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)
Read more about this topic: Concrete Cancer
Famous quotes containing the word types:
“The American man is a very simple and cheap mechanism. The American woman I find a complicated and expensive one. Contrasts of feminine types are possible. I am not absolutely sure that there is more than one American man.”
—Henry Brooks Adams (1838–1918)
“Our major universities are now stuck with an army of pedestrian, toadying careerists, Fifties types who wave around Sixties banners to conceal their record of ruthless, beaverlike tunneling to the top.”
—Camille Paglia (b. 1947)
“Science is intimately integrated with the whole social structure and cultural tradition. They mutually support one other—only in certain types of society can science flourish, and conversely without a continuous and healthy development and application of science such a society cannot function properly.”
—Talcott Parsons (1902–1979)