Lotots'kyj Y. Acoustic emission estimation of the early stages of crack propagation in concrete and reinforced concrete

3. The object of the research - elastic wave fields generated during initiation and propagation of fracture in solids. The aim of the research is to quantita-tively evaluate the parameters of acoustic emission (АЕ) signals that accom-pany the early stages of fracture in either concrete or reinforced concrete and, on the basis of that evaluation, to develop a methodology of AE diagnostics of large-size structure elements. Methods used in the research: mathematic mod-eling, numeric methods, linear fracture mechanics approaches, fractographic analysis, ultrasonic and AE methods, mechanical testing, statistical methods for experimental data analysis. Novelty: a logic scheme of the relationships and the sequences of physico-chemical factors on initiation of crack-like de-fects in concrete (with or without reinforcement) and their connection with the elastic AE wave generation. Crack initiation caused by disbonding of inclusion from cement matrix was proved theoretically. It was established that the intensity of formation and an equivalent area of such defects depends on both the orientation of inclusion within the cement matrix and its shape. Re-sults - the numeric values AE signal parameters were obtained for the follow-ing: the initial stages of cement matrix fracture; disbonding of gravel and crashed stone from the matrix; disbonding of the reinforced bars from the concrete matrix. The AE elastic wave attenuation coefficient was determined for different kinds of concrete and reinforced concrete. A combined theoretic-experimental method was introduced for the evaluation of the numeric values of the AE signal parameters during the initiation and subcritical growth of a macrocrack in reinforced concrete. An optimization algorithm was developed for the AE transducers placement at the tested objects. Guidelines for the AE diagnostics of large-scale structures are proposed. The results of this research were implemented during the field testing of the bridges belonging to the Ukrainian highways. The application field - civil engineering.