单轴加载下热处理混凝土声电信号特征

为研究火灾发生后混凝土力学性能变化及结构失稳的前兆特征，对混凝土试样进行20、100、200、300、400 ℃的热处理，并进行单轴压缩实验，监测试样受载破坏过程的声电响应信号，识别结构失稳的前兆特征。结果表明：高温热处理后，混凝土试样的外观颜色、内部结构及力学性质均发生了变化，且目标温度越高，试样外观的色变越显著，裂隙发育越丰富，峰值应力越低，而峰值应变越高；随着目标温度的增高，声发射信号和表面电位信号更加活跃，且两种信号的响应与裂纹的扩展密切相关，能够反映试样内部结构损伤演化的过程；对声发射及电位的时序信号进行变异性系数统计，结果表明声发射的变异性系数在试样受载过程中相对稳定，并在试样失稳前具有快速增大至峰值的异常响应，可作为判断试样结构稳定性的前兆。相比声发射信号，电位信号的变异性特征在试样受载初期处于较高值，随后下降，并在试样失稳前快速增大至峰值。

Acoustic emission signal characteristics of heat-treated concrete under uniaxial loading

To study the change of mechanical properties of concrete and the precursory characteristics of structural instability after fire, the uniaxial compression experiments were carried out on concrete specimens after heat treated at 20, 100, 200, 300, 400 ℃ to monitor the acoustic and electrical response characteristics of the specimen under load failure, so as to identify the precursory features of structural instability. The results showed that the appearance color, internal structure and mechanical properties of concrete changes after heated. With the higher temperature, the more obvious color change and the more abundant crack development and the lower maximum stress, the higher maximum strain. AE signal and AP signal become more active with the increase of temperature and the response of the two signals is closely related to the crack growth, these two signals can reflect damage evolution process of the internal structure of the specimen. The AE signals and AP signals were statistically analyzed by variability coefficients. The results showed that the variability coefficient of AE signal is relatively stable during the loading process of the sample, and it has a rapid increase to peak as abnormal response before the sample is unstable, which can be used as a precursor to judge the structural stability of the sample. Compared with the AE signal, the variability characteristic of the AP signal is at a higher value at the initial stage of the sample loading, then decreases, and rapidly increases to a peak before the sample is destabilized.