Water Content Effect on Concrete Response in UPV tests

One main feature of previous literature results on Ultrasonic Pulse Velocity (UPV) tests is that direct to indirect UPV test results could be very different. Differences depend strongly on in situ concrete conditions (stress, cracking, rebar arrangement, ...) and humidity level while depend lesser on apparatus and operator. The Authors studied in the past the in situ conditions influence on UPV, now they are studying the influence on laboratory specimens. Test results show that if the water content is disregarded the usual survey techniques (like SonReb approach) could fail dramatically. In particular, it is possible to point out that the ratio of direct to indirect UPV test results is pseudo-linear with humidity. UPV test results strongly depend on humidity content for higher humidity level: in dry specimens, UPV values of indirect tests are lower than direct ones while in wet specimens UPV values of indirect tests are quite the same than the direct ones. A correlation between in situ to laboratory humidity level is of paramount importance for a correct use of the UPV test results and a control of in-situ humidity level has to be considered as mandatory for a correct approach to this kind of NDT test