Table 2. Aggregate data by decreasing durability (blast furnace slags
listed separately at the end of the table).
Expansion
Calculated
per 300
equivalent
Sample
Sedimentary All FT cycles
durability
no.
Igneous
Metamorphic Carbonate Soft Chert others
(%)
factor
3704
55.2
32.6
0.0
0.0
0.0
12.2
0.000
100
3987
100.0
0.0
0.0
0.0
0.0
0.0
0.000
100
4205
0.0
0.0
100.0
0.0
0.0
0.0
0.015
88
3632
80.9
9.4
2.9
0.0
1.0
5.8
0.024
81
4014
0.0
0.0
100.0
0.0
0.0
0.0
0.030
77
3666
5.8
2.8
91.1
0.0
0.2
0.1
0.033
75
4015
0.0
0.0
100.0
0.0
0.0
0.0
0.048
66
4141
3.7
4.0
91.9
0.2
0.1
0.1
0.072
54
4033
3.0
0.1
96.2
0.2
0.3
0.2
0.081
50
3595
4.1
0.8
94.5
0.0
0.6
0.0
0.105
41
3990
27.8
22.2
45.0
0.8
4.0
0.2
0.138
32
3035
16.2
5.7
72.8
2.4
2.1
0.8
0.150
29
4206
18.9
24. 1
50.4
0.6
5.6
0.4
0.159
27
3992
21.7
19.4
51.9
2.0
3.8
1.2
0.174
24
3791
17.0
17.6
56.7
1.5
6.2
1.0
0.189
22
3989
21.6
20.5
49.7
1.5
6.2
0.5
0.309
10
3593
0.0
0.0
99.3
0.1
0.6
0.0
0.402
<10
3991
21.7
19.8
47.1
3.6
6.9
0.9
0.468
<10
Vesicular
Vesicular
dense
Dense
Glassy
4204
64.1
20.3
14.4
1.2
--
--
0.003
100
4130
72.4
17.0
9.2
1.4
--
--
0.006
96
of the field situation. Owing to the complexity of
ual pieces of aggregate act similarly in one impor-
accurately simulating field conditions and con-
tant regard: freezing occurs omnidirectionally. In-
straints on time, the MDOT laboratory test method
ward freezing inhibits the escape of water by
approaches this ideal situation by using small-
sealing outer pores of the aggregate with ice at the
scale concrete prisms made with a concrete mix
start of freezing. Consequently, volume increases
similar to that used in the field. It deviates from the
created by freezing of the remaining entrapped
ideal by using more rapid freeze rates than those
water must be elastically accommodated by the
encountered by pavements in nature so as to pro-
aggregate whether freezing is fast or slow.
duce timely results.
Aggregate samples were cryogenically tested
The simplest and fastest way to test aggregate is
using the following equipment: a water bath, a
to leave it unconfined, i.e., not embedded in con-
5/ in. [25, 19 and 16 mm]) and a scale. Aggregate
crete. This avoids the delays and variables inher-
8
ent with mixing and curing concrete specimens.
samples were prepared by thoroughly washing,
Though unconfined freezing does not duplicate
oven drying and separating the aggregate into a
size passing the 1-in. and retained on the 3/4-in.
confinement of aggregate by mortar, the results
are usually considered meaningful as relative
sieve. Smaller sized aggregate was also tested and
measures of aggregate quality.
yielded similar results, which are not reported
We chose to test aggregates separately by modi-
here.
fying AASHTO T-103 (AASHTO 1978), which de-
Testing consisted of soaking approximately
scribes a rapid procedure for freezethaw testing
500 g of the prepared aggregate in water for 24
of aggregates. Instead of conventional refrigera-
hours, followed by freezethaw cycling. Each cy-
tion equipment, we chose liquid nitrogen as the
cle consisted of 1.2 minutes of submersion in
196C liquid nitrogen, followed by a 0.5-minute
freezing medium and instead of room-tempera-
drain period, immersion in 90 to 100C water for 2
ture air, we used hot water for thawing. High
freezing rates can be more destructive to speci-
minutes and another 0.5-minute drain period. On
mens of concrete than are low rates. However, in
the basis of heat transfer calculations, the center of
this instance, the freezing rate was not considered
each piece of aggregate cycled from approximate-
ly 50 to 100C and back again during each 4.2-
a problem as low or high freezing rates on individ-
3
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