Failure precursors in rocks and concrete

We monitor the damage process in different types of rocks and concrete specimens during laboratory fracture tests by low-frequency acoustic emission (elastic emission or ELE) analysis. Specimens made of dry Green Luserna Granite and concrete enriched with Iron are subjected to compressive loading at constant displacement rate and under ordinary room conditions. ELE signals are detected by applying to the specimen surface an accelerometric transducer, sensitive in the frequency range from few Hz to 10 kHz. We find that irreversible deformations are associated with relative electrical resistance variation, which is monitored by using copper electrodes coupled to specimens by conductive silver paint and connected to a multimeter. The experimental results show that ELE activity and change in electrical resistance are strictly correlated during the entire loading process and precede the failure of all tested specimens. These two techniques are complementary for damage monitoring in rocks and concrete.