gates, such as the two slags, having high 24-hr
for the aggregate in the lower left quadrant of
absorptions (Table 4) would have a high potential
Figure 3, which have low calculated equivalent
for reducing the freezethaw durability of con-
durability factors and low percent passings. Thus,
crete. The slags' surfaces, honeycombed with
the cryogenic test was best at identifying frost-
visible pores and cavities, can readily fill with
susceptible aggregate. However, as discussed next,
water when in direct contact with bulk water,
pore size measurements offer the possibility that
reducing performance in the cryogenic test. How-
the questionable aggregates, those in the lower left
ever, in concrete the large pores in the slag may
quadrant of Figure 3, can be properly identified
act like bubbles of entrained air that can remain
without having to resort to the tedious conven-
empty for long periods, even when surrounded by
tional testing.
water-saturated paste. Indeed, aggregates with
Typically, aggregates that have large pore vol-
large pores can contribute to the overall frost resis-
umes and high amounts of fine pores are likely to
tance of concrete by providing functional relief
be susceptible to frost damage. According to Table
space into which water can escape during the for-
6, sample 3791, the only one of the three samples
mation of ice in the surrounding cement paste. As
tested for pore size and located in the "question-
previously discussed, the slag was not vacuum-
able" lower left quadrant in Figure 3, contained
saturated.
over 95% of its measurable pore volume in pores of
This would suggest that the slag was not satu-
rated and may perform very well in concrete until
be a natural pore size deliminator in Fig. 2). Con-
it becomes critically saturated, which may take a
versely, aggregates with high amounts of coarse
considerable amount of time, but that after becom-
pores are usually durable. The aggregates in the
ing critically saturated deterioration would be
"durable" upper left quadrant of Figure 3 that
swift. Further study is needed to confirm this
were tested for pore size (4205, 3666, 3632, 3704)
hypothesis.
contained significantly more intrusion volume in
pores of diameters greater than 5 m than was in
Once the two slags are dismissed, the two test
methods correlate closer, though they are not in
3791, as shown in Figure 4.
full agreement to one another in distinguishing
Figure 4, a plot of pore volume fractions vs.
durable from frost-susceptible aggregate. Figure 3
calculated equivalent durability factors, demon-
shows this. While there is significant data scatter,
strates the close relationship between these two
parameters when 5 m is used as the benchmark.
two facts emerge--no aggregate with a calculated
Expressly, as pore structure becomes finer (> 95%)
equivalent durability factor above 60 in the con-
durability decreases and as pore structure coars-
ventional test had more than 1.5% passing in the
ens (< 95%) durability increases. The reader will
cryogenic test and all aggregate with more than
recall that the two slag samples, 4130 and 4204,
1.5% passing had a calculated equivalent durabil-
were not amenable to the cryogenic test but were
ity factor below 60%. The two methods disagree
100
4130
3704
4204
4205
80
3632
3666
60
3595
40
4206
20
3791
3593
0
50
60
70
80
90
100
Volume in Pores < 5 m Diameter (%)
Figure 4. Calculated equivalent durability factor vs. volume percentage of
measurable pores less than the 5-m diameter.
8
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