Cement, carbon dioxide from

Mixed with sand it hardens as mortar and plaster by taking up carbon dioxide from the air. Calcium from limestone is an important element in Portland cement. 

Fresh concrete and cement mortars—which are identical from a chemical point of view—are relatively strongly alkaline (pH approximately 12.5). It later falls, however, due to the binding of carbon dioxide from the air. Depending on the special chemistry of the cement mortar, this process proceeds very slowly in the depth of the material. According to the composition of the cement mortar, this may last from a few months to many decades, until the pH value of such a mortar or concrete becomes neutral, even in the deepest layers.396"398 This chemical behavior explains the entire secret of the stability of reinforced concrete, which prevents the embedded steel from rusting further in the environment within the concrete, which remains alkaline for lengthy periods of time.399... 

Its natural and prepared compounds are widely used. Quicklime (CaO), which is made by heating limestone that is changed into slaked lime by carefully adding water, is a great base of chemical refinery with countless uses. Mixed with sand, it hardens as mortar and plaster by taking up carbon dioxide from the air. Calcium from limestone is an important element in Portland cement. 

The term hydraulic means that the product is water-resistant when hardened. Non-hydraulic materials are those that decompose when subjected to moisture and cannot harden under water. Among non-hydraulic cements, lime may be quoted as an exception, because its hardening is caused by carbon dioxide from atmospheric air however formed CaC03 (calcium carbonate) is water resistant. 

Seasonal fluctuations are primarily due to summertime maxima and wintertime minima in the net rate of photosynthesis, which removes CO2 from the atmosphere. The long-term trend, however, is clearly upward, and reflects anthropogenic releases of carbon dioxide from fossil fuel combustion, land alteration (in large part, the clearing and burning of tropical forests for agriculture), and, to a lesser extent, cement production. 

Marland, G., Boden, T. A., Griffin, R. C., Huang, S. F., Kanciruk, P. and Nelson, T. R. (1989). Estimates of CO2 emissions from fossil fuel burning and cement manufacturing, based on the US Bureau of Mines cement manufacturing data. Rep. ORNL/CDIAC-25, NDP-030, Carbon Dioxide Information Analysis Center, Oak Ridge Natl. Lab., Oak Ridge, TN. 

The use of the lignin fraction is much more cumbersome currently the best-known chemical of a real commercial importance is vanillin, which is obtained by oxidation of the black liquor. Another example is a product called spray-dried lignosulfonate (as sodium salt) obtained from the older, acidic sulfite pulping process. It is sold as a commercial product primarily as a concrete additive for enhanced strength. Since the cement industry is one of the big contributors of carbon dioxide emissions (due to the production of calcium oxide from calcium carbonate), the use of this renewable, wood-derived product not only is fossil-carbon neutral in itself but also reduces carbon dioxide emission due to the diminished need for cement in large infrastructures made of concrete. 

The abundance and nontoxic nature of carbon dioxide also make it an attractive carbon feedstock. Potential sources of carbon dioxide include the atmosphere (where it is present in concentrations of approximately 370 ppm), natural reservoirs including natural gas wells and pure CO2 wells, waste streams of fermentation reactions, and flue stacks from power plants, cement production, and so on. Because CO2 is not toxic, development of chemical processes in which CO2 can be used to... 

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