4th August 2006 - New roads for old
By Dr Howard Robinson, head of product development, Tarmac Ltd. Road recycling is becoming an increasingly dynamic area of development as the construction industry looks for ways to recover old, worn out road surfaces and re-use them on some of the country's busiest trunk roads and motorways.
The most exciting example of road recycling to date is the successful completion of Britain's biggest road recycling contract on the A38 in Devon, which used around 30,000 tonnes of recovered asphalt to create a new surface for this popular commuter and tourism route. To put this achievement into context, prior to this, the biggest road recycling contract had involved just 2,500 tonnes of recycled material for use on a 1.7 km stretch of the M6 in Cumbria.
Road recycling involves planing away the old road surface and re-processing the recovered material, using specialist plant and equipment. Once crushed and graded the planings can then be reused to produce a high performance foamed bitumen material and re-laid to provide a base layer for the new road surface.
Demand for road recycling is growing steadily in response to the sustainability agenda, which is influencing the requirements of the Highways Agency, local authorities and industrial end-users alike. In response, Tarmac has invested in the development of its road recycling capability to ensure it can fulfil this demand in the future.
But recycled road surfaces are only part of the story. In order to conserve supplies of crushed rock and gravel, the industry is also working hard to develop alternative surfacing solutions from waste materials.
Working in partnership with Scott Wilson and the Transport Research Laboratory (TRL), Tarmac is currently supporting a research project funded by WRAP (the Waste and Resources Action Programme) to develop new forms of green pavement technology.
As part of this project, specification trials are underway at Colchester Quarry to test the performance of recycled and secondary aggregates used in hydraulically bound mixtures (HBMs). These mixtures are produced using slow cementing binders derived from industrial by-products like granulated blastfurnace slag and pulverised fuel ash (PFA).
While HBM technology has been around in the UK for sometime, take-up has been slower than initially expected. This is due to difficulties in maintaining supplies of some recycled materials, combined with a lack of certainty about the performance and durability of the mixtures. With this in mind, the new research will help to establish a clear performance standard for HBMs produced using recovered materials that are more readily available.
An additional advantage of this new HBM technology is that it can be produced using the same mobile mixer plant used to produce foamed bitumen-based mixtures, such as Tarmac FoamMaster. This mobile plant and equipment can be brought as close to the site as possible in order to minimise the traffic movements needed to transport the planings to the processing area.
HBM technology presents the road surfacing industry with an opportunity to produce more sustainable road surfacing systems from a lower cost base. Once its performance can be verified, this should make HBM technology very attractive to the marketplace.
To date the potential benefits of HBM technology have only really been understood by the highways construction industry. However, there are many other applications where HBM technology could be used. For example, (more information needed).
As the original founders of one of the most well known road surfacing materials, known as 'tarmacadam', we aim to continue our focus on innovation. Once completed, the HBM trials will establish the material as a new and viable alternative for a wider range of surfacing applications and the research findings will create a benchmark for other engineers and contract teams to specify against in the future.
