ULTILAYER SMA delivers single layer pavement upgrade in Northolt 

Mandeville Road is a busy A-road servicing the London Underground Station at Northolt. It is a major route linking the A40 to Harrow. The site comprises two dual carriageways which traverse a London Underground bridge over the railway line. Each approach is on a gradient with a pedestrian crossing on the brow of the hill directly outside the station. The original design for the work was for a conventional build of 70mm of binder course and 40mm of surface course. However, cores taken from over the bridge showed that this design was not suitable. The cores revealed hazardous, tar bound materials and a maximum planing depth of 80mm. London Borough of Ealing came to Tarmac for a solution. 

ULTILAYER SMA 14 steel slag, Warm Mix Asphalt installed in a single layer. A high-grade Polymer Modified Bitumen (PMB), suitable for heavy vehicles and traffic volumes - with a strong track record of use in Central London including Marylebone Road, Oxford Circus, Regent’s Street and the A12 Blackwall Tunnel. ULTILAYER is a dense, durable PMB asphalt offering excellent resistance to the deformation, rutting and fretting associated with heavy vehicle movements. ULTILAYER SMA 14 was selected using a steel slag aggregate. Materials where produced warm to allow quicker trafficking and reduced CO₂ emissions at manufacture. The location of the site and the extent of the works necessitated road closures – Shift 1 Northbound, Shift 2 Southbound and it was critical to re-open the road in time for the morning rush hour. Given that the material was to be laid at 80mm in a single layer Tarmac advised that the ULTILAYER should be supplied in a warm mix (typically 40°C lower than conventional) so that the new asphalt would cool more quickly, allowing the white lines to be applied at <60°C and the road reopened at <40°C by the hand-back time.

London Borough of Ealing has previously used ULTILAYER in high stress, high volume sites but this was the first time it had been used as a deep inlay, single layer. The original programme allowed for 4 shifts (1 x binder, 1 x surface for each carriageway). Use of the single layer solution enabled the contractors to complete the scheme in just 2 shifts saving both time and money and halving the disruption to residents and bus services due to the road closure. The change to a single layer at 80mm rather than a two-layer system at 110mm saved the client approximately 220t of material. In addition, the steel slag aggregate, which is sourced from Tarmac’s facility at the steel works in Port Talbot, South Wales and transferred to London by rail, is classed as a secondary aggregate and saves use of primary aggregate. We transport this to London by rail to reduce congestion and further transport emissions, helping to achieve additional resource efficiency savings.. There was also a 10% saving through reduced energy usage at the plant and associated CO₂ emissions gained by utilising a warm mix asphalt with no compromise to the material’s performance. Warm mix asphalt also reduces fumes emitted by approximately 90% which benefits the site operatives, passers-by and public health in the Capital.