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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.
In order to avoid frequent cleanings of new church's concrete "sails", new development was used - white self-cleaning coating of the walls. [3] However, back then it wasn't known that this colouring plaster containing titanium dioxide and white pigment absorbs exhaust gases and other elements of city fog.
Hydrophobic concrete can be used in the same applications as regular concrete, most often where regular concrete is dangerous to repair or the cost of structural damage would be highly detrimental. Tunnel work is a major application of hydrophobic concrete as underground repairs are difficult and costly. [ 8 ]
Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures to a solid over time. Concrete is the second-most-used substance in the world after water, [1] and is the most widely used building material. [2] Its usage worldwide, ton for ton, is twice that of steel, wood, plastics, and aluminium combined. [3]
Calcium aluminates can form complex salts in combination with different types of anions.Two series of calcium aluminates are known in cement chemistry: AFm and AFt phases, being respectively mono- or tri-substituted with a given divalent anion X (e.g. SO 2− 4, CO 2− 3, or hosting a divalent impurity such as SeO 2− 4 [3]...), or with two units of a monovalent anion, e.g. OH −, Cl − ...
To avoid the flash setting of concrete, due to the very fast hydration of the tricalcium aluminate (C 3 A), 2–5 wt. % calcium sulfate is interground with the cement clinker to prepare the cement powder. In cement chemist notation, CaSO 4 is abbreviated as C S, and CaSO 4 ·2H 2 O as C S H 2.
When water is added to cement, each of the compounds undergoes hydration and contributes to the final state of the concrete. [2] Only calcium silicates contribute to the strength. Tricalcium silicate is responsible for most of the early strength (first 7 days). [3] Dicalcium silicate, which reacts more slowly, only contributes to late strength.
Alite is an impure form of tricalcium silicate, Ca 3 SiO 5, sometimes formulated as 3CaO·SiO 2 (C 3 S in cement chemist notation), typically with 3-4% of substituent oxides. [1] It is the major, and characteristic, phase in Portland cement.
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