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Portland slag cement is basically:
Portland Cement Clinker + Gypsum+ Granulated Blast Furnace Slag
The
slag constituent is normally less than 25 % and not more than 65 % by
mass of Portland-slag cement. The %age of slag goes up to 85% in some
countries.
This
cement enables utilization of blast furnace slag, a waste product from blast
furnaces.
Concrete made with Ground
Granulated Blast furnace Slag Cement sets more slowly than concrete made with ordinary
Portland cement depending on the amount of GGBS present in the cementitious material It also continues to gain strength for longer period in
production condition. This results in lower
heat of hydration and lower temperature rises, and makes avoiding cold
joints easier, but may also affect construction schedules where quick
setting is required.
By combining GGBSC with OPC in varying proportions, concrete with different
properties (as per requirement) can be made.
Benefits of using GGBSC
- Better workability,
making placing and compaction easier,
- Lower temperature rise,
reducing the risk of thermal cracking in massive concrete structures,
- Elimination of the risk of damages caused by Alkali-silica
Reaction (ASR),
- High resistance to chloride ingress, reducing the risk of reinforcement corrosion,
and
- High resistance to attacks by sulphates, Acidic waters and other
chemicals: recommended for use
in concrete foundations exposed to aggressive conditions.
- Better pore structure & reduced permeability: recommended for use in water retaining
structures
Manufacturing
of Portland cement is a major contributor of greenhouse gases, responsible for
about 5% of all global carbon dioxide emissions. In comparison, manufacturing of GGBSC requires less than a fifth the
energy and produces less than a tenth of the carbon dioxide emissions.
The relatively
low energy requirement in manufacture of this cement is important these days.
The cement is extensively being used in many countries which have a large
production of slag. For example: in Netherlands, 60% of all cement used
is of Portland Blast Furnace type.
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