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The cement industry is one of the main producers of carbon dioxide, a greenhouse gas. [2] Concrete causes damage to the most fertile layer of the earth, the topsoil. Concrete is used to create hard surfaces which contribute to surface runoff that may cause soil erosion, water pollution and flooding.
Some companies are creating carbon-negative building materials by storing excess carbon dioxide in concrete.
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).
The carbon dioxide in the air reacts with the alkali in the cement and makes the pore water more acidic, thus lowering the pH. Carbon dioxide will start to carbonatate the cement in the concrete from the moment the object is made. This carbonatation process will start at the surface, then slowly moves deeper and deeper into the concrete.
Calcium oxide is a crucial ingredient in modern cement, and is also used as a chemical flux in smelting. Industrial calcination generally emits carbon dioxide (CO 2). A calciner is a steel cylinder that rotates inside a heated furnace and performs indirect high-temperature processing (550–1150 °C, or 1000–2100 °F) within a controlled ...
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 ...
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Cement kilns are used for the pyroprocessing stage of manufacture of portland and other types of hydraulic cement, in which calcium carbonate reacts with silica-bearing minerals to form a mixture of calcium silicates. Over a billion tonnes of cement are made per year, and cement kilns are the heart of this production process: their capacity ...