Quantification of self-healing in bacteria-based engineered cementitious composites

Crack repair in concrete is crucial, since cracks are the main cause of decreased service life in concrete structures. An original and promising way to repair cracks is to pre-incorporate healing agents inside the concrete matrix to heal cracks the moment they appear. By incorporating bacteria and nutrients as a two-component healing agent, the process of bacterially mediated calcium carbonate deposition is triggered on crack formation, and self-healing of cracks can be expected. This paper investigates the recovery of mechanical properties due to self-healing behaviour of bacteria-based engineered cementitious composites (ECCs). In this research study, Sporosarcina pasteurii and Bacillus subtilis subsp. spizizenii were selected as two different bacterial strains, with zeolite as a protective carrier. Four-point bending and ultrasonic pulse velocity tests were performed on ECC specimens to evaluate their mechanical properties during damage and healing processes. Microstructural observations to quantify self-healing compounds were performed using X-ray diffraction analyses and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The bacteria-incorporated ECC specimens were found to be promising in the healing of cracks (showing total healing of 80 mu m wide cracks) and recovery of flexural strength and stiffness.