Civil Engineering Reference
In-Depth Information
appeared to act as a slight accelerator. Lorprayon and Rossington who
studied the hydration of C
4
AF with lignosulfonate containing sugar found
that C
4
AF hydration was retarded even at a dosage of 0.125% lignosul-
fonate.
[7]
In the presence of a mixture of sugar-free LS (2.5%) + Na
2
CO
3
(2.5%), C
4
AF hydration was inhibited up to about 1 day.
[6]
2.4
Tricalcium Silicate-Lignosulfonate-Water
Conduction calorimetric curves of C
3
S hydrated in the presence of
0.3% calcium lignosulfonate show that the induction period is extended
from seven hours to about twenty hours. At 0.5% addition, the hydration of
C
3
S is completely inhibited.
[8]
Other studies have shown that addition of
small amounts of different types of CLS
(0.5%) to C
3
S pastes retard setting
indefinitely, although some of them contained calcium chloride. XRD
showed absence of calcium hydroxide in these pastes.
[9][10]
The inhibitive action of CLS on the hydration of C
3
S does not seem
to be a simple function of the percentage
of admixture added. The concen-
tration in the aqueous phase has to be taken into account. In Fig. 4,
[11]
calorimetric curves A, B, C, and D represent those of C
3
S treated with 0,
0.125, 0.25, and 1% solution of CLS at a water/solid ratio of 2. The samples
B and C show reduced peaks occurring at longer periods indicating
retardation. The sample D, containing 1% CLS, completely inhibits hydra-
tion. If C
3
S is treated with 1% CLS solution at a water/solid ratio 0.5, the
percentage of CLS based on C
3
S would be 0.5, the same as sample C. The
resulting curve, however, would be similar to D. These results suggest that
C
3
S is stabilized in contact with a CLS solution of concentration above
0.25%.
The TG and DTA techniques have been used to study the effect of
0.5% CLS on C
3
S hydration. Free lime and combined water contents were
determined at different times of hydration. The initial rate of hydration of
C
3
S was retarded. At a dosage of 0.8%, the hydration is inhibited up to thirty
days.
[11][12]
DTA was used by Ramachandran to explain the adsorption-desorp-
tion of calcium lignosulfonate in the C
3
S-H
2
O system.
[11][13]
The adsorption
and desorption curves for C
3
S containing CLS are given in Fig. 5. Ligno-
sulfonate does not adsorb on the anhydrous C
3
S in a nonaqueous system. A
