Insights into delayed ettringite formation damage through acoustic nonlinearity

A nonlinear acoustic approach for the detection and quantification of damage in mortars affected by delayed ettringite formation (DEF) is used to provide insights into the degradation mechanism at the microscale and its correlation with bulk expansion. The nonlinear acoustic technique, Nonlinear Impact Resonance Acoustic Spectroscopy (NIRAS) successfully differentiates among mortars experiencing various amounts of expansion and microstructurally-evident distress due to DEF. Results indicate that mortars are damaged both during the early-age high-temperature curing and subsequent 23 °C-limewater curing. However, the time of initiation of expansion occurs earlier for samples showing higher damage level (as measured by average nonlinearity parameter) at the end of high-temperature curing. During the exposure period, the ratio of absolute maximum to the initial average nonlinearity parameter of DEF-affected mortars varies from 3 to 30, indicating that the DEF damage can increase more than an order of magnitude greater than that experienced during the high-temperature curing.