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<p>This study investigates the self-healing performance and microstructural evolution of ultra-high performance cementitious composites (UPCs) incorporating ultra-fine fly ash (UFA) and metakaolin (MK) for sustainable construction and mining applications. Portland cement was replaced by 25 wt.% UFA or MK, either individually or as a binary blend of 12.5 wt.% each, to enhance durability and autogenous crack healing. All mixes included 1.5&#xa0;vol.% basalt fibers for crack control. Pre-cracked specimens (40–200&#xa0;μm) were subjected to 28&#xa0;days of water immersion followed by CO<sub>2</sub> carbonation at 25°C (5&#xa0;mL/min) for up to 56&#xa0;days. Results showed that UFA-containing mixes achieved flexural strength recovery exceeding the original uncracked values, with UPC-UFA exhibiting the highest impermeability recovery index after 56&#xa0;days. Cracks up to 40&#xa0;μm were almost completely sealed in all mixes by day 28, while effective closure of 200-μm cracks occurred only in the UFA and UFA-MK systems. Thermogravimetric analysis indicated reduced portlandite and increased formation of C-S-H and ettringite in pozzolan-rich mixes. Nitrogen adsorption revealed a dominant gel pore size of 5–8&#xa0;nm, while MK reduced cumulative pore volume to 0.07&#xa0;cm<sup>3</sup>/g and shifted pore distribution toward 2–4&#xa0;nm by confirming a significant microstructural densification.</p>

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Tailoring Self-Healing and Pore Characteristics of Cracked Ultra-high-performance Cementitious Composites Through Dual Pozzolanic Additive Integration and Carbonation

  • 期刊论文

  • 发表日期：

    2026年6月26日

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  • Nejib Ghazouani,
  • Ahmed Babeker Elhag,
  • Ali Raza

摘要

This study investigates the self-healing performance and microstructural evolution of ultra-high performance cementitious composites (UPCs) incorporating ultra-fine fly ash (UFA) and metakaolin (MK) for sustainable construction and mining applications. Portland cement was replaced by 25 wt.% UFA or MK, either individually or as a binary blend of 12.5 wt.% each, to enhance durability and autogenous crack healing. All mixes included 1.5 vol.% basalt fibers for crack control. Pre-cracked specimens (40–200 μm) were subjected to 28 days of water immersion followed by CO2 carbonation at 25°C (5 mL/min) for up to 56 days. Results showed that UFA-containing mixes achieved flexural strength recovery exceeding the original uncracked values, with UPC-UFA exhibiting the highest impermeability recovery index after 56 days. Cracks up to 40 μm were almost completely sealed in all mixes by day 28, while effective closure of 200-μm cracks occurred only in the UFA and UFA-MK systems. Thermogravimetric analysis indicated reduced portlandite and increased formation of C-S-H and ettringite in pozzolan-rich mixes. Nitrogen adsorption revealed a dominant gel pore size of 5–8 nm, while MK reduced cumulative pore volume to 0.07 cm3/g and shifted pore distribution toward 2–4 nm by confirming a significant microstructural densification.