Page 245 - Handbook of Thermal Analysis of Construction Materials

226 Chapter 6 - Retarding and Water Reducing Admixtures

appeared to act as a slight accelerator. Lorprayon and Rossington who
studied the hydration of C AF with lignosulfonate containing sugar found
4
that C AF hydration was retarded even at a dosage of 0.125% lignosul-
4
[7]
fonate. In the presence of a mixture of sugar-free LS (2.5%) + Na CO
2 3
(2.5%), C AF hydration was inhibited up to about 1 day. [6]
4
2.4 Tricalcium Silicate-Lignosulfonate-Water

Conduction calorimetric curves of C S hydrated in the presence of
3
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
[8]
C S is completely inhibited. Other studies have shown that addition of
3
small amounts of different types of CLS (0.5%) to C S pastes retard setting
3
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 S does not seem
3
to be a simple function of the percentageof 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 S treated with 0,
3
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 S is treated with 1% CLS solution at a water/solid ratio 0.5, the
3
percentage of CLS based on C S would be 0.5, the same as sample C. The
3
resulting curve, however, would be similar to D. These results suggest that
C S is stabilized in contact with a CLS solution of concentration above
3
0.25%.
The TG and DTA techniques have been used to study the effect of
0.5% CLS on C S hydration. Free lime and combined water contents were
3
determined at different times of hydration. The initial rate of hydration of
C S was retarded. At a dosage of 0.8%, the hydration is inhibited up to thirty
3
days. [11][12]
DTA was used by Ramachandran to explain the adsorption-desorp-
tion of calcium lignosulfonate in the C S-H O system. [11][13] The adsorption
3
2
and desorption curves for C S containing CLS are given in Fig. 5. Ligno-
3
sulfonate does not adsorb on the anhydrous C S in a nonaqueous system. A
3