Macro and microstructure evaluation of self-healing cement mortar enhanced with microbe-immobilized hemp fiber

Abstract

Sustainable construction materials are gaining attention in structural engineering to improve performance and reduce environmental impact. This study presents an eco-friendly composite of hemp fiber-reinforced cement mortar with self-healing bacteria, aimed at improving mechanical properties and crack repair efficiency. Microbe immobilized fiber enhanced (MIFE) cement mortar was developed by incorporating dormant bacterial spores of Priestia megaterium and Bacillus licheniformis through the mixing water, with hemp fibers serving as carrier medium. The MIFE mortar was tested at various fiber content levels, specifically 0 %, 0.5 %, 1 %, and 1.5 % by weight of cement, to evaluate its structural efficacy through comprehensive compressive strength tests, strength regain assessments, water absorption analysis, and detailed microstructural evaluations. The results revealed a significant 22 % increase in compressive strength with 1 % hemp fiber content, attributed to enhanced particle cohesion and reduced microstructural voids. The fiber's ability as a carrier to uniformly facilitate calcite precipitation also led to a notable 4.31 % reduction in water absorption. Morphological studies of CaCO<inf>3</inf> from healed cracks in biomortar specimens demonstrated that the bio-environment and microbial interactions significantly influenced calcite polymorph formation, with vaterite crystals showing improved mechanical integrity and reduced chemical reactivity. The present study underscores the potential of microbe-immobilized hemp fibers as a green reinforcement option in cementitious materials, offering improved mechanical performance, self-healing capabilities, and environmental sustainability. These findings also align with the increasing focus on bio-based composites in the evolution of structural engineering, complementing the industry's shift toward sustainable construction materials. © 2025 Institution of Structural Engineers