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6 2019年度 英語
Ordinary Portland cement-t
produced by baking lime in a kiln and emits approximately one ton of carb
a kiln and emits
Cement production is responsible for
cement.
dioxide for every ton of
approximately 5% of global man-made CO2 emissions, according to the World
Business Council for Sustainable Development.
Cement does absorb some carbon dioxide back from the atmosphere over time,
One 2016 study estimated that between 1930 and 2013, the
equivalent of 43% of CO2 released from lime during heating was reabsorbed by
- although that percentage does not include carbon
concrete products worldwide
dioxide emitted by the fossil fuels burned to heat kilns, a significant contributor of
says.
Fennell notes.
東京医科歯科大前駅
- the most common form in concrete-
CO2 emissions during production.
Unfortunately, this absorption comes at a price, particularly when cement is
used in structures that feature steel reinforcement bars (rebar) within concrete.
vl(As) CO₂ moves through cement it changes the pH of the surroundings,
Fennell says. Concrete loses its alkalinity and, when moisture and oxygen are
present, causes the rebar to rust.
2)
ad "Rusting steel can expand with great force to as much as nine times its
original dimensions if you add up all of the layers of iron oxide," says Randolph
Langenbach, an international consultant in building conservation. This expansion
causes the concrete to crack, flake and crumble.
Svi aft ni adosband huma
Degradation is a massive concern, he argues, and problems are not limited to
rusting rebar. Everything from air pockets left in the concrete mix when it's laid
to salt air buffeting coastal-facing walls, or the use of beach sand in the concrete,
can shorten a building's lifespan.
As one specialist once put it to Langenbach: "If it ain't cracked, it aint
concrete."qubong ao yas
guidtyns ogde stornos 90 s of
fshoqml is vatns mash
*** long llopsd lust ay
to Given the concerns about the environmental impact and structural longevity of
concrete, why do we continue to build with it?
addi
Simply put, concrete is cheap, versatile, quick to erect and requires no
of weight
J
