摘要
为了评估阻锈剂对再生混凝土中钢筋的保护作用,设计了钢筋再生混凝土恒电流通电加速锈蚀试验,对再生混凝土中钢筋进行电化学试验,分析钢筋极化曲线及交流阻抗,计算钢筋腐蚀电流密度,并以腐蚀电流密度作为损伤变量,运用Weibull分布函数建立再生混凝土中钢筋的可靠度函数.钢筋通电加速试验后,对钢筋进行微观形貌观测.结果表明:随着通电时间的增加,未掺阻锈剂的再生混凝土试件中钢筋表面出现颗粒状的锈蚀物;掺加阻锈剂的再生混凝土试件中钢筋表面出现大量的微裂纹;可靠度为60%时未掺和掺加阻锈剂试件中钢筋失效时间分别为880、2 060 h,阻锈剂可以使再生混凝土使用寿命延长至原来的2.34倍.
20世纪以来,钢筋混凝土结构成为世界上应用最为广泛的结构形
分析混凝土中钢筋锈蚀情况,对研究钢筋混凝土结构使用寿命非常重要.刘
采用合理有效的防护措施,可以延长钢筋混凝土结构使用寿命.张晏
综上,国内外诸多学者对于钢筋锈蚀状态及防护技术进行了大量研究,但是,对于钢筋再生混凝土中钢筋的研究较
甘肃省祁连山水泥厂生产的P42.5普通硅酸盐水泥;兰州某商砼公司提供的堆积密度为1 569 kg/
再生混凝土配合比见
本文采用湿盐砂通电方案,将埋入砂土中的钢筋混凝土作为阳极,直径12 mm的石墨碳棒作为阴极,选用量程为5 V和3 A的PS‑3002D‑Ⅱ型直流电源进行恒电流通电.配制质量分数为5%的NaCl与质量分数为5%的MgSO4复合盐溶液,对砂土进行喷洒,用来模拟西部盐渍土环境.在通电过程中不定期对砂土洒水,采用土壤湿度检测仪控制砂土湿度,确保通电过程中砂土湿度适中一致;同时定期喷洒复合盐溶液,以保证腐蚀离子浓度,通电加速锈蚀试验示意图如

图1 通电加速锈蚀试验示意图
Fig.1 Schematic diagram of electrification accelerated corrosion test
(1) |
式中:i为外测极化电流密度;ΔE为极化电位;βa为阳极Tafel斜率;βc为阴极Tafel斜率.

图2 再生混凝土中钢筋的极化曲线
Fig.2 Polarization curves of steel bars in recycled concrete

图3 再生混凝土中钢筋腐蚀电流密度
Fig.3 Corrosion current density of steel bars in recycled concrete

图4 RC组钢筋交流阻抗图
Fig.4 AC impedance diagrams of steel bars in RC group

图5 RC‑R组钢筋交流阻抗图
Fig.5 AC impedance diagram of steel bars in RC‑R group
分析可知钢筋混凝土体系有1~2个时间参数,等效电路拟合如下:
①1个时间参数:
(2) |
②2个时间参数:
(3) |
式中:ω为角频率;RC为初始氧化层阻抗;QC为初始氧化层电容;RS,C、QS,C分别为溶液与再生混凝土串联的阻抗和电容;RCr/C、QCr/C分别为钢筋锈蚀层或阻锈剂氧化层的阻抗和电容;Rt为阻锈剂氧化层腐蚀反应的电荷转移阻抗;QD为阻锈剂氧化层表面的双电层电容;QW为Warburg阻抗.
在可靠度统计分析中,Weibull分布因其在对小样本数据的预测中具有精确度高的特点而被广泛应
(4) |
式中:R为可靠度;t为通电时间;m为形状参数,表示密集程度;β为尺度参数.

图7 钢筋腐蚀电流密度概率图
Fig.7 Probability diagram of corrosion current density of steel bars
本文以钢筋腐蚀电流密度的变化作为钢筋损伤变量D:
(5) |
式中:icorr,t为通电t时间的腐蚀电流密度;icorr,N为腐蚀电流密度的阈值.根据
用钢筋损伤变量计算退化量ω0,取钢筋的锈蚀程度为60%时达到钢筋破坏阈
(6) |
本文利用最小二乘法计算形状参数和尺度参数.将其代入

图8 再生混凝土中钢筋的可靠度曲线
Fig.8 Reliability curves of steel bars in recycled concrete
由
(1)在288 h通电加速锈蚀试验后,添加阻锈剂的RC‑R组钢筋腐蚀电流密度为0.491 6 µA/c
(2)对比2组试件经过288 h通电加速锈蚀试验后钢筋的SEM图发现,RC组钢筋表面的锈蚀较严重,有颗粒状锈蚀物的出现,RC‑R组钢筋表面呈现网格状裂纹,锈蚀较轻微.
(3)使用Weibull分布函数对再生混凝土中钢筋的可靠度进行评估,发现通电前期,RC组试件的可靠度下降速率较快,可靠度为60%时RC组和RC‑R组钢筋的失效时间分别为880、2 060 h,阻锈剂可使钢筋再生混凝土的使用寿命延长至原来的2.34倍.
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