Evaluation of self-healing in concrete using linear and nonlinear resonance spectroscopy

Abstract

In this study, self-healing in concrete incorporating two types of healing agents, i.e., 1) a self-healing capsule and 2) supplementary cementitious materials with crystalline admixtures, is monitored using linear and nonlinear resonance acoustic spectroscopy techniques. Beam-shaped concrete specimens are prepared using the healing agents, and after 28 days, a single vertical crack with a width ranging from 0.25 to 0.35 mm is generated at the center of the specimens. To monitor the self-healing process in concrete, the samples are vibrated via impact-based excitation methods in the flexural and longitudinal directions, whereas the linear resonance frequency and acoustic nonlinearity parameter are measured for two months. Additionally, the acoustic nonlinearity parameter is analyzed using two different methods: 1) multiple impacts with manually controlled amplitude, and 2) single impact with artificially controlled amplitude by changing the windowing region in a signal. Test results show that the linear resonance frequency increases up to 86%–97% that of the uncracked condition after 63 days of self-healing. The linear trend of the resonance frequency is correlated significantly with the decrease in the external crack area, but the change in is affected by the presence of partially filled cracks than by the overall crack area.