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<p>While the use of seawater (SW) and dredged marine sand (DMS) offers a sustainable alternative to conventional freshwater–river sand concrete systems, their elevated concentrations of Cl⁻, SO<sub>4</sub><sup>2</sup>⁻, Ca<sup>2</sup>⁺, and Mg<sup>2</sup>⁺ create a multi-ionic environment that fundamentally alters the durability performance of seawater sea-sand concrete (SWSSC). This study examines the coupled effects of silica fume (SF), metakaolin (MK) and bacillus-subtilis (B.S) driven microbial calcite precipitation (MICP) on crack healing, ion transport and microstructural evolution of SWSSC. Results show that MICP in SWSSC follows a distinct ion-regulated pathway, shaped by competitive interactions that modify bacterial activity, carbonate polymorphs and pore connectivity. Ca<sup>2</sup>⁺ availability emerged as the primary regulator of MICP; SF sharply reduced the Ca/Si ratio and densified the matrix, limiting Ca<sup>2</sup>⁺ for microbial mineralisation and producing non-uniform healing. MK, by contrast, preserved a more favourable calcium balance that enabled sustained precipitation. Elevated Mg<sup>2</sup>⁺ shifted carbonate formation from trigonal calcite toward orthorhombic, and at high Mg/Ca ratios, poorly crystalline aragonite, revealing a previously unreported polymorph competition that enhanced crack bridging but offered limited densification. Concurrently, SO₄<sup>2</sup>⁻ promoted ettringite formation that partially offset microbial benefits. Multi-scale analyses confirmed that MK generated the strong pozzolan–microbial synergy, while SF produced a dense but biologically less responsive binder requiring tighter calcium-budget control. These findings provide a mechanistic blueprint for designing next-generation bio-enhanced marine concretes capable of autonomous crack repair under chloride–magnesium–sulphate conditions.</p>

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Self-Healing Performance of Seawater Sea-Sand Concrete Incorporating Bacteria and Supplementary Cementitious Materials: Mechanistic Insights and Durability Enhancement

  • 期刊论文

  • 发表日期：

    2026年5月7日

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  • Seyed Mohammad Mehdi Asadzadeh,
  • Mohammadreza Baradaran,
  • Gholam Reza Atefatdoost

摘要

While the use of seawater (SW) and dredged marine sand (DMS) offers a sustainable alternative to conventional freshwater–river sand concrete systems, their elevated concentrations of Cl⁻, SO42⁻, Ca2⁺, and Mg2⁺ create a multi-ionic environment that fundamentally alters the durability performance of seawater sea-sand concrete (SWSSC). This study examines the coupled effects of silica fume (SF), metakaolin (MK) and bacillus-subtilis (B.S) driven microbial calcite precipitation (MICP) on crack healing, ion transport and microstructural evolution of SWSSC. Results show that MICP in SWSSC follows a distinct ion-regulated pathway, shaped by competitive interactions that modify bacterial activity, carbonate polymorphs and pore connectivity. Ca2⁺ availability emerged as the primary regulator of MICP; SF sharply reduced the Ca/Si ratio and densified the matrix, limiting Ca2⁺ for microbial mineralisation and producing non-uniform healing. MK, by contrast, preserved a more favourable calcium balance that enabled sustained precipitation. Elevated Mg2⁺ shifted carbonate formation from trigonal calcite toward orthorhombic, and at high Mg/Ca ratios, poorly crystalline aragonite, revealing a previously unreported polymorph competition that enhanced crack bridging but offered limited densification. Concurrently, SO₄2⁻ promoted ettringite formation that partially offset microbial benefits. Multi-scale analyses confirmed that MK generated the strong pozzolan–microbial synergy, while SF produced a dense but biologically less responsive binder requiring tighter calcium-budget control. These findings provide a mechanistic blueprint for designing next-generation bio-enhanced marine concretes capable of autonomous crack repair under chloride–magnesium–sulphate conditions.