Furthermore, much of the concrete used in construction is reinforced with steel, whose environmental credentials are also poor. Not only does steel require the extraction of iron ore and the use of fossil fuels in blast furnaces but its production has damaging side-effects such as water contamination and air pollution.
One way of making concrete more environmentally friendly is to replace the steel meshes that reinforce it with something more sustainable. A team of scientists at James Cook University (JCU) in Australia, for example, has developed a type of concrete reinforced with plastic waste.
“Using recycled plastic, we were able to get more than a 90 per cent saving on CO2 emissions and fossil fuel usage compared to using the traditional steel mesh reinforcing,” says Rabin Tuladhar, the lead researcher from JCU. “The recycled plastic also has obvious environmental advantages over using virgin plastic fibres.”
The concrete was reinforced using recycled polypropylene plastic instead, and strength and durability tests show that the end result could be used to build footpaths and precast structures such as drainage pits and concrete sleepers.
Tuladhar and his team are also working on making concrete more sustainable in other ways. One option they are investigating is the replacement of natural sand with so-called ‘crusher dust’, a by-product of stone quarries, and incorporating mining waste into cement production.
Self-repairing biological concrete
Another problem with concrete is its tendency to degrade and crack, which means it must be regularly patched up.
Scientists are addressing this shortcoming by trying to develop self-repairing “biological concrete”, which involves infusing the material with bacteria. When the concrete is dry, the bacteria are dormant. But when water seeps in, the bacteria activate and multiply, producing a limestone-like substance that fills in the damage. In short – self-healing concrete with organic qualities.
Meanwhile, Swedish construction conglomerate Skanska has teamed up with Loughborough University in the UK to develop the use of 3D printing in construction. Under this process, successive layers of concrete are placed on top of one another to create an object which could be a complex structural component. The scientists involved say that, in theory at least, 3D printing could eventually be used to construct an entire building.
“3D concrete printing … has the potential to reduce the time needed to create complex elements of buildings from weeks to hours,” says Rob Francis, Skanska’s director of innovation and business improvement.