Experimental simulation for pile integrity: Electromagnetic assessment and pore topology analyses

This paper describes the assessment of concrete pile integrity using time domain reflectometry. Miniature concrete piles with voids or concrete quality defects were prepared for this experiment. Two types of transmission lines (with and without connectors) were installed inside the piles to measure electromagnetic wave signals obtained and analyzed over a curing period of 28 d. The experimental results revealed the possibility of identifying voids and concrete quality defects using electromagnetic wave signals. All transmission lines identified void defects owing to the higher wave velocity in the void compared to that in concrete. For concrete quality defects, the transmission line without connectors proved inadequate, whereas the transmission line with connectors successfully differentiated various concrete qualities by comparing the wave velocities in sections divided by the connectors. The results regarding concrete quality indicated that a lower water-cement (w/c) ratio of 0.35 initially exhibited higher wave velocity (1.49 ×10⁸ m/s) than the higher w/c ratio of 0.55 (1.46 ×10⁸ m/s). However, as the curing period progressed, a higher w/c ratio of 0.55 resulted in a higher velocity (1.59 ×10⁸ m/s) than that with a lower w/c ratio of 0.35 (1.53 ×10⁸ m/s). The crossing of the velocities was explained by the changes in permittivity and porosity during the curing period. Furthermore, the permittivity estimation showed consistent results based on the porosity and material properties. This study presents the potential of transmission lines with connectors in assessing the integrity of specific sections in concrete piles.