Fosroc’s Constructive Solutions at London’s Heathrow Airport

When BAA, owners of the infrastructure at Heathrow, one of the world’s busiest airports globally, with over 67 million passenger journeys per year, reviewed the state of a multi-storey car park, they found extensive corrosion to areas of the concrete’s reinforcement steel. After considering the wider impacts of demolition and replacement, they looked to Fosroc’s expertise to rejuvenate the existing structure. Fosroc’s Wayne Zakers, General Manager for electrochemical products, examines some of the factors that affected their decision.

In reviewing the alternatives available today, full consideration was given to various options. The car park is physically linked to the terminal building, and closure of the car park would have caused major disruption for users, especially those requiring disabled access. It was therefore a key requirement to carry out any work in sections, with a high percentage of the structure being available throughout.

A further significant effect considered by BAA was the degree to which closure of the car park would compromise local traffic flows. Normal access to the busy airport is via a two lane tunnel, forming an occasional bottleneck at peak periods. Overall traffic flows in such a populous area already routinely exceed capacity levels of surrounding roads, including the M25 London orbital motorway.

Complete or substantial closure of the car park for demolition and replacement would significantly reduce parking capacity for many weeks, and motorists would face delays in locating free spaces in the other facilities on the sprawling site. The knock-on effect would be creation of serious daily congestion issues on airport access and surrounding roads. The negative commercial effects to businesses, locally and nationally, would be dramatic as goods and staff were extensively delayed. The environmental and health impacts of large numbers of queuing vehicles would also be serious, especially for those living and working in close proximity to the airport.

Further environmental impact would arise from the removal of waste materials from the car park structure and its access routes. Though areas of the car park were in clear need of repair or replacement, much of the structure remained in sound condition, requiring perhaps cosmetic levels of work. Not only would the any structural demolition, and the reduction and removal of spoils have created considerable noise and dust, but also the disposal to landfill would have had wider environmental impacts. New, replacement structures would require consumption of natural resources, directly and indirectly liberating huge quantities of carbon dioxide and other pollutants.

In considering all available options, BAA and contractors Taylor Woodrow and Mannions, also reviewed different repair choices. Removal of corroded areas, and replacement with new sections or infilling with repair products, would have lower environmental impacts than rebuild. However, the consulting and design engineers were aware of the mechanisms of corrosion to concrete reinforcement, and the knock-on problems that repairs can cause to adjacent, sound areas. As corrosion is an electrochemical reaction, whereby areas of steel become cathodic, driving corrosion in adjacent anodic areas, there was a need to interrupt the corrosion mechanism. Installation of fresh mortar and steel would merely shift the anodic areas to the older, adjacent areas and so move and magnify the corrosion problems.

The chosen method of arrest, that of cathodic protection, uses principles established by Sir Humphrey Davy in the 1820’s, and widely used for nearly two centuries in protecting ships’ hulls, where the steel is made cathodic and resistant to corrosion. Cathodic protection has been in use in concrete reinforcements for over thirty years, but has developed at a pace in recent years. Two key methods exist, impressed current cathodic protection (iccp), whereby an external power source holds the steel in a cathodic state, and galvanic, whereby a more noble metal is used as a sacrificial anode, corroding in preference to the steel over a period of many years.

BAA opted to install a combination of both iccp and galvanic systems, supplied by Fosroc. The unique benefits of the discrete Ebonex anodes, including their high current densities, extreme chemical resistance to acid attack, ability to vent any gases generated in operation to a remote and safe location, and their longevity in service, were all features required in parts of the structure. In other areas, Fosroc Galvashield galvanic anodes were installed, their fit-and-forget, self-regulating, high efficiency properties making them particularly suitable for areas containing pre- and post-stressed reinforcement. With both systems being installed with cementitious, non-polymer-modified repair mortars as part of an holistic repair solution, BAA are looking forward to achieving a minimum 20 year lifetime extension on the car park structure, as high a level of durability as would be obtained for an entirely new structure.

BAA are also pleased that the chosen solution has minimised their wider economic, societal and environmental impacts, a key feature of the company’s Corporate Responsibility policy, to work in partnership with the industry to achieve maximum efficiency, continuous improvement and higher standards in construction projects.

Fosroc wish to thank BAA for their kind permission to use this case study as an example of the need to consider the wider socio-economic impacts, when making investment decisions entailing construction and repair of key infrastructure.