Rapid nondestructive assessment of water penetration into cementitious materials using smartphone-equipped handheld ground penetrating radar

Water penetration critically governs durability of cementitious materials, yet existing evaluation methods remain destructive, time-consuming, and costly. Especially the water indicator specified in certain standards has been reported to be unreliable for application in blast furnace slag (BFS)-blended cementitious materials. To address these limitations, this study developed a rapid nondestructive method to assess water penetration into cementitious materials with BFS using smartphone-equipped handheld ground penetrating radar (GPR). Multiscale pore structure was characterized using Mercury intrusion porosimetry and Nitrogen adsorption–desorption test, while Thermogravimetric and X-ray diffraction analyzed hydration products and phase evolution. Furthermore, the changes in electromagnetic waves during the water absorption process were analyzed, and the GPR-derived penetration depths were calculated and further validated. On this basis, the staged water absorption behavior was quantified and correlated with pore structure parameters to clarify the influence of different pore water states on dielectric response. Results show that electromagnetic waves exhibited a clear two-stage mechanism during the process of specimen absorption. The rapid filling of interconnected pores by free water markedly increased dielectric constant during the capillary-dominated first stage, causing pronounced time delay and amplitude attenuation of the second interface signal. In the gel-controlled second stage, dielectric variations became limited, leading to signal stabilization and reduced sensitivity. GPR-derived penetration depths agreed well with visual measurements, with statistical validation confirming strong consistency. This proposed GPR-based approach provides a reliable, nondestructive tool for evaluating water transport, supporting durability-oriented design and sustainable infrastructure development.