Recycling the road

A recyclable, energy efficient concrete that utilises used steel reinforced tyres could be the key to fewer road closures in the future.

The eco-friendly concrete – developed by scientists from the University of Sheffield as part of the EcoLanes FP6 project – is cheaper than normal concrete and ready for light traffic immediately after laying. The new dry mix concrete is reinforced with processed steel fibres from used tyres which have been subjected to shredding and granulation before being combined with other materials.

“The steel tyre-cord wire was the only part of the tyre used,” Dr Kyriacos Neocleous, senior research fellow from the department of civil and structural engineering told Laboratory News, “To best utilise the fibres (and avoid fibre balling in concrete), it was necessary to further treat the fibres in order to minimise their geometrical irregularities and remove the residual rubber from the surface.”

The new concrete requires less cement than conventional concrete and is stable enough for light traffic straight after being laid, compared to between seven and 28 days for conventional concrete. It was tested for durability and resistance to corrosion: it was kept in a climate chamber for 56 days and subjected to temperatures from -20 to 20°C, and submerged in salty water for several months while being exposed to wet-dry cycles. It was also subjected to a bending experiment to test how it coped in extreme temperatures and moisture, as well as one million load cycles.

Testing revealed the concrete was highly durable, especially when a modest dosage of fibre is used and although steel fibres on the surface expanded through corrosion, this was not enough to crack the concrete. It also showed excellent performance even after the equivalent of 30 years of traffic.

“The new material will provide a better infrastructure in the future: Fewer potholes, less maintenance required and therefore less impact on the traffic,” said project coordinator Professor Kypros Pilakoutas, “Furthermore, when the material is disused, it can be removed, crushed and recycled for new pavement.”