Page 255 - Handbook of Thermal Analysis of Construction Materials

236 Chapter 6 - Retarding and Water Reducing Admixtures

Figure 10. DTG curves for anhydrous and hydrated C S with or without 0.3% sugar-free
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sodium lignosulfonate.

Chatterji’s work [23] on C A hydration shows that sugar-free ligno-
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sulfonate is an inferior retarder in comparison with commercial lignosul-
fonate. Disagreement amongst researchers is due to the differences of
methods adopted for separation of sugars, variability of materials, and
molecular weights and methods adopted for following the hydration. Based
on XRD results, Pauri, et al., [24] found that sugar-free lignosulfonate retards
the hydration of C A. The retarding effect was less significant on C A-
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Na O solid solution than that on pure C A.
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Studies have indicated that calcium lignosulfonate is an active
admixture in concrete, interacting with the hydrating cement minerals. [14]
[8]
Ramachandran examined the effect of sugar-free Na lignosulfonate
prepared by continuous diffusion (using a Dowex 50WX2 resin bed) on the
hydration of portland cement. The effect of 0.1–0.3% sugar-free lignosul-
fonate on DTA thermograms of C A hydrated from 1 day to 60 days are
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shown in Fig. 11. The peak at about 100°C is due to the expulsion of
adsorbed water. The endothermal effects at about 200° and 250–280°C are
ascribed to the dehydration of hexagonal phases C AH -C AH . The
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