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<p>Current ultrasonic testing methods for detecting defects in concrete primarily rely on transmission testing, which requires access to both sides of the structure. However, owing to the semi-infinite foundation support characteristics of pavement systems, traditional transmission-based approaches are impractical for identifying internal defects. To address this limitation, an experimental framework was designed in this study that utilized prefabricated void defects within concrete pavement samples to systematically analyze reflected ultrasonic signals. Three distinct signal acquisition techniques were compared: vertical incidence, 15° oblique incidence, and 20° oblique incidence. Advanced signal processing via Short-time fourier transform (STFT) generates high-resolution time–frequency spectrograms for defect characterization. The key findings indicate that ultrasonic reflection methods effectively detect void interfaces in pavement slabs, with maximum acoustic pressure peaks occurring at impedance mismatch boundaries (e.g., concrete-air interfaces). The STFT-derived time–frequency maps exhibited distinctive energy distribution patterns, where void regions showed pronounced color intensity shifts compared to intact areas. Notably, the 15° oblique incidence demonstrated superior defect discriminability, as its time–frequency profiles consistently resolved overlapping reflections from multilayered media.</p>

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Experimental Study on Void Detection in Pavement Using Ultrasonic Testing Based on Short-Time Fourier Transform

  • 期刊论文

  • 发表日期：

    2026年7月25日

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  • Lifang Zhang,
  • Shuqi Wang,
  • Hanwei Tian

摘要

Current ultrasonic testing methods for detecting defects in concrete primarily rely on transmission testing, which requires access to both sides of the structure. However, owing to the semi-infinite foundation support characteristics of pavement systems, traditional transmission-based approaches are impractical for identifying internal defects. To address this limitation, an experimental framework was designed in this study that utilized prefabricated void defects within concrete pavement samples to systematically analyze reflected ultrasonic signals. Three distinct signal acquisition techniques were compared: vertical incidence, 15° oblique incidence, and 20° oblique incidence. Advanced signal processing via Short-time fourier transform (STFT) generates high-resolution time–frequency spectrograms for defect characterization. The key findings indicate that ultrasonic reflection methods effectively detect void interfaces in pavement slabs, with maximum acoustic pressure peaks occurring at impedance mismatch boundaries (e.g., concrete-air interfaces). The STFT-derived time–frequency maps exhibited distinctive energy distribution patterns, where void regions showed pronounced color intensity shifts compared to intact areas. Notably, the 15° oblique incidence demonstrated superior defect discriminability, as its time–frequency profiles consistently resolved overlapping reflections from multilayered media.