本帖最后由 choi 于 11-30-2021 14:11 编辑
(3) Greenhouse gases | Set in Green Concrete; How cement, a bane of environmentalists, may yet help slow global warming.
https://www.economist.com/scienc ... al-warming/21806083
paragraph 1: "THE ROMANS perfected concrete, and their legacy still stands in the form of the magnificent roof of the Pantheon, the world’s largest unreinforced concrete dome. Since it was completed in around 125ad by the Emperor Hadrian * * *
paragraph 2: "This is bad news for global warming. The problem is that concrete's crucial ingredient, cement, which is mixed with sand, gravel and water to make the stuff, is responsible for a huge amount of greenhouse-gas emissions/ Taking in its various stages of production, th e5bn tonnes of cement produced each yeat account for 8% of the world's anthropogenic CO2 emissions. If the cement industry were a country it would be the third largest emitter in the world, after China and America.
paragraph 3: "So far, concrete has few practical alternatives. * * *
paragraph 4: "The place to start is where emissions are greatest. Cement production begins with the quarrying of limestone, the main component of which is calcium carbonate (CaCO3). This is mixed with clay and passed through a rotating kiln at more than 1,400ºC in a process called calcination. The heat drives off the carbon and part of the oxygen, which combine to form CO2. The remaining lumps, called clinkerm are made of molecular complexes of calcium oxide and silicates. The clinker is then cooled and milled into cement. More than half of the emissions involved in concrete-making are a consequence of calcination, and most of the rest result from burning coal and other fossil fuels to power the process (see chart, overleaf). All told nearly one tonne of CO2 is released for every tonne of fresh cement.
paragraph 5: "The inevitability of calcination's creation of CO2 makes capturing the gas before it can enter the atmosphere, and storing it away, the most effective approach to decarbonise the cement industry, according to a study by Paul Fennell of Imperial College London, and his colleagues, published earlier this year i Joule. * * *
Note:
(a)
(i) Pantheon, Rome
https://en.wikipedia.org/wiki/Pantheon,_Rome
(Pantheon "is a former Roman temple and since the year 609 a Catholic church (Basilica di Santa Maria ad Martyres or Basilica of St Mary and the Martyrs)")
, whose caption of a photo of pantheon looking up from the ground to the roof hasa caption:
The Pantheon dome. The coffered dome has a central oculus as the main source of natural light."
(ii) Latin-English dictionary:
* oculus (noun masculine): "1: (literally, anatomy) eye"
https://en.wiktionary.org/wiki/oculus
(iii) Freda Parker, The Pantheon — A temple to all gods. Monolithic Dome Institute, June 21, 2001
https://monolithicdome.com/pantheon-a-temple-to-all-gods
(photo caption: "The concrete dome is 20 feet (6 m) thick at the base and tapers to 7.5 feet (2.3 m) thick at the oculus. Without materials like rebar to hold the dome in tension, the massive rings of concrete were used to create a buttress-like effect that forces the dome into constant compression. The concrete dome weighs an astounding 5,000 tons (4,535 t).")
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