The effects of moisture and micro-structural modifications in drying mortars on vibration-based NDT methods

In this paper, we investigate the utility of vibration-based NDT tests to detect the subtle microstructural modifications and cracking damage in Portland cement mortars subjected to oven drying treatment. Both linear (resonant mode frequency and damping) and nonlinear (nonlinear hysteretic behavior) vibration test data are reported, collected from samples having a range of water to cement ratios and at two different aggregate contents. All test data are affected by the drying treatments, but it appears that the resonant mode frequency response is dominated by the reduction in internal moisture content with drying and changing aggregate cement ratio of the mixture. On the other hand, the linear mode damping, and more so the nonlinear hysteretic parameter, are more influenced by the microstructural modification and cracking damage caused by drying. In particular it appears that the nonlinear hysteretic parameter is very sensitive to internal damage and microstructural modifications caused by oven drying, but not notably sensitive to pore moisture content, and water to cement and aggregate to cement ratios.