Civil Engineering Reference
In-Depth Information
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
3
A or alkali content cement. In a cement containing 9.4% C
3
A,
the water reduction was found to be about 10%, and with 14.7% C
3
A, the
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.
