Energy-efficient concrete could reduce road closures

The road type, made of dry-mix concrete reinforced with recycled steel fibres from waste tyres, is 12 per cent cheaper than conventional road construction and its construction time is 15 per cent less. In addition, over the lifetime of the concrete pavement, there is a 40 per cent reduction in energy consumption.

Each year in the EU, 3.2m tons of tyres are produced annually − all of which have to be recycled. However, 15-25 per cent of the tyre is comprised of steel fibres, which hold a lot of rubber and plastic from the reinforcement, limiting the options for reuse in new steel production.

The new fibre-reinforced concrete, developed by the team at Sheffield and their EU partners as part of the Ecolanes FP6 project, is able to use processed steel fibres for the first time. These steel fibres from post-consumer tyres are at least 50 per cent cheaper than manufactured steel fibre reinforcement and using the fibres from waste tyres means there is no need for raw material to be mined and formed, which would require extra energy.

An additional benefit of the concrete is that it uses a very different consolidation method, called roller-compaction, and therefore the dry mix requires less cement than conventional concrete and is stable enough for light traffic straight after being laid. Conventional concrete normally requires between seven and 28 days before traffic can be allowed on. This is something that could significantly reduce road closure times and traffic build-ups after a new road has been laid.

The concrete, which was developed for the project as part of a bid to create long-lasting rigid pavements for the transport industry, was then tested for its durability. The team kept the material within a climate chamber for 56 days, with a daily changing temperature from 20 to -20°C.

Researchers also tested the corrosion of the fibres by placing the fibre-reinforced concrete into a basin of salty water for several months and exposing it to wet-dry cycles. Corrosion normally leads to an expansion of the steel fibres on the surface, however the expansion was not high enough to crack the concrete.

The Ecolanes researchers used a bending experiment to test how well the material coped with the exposure to extreme temperatures and moisture, as well as one million load cycles. The experiments revealed that the new concrete can be highly durable, especially when a relatively modest dosage of fibres is used.

Large-scale Accelerated Load Testing (ALT) of a circular concrete pavement 3m wide and 18m in diameter was also undertaken by Romanian experts working on the project, using a standard single-axle load of 11.5 tonnes. After 1.5m cycles the pavement was still performing well, indicating excellent performance even after the equivalent of 30 years of traffic.

The concept of the Ecolanes project has now been validated by constructing demonstration pavements in four different European environments in the UK, Romania, Cyprus and Turkey.

Prof Kypros Pilakoutas from the university´s Department of Civil and Structural Engineering, who coordinated the EU research project, said: ’The new material will provide a better infrastructure in the future; fewer potholes, less maintenance required and therefore less impact on the traffic. Furthermore, when the material is disused, it can be removed, crushed and recycled for a new pavement.’