Steel Corrosion Monitoring Based on Partial Modulus of Magnetic Gradient Tensor
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摘要:
为研究钢筋混凝土中钢筋锈蚀的无损及定量监测方法，分析地球背景磁场和环境干扰磁场的影响，探讨钢筋的锈蚀率与磁场梯度张量局部模量的理论公式. 通过8根钢筋进行通电加速锈蚀试验模拟钢筋不同程度的锈蚀. 研制钢筋锈蚀监测系统，测量锈蚀前后钢筋的磁感应强度，采用磁场梯度张量局部模量反演钢筋的锈蚀率. 试验结果表明：在钢筋锈蚀后测试的磁感应强度曲线发生非等距离的偏移，磁感应强度绝对值相比锈蚀前有增大也有降低，没有一致性的规律；在锈蚀后钢筋磁场梯度绝对值及局部模量的平均值减小；在钢筋锈蚀的磁场监测中，钢筋自身的磁场梯度及局部模量远远大于环境磁场，环境磁场的梯度及其局部模量可忽略不计；8根试件的计算锈蚀率与试验中实际失重率的最小误差为0.22%，最大误差为9.40%，误差的平均值为3.92%，误差的标准差为3.32%.
Abstract:In order to find a nondestructive and quantitative monitoring method for steel corrosion in reinforced concrete, theoretical formulas of the partial modulus and corrosion rate of rebar are derived with consideration of the influence of the Earth’s background magnetic field and environmental interference magnetic field. Accelerated corrosion tests were performed on 8 steel bars through electrification to obtain specimens with different degrees of corrosion. A rebar corrosion monitoring system was then developed to measure the magnetic field intensity of rebar before and after corrosion. Finally, the partial modulus of the magnetic gradient tensor is used to calculate the corrosion rate of the rebar. Results show that the magnetic field intensity curve of the rebar is generally shifted after corrosion, but the absolute value after corrosion may increase or decrease compared with that before corrosion, without consistency. The absolute value of the magnetic gradient and the average value of the partial modulus of the steel bar after corrosion are less than their counterparts before corrosion. In the magnetic monitoring of rebar corrosion, the magnetic gradient and partial modulus of the rebar are much larger than those of the environmental magnetic field, and therefore the gradient of the environmental magnetic field and its partial modulus are negligible. The minimum error between calculated and measured corrosion rates of the 8 specimens is 0.22%, while the maximum error is 9.40%, and the average error is 3.92%, with a standard deviation of 3.32%.
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Key words:
- reinforced concrete /
- rebar /
- corrosion monitoring /
- magnetic gradient /
- partial modulus
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图 5 钢筋锈蚀前、后的磁感应强度
Figure 5. Magnetic field intensity of rebar before and after corrosion
表 1 试件设计
Table 1. Specimen design
编号 D0/mm l0/m m0/g t/d 1 9.54 503 278.74 4 2 9.43 481 261.81 4 3 9.43 484 265.83 4 4 9.39 485 266.93 4 5 9.48 504 275.56 4 6 9.44 495 272.38 4 7 9.72 500 277.48 5 8 9.60 496 274.91 5 
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表 2 钢筋锈蚀前后对比
Table 2. Comparison before and after corrosion
编号 D0/mm Dc/mm l0/mm lc/mm m0/g mc/g ζ/% 1 9.54 7.90 503 498 278.74 201.70 27.64 2 9.43 8.82 481 478 261.81 237.87 9.14 3 9.43 7.99 484 480 265.83 181.57 31.70 4 9.39 9.19 485 481 266.93 244.68 8.34 5 9.48 8.85 504 502 275.56 231.47 16.00 6 9.44 9.08 495 492 272.38 249.73 8.32 7 9.72 8.88 500 499 277.48 237.56 14.39 8 9.60 9.08 496 491 274.91 249.26 9.33
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表 3 环境磁场参数绝对值的平均值
Table 3. Average absolute values of environmental magnetic
$E\left( {\left| { {B_{{\rm{S} }x} } } \right|} \right)$/nT $E\left( {| { {B_{{\rm{S} }y} } } |} \right)$/nT $E\left( {\left| { {B_{{\rm{S} }{\textit{z}}} } } \right|} \right)$/nT $E\left( {| { {B_{{\rm{S} }xy} } } |} \right)$/（nT•mm−1） $E\left( {| { {B_{{\rm{S}}yy} } }|} \right)$/（nT•mm−1） $E\left( {| { {B_{{\rm{S}}{\textit{z}}y} } } |} \right)$/（nT•mm−1） $E\left( { { {C_{{\rm{S} }y}} } } \right)$/（nT•mm−1） 29142 12439 36654 2.92 6.88 5.01 10.14
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表 4 1号钢筋锈蚀前后磁场参数的平均值对比
Table 4. Comparison of average values of magnetic parameters before and after corrosion of specimen No. 1
项目 E(|Bx|)/nT E(|By|)/nT E(|Bz|)/nT E(|Bxy|)/(nT•mm−1） E(|Byy|)/（nT•mm−1） E(|Bzy|)/（nT•mm−1） E（Cy）/（nT•mm−1） 锈蚀前 36684.76 14767.02 47463.04 647.70 709.75 832.91 1464.17 锈蚀后 32380.07 27619.37 38090.48 468.86 489.32 615.00 1062.76 锈蚀后/
锈蚀前0.882 7 1.870 3 0.822 5 0.723 9 0.689 4 0.738 4 0.725 8
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Table 5. Comparison of calculated and measured corrosion rates
试件编号 η/% ζ/% 误差/% 1 27.42 27.64 0.22 2 12.46 9.14 3.32 3 41.10 31.70 9.40 4 16.00 8.34 7.66 5 18.75 16.00 2.75 6 9.02 8.32 0.70 7 8.83 14.39 5.56 8 11.11 9.33 1.78
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