The 2022 vision of RM4L to "transform construction by creating biomimetic cementitious materials that adapt to their environment, develop immunity, self-diagnose damage, and self-heal when required" will engender a step-change in the value placed on infrastructure materials and provide a much higher level of confidence and reliability in the performance of infrastructure systems not only in the UK but around the world.
- Development of a set of self-healing (SH) technologies that are ready for use.
- Data on SH performance sufficient for the systems to be accredited and accepted by the industry.
- Proof of the viability of integrated self-diagnosing (SD)/self-healing (SH) material systems.
- New means of providing self-immunity (SI) to damage using SH technologies.
- Having an approach for tailoring SD and SH systems for structural design.
- Numerical analysis tools, optimisation procedures and design methods for SD/SI/SH systems.
These objectives will be achieved through an ambitious programme based on the following four research themes (RTs):
- RT1: Self-healing of cracks at multiple scales.
- RT2: Self-healing of time-dependent and cyclic loading damage.
- RT3: Self-diagnosis and immunisation against physical damage.
- RT4: Self-diagnosis and healing of chemical damage.
Whilst research at the University of Bath is involved in all four RTs our work can be divided into two main fields of research: (i) bacteria-based self-healing, and (ii) impedance-based self-sensing, of cementitious composites.
Bacteria-based self-healing of cementitious composites
To achieve autonomic healing in concrete, we are interested in the use of bacteria to precipitate calcium carbonate within the crack. Calcium carbonate occurs naturally in concrete as it ages, and consequently its use as a healing compound is entirely appropriate.
Bacteria-based self-healing is achieved by embedding bacterial spores within the concrete and providing them with the nutrients that they need to grow. Whilst the bacteria are in their spore form, they are inactive. However, when conditions become favourable, they germinate into active cells and these multiply. These more favourable conditions occur when a crack forms in the concrete and water and oxygen ingress.
Within RM4L, we are working to develop bacteria-based self-healing of cementitious composites towards application by isolating spore‐forming, aerobic bacteria from environmental samples where cool and/or high‐salt conditions predominate. This will enable healing in conditions more realistic of those where concrete cracks in the UK.
As it is unlikely a singular species of bacteria will be able to meet all requirements; we are also investigating whether a mixed community of bacteria will be useful. We are also investigating whether the use of bacteria can lead to a multiple long-term healing system.
Self-sensing of damage in concrete
The use of self‐healing construction materials is of great significance to structures in which conventional monitoring and repair is difficult or even dangerous, e.g. power stations, underground and underwater structures. In order to minimise human interaction, it is proposed that intelligent and resilient construction materials also need the capability to self-sense damage.
Whilst there has been research on self‐sensing construction materials for structural health monitoring, it has not, until now, been used as a method for provisioning construction materials with a means of self‐improvement. This is therefore a novel area of research.
Research at Bath is investigating the change in the electrical properties of concrete as a means for detecting damage. Of note is the use of electromechanical impedance (EMI) in which, damage in a structure can be observed from fluctuations in the admittance/impedance signature caused by changes in the intrinsic material properties such as mass, stiffness and damping.
In addition, we are investigating the use of functional highly electrically conductive fillers (carbon nanotubes, carbon fibres) to modify the resistance of the concrete in order to improve the quality of signals or as an alternative intrinsic sensing system.
A fundamental part of RM4L is its alliance with key industry partners across the construction industry. These companies include contractors (Costain, Griffiths), consultants (Arup, Atkins), client organisations (HS2, Highways England), material suppliers and chemical manufacturers (CEMEX, Lambson, Travis Perkins, Graphitene) and a software company (LUSAS).
The primary beneficiaries of RM4L will be the building materials industry, including RM4L industrial partners, throughout the construction supply chain and those responsible for the provision, management and maintenance of the world's built environment infrastructure. RM4L will develop a suite of real-life demonstration projects by working directly with their industrial partners across the supply chain and engaging with complementary initiatives.
RM4L will establish the UK as the world leader in this emerging area of intelligent construction materials while delivering world-leading research in ground and structural engineering.