100,000
Granite Gneiss (γd=141 pcf, w=6.2%)
Gravel (γ d=126 pcf, w=3%)
Shale (γ d=130 pcf, w=4%)
10,000
5000
100
10
4
Sum of Principal Stresses (psi)
Figure 3. Influence of material type and stress state on resilient modulus. (After Barksdale
and Itani 1994.)
ently sized aggregates: passing the 3/4-in. and retained
study was conducted to determine the moisture density
on the 1/2-in. sieve; passing the 1/2-in. and retained on
relationship of the test material. Finally, PI tests were
the 3/8-in. sieve; passing the 3/8-in. and retained on the
conducted to determine the index of the various aggre-
gate materials.
No. 4 sieve. For each size, the test involved tamping
the uniform-sized aggregate into a mold in three equal
layers using a standard tamping rod with 10 strokes per
TEST MATERIAL
layer. The tamping rod was raised to a height of 50 mm
Gravel samples were obtained from W.E. Dailey's
from the top of the aggregate surface. At the end of the
crusher plant in South Shaftsbury, Vermont, for this
third layer, material was added to ensure that the aggre-
research effort. The material consisted predominantly
gate surface was flush with the mold's rim. The test
of quartz and quartzite with lesser amounts of carbon-
was repeated using 50 strokes and the percentage of
ate rock types (limestone and dolomite). There was little
void in the aggregate was calculated using the follow-
to no micaceous rock in this gravel and, overall, the
ing equation:
material was hard and durable and contained no delete-
W
rious substances.
(3)
Vn = 1 - n 100
The gravel was initially separated into each of the
s * v
size fractions shown in Table 1 using a Gilson testing
screen. All fractions were subsequently washed, oven-
where Vn = % of voids at n strokes per layer
dried, and allowed to cool. Aggregate particles larger
Wn = net weight of aggregate in the mold at n
than the No. 4 sieve were individually sorted into frac-
strokes per layer (g)
tured (crushed) and naturally rounded groups.
s = bulk specific gravity of the aggregate
Fractured aggregate was defined as particles hav-
v = volume of mold (cc).
ing two or more freshly fractured faces; however, some
Additional test details can be found in Huang (1965) or
particles with a single fracture were used to obtain the
Janoo (1998).
weights necessary for testing. Every attempt was made
In Phase II, several studies were conducted on base
to use only aggregate pieces having sharp, well-defined
course materials containing 0, 25, 50, 75, and 100%
edges in the "fractured" group. However, particles that
crushed aggregates. Resilient modulus and shear strength
may have been broken or fractured during trucking or
tests were conducted on 300-mm-diameter and 762-mm-
handling, or through natural means resulting in
height samples. Prior to conducting these tests, another
subangular shapes, were grouped with the fractured
3
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