Stress absorbing membrane delivers a stronger, safer and more reliable motorway
A Stress Absorbing Membrane Interlayer has delivered stronger, safer and more reliable running lanes for the M3 smart motorway project in Surrey.
More than 130,000 vehicles use the M3 between Junctions 2 (Thorpe and the M25) and 4a (Farnborough) every day.
As part of Highways England’s smart motorways programme, the capacity of this congested three lane section has been increased, with hard shoulders converted to an additional running lane. The aim is to relieve congestion, smooth traffic flow and to improve journey reliability.
Construction began on site in November 2014. Asphalt surfacing contractor Tarmac, working for Principal Contractor Balfour Beatty, carried out structural resurfacing of the carriageway as part of the project.
“The road was in poor condition, the result of reflective cracking of the asphalt, due to movement of the underlying layers that were made up of both lean mix concrete and bituminous road base,” says Tarmac Project Manager Barrie Farquhar. “Repairs were needed to strengthen the road and to prevent further cracking, which could have led to water ingress and further deterioration of the concrete.”
Highways England needed a pavement solution that would reduce initial costs, increase service life, as well as minimise maintenance and future disruption.
Consultant Aecom had specified asphalt reinforcement in the pavement design. Tarmac, subcontractor Foster Contracting and Tensar International proposed Tensar’s Stress Absorbing Membrane Interlayer (SAMI) Glasstex solution, while supporting the required departure from the standard process.
“The SAMI adds tensile stiffness, increasing pavement strength at low strain and mitigating reflective cracking from both traffic-induced stress and from defects in the underlying pavement structure. It also acts as a moisture barrier,” explains Tensar Highways Manager Craig Andrews. “This low-maintenance solution will extend the operating life of the pavement, reducing whole life costs.”
A total of 300,000m² of Tensar’s Glasstex P100 composite was laid by Foster Contracting, on both the northbound and southbound carriageways, along the 26km stretch of road (ie a total of 52km). This composite of glass yarn grid and paving fabric formed an interlayer between the fractured substrate and the asphalt overlay.
“The Glasstex adheres 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,” Andrews says. “Combined with Tarmac’s Ultilayer polymer-modified binder course, this delivers maximum possible crack resistance and durability.”
An added benefit of installing a SAMI Glasstex solution on motorway projects is speed, Andrews adds. “Work typically has to be carried out at night, which obviously limits the amount of time available. Using Glasstex means the reconstruction depth is far shallower: on the M3 it is just 120mm to 150mm, rather than a minimum 360mm with a standard approach, which obviously saves time and, as a result, construction costs.”
As well as resurfacing, the M3 smart motorway project has included construction of new gantries for electronic signage, replacement of bridge joints, complete reconstruction of Woodlands Bridge and drainage repairs. Main construction was completed on 30 June 2017 with four lanes open to the travelling public .