Smart solution for M3
2nd September, 2020
More than 130,000 vehicles use the M3 between Junctions 2 and 4a every day. As part of Highways England’s Smart Motorways programme, the capacity of this congested three lane section was being increased, with hard shoulders converted to ‘smart’ running lanes. Asphalt surfacing contractor Tarmac, working for main contractor Balfour Beatty, carried out structural resurfacing of the carriageway. The road was in poor condition, a result of reflective cracking of the asphalt due to movement of lean mix concrete and bituminous road base. Repairs were needed to strengthen the road and to prevent cracking, which could have led to water ingress and further deterioration of the concrete. AECOM had specified asphalt reinforcement in the pavement design. Tarmac, subcontractor Foster Contracting and Tensar proposed Tensar’s Stress Absorbing Membrane Interlayer (SAMI) Glasstex solution, while supporting the required departure from the standard process. Glasstex P100 is a composite of glass yarn grid and paving fabric, which formed an interlayer between the fractured substrate and the asphalt overlay. It was adhered to the underlying pavement structure using a straight run bitumen (160/220 pen)
bond coat, with a calibrated spray rate of 1.1kg/m2, to activate both stress relief and interlayer barrier functions (as given by BS EN 15381: 2008), with reinforcement provided by the grid. Combined with Tarmac’s Ultilayer polymer-modified binder course, this delivered maximum possible crack resistance and durability. Glasstex mitigates reflective cracking propogation and dissipates peak strain energy caused by movement in the substrates and traffic-induced bending. The result was a pavement with a longer operational life, requiring less maintenance. Installation of the Tensar solution was carried out during several nights by subcontractor Foster Contracting, which has developed plant specifically for efficient and safe installation of Glasstex. The standard approach would have involved a minimum 360mm reconstruction depth but using Glasstex meant only 120mm to 150mm had to be removed, saving significant construction time and cost.