A primary challenge for the current fleet of light water reactors in the United States is age-related degradation of their passive assets that include concrete, cables, piping, and the reactor pressure vessel. Various nondestructive techniques exist for locally assessing degradation in passive structures in nuclear power plants. This paper presents results from the analysis of acoustic data acquired using the vibro-acoustic modulation (VAM) technique on a medium-sized concrete slab (2 × 2 × 0.5 ft), which has undergone degradation due to alkali-silica reaction (ASR). VAM is a nonlinear vibration technique in which the structure of interest is excited using a combination of specific frequencies and the response is recorded. VAM assumes that an undamaged structure can be represented by a linear system while the representation of a damaged structure must include nonlinearity. Two piezo-stack actuators are used to excite the slab. One stack is dedicated to excite the slab at a low frequency, referred to as pump frequency, and another stack is dedicated to excite the slab at a high frequency, referred to as probe frequency. The concrete slab was cured in an environmental chamber to accelerate ASR-related degradation. In this paper, the measured acoustic signals are analyzed in both the time and frequency domains to understand state of health of the concrete specimen.

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