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Building Materials of the Future: Self-Healing & Self- Preserving

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on December 08, 2015 at 02:29 PM

Concrete cracks, making a building dangerous to inhabit, asphalt caves in to form life threatening potholes on roads and metals get dented and torn in response to applied stresses, not to speak of a limited lifespan beyond which these are not expected to last. The current answer to these problems lies in repair or replacement which cost dearly both, our pockets and the environment. We wish for solutions to the problem of sustainability of building materials which would be less of a bother in terms of various costs, something more like our human body which has a capacity to heal itself in any part which is damaged within a short time with some external medical aid. The field of ‘materials science’ is the magic lab where intensive research in the behaviour of various materials under different conditions has led to the discovery of certain materials which can actually repair themselves under certain circumstances. This has become the new way to look forward in the building industry, and similar fields where roads, rails, ships, aeronautical and space carriers are built. Some of these Terminator style self-repairing materials created by this critical field, if developed further in terms of commercial viability and applicability on large scales, may well be the materials that make up our world in future.

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“Bio-concrete” that can “self-heal” (images 2-8) was discovered, or created, by microbiologist Hendrick Jonker, who is hence a finalist for the European Inventor Award 2015, when he set about trying to find a solution to the cracking of concrete using a biological approach. No matter how well it is mixed and set, concrete, which has been in use since Roman times, inevitably tends to crack at some point (cover image and img 1). Jonker introduced encapsulated bacteria, named Bacillus pseudofirmus, into the concrete, which get activated when they come in contact with water to feed on calcium lactate and release limestone. These bacteria remain dormant in the microscopic water-permeable capsules within the concrete till it cracks and water seeps in. The limestone released by the bacteria at this juncture sets into the crack and thus repairs it. So, voila! Just as human flesh, skin and bones repair themselves, so does this bacteria infested concrete. 

This biologically approached self-healing technique could be considered a step ahead of the earlier method of self- healing which involved introducing chemical polymers inside fibres embedded in what is called fibre reinforced concrete instead of bacteria inside capsules. If bio-concrete could be produced commercially and finds large scale application, then not only would built structures have an increased life-span, it would cause a significant reduction in our carbon footprint as cement production alone is said to contribute a whopping 5% to global carbon emissions. The only deterrent seems to be the cost of the procuring the specific bacteria, which doubles the cost of the concrete, though trials are being done using more easily available bacteria. The assumption is that soon this self- healing bio-concrete should be a viable option at least for major bridges and flyovers, if not for buildings, pavements and minor roads. But, we positively hope and wait for the day when bio-concrete would be commercially viable for all building projects.

The other miraculously self-healing building material created recently is "steel wool asphalt" (image 9-11). Pot holes, undulations and tears in roads of all grades make them high maintenance, and consequently high expense, indents in infrastructure lists anywhere in the world, requiring repair and restoration of their asphalt carpeting around the year. It is critical to find an alternative where the asphalt could be repaired without incurring these costs and inconveniences.  Dr. Eric Schlangen has developed in his laboratory some self-healing asphalt by introducing steel wool fibres in it. When heated, this steel heats up and melts the bitumen around it and it rearranges the aggregate mix in its turn. On cooling, the bitumen solidifies and we have a finely reset surface. To answer the question of large scale applicability of this, Dr.Schlangen has developed a special vehicle that presses induction coils onto a road surface to apply the heat needed to repair it. This makes self-healing of road surfaces, with some heating help, a very viable possibility in future, resulting in huge savings of financial and environmental costs.

Another recent discovery was made in the field of metallurgical science, where it has been observed that, while metals tend to rupture under certain pressure, they actually fuse back together under certain circumstances (image 12). This was observed while studying the behaviour under different pressures of boundaries of the grains or crystals that make up the structure of alloys. Further research down this path could lead to the production of self-healing metals with impenetrable surfaces and everlasting life-spans, making a big difference to the design of many metallic objects and gadgets, especially aircraft and space carriers.

Of course, the most exciting discovery has been in the field of air spacecraft design, where scientists have developed a material which, on rupturing, releases from within its cavity a polymer that solidifies to seal the hole within seconds, to be used to sheath the craft on the exterior. This makes space relatively accident free and hurtling through it in a spaceship a lot safer!

Call it miracle, alchemy or science, these material possibilities give us hope for the future of both, our built and natural environments.

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