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<p>The construction industry is a major contributor to environmental pollution and CO₂ emissions, with cement production being a primary factor. This study explored reducing cement consumption by developing a sustainable self-healing concrete incorporating ferrock as a partial cement substitute (5%, 15%, 25%) and <i>Bacillus tropicus</i> immobilized on natural Sisal Fibers (SF). A dual-nutrient strategy combining Artificial Nutrients (AN) with Watermelon Seed Powder (WMSP) was adopted. M40 grade concrete (1:1.46:2.84, w/c = 0.34) was prepared, with four groups: control (Mix 0), ferrock (Mix 1), ferrock with fibers (Mix 2), and ferrock with immobilized fibers (Mix 3). After 28 days of curing, Mix 3B achieved the highest compressive strength (60.75&#xa0;MPa) and density (2521&#xa0;kg/m³). Flexural strength increased by 1.40 (M3A) and 1.58 (M3B) compared to control, while bond strength with reinforcement also improved. Though water absorption increased with ferrock and fiber combinations, Ultrasonic Pulse Velocity (UPV) indicated excellent quality across all mixes, including pre-cracked bacterial specimens. Mix 3 demonstrated over 16% higher regain compressive strength relative to the control bacterial mix (M0B). Crack widths ranged from 0.31 to 0.92&#xa0;mm, with M3B exhibiting the highest healing efficiency (90.22%). Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) analyses confirmed formation of calcite, vaterite, CaCO₃, Fe₂O₃, and C–S–H gel, validating the synergistic self-healing action of ferrock and bacteria. Ferrock enhances strength through dense packing, resulting in an increase in the iron-silicate matrix. Bacteria improve both pre- and post-cracking strength by precipitation of CaCO<sub>3</sub>, which fills the pores and microcracks and polishes the Interfacial Transition Zone (ITZ). The fibers of sisal manage the crack width and prevent the crack from developing. WMSP supplies urease, which is used to realize a repeated growth of CaCO<sub>3</sub>, so that it self-heals. Cement Use Efficiency (CUE) and Economy Index (EI) analyses showed conventional mixes offered higher short-term efficiency but Mix 3B provided the optimal balance of mechanical performance, reduced carbon footprint, and sustainability. The results highlight ferrock–bacteria synergy as a viable strategy for eco-friendly, durable concrete in repair applications.</p>

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Performance of Dual Nutrient on Immobilized Bacterial Self-healing Concrete with Ferrock as a Sustainable Cement Substitute

  • 期刊论文

  • 发表日期：

    2026年4月8日

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  • K. Elakkiya,
  • P. V. Monishka Kamala Durga,
  • A. Sumathi

摘要

The construction industry is a major contributor to environmental pollution and CO₂ emissions, with cement production being a primary factor. This study explored reducing cement consumption by developing a sustainable self-healing concrete incorporating ferrock as a partial cement substitute (5%, 15%, 25%) and Bacillus tropicus immobilized on natural Sisal Fibers (SF). A dual-nutrient strategy combining Artificial Nutrients (AN) with Watermelon Seed Powder (WMSP) was adopted. M40 grade concrete (1:1.46:2.84, w/c = 0.34) was prepared, with four groups: control (Mix 0), ferrock (Mix 1), ferrock with fibers (Mix 2), and ferrock with immobilized fibers (Mix 3). After 28 days of curing, Mix 3B achieved the highest compressive strength (60.75 MPa) and density (2521 kg/m³). Flexural strength increased by 1.40 (M3A) and 1.58 (M3B) compared to control, while bond strength with reinforcement also improved. Though water absorption increased with ferrock and fiber combinations, Ultrasonic Pulse Velocity (UPV) indicated excellent quality across all mixes, including pre-cracked bacterial specimens. Mix 3 demonstrated over 16% higher regain compressive strength relative to the control bacterial mix (M0B). Crack widths ranged from 0.31 to 0.92 mm, with M3B exhibiting the highest healing efficiency (90.22%). Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) analyses confirmed formation of calcite, vaterite, CaCO₃, Fe₂O₃, and C–S–H gel, validating the synergistic self-healing action of ferrock and bacteria. Ferrock enhances strength through dense packing, resulting in an increase in the iron-silicate matrix. Bacteria improve both pre- and post-cracking strength by precipitation of CaCO3, which fills the pores and microcracks and polishes the Interfacial Transition Zone (ITZ). The fibers of sisal manage the crack width and prevent the crack from developing. WMSP supplies urease, which is used to realize a repeated growth of CaCO3, so that it self-heals. Cement Use Efficiency (CUE) and Economy Index (EI) analyses showed conventional mixes offered higher short-term efficiency but Mix 3B provided the optimal balance of mechanical performance, reduced carbon footprint, and sustainability. The results highlight ferrock–bacteria synergy as a viable strategy for eco-friendly, durable concrete in repair applications.