vc

– Rc is the cubic compressive strength in [MPa];
– S is the sclerometric index;
– V is the ultrasonic speed [m/s];
– coefficients a, b, c allow to best correlate the experimental direct data. Consequently, they differ in a significant way in terms of result.

For the Sonreb combined method, the dependent variable is Rcub, while the independent variables are respectively the average sclerometric index Ir and the ultrasound propagation speed Vus. The correlation that follows is expressed in the following way:

Rcub = a·Ir·b·Vus·c [MPa, m/s]

Parameters a, b and c represent the values ​​to be determined to calibrate the correlation law to the specific case. Having now available, in addition to non-destructive parameters, also the laboratory values, even for the same structural element, it’s interesting to see in what position is placed (with respect to the curves created with the expressions of the literature) the curve that we can call of laboratory. Of course to do this we need to previously have turned the cylinder compression resistances Fc in cubic compression resistances Rc.