硫酸盐侵蚀下混凝土灌注桩的损伤效应

Damage effect of concrete cast-in-situ piles under sulfate attack

摘要:

为分析外部硫酸盐腐蚀对混凝土灌注桩截面损伤和承载力的影响,研究了硫酸根离子在混凝土灌注桩中的扩散反应规律并探讨了桩身结构性能退化的影响因素.基于Fick第二定律建立了柱坐标下硫酸根离子的非稳态扩散反应方程,采用数值方法得到了扩散方程求解的有限差分格式,并通过相关试验结果验证了理论模型与计算方法的正确性.根据化学反应生成的膨胀产物计算膨胀应变,并通过损伤演化函数计算桩身截面损伤和承载力,建立了桩基损伤度与桩身承载力的相关关系,对比分析了不同腐蚀因素和腐蚀时间对桩基损伤与桩身承载力的影响.研究结果表明:内膨胀应变和损伤在表层的发展速度比内层发展更为迅速,增大桩半径能显著提高桩基的耐久性和承载能力,而水灰比大于0.4时,桩基损伤增长幅度最大.因此,合理增加桩半径并采用较小的水灰比能有效减小桩身混凝土损伤,提高桩基的耐久性并减少桩身承载能力的损失.

Abstract:

In order to analyze the effect of external sulfate attack on the durability of concrete cast-in-situ piles, the diffusion-reaction behavior of sulfate ion for concrete cast-in-situ piles was studied and the factors that affect the degradation of pile structure were analyzed. Based on the Fick’s second law, the non-steady diffusion-reaction equation of sulfate ion under column coordinates was established. The finite difference scheme for solving the diffusion equation was obtained by the numerical method. The accuracy of the theoretical model and the calculation method was verified by related experimental results. Expansion strain was obtained according to the expansion product produced by chemical reaction. The damage and bearing capacity of pile were calculated by damage evolution equation. The correlation between damage degree and bearing capacity was established. Influences of different corrosion factors and corrosion time on the damage and bearing capacity of pile were compared and analyzed. Results indicate that the internal expansion strain and damage developed more rapidly on the surface than in the interior layers. The increase of pile radius could significantly improve the durability and bearing capacity of the pile. When the water-cement ratio was larger than 0.4, the damage degree of the pile experienced the biggest growth. Therefore, the reasonable increase of pile radius and the use of smaller water-cement ratio can effectively reduce concrete damage, improve pile durability, and reduce the loss of bearing capacity of pile.