Civil Engineering Reference
In-Depth Information
compensated by increasing the calcium content of the clinker. burnability is
improved when HPO
4
3−
, HPO
4
3−
with F
−
, or with F
−
and SO
3
2−
are added into
the raw meal and the strength is increased with the addition of HPO
4
3−
and
F
−
(Guan et al., 2007).
The addition of chloride-containing components increases the burnability
of the raw meal and allows higher alite contents at the same clinkering
temperature. Halogens have a great capacity for reducing the viscosity of
the liquid phase and CaO is highly soluble in liquid phases rich in halogen
(Maki, 2006).
Sulfur (S
6+
) has a strong preference for belite. by increasing SO
3
in the
clinker, the alite becomes richer in al and Fe, particularly in al, with an
increase in the al/Fe ratio. the C
3
a content decreases and C
4
aF increases
with increasing SO
3
content. an increase in the SO
3
content causes a reduction
of the primary phase volume of C
3
S (decrease of C
3
S/C
2
S ratio); 2.5% of
SO
3
seems to be the threshold of formation of C
3
S. SO
3
and P
2
O
5
decrease
both the viscosity and surface tension of the liquid and the polymorphic
form of C
3
S, M1, is predominant as the constituent phase. MgO and SO
have opposite effects on the size and the phase constitution of alite. MgO
favors the occurrence of the M3 polymorph, whereas SO
3
favors M1 (Maki,
2006). the addition of SO
3
or SO
3
+ HPO
4
3−
simultaneously reduces the
burnability, whereas it is improved with the addition of SO
3
+ HPO
4
3−
and F
−
.
the increase in Na
2
O content modifies the polymorphism of C
3
a
(orthorhombic) with a limit of 4%. Na is partially incorporated in C
2
S,
stabilizing the form
a
and
a
¢ at room temperature. When Na
2
O is added, C
2
S
decreases and C
3
S increases with a possible occurrence of free lime (Gotti
et al., 2007). alkali metal oxides (Na
2
O and K
2
O) increase the viscosity and
decrease the surface tension of the liquid phase. the nucleation and growth
decrease in rate and large alite crystals are grown with distinct facets. a
small content of chromium is found in cement. It arises primarily from the
raw material and the wear of steel devices. When it is present as chromate
CrO
4
2−
, it provokes skin allergies. reducing agents such as ferrous iron
sulfate are added to prevent this shortcoming (bensted, 2006).
the maximum amount of Cu, Ni, Sn, and Zn that could be incorporated
in a laboratory clinker has been determined experimentally. this threshold
limit is found to be 0.35% of Cu, 0.5% of Ni, 1% of Sn and 0.7% for Zn
(Gineys et al., 2011).
a recent study has evaluated the perspective of alternative fuel used and
has shown that in developed countries a ratio of 40-60% of alternative fuel
in 2050 can be achieved while in the developing countries this ratio will
be around 25-35% (WBCSD, 2009). Technically, much higher substitution
rates are possible. In some european countries, the average substitution
rate is over 50% for the cement industry and up to 98% as yearly average
