099
100199
200299
300399
400499
500599
600699
700799
800899
900999
10001099 11001199
12001299 13001399 14001499
15001599
Figure 4. Degree of angularity.
Particle index
voids in the aggregate mass decreased as the
Another index for characterizing the coarse
aggregates became more rounded. He also found
and fine aggregates in an HMA mixture is the par-
that as the amount of round gravel increased in a
ticle index (Ia). The particle index is based on the
mixture of natural and crushed aggregates, the
concept that the shape, angularity, and surface
percentage of voids also decreased. Using round
texture of uniformly (single) sized aggregate
gravel as a reference point, he characterized the
affects not only the void ratio but also the rate at
angularity of all other aggregates as the differ-
which the voids change when compacted in a
ence between the percent voids and 33%. AN is
standard mold (Huang 1962). The particle index
found to range between 0 and 12:
(Ia) is calculated using eq 2:
AN = percent voids 33.
(1)
16
Crushed Aggregate
14
12
10
Natural Rounded Aggregate
8
6
4
2
No. 4 6
69
9 13
13 19
19 25
Gradation of Samples
Figure 5. Comparison of particle index values for rounded and crushed coarse
aggregates.
4
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