The two-lane M4 is elevated along a 5 .5km stretch through Chiswick, above the A4. These two roads carry more than 138,000 vehicles  each day into and out of London. De-icing salts used on the elevated section during winter had seeped past the asphaltic plug joints and penetrated the crosshead concrete beams that form the soffit of the road deck. This penetration had caused the near-surface reinforcement to corrode, weakening the elevated M4 section and posing a risk to the A4 below.

Highways Agency trials had shown that wide-scale replacement of the beams would require a 9.1km detour of all M4 traffic onto the A4, which would itself require major traffic management to enable the works. This solution was impractical, with the cost estimated at £5million per beam. VolkerLaser were appointed to apply our specialist knowledge to this complex problem.