Detection of setting time during cement hydration using ground penetrating radar

Abstract

The setting time of concrete needs to be detected to ensure the construction quality control. This research provides a new non-contact, nondestructive remote sensing detection method based on ground penetrating radar (GPR) for monitoring cement setting time. The moisture content of cement paste decreases during hydration, resulting in a change of its dielectric constant. Furthermore, dielectric permittivity affects the wave velocity and echo intensity of electromagnetic waves. Based on these characteristics, this paper utilizes GPR to measure the moisture content of cement paste in terms of changing dielectric permittivity, and then assess the setting time depending on the link between the moisture content and setting state of the cement paste. To detect an object smaller than one-wavelength, the full-waveform inversion is used to analyze the GPR echo data instead of the traditional velocity inversion measurement. The positive correlation between the reflection coefficient and dielectric constant is verified by both simulations and experiments. The experiment results accurately determine the initial and final setting time of cement paste, compared with the Vicat apparatus test. The method of GPR monitoring cement paste setting time based on full-waveform inversion theory can solve the quality control problems of concrete leveling automation and concrete layered construction automation.