The overall objective of the SmartCoDur project revolves around researching strategies to increase the durability of concrete structures reinforced with shape memory steel (Fe-SMA). The proposed approach is based on the development of new environmentally friendly smart coatings that can self-repair damaged films applied to Fe-SMA. This would ensure a longer service life with significant energy and maintenance savings.
There is great interest in finding new ways to extend the life of concrete infrastructure due to the deterioration and ageing of much of our critical infrastructure, such as bridges, dams, etc. According to the European Innovation Partnership for Smart Cities and Communities, much of this infrastructure is over 40 years old and designed for a service life of 50 years; they also estimate that 40% of it has damage of varying degrees.
One of the most widely studied methods for extending the service life of this infrastructure is the application of metal strapping. Shape memory steels are particularly promising for the manufacture of such strapping, but they have moderate corrosion tolerance.
What are shape memory steels (Fe-SMAs)?
The defining characteristic of these shape memory steels or Fe-SMAs (Shape Memory Steels) is their shape memory, i.e. their ability to recover their original shape through the application of heat (thermal activation) after undergoing deformation due to an external stimulus, usually mechanical stress. At the microstructural level, shape memory is produced by the reversible transformation of epsilon martensite (hcp) and gamma austenite (fcc), as illustrated in Figure 1.
This effect can be exploited to generate compressive forces in structural reinforcement systems by restricting the contraction associated with the volume change from epsilon martensite to gamma austenite. (Fig. 2).
Figure 1: Transformation between ε martensite and ϒ austenite in shape memory steels.
Figure 2: Diagram of the use of Fe-SMAs as structural reinforcement.
What is a smart coating? And what is a self-healing coating?
A smart coating is one that is capable of responding to an external stimulus in a predetermined way. Within the category of smart coatings, self-healing coatings stand out for their ability to repair themselves autonomously after mechanical damage to the coating itself.
One of the most widespread methodologies for designing this type of coating, which we will use in this project, consists of encapsulating corrosion inhibitors in polymeric vesicles. These capsules are mixed with paint and applied to the metal to be protected, so that the inhibitors are only released when an external stimulus occurs, such as a change in pH or mechanical breakage of the paint layer.