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<p>To the best of the authors’ knowledge, this study investigates the monitoring of self-healing in low carbon Limestone Calcined Clay (LC₃) concrete that incorporates crude urease derived from <i>Bacillus sphaericus</i> using diffuse ultrasound and S-Transform time frequency analysis. Bacterial crude urease (obtained via ultrasonic cell lysis) and a cementation solution containing 0.5&#xa0;M urea and 0.5&#xa0;M calcium lactate were applied to pre-cracked LC₃ specimens (crack width 0.5–0.7&#xa0;mm). Diffuse ultrasonic wave measurements (200–450&#xa0;kHz) were used to track the healing process over a 40-day period. The ultrasonic diffusivity coefficient (D) increased from 5.8 to 15.2 m<sup>2</sup>/s (approaching the uncracked value of 18.5 m<sup>2</sup>/s) with increasing healing, according to the results, while the dissipation coefficient (σ) reduced from 18.1 to 6.4 1/ms, showing calcium-carbonate-rich deposits. For LC₃ + <i>B. sphaericus</i> urease, the average healing exponent n = 0.41, which was significantly larger than the control LC₃ without bacteria (<i>n</i> = 0.12). The S-Transform determined healing intensity followed an exponential trend I = I₀h<sup>n</sup>. After 35&#xa0;days of healing, water permeability tests verified that the flow rate decreased from an initial 8.5&#xa0;mL/min to below detectable levels (&lt; 0.1&#xa0;mL/min), which correlated well with ultrasonic intensity gain (R<sup>2</sup> = 0.94). After healing, electrical resistivity rose from 85 Ω·m (cracked condition) to 210 Ω·m, or 92% of the uncracked LC₃ value (228 Ω·m). The precipitation of calcium-carbonate-rich precipitates inside fissures was verified by SEM EDS. The proposed diffuse ultrasound, S-Transform framework demonstrates potential as a laboratory-based tool for quantitative, non-destructive monitoring of healing progression. With further development, it could inform future smart infrastructure monitoring systems, though field validation remains necessary.</p> Graphical Abstract <p></p>

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Quantification of Bio-Mediated Crack Healing in LC₃ Low-Carbon Concrete Using Diffuse Ultrasound and S-Transform Analysis

  • 期刊论文

  • 发表日期：

    2026年6月14日

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  • Mahakavi Palanichamy,
  • Azween Bin Abdullah,
  • A. Daniel

摘要

To the best of the authors’ knowledge, this study investigates the monitoring of self-healing in low carbon Limestone Calcined Clay (LC₃) concrete that incorporates crude urease derived from Bacillus sphaericus using diffuse ultrasound and S-Transform time frequency analysis. Bacterial crude urease (obtained via ultrasonic cell lysis) and a cementation solution containing 0.5 M urea and 0.5 M calcium lactate were applied to pre-cracked LC₃ specimens (crack width 0.5–0.7 mm). Diffuse ultrasonic wave measurements (200–450 kHz) were used to track the healing process over a 40-day period. The ultrasonic diffusivity coefficient (D) increased from 5.8 to 15.2 m2/s (approaching the uncracked value of 18.5 m2/s) with increasing healing, according to the results, while the dissipation coefficient (σ) reduced from 18.1 to 6.4 1/ms, showing calcium-carbonate-rich deposits. For LC₃ + B. sphaericus urease, the average healing exponent n = 0.41, which was significantly larger than the control LC₃ without bacteria (n = 0.12). The S-Transform determined healing intensity followed an exponential trend I = I₀hn. After 35 days of healing, water permeability tests verified that the flow rate decreased from an initial 8.5 mL/min to below detectable levels (< 0.1 mL/min), which correlated well with ultrasonic intensity gain (R2 = 0.94). After healing, electrical resistivity rose from 85 Ω·m (cracked condition) to 210 Ω·m, or 92% of the uncracked LC₃ value (228 Ω·m). The precipitation of calcium-carbonate-rich precipitates inside fissures was verified by SEM EDS. The proposed diffuse ultrasound, S-Transform framework demonstrates potential as a laboratory-based tool for quantitative, non-destructive monitoring of healing progression. With further development, it could inform future smart infrastructure monitoring systems, though field validation remains necessary.

Graphical Abstract