Chemical admixtures - Concrete Mix Design, Quality Control and Specification - page 77

4. Reduced penetrability

5. Improved pumpability for short pump distance (but high air content
decreases pumpability)

6. Better surface finish

The amount of entrained air required for these purposes is somewhat
less than may be required for high frost resistance, 3% to 4% being normal
in Australia. The disadvantage of air entrainment is that it is an additional
factor to control and test, since excessive air can severely reduce strength
and pumpability. Entrained air is generally considered undesirable in mixes
of high cement (or other fines) content where frost resistance is not required.
However, the authors have used entrained air to provide lubrication in
mixes where fines were excessive and strength relatively unimportant.
Relationship between the durability factor and hardened air content of
mixes with Vinsol resin admixture (Set 1) or synthetic admixture (Set 2)
is shown in Figure 4.1. This demonstrates that examination of the air
void properties is a good idea for new products, which in fact may only be
appropriate as a car washing detergent.
Many investigations show that entrained air is still necessary for resis-
tance to freezing and thawing, even in very high-strength concrete. The
authors are dubious about this, considering that it may only apply to fully
saturated specimens used in laboratory investigations with the extreme
freeze-thaw cycling rather than to real structures. There are plenty of
examples of structures that have performed well in freeze-thaw environ-
ments without air entrainment. However, the omission of entrained air in
concrete subject to freezing and thawing represents a risk.

100

80

60

40

Set 1 (VR AEA)
Set 2 (SYN AEA)

20

0 0

1 2

Air ASTM C 457 (%)

3 4 5 6

Figure 4.1 Relationship between the durability factor and hardened air content of mixes
with Vinsol resin admixture (Set 1) or synthetic admixture (Set 2). (From U.S.
Federal Highway Administration, 2006.)