Concrete cancer

Concrete cancer is a colloquial name for the deterioration of concrete caused by the presence of contaminants or the action of weather combined with atmospheric properties. While often used in the context of the rusting of concrete reinforcement bar (rebar), the term can equally be applied to any number of concrete failures, notably carbonation or the Alkali - silica reaction. 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.

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.[1]

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)

When this reaction occurs in household situations, a stop leak specialist should be consulted for advice.[citation needed]

Contents

Treatment

Concrete cancer can be treated in some structures[2]. 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 techniques [1].

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.[citation needed]

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.[citation needed] 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.[citation needed]

Structures said to be affected

Australia

New Zealand

  • Fairfield Bridge in Hamilton, New Zealand. Repaired in 1991 at a cost of NZ$1.1 million.[6]
  • Wellington Hospital Clinical Services Block in Wellingon, New Zealand. Currently being repaired at an estimated cost of NZ$3 million.[7]

United Kingdom

References

  1. ^ a b BBC h2g2 Encyclopaedia Project – Concrete Cancer entry
  2. ^ ”Our House” TV program – Nine Network - Fact Sheet (NineMSN)
  3. ^ http://manly-daily.whereilive.com.au/news/story/upgraded-pool-is-reopening-today/
  4. ^ Anna Vlach, The Adelaide Advertiser, “Pat bridge load fears”, 8 August 2007, page 9
  5. ^ http://www.architecture.com.au/i-cms?page=6822
  6. ^ "Fairfield Bridge". Hamilton City Libraries. Archived from the original on 2009-10-23. http://www.webcitation.org/5kjlkj34C. Retrieved 2009-10-23. 
  7. ^ "Concrete Cancer Hits Hospital". Dominion Post. http://www.stuff.co.nz/dominion-post/news/wellington/746263. Retrieved 2010-01-15. 
  8. ^ [1]
  9. ^ Laura Kemp, Wales on Sunday, “THE Millennium Stadium is suffering from concrete cancer, we can reveal”, 8 July 2007; [2]

Further reading


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