Life-Cycle Study: Concrete



Prezentare generala

Calcat in picioare de mai mult de 2300 ani, betonul primeste rareori respectul pe care il merita. Poate cel mai omniprezent material de constructii, betonul intareste casele noastre, scolile, cladirile de birouri si spitalele. Fabricarea sa se numara printre cele mai mari consumatoare de energie si cele mai poluante procese industriale. Analistii se asteapta ca emisiile de gaze cu efect de sera provenite din productia mondiala de beton sa devina un contribuitor mai mare la schimbarile climatice decat Uniunea Europeana in urmatorii 20 de ani.

Betonul - un amestec de ciment, nisip si apa, incalzit intr-un cuptor - devenise un lucru obisnuit in timpul Imperiului Roman. Desi Vitruviu, un vizionar arhitect, a scris ca nisipul ar trebui sa fie lipsit de orice impuritati de pamant, cimentul romanilor in sine a fost uneori amestecat cu grasimi, lapte, sange de bou pentru a ii creste proprietatile adezive.




The spread of concrete ever since reflects global distributions of wealth and prosperity. Cement production boomed during recent decades, from 594 million tons in 1970 to 2.3 billion tons in 2005. As the growth of leading producers China and India continues, global cement production may reach 5 billion tons in 2030, the conservation group WWF estimates.



Modern concrete's main ingredient, cement, is most commonly produced using a method invented by Englishman Joseph Aspdin in 1824. His Portland cement (named after the limestone used in St. Paul's Cathedral and Buckingham Palace) mixes a powder of alumina, silica, lime, iron oxide, and magnesium oxide, which is then heated at temperatures up to 1,450 degrees Celsius.

Heating and grinding the cement materials consumes an average of 4-5 gigajoules of energy per cement ton. The industry as a whole uses at least 8 billion gigajoules each year. Cement production-through cement plants' fossil-based energy consumption, the CO2 burned off when limestone is heated, associated vehicle use, and other factors-accounts for about 6 percent of global anthropogenic greenhouse gas emissions, according to a recent WWF report.

In addition to its contribution to climate change, concrete production generates substantial amounts of waste. In China, it is responsible for more than 40 percent of industrial dust emissions. The dust can be recycled into the production process, but the U.S. Environmental Protection Agency warns that the highly acidic substance could pose "toxicological problems, human tissue burns...corrosion in pipes, and objectionable taste in drinking water" if released into the air or water.

Doing It Better


The cement industry's interest in reducing energy costs has led many countries to replace small-scale cement plants with larger, more efficient models. The most efficient kiln models accounted for about 6 percent of China's cement output in 1995, but these are expected to provide 80 percent of Chinese cement next year.

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