混凝土灌注桩中混含硫酸盐的时变分布规律

硫酸盐环境下，为模拟混凝土灌注桩施工时混入的硫酸盐在桩中的时变分布行为，基于Fick第二定律并结合初始条件与边界条件，应用分离变量法，建立硫酸盐在桩中的时变分布模型。通过算例将本文解与传统解进行比较，并进一步探讨了硫酸盐扩散分布的影响因素和影响规律。结果表明，传统解用于分析混凝土灌注桩桩中硫酸盐扩散有局限性，而本文解相对于传统解具有一定的优势。混凝土灌注桩半径越小，应用传统解分析灌注桩中硫酸盐时变分布误差较大，同时，误差随时间增大。硫酸盐在混凝土灌注桩中的时变分布呈沙漏形，沿半径方向x=0处和桩表面处扩散行为明显，在x=0处附近区域，初始第一年扩散速率较快，在后续的50 a内扩散速率显著减小，但每10 a的平均速率基本相同。扩散系数和初始浓度梯度对硫酸盐在混凝土灌注桩中的时变分布影响较大。

Theoretical analysis of the time-varying distribution behavior of bored pile internal mixed sulfate

The time-varying distribution behavior of sulfate with diffusion is investigated for bored pile internal mixed corrosion at different amounts of service times. The formulation of diffusion, based on Fick-second law combined with the initial condition and the boundary condition, for sulfate in the bored pile is formed with the method of separation of variables. A model of concrete pile is offered as an example for illustrating the time-varying distribution behavior of sulfate and making comparison with the traditional model. Further, the influence factors and their effects on the sulfate diffusion distribution are also analyzed. The results show that the application of traditional method in analysis of sulfate diffusion in bored pile has some limitations and advantages of the proposed method are obvious. The radius of bored pile decreasing induces the discrepancy of sulfate distribution increasing with employing the traditional method, while the discrepancy increases over time. The time-varying distribution of sulfate in bored pile resembles hourglass figure that along the radius direction, diffusion behavior at x=0 and surface of pile is significant. In the region near x=0, the diffusion rate of sulfate is fast during the first year and then the diffusion rate is dramatically reduced to constant rate during the 50 years. Diffusion coefficient and the concentration gradient of sulfate in bored pile have a pronounced effect on the time-varying distribution of sulfate.