The Cement clinkers (which
are formed when calcareous and
argillaceous raw
materials are mixed and burned in rotary kilns) consist of following major compounds:
|
Compound
|
Common Proportion
|
Cement chemist
notation
|
|
Tricalcium Silicate (3CaOSiO2)
|
40-65%
|
C3S
|
|
Dicalcium Silicate (2CaOSiO2)
|
20-35%
|
C2S
|
|
Tricalcium Aluminate (3CaO Al2O3)
|
5-15%
|
C3A
|
|
Tetracalcium Aluminium Ferrite (4CaO Al2O3
Fe2O3)
|
8-18%
|
C4AF
|
|
Gypsum (CaSO4)
|
3.0-4.0%
|
|
|
Other Constituents
|
0-5.0%
|
|
Tricalcium Silicate / (C3S) / {Alite}
·
Generate heat more rapid
·
Hydrate more rapidly
·
Possess less resistance to
chemical attack
·
Develop early strength
Dicalcium Silicate / (C2S) / {Belite}
·
Imparts ultimate strength of
the cement
·
Offers more resistance to
chemical attack
·
Hardens more slowly
·
Less heat of hydration
·
Largely responsible for increase in strength beyond 7 days
Tricalcium Aluminate / (C3A) / {Celite}
·
Weak against sulphate attack
·
Reacts fastly generating a large amount of heat
·
Does not contribute to
develop strength
·
Causes initial setting of
cement
·
It is the first compound
which reacts with water
when mixed with cement.
Tetracalcium Aluminium Ferrite / (C4AF) / {Felite}
·
Poor cementing
value
·
Reacts slowly generating small
amount of heat
·
Comparatively inactive
·
Most Portland cement colour
effect are due to C4AF
·
It has been observed that most of the strength developing properties of cement are
controlled by C3S
and C2S
(the sum of their percentage varies from 70 to 80
percentage)
High percentage of C3S and low C2S
result in
·
Rapid hardening
·
High early
strength
·
High early
strength with high heat generation
·
Less resistance to chemical attack
Low percentage of C3S and high percentage
of C2S result in
·
Slow hardening
·
Much more
ultimate strength with less heat generation
·
Greater resistance
to
chemical attack.
No comments:
Post a Comment