Civil Engineering Reference
In-Depth Information
Fig. 6-3. Scaled concrete surface resulting from lack of air
entrainment, use of deicers, and poor finishing and curing
practices. (52742)
cracks in concrete. Using a water reducer to reduce the
cement and water content of a concrete mixture—while
maintaining a constant water-cement ratio—can result in
equal or reduced compressive strength, and can increase
slump loss by a factor of two or more (
Whiting and
Dziedzic 1992
).
Water reducers decrease, increase, or have no effect on
bleeding, depending on the chemical composition of the
admixture. A reduction of bleeding can result in finishing
difficulties on flat surfaces when rapid drying conditions
are present. Water reducers can be modified to give vary-
ing degrees of retardation while others do not signifi-
5
125
Control
Water reducer L
Water reducer H
4
100
3
75
Fig. 6-2. Frost damage (crumbling) at joints of a pavement
(top), frost induced cracking near joints (bottom), and
enlarged view of cracks (inset). (61621, 67834, 67835)
2
50
1
25
reduced. For concretes of equal cement content, air content,
and slump, the 28-day strength of a water-reduced
concrete containing a water reducer can be 10% to 25%
greater than concrete without the admixture. Despite re-
duction in water content, water-reducing admixtures may
cause increases in drying shrinkage. Usually the effect of
the water reducer on drying shrinkage is small compared
to other more significant factors that cause shrinkage
0
0
0
20
40
60
80
100
120
140
Elapsed time, minutes
Fig. 6-4. Slump loss at 23°C (73°F) in concretes containing
conventional water reducers (ASTM C 494 and AASHTO
M 194 Type D) compared with a control mixture (
Whiting
and Dziedzic 1992
).
