环境温度对混凝土管桩氯离子扩散性能的影响

Effect of environment temperature on chloride diffusion in RC pipe piles

基于Fick第二扩散定律,建立混凝土管桩中考虑环境温度和氯离子结合能力的氯离子扩散模型。针对环境温度对混凝土管桩中氯离子扩散性能的影响开展试验研究,将不同水灰比(0.30、0.45和0.55)混凝土管桩置于不同温度(21、30、50℃)的5%氯化钠盐雾中,开展为期32d的浸泡试验。依据试验结果和氯离子扩散模型,得到不同温度条件下、不同水灰比混凝土管桩中的自由氯离子浓度分布、表面氯离子浓度、氯离子表观和有效扩散系数、活化能和氯离子结合能力值。试验结果表明:随着环境温度的升高,自由氯离子浓度、表面氯离子浓度、氯离子表观和有效扩散系数增大。随着环境温度从21℃升高到30℃,氯离子结合能力显著增加,但随着环境温度从30℃升高到50℃,氯离子结合能力却略有减小。由于表观氯离子扩散系数的对数与环境绝对温度的倒数呈线性变化规律,因此,可推断氯离子在混凝土管桩中的扩散符合Arrhenius理论。

Based on Fick’s second law of diffusion, the chloride diffusion equation in reinforced concrete (RC) pipe pile was developed considering the effects of environment temperature and chloride binding. The experimental study on the effect of environment temperature on chloride diffusion in RC pipe pile was conducted in this paper. RC pipe piles with different water-to-cement ( w/c ) ratios (0.30, 0.45 and 0.55) were exposed to 5% chloride salt spray for 32 days at different exposure temperatures (21, 30, 50 ℃). Based on the experimental results and proposed model, the chloride concentration profiles, surface chloride concentration, apparent and effective diffusion coefficients, activation energy and binding capacity values of RC pipe piles with different w/c ratios at different exposure temperatures were explored. The experimental results show that the free chloride concentration, surface chloride concentration, apparent and effective diffusion coefficients increase with the environment temperature. The binding capacity increases significantly with the increase of environment temperature from 21 to 30 ℃. However, the binding capacity decreases slightly when the environment temperature increases from 30 to 50 ℃. It could be concluded that the chloride diffusion into RC pipe pile follows the Arrhenius theory due to the linear distribution of the log-variation of apparent diffusion coefficient with the inverse of absolute temperature.