Ageing infrastructure is an increasing economic and environmental problem. Economic because, while the production cost of one cubic metre of concrete varies between £45 - £55, it is estimated that currently the direct cost for repairing/maintaining one cubic metre of the same material is around £100. Environmental because production of cement generates 5 to 8% of the world's carbon dioxide emissions. Counteracting the degradation of concrete would lower the requirement for new materials and thus reduce the consumption of resources and the emission of greenhouse gases.
Engineers have proposed a revolutionary solution, which was inspired by nature: self-healing materials able to self-repair as a result of the metabolic activity of bacteria. The main mechanism of concrete healing is the microbial-induced precipitation of calcium carbonate (MICP), which fills the cracks of the damaged material. However, the current approach in microbial self-healing concrete technology is to identify a few species of bacteria that work for limited sets of concretes and environments, and to optimise their MICP performance incrementally by experiments. This leads to solutions that are poorly transferable to new applications, unless new costly experimental campaigns are undertaken. In this proposal we aim to provide a new theoretical basis to predict the most promising combinations of bacteria and concrete, once the application-specific chemical compositions of the concrete of the surrounding environment are identified. This will establish a new paradigm for the digital design of concrete-bacteria systems and will enable technology transfer across the constructions sector.
The approach we propose entails two main steps:
1) developing and validating the world-first simulator of bacterial self-healing in concrete, starting from the length-scale of a single crack (1-100 micrometres) and then transferring information on the kinetics of self-healing to macroscale simulations of concrete manics;
2) using the new simulator to inform an experimental campaign aimed at optimising the formulation of self-healing concrete for application in the aggressive chemical environment of an industrial wastewater treatment.
The new simulator will be obtained by building on three existing state-of-the-art simulators that have been very recently developed at Newcastle and Cardiff universities and that model, to date separately, the three main steps involved in self-healing: i) bacterial growth; ii) kinetic evolution of an aggregate of mineral particles immersed in a solution; and iii) macro-mechanics of concrete elements with evolving strength and stiffness.
The experiments will first provide inputs to the simulations and data for their validation. These experiments will be carried out in university laboratories and will address all the relevant length scales, from the nanoscale of the morphology of the mineral phases in concrete, to the microscale of the self-healing process inside single cracks, to the macroscale of self-healing concrete samples.
The validated simulations will be run predictively to simulate the environmental conditions inside a wastewater treatment plant. The simulations will identify the best combinations of bacteria and concrete chemistry to ensure self-healing in such conditions, and the final experiments will produce the simulation-guided self-healing concrete and test their performance in the facilities of our industrial partner Northumbrian Water.
If successful, this project will provide a completely new way to approach the design of self-healing materials via simulations. This would drastically reduce the cost, time, and uncertainty related to developing these materials, enhancing the rate of progress in the field by orders of magnitude and putting the UK at the forefront worldwide in this new technology.