The bridge which was constructed in 1962 carries Ash Flats Lane over one of the busiest sections of motorway in the UK, - the M6 between junctions 13 and 14 in Stafford.
The Highways Agency decided the current vehicle safety barrier was no longer adequate and needed to be upgraded to current loading standards, requiring the bridge edge beam to be reconstructed to accommodate the loadings from the new barrier system.
As only limited temporary lane closures at night were permitted to install the temporary works, Concrete Repairs Ltd in conjunction with RMD Kwikform devised a novel temporary works design, - minimising the number of night possession required to install the temporary works access across the 48m long bridge.
All of the road mounted frames were preassembled on the closed Ash Flats Lane and then attached to the existing bridge deck with the kentledge in place. The over slung modular sections were fabricated on the hard shoulder of the M6 and then lifted into place in one piece during night time closures and attached to the road mounted frames.
CRL then enclosed the cantilevered access gantries with a double layer of plywood, sealed the joints with a silicone sealant and applied a final layer of roofing felt bonded to the plywood to form a near watertight enclosure. This frame enabled all the work required to the edge beam to then proceed without further road closures.
To enable the new reinforcement cage to be tied into the bridge deck CRL used hydrodemolition inside the existing vehicle barrier to remove the top layer of concrete along a strip 750mm wide and 75mm deep. This exposed the top mat of reinforcement allowing for the new reinforcement to be tied into position. To manage the wastewater from this operation CRL used sumps, puddle pumps and a Siltbuster to remove and filter the water.
To remove the existing concrete bridge parapet over the live motorway, CRL used angled core drilling and ringsaw cutting to carve the concrete into manageable blocks. The concrete blocks were then removed by
mechanical lifting through the congested RMDK framework. Once removed CRL fixed the new steel reinforcement
cage into position, shuttered the new profile and recast the edge beam using 8mᶟ of pumped readymix concrete with sockets for the new barrier fixings.
After the new barrier on one side was completed, the process was repeated on the other side of the bridge. The novel RMDK access system allowed the kentledge system to be utilised for both edge beams and the over slung modular section was simply lifted over to the other side during a night time possession. The wing walls on each side of the bridge were also reconstructed and extended to accept the new vehicle
All this work was carried out over a busy motorway near residential properties and with pedestrian access maintained across the bridge at all times!
Gerry Lister (Contracts Manager for CRL) commented, – “It has been a challenging scheme which has highlighted the importance of suppliers and contractors working together to achieve a successful outcome.”