Dicalcium Silicate-Lignosulfonate-Water System

Not much work has been reported on the influence of lignosulfonate on the hydration of dicalcium silicate. The rate of hydration of dicalcium silicate is slow, and it is further retarded by the addition of lignosulfonate. Evidence of this is the lower amounts of lime formed in the hydrated product in the presence of 0.3% lignosulfonate. It has been reported that sugar-free Na-lignosulfonate (0.3%) retards the hydration of C2S, but to a lower extent than the commercial lignosulfonate. 

6 Tricalcium Silicate-Tricalcium Aluminate-Lignosulfonate-Water System 

The effect of the addition of CLS on the hydration of C3S in the system C3S-C3A-H2O ean be demonstrated with referenee to Fig. 

Thermal investigations have shown that the rate of hydration of C3A and the inter-conversion of ettringite to the low monosulfoaluminate in the C3A-CaS04 2H20-CLS-H20 system, and hydration of individual cement phases C4AF, C3S, and C2S are all retarded by lignosulfonates. Thus, it is expected that the rate of hydration of cement should also be retarded by the addition of lignosulfonates. 

An addition of 0.1% CLS may extend the initial and final setting times of cement mortar by two and three hours, respectively. The influence of 0.3% CLS on the hydration of cement is shown in Fig. 9. Thermograms indicate that the reference cement containing no admixture exhibits a broad endothermal peak below 200°C, representing the formation of both ettringite and C-S-H phase. These peaks increase in intensity as the hydration period is increased. The effect between 450 and 500°C is caused by the dehydration of Ca(OH)2 and its intensity indicates the extent to which the hydration of the C3S component has progressed. The cement hydration, in the presence of lignosulfonate, is retarded as seen by the lower intensity of the Ca(OH)2 decomposition peak. The low temperature effect below 300°C in the presence of CLS is not sharp as that obtained in the reference sample. 

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