Electromagnetic non-destructive evaluation techniques for the monitoring of water and chloride ingress into concrete: a comparative study

One of the principal causes of deterioration in reinforced concrete structures is steel corrosion caused by the penetration of aggressive agents into the protective cover concrete layer (particularly water containing chlorides). Electromagnetic non-destructive evaluation (EM NDE) techniques are sensitive to these aggressive agents and can be used to assess concrete durability in terms of corrosion risk. The electromagnetic (EM) properties that are the focus of the study presented here are electrical resistivity and dielectric permittivity-inherent material properties that are both sensitive to degree of saturation and the salinity of the pore solution. Three EM NDE techniques suitable for the in situ investigation of concrete are used to obtain these EM properties: electrical resistivity tomography, capacimetry and ground penetrating radar. Experimental work is conducted on in a controlled laboratory environment with the aim of comparing the ability of the three EM NDE techniques to monitor the ingress of saline solutions into concrete slabs and discern between their chloride content. All three methods are found to be capable of detecting variation in water and chloride content and therefore show promise for the in situ monitoring of water and chloride ingress. However, more research is needed on the quantification of the EM properties over depth as well as on the combination of these methods in order to separate the influence of these two parameters on the EM responses.