抛石环境中铝合金阳极性能评价及其对海底隧道钢壳保护效果评估

The Evaluation of Aluminum Alloy Anode and Its Associated Protection Simulation in the Brine With Backfilled Stone for the Steel Sheet of Immersed Tunnel

目的解决埋覆介质中牺牲阳极电化学性能评价的不确定性,实现非匀质介质中牺牲阳极电容量测试结果的评价和对比。方法模拟沉管隧道埋覆的环境介质,对铝合金牺牲阳极的电容量和溶解形貌进行评测。为区别于现有的海水等匀质介质中阳极的检测方法,建立非匀质介质中铝阳极电化学性能评价方法。另外,在上述埋覆介质中,测定阳极和阴极的极化曲线,修正仿真计算的边界条件,有利于模拟这种高电阻率介质环境下阴极保护电位分布。结果测试箱所测电阻率与商用便携式电导率仪测定精度相当。A1阳极在低电阻率的海水中(25-40Ω·cm)性能稳定,电容量稳定在2500 A·h/kg,溶解性能良好;在40Ω·cm海淡水+回填石的混合介质中,电容量测试值数据波动大,重现性差。B1阳极在海水(25-40Ω·cm)中的电容量和A1阳极相当,未见到差异,在40Ω·cm海淡水+回填石混合介质中,电容量数值分散性小,电化学活性高。结论混合介质中的评价试验体现了海淡水、混合介质电阻率和回填石对阳极溶解产物阻滞的综合效应,提高了抛石环境中铝阳极寿命评估的准确性,尤其适用于沉管隧道钢壳用铝合金阳极电化学性能评价和牺牲阳极保护效果评估。

This paper aims to solve the uncertainty of electrochemical performance evaluation of sacrificial anode in buried medium and realize the evaluation and comparison of capacitance test results of sacrificial anode in heterogeneous medium.The capacitance and dissolution morphology of aluminum alloy sacrificial anode were evaluated by simulating the environmental medium buried in immersed tunnel.In order to distinguish the existing detection methods of aluminum anode in homogeneous medium such as seawater,an evaluation method of electrochemical performance of aluminum anode in heterogeneous medium was developed.In addition,in the above buried medium,measuring the polarization curves of anode and cathode and modifying the boundary conditions of simulation calculation were conducive to simulate the cathodic protection potential distribution in this high resistivity medium environment.The resistivity measured by the test box was equivalent to that measured by the commercial portable conductivity meter.A1 anode had stable performance in seawater with low resistivity(25~40Ω·cm),stable capacitance at 2500 A·h/kg and good solubility;in the mixed medium of 40Ω·cm sea fresh water+backfilled stone,the capacitance test value data fluctuated greatly and the reproducibility was poor.The capacitance of B1 anode in seawater(25~40Ω·cm)was equivalent to that of A1 anode,and there was no difference.In the mixed medium of 40Ω·cm sea and fresh water+backfilled stone,the dispersion of capacitance value was small and the electrochemical activity was high.The associated results displays the comprehensive effects under the salinity of brackish water,overall resistivity of heterogeneous medium and the block effect of dissolved product in the stones.The testing under the marine brackish/backfilled stone/deposited sea mud will be appropriate for evaluation of aluminum alloy anode and its protection performance for the steel shell immersed tube tunnel and also the predicted usage life of anode in the backfilled stone condition will be accurately.