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Cement manufacture is a source of the following airborne contaminants: particulate matter, nitrogen oxides, sulfur dioxide, carbon monoxide, and carbon dioxide. [3] Cement production releases carbon dioxide by sintering limestone or shells. It is also very energy-intensive, with the result that the cement industry is a large emitter of carbon ...
Its setting behavior and strength development are essentially the same as that expected in gray cement, and it meets standard specifications such as ASTM C 150 and EN 197. In practice, because much white cement is used in pre-cast concrete products, it is commonly made to a high-early strength specification such as ASTM C 150 Type III.
[12] [19] Type I portland cement is known as common or general-purpose cement. It is generally assumed unless another type is specified. It is commonly used for general construction, especially when making precast, and precast-prestressed concrete that is not to be in contact with soils or ground water.
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The sight of calthemite is a visual sign that calcium is being leached from the concrete structure and the concrete is gradually degrading. [12] [17] In very old concrete where the calcium hydroxide has been leached from the leachate seepage path, the chemistry may revert to that similar to "speleothem" chemistry in limestone cave.
Alteration of hardened cement paste composition, with monosulfate aluminates phase converting to ettringite and, in later stages, gypsum formation. The necessary additional calcium is provided by the calcium hydroxide and calcium silicate hydrate in the cement paste; The effect of these changes is an overall loss of concrete strength.
Chromium present in the cement as Cr[III] is of no consequence. Mn 2 O 3 is not deleterious, acting as a substitute for iron. But it contributes more color to the cement than iron, and high-Mn 2 O 3 cements (>1%) are almost black. ZnO is encountered in some rawmix additives (as well as tires used as kiln fuel). At levels above 0.2%, it causes ...
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