Introduction to Concrete Admixtures - Thermal Analysis of Construction Materials - page 171

C 3 A. [76]-[78] Hydration of C 3 S is known to be retarded by the superplasti-
cizer. [79][80] There is also evidence that the C/S ratio of the C-S-H phase is
changed. In cements, the hydration of the C 3 S phase is retarded, but to a
lesser extent than when hydrated in the pure form because part of the
admixture is adsorbed by the C 3 A phase. Formation of ettringite may be
accelerated or retarded by the superplasticizer, depending on the amount of
alkali sulfates present in cement.
The amount of water reduction achievable with a particular super-
plasticizer depends on the dosage and initial slump. Some results are given
below (Table 10). [40] There is evidence that beyond a particular dosage,
further water reduction is not possible. In all types of cements, water
reduction occurs to different extents.

Table 10. Water Reductions in Concrete with an SNF Superplasticizer

Dosage w/c Ratio Water Reduction Slump

Reference 0.60 0 100

Normal 0.57 5 100

Double 0.52 15 100

Triple 0.48 20 100

Reference 0.55 0 50

Normal 0.48 13 55

Double 0.44 20 50

Triple 0.39 28 45

In flowing concrete in the presence of a superplasticizer, the 28 day
strength is equal or greater than the corresponding strength of the reference
concrete. The strength for flow and water-reduced concrete made with three
types of cement is generally commensurate with the values expected from
the w/c ratios. [81] Figure 12 gives the strengths developed by concrete
containing an SMF superplasticizer. [40][81] Strengths are always higher in
the presence of the superplasticizer at any particular w/c ratio. In addition,
strengths are higher at lower w/c ratios.