Finite difference time domain modelling as support to ground penetrating radar surveys of precast concrete units
Precast concrete elements are commonly employed in the construction industry, how-ever failing to comply with manufacturers’ guidelines and poor construction practice can lead to loss of efficiency compromising the usability of the building. This paper presents two case studies where ground penetrating radar surveys, performed to in-vestigate the cause of failure of precast concrete elements, were supported by the finite difference time domain numerical approach. In the first case, the model was built after the survey for a better understanding of the complex reflection patterns unexpectedly experienced and to provide a clear interpretation; in the second case, the numerical simulation was performed prior to the survey, according to the information already available on the precast unit. The synthetic radargrams were then used as a valuable reference to assess the precast element internal conditions: on site, the comparison of the real radargrams with the synthetic ones allowed to address safely the intrusive works necessary to determine the concrete quality and during the processing step, any deviation from the ideal ground penetrating radar response gave potentially an indication of anomalies in the assembly operations that could be identified. The fi-nite difference time domain method should then be considered as complementary to ground penetrating radar surveys aimed to investigate precast elements.