非饱和水泥基复合材料的氯离子传输性能研究进展

Research Progress on Chloride Ion Transport Properties in Unsaturated Cement-based Composites

混凝土结构过早失效及日常维护等耐久性问题近年来引起了极大的关注,氯离子传输是决定钢筋混凝土结构使用寿命预测和耐久性评估的重要因素之一。由于在结构工程实际服役过程中,水泥基复合材料很难达到饱和状态,近年来越来越多的学者研究非饱和状态下水泥基材料氯离子的传输性能。过去几十年里,有各种不同测试氯离子传输的实验方法,如自然扩散法、电迁移法、电阻法和压力渗透法等。虽然自然扩散法符合实际情况,但是操作繁琐,达到稳态扩散非常耗时。为了加速氯离子的迁移,研究者们提出了电加速实验、加压力渗透的方法。除了传统的氯离子传输实验外,也有一些新的实验方法被提出,如半电池法,根据元素示踪法测定氯离子分布。除了实验外,还可通过模型来模拟氯离子在非饱和水泥基复合材料中的传输,依据模型主要有考虑氯离子扩散的Fick定律,考虑扩散和对流耦合的扩散-对流模型。此外,考虑湿度、干湿交替和水分子传输等影响因素,研究者们从不同角度建立了氯离子传输模型。本文综述了氯离子在非饱和水泥基复合材料中的传输性能,包括氯离子的传输实验、氯离子非饱和传输模型和氯离子传输的影响因素。最后对现有研究进行了总结:非饱和水泥基复合材料的传输性能在很大程度上取决于材料的水分含量,低于临界饱和度时由于没有水分连通孔隙导致氯离子无法传输;掺合料混凝土比普通硅酸盐水泥(OPC)混凝土有更小的氯离子扩散系数;扩散-对流模型更适用于非饱和水泥基材料。展望未来,需要简单、准确的实验方法,考虑多方面因素对氯离子传输的影响。

Durability problems such as premature failure of concrete structures and routine maintenance have drawn great attention in recent years.Chloride ion transport is one of the important factors determining the service life prediction and durability evaluation of reinforced concrete structures.Due to the fact that cement-based composite materials are difficult to reach saturation during the actual service of structural engineering,more and more people have studied the transport properties of chloride-based materials in cement-based materials in unsaturated state in recent years.In the past few decades,there have been various experimental methods for testing chloride ion transport,such as natural diffusion,electromigration,electrical resistance,and pressure infiltration.Although the natural diffusion method is in line with the actual situation,the operation is cumbersome and it is very time consuming to achieve steady state diffusion.In order to accelerate the migration of chloride ions,the researchers proposed an electric acceleration experiment and a method of adding pressure.In addition to the traditional chloride ion transfer experiments,some new experimental methods have been proposed,such as the half-cell method,to determine the chloride ion distribution according to the elemental tracer method.In addition to experiments,models can be used to simulate the transport of chloride ions in unsaturated cement-based composites.According to the model,Fick s law,which considers the diffusion of chloride ions,and diffusion-convection models considering diffusion and convection coupling are considered.In addition,considering the influencing factors such as humidity,dry-wet alternation and water molecule transport,the researchers established a chloride ion transport model from different angles.In this paper,the transport properties of chloride ions in unsaturated cement-based composites are reviewed,including:chloride ion transport experiments,chloride ion unsaturated transport models,and chloride ion transport factors.Finally,the existing research is summarized:the transmission performance of unsaturated cement-based composites depends largely on the moisture content of the material;below the critical saturation,the chloride ions cannot be transported due to the absence of moisture-connected pores;the admixture concrete has a smaller chloride ion diffusion coefficient than OPC concrete;the diffusion-convection model is more suitable for unsaturated cement-based materials.Looking to the future,simple and accurate experimental methods are needed to consider the impact of various factors on chloride ion transport.