Flooring the aircraft hangar

Concrete, Apr 2007 by Mackenzie, Andrew

The RAF Museum at Cosford opened in a stunning new building in February 2007. It needed a bright environment and maintenance-free building solutions. But the size of the aircraft exhibits also placed special requirements and constraints on the type of flooring.

The new museum building, designed by Fielden Clegg Bradley Architects, is an aircraft hangar and displays many planes, including all three 'V' bombers - Vulcan, Valiant and Victor- and comprises the new National Cold War Exhibition. Some planes are situated on the floor and some are suspended in mid-air.

The nature and size of the exhibits places constraints on the building size and shape. This led to restrictions on Galliford Try's construction planning and on Snowden Flooring, who constructed the in-situ concrete floor.

Building design

The architect has designed a splendid building, which looks equally good from the air (see front cover inset). There is very little natural light except through the smaller canvas walls at each end of the building. However, a bright environment is essential in such a building, as is a long, maintenance-free life, so the architect selected Permashake Light Grey coloured dry shake concrete hardener for the museum floor. As well as hardening the floor this gives a light, airy feel to the building. Coloured dry shake concrete floor slab hardeners are also widely used in retail warehouse outlets, where the buildings have similar operational requirements, although without the same construction constraints.

As in retail warehouses, the dry shake concrete floor is also the final museum floor, with no other covering. AlphaJoint was selected tor the free contraction joints, which are also used as the day-joints. This minimised the risk of any cracking and protected all the formed concrete arris edges.

Flooring solutions

Due to very high point loadings from plane wheels, steel-fibre-reinforcement was selected for the floor. Permashake is graded and quartz-based, so it has the added advantage of reducing any tendency of the steel fibres to be visible at the surface. It also provides a surface that is extremely durable - the Permashake hardened surface is even suitable to be trafficked by tracked vehicles such as tanks.

Some of the exhibits are very large and all are precious. For example, to bring the Victor bomber into the building the floor had to be laid without the south wall. Since dry shake hardened concrete floors must be constructed in a weatherproof environment, considerable efforts were undertaken to provide temporary weatherproofing. For construction reasons the perimeter ground beam had to be installed without weather protection - its excellent appearance and absence of steel fibres visible in the surface are a credit to the floor layer's professionalism.

Dry shake hardened and coloured concrete floors were originally developed for heavy industry and engineering. There are many floors still performing trouble-free after more than 20 years in heavy-duty situations. They are constructed monolithically with the floor slab by sprinkling on the dry shake powder. This absorbs moisture from the concrete and the slab is then panned and repeat power-trowelled to a finish as normal. The action of the panning in effect mixes on the concrete surface a fine coloured screed, which is only about 2-4mm thick but is monolithic with the concrete slab and achieves the long-term durability. The surface abrasion resistance far exceeds the highest requirements in BS 8204(1) and TR34(2). By selection of the aggregate type used in the dry shake grade, a number of extra benefits can be achieved for the floor, e.g. enhanced wet slip resistance, impact resistance and anti-static properties.

Laying a dry shake floor with a laser screed and telescopic dry shake spreader is a fast-track operation - each area of typically up to 1500m^sup 2^ is complete in a day - the only other operation being to saw-cut induced joints where required. Thus, a coloured, chemical-resistant, low-cost finished floor is achieved with great speed. Although the time-to-loading criteria are the same as for the concrete slab, there are no difficult surface dpm/moisture requirements, such as for resin or vinyl flooring, and the durability of the Permashake floor is much better.

Concluding remarks

When considering a particular floor, Permaban would always suggest the specifier request a reference visit to a building where a finished floor may be seen. This should be the same colour and grade, in relevant industry usage and ideally have been laid by the specialist subcontractor selected for the project. The RAF Cosford Museum is open to the public and admission is free so there is one site to visit. As well as the floor, there are also some planes to be seen!

References:

1. BRITISH STANDARDS INSTITUTION. BS 8204: Screeds, bases and in-situ floorings. 2003.

2. THE CONCRETE SOCIETY. Technical Report 34, Concrete industrial ground floors - a guide to design and construction, Third Edition. Camberley, 2003.