Bacteria induced calcium carbonate precipitation based on metabolic conversion of nutrients has been acknowledged for having potentials in self-healing cement-based materials. Recent studies have shown the development of bacteria-based repair solution (liquid) for concrete surface repair. This article demonstrates the feasible application of the solution as healing agent to be injected into porous network concrete (PNC). This type of concrete has a porous core which can be used as a media to transport healing agents into the fracture zone. The repair capacity of the solution have been assessed by monitoring the bio-mineral precipitation in the porous cylinder cores. The X-ray tomography and permeability tests at certain time interval were carried out before and after injection of the solution. Polished sections were prepared and examined under ESEM after healing period to investigate healing capacity. The healing potential was then tested by injecting the solution into PNC. The injection of tap water and bacteria based solution was performed through porous network until it reached and flew out through the crack which was formed by three-point bending loading. The healing efficiency was measured by water permeability test before and after injection at several time intervals. The specimens injected with bacteria based solution and cured in wet condition showed higher healing efficiency compared to dry cured specimens.

This work presents a bacteria-based bead for potential self-healing concrete applications in low-temperature marine environments. The bead consisting of calcium alginate encapsulated bacterial spores and mineral precursor compounds was assessed for: oxygen consumption, swelling, and its ability to form a biocomposite in a simulative marine concrete crack solution (SMCCS) at 8 °C. After six days immersion in the SMCCS the bacteria-based beads formed a calcite crust on their surface and calcite inclusions in their network, resulting in a calcite-alginate biocomposite. Beads swelled by 300% to a maximum diameter of 3 mm, while theoretical calculations estimate that 0.112 g of the beads were able to produce ∼1 mm³ of calcite after 14 days immersion; providing the bead with considerable crack healing potential. The bacteria-based bead shows great potential for the development of self-healing concrete in low-temperature marine environments, while the formation of a biocomposite healing material represents an exciting avenue for self-healing concrete research.

The concept of self-healing concrete - a concrete which can autonomously repair itself after crack formation, with no or limited human intervention - has received a lot of attention over the past 10 years as it could help structures to last longer and at a lower maintenance cost. This paper gives an overview on the key aspects and recent advances in the development of the bacteria-based self-healing concrete developed at the University of Technology of Delft (The Netherlands). Research started with the screening and selection of concrete compatible bacteria and nutrients. Several types of encapsulated bacteria and nutrients have been developed and tested. The functionality of these healing agents was demonstrated by showing metabolic activity of activated bacterial spores by oxygen consumption measurements and by regain of material functionality in form of regain of water tightness. Besides development of bacteria-based self-healing concrete, a bacteria-based repair mortar and liquid system were developed for the treatment of aged concrete structures. Field trials have been carried out with either type of bacteria-based systems and the promising results have led to a spinoff company Basilisk Self-Healing Concrete with the aim to further develop these systems and bring them to the market.

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.

Self-healing concrete has drawn a lot of attention in recent years. There are numerous projects worldwide that work on the development of self-healing agents. Among those, bacteria-based self-healing concrete is a very promising solution to prevent durability problems in concrete that are related with cracking. Bacteria-based self-healing concrete not only provides sealing of open micro-cracks that endanger the structure’s health, but it also has economical and environmental benefits, since it will extend the lifetime of the structure and reduce repair costs. In this study, the bacteria-based self-healing agent consists of alkaliphilic bacterial spores, organic mineral precursor compounds and LightWeight Aggregates (LWA). Although the success of the concept has been proven in previous research, in this study an optimized method for the incorporation of the organic compounds into the LWA has been developed. The method allows more of the organic compounds to be stored into the LWA. This paper focuses on comparing performance on mechanical properties and sealing efficiency of cracks of mortar samples from past and current research. The initial hypothesis of the study was that the lightweight mortar with the higher amount of healing agent will show faster and more efficient crack sealing capacity. The comparison revealed different results than expected. In fact, the sealing efficiency trend proved to be similar for the two studies which was speculated to be due to oxygen limitation rather than healing agent limitation in permanently water submersed specimens.