Civil Engineering Reference
In-Depth Information
Sample Problem 5.5
Coarse aggregates from two stockpiles having coarse aggregate angularity (crushed
faces) of 40% and 90% were blended at a ratio of 30:70 by weight, respectively. What
is the percent of crushed faces of the aggregate blend?
Solution
Crushed faces of the
blend
=
1
0.3
21
40
2
+
1
0.7
21
90
2
=
75
%
Equation 5.17a is used for properties that apply to the whole aggregate
materials in all stockpiles that are blended. However, some properties apply
to either coarse aggregate only or fine aggregate only. Therefore, the per-
centage of coarse or fine aggregate in each stockpile has to be considered.
The relationship in this case is expressed as
Á
1
x
1
P
1
p
1
+
x
2
P
2
p
2
+
+
x
n
P
n
p
n
2
X
=
(5.17b)
Á
1
P
1
p
1
+
P
2
p
2
+
+
P
n
p
n
2
where,
test value for the aggregate blend
test result for stockpile
i
percent of stockpile
i
in the blend
the percent of stockpile
i
that either passes or is retained on the
dividing sieve
X
=
the
x
i
=
the
P
i
=
the
p
i
=
Sample Problem 5.6
Aggregates from two stockpiles, A and B having coarse aggregate angularity (crushed
faces) of 40% and 90% were blended at a ratio of 30:70 by weight, respectively. The
percent material passing the 4.75 mm sieve was 25% and 55% for stockpiles A and B,
respectively. What is the percent of crushed faces of the aggregate blend?
Solution
Crushed faces of the
blend
=
Á
1
x
1
P
1
p
1
x
2
P
2
p
2
x
n
P
n
p
n
2
+
+
+
X
=
Á
1
P
1
p
1
+
P
2
p
2
+
+
P
n
p
n
2
1
40
*
30
*
1
100
-
25
2
+
90
*
70
*
1
100
-
55
22
=
=
69
%
1
30
1
100
25
2
70
1
100
55
22
*
-
+
*
-
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