Encapsulation Techniques and Test Methods of Evaluating the Bacteria-Based Self-Healing Efficiency of Concrete: A Literature Review

Abstract

Crack formation in concrete structures due to various load and non-load factors leading to degradation of service life is very common. Repair and maintenance operations are, therefore, necessary to prevent cracks propagating and reducing the service life of the structures. Accessibility to affected areas can, however, be difficult as the reconstruction and maintenance of concrete buildings are expensive in labour and capital. Autonomous healing by encapsulated bacteria-based self-healing agents is a possible solution. During this process, the bacteria are released from a broken capsule or triggered by water and oxygen access. However, its performance and reliability depend on continuous water supply, protection against the harsh environment, and densification of the cementitious matrix for the bacteria to act. There are vast methods of encapsulating bacteria and the most common carriers used are: encapsulation in polymeric materials, lightweight aggregates, cementitious materials, special minerals, nanomaterials, and waste-derived biomass. Self-healing efficiency of these encapsulated technologies can be assessed through many experimental methodologies according to the literature. These experimental evaluations are performed in terms of quantification of crackhealing, recovery of durability and mechanical properties (macro-level test) and characterization of precipitated crystals by healing agent (micro-level test). Until now, quantification of crack-healing by light microscopy revealed maximum crack width of 1.80mm healed. All research methods available for assesing self-healing efficiency of bacteria-based healing agents are worth reviewing in order to include a coherent, if not standardized framework testing system and a comparative evaluation for a novel incorporated bacteria-based healing agent.

A Biomineralization, Mechanical and Durability Features of Bacteria-Based Self-Healing Concrete—A State of the Art Review

“…Seifan [70,171] is the only researcher who has examined the evaluation of the self-healing performance of nanomaterial bacterial vehicles with respect to durability and mechanical qualities. More experimental procedures and investigation on self-healing bacterial vehicles are strongly recommended to improve reliability [172]. Testing of mechanical properties and durability in cemented materials is limited to compression and water penetration, respectively.…”

A Review of Lightweight Self-Healing Concrete

“…The research on self-healing concrete is often carried out by encapsulating bacteria in carriers. The most commonly used carriers are a polymer material, LWA, cementitious material, special minerals, nanomaterial, and waste-derived biomass [ 62 ]. The carrying performance of LWAs for bacteria is discussed here.…”

Self-Healing Concrete: Concepts, Energy Saving and Sustainability

“…Structural tests are performed on the macro-, micro-, and nanoscales to define a performance criterion for hardened concrete. Assessments of macrostructure, microstructures, and nanostructures are also performed [8].…”