Ceramics-Silikáty 38, (1) 9 - 15 (1994)

The effect of soda and sodium sulphonated polyphenolate (SSP) on the setting of cement based on Portland clinker was investigated by means of the time dependence of consistency established by the penetrometric method. The results were used to determine the length of incubation periods for the hydration of C₃A and C₃S). The incubation period of C₃A hydration (t₁) exhibits a non-zero value only for the reaction of C₃A with the solution of SSP and soda. At a suitable addition of SSP, its value increases with increasing soda addition. On the other hand, the incubation period of C₃S hydration (t₂) decreases with increasing soda additions. The soda addition, at which for a given amount of SSP t₁ = t₂, then represents the longest attainable time of initial set of the cement. The optimum addition of SSP is very probably that capable of ensuring steric stabilization of the suspension by creating a protective adsorption layer. The time of early set is distinctly reduced by increasing the time and intensity of mixing. The impossibility of maintaining an identical mechanical history of the binding agent during its preparation and forming is probably the main cause of the poor reproducibility of its behaviour observed earlier.