干湿循环对混凝土氯离子结合能力的影响研究

Effect of dry-wet cycle on chloride Ion binding capacity of concrete

海洋环境下氯离子侵蚀是钢筋混凝土耐久性破坏的主要因素之一,目前普遍运用的基于Fick第二定律解析解的氯离子浓度预测方法是基于氯离子不与混凝土结合的假设。但在实际情况中,氯离子可以通过化学结合与物理吸附的方式与混凝土结合,混凝土对氯离子的结合作用会降低自由氯离子浓度,从而降低氯离子扩散速率和钢筋前沿的氯离子浓度累积量。文章进行了8组不同干燥时间比和5个暴露时间点的干湿循环试验,研究干湿循环作用和暴露时间对混凝土氯离子结合能力的影响。分别采用线性吸附理论和Freundlich吸附理论对试验数据进行拟合分析,预测氯离子的结合能力。结果表明两种吸附理论表达出的氯离子结合能力均随着干燥时间比的增加而降低,但Freundlich吸附理论的预测结果更为准确,故选取该理论建立了干燥时间比、暴露时间影响下的氯离子结合能力表达式。根据建立的氯离子结合能力公式,建立合理描述氯离子传输特性的数值模型。并通过数值模拟比较考虑氯离子结合能力的氯离子传输模型与基于Fick第二定律解析解的氯离子扩散模型的差异。

Chloride ion erosion in marine environment is one of the main factors of durability failure of reinforced concrete,and the commonly used method for predicting chloride ion concentration based on the analytical solution of Fick′s second law is based on the assumption that chloride ions do not combine with concrete.However,in practice,chloride ions can be combined with concrete by chemical binding and physical adsorption,and the binding of concrete to chloride ions will reduce the concentration of free chloride ions,thereby reducing the chloride ion diffusion rate and the accumulation of chloride ion concentration at the front of the rebar.In this paper,eight sets of dry-wet cycles with different wet-dry ratios and five exposure time points were carried out to study the effects of dry-wet cycle action and exposure time on the chloride binding capacity of concrete.Linear adsorption theory and Freundlich adsorption theory were used to fit and analyze the experimental data to predict the binding capacity of chloride ions.The results show that the chloride binding capacity expressed by the two adsorption theories decreases with the increase of the dry time ratio,but the prediction results of Freundlich adsorption theory are more accurate,so the expression of chloride binding capacity under the influence of dry time ratio and exposure time were established by this theory.According to the established chloride binding capacity formula,a meso-numerical model that reasonably described the chloride ion transport characteristics was established.The difference between the meso-analog method considering the binding capacity of chloride ions and the numerical analogue method with the analytical solution of Fick′s second law was compared by numerical simulation.