Bacteria-based self-healing concrete has the ability to heal cracks due to the bacterial conversion of incorporated organic compounds into calcium carbonate. Precipitates seal the cracks, theoretically increasing the service life of constructions. The aim of this paper is to propose a precursor for bacteria-based self-healing concrete derived from organic waste streams, produced is in line with the circular economy principle and ideally more affordable than other substrates. To verify the applicability of the proposed healing agent, some fundamental requirements of the proposed system are studied, such as its influence on functional properties, crack sealing capacity and evidence of bacterial activity in concrete.

Bacteria‐based self‐healing concrete is an innovative concrete that contains a self‐healing agent that provides the material with enhanced autonomous crack‐sealing performance. A specific type of this concrete, based on a healing agent composed of bacterial spores and lactate as carbon source, has been developed and applied by the Delft University of Technology for over ten years. Under laboratory conditions it was proven that, depending on the dosage of healing agent, self‐healing of cracks up to 0.8 mm widths occurs. As such the material potentially allows reduction of steel reinforcement used for crack width limitation in watertight constructions. Application of self‐healing concrete would therefore not only result in a reduction of costs but also in improvement of environmental performance (lower CO2 footprint) and ease of in situ casting due to reduction of use of steel in waterproof applications. However, according to the EN 1990 Eurocode (Basis of structural design), customary application of a novel type of concrete must be preceded by full scale demonstrators proving evidence for safe and functional performance. In this contribution we portray full scale application of bacteria‐based self‐healing agent as developed by the Delft research group in two repair mortar‐ and in two concrete construction demonstrator projects. These demonstrator projects show that addition of the bacteria‐based self‐healing agent to the concrete mix is safe as no negative side effects on construction performance was observed. However, it also proved difficult to find evidence for increased crack‐healing performance as cracking in the demonstrator constructions hardly occurred. In further full scale demonstrators we therefore plan to drastically reduce amount of crack width‐restraining reinforcement to show crack-healing capacity and potential to save on use of reinforcement steel in watertight concrete constructions.

Lactate, produced by fermentation of e.g. cane or corn residues, can serve as a carbon source in bacterial healing for cement-based materials such as concrete. Bacterial spores, activation nutrients and a carbon source are mixed in with dry concrete or mortar constituents upon material production. Upon cracking of the concrete matrix and ingress of water, an active bacterial colony forms and starts to convert the included carbon source to CO₂. In the alkaline surrounding of concrete carbonates form and deposit as minerals on the crack surface, sealing the entrance to further ingress. In this work a lactate derivative based healing agent containing bacteria and activation nutrients is added to a commercial mortar, exerting negligible effect on the mortar strength development. Functionality of the agent is indicated by oxygen consumption under aerobic conditions and shown by regain of crack water tightness beyond the autogenous healing capacity in a permeability test. In order to indicate feasibility for healing agent application in a commercial setting, the environmental burden is discussed and a competitive production price is estimated.

In this chapter an overview will be given of the biotechnological possibilities for repair of concrete with focus on application of limestone-producing bacteria and the different metabolic pathways involved, e.g., via hydrolysis of urea and heterotrophic CO₂ production under alkaline conditions. The first paragraph comprises an overview of previously published reports on this subject. In the two succeeding paragraphs, two specific systems for biotechnological repair of concrete structures will be discussed. The first one covers liquid biobased repair systems for durable repair of cracked and porous concrete surfaces, and the second one addresses biobased mortar systems for repair of larger defects of concrete structures. The cases discussed here indicate that concrete repair applying biotech solutions results in improved material durability that can save money and at the same time lower the environmental impact of civil engineering activities.