1.64
1.62
1.60
1.58
1.56
1.54
1.52
1.50
0.2
0.0
0.6
0.8
0.4
0.2
0.4
1.0
1.2
Log, d
Limestone
Limestone & Rounded Gravel (0.875:0.125 v/v)
Limestone & Rounded Gravel (0.750:0.250 v/v)
Limestone & Rounded Gravel (0.625:0.375 v/v)
Limestone & Rounded Gravel (0.500:0.500 v/v)
Limestone & Rounded Gravel (0.333:0.667 v/v)
Limestone & Rounded Gravel (0.167:0.835 v/v)
Crushed Quartzite
Rounded Gravel
Figure 12. Relationship between mean aggregate diameter and porosity. (After Gupta 1985.)
for 24 hours. The amount of water displaced by
Table 8. Value of shape factor (C) for various mate-
these particles is the volume of the aggregates.
rials. (After Gupta 1985.)
Gupta (1985) divides this volume by the number
Materials
Value of C
of particles to get the mean volume size of the in-
dividual particles. The mean volume size is then
Angular limestone
45.43
Subangular crushed quartzite
41.44
converted to the volume mean diameter. The ex-
Rounded gravel
37.89
ponent (n) was found to be a constant equal to
Limestone + rounded gravel (0.875 : 0.125 v/v)
43.49
0.032 for all the materials and mixtures tested.
Limestone + rounded gravel (0. 75 : 0.25 v/v)
42.63
The coefficient C was found to be a function of
Limestone + rounded gravel (0.50 : 0.50 v/v)
41.98
the aggregate shape. It was also found to be a
Limestone + rounded gravel (0.333 : 0.667v/v)
40.58
Limestone + rounded gravel (0.167 : 0.733v/v)
39.40
function of the amount of rounded gravel in the
mixture. Values of C as reported by Gupta (1985)
are presented in Table 8. The coefficient C ranged
Particle index
between 39 and 45 and was found to decrease as
The particle index (Ia) is based on the concept
the material changes from an angular to a round-
that the shape, angularity, and surface texture of a
ed material. Also, C decreased as the amount of
uniformly (single) sized aggregate affects not
rounded gravel in a mix increased.
only the void ratio but also the rate at which the
Gupta (1985) also reported that the size of sim-
voids change when the aggregate is compacted in
ilarly shaped material had an effect on the per-
a standard mold (Huang 1962). Through experi-
centage of voids. For all of the materials tested, he
mentation with different types of molds and dif-
found that the percentage of voids decreased as
ferent types of aggregates, and with a specific
the size of aggregate increased. For example, he
procedure, Huang (1962) found a linear relation-
reported a 5% decrease in porosity when the
ship between the number of compactive strokes
mean size of rounded gravel increased from 5
(10 to 50) and the void ratio. There was no general
mm to 32 mm. Likewise, a 3% decrease in poros-
relationship found with fewer than 10 compac-
ity was reported for a similar change in aggregate
tive strokes. The resulting change in the void
size for angular limestone. Therefore, the size of
ratio became insignificant when more than 50
the particles has an effect on the AN value. When
compactive strokes were used (Huang 1962). The
using AN to characterize angularity it is impor-
hypothetical void ratio at zero strokes was line-
tant to ensure that the comparison is done on
arly extrapolated from the measured void ratio at
material of the same size.
the end of 50 strokes and the rate of void change
10
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