The condition assessment of concrete is a key point for structural reassessment, since material ageing can result in some performance loss and lower the safety level. Progressive decay of performances also induces important maintenance costs, so as to prevent future deterioration and ultimate failure. Non-destructive techniques (NDT) have been used for many years to assess the condition of existing reinforced concrete structures, but they suffer several drawbacks, including the lack of standards and the fact that practitioners commonly do not have enough expertise. However, the most important drawback is that NDT does not enable a direct assessment of the parameters that are sought. The abilities of various techniques with respect to given problems have been summarized in several state-of-the-art books [1 - 3].