It may sound like science-fiction, but buildings that can repair cracks, and help regulate their own temperature, have moved closer to reality – with an innovative post-doctoral research program presented at the University of the Basque Country, Spain.
The research, conducted by Dr. Idurre Kaltzakorta, doctor in Chemical Sciences, looked into the novel uses of organic capsules in cement. The use of nanoparticles to produce hybrid construction materials has been a particularly fruitful field, over recent years.
As part of her PhD thesis, Dr. Kaltzakorta was looking at how the properties of cement could be improved, by adding silica nanocapsules to the mix. These are filled with different types of organic materials, which give the cement its amazing new properties. Creating these capsules, so that they can hold organic substances, is problematic. But this research claims to have achieved this at the lower temperatures and pressures needed – using a combination of emulsion technology and sol-gel chemistry.
Cement is made from heated limestone, and forms the basis of most buildings, in both concrete and mortar. It is, however, prone to weathering and cracking. By adding a variety of epoxy resins to the nanocapsules, it was hoped that the cracks would tend to heal themselves as they formed. And a variety of scanning technologies and mechanical tests have confirmed this to be the case.
This new technique was also successfully used to fill the capsules with phase-change materials. These store energy as they switch from solid to liquid – or vice versa – and so offer the prospect of buildings storing heat during the day, and releasing it during the night.
Although there has been some concern about the health risks posed by the unregulated use of nanotechnology, most of these relate to the use of so-called 'free' nanoparticles. For the applications described in this thesis, the nanoparticles are firmly fixed in the materials – and so unable to leak into the environment.
And both of these new applications could do much to repair the bad-boy image of concrete. The production of cement is thought to be responsible for 5% of global CO2 emissions. By making buildings that repair themselves, their lifespan will be extended greatly – and so require less cement for rebuilding. And by making the most of ambient energy inputs, buildings could be made much more energy efficient – and so less emissions produced from their heating and cooling needs.