Fast non-destructive testing of concrete thicknesses using GPR

This paper reports the non-destructive testing of concrete thickness using GPR reflection technique without drilled cores. Laboratory concrete slabs made varying 5~15 cm according to two typical compositions were tested using a GPR system with a 1.5-GHz antenna. The dielectric constant of concrete specimens was calculated by reflected wave method, and then the authors researched the variation of electromagnetic wave velocity with concrete ages and established the dielectric model of concrete. It seems that there is an exponential relationship between dielectric constant and concrete ages. Comparison between measured and calculated values confirmed the concrete dielectric constant change follows different models at different stages. It obeys CRIM model when the concrete losses all the pore water. This theory could help to determine the GPR wave velocity according to the concrete composition or age, which would improve the detecting efficiency. This technique was successfully applied to field GPR data collected from an experimental site in Shandong province, which confirmed the relative error of this method was less than 10%.