Barrett Byrd Associates

Stockpiles of waste glass have been put to good use in an asphalt surfacing material laid for the first time on a British motorway this spring. Mike Walter reports

Around 35,000 tonnes of asphalt containing crushed glass that would otherwise likely have ended up at landfill was used to resurface both carriageways of the M50 motorway earlier this year.

The asphalt material is known as Glasphalt and contains 30 percent crushed glass. The glass used in the material is predominantly green glass which, when crushed, has very few end markets.

Glasphalt has been developed by RMC Aggregates to provide a sustainable resurfacing solution to repair worn roads suffering from lateral cracking and rutting.

The material was laid on a 5.4km stretch of the M50 motorway linking Gloucestershire with Herefordshire by specialist contractor RMC Surfacing this spring. The macadam was specified as a base and binder course – the foundation layers of a road – and its use on the M50 represents the first time crushed glass has been used to resurface a British motorway.

Reuse of crushed glass in a coated macadam helps local authorities cut costs associated with disposal of glass at landfill and reduce the consumption of primary aggregate used in road renewal work.

Glasphalt has been laid on many local authority road reconstruction contracts in recent years but, as yet, is not fully approved for motorway use under the Highway Authorities’ Product Approval Scheme (HAPAS). Before it could be used on a motorway, it had to be granted a special dispensation by the Highways Agency.

“Glasphalt has reached the latter stages of HAPAS approval and transport research body TRL is compiling an independent report on the material’s use,” says RMC Surfacing’s technical services manager Mark Murrin-Earp.
“The material meets relevant end performance criteria and fully complies with the Specification for Highway Works clause 929. Glasphalt includes the use of an adhesion agent, but is laid in the same way as traditional macadam.”

Pubs and clubs in the south west of England are two of the most likely sources of crushed glass used in the Glasphalt material laid on the M50. Large volumes of green and mixed coloured glass were collected form the local area and delivered to RMC Aggregates’ Wickwar asphalt production facility in south Gloucestershire. There it was crushed and screened before being mixed with limestone aggregate.

Bitumen enhanced with an adhesion agent was added to the asphalt mix to produce around 240 tonnes of Glasphalt every hour. The material was then stored ready for delivery in hot storage bins.

The process of renewing the motorway began on the eastbound carriageway of the M50, with three planers working to scarify the existing road surface to the required depth. A contraflow was set up for traffic on the westbound carriageway, that remained in place until the works switched to the westbound carriageway and the traffic moved to the eastbound side.

Road material was taken away before fresh quantities of Glasphalt were brought to site in insulated trucks at a rate that ensured the contract was supplied with a consistent quantity of material. A conventional tracked paving machine worked to lay the material to seven different thicknesses of base and binder course material, specified depending on the condition of the particular section of carriageway being overlaid or reconstructed.

Results of non destructive pavement tests carried out prior to the surfacing work gave the project team the information they needed to specify the most appropriate renewal specification for each part of the road. The most deteriorated sections of highway and areas which receive the heaviest use, such as the inside lane, generally under went full depth reconstruction.

This included application of 200mm of bituminous material that was topped with a 35mm surface course of RMC’s Viatex thin surfacing. Viatex has noise and spray reducing properties that help to increase safety and improve environmental benefits for drivers.

Full depth reconstruction was also specified for much of the hard shoulder on each carriageway as it was often of a poor standard, and on the approaches to and departures from six bridge decks along the route.

Quality control of the material was observed by a team of technicians based on site. Cores of the new surface were taken at 500 metre intervals on each lane to check the condition and density of the material and verify that it remained within the parameters of the works specification.

Fact box:
Scheme: M50 resurfacing works between junctions one to two – Bushley Brook to Longdon Brook.
Value of contract: £7.2M
Contract timescale: February to July 2003
Managing agent contractor: AmeyMouchel
Civil engineering contractor: John Martin Construction
Specialist surfacing contractor: RMC Surfacing
Traffic management contractor: H.W. Martin

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