Durability diagnosis of a concrete structure in a tidal zone by combining NDT methods: Laboratory tests and case study

To successfully implement non-destructive techniques (NDTs) for surveying concrete structures in marine environments, non-destructive measurement results must be correlated with concrete durability indicators such as porosity and water and chloride contents. For this purpose, tests introducing two electromagnetic methods (GPR and the capacitive technique), as well as the impact-echo method, were run on six different concrete mixes containing various porosities, with five water content values and three chloride concentrations. A reinforced concrete beam, extracted from the wharf of the Nantes–Saint-Nazaire Port, exposed to ocean tides was also tested under actual conditions. The NDT laboratory results exhibit linear correlations with concrete indicators, which in turn allows building a three-dimensional empirical model. This 3D cross-correlation model, coupled with onsite NDT results, is then used to perform a durability diagnosis of the actual structure. Moreover, these results serve to illustrate the advantages of the 2D data fusion models developed during this project.