Specification - Concrete Mix Design, Quality Control and Specification - page 118

spacing factor of <0.2 mm, and a durability factor of 80% according to
ASTM C666 is often specified. Figure 6.1 shows the relationship between
air content and durability factor.
ASTM C666 involves 300 freeze-thaw cycles and therefore cannot be
used as a compliance test. Until the development of the Air Void Analyser™
(AVA), the only means of determining the spacing factor was the labor-
intensive ASTM C457, which involves microscopic examination of a
polished specimen of hardened concrete. Accordingly, unless the site has
an AVA, the quality control of freeze-thaw resistance has been based on
the air content. A recent study was conducted by the U.S. Federal Highway
Administration (FHWA) (2006) on the freeze thaw resistance of Vinsol-
resin-based air entraining agents compared to a synthetic product. It found
that “there are well-established thresholds for the air void parameters that
would be expected to give good concrete freeze-thaw resistance. The test
data presented in this study suggest these limits may not be applicable in all
cases to air entrained concrete containing synthetic admixtures”. The fact
that changing the chemistry of the air entraining agent had a significant
effect on performance but not on the air void parameters believed to be
responsible for the performance highlights one of the potential dangers of
performance specification. The relationships established with one material
may not be valid with another.
Another important point when considering freeze-thaw resistance is that
many concrete structures constructed before air entrainment have exhib-
ited good performance over 50 or more years. In Europe, most concrete

100

80

Good durability above 80

60

40

20

Poor durability below 20

0

0 1 2 3 4

Air Content, Percent

5 6 7 8

Figure 6.1 Freeze-thaw durability factor for different levels of total air contents.
(From Cordon, W.A., and Merrill, D., Requirements for Freezing and
Thawing Durability for Concrete, Proceedings of ASTM 63, 1026-1036, 1963.
With permission.)