Page 187 - Handbook of Thermal Analysis of Construction Materials

170 Chapter 4 - Introduction to Concrete Admixtures

electrostatic repulsion, and steric repulsion. A more detailed interpretation
may be needed to explain various physical and chemical phenomena.
Figure 10 shows the effect of a SMF-based superplasticizer on a
cement paste. Large irregular agglomerates of cement particles predomi-
nate in a water suspension (Fig. 10a). The addition of a superplasticizer
causes dispersion into small particles (Fig. 10b). A viscometer is used to
measure the effect of a superplasticizer on rheology. Figure 11 plots the
viscosity changes in cement containing SNF exposed to different times. [75]
At any particular time, the viscosity is lower for the paste containing the
admixtures. It has been reported that 1% superplasticizer at a w/c ratio of
0.3 shows the same fluidity as cement paste at a w/c ratio of 0.4 without the
admixture.

(a)

(b)

Figure 10. Dispersion of cement paste: a) without superplasticizer; b) with a melamine-
based superplasticizer.