ing through the many possible ranges, 0.01 to 5 m
is too great to provide usable information in either
the cryogenic or the conventional tests. More test-
(Fig. 5a) seemed to produce a good correlation with
ing of statistically larger sample sizes is needed to
the durability factor, suggesting that this mid-range
of pore sizes is important to conventional freeze
develop this possible relationship between early
thaw tests. That is, pores smaller than 0.01 and
age absorption and durability.
larger than 5 m are little affected by the low
temperatures imposed upon them. Except for 3666,
CONCLUSION
aggregates with more than 75% of their measurable
pore volume in this range are frost-susceptible.
We assessed cryogenic frost cycling as a meth-
A pore range that relates pore diameters to
od for testing the freezethaw resistance of aggre-
durability factors about as well as the one shown in
Figure 5a is that for pore sizes less than 1 m. Figure
The cryogenic freezethaw test was able to differ-
5b shows that, except for 4205 being borderline,
entiate among a series of 20 aggregates on the basis
aggregates with more than 88% of their pore vol-
of frost damage. There was not a one-to-one corre-
ume in this range are frost-susceptible. (Table 6
lation in durability rankings between this test and
shows that aggregate 4205 has a very low total
the conventional test. However, all aggregates
intrusion volume, which would tend to limit the
identified as frost-susceptible by the cryogenic test
effect.)
were deemed frost-susceptible by the convention-
The same pore ranges were compared to the
al test.
cryogenic test results. Figure 6 plots percentage
Pore size distribution measurements reveal a
passing against percentage of total intrusion be-
pore range critical to freezethaw durability. Ag-
tween 0.01 and 5 m, and less than 5 m. Though
gregates containing more than 75% of their total
pore volume between 0.01 and 5 m were nearly
percentage passing tends to increase with percent-
age of total intrusion, the correlation to durability
always frost-susceptible. A somewhat better re-
factor is not as good as it was with the conventional
sult was found for aggregates containing less than
test results. Even less correlation existed in the less
5% of their total pore volume in pores of greater
than 1-m range, so this plot is not shown.
than 5 m in diameter.
Additional deterioration because of ice forming
On the basis of the limited testing done in this
in small pores at the extremely low temperature
study, the cryogenic freezethaw test appears to
used in the cryogenic test may explain the poor
have potential as a very rapid test for identifying
correlation between pore size and measured frost
aggregate that should not be considered for high-
damage. However, the pore size analysis could not
way use. For those aggregates that pass the cryo-
accurately measure pore volumes below the small-
genic test, it appears that some sort of pore-distri-
est pore freezable (0.0035 m) in the conventional
bution measurement, such as high-pressure mer-
test to confirm this supposition. Possible ice accre-
cury porosimetry, should be used to single out
tion is another explanation. The cryogenic test caus-
freezethaw durable aggregate acceptable for high-
es pore water to freeze in minutes, whereas in the
way pavement. The standard ASTM C666 test
may only be resorted to if time allows.
conventional test, freezing takes place over a peri-
These conclusions are considered valid for the
od of an hour or more. The slower the freezing rate,
aggregates tested. More research is needed to de-
the more chance water has to migrate from smaller
termine the suitability of this test combination for
pores into larger pores, and the greater the possible
general use.
deterioration. Without detailed measurements, this
also is difficult to substantiate.
Absorption values have been suggested in the
NEEDED RESEARCH
past as being a possible indicator of relative freeze
thaw resistance of aggregates. Normally, aggre-
The performance of aggregates exposed to freez-
gates with the lowest absorptions are believed to
ing and thawing depends heavily on pore size
make the most durable concrete. Figure 7, which
distribution and porosity. Though others have
compares 24-hour absorption values to CRREL per-
studied these issues, a better understanding of this
cent passing values, shows an unmistakable trend
interrelationship is needed to give us confidence
of decreasing durability with increasing absorp-
in developing improved freezethaw test meth-
tion. A similar trend existed when absorptions
ods. The following are proposed research areas.
were plotted against durability factors. However,
1. Examine rapid freezethaw testing of uncon-
data scatter in the mid-range of absorption values
fined aggregates using other temperature ranges.
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