Detection of alkali-silica reaction within large-scale concrete by ultrasound non-collinear wave mixing

Early detection of alkali-silica reaction (ASR) with nondestructive evaluation (NDE) is important for the monitoring of damage and assessment of repair performance, while effective NDE in large-scale reinforced concrete elements remains challenging. Nonlinear acoustic methods have shown promise for this application due to their sensitivity to the microscale damage characteristic of early-stage ASR. The objective of this investigation is to examine if a recently introduced NDE method employing ultrasonic non-collinear wave mixing may be used to detect and quantify internal ASR damage in large-scale reinforced concrete elements. Measured nonlinearity parameters from an undamaged concrete column are compared with those from reinforced and unreinforced concrete columns both experiencing ASR damage. This study incorporates corrections for attenuation and diffraction in the measured amplitudes of the mixed wave signals to allow for direct comparisons among the three columns, and at two different depths. The nonlinearity parameters measured for the undamaged and ASR-affected columns show clear differences, which are independently validated through scanning electron microscopy (SEM) and ultrasonic second harmonic wave generation (SHG) testing on an extracted core. While severities of damage at two depths were not clearly discernible by SEM, the nonlinearity metrics from both wave mixing and SHG measurements exhibit similar trends of higher nonlinearity at greater depths. These experimental results demonstrate that the non-collinear wave mixing technique is a promising NDE method for detecting and quantifying internal microscale damage in large-scale concrete members.