Assessment of sulfate attack and freeze-thaw cycle damage of cement-based materials by a nonlinear acoustic technique

In this work, a nondestructive evaluation technique (NDE) based on nonlinear impact resonance acoustic spectroscopy (NIRAS) is applied to the assessment of mortar and concrete damage caused by the sulfate attack and freeze-thaw cycles. The nonlinear parameter is defined as the relative shift of resonance frequency against the vibration acceleration magnitude and compared with traditional parameter (i.e. linear resonance frequency) for damage characterization. The nonlinear parameter increases with the development of sulfate attack damage in mortar samples and presents a positive correlation with the expansion results in the standard accelerated experiments, indicating the feasibility of NIRAS technique in assessment of sulfate attack damage. The experimental results also validate the sensitivity of NIRAS technique to sulfate attack damage. The nonlinear parameter increases about 140 % and 3700 % after 2 and 3 months of sulfate solution exposure, while the linear resonance frequency changes about 5 % and 24 %, respectively. On the other hand, the nonlinear parameter shows a monotonically increasing trend for concrete samples subjected to increased freeze-thaw cycles and presents an appreciable distinction for samples having different capillary water. The nonlinear parameter of concrete samples with 0.55 w/c ratio is about 10 times that of concrete samples with 0.45 w/c ratio after 150 freeze-thaw cycles. The experimental results in this paper demonstrate that the developed NIRAS technique not only can be used a good NDE method for damage assessment of cement-based materials caused by durability problem such as sulfate attack and freeze-thaw cycles, but also has the potential to reveal the variation of microstructural characteristics of materials such as the microcracking development and moisture content change.