Green paths

Specification trials are now underway to test a new kind of green pavement technology, used to create foundation layers of modern road surfaces.



Tarmac, Scott Wilson and the Transport Research Laboratory (TRL) are leading the trials -which are integral to two projects being funded by WRAP (Waste & Resources Action Programme).



They are taking place at Tarmac’s Colchester Quarry and involve using 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, said: “HBM technology has been around in the UK for sometime. However, difficulty in maintaining supplies of some materials, combined with a lack of certainty about the performance and durability of the mixtures, have 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 pulverised 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 using the same mobile mixer plant used for foamed bitumen-based mixes, such as Tarmac FoamMaster. In the future we believe a significant proportion of sub-bases and bases used will consist of HBMs produced from recycled materials”


Dr Nizar Ghazireh, technical director at Scott Wilson, added: “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.”