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<p>Microcracks are a major cause of long-term deterioration in concrete structures, as they permit water and aggressive chemicals to enter and weaken the matrix. In this study, a self-healing approach was explored using expanded clay pellets impregnated with Bacillus subtilis, which can precipitate calcite and seal cracks. The pellets protect the bacteria from the high alkalinity of cement and create a favorable microenvironment when combined with calcium lactate as a nutrient source. Mortar specimens were prepared with 0–35% pellet replacement and tested for compressive strength, flexural strength, and ultrasonic pulse velocity. Microstructural studies confirmed the presence of dense calcite formations that bridged voids and refined the pore networks. The optimal performance occurred at a 20–25% replacement rate, yielding the highest compressive and flexural strengths and improved UPV, indicating a denser and less permeable matrix. Machine learning models: Response Surface Methodology, Gradient Boosting Trees, and Extreme Gradient Boosting were developed to predict the mechanical response using mixed variables and UPV. Among them, GBT delivered the strongest prediction accuracy with low error. This study demonstrates that bacteria-infused pellets can partially replace fine aggregates while facilitating autonomous crack healing, providing a practical, scalable, and sustainable approach for durable cement-based materials. In addition to mechanical and microstructural improvements, the proposed system offers potential economic and environmental advantages by partially replacing natural fine aggregates with lightweight expanded clay pellets, thereby reducing raw material consumption and waste generation. The use of non-toxic <i>Bacillus subtilis</i> and calcium lactate aligns with environmentally safe and regulatory compliant practices. Furthermore, this approach supports sustainable construction by enhancing durability and reducing long-term maintenance costs.</p>

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Optimizing mechanical performance and self-healing efficiency of cement mortar using bacteria-infused expanded clay pellets: an experimental and machine learning approach

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月14日

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  • T. Soumya,
  • Gautam,
  • P. V. Siva Kumar,
  • P. Kanchanamala,
  • Grandhi Siva Sankar,
  • M. Sumesh,
  • Sivarethinamohan R,
  • Sathvik Sharath Chandra

摘要

Microcracks are a major cause of long-term deterioration in concrete structures, as they permit water and aggressive chemicals to enter and weaken the matrix. In this study, a self-healing approach was explored using expanded clay pellets impregnated with Bacillus subtilis, which can precipitate calcite and seal cracks. The pellets protect the bacteria from the high alkalinity of cement and create a favorable microenvironment when combined with calcium lactate as a nutrient source. Mortar specimens were prepared with 0–35% pellet replacement and tested for compressive strength, flexural strength, and ultrasonic pulse velocity. Microstructural studies confirmed the presence of dense calcite formations that bridged voids and refined the pore networks. The optimal performance occurred at a 20–25% replacement rate, yielding the highest compressive and flexural strengths and improved UPV, indicating a denser and less permeable matrix. Machine learning models: Response Surface Methodology, Gradient Boosting Trees, and Extreme Gradient Boosting were developed to predict the mechanical response using mixed variables and UPV. Among them, GBT delivered the strongest prediction accuracy with low error. This study demonstrates that bacteria-infused pellets can partially replace fine aggregates while facilitating autonomous crack healing, providing a practical, scalable, and sustainable approach for durable cement-based materials. In addition to mechanical and microstructural improvements, the proposed system offers potential economic and environmental advantages by partially replacing natural fine aggregates with lightweight expanded clay pellets, thereby reducing raw material consumption and waste generation. The use of non-toxic Bacillus subtilis and calcium lactate aligns with environmentally safe and regulatory compliant practices. Furthermore, this approach supports sustainable construction by enhancing durability and reducing long-term maintenance costs.