不同温度条件下混凝土中硫酸根离子扩散规律研究

Diffusion pattern of sulfate ions in concrete under different temperature conditions

为了探究盐渍土地区埋地混凝土构件内部的硫酸根离子扩散规律,利用可设置不同温度(-15℃、20℃、35℃)的标准恒温恒湿养护箱,进行了室内混凝土硫酸盐全侵蚀试验。结果表明:随着浸泡时间的增长,35℃、20℃下的硫酸根离子在混凝土中的侵蚀深度逐渐增加,并且同一侵蚀深度下的硫酸根离子含量也随之上升;-15℃下的硫酸根离子扩散速率较慢,混凝土试块受侵蚀部分在浸泡后期(480 d)只有3~5 mm,主要集中于表层部位。结合表观特征和SEM-EDS结果预测温度变化对于混凝土内部化学反应速率具有重要影响,并通过热重试验对主要侵蚀产物进行了定量分析,发现35℃与20℃下混凝土试块内部生成的钙矾石数量远多于低温条件,这些侵蚀产物吸水膨胀进而使混凝土中微裂缝增多,为后续硫酸根离子的迁移创造了有利条件。基于PETER建立的非稳态硫酸盐扩散模型,考虑温度场对其进行修正,对比数值结果与试验结果,表明不同温度下该模型的预测结果与试验数据吻合较好。通过研究混凝土构件中硫酸根离子的扩散规律,可以与盐渍土地区中混凝土结构耐久性相联系,为实际工程建设提供一定参考。

In order to explore the diffusion law of sulfate ions in buried concrete components in saline soil area,the indoor total sulfate corrosion test of concrete is carried out by using standard constant temperature and humidity curing boxes with different temperatures(-15℃,20℃and 35℃).The results show that with the increase of immersion time,the erosion depth of sulfate ion in concrete increases gradually at 35℃and 20℃,and the sulfate ion content at the same erosion depth also increases.The sulfate ion diffusion rate is slow at 15℃,and the corroded part of the concrete test block is only 3~5 mm in the later stage of immersion(480 d),which is mainly concentrated in the surface layer.Combined with the apparent characteristics and SEM-EDS results,it is predicted that the temperature change has an important impact on the internal chemical reaction rate of concrete,and the main erosion products are quantitatively analyzed by thermogravimetric test.It is found that the amount of ettringite generated in the concrete test block at 35℃and 20℃is much more than that at low temperature,and these erosion products absorb water and expand,resulting in the increase of micro cracks in concrete,which creates favorable conditions for the subsequent migration of sulfate ions.Based on the existing unsteady sulfate diffusion model and considering the temperature field,the numerical results are compared with the experimental results,which shows that the prediction results of the model are in good agreement with the experimental data at different temperatures.By studying the diffusion law of sulfate ions in concrete components,it can be related to the durability of concrete structures in saline soil area,and provide some reference for practical engineering construction.