1. Senior/Graduate
HMA Course
Blending Aggregate Stockpiles
Aggregates Blending Stockpiles 1

2. Blending of Aggregates
• Reasons for Blending
– Obtain desirable gradation
– Single natural or quarried material not
enough
– Economical to combine natural and
process materials
Aggregates Blending Stockpiles 2

3. Blending of Aggregates
• Numerical Method
– Trial and Error
– Basic Formula
Aggregates Blending Stockpiles 3

4. Blending Stockpiles
• Plot individual gradations
• Plot specification limits
• Can be used for initial assessment
– Can blend be made from available
materials?
– Identification of critical sieves
– Est. trial proportions
Aggregates Blending Stockpiles 4

5. All possible combinations fall between A and B
Control points for
Percent Passing, % 12. 5 nominal max. size
100
90
Gradation B
80
70
60
50
40
30
20 Gradation A
10
0
0.075 0.3 1 .18 4.75 9.5 12.5 19
Sieve Size, mm
Aggregates Blending Stockpiles 5

6. No poss. combination of A and B will meet spec.
Percent Passing, %
100
90 Gradation B
Gradation A
80
70
60
50
40 Control points for
30 12. 5 nominal max. size
20
10
0
0.075 0.3 1 .18 4.75 9.5 12.5 19
Sieve Size, mm
Aggregates Blending Stockpiles 6

7. All poss. combinations pass through cross-over point
Blends containing more A than B will be closer to A
Percent Passing, %
100
90
80 Gradation A
70
60
Gradation B
50
40
30
20 Control points for
12. 5 nominal max. size
10
0
0.075 0.3 1 .18 4.75 9.5 12.5 19
Sieve Size, mm
Aggregates Blending Stockpiles 7

8. Trial and Error Steps
• Select critical sieves in blend
• Determine initial proportions which will meet
critical sieves
• Check calc. blend against specification
• Adjust if necessary and repeat above steps
Aggregates Blending Stockpiles 8

9. Blending of Aggregates
· P = Aa + Bb + Cc + ….
– Where:
• P = % of material passing a given sieve for the
blended aggregates A, B, C, …
• A, B, C, … = % material passing a given sieve
for each aggregate A, B, C, …..
• a, b, c, …. = Proportions (decimal fractions)
of aggregates A, B, C, … to be used in
Blend
Aggregates Blending Stockpiles 9

10. Blending of Aggregates
Material Agg. #1 Agg. #2
% Used Blend Target
% % % %
U.S. Sieve
Passing Batch Passing Batch
3/8 “ 100 100
No. 4 90 100
No. 8 30 100
No. 16 7 88
No. 30 3 47
No. 50 1 32
No. 100 0 24
No. 200 0 10
Aggregates Blending Stockpiles 10

11. Blending of Aggregates
Material Agg. #1 Agg. #2 First Try
(remember trial & error)
% Used 50 % 50 % Blend Target
% % % %
U.S. Sieve
Passing Batch Passing Batch
3/8 “ 100 50 100 100 * 0.5 = 50 100
No. 4 90 45 100 90 * 0.5 = 45 80 - 100
No. 8 30 15 100 30 * 0.5 = 15 65 - 100
No. 16 7 3.5 88 7 * 0.5 = 3.5 40 - 80
No. 30 3 1.5 47 3 * 0.5 = 1.5 20 - 65
No. 50 1 0.5 32 1 * 0.5 = 0.5 7 - 40
No. 100 0 0 24 0 * 0.5 = 50 3 - 20
No. 200 0 0 10 0 * 0.5 = 0 2 - 10
Aggregates Blending Stockpiles 11

12. Blending of Aggregates
Material Agg. #1 Agg. #2
% Used 50 % 50 % Blend Target
% % % %
U.S. Sieve
Passing Batch Passing Batch
3/8 “ 100 50 100 50 100 100
No. 4 90 45 100 50 95 80 - 100
No. 8 30 15 100 50 65 65 - 100
No. 16 7 3.5 88 44 47.5 40 - 80
No. 30 3 1.5 47 23.5 25 20 - 65
No. 50 1 0.5 32 16 16.5 7 - 40
No. 100 0 0 24 12 12 3 - 20
No. 200 0 0 10 5 5 2 - 10
Aggregates Blending Stockpiles 12

13. Blending of Aggregates
Material Agg. #1 Agg. #2
% Used 50 % 50 % Blend Target
% % % %
U.S. Sieve
Passing Batch Passing Batch
3/8 “ 100 50 100Let’s Try50 100 100
No. 4 90 45 100 and get 50 95 80 - 100
No. 8 30 15 100little closer
a 50 65 65 - 100
No. 16 7 3.5 to the middle of
88 44 47.5 40 - 80
the target values.
No. 30 3 1.5 47 23.5 25 20 - 65
No. 50 1 0.5 32 16 16.5 7 - 40
No. 100 0 0 24 12 12 3 - 20
No. 200 0 0 10 5 5 2 - 10
Aggregates Blending Stockpiles 13

14. Blending of Aggregates
Material Agg. #1 Agg. #2
% Used 30 % 70 % Blend Target
% % % %
U.S. Sieve
Passing Batch Passing Batch
3/8 “ 100 30 100 70 100 100
No. 4 90 27 100 70 97 80 - 100
No. 8 30 9 100 70 79 65 - 100
No. 16 7 2.1 88 61.6 63.7 40 - 80
No. 30 3 0.9 47 32.9 33.8 20 - 65
No. 50 1 0.3 32 22.4 22.7 7 - 40
No. 100 0 0 24 16.8 16.8 3 - 20
No. 200 0 0 10 7 7 2 - 10
Aggregates Blending Stockpiles 14

15. Blended Aggregate Specific Gravities
• Once the percentages of the stockpiles have
been established, the combined aggregate
specific gravities can also be calculated
Aggregates Blending Stockpiles 15

16. Combined Specific Gravities
1
G=
P1 + P2 + ……. Pn
100 G1 100 G2 100 Gn
Aggregates Blending Stockpiles 16

17. QUESTIONS?
Aggregates Blending Stockpiles 17