摘要
研究了阳极型阻锈剂Na2CrO4和Na2MoO4、阴极型阻锈剂苯并三氮唑(BTA)和N,N‑二甲基乙醇胺(DMEA),以及由这些阻锈剂复配得到的复合型阻锈剂在碳化钢筋混凝土中的阻锈作用,通过钢筋的自然电位、腐蚀面积率、失重率和电化学法研究了钢筋在碳化混凝土中的腐蚀程度和腐蚀速率.结果表明:碳化混凝土中钢筋的抗腐蚀性随着阻锈剂掺量的增加而提高,随着碳化时间的增加而降低;复掺1.00%Na2MoO4和1.00%BTA时,碳化混凝土中钢筋的腐蚀程度最小,阻锈剂的阻锈效果最佳;复合型阻锈剂延缓钢筋腐蚀速率的效果优于单一型阻锈剂,同一掺量条件下,复掺Na2MoO4和BTA阻锈剂延缓钢筋腐蚀速率的效果最佳.
碳化是引起钢筋腐蚀的主要原因之
本文研究了碳化作用下,内掺不同类型钢筋阻锈剂的混凝土中钢筋的自然电位、腐蚀面积率和失重率、电化学交流阻抗Nyquist曲线和极化曲线等,阐明了常用阻锈剂对钢筋腐蚀的影响机理,以期为阻锈剂在钢筋混凝土中的优化使用提供理论依据.
强度等级为42.5的普通硅酸盐水泥,其化学组
SiO | Fe2O3 | Al2O3 | MgO | CaO | SO3 | K2O | Na2O | Other |
---|---|---|---|---|---|---|---|---|
20.89 | 5.44 | 3.96 | 1.71 | 62.24 | 2.65 | 0.21 | 0.27 | 2.63 |
C | Si | Mn | P | Al | Cr | Ni | S | Fe |
---|---|---|---|---|---|---|---|---|
4.00 | 3.00 | 21.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 67.00 |
钢筋埋入试件前,先用10%的柠檬酸铵溶液浸泡5 d以去除其表面的氧化皮,随后将其从溶液中取出并用水冲洗干净,经毛巾擦干后放入约100 ℃的烘箱内烘10 min,再用粗、细砂纸将烘干后的钢筋打磨光亮,用无水乙醇除去其表面的油脂,经检查无锈痕后用保鲜膜将其密闭包裹备用.
制备混凝土和水泥净浆试件,分别用于钢筋的腐蚀程度和腐蚀速率测试.
混凝土和水泥净浆试件的尺寸和构造如

图1 混凝土和水泥净浆试件的尺寸和构造示意图
Fig.1 Schematic diagram of dimension and structure of concrete and cement paste specimens(size: mm)
混凝土的配合比为m(水泥)∶m(水)∶m(砂)∶m(石)=1.0∶0.4∶2.5∶3.6.水泥净浆的水胶比为0.4.在混凝土和水泥净浆中分别掺入0.50%、1.00%、2.00%的阻锈剂(以水泥质量计),复掺2种阻锈剂时,其质量比为1∶1,未掺阻锈剂的混凝土和水泥净浆试件为参比样(reference).文中试件编号以掺量+阻锈剂代号记,如0.50C为掺0.50%Na3CrO4阻锈剂的试件,0.25C0.25B为复掺0.25%Na3CrO4和0.25%BTA阻锈剂的试件.试件成型后置于标准条件下((20±2) ℃、相对湿度为95%以上)养护至24 h拆模,再置于标准条件下继续养护至28 d,最后放入二氧化碳体积分数为(20±3)%、(20±5) ℃、相对湿度为(70±5)%的碳化箱中碳化至预定龄期后进行各项测试.
用加拿大Giatec公司生产的CELL型半电池电位测定仪分别测定混凝土试件碳化7、14、28、90、120、150、180、240、270、300 d时钢筋的自然电位,并根据ASTM C87
将碳化360 d的混凝土试件压碎后取出内置钢筋,以钢筋的腐蚀面积率(P)和失重率(R)判断钢筋的腐蚀程度,评估阻锈剂的阻锈效果.用一张透明硫酸试纸包裹在钢筋表面,在纸上描出并涂黑钢筋的腐蚀部分,再用计算面积方格纸求出腐蚀部分的面积,记为S,钢筋的原表面积记为S0,用
(1) |
(2) |
用普林斯顿公司生产的PARSTAT 3000A型电化学工作站分别测试水泥净浆试件碳化7、28、90、120 d时的电化学交流阻抗Nyquist曲线,以及碳化28、90 d时的极化曲线,以判断钢筋的腐蚀速率.电化学交流阻抗Nyquist曲线的频率范围为1 Hz~10 kHz,正弦交流振幅值为5 mV,应用电压范围为±6 V;极化曲线的开路电位为±10 mV,极化方向为相对开路电位的-10~+10 mV,扫描速率为9 mV/min,用CView软件进行极化曲线拟合.
钢筋腐蚀时会形成原电池作用,从而使其自然电位偏离零电位点,因此测试混凝土中钢筋的自然电位偏离零电位点的程度,可以表征其耐腐蚀性的差异.

图2 碳化钢筋混凝土中钢筋的自然电位
Fig.2 Spontaneous potentials of steel bars in carbonated reinforced concrete

图3 碳化钢筋混凝土中钢筋的腐蚀面积率和失重率
Fig.3 Corrosion area percent and mass loss percent of steel bars in carbonated reinforced concrete
由
阻锈剂类型不同时,钢筋的腐蚀面积率和失重率有较大差别,这与不同类型阻锈剂的阻锈原理有关.钢筋腐蚀是由于其发生了电化学反应,该反应通过阴、阳极之间的电子传递完成.阳极型阻锈剂通过抑制阳极区铁基体失去电子或减缓其失去电子的速率来减缓钢筋腐蚀的进程,并且能够在钢筋表面生成较为致密的Fe2O3和羟基氧化铁(FeOOH)以阻止钢筋的进一步腐
由

图4 碳化水泥净浆的交流阻抗Nyquist曲线
Fig.4 Nyquist plots of carbonated cement pastes
为进一步分析掺加阻锈剂的碳化水泥净浆中钢筋的导电机理,结合ZSimpWin软件进行等效电路拟合分

图5 预埋钢筋的水泥净浆示意图及其电化学阻抗等效电路模型
Fig.5 Schematic diagram of cement paste with embedded steel bar and its equivalent circuit model

图6 碳化水泥净浆的极化曲线
Fig.6 Polarization curves of carbonated cement pastes
有研究指
(3) |
式中:v为腐蚀速率,g/(
经极化曲线外推法拟合计算后得到碳化水泥净浆中钢筋的腐蚀速率,如

图7 碳化水泥净浆中钢筋的腐蚀速率
Fig.7 Corrosion rate of steel bars in carbonated cement pastes
(1)碳化混凝土中钢筋的抗腐蚀性随着阻锈剂掺量的增加而提高,随着碳化时间的增加而降低.
(2)单一型阻锈剂按阻锈效果排序为Na2MoO4优于Na2CrO4、BTA优于DMEA;复掺1.00%Na2MoO4和1.00%BTA时,碳化混凝土中钢筋的腐蚀程度最小,阻锈剂的阻锈效果最佳.
(3)复合型阻锈剂延缓钢筋腐蚀速率的效果优于单一型阻锈剂,同一掺量条件下,复掺Na2MoO4和BTA阻锈剂对钢筋腐蚀速率的延缓效果最佳.
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