Use of Ground Penetrating Radar measurement combined to resistivity measurement for characterization of the concrete moisture

摘要

Durability of concrete structures is mainly affected by the corrosion, because corrosion causes extensive damages inside the structure and loss of structural integrity of the material. Basically, the cause of corrosion appearance is contact the reinforcement with water and chlorides, therefore the durability of concrete varies the facility of penetrating of water and chemical agents into concrete. To service the existing concrete structures in order to embalm their durability means to measure water penetrability and water content thereto. In this context the non-destructive techniques of testing structures play promising role, especially the techniques based on electromagnetic waves. Mainly the radar waves emitted by Ground Penetrating Radar (GPR) are very sensitive to water content of the medium through which they propagate. The paper presents great potential of the radar measurement combined with resistivity measurement for the characterization of potential concrete corrosion in an early stage. Two laboratory experiments were performed. First one was performed in order to study the GPR capacity to assess the changing of water content in the concrete samples. Two samples were prepared, one with reinforcement and one without. At the beginning of the test the samples were completely saturated. Then measurement were carried out during 2 months in order to observe the relationship between saturation degree of the concrete and the direct waves amplitude, the propagation velocity of the radar waves, as well as the dielectric permittivity and the resistivity of concrete. It was observed a great agreement between the parameters of the radar waves and concrete moisture. Next experiment were conducted to study the capacity of GPR to assess the water penetrability in hardened concrete. For this purpose concrete specimen was dried in an oven. The specimen had inside the sensors which had been measured the water content. Right after drying the sample had been put into the water and then GPR measurement were acquired. The results shown that there is a link between analyzed wave parameters and the waterfront advance.