Цемент, портленд, химикаты химические свойства, назначение, производство
Описание
Portland cement refers to a class of hydraulic
cements in which the two essential constituents
are tricalcium silicate (3CaO·SiO2) and dicalcium silicate (2CaO·SiO2) with varying
amounts of alumina, tricalcium aluminate, and iron oxide. It is insoluble in water. The quartz
content of most finished cements is below 1%.
Chromium may be present.
Химические свойства
odourless fine white to grey powder
Использование
The majority of the cement used in construction is mixed
with sand and gravel and water at a central plant and trucked
wet to the construction site. Thus, there is little opportunity
for exposure of workers at the site to cement dust. Nevertheless,
many construction workers may be exposed to cement
dust when small amounts are mixed on site or when cement or
concrete materials are cut or ground.
Определение
A type of hydraulic cement in the form of finely
divided, gray powder composed of lime, alumina,
silica, and iron oxide as tetracalcium alumino-
ferrite (4Ca O?Al
2
O
3
?Fe
2
O
3
), tricalcium aluminate
(3Ca O?Al
2
O
3
), tricalcium silicate (3Ca O?Si O
2
),
and dicalcium silicate (2Ca O?Si O
2
). These are
abbreviated, respectively, as C
4
AF, C
3
A, C
3
S, and
C
2
S. Small amounts of magnesia, sodium, potas-
sium, and sulfur are also present. Hardening does
not require air and will occur under water. Cement
may be modified with various plastic latexes in pro-
portions up to 0.2 part latex solids to one part cement
to improve adhesion, strength, flexibility, and cur-
ing properties. Water evaporation can be retarded by
adding such resins as methylcellulose and hydrox-
yethylcellulose. For further information, refer to the
Portland Cement Association, 5420 Old Orchard
Road, Skokie, IL 60077-1083.
Общее описание
A gray to white, odorless powder. A finely ground (powdered) mixture of mainly 3CaO.SiO2 (tricalcium silicate), 2CaO.SiO2 (dicalcium silicate), CaO.Al2O3 (tricalcium aluminate), 4CaO.Al2O3.Fe2O3(tetracalcium aluminoferrite) and CaSO4.2H2O (calcium sulfate dihydrate).
Профиль реактивности
Sets in an exothermic reaction to a solid of low strength within hours after mixing with water. Continuing slower exothermic reactions harden the product to a tough gray stony mass. Incompatible with acids, acid chlorides, and acid anhydrides when set. Incompatible with ammonium salts and aluminum metal when wet and unset.
Опасность
Pulmonary function effects, asthma, respi-
ratory symptoms.
See concrete (1).
Угроза здоровью
Portland cement is an irritant of
the eyes and causes dermatitis.
Профиль безопасности
A nuisance dust. A skin
irritant. See also NUISANCE DUSTS and
AEROSOLS.
Канцерогенность
Earlier studies have suggested increases in
various types of cancer, including lung and
stomach, with exposure to cement, but numerous limitations prevent any conclusions in this
regard.
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сырьё
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