不同导电相对混凝土裂缝智能化自监测的灵敏度与噪声水平的影响

采用四电极法测量了弯曲荷载作用下智能混凝土梁受拉侧裂缝扩展过程的电阻变化率(ρ_FCR)，对比了碳黑（CB）、钢纤维（SF）、碳纤维（CF）不同组合及掺量对裂缝自监测灵敏度系数(K)的影响；并基于分形理论研究了归一化处理后的电阻变化率-裂缝扩展宽度曲线(ρ’_FCR-w’_COD)的粗糙程度，以反映不同导电材料对监测信号电阻变化率-裂缝扩展宽度曲线(ρ_FCR-w_COD)噪声水平的影响。研究表明:用线性函数拟合混凝土裂缝智能化自监测信号ρ_FCR-w_COD曲线的效果较好，K可用拟合直线的斜率来表征；随着SF掺量的增加，试件的K随之减小；双掺SF与纳米CB试件表现出最佳的裂缝智能化自监测性能，适量纳米CB的掺入对混凝土裂缝监测的K值有提升作用，同时可降低ρ’_FCR-w’_COD曲线的噪声水平，随着CB掺量的增加，试件的K值呈现先增后减、分形维数D值呈先减后增的规律，纳米CB的最佳掺量为1.0~1.5 kg/m3；CF的掺入对K值有一定的负面影响，但掺入CF的试件裂缝监测信号D值随导电相掺量变化而变化的程度不大。 

Influence of conductive materials on the crack sensing sensitivity and noise signal of smart concrete

The four-electrode method was used to measure the fraction change in resistance (ρ_FCR) during the crack propagation of the concrete beam subjected to bending. The effect of carbon black(CB), steel fiber (SF) and carbon fiber (CF) content and their combination on the crack self sensing gauge factor (K) of the concrete beam was compared and analyzed. Based on the fractal theory, the effect of different conductive materials on the noise level of the normalized fractional change in resistance - crack opening displacement curve (ρ’_FCR-w’_COD) was studied. The results show that the linear fitting analysis fit well with the fraction change in resistance-crack opening displacement curve (ρ_FCR-w_COD) and K can be characterized as the slope of the fitted line. In addition, K decreases with the increasing of the SF content. The specimens with the addition of SF and nano CB reveal the best crack self sensing ability among all the specimens. K can be improved while the tortuosity of the ρ’_FCR-w’_COD curve is reduced by the addition of nano CB. Specifically, the K values exhibit an increasing tendency till the CB increases to a certain content and then K decreases for even higher content of CB. However, the fractal dimensions (D) of the specimens and CB content show an inverse tendency. Furthermore, the optimum dosage of nano CB is 1.0-1.5 kg/m3. There exists a negative effect on the K value with the addition of CF, however, the standard deviation of D of the ρ'_FCR-w'_COD curves is reduced for the specimens with CF.