应变硬化水泥基复合材料氯盐传输行为的细观数值分析

Mesoscale numerical analysis of chloride ingress behavior of strain hardening cement-based composites

应变硬化水泥基复合材料(SHCC)因其具有高延性、裂缝宽度可控等优点已被广泛应用于海洋腐蚀严重区域的混凝土结构加固与修复工程中。基于此,提出了海洋干湿循环作用下SHCC中氯离子传输的对流-扩散模型,并利用COMSOL仿真软件建立考虑纤维乱向分布的二维细观模型;通过开展人工室内模拟海洋浪溅区SHCC氯离子传输试验,分析了不同干湿循环比(3.0∶1、11.0∶1和85.4∶1)和不同暴露时间(30天、90天和180天)下的氯离子含量时空分布规律,对比验证了模拟氯盐传输行为的细观数值模型的有效性。结果表明:随着暴露时间的延长,SHCC氯离子峰值浓度增大,且随着干湿循环比的增加峰值浓度升高;随着渗透深度增大,氯离子浓度迅速下降并最终趋于稳定,使氯离子浓度整体表现出峰值浓度较高而传输深度较小的规律;基于Fick第二定律解析解并考虑对流区的影响,SHCC的表面氯离子浓度(Cs)和表观氯离子扩散系数(Dapp)均呈现明显的时变性,干湿循环比一定时,随着暴露时间的延长而分别增大和减小;当干湿循环比为85.4∶1,暴露时间为90天和180天时Cs相较于30天分别提高了51.72%和83.45%,Dapp分别降低了27.71%和48.50%;暴露时间一定时,随着干湿循环比的增加,Cs和Dapp均呈现先增大后减小的趋势;最后将氯离子含量分布实测值与计算值进行对比,验证了所建立的干湿循环作用下氯盐传输的扩散-对流模型的适用性。

Strain hardening cement-based composite(SHCC)owning to its advantages of high ductility and controllable crack width has been widely used in the strengthening and repairing of concrete structures exposed to severe marine corrosion zones.Based on this,a convection-diffusion model of chloride transport in SHCC subjected to marine drying-wetting cycles was proposed,and a two-dimensional mesoscopic model considering the chaotic distribution of fibers was established by COMSOL simulation software.The spatial and temporal distribution of chloride content under different drying-wetting ratios(3.0∶1,11.0∶1 and 85.4∶1)and exposure durations(30 days,90 days and 180 days)was analyzed by conducting a simulated indoor test of chloride ingress into SHCC.The effectiveness of the mesoscopic numerical model to simulate chloride ingress behavior was contrastively veri-fied.The results show that the peak chloride concentration inside SHCC increases with the extension of exposure time,and similarly increases with the increase of drying-wetting ratio.However,with the increase of penetration depth,the chloride concentration rapidly decreases and tends to be stable eventually,which make the chloride content as a whole show a higher peak concentration and a smaller penetration depth.According to the analytical solution to Fick's second law and considering the effect of convection zone,both the surface chloride concentration(Cs)and apparent chloride diffusion coefficient(Dapp)of SHCC show obvious time-varying characteristics.At a given drying-wetting cycle ratio,the Cs and Dapp increase and decrease as the exposure time increases,respectively.When the drying-wetting cycle ratio is 85.4∶1,compared to 30 days,the Cs of SHCC for exposure to 90 days and 180 days increase by 51.72%and 83.45%,and the Dapp decreases by 27.71%and 48.50%,respectively.At the same exposure time,as the drying-wetting cycle ratio increases,both the Cs and Dapp first increase and then decrease.Finally,the comparison between the measured data and calculated results of the chloride content distribution indicates the feasibility of the proposed convection-diffusion model under the cyclic drying-wetting action to depict the chloride transport behavior in SHCC.