Relationship between Moisture Content and Dielectric Values of Concrete using Ground Penetrating Radar Method

Abstract

The moisture content (MC) in concrete structures is an agent that may result in corrosion of steel reinforcement and further deterioration of concrete. The nondestructive technique (NDT) of the Ground Penetrating Radar (GPR) is a technique to assess concrete structures’ condition. However, the propagation of GPR electromagnetic waves (EW) is strongly influenced by the MC of propagation medium. Hence, the objective of this study is to determine the effect of MC on EW velocity and dielectric value based on different MC of concrete and at various steel reinforcement diameters. Antenna frequency of 1.6 GHz is used based on the depth of the reinforcement which is less than 0.5 m. A concrete slab of 0.15 x 0.20 x 0.35 m3 was prepared using three different sizes of steel reinforcement of 12, 16, 20 (mm) at different depths of 25, 60 and 120 (mm). After 28 days wet cured, the sample is ovendried to remove moisture. Next, the sample was immersed in water for 5 min, 10 min, 30 min, 60 min, per hour to 6 hours, from day 1-9 to obtain different MC. The effect of concrete MC on GPR EW can be seen through the hyperbola image, which begins to fade on the 3rd day of immersion, at MC of 2.31%. The dielectric values obtained are 10.11 for concrete that are immersed for more 9 days (MC 2.54%). The range of dielectric values obtained are within the range in ASTM D-6432, which is 5-
10 for concrete. Finally, the percentage difference (%) of the diameter steel reinforcement obtained for relative MC is 0.3% for size 12 mm, 28.56 for size 16 mm
and -7.7% for size 20 mm. The percentage difference (%) increases when MC increases. Relationship between %MC within the value obtained and dielectric value is proposed.