Abstract: To address the issue of crystallization and blockage in tunnel drainage pipes, the authors systematically investigate the effects and mechanisms of coating materials on the anti-crystallization performance of drainage pipes. Initially, under laboratory conditions, the crystallization characteristics of uncoated high-density polyethylene (HDPE) drainage pipes and HDPE pipes coated with three different coating materials (epoxy resin DGEBA, silicone SR, and polytetrafluoroethylene PTFE) were analyzed. By measuring the crystallization coverage area, it was found that the uncoated HDPE surface had the largest average crystallization coverage area ((19.75±1.06) mm²), while the crystallization coverage areas of the three coated surfaces were in the order of DGEBA ((14.39±0.87) mm²) > SR ((7.68±0.98) mm²) > PTFE ((0.38±0.31) mm²). Based on dissipative quartz crystal microbalance (QCMD) experiments, the crystal growth process on each coating surface was monitored in situ, and the crystallization mass was converted using the Sauerbrey equation. The results show that the crystallization masses of DGEBA, SR, and PTFE coatings were 425.72, 173.46, and 41.01 ng/(cm²•h), respectively. Scanning electron microscopy images verified the consistency between the number of crystal grains and the crystallization mass. Further molecular dynamics simulations were used to calculate the absolute value of the binding energy between the coating surface and the calcium carbonate solution, with results indicating that HDPE (124.49 kcal/mol) > DGEBA (87.55 kcal/mol) > SR (48.12 kcal/mol) > PTFE (24.25 kcal/mol). This reveals the susceptibility of crystallization in drainage pipes and the anti-crystallization mechanism of coatings from a microscopic perspective. Field test results are consistent with laboratory experiments and simulation analyses, with uncoated HDPE drainage pipes having the largest amount of crystallization (1.65 kg), followed by pipes coated with DGEBA (1.05 kg) > SR (0.68 kg) > PTFE (0.20 kg). The multi-scale experimental and numerical simulation results indicate that uncoated HDPE drainage pipes had poor anti-crystallization performance, while the PTFE coating could significantly inhibit the adsorption and growth of calcium carbonate crystals, providing quantifiable performance data and theoretical basis for the anti-crystallization design of tunnel drainage systems.

Key words: tunnel drainage system, calcium carbonate crystallization blockage, anti-crystallization coating, multi-scale experiments, molecular dynamics simulation