摘要
采用氯盐溶液和硫酸盐溶液浸泡镁水泥钢筋混凝土构件,使构件中的涂层钢筋加速锈蚀,并利用电化学工作站进行电化学试验;以腐蚀电流密度作为钢筋耐久性退化指标,建立一元Wiener过程预测模型进行钢筋腐蚀寿命预测.结果表明:在氯盐溶液环境下,镁水泥混凝土构件中的钢筋受腐蚀问题较之硫酸盐溶液环境更为突出,且涂层在2种盐溶液环境中均对钢筋起到了较好的防护效果;在氯盐溶液环境中,涂层钢筋在1 500 d附近进入中等腐蚀阶段,在硫酸盐溶液环境中,涂层钢筋在22 000 d进入中等腐蚀阶段.
中国西北地区气候干旱,水分容易蒸发,受盐分流动迁移的影响,形成了大片盐渍土地
通过电化学工作站对镁水泥混凝土中的钢筋持续监测720 d,发现钢筋涂层可以有效降低其腐蚀程度.由于腐蚀电流密度能够直观反映镁水泥混凝土构件的结构损伤速率,因此将其作为耐久性退化指
镁水泥钢筋混凝土构件主要组成为:轻烧氧化镁(MgO) 、氯化镁(MgCl2)、粗细骨料、粉煤灰、减水剂、耐水剂和钢筋.钢筋涂层采用内含超细锌铝鳞片的达克罗(DKL)涂层,其主要成分(质量分数)见
试验所用钢筋为长度115 mm、直径12 mm的光圆钢筋.首先对钢筋表面进行去污处理,再进行酸洗、碱洗.在钢筋表面涂刷的DKL涂层平均厚度控制在0.2 mm.将无涂层和有涂层的钢筋分别置于100 mm×100 mm×100 mm镁水泥混凝土试块中,制成2组镁水泥钢筋混凝土试件,混凝土保护层厚度均设置成25 mm.将2组钢筋混凝土试件分别浸泡在1.5 mol/L NaCl溶液和1.5 mol/L Na2SO4溶液中,每隔90 d测定一次电化学参数,到720 d止;测试仪器为CS350电化学工作站.仪器中辅助电极为薄钢片,参比电极为KCl甘汞,电化学工作站三电极测试系统示意图见

图1 三电极系统电解池示意图
Fig.1 Schematic diagram of electrolytic cell of three electrode system
图

图2 氯盐溶液环境中的裸露钢筋极化曲线
Fig.2 Polarization curves of bare steel bar in chloride salt solution environment

图3 氯盐溶液环境中的涂层钢筋极化曲线
Fig.3 Polarization curves of coated steel bar in chloride salt solution environment
由图

图4 硫酸盐溶液环境中的裸露钢筋极化曲线
Fig.4 Polarization curves of bare steel bars in sulfate solution environment

图5 硫酸盐溶液环境中的涂层钢筋极化曲线
Fig.5 Polarization curves of coated steel bar in sulfate solution environment
由图
对比2种盐溶液环境中镁水泥混凝土构件中钢筋的腐蚀电流密度发现:在氯盐溶液环境中,90~720 d时裸露钢筋均处于严重腐蚀阶段,而涂层钢筋基本处于低腐蚀阶段,尤其是180~270 d时,涂层钢筋处于未受腐蚀阶段;在硫酸盐溶液环境中,90~720 d时裸露钢筋均处于严重腐蚀阶段,而涂层钢筋处于低腐蚀阶段;氯盐溶液环境下,镁水泥混凝土构件中的钢筋受腐蚀问题较之硫酸盐溶液环境更为突出,而涂层在2种盐溶液环境中均对钢筋起到了较好的防护作用.
一元Wiener过程表示
(1) |
式中:t为时间;μ为漂移系数;σ为扩散系数;W(t)为标准布朗运动公式.
对于一元连续随机过程{X(t),t≥0},有如下性质:
(1)时刻t到时刻t+∆t之间的增量满足:.
(2)任意2个不相交的时间区间[t1,t2],[t3,t4],t1<t2< t3<t4且增量间相互独立.
(3)X(0)=0,并且在t=0处连续,
(2) |
时刻t时Z(t)的概率密度函数为g(z,t),产品在t时间内的不失效概率P为:
(3) |
式中:τ为阈值.
g(z,t)表达式(Fokker‑Planck方程)
(4) |
结合式(
(6) |
分析电化学试验得到的2种盐溶液环境中钢筋腐蚀电流密度可知:裸露钢筋在90 d之前就已经进入严重腐蚀状态,其腐蚀寿命在90 d以内;涂层钢筋在90 d时也已处于发生锈蚀阶段,但未达到严重腐蚀状态.因此本文只对涂层钢筋作腐蚀寿命预测.对表
利用P‑P图对涂层钢筋腐蚀电流密度增量进行检验,见图

图6 氯盐溶液环境中涂层钢筋P‑P图
Fig.6 P‑P diagram of coated steel bar in chloride saltsolution environment

图7 氯盐溶液环境中涂层钢筋去趋势P‑P图
Fig.7 Detrend P‑P diagram of coated steel bar in chloride salt solution environment

图8 硫酸盐溶液环境中涂层钢筋P‑P图
Fig.8 P‑P diagram of coated steel bar in sulfate solution environment

图9 硫酸盐溶液环境中涂层钢筋去趋势P‑P图
Fig.9 Detrend P‑P diagram of coated steel bar in sulfate solution environment
由
由
(7) |
对
(8) |
(9) |
式中:为腐蚀电流密度退化量;;-.
计算得到氯盐溶液环境中Wiener过程参数=5.079 37×1
在氯盐溶液环境中,计算得到参数对应的可靠度函数和概率密度函数为:
(10) |
(11) |
同理,在硫酸盐溶液环境中,计算得到参数对应的可靠度函数和概率密度函数为:
(12) |
(13) |
图

图10 氯盐溶液环境中涂层钢筋可靠度
Fig.10 Reliability of coated steel bar in chloride salt solution environment

图11 氯盐溶液环境中涂层钢筋概率密度
Fig.11 Probability density of coated steel bar in chloride salt solution environment

图12 硫酸盐溶液环境中涂层钢筋可靠度
Fig.12 Reliability of coated steel bar in sulfate solution environment

图13 硫酸盐溶液环境中涂层钢筋概率密度
Fig.13 Probability density of coated steel bar in sulfate solution environment
由
(1)与硫酸盐溶液环境相比,90~720 d时,镁水泥混凝土中的裸露钢筋在氯盐溶液环境中受到更严重的腐蚀.对于涂层钢筋而言,在氯盐溶液环境中,90~720 d时其基本处于低腐蚀阶段,180~270 d附近则处于未受腐蚀阶段;在硫酸盐溶液环境中,90~720 d时其处于低腐蚀阶段.涂层在钢筋受腐蚀时保护作用明显,利用涂层来保护镁水泥混凝土中的钢筋是可行的.
(2)采用腐蚀电流密度作为钢筋耐久性退化指标,利用Wiener过程来建立钢筋腐蚀寿命预测模型可行;Wiener过程得出的可靠度预测方式可以反映钢筋的腐蚀过程,可以用于预测达到不同腐蚀程度时钢筋的腐蚀寿命.利用Wiener过程得出的钢筋腐蚀寿命预测模型表明,镁水泥混凝土中,氯盐溶液环境中涂层钢筋在1 500 d附近由低腐蚀阶段进入中等腐蚀阶段,硫酸盐溶液环境中涂层钢筋在22 000 d进入中等腐蚀阶段.
参考文献
廉发军.盐渍土地区房屋基础的防腐措施[J].全面腐蚀控制,2019,33(7):83‑84. [百度学术]
LIAN Fajun. Antisepsis measures for house foundation in saline soil area[J]. Total Corrosion Control,2019,33(7):83‑84.(in Chinese) [百度学术]
汪林,甘泓,于福亮,等.西北地区盐渍土及其开发利用中存在问题的对策[J].水利学报, 2001(6):90‑95. [百度学术]
WANG Lin, GAN Hong, YU Fuliang, et al. Salinized soil in northwest China and countermeasures for problems in its development and utilization[J]. Journal of Hydraulic Engineering, 2001(6):90‑95. (in Chinese) [百度学术]
李颖,余红发,董金美,等.氯氧镁水泥的水化产物、相转变规律和抗水性评价方法的研究进展[J].硅酸盐学报,2013,41(11):1465‑1473. [百度学术]
LI Ying, YU Hongfa, DONG Jinmei, et al. Research progress in hydration products, phase transition law and water resistance evaluation method of magnesium oxychloride cement [J]. Journal of the Chinese Ceramic Society, 2013, 41 (11): 1465‑1473. (in Chinese) [百度学术]
严育通,景燕,马军.氯氧镁水泥的研究进展[J].盐湖研究,2008(1):60‑66. [百度学术]
YAN Yutong, JING Yan, MA Jun. Research progress of magnesium oxychloride cement [J]. Salt Lake Study, 2008 (1): 60‑66. (in Chinese) [百度学术]
文静,余红发,吴成友,等. 氯氧镁水泥水化历程的影响因素及水化动力学 [J]. 硅酸盐学报,2013,41(5):588‑596. [百度学术]
WEN Jing, YU Hongfa, WU Chengyou, et al. Hydration kinetic and influencing parameters in hydration process of magnesium oxychloride cement[J]. Journal of the Chinese Ceramic Society, 2013,41(5):588‑596. (in Chinese) [百度学术]
MAZURANIC C, BILLINSKI H, MATKOVIC B. Reaction products in the system MgCl2‑NaOH‑H2O [J]. Journal of the American Ceramic Society,1982,65(10):523‑526. [百度学术]
POWER I M, DIPPLE G M, FRANCIS P S. Assessing the carbon sequestration potential of magnesium oxychloride cement building materials[J].Cement and Concrete Composites,2017,78:97‑107. [百度学术]
乔宏霞,巩位,程千元,等. 盐湖地区镁水泥钢筋混凝土耐久性试验[J]. 煤炭学报,2015,40(增刊2):346‑352. [百度学术]
QIAO Hongxia, GONG Wei, CHENG Qianyuan, et al. Durability of magnesium cement reinforced concrete in saline soil area[J]. Journal of China Coal Society,2015,40(Suppl 2):346‑352. (in Chinese) [百度学术]
乔宏霞,巩位,陈广峰,等. 基于极化曲线的镁水泥混凝土中钢筋腐蚀试验[J]. 华中科技大学学报(自然科学版),2016,44(1):6‑10. [百度学术]
QIAO Hongxia, GONG Wei, CHEN Guangfeng, et al. Experimental study on corrosion of steel bar in magnesium cement concrete based on polarization curves[J]. Journal of Huazhong University of Science and Technology(Nature Science),2016,44(1):6‑10. (in Chinese) [百度学术]
乔宏霞,巩位,高升,等. 镁水泥混凝土中钢筋的电化学腐蚀研究 [J]. 材料科学与工艺,2016,24(1):63‑69. [百度学术]
QIAO Hongxia, GONG Wei, GAO Sheng, et al. Electrochemical corrosion of steel bar in the magnesium cement concrete[J]. Materials Science and Technology, 2016,24(1):63‑69. (in Chinese) [百度学术]
乔宏霞,巩位,王鹏辉,等.硫酸盐环境氯氧镁水泥混凝土中钢筋防护试验[J].西南交通大学学报,2017,52(2):247‑253. [百度学术]
QIAO Hongxia, GONG We, WANG Penghui, et al. Experimental study on steel reinforcement protection in magnesium oxychloride cement concrete under sulfate environment[J]. Journal of Southwest Jiaotong University,2017,52(2):247‑253. (in Chinese) [百度学术]
杨勇涛,贡金鑫,赵尚传.钢筋混凝土结构中钢筋的腐蚀电流密度[J].公路交通科技(应用技术版),2010,6(5):135‑139. [百度学术]
YANG Yongtao, GONG Jinxin, ZHAO Shangchuan. Corrosion current density of reinforcement in reinforced concrete structures[J]. Highway Traffic Technology (Applied Technology) ,2010,6(5):135‑139. (in Chinese) [百度学术]
朱磊,左洪福,蔡景.基于Wiener过程的民用航空发动机性能可靠性预测[J].航空动力学报,2013,28(5):1006‑1012. [百度学术]
ZHU Lei, ZUO Hongfu, CAI Jing. Performance reliability prediction for civil aviation aircraft engine based on Wiener process.[J]. Journal of Aerospace Power,2013,28(5):1006‑1012. (in Chinese) [百度学术]
安秀杰.非线性模拟电路Wiener核故障特征提取的优化方法研究[D].哈尔滨:哈尔滨理工大学,2014. [百度学术]
AN Xiujie. Research on optimization method of Wiener kernel fault fearture extraction for non‑linear analog circuit[D].Harbin: Harbin University of Science and Technology,2014. (in [百度学术]
Chinese) [百度学术]
王兵,郑秋红,郭浩.基于Shannon‑Wiener指数的中国森林物种多样性保育价值评估方法[J].林业科学研究,2008,21(2):268‑274. [百度学术]
WANG Bing, ZHENG Qiuhong, GUO Hao. Economic value assessment of forest species diversity conservation in China based on the Shannon‑Wiener index[J]. Forest Research,2008,21(2):268‑274. (in Chinese) [百度学术]
彭宝华.基于Wiener过程的可靠性建模方法研究[D].长沙:国防科学技术大学,2010. [百度学术]
PENG Baohua. Economic value assessment of forest species diversity conservation in China based on the Shannon‑Wiener index[D]. Changsha: National University of Defense Technology, 2010. (in Chinese) [百度学术]
COX D R, MILLER H D. The theory of stochastic processes[M]. London: Chapman and Hall, 1965:5‑25. [百度学术]
杨兴民,刘保东,李娟.基于Gaussian Copula与t‑Copula的沪深股指相关性分析[J].山东大学学报(理学版),2007,42(12):63‑68,72. [百度学术]
YANG Xingmin, LIU Baodong , LI Juan. Correlation analysis of the Shanghai‑Shenzhen stock index based on Gaussian Copula and t‑Copula[J]. Shandong Daxue Xuebao(Lixue Ban), 2007,42(12):63‑68,72. (in Chinese) [百度学术]