饱水混凝土氯离子侵蚀数值试验随机细观分析

Mesoscopic and stochastic analysis of chloride ion erosion in saturated concrete by numerical tests

为研究饱水状态混凝土中氯离子侵蚀的规律,首先基于Fick第二定律,在前人研究的基础上推导出综合考虑混凝土劣化、荷载作用、混凝土对氯离子的结合作用、温度、混凝土内部相对湿度、氯离子扩散的时间依赖性、离子静电场作用和表面氯离子浓度影响的新扩散方程。然后针对氯离子侵蚀的随机性,建立混凝土随机细观模型,并将氯离子侵蚀宏观数值模型与混凝土随机细观模型融合,提出混凝土氯离子侵蚀的随机细观研究新方法。通过编制相应的MATLAB程序,可生成任意骨料含量并满足不同级配要求的随机混凝土试件,并编制程序将MATLAB生成的.fig格式图形文件转换为通用的.dxf格式,以便于建立的模型可被有限元软件调用。最后,通过对105个混凝土随机试件进行氯离子侵蚀数值试验模拟,采用概率和数理统计的研究方法,总结出混凝土中氯离子侵蚀的一般规律。研究结果表明:细观层次上的物质传输浓度分布和数值上与宏观层次都有显著区别,氯离子在混凝土中的传输具有显著的随机性,相同骨料含量的混凝土试件在同一深度的氯离子含量是随机变量,骨料对氯离子传输具有显著的阻碍作用,骨料改变了氯离子在混凝土中的传输路径,氯离子分布在骨料周围有绕流现象,试件某一深度处的氯离子浓度近似服从正态分布。

To study the law of chloride ion erosion in saturated state concrete, firstly, based on Fick＇s second law, the new diffusion equation was proposed on the basis of the former considering factors such as the deterioration of concrete, loading, effect of chloride binding capacity, temperature, relative humidity inside concrete, time dependence of chloride diffusion, effect of electrostatic field of ion and the new diffusion equation affecting the surface chloride concentration. Then aimed at the randomness of chloride erosion, a meso scale model of concrete was established, and the macro model of chloride erosion was combined with the mesoscopic stochastic concrete model, thus, a new method for the study of chloride ion erosion of concrete was proposed from stochastic and mesoscopic level. The corresponding software was programmed based on the platform of MATLAB, and stochastic concrete specimens could be generated with arbitrary aggregate content and meet different grading requirements. And the fig format graphics files generated by MATLAB could be converted into dxf format, so that the established stochastic concrete model could be called expediently by finite element softwares. Finally, the general law of chloride ion erosion in concrete was summarized with mathematical statistics and probability method by means of numerical tests of 105 stochastic concrete specimens. The results show that the material transport in meso level is strikingly different from the macro level both in concentration distribution and numerical value. The transmission of chloride ions in concrete has significant randomness. Chloride ions contents in concrete with the same aggregate content and depth are random variables. The transport of chloride ions is impeded remarkably by the aggregate. The transmission path of chloride ion in concrete is changed because of the aggregate. The chloride ions transfer around the aggregate. The distribution of chloride ions content in concrete at a certain depth approximately accords with the normal distribution. 2 tabs, 5 figs, 28 refs.