Subsurface Concrete Damage Detection Using Multifrequency Acoustic Hammer Testing

Abstract

Subsurface crack detection in coated concrete structures is critical to maintaining their structural integrity. The hammer test, a nondestructive and validated technique, is traditionally employed for subsurface crack detection. However, manual hammer testing is often influenced by the subjective judgments of technicians, and the monotony of automated mechanical hammer patterns results in ineffectiveness in some scenarios. To address these limitations, this study devised a novel acoustic detection method that employs multifrequency hammering to identify the damage concealed beneath concrete with fireproof coating. This approach leverages the distinctive excitation effects associated with various hammering frequencies to transform a monotonous hammer soundwave into a composite sound sequence tailored to specific frequencies. It involves collecting acoustic signals from both healthy and damaged concrete specimens subjected to hammering frequencies in the 1–10 Hz range, followed by an analysis of the evolution of the acoustic characteristics with changes in the hammering frequency. The fundamental acoustic features appropriate for concrete excitation were identified, and a qualitative index based on the variations of these characteristics relative to the hammering frequency was developed. This index enabled the effective detection of concealed concrete damage. The results demonstrated that the response of damaged concrete to varying hammering frequencies was markedly more pronounced than that of healthy concrete, thus confirming the efficacy of the proposed method for detecting subsurface cracks under 10 mm-thick fireproof coatings.