Page 184 - Handbook of Thermal Analysis of Construction Materials

Section 3.0 - Water Reducers and Retarders 167

3.3 Water Reducers

The effectiveness of water reducers in reducing water require-
ments for a given consistency depends on the type and amount of water
reducer, type of cement, cement content, type of aggregate, aggregate/
cement ratio, presence of other admixtures, and the time of addition of the
admixture.
A partial explanation of the water reduction by lignosulfonate
admixture is its ability to entrain air. It is reported that lignosulfonate
promotes higher water reduction than hydroxycarboxylic acid-based ad-
mixtures.
There is evidence that water-reducing admixtures are less effective
with a high C A or alkali content cement. In a cement containing 9.4% C A,
3
3
the water reduction was found to be about 10%, and with 14.7% C A, the
3
reduction was 4%. [74]

Table 8. Effect of Water-Reducing Admixtures on Water Reduction

Water Reducer Nil Na Gluconate Glucose Sugar-free
Lignosulfonate

Slump (mm) 95 100 95 100

Water/Cement 0.68 0.61 0.63 0.65
Water Reduction (%) — 10.3 7.3 4.4

The relative water-reducing effects of three water reducers added
at 0.1% dosage are shown in Table 8. [40] Sodium gluconate appears to be
more effective than glucose or lignosulfonate.
Water-reducing and retarding admixtures are required to extend
the setting time from 1 to 3.25 hours with respect to the reference concrete.
Water-reducing and accelerating admixtures accelerate the setting time
between 1 and 3.5 hours.