Abstract: 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.

Key words: concrete, uniaxial compression, heat treatment, acoustic emission and surface potential signals, coefficient of variation