Flexcrete products have been used as part of a major 3 year £85 million contract being undertaken by principal contractor BAM Nuttall to refurbish and strengthen the Central Terminal Area (CTA) road tunnels at Heathrow Airport.
Originally built in the 1950’s, the Main Tunnel is a 630m twin-bore road tunnel with two lanes per bore and two additional single lane side bores. The tunnels are critical assets with the Main Tunnel handling on average 600 passengers per hour entering and exiting Terminals 1,2 and 3, as well as being the main arterial for all key services that keep the airport running.
In addition to strengthening the tunnel, to allow for the new generation of heavier planes using the runway above, the aims of the project are also to provide new life-safety systems and improve business resilience should an incident occur, as well as replacing key life expired assets. The scope of work includes installing new ventilation equipment, lighting systems, telephones, CCTV systems, drainage, doors and escape routes, emergency signage and tunnel closure systems. This requires the tunnels to be stripped back to their bare structure to allow structural repairs and waterproofing of the tunnel joints to be carried out.
As the project cannot impact on airport resilience, performance and reputation, construction work is being carried out between 10.30pm and 5.30am, with one inbound lane and one outbound lane always remaining open during the construction working hours, so the airport can operate as normal during the day. The project is being carried out on behalf of Heathrow Airport Holdings and Flexcrete products were specified by Mott MacDonald Bentley.
The expansion joints in the access tunnel had previously been waterproofed with a Hypalon over bandage system adhered with an epoxy resin, but this had reached its design life and neededreplacing. Following its removal it was necessary to fill voids and defects to reinstate the surface profile. Monolevel 844SP, a single component, polymer modified engineering grade screed, was rapidly applied by trowel to provide an even substrate for coating.
Any water seeping through the joint sections was then controlled and directed into drainage channels using Cemprotec 2000-S. The Cemprotec 2000-S consists of an outer non-woven polypropylene fleece surrounding a thermoplastic waterproof polyurethane membrane, which has an elongation of 600% to accommodate any movement across the joint. It is supplied in two widths; smaller joints were covered with 120mm tape and any joints larger than 40mm were treated with 200mm tape.
Cemprotec 2000-S was adhered to the surface using Cementitious Coating 851, a two component, water based, cementitious coating which provides exceptional waterproof protection, is backed by British Board of Agrément (BBA) approval and is CE marked in accordance with BS EN 1504 Part 2. As 851 is water-based, it releases no strong odour or harmful solvents during application which is critical in enclosed environments and all equipment is quickly and easily cleaned in water.