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Carbonatation induced rebar corrosion. Carbonatation is a slow process that occurs in concrete where lime (CaO, or Ca(OH) 2 ) in the cement reacts with carbon dioxide (CO 2) from the air and forms calcium carbonate. The water in the pores of Portland cement concrete is normally alkaline with a pH in the range of 12.5 to 13.5.
Calcium carbonate is the active ingredient in agricultural lime and is produced when calcium ions in hard water react with carbonate ions to form limescale. It has medical use as a calcium supplement or as an antacid , but excessive consumption can be hazardous and cause hypercalcemia and digestive issues.
When atmospheric carbon dioxide (CO 2), or carbonate ions (HCO − 3, CO 2− 3 dissolved in water) diffuse into concrete from its external surface, they react with calcium hydroxide (portlandite, Ca(OH) 2) and the pH of the concrete pore water progressively decreases from 13.5 – 12.5 to 8.5 (pH of water in equilibrium with calcite).
As new cold water with dissolved calcium carbonate/bicarbonate is added and heated, the process continues: CO 2 gas is again removed, carbonate concentration increases, and more calcium carbonate precipitates. Scale is often colored because of the presence of iron-containing compounds.
Pure lime is soluble in water containing carbonic acid, a natural, weak acid which is a solution of carbon dioxide in water and acid rain so it will slowly wash away, but this characteristic also produces autogenous or self-healing process where the dissolved lime can flow into cracks in the material and be redeposited, automatically repairing ...
The formation of biogenic calcium carbonate by marine calcifiers is one way to add ballast to sinking particles and enhance transport of carbon to the deep ocean and seafloor. [46] The calcium carbonate counter pump refers to the biological process of precipitation of carbonate and the sinking of particulate inorganic carbon. [47]
Rain water contains dissolved carbon dioxide taken from the atmosphere. Some of the dissolved carbon dioxide reacts with the water to form carbonic acid, which remains in solution. Minerals containing calcium and magnesium form soluble bicarbonates when exposed to carbonic acid. Water containing these minerals is known as "hard water".
Chlorine can be manufactured by the electrolysis of a sodium chloride solution , which is known as the Chloralkali process. The production of chlorine results in the co-products caustic soda (sodium hydroxide, NaOH) and hydrogen gas (H 2). These two products, as well as chlorine itself, are highly reactive.