Concrete cancer
Encyclopedia
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.
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.
ed 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 .
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.
Rebar
A rebar , also known as reinforcing steel, reinforcement steel, rerod, or a deformed bar, is a common steel bar, and is commonly used as a tensioning device in reinforced concrete and reinforced masonry structures holding the concrete in compression...
), the term can equally be applied to any number of concrete failures, notably carbonation
Carbonatation
Carbonatation is a chemical reaction in which calcium hydroxide reacts with carbon dioxide and forms insoluble calcium carbonate:The process of forming a carbonate is sometimes referred to as "carbonation", although this term usually refers to the process of dissolving carbon dioxide in...
or the Alkali - silica reaction
Alkali Silica Reaction
The alkali–silica reaction is a reaction which occurs over time in concrete between the highly alkaline cement paste and reactive non-crystalline silica, which is found in many common aggregates....
. 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
Rust
Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...
and expand which in turn creates stresses on the surrounding concrete which can then spall
Spall
Spall are flakes of a material that are broken off a larger solid body and can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure...
(break away). The use or presence of Chloride
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
based compounds, together with a reduction in alkalinity, can cause corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
of the reinforcing steel bars
Rebar
A rebar , also known as reinforcing steel, reinforcement steel, rerod, or a deformed bar, is a common steel bar, and is commonly used as a tensioning device in reinforced concrete and reinforced masonry structures holding the concrete in compression...
then expansion and spalling. Alternatively, if the cement component is too alkaline, it reacts with atmospheric carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, 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
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....
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
Calcium hydroxide
Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca2. It is a colourless crystal or white powder and is obtained when calcium oxide is mixed, or "slaked" with water. It has many names including hydrated lime, builders lime, slack lime, cal, or...
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
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
. 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.
Treatment
Concrete cancer can be treated in some structures. In order to effect repairs, the spallSpall
Spall are flakes of a material that are broken off a larger solid body and can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure...
ed 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 .
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.Australia
- Macquarie Wharf, HobartHobartHobart is the state capital and most populous city of the Australian island state of Tasmania. Founded in 1804 as a penal colony,Hobart is Australia's second oldest capital city after Sydney. In 2009, the city had a greater area population of approximately 212,019. A resident of Hobart is known as...
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in Hamilton, New Zealand. Repaired in 1991 at a cost of NZ$1.1 million. - Wellington HospitalWellington Hospital, New ZealandWellington Hospital is Wellington, New Zealand's main hospital located in the suburb of Newtown. It is the main hospital run by Capital & Coast District Health Board , the others including Kapiti Health Centre, and Kenepuru Hospital...
Clinical Services Block in Wellingon, New Zealand. Currently being repaired at an estimated cost of NZ$3 million.
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(several raised portions), Birmingham, EnglandEnglandEngland is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental... - BBC Pebble Mill, former television studios in Birmingham, England, demolished
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