Paving the road to waste recovery
Stockpiles of crushed glass are increasingly being used in the construction and repair of our roads, thanks to a material known as ‘Glasphalt’.
Glasphalt is produced by construction materials firm RMC Aggregates and laid by the company’s contracting division, RMC Surfacing Northern. Technical manager Richard Thorpe says: “Sales of Glasphalt in northern England in particular have greatly improved in recent months and in Lincolnshire nearly every binder course we lay is Glasphalt.”
Local authorities can significantly improve their chances of meeting statutory recycling targets by specifying Glasphalt, adds Thorpe. For instance, the government’s Waste Strategies report sets a target of at least one quarter of all household waste being recycled and composted by 2005, with the figure rising to one third by 2015.
RMC Aggregates has looked at increasing the proportion of glass in Glasphalt and started to incorporate recycled asphalt planings into the material after one of its clients asked to see a proportion of recycled planings in the Glasphalt it used. RMC now produces a range of high performance mixes containing glass.
Glass used in the asphalt material is predominantly of the green variety and is supplied, in the main, by packaging waste compliance scheme, Valpak. It is sourced from bottle banks and central refuse points and supplied to around 15 of RMC’s asphalt plants in England and Wales.
RMC Aggregates crushes the glass using a mobile Ammann asphalt granulator and sorts out impurities from the mix. Glass is screened into six sizes at the coating plant and mixed with primary aggregate and bitumen using conventional asphalt production methods.
Glasphalt is delivered to site at slightly cooler temperatures than conventional asphalt, largely because the presence of glass helps retain heat within asphalt and aids workability. “Glasphalt remains workable for a longer period of time than conventional asphalt, giving the gangs on site an extra couple of hours to lay the material. This aids compaction and significantly cuts down on the volume of material wasted,” says Thorpe.
Earlier this year, RMC Surfacing Northern laid 14,000 tonnes of Glasphalt as a base and binder course on a 1.5km stretch of the A617 Newark Road in Mansfield. Glasphalt used for both the 150mm thick base and the 65mm binder course incorporated 30 per cent glass with a range of aggregate grades from 14mm down to dust. Conventional plant including a Dynapak twin action paver and a Bomag 161 tandem twin roller was used to lay and compact the Glasphalt, before a 35mm thick surface course was used to finish off the road.
“One clear advantage of using glass is that transport costs between quarries and coating plants are reduced,” says Thorpe, “During the Mansfield project, because the material used less primary aggregate, movements of raw materials to satellite plants were cut, which helped reduce congestion on many of Derbyshire’s roads.”