Concrete cancer

Concrete cancer is concrete degradation caused by the presence of contaminants or the action of weather combined with atmospheric properties. It includes rusting of concrete reinforcement bar and any number of concrete failures, notably carbonatation or the Alkali - silica reaction.

Etymology

Concrete cancer is a layman's term which is often used by the media, but it has no specific definition universally recognised by building professionals. It is often used in relation to the failure of pre-cast concrete sections used in the construction of postwar non traditional housing, such as prefabs, Parkinsons, Waites, Dorloncos, Airey, Woolaway and Laing Easyform.

Types

Several forms of concrete defect are possible: water penetration causes the concrete reinforcement to rust and expand which in turn creates stresses on the surrounding concrete which can then spall (break away). The use or presence of Chloride based compounds, together with a reduction in alkalinity, can cause corrosion of the reinforcing steel bars then expansion and spalling. Alternatively, if the cement component is too alkaline, it reacts with atmospheric carbon dioxide, and the structure will begin to deteriorate as star-shaped cracks appear which allow rainwater to penetrate. This deterioration is then accelerated by freeze-thaw cycling of water in the cracks, which, again, causes the surface to spall.

The initial cause of concrete cancer is usually water penetration. When calcium oxide reacts with water that penetrates the concrete it forms a solution of calcium hydroxide. The chemical formula for this is:

CaO(s) + H₂O(l) → Ca(OH)₂(aq)

Over time this calcium hydroxide solution will reach the edge of the concrete slab. When this happens the solution reacts with carbon dioxide in the air and transforms into calcium carbonate. On the top of the slab calcium carbonate causes cracks above the slab (allowing more water penetration, and below the slab stalactites form:

Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)

Treatment

Concrete cancer can be treated in some structures. In order to effect repairs, the spalled concrete must be removed and any exposed steel must either be replaced or cleaned and treated. The area is then repaired to the original concrete profile using cement mortar, epoxy mortar or concrete, depending on the size of the damage and the structural requirements. Cracks are repaired using suitable epoxy resins, special mortars and injection utilising appropriate remedial building solutions.

This process is referred to as 'crack injection' and may constitute a negative membrane. Negative membranes will not prevent water from entering the concrete, merely shift the water's direction through the slab. Treatment of concrete cancer must incorporate proper waterproofing or risk being a temporary solution.

Incidence

Concrete cancer is increasingly common in structures which have not been sufficiently waterproofed. As builders cut costs on waterproofing membranes, the problems are increasing. The incidence of concrete cancer is particularly high in countries such as Australia where liquid applied membranes are still commonly used. Liquid membranes are often used inappropriately, and lead to water penetrating into the concrete. If early symptoms including the presence of calcium stalactites beneath the slab and visible rust from the slab are apparent, a stop leak specialist should be called immediately to assess the potential for damage.

Structures said to be affected

Australia

• Macquarie Wharf, Hobart, Tasmania, Australia
• Brisbane City Hall, Brisbane, Australia
• Rydges Swanston St, Melbourne, Victoria
• Centennial Hall, Adelaide, Australia (demolished in 2007)
• Dee Why ocean pool, Dee Why, Australia
• King St Bridge (crossing the Patawalonga River, Glenelg North, South Australia)
• Manly Surf Pavilion, Manly, Australia (1939–81)
• The Stack, Port Kembla, Australia
• Old Southern Stand, Melbourne Cricket Ground (demolished 1990)
• Sandy Point Beach Resort, Labrador, Queensland, Gold Coast, Queensland
• Pylons holding up the Cahill Expressway and Circular Quay railway station, Sydney

Italy

• Many of the raised concrete freeways in Sicily around Palermo

New Zealand

• Fairfield Bridge in Hamilton, New Zealand. Repaired in 1991 at a cost of NZ$1.1 million.
• Wellington Hospital Clinical Services Block in Wellingon, New Zealand.

United Kingdom

• ATV Centre, former television studios in Birmingham, England, demolished
• M6 motorway (several raised portions), Birmingham, England
• BBC Pebble Mill, former television studios in Birmingham, England, demolished
• Ca. 1920s housing, Horfield, Bristol, England
• Coaling Tower & Ash Plant, Carnforth MPD, Carnforth, England
• Derby railway station, Derby, England
• Keybridge House, South Lambeth Road, Vauxhall, London, England
• Millennium Stadium North Stand (part of the old National Stadium), Cardiff, Wales
• Kingsway Shopping Centre, Newport, Wales
• Somerton TARDIS, Newport, Wales
• Former Gwent County Hall, Croesyceiliog, Cwmbran, Wales
• Royal Devon and Exeter Hospital before demolition in the 1990s, a new hospital building was opened in stages starting from 1992
• Church of the Good Shepherd, Nottingham
• Lancastrian Hall and Central Library, Swinton, Salford
• Merafield Road Bridge over the A38 near Plympton, Plymouth Part of the A38 in Plymouth. Demolished May 2016

Further reading

• Australian Paint Manufacturers Association – Information Paper – June 2003