BBC News, Paul Rincon, Science editor, 30 October 2012
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| Bacterial spores are added to the concrete mix; they are activated by water |
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Experimental
concrete that patches up cracks by itself is to undergo outdoor testing.
The
concrete contains limestone-producing bacteria, which are activated by
corrosive rainwater working its way into the structure.
The new
material could potentially increase the service life of the concrete - with
considerable cost savings as a result.
The work is
taking place at Delft Technical University, the Netherlands.
It is the
brainchild of microbiologist Henk Jonkers and concrete technologist Eric
Schlangen.
If all goes
well, Dr Jonkers says they could start the process of commercialising the
system in 2-3 years.
Concrete is
the world's most widely used building material. But it is prone to cracks,
which means that structures need to be substantially reinforced with steel.
"Micro-cracks"
are an expected part of the hardening process and do not directly cause
strength loss. Fractures with a width of about 0.2mm are allowed under norms
used by the concrete industry.
But over
time, water - along with aggressive chemicals in it - gets into these cracks
and corrodes the concrete.
Longer life
"For
durability reasons - in order to improve the service life of the construction -
it is important to get these micro-cracks healed," Dr Jonkers told BBC
News.
Bacterial spores
and the nutrients they will need to feed on are added as granules into the
concrete mix. But water is the missing ingredient required for the microbes to
grow.
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| Concrete is the world's most popular building material, but cracking is a problem |
The
bacterial food incorporated into the healing agent is calcium lactate - a
component of milk. The microbes used in the granules are able to tolerate the
highly alkaline environment of the concrete.
"In
the lab we have been able to show healing of cracks with a width of 0.5mm - two
to three times higher than the norms state," Dr Jonkers explained.
"Now
we are upscaling. We have to produce the self-healing agent in huge quantities
and we are starting to do outdoor tests, looking at different constructions,
different types of concrete to see if this concept really works in
practice."
The main
challenge is to ensure the healing agent is robust enough to survive the mixing
process. But, in order to do so, says Dr Jonkers, "we have to apply a
coating to the particles, which is very expensive".
The team is
currently trying to reduce the cost this adds to the process. But he expects an
improved system to be ready in about six months.
The outdoor
tests should begin after this; the team is already talking to several
construction firms that could provide help.
The
concrete will then have to be monitored for a minimum of two years to see how
it behaves in this real-world setting.
"Then,
if everybody's happy, we can think about trying to commercialise the
product," said the TU Delft researcher.
Even if the
healing agent adds 50% to the concrete cost, this makes up just 1-2% of the
total construction cost. Maintenance is a much higher percentage of this total
cost, so Dr Jonkers expects big savings through extending the concrete's
service life.
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