Award of Merit: Transportation Category
M4 Elevated Freeway Repair
Submitted by Mott MacDonald
Dorking, United Kingdom
Surrey, United Kingdom
Laser Special Projects
Worchester, United Kingdom
Birse Civils Limited
Kent, United Kingdom
Altrincham, United Kingdom
The M4 is a critical artery linking London to Heathrow Airport and the west of the country. Decades of deicing salt application resulted in significant corrosion damage to the reinforced concrete substructure, requiring an extensive program of repairs.
Cathodic protection was identified over 10 years ago as the most promising approach for remediation. Existing conventional approaches to this method, however, were considered to be inappropriate due to the need to maintain traffic flow and avoid unnecessary noise and disruption to nearby residents.
Careful assessment of the structure identified a possible solution. Rather than installing numerous individual anodes though holes drilled from the soffit, a string of anodes could be threaded through a single core hole cut through the center of the crosshead. Once grouted in place, the design calculations showed this would, when operated in combination with a more conventional mesh and overlay system applied to the body of the pier, be capable of providing the required level of protection.
The directional coring required to allow this approach proved to be more straightforward than had initially been feared and an initial installation was carried out. This was successfully completed in the spring of 2008 and immediately followed by a rolling program of repairs to the remaining 120 structures at a potential cost savings of more than $1 billion (U.S.) compared with the only other viable alternative of replacement.