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Aggregate Properties

Aggregate Properties. Gradation. Types of Gradations. * Uniformly graded. - Few points of contact. - Poor interlock (shape dependent). - High permeability. * Well graded. - Good interlock. - Low permeability. * Gap graded. - Only limited sizes. - Good interlock.

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Aggregate Properties

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  1. Aggregate Properties Gradation NCAT

  2. Types of Gradations * Uniformly graded - Few points of contact - Poor interlock (shape dependent) - High permeability * Well graded - Good interlock - Low permeability * Gap graded - Only limited sizes - Good interlock - Low permeability NCAT

  3. Aggregate Gradation • Use 0.45 Power Gradation Chart • Blend Size Definitions • maximum size • nominal maximum size • Gradation Limits • control points • restricted zone NCAT

  4. 0.45 Power Grading Chart Percent Passing 100 80 Example: 4.75 mm sieve plots at (4.75)0.45 = 2.02 60 40 20 0 0 1 2 3 4 Sieve Size (mm) Raised to 0.45 Power NCAT

  5. 0.45 Power Grading Chart Percent Passing 100 80 max size 60 40 20 maximum density line 0 0 .075 .3 .6 1.18 2.36 4.75 9.5 12.5 19.0 Sieve Size (mm) Raised to 0.45 Power NCAT

  6. 100 100 90 72 65 48 36 22 15 9 4 100 99 89 72 65 48 36 22 15 9 4 Aggregate Size Definitions • Nominal Maximum Aggregate Size • one size larger than the first sieve to retain more than 10% • Maximum Aggregate Size • one size larger than nominal maximum size NCAT

  7. Percent Passing 100 max density line restricted zone control point nom max size max size 0 .075 .3 2.36 4.75 9.5 12.5 19.0 Sieve Size (mm) Raised to 0.45 Power NCAT

  8. Superpave Aggregate Gradation Percent Passing 100 Design Aggregate Structure 0 .075 .3 2.36 12.5 19.0 Sieve Size (mm) Raised to 0.45 Power NCAT

  9. Superpave Mix Size Designations Superpave Nom Max SizeMax Size Designation (mm) (mm) 37.5 mm 37.5 50 25 mm 25 37.5 19 mm 19 25 12.5 mm 12.5 19 9.5 mm 9.5 12.5 NCAT

  10. - Larger max size Gradations * Considerations: - Max. size < 1/2 AC lift thickness + Increases strength + Improves skid resistance + Increases volume and surface area of agg which decreases required AC content + Improves rut resistance + Increases problem with segregation of particles - Smaller max size + Reduces segregation + Reduces road noise + Decreases tire wear NCAT

  11. Target Gradation • Acceptable gradation band specified • Mix design selects a job mix formula (JMF) which falls within band and meets design criteria • Superpave • 5 nominal sizes (37.5, 25, 19, 12.5, and 9.5 mm) • Four sieve sizes used to set upper and lower limits • Staying out of the restricted zone in suggestedto minimize problems with natural sands NCAT

  12. Blending Stockpiles • Basic formula for combining stockpiles to achieve a target gradation is: p = Aa + Bb + Cc + …. where: p = percent of material passing given sieve size A, B, C, .. = percent passing given sieve for each agg. a, b, c, … = decimal fraction of A, B, C, … to be used NCAT

  13. 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 NCAT

  14. All possible combinations fall between A and B Percent Passing, % Gradation B Control points for 12. 5 nominal max. size Gradation A 0.075 0.3 1 .18 4.75 9.5 12.5 19 Sieve Size, mm NCAT

  15. No poss. combination of A and B will meet spec. Percent Passing, % Gradation B Gradation A Control points for 12. 5 nominal max. size 0.075 0.3 1 .18 4.75 9.5 12.5 19 Sieve Size, mm NCAT

  16. All poss. combinations pass through cross-over point Blends containing more A than B will be closer to A Percent Passing, % Gradation A Gradation B Control points for 12. 5 nominal max. size 0.075 0.3 1 .18 4.75 9.5 12.5 19 Sieve Size, mm NCAT

  17. 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 NCAT

  18. Blended Aggregate Specific Gravities • Once the percentages of the stockpiles have been established, the combined aggregate specific gravities can also be calculated NCAT

  19. 1 G = P1 + P2 + ……. Pn 100 G1 100 G2 100 Gn Combined Specific Gravities NCAT

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

  21. Blending of Aggregates • Numerical Method • Trial and Error • Basic Formula NCAT

  22. 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 NCAT

  23. Blending of Aggregates Agg. #1 Agg. #2 Material Blend Target % Used % Passing % Passing % Batch % Batch U.S. Sieve 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 NCAT

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

  25. Blending of Aggregates Agg. #1 Agg. #2 Material Blend Target 50 % 50 % % Used % Passing % Passing % Batch % Batch U.S. Sieve 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 NCAT

  26. Blending of Aggregates Agg. #1 Agg. #2 Material Blend Target 50 % 50 % % Used % Passing % Passing % Batch % Batch U.S. Sieve Let’s Try and get a little closer to the middle of the target values. 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 NCAT

  27. Blending of Aggregates Agg. #1 Agg. #2 Material Blend Target 30 % 70 % % Used % Passing % Passing % Batch % Batch U.S. Sieve 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 NCAT

  28. Questions - ? NCAT

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