Microbial calcite induction: a magic that fortifies and heals concrete
Résumé
Prevention of concrete structure from premature deterioration has become a major challenge around the world, and its high maintenance cost demands an eco-friendly and economical alternative. Apart from the conventional healing of cracks using chemicals, a microbial crack repairing strategy has given promising results. The concept of bio-concrete is based on Microbially Induced Calcium Carbonate Precipitation (MICCP) which involves the usage of microorganisms (direct or encapsulated) to increase the durability of concrete structure, reduce its water permeability, and self-healing of cracks. MICCP involves autotrophic and heterotrophic pathways of bio-mineralization, while calcite is the most common and stable polytype of calcium carbonate. Bacteria possess various coding and regulatory genes for enzymes (urease and carbonic anhydrase) involved in calcite precipitation; however, most of the genetic studies in this perspective are done on pathogenic organisms. The respective technique is now being successfully employed in the fields of geo-technology and civil engineering for concrete strengthening, soil consolidation, monument restitution, and low energy construction. The formulation of smart cement and space bricks are some recent developments. The efficacy of different bacteria for fortification of concrete and aggregates, auto-repairing of cracks, restoration architecture, and potential properties of smart cement are focused on, in this review article.