AGGREGATES - Materials for Civil and Construction Engineers - page 199

5.24 Laboratory specific gravity and absorption tests are run on two
coarse aggregate sizes, which have to be blended. The results are as
follows:
Aggregate A: Buck specific
Aggregate B: Buck specific
a. What is the specific gravity of a mixture of 50% aggregate A and
50% aggregate B by weight?
b. What is the absorption of the mixture?
5.25 The mix design for an asphalt concrete mixture requires 2 to 6 per-
cent minus No. 200. The following three aggregates are available:
Minus No. 200
Coarse 0.5%
Intermediate 1.5%
Fine Aggregate 11.5%
Considering that approximately equal amounts of coarse and inter-
mediate aggregate will be used in the mix, what is the percentage of
fine aggregate that will give a resulting minus No. 200 in the mix-
ture in the middle of the range, about 4 percent?
5.26 Define the fineness modulus of aggregate. What is it used for?
5.27 Calculate the fineness modulus of aggregate B in problem 5.21.
(Note that the percent passing the 1.18-mm (No. 16) sieve is not
given and must be estimated.)
5.28 A portland cement concrete mix requires mixing sand having a grada-
tion following the midpoint of the ASTM gradation band (Table 5.4)
and gravel having a gradation following the midpoint of size number
467 of the ASTM gradation band (Table 5.5) at a ratio of 2:3 by
weight. On a 0.45 power gradation chart, plot the gradations of the
sand, gravel, and the blend. Is the gradation of the blend well graded?
If not, what would you call it?
5.29 Discuss the effect of the amount of material passing the 0.075-mm
(No. 200) sieve on the stability, drainage, and frost susceptibility of
aggregate base courses.
5.30 Aggregates from three sources having the properties shown in
Table P5.30 were blended at a ratio of 60:30:10 by weight. Determine
the properties of the aggregate blend.

gravity = 2.814; absorption = 0.4%

gravity = 2.441; absorption = 5.2%

Table P5.30

Property Aggregate 1 Aggregate 2 Sand

Coarse aggregate angularity,
percent crushed faces 100 87 N/A

Bulk specific gravity 2.631 2.711 2.614

Apparent specific gravity 2.732 2.765 2.712