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OCR for page 48
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Micro Deval Value
25
y = 0.5392x + 7.8803
R2 = 0.7646
20
15
10
5
0
0 10 20 30 40 50 60 70
MgSO4 Soundness, %
Figure 15. Relationship between magnesium sulfate soundness and micro-deval
loss (2, 23).
type. A micro-deval abrasion loss of 25% was proposed for The sample is then sieved by hand over a smaller sieve
Oklahoma. appropriate for the size fraction. For 9.5-mm to 19.0-mm
aggregates, the sample is sieved over an 8-mm (5/16-in.) sieve.
The weighted average percent passing the smaller sieve sizes
2.7.2 Aggregate Tests Related to Weathering expressed as a percentage of the original sample weight is the
and Freeze-Thaw Durability
sulfate soundness loss. As discussed previously, there is a
There is some question as to whether aggregates used in reasonable correlation between magnesium sulfate sound-
HMA need to be resistant to freezing and thawing. Sound- ness and micro-deval loss. The relationship is fair to poor for
ness tests such as magnesium or sodium sulfate soundness sodium sulfate soundness (2, 118).
have commonly been used to assess degradation from freez- Currently, equipment is available to perform actual freeze-
ing and thawing as well as from wetting and drying. Sulfate thaw testing. AASHTO T103, "Soundness of Aggregates by
soundness tests were developed in the early 19th century to Freezing and Thawing," describes three procedures to con-
simulate the expansion of water within stone that resulted duct freeze-thaw testing. A sample is initially washed and
from freezing and thawing water (117). However, it has pre- dried to a constant mass, after which it is sieved into size frac-
viously been shown that the magnesium sulfate soundness tions. The three procedures for immersion and freezing are
test is correlated with micro-deval loss. This may indicate summarized in Table 11. The ethyl alcohol used in Procedure
that the magnesium soundness test better simulates the slak- B is to aid the penetration of water. After the final cycle of
ing caused by wetting and drying rather than freeze-thaw freezing and thawing, the samples are dried to a constant mass
deterioration. and are sieved. The resulting weighted average loss for each
To perform the sulfate soundness test (AASHTO T104), a size fraction is the soundness loss. Iowa, Ontario, and Michi-
graded sample of coarse aggregate is prepared based on the gan currently use test methods for freeze-thaw testing.
NMAS of the aggregate being tested. A graded fine aggregate Senior and Rogers (115) investigated the use of the uncon-
sample is prepared with at least 100 g of material retained on fined freeze-thaw test that is similar to AASHTO T103 for
each of the 4.75-mm, 2.36-mm, 1.18-mm, 0.600-mm, and coarse aggregates. Individual size fractions retained on the
0.300-mm sieves. The sample is soaked in a saturated solu- 13.2-mm, 9.5-mm, and 4.75-mm sieves are placed in separate
tion of sodium of magnesium sulfate for 16 to 18 h. The sam- 1-liter jars. The samples are soaked for 24 h in a 3% NaCl
ples are then briefly drained and dried in a 110°C oven to a solution. The samples are drained and sealed, frozen for 16 h,
constant mass. Upon rewetting, the sulfate crystals expand in and then thawed at room temperature for 8 h. The freezing-
the aggregate pores, simulating the expansion of water upon and-thawing cycle is repeated five times after which the sam-
freezing. The cycle of wetting and drying is typically repeated ples are dried and sieved similar to AASHTO T103. Testing
five times. After the final cycle, the sample is rinsed to remove by Senior and Rogers (115) suggests that the Ontario Uncon-
the sulfate solution and dried at 110°C to a constant mass. fined Freeze-Thaw test is "to be preferred because it shows
