Mechanisms of Crack Propagation in Concrete and Control of Cracking

点击翻译按钮获取中文摘要

Mechanisms of crack propagation are investigated to control cracking in concrete. To clarify mechanisms of crack nucleation, a stress intensity factor in the linear elastic fracture mechanins was studied. A new method to determine a critical stress intensity factor is proposed. In experiments of notched beams, acoustic emission (AE) events were monitored, and critical load levels of frequent AE generation were determined. The stress intensity factor in a tested beam was analyzed numerically by the boundary element method (BEM), to take into account the exact notch configuration. From these AE observation and BEM analysis, the critical stress intensity factors of concrete materials were determined. Although the conventional critical values of the stress intensity factor were reported as dependent on specimen size and notch depth, obtained values are reasonably independent of them.A quantitative AE waveform analysis is investigated, on the basis of a generalized theory of AE which we previously proposed. The method developed can provide information on crack location, crack type, and crack orientation.To control cracking in existing concrete structures, a diagnostic method for cracks is proposed, which consists of the critical stress intensity factor, the AE waveform analysis, the ultrasonic spectroscopy, and AE characteristics in the core test. In the design phase, limit designs for controlling crack widths were investigated. Experiments on reinforced concrete beams with notches were carried out. Results confirm the applicability of limit designs proposed to control crack widths.