Civil Engineering Reference
In-Depth Information
T ABLE 5.9
Example of Aggregate Blending Analysis by Iterative Method.
Sieve
12.5 mm 9.5 mm 4.75 mm 2.00 mm 0.425 mm
0.180 mm 0.075 mm
(1/2 in.)
(3/8 in.)
(No. 4)
(No. 10)
(No. 40)
(No. 80)
(No. 200)
Specification
100
95-100
70-85
55-70
20-40
10-20
4-8
Target gradation 100
98
77.5
62.5
30
15
6
% Agg. A (A)
100
100
98
90
71
42
19
% Agg. B (B)
100
94
70
49
14
2
1
30% A (a)
30
30
29.4
27
21.3
12.6
5.7
70% B (b)
70
65.8
49
34.3
9.8
1.4
0.7
Blend
1
P
i
2
100
96
78
61
31
14
6.4
gradation, usually the midpoint of the specification. A trial percentage of
each aggregate source is assumed and is multiplied by the percentage pass-
ing each sieve. These gradations are added to get the composite percentage
passing each sieve for the blend. The gradation of the blend is compared to
the specification range to determine if the blend is acceptable. With practice,
blends of four aggregates can readily be resolved. These calculations are eas-
ily performed by a spreadsheet computer program.
Properties of Blended Aggregates
When two or more aggregates from differ-
ent sources are blended, some of the properties of the blend can be calcu-
lated from the properties of the individual components. With the exception
of specific gravity and density, the properties of the blend are the simple
weighted averages of the properties of the components. This relationship
can be expressed as
Á
X
=
P
1
X
1
+
P
2
X
2
+
P
3
X
3
+
(5.17a)
where
X
=
property of the blend
of fractions 1, 2, 3
fractions by weight of aggregates 1, 2, 3 used in
the blend, where the total is 1.00
composite
X
1
, X
2
, X
3
=
properties
P
1
, P
2
, P
3
=
decimal
This equation applies to properties such as angularity, absorption, strength,
and modulus.
Search WWH ::
Custom Search