Water penetrability in hardened concrete by GPR

This paper describes the laboratory experiments carried out to analyze the water penetrability in hardened concrete by means of GPR. For this purpose, concrete specimens were fabricated (W/C = 0,8) and after 28 days in a wet chamber, they were dried in a kiln (105 degrees C). Afterwards, they were put into water and in all faces sealing paint was applied, except for the one in contact with water. GPR measurements were acquired at different intervals of time and they were based on coupling a 2,0 GHz antenna (GSSI) on the surface opposite to the one immersed into water. Firstly, the survey was conducted by measuring the time delays between reflected and direct wave arrivals, before introducing the samples into water (calibration session). Secondly, GPR measurements were recorded in different time intervals. All the wave parameters studied were influenced by the presence of water and the sensibility of the technique to assess the waterfront depth variation was proved. Nevertheless, a specific processing of the data acquired when the antenna was placed opposite from the water contact surface was developed. This process consisted of the isolation of the reflection due to the waterfront, produced just before the reflection of the bottom of the samples and provided the assessment of the waterfront location (cm) at different times.