Influence of frequency condition of dynamic hydraulic pressure on chloride transport in concrete

Concrete structures, including bridge piers and breakwaters operating in splash zones, along with ship locks, frequently encounter dynamic hydraulic pressures. To investigate the influence of frequency conditions of dynamic hydraulic pressure on mass transport in concrete, the water transport depth, chloride concentrations, and microstructure characteristics were analyzed using potentiometric titration, MIP, N2 absorption, and AFM tests. Results demonstrated that the water-wetting front disperses more evenly under dynamic hydraulic pressure, a phenomenon that can be linked to the quickening water mixing rate between well-connected and poorly connected pores due to the disturbance of flow equilibrium between pressure maintenance and release stages. The chloride concentration escalates as the frequency increases. Under the same pressure maintenance time, concrete with different w/c ratios can experience an elevation in chloride concentration by a maximum of 68∼85 % under dynamic hydraulic pressure compared to those subjected to static hydraulic pressure. The most probable pore size in concrete subjected to dynamic hydraulic pressure (w2) is approximately 2 times as large as that under static hydraulic pressure (w0). To further examine chloride transport, a chloride diffusion-convection model under dynamic hydraulic pressure was proposed. In the presence of low-frequency conditions, the chloride concentration within the concrete tends towards the concentration observed during the actual pressurization time under static hydraulic pressure. Despite having only half the actual pressurization time, the chloride concentration under dynamic hydraulic pressure presenting a frequency of over 1/12, surpasses the chloride concentration found under static hydraulic pressure. © 2024 Elsevier Ltd