Embedding bacteria into concrete that can seal cracks on its own can potentially extend the life of bridges, tunnels, and buildings.
Concrete is the most widely used building material in the world; despite this, it suffers from cracking and deterioration under stress and environmental conditions, and repairing this damage is a laborious and carbon-intensive process.
To counter this, researchers are now looking at developing self-healing concrete, which can heal its cracks on its own. At the University of Bath, a team led by Professor Kevin Paine is using dormant bacteria and nutrients in concrete mixes so that any cracks in the concrete are filled with limestone, which will heal the damage. In 2025-26, their “smart concrete” research project, under the EPSRC RM4L scheme, culminated in a trial in which a reinforced concrete panel on a highway upgrade was constructed with bacterial healing agents and tested under stress conditions. As Professor Paine says, their aim is to develop “smart materials can evolve over their lifespan”, embedding “self-immunity and resilience” to improve safety and cut maintenance costs.Concrete structures such as bridges, dams, tunnels, and pavements will inevitably have microcracks, allowing water and chloride ions to penetrate, leading to corrosion and failure. In the UK, ~£40 billion is spent annually on repairing such structures. Climate change, leading to extreme weather events, and a predicted doubling of cement-based CO2 by 2050 mean that engineers are looking for sustainable, self-sustaining structures. One such innovative solution is to utilize the natural ability of microbes to precipitate minerals. The basic principle of microbiologically induced calcite precipitation is that extremophile bacteria, such assp., can remain dormant in an alkaline environment, such as that found in concrete . However, upon germination in the presence of a moisture-rich environment, such as that found in a crack, they metabolize a compound such as calcium acetate, producing limestone as a byproduct. This has the effect of forming limestone bridges to close a crack. University of Bath researchers note that this process yields CO₂ and water only . For example, the Bath team describes: “If the concrete cracks, the bacteria are released and exposed to oxygen and water. They feed on the growth media, they multiply, and as a result of metabolic actions, calcium carbonate forms to seal the crack before it has a chance to enlarge”. This harnesses a natural “self-healing” pathway, analogous to how living tissues repair damage. The major engineering problem is how to protect the bacteria during mixing and curing. The mixing of concrete is lethal to bacteria. The last decade of research has demonstrated that the answer is micro-encapsulation of bacterial spores and nutrients in a protective vehicle until needed. Previous research involved encapsulating calcium lactate, nutrients, and spores in lightweight aggregates and/or capsules. The Bath group has a new and refined method. Professor Paine summarizes the vision: “Our novel approach into smart materials could transform our infrastructure by embedding self-immunity and resilience so that structures can evolve over their lifespan. This will improve durability, serviceability, safety and reduce maintenance costs.” In other words, self-healing concrete would react to damage rather than simply resisting it, reshaping how we build and maintain in the future.The Bath team, under Dr. Susanne Gebhard and Paine, developed a mix of concrete that encapsulated healing agents. The mix uses a 90 L tilting drum mixer. The mix composition consists of: CEM II/B-V 32.5N type Portland cement, fine and coarse aggregates, a water/cement ratio of approximately 0.40, and 45 kg/mThe perlite beads contained the spores, and calcium acetate and yeast extract were encapsulated in a second perlite batch. Before mixing, each perlite batch was soaked in its respective solution and then coated with sodium silicate and fly ash to encapsulate the nutrients and bacteria. This two-stage encapsulation guaranteed that the spores would not germinate during the mixing process. The spores only germinate after the concrete cracks, letting water and oxygen in. The test sought to address two issues: delivery and performance. First, can spores and nutrients in a solid form be mixed in a workable concrete without deteriorating it? The tests by the Bath lab confirmed that yes, it can. Preliminary mixes of 1.9% – 3.8% Ca-acetate by cement weight had 28-day strengths of ~30-33 MPa . Crucially, there was “no noticeable delay in setting or early strength” despite the additives. The viability tests on spores encapsulated in perlite indicated that virtually all spores were alive. Only 0.01% of spores were lost over 30 days in the coating. Second, what does the self-healing mix do under actual structural loading? For this, Bath created a reinforced concrete panel with the self-healing mix in a “weak” section, which would be expected to have cracks at ~500 mm height. A total of five panels were cast: one control panel and four other panels with different self-healing systems, including the bacterial mix. This was for a highway project in Wales. The panel made with the bacteria mix was created with the M2 mix and the coated perlite , which contained ~4×10¹³ spores/m³. A capillary network of hollow tubes made of polypropylene was added near the expected area of cracking to allow for the possible injection of more nutrients.University of BathOnce cured, the panel was cracked at 36 days using a hydraulic jack to open a 0.1 mm-wide crack . During the trial, the team instrumented the panel heavily: crack width gauges, LVDTs, load cells, DEMEC points, and optical microscopes to monitor crack growth and healing in real time. After cracking, water was applied to trigger the bacteria. Over the following weeks, visible mineral deposits began to appear in the crack under the microscope. At the time of reporting, Bath noted “a degree of crack healing” in the bacteria panel, though they prudently awaited further testing to confirm the biogenic source. Importantly, there was no detrimental effect on strength or durability from the additives. Bath reports that even after full casting, “mechanical properties can be maintained and setting/hardening is unaffected by encapsulated agents”.The trial also provided several important engineering observations. The cube strength of the bacterial concrete was ~30 MPa after 7 days, and the 28-day strength is comparable to that of normal concrete. This is slightly less than expected , probably due to the presence of perlite and difficulties in mixing on site. However, the self-healing section panel is performing as required. Visual observations have also shown that the coated perlite did not leach out prematurely. In the fresh concrete, the white beads were visible, but no leaching of the nutrient was seen until cracking. The viability tests showed that the spore content remained relatively constant over a month, so the bacteria were dormant and ready to go. This suggests that a self-healing concrete could theoretically be stored for a long period without ‘using up’ the healing agents. Upon cracking, the perlite beads purposely shattered, releasing nutrients and spores into the fissure. Subsequent monitoring did indeed show calcite precipitate bridging parts of the crack. While the Bath report notes further analysis to isolate the bio-mechanism, the preliminary evidence is promising: concrete cracks that would normally remain open had begun to seal. Bath’s engineers emphasize using a two-part encapsulation to improve reliability. They also highlight temperature resilience: Bath isolates include psychrotrophic cave bacteria that germinate at 5–20 °C, ensuring healing can occur in cold climates. The capillary network was another innovation, allowing post-construction injections of air or nutrients if needed. Professor Kevin Paine calls the results “ground-breaking stuff”, noting that most bacterial data is from human body temperatures, and they had to verify performance at low temperatures. In practice, the Bath team verified healing even at ~20 °C . Crucially, the full-scale trial demonstrated that adding bacteria and nutrients did not harm concrete’s core properties. As one conclusion states, these “self-healing concretes… successfully demonstrated that mechanical properties can be maintained”. In other words, engineers can adopt these materials without sacrificing strength or safety.For the construction industry, bacteria-infused concrete represents a potential paradigm shift. It promises reduced maintenance and longer life for structures. As Cardiff’s Resilient Materials lead Prof. Bob Lark notes, infrastructure sustainability will benefit immensely: “We are confident our research will have a significant impact on the sustainability of our infrastructure”. This means that should cracks heal by themselves, the cost of repair can be reduced considerably, as can the carbon emissions of newly made concrete. In carbon terms, longer-lasting buildings mean lower carbon emissions over the course of a structure’s lifetime. Moreover, there is the possibility of new business models for insurers and asset managers: buildings can be made to last longer than intended, not because of obsolescence, but because of healing. Of course, technical and regulatory barriers still exist. The process used in Bath requires the implementation of precise mixing procedures, including the use of specialized aggregates and coatings. This process also requires quality controls to ensure the viability of the bacteria. The process will also necessitate the implementation of new guidelines to standardize the materials used for mass-scale implementation. Nevertheless, the large players in the industry are taking heed. Recent trials within the EU and US, including those carried out by BAM, Siemens, and Toshiba, among others, indicate an increased interest in bioconcrete. The project includes various industrial players, as well as government infrastructure strategies. If the companies can successfully integrate the self-healing agents within the ready mix process, the potential gains are enormous. As Professor Paine points out, smart concrete is part of a larger trend towards what he calls “bio-integrated” infrastructure. He sees a future in which the age of materials is managed as a resource; in which buildings monitor themselves and adapt themselves as they age. Self-healing concrete fits in well with ideas around sensor technology and digital twins – in which cracks in a structure could serve as a warning of damage and then repair themselves, needing little more than periodic checking. As the University of Bath team concludes, embedding living components into concrete could allow infrastructure to heal itself from within, extending service life and mitigating climate impact. The potential for self-healing concrete to lead to roads that repair their own cracks, bridges that get stronger over time, is significant. At least for now, Bath’s example illustrates the possibilities in terms of both promise and avenues for development—by emulating nature and pharmaceutical engineering , civil engineers are rethinking concrete from the inside out.
Civil Engineering Concrete Technology Construction Technology Infrastructure Materials Science Smart Materials Sustainable Engineering Urban Innovation
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