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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.
The initiation time is related to the rate at which carbonation propagates in the concrete cover thickness.Once that carbonation reaches the steel surface, altering the local pH value of the environment, the protective thin film of oxides on the steel surface becomes instable, and corrosion initiates involving an extended portion of the steel surface.
Carbonation-initiated deterioration of concrete at Hippodrome Wellington, Belgium. Carbon dioxide (CO 2) from air (~ 412 ppm vol.) and bicarbonate (HCO − 3) or carbonate (CO 2− 3) anions dissolved in water react with the calcium hydroxide (Ca(OH) 2, portlandite) produced by Portland cement hydration in concrete to form calcium carbonate (CaCO
Weathering carbonation occurs in concrete when calcium compounds react with carbon dioxide (CO 2) from the atmosphere and water (H 2 O) in the concrete pores. The reaction is as follows. First, through chemical weathering, CO 2 reacts with water in the concrete pores to form carbonic acid: CO 2 + H 2 O ⇌ H 2 CO 3
Concrete has a very low coefficient of thermal expansion, and as it matures concrete shrinks. All concrete structures will crack to some extent, due to shrinkage and tension. Concrete which is subjected to long-duration forces is prone to creep. The density of concrete varies, but is around 2,400 kilograms per cubic metre (150 lb/cu ft). [1]
AFm form inter alia when tricalcium aluminate 3CaO·Al 2 O 3, or C 3 A in CCN, reacts with dissolved calcium sulfate (CaSO 4), or calcium carbonate (CaCO 3). As the sulfate form is the dominant one in AFm phases in the hardened cement paste (HCP) in concrete, AFm is often simply referred to as Aluminate Ferrite monosulfate or calcium aluminate ...
Concrete floor of a parking garage being placed Pouring and smoothing out concrete at Palisades Park in Washington, DC. Workability is the ability of a fresh (plastic) concrete mix to fill the form/mold properly with the desired work (pouring, pumping, spreading, tamping, vibration) and without reducing the concrete's quality.
(2) The thermal expansion coefficients of concrete and steel are so close (1.0 × 10 −5 to 1.5 × 10 −5 for concrete and 1.2 × 10 −5 for steel) that the thermal stress-induced damage to the bond between the two components can be prevented. (3) Concrete can protect the embedded steel from corrosion and high-temperature induced softening.