Field study of the dielectric constant of concrete: A parameter less sensitive to environmental variations than electrical resistivity

In this work, a field study was conducted to evaluate the curing effectiveness of concrete slabs cured by air and compound. Two non-destructive testing methods including ground penetrating radar (GPR) and electrical resistivity measurement were used. The dielectric constant value developments of air and compound cured concrete slabs were determined by GPR measurement. The compressive strength development was tested by concrete cylinders. The hydration degrees of air and compound cured slabs were determined by Ca(OH)2 (CH) content through thermogravimetric analysis (TGA) by a modified calculation method. The microstructure development of air and compound cured concrete slabs were characterized by mercury intrusion porosimetry measurement (MIP). It has found that the dielectric constant value of compound cured concrete slab was always higher than air cured concrete slab. The second reflected pulse peak amplitude of GPR waveform was less influenced by weather conditions, making it a reliable indicator of the dielectric constant value. On the other hand, the dielectric constant value determined by the first reflected pulse peak amplitude was greatly influenced by the weather conditions. The dielectric constant value determined by the two-way travel time method exhibited strong correlations with compressive strength, CH content and porosity. However, the electrical resistivity development of air and compound cured concrete slabs were not consistent with compressive strength, CH content and microstructure development. Our findings suggested that the GPR measurement can be practically used to evaluate the curing effectiveness of concrete and can be a good indicator of "hydration potential" from a development perspective.