Civil Engineering Reference
In-Depth Information
The crystalline lattice of alinite can also accommodate limited amounts of additional
ions, such as Fe
3+
, P
5+
, Ti
4+
, Na
+
, and K
+
(Noudelman
et al.,
1980; Boikova
et al.,
1986).
At least four modifications of alinite have been identified, and designated ,
′
, , and
(Noudelman and Gadaev, 1986).
Bromine (Kurdowski and Moric, 1989) and fluorine (Burger and Ludwig, 1986)
analogues of alinite have been also synthesized.
A
linite is isostructural with jasmundite, a silicate sulfide mineral [Ca
2
2(SiO
4
)
8
O
4
S
2
],
which does not, however, exhibit any hydraulic reactivity (Bikbaou, 1986).
A chlorine-containing phase similar to belite and designated
belinite
has also been
synthesized (von Lampe
et al.,
1986; Pradip and Kapur, 1990). It has the chemical
formula Ca
8
Mg[(SiO
4
)
4
Cl
2
]. Whereas the hydration characteristics of alinite are superior
to those of alite, belinite does not hydrate as easily as belite.
Another silicate phase containing chlorine that may also be present in alinite cements
in limited amounts is calcium chloride orthosilicate, Ca
3
SiO
4
Cl
2
(Agarwal
et al.,
1986;
Miskiewicz and Pyzalski, 1988).
A
linite may be synthesized from a starting mix containing CaCO
3
, SiO
2
, Al
2
O
3
, MgO,
and CaCl
2
by burning it at a temperature of 1000-1200 °C. At this temperature the rate of
alinite formation exceeds that of tricalcium silicate (at 1400-1500 °C) by about 7-8 times
(Bikbaou, 1986). At even higher temperatures alinite converts to alite, and this process is
accompanied by a release of chlorine (Agarwal
et al.,
1986).
Alinite exhibits a high hydraulic reactivity, which is distinctly greater than that of
tricalcium silicate. The following degrees of hydration have been reported for both
compounds (Boikova
et al.,
1986; Ji
et al.,
1997):
hydration time
Degree of hydration (%)
Tricalcium silicate (Boikova)
Alinite (Boikova)
Alinite (Ji)
15min
-
-
9
1h
10
22
-
6h
15
64
36
12h
20
70
-
1d
25
80
43
3d
40
85
53
28 d
-
-
62
The hydration of alinite takes place without any distinct induction period (Boikova
et al,
1986), and is associated with a single exothermic peak about 60-120 min after mixing
(Neubauer and Pöllmann, 1994). The rate of hydration is not affected by the SiO
4
/AlO
4
ratio in the crystalline lattice (Neubauer and Pöllmann, 1994). It has been observed,
however, that alinite without impurities in the crystalline lattice is more reactive than that
which constitutes alinite clinker, and contains distinct amounts of foreign ions (Boikova
et al.,
1986; Ji
et al.,
1997). The hydration of alinite is significantly accelerated by the
