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Nitrocalcite is the name for a mineral which is a hydrated calcium nitrate that forms as an efflorescence where manure contacts concrete or limestone in a dry environment as in stables or caverns. A variety of related salts are known including calcium ammonium nitrate decahydrate and calcium potassium nitrate decahydrate. [3]
Concrete is damaged if it does not reach a strength of 500 pounds per square inch (3.4 MPa) before freezing. [3]: 19 Typical chemicals used for acceleration today are calcium nitrate (Ca(NO 3) 2), calcium nitrite (Ca(NO 2) 2), calcium formate (Ca(HCOO) 2) and aluminium compounds.
Calcium nitrite is widely used in concrete for high-rise construction, highways, bridges, railroads, airports, and large-scale hydraulics. It also might enable coastal areas to use chloride-containing sea sand in concrete. [7] Calcium nitrite is also used as a heavy oil detergent and in pharmaceuticals, dyes and metallurgy industries.
Accelerators speed up the hydration (hardening) of the concrete. Typical materials used are calcium chloride, calcium nitrate and sodium nitrate. However, use of chlorides may cause corrosion in steel reinforcing and is prohibited in some countries, so that nitrates may be favored, even though they are less effective than the chloride salt.
The environmental impact of concrete, its manufacture, and its applications, are complex, driven in part by direct impacts of construction and infrastructure, as well as by CO 2 emissions; between 4-8% of total global CO 2 emissions come from concrete. [1] Many depend on circumstances.
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 ...
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.
Properties of concrete. Concrete has relatively high compressive strength (resistance to breaking when squeezed), but significantly lower tensile strength (resistance to breaking when pulled apart). The compressive strength is typically controlled with the ratio of water to cement when forming the concrete, and tensile strength is increased by ...