Wave mixing technique for nondestructive assessment of alkali-silica reaction damage in concrete prism samples

Alkali-silica reaction (ASR) is a deterioration mechanism in concrete that degrades the concrete's strength over time. In a humid environment, concrete may absorb moisture from the surrounding environment. As the absorbed moisture diffuses through the concrete, the ASR gel expands its volume and such volumetric expansion of the ASR gel produces large internal pressure, which may then cause microcracking of the concrete. In this study, we proposed a collinear wave mixing technique with two longitudinal waves to nondestructively evaluate (NDE) the damage induced by ASR in concrete. For experiments, we produced three ASR reactive samples and the other three non-reactive samples. Next, all samples were aged at 38 C° to induce ASR damages. A linear and a nonlinear ultrasonic technique were employed on the concrete prism samples after 30 days and 120 days of aging. Destructive tests were also carried out for the benchmark data of the proposed technique. The result shows the changes in wave velocities are not sufficient or sensitive enough to discern ASR damages. On the other hand, the acoustic nonlinearity parameter shows obvious difference between damaged and non-damaged samples. This result corelates well with the degradation of compressive strength, and thus can be used as a measure of ASR damage for NDE purposes.