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.

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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.@en

Soft inclusions, such as capsules and other particulate admixtures are increasingly being used in cementitious materials for functional purposes (i.e. self-healing and self-sensing of concrete). Yet, their influence on the fracture behaviour of the material is sometimes overlooked and requires in-depth study for the optimization of mechanical and/or smart properties. An experimental investigation is presented herein on the role of bacteria-based lactate-derived particles on the fracture behaviour of cement paste in tensile configuration. These admixtures are currently used for the purpose of self-healing. Digital Image Correlation was used to obtain strain contours on the surface of the samples during the test. The influence of soft particles addition and age of the samples on the fracture mechanics of the composite were investigated.@en

In case of water retaining structures healing should occur under active flow conditions, with various water pressures and speeds of leakage. The present study was undertaken in order to evaluate the effect on crack repair of mortar by bacteria-based healing under active water flow. The mortar with the bacteria-based lactate-derived healing agent (HA) was added by 2% of cement mass. The results of the crack healing effect which was evaluated based on water permeability test were compared with normal mortar. The permeability test was carried out with various heights of water head. Disks with above 0.5mm crack in the middle was used as specimens. Consequently, the water flow rate increased as the water head became large, however it started to decrease as time goes by. It is probable that cracks will be repaired by bacteria-based healing under active water flow because the water tightness of with HA mortar reached 99%. On the other hand the tightness of normal mortar did not reach more than 97%. It was observed that the crack surface was healed by some material. from microscopic observation. The results of this study shows that the HA can be applied to crack repair system under active water flow. @en

Water tightness of a concrete cover layer is important, as it is typically used as a protective coating of the steel reinforcement. Water tightness can be impaired by crack formation or by permeability. A bacteria-based lactate-derived healing agent (HA) can be added to concrete to enhance the potential for restoration of water tightness. Bacterial conversion of the included carbon source results in CO2 production and subsequent CaCO3 precipitation, similar to the mechanism of concrete carbonation. Carbonation is known to densify concrete, particularly when using ordinary Portland cement (OPC), but to a much lower extend in slag-based concrete (CEM III/B). To identify the effect of HA addition on concrete properties, this study focusses on the ingress of moisture in non-cracked concrete surfaces by assessing capillary water absorption. Surface properties were determined for sealed and unsealed surfaces of concrete—either based on OPC or CEM III/B—before and after curing under three different conditions: Dry, wet, or humid. HA addition to concrete containing slag cement generated a surface less prone to continued drying, but resulted in higher water absorption. In contrast, surface water absorption significantly decreased upon HA addition to OPC-based samples, independent of the curing regime. It is therefore concluded that HA in its current form is suitable for application in OPC, but less in CEM III/B-based mixtures@en

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.

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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.

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Self-healing of cracks in concrete can be achieved by application of bacteria which metabolically convert organic compounds under aerobic conditions yielding limestone. Added to the concrete mix as part of a healing agent, bacteria can, via metabolic activity resulting in limestone formation, seal cracks of up to 0.8mm width resulting in waterproofing and increased frost damage resistance of the concrete. Besides increasing the autogenous crack healing capacity of concrete, these bacteria can also be applied to improve bond strength of repair mortar and act as limestone producing agent in liquid concrete repair systems. This paper will review current state-of-the art bacteria-based self-healing concrete technologies investigated and applied by the Delft University research group specifically using bacteria which yield limestone after aerobic metabolic conversion of organic compounds under alkaline conditions.@en