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This
type of cement is not liable to cause staining, since it has a low
content of soluble alkalis. The goal in the manufacture of this cement is
to minimize the content of oxides (particularly iron and manganese) that
impart the grayish color normally associated with Portland cement.
The
process of manufacture of white cement is essentially same as that of OPC.
However, the raw materials (particularly the lime stone) used should be of
high purity. The amount of compounds like Cr2O3,
Mn2O3, Fe2O3 in raw material is
required to be kept relatively lower. For example, the limestone used in
manufacture of normal cement contains up to 1% Fe2O3,
whereas levels below 0.1% are required for manufacture of white cement.
Sea shells and coral can also be used as raw material for production of white
cement.
White
cement is typically ground a little finer than gray cement. Oil may
be used as fuel in the kiln in order to avoid contamination by coal ash.
There are only slight chemical and physical
differences between gray Portland cement and white Portland cement.
These differences are due to raw material differences
and sometimes, though not always, slight differences in manufacturing (like
higher kiln temperature requiring 20-30% higher fuel consumption).
White cement is more expensive than OPC (often more than double the price).
The
strength of white cement is usually lower than that of OPC but white
cement nevertheless satisfies the requirements of BS 12:1978.
Under ASTM, White Cement has not been specified under a separate specification.
However it can be specified via a number of different standards—Portland
cements, masonry cements, and plastic (stucco) cements.
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