superplasticizer admixture is used in CONCRETE formulations to reduce water requirement and to make the concrete stronger. It retards the setting of concrete and is also useful for transporting ready-mixed concrete.
The correct formulation of the admixture is important to ensure that concrete can be placed quickly and without slump loss. This is especially important in projects where ready-mixed delivery trucks need to be transported long distances and whose final concrete must be placed soon after the admixture is added.
Both NSF and PCE show a similar tendency to adsorb onto the surface of cement particles. However, their decreasing pattern of dynamic yield stress and thixotropic index differs for these two admixtures (Figure 20.5).
VMA effects on the plastic viscosity and yield stress of cement mortars: welan gum compared with diutan gum
Welan gum increases the plastic viscosity and yield stress more than diutan gum by about 2 to 5 times, depending on the concentration (Khayat and Mikanovic 2012; Figure 20.4(b)). The increase is mainly caused by bridging flocculation.
Welan gum adsorption may also be competing with the adsorption of the PCE superplasticizer to adsorb onto cement particles, as shown in Figure 20.5(b). However, this competition would not result in an increase in the yield stress due to depletion flocculation, because the PCE polymer has a much higher affinity for cement surface than welan gum.
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