Industry supports WRAP projects on green pavement technology

SPECIFICATION trials are taking place to test a new kind of ‘green’ pavement foundation technology. The trials, which are integral to two projects being funded by WRAP (the Waste & Resources Action Programme), are being led by Tarmac, Scott Wilson and the Transport Research Laboratory (TRL).

The trials are taking place at Tarmac’s Colchester Quarry and involve the use of recycled and secondary aggregates (RSA) in hydraulically bound mixtures (HBMs) produced using slow-cementing binders derived from various industrial by-products.

Dr Howard Robinson, Tarmac’s head of product development, commented: ‘HBM technology has been around in the UK for some time. However, difficulty maintaining supplies of some materials, combined with a lack of certainty about the performance and durability of the mixtures, has been a barrier to specification.

‘Over the past decade we have been experimenting to produce HBMs made using various alternative materials, such as granulated blastfurnace slag and pulverized fuel ash (PFA), and we believe these are much more viable industry alternatives. In particular, these HBM materials are more readily available and can be produced by the same mobile mixer plant used for foamed bitumen-based mixes.’

In total, four different HBMs are being tested as part of the trials. The tests will produce in-situ performance data to relate the performance of these materials to the new specifications and design guidance. The results of the trials will be published by WRAP during 2007.

‘This new performance data will enable local authorities, the Highways Agency and other customers to specify HBM foundation layers with confidence and we are predicting this will lead to an increase in demand. In the future we believe a significant proportion of sub-bases and bases will contain HBMs produced from recycled materials,’ said Dr Robinson.