Chloride erosion test and life prediction of HPC-NC gradient column under dry-wet cycles
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摘要: 为提高海洋潮汐与浪溅区钢筋混凝土结构受氯盐侵蚀的耐久性，提出了一种高性能混凝土(HPC)-普通混凝土(NC)梯度柱新型结构，设计了一种干湿循环试验方法进行氯盐侵蚀试验，研究其在不同试验参数影响下内部氯离子的传输规律；通过理论推导与拟合计算，建立了混凝土内部氯离子分布的简化计算模型，并验证了模型的合理性；基于所建简化模型，对设计的梯度柱进行了钢筋初锈时间的寿命预测。研究结果表明：采用功能梯度结构能有效适应潮汐与浪溅区结构上部受干湿循环作用、下部受长期浸泡作用的侵蚀特点，不同外掺剂组合作用抑制了氯离子的侵蚀，HPC内自由氯离子含量比NC降低了17.7%；表面氯离子含量随时间而增大，并有趋于稳定的趋势，符合指数分布特征；无论是长期浸泡作用还是干湿循环作用下，氯离子扩散系数均随作用时长增加而减小，其减小速率随时间增加而降低，最终趋于稳定；根据建立的氯离子分布简化计算模型得到的氯离子分布曲线，与试验及相关文献的氯离子分布曲线相对误差在12%以内；得到了60~80 mm保护层厚度下有无外掺剂时钢筋初锈的预警时间分别为41~85和26~47年，因此，掺加阻锈剂与侵蚀抑制剂可显著提高HPC-NC梯度柱的寿命。Abstract: In order to improve the durability of steel-reinforced concrete structures subjected to chloride erosion in marine tidal and splash zone, a new structure of high performance concrete(HPC) -normal concrete(NC) gradient column was proposed. A dry-wet cycle test method was designed to conduct the chloride erosion test. The transmission law of internal chloride ions under the influence of different test parameters was studied. A simplified calculation model of chloride ion distribution in concrete was established by theoretical derivation and fitting calculation, and the rationality of the model was verified. The life prediction of initial corrosion time of steel bars was performed for the designed gradient structure based on the simplified model. Research results show that the functional gradient structure can effectively adapt to the erosion characteristics of the upper part in the tidal and splash zone subjected to dry-wet cycles and the lower part subjected to long-term immersion. The combination of different admixtures inhibits the erosion of chloride ions, and the free chloride ion content in HPC is 17.7% lower than that in NC. The surface chloride ion content increases with time and tends to stabilize, which conforms to the exponential distribution. The chloride ion diffusion coefficient decreases with action time under long-term immersion or dry-wet cycles. Its reduction rate decreases with time, and finally tends to stabilize. Compared with the values from the test and related literatures, the relative error of chloride ion distribution curve obtained by the simplified calculation model is within 12%. The early warning times of initial corrosion of steel bars with and without admixture under the protective layer thickness of 60-80 mm are 41-85 and 26-47 years, respectively, proving that the addition of rust inhibitor and erosion inhibitor can significantly improve the service life of HPC-NC gradient column.
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图 1 混凝土柱尺寸与配筋(单位: mm)
Figure 1. Sizes and reinforcements of concrete columns (unit: mm)
图 6 非梯度与梯度试件自由氯离子含量对比
Figure 6. Comparison of free chloride ion contents in gradient and non-gradient specimens
图 7 不同外掺剂作用下HPC自由氯离子含量
Figure 7. Free chloride ion contents of HPC under different admixtures
图 9 下部长期浸泡表面氯离子含量拟合曲线
Figure 9. Fitting curves of chloride ion content on surface of lower part after long-term immersion
图 10 不同试验时长试件氯离子扩散系数
Figure 10. Chloride ion diffusion coefficients of specimens with different test times
表 1 HPC混凝土配合比
Table 1. Mix proportion of high performance concrete
材料 水泥 粉煤灰 矿粉 水 砂 石子 抑制剂 减水剂 阻锈剂 用量/(kg·m-3) 282.0 94.0 94.0 155.0 739.0 1 022.0 6.1 18.8 6.1 
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表 2 C40 NC配合比
Table 2. Mix proportion of C40 normal concrete
材料 水泥 水 砂 石 减水剂 用量/(kg·m-3) 487 185 533 1 245 6.8
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表 3 HPC-NC梯度柱氯盐干湿循环试验工况
Table 3. Chloride dry-wet cycle test conditions of HPC-NC gradient columns
试件编号 构件类型 阻锈剂 侵蚀抑制剂 干湿循环周期/d T1-1-1-120 梯度 有 有 120 T2-1-0-120 梯度 有 无 120 T3-0-0-120 梯度 无 无 120 T4-1-0-120 梯度 有 无 120 T5-0-0-120 梯度 无 无 120 T6-0-0-90 梯度 无 无 90 T7-0-0-60 梯度 无 无 60 P0-0-0-120 普通 无 无 120
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表 4 不同试验时长氯离子侵蚀深度
Table 4. Chloride ion erosion depths at different test times
试件 各测点氯离子侵蚀深度/mm 平均深度/mm 1 2 3 4 5 6 7 T5-0-0-120 上部干湿循环 22.1 22.7 17.8 19.6 21.5 23.1 17.5 20.6 下部长期浸泡 19.8 24.7 22.5 18.9 16.7 20.3 19.9 20.4 T6-0-0-90 上部干湿循环 16.7 21.2 17.8 21.3 18.4 17.5 18.8 18.8 下部长期浸泡 17.3 16.9 18.3 15.4 17.7 21.3 16.4 17.6 T7-0-0-60 上部干湿循环 15.3 18.6 11.1 10.6 14.8 13.2 18.3 14.5 下部长期浸泡 11.6 15.7 14.5 18.5 19.4 11.4 15.7 15.3
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表 5 各试件氯离子含量峰值
Table 5. Peak chloride ion contents of each specimen
% 试验条件 T1-1-1-120 T2-1-0-120 T3-0-0-120 T4-1-0-120 T5-0-0-120 T6-0-0-90 T7-0-0-60 P0-0-0-120 下部长期浸泡 0.521 0.536 0.531 0.524 0.504 0.457 0.406 0.517 上部干湿循环 0.511 0.518 0.561 0.522 0.549 0.467 0.426 0.621
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表 6 扩散系数拟合结果
Table 6. Fitting results of diffusion coefficient
试件 扩散系数/(10-6 mm2·s-1) 相关系数 标准差/(10-10 mm2·s-1) 干湿循环 长期浸泡 干湿循环 长期浸泡 干湿循环 长期浸泡 T7-0-0-60 2.21 4.55 0.982 3 0.990 2 3.06 1.59 T6-0-0-90 1.94 3.99 0.973 9 0.993 3 6.98 1.48 T5-0-0-120 1.78 3.57 0.979 1 0.992 3 4.67 1.47 P0-0-0-120 4.18 3.54 0.971 0 0.972 6 10.00 5.74
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表 7 不同保护层厚度下钢筋初锈预警时间
Table 7. Early warning times of initial rust of steel bars with different protective layer thicknesses
保护层厚度/ mm 钢筋初锈时间/a 无外掺作用技术基准 单阻锈剂作用HPC 双掺作用HPC 60 26 35 41 65 30 46 56 70 35 54 64 75 41 63 73 80 47 71 85
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