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Contractors World UK & Ireland
2012 Vol 2 No 6   
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New asphalt mix using recycled tyres promises significant all round benefits - page 2 of 4

Recycled rubber with white polymer pellets.Laboratory Design

Following a study visit to Germany, Breedon carried out extensive tests on the modifier in its central laboratory and then set out to design a thin surfacing asphalt appropriate for Britain’s roads.

Recycled rubber with white polymer pellets.

The Road+ additive forms part of the binding agent, along with bitumen in the asphalt. This is achieved by the double bonds of the polyoctenamer in Road+ reacting with the sulphur on the surface of the rubber and the maltenes and asphaltenes in the bitumen.

Cross-linkage between the bitumen and rubber therefore takes place without the need for the rubber to be melted. This allows the production temperature to be kept below 170º C, yielding obvious environmental benefits.

Different proportions of the additive can be added depending on the level of performance modification required and, as increasing amounts are added, the binder moves from being a thermoplastic to a thermoset material. The laboratory design work identified the optimum blend of Road+ with bitumen to give the correct volumetrics to ensure durability, rut resistance and high surface texture in the final material.

Plant and surfacing trials were then carried out in Breedon’s Benninghoven asphalt plants in its quarries at Clatchard and Ethiebeaton in Scotland, to check the functionality of the material and ensure that the designs were achieving the demanding performance criteria required.

As with standard asphalt, the aggregate in the mix is first dried and heated to around 165º C and then blended in a mixer. Typically, around two tonnes is batched at a time. The Road + is then added in low-melt bags which instantly disintegrate, allowing the Road+ to disperse into the blended aggregate. The final part of the mix, the bitumen, is added last. The total mix time for all these ingredients is typically around one minute, depending on the efficiency of the mixer.

The finished product is transferred to large insulated “hot bins” for storage prior to dispatch. The key production difference between this material and normal asphalt is that, at this point, it must be left for around one hour to allow the chemical cross-linking to occur, although part of this hour can be used to transport the material to site for laying. Production and laying of this material can be done with standard kit without any major issues. The mixing system can be fully automated, although this was unnecessary for the initial trials.

Breedon doing trials of new skid resistance measuring device on a trial strip at the batching plant.Trials with Transport Scotland

The plant trials were conducted with the close involvement of Transport Scotland, which subsequently decided that the material warranted the formation of a Transport Scotland Pavement Forum subcommittee to develop a standard specification for this type of material.

Breedon doing trials of new skid resistance measuring device on a trial strip at the batching plant.

Following the preliminary plant and laying trials, Breedon concluded that a very high performance thin-surfacing material incorporating the new rubber modifier could be produced in volume, that will bring significant installation and performance benefits on Britain’s roads. A Technical Submission was therefore made to Transport Scotland through Breedon’s associate company, BEAR Scotland (which manages a sizeable proportion of Scotland’s trunk road network) for a formal trunk road trial of the new material.

Following Transport Scotland’s approval for the trial to go ahead, a short stretch of the A90 dual carriageway between Perth and Dundee was resurfaced with the revolutionary material in May 2012. This stretch of road is one of the busiest in Scotland, carrying around 35,000 vehicles a day.

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