aggregatepropertiespavement05jb1lect2grad.ppt
- 2. NCAT 2 * 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 Types of Gradations
- 3. NCAT 3 Aggregate Gradation • Use 0.45 Power Gradation Chart • Blend Size Definitions – maximum size – nominal maximum size • Gradation Limits – control points – restricted zone
- 4. NCAT 4 Example: Example: 4.75 mm sieve plots at (4.75) 4.75 mm sieve plots at (4.75)0.45 0.45 = 2.02 = 2.02 Sieve Size (mm) Raised to 0.45 Power Sieve Size (mm) Raised to 0.45 Power 0 0 20 20 40 40 60 60 80 80 100 100 0 0 1 1 2 2 3 3 4 4 Percent Passing Percent Passing 0.45 Power Grading Chart 0.45 Power Grading Chart
- 5. NCAT 5 0.45 Power Grading Chart 0 .075 .3 .6 1.18 2.36 4.75 9.5 12.5 19.0 0 .075 .3 .6 1.18 2.36 4.75 9.5 12.5 19.0 Sieve Size (mm) Raised to 0.45 Power Sieve Size (mm) Raised to 0.45 Power 0 0 20 20 40 40 60 60 80 80 100 100 maximum density line maximum density line Percent Passing Percent Passing max max size size
- 6. NCAT 6 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 100 100 100 100 90 90 72 72 65 65 48 48 36 36 22 22 15 15 9 9 4 4 100 100 99 99 89 89 72 72 65 65 48 48 36 36 22 22 15 15 9 9 4 4
- 7. NCAT 7 100 100 0 0 .075 .075 .3 .3 2.36 2.36 4.75 4.75 9.5 9.5 12.5 19.0 12.5 19.0 Percent Passing Percent Passing control point control point restricted zone restricted zone max density line max density line max max size size nom nom max max size size Sieve Size (mm) Raised to 0.45 Power Sieve Size (mm) Raised to 0.45 Power
- 8. NCAT 8 Superpave Aggregate Gradation 100 100 0 0 .075 .075 .3 .3 2.36 2.36 12.5 12.5 19.0 19.0 Percent Passing Percent Passing Design Aggregate Structure Design Aggregate Structure Sieve Size (mm) Raised to 0.45 Power Sieve Size (mm) Raised to 0.45 Power
- 9. NCAT 9 Superpave Mix Size Designations Superpave Superpave Nom Max Size Nom Max Size Max Size Max Size Designation Designation (mm) (mm) (mm) (mm) 37.5 mm 37.5 mm 37.5 37.5 50 50 25 mm 25 mm 25 25 37.5 37.5 19 mm 19 mm 19 19 25 25 12.5 mm 12.5 mm 12.5 12.5 19 19 9.5 mm 9.5 mm 9.5 9.5 12.5 12.5
- 10. NCAT 10 Gradations * Considerations: - Max. size < 1/2 AC lift thickness - Larger max size + 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
- 11. 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 suggested to minimize problems with natural sands
- 12. 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
- 13. 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
- 14. NCAT 14 0 10 20 30 40 50 60 70 80 90 100 0.075 0.3 1 .18 4.75 9.5 12.5 19 Sieve Size, mm Percent Passing, % Control points for 12. 5 nominal max. size Gradation A Gradation B All possible combinations fall between A and B
- 15. NCAT 15 0 10 20 30 40 50 60 70 80 90 100 0.075 0.3 1 .18 4.75 9.5 12.5 19 Sieve Size, mm Percent Passing, % Control points for 12. 5 nominal max. size Gradation A Gradation B No poss. combination of A and B will meet spec.
- 16. NCAT 16 0 10 20 30 40 50 60 70 80 90 100 0.075 0.3 1 .18 4.75 9.5 12.5 19 Sieve Size, mm Percent Passing, % Control points for 12. 5 nominal max. size Gradation A Gradation B All poss. combinations pass through cross-over point Blends containing more A than B will be closer to A
- 17. 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
- 18. NCAT 18 Blended Aggregate Specific Gravities • Once the percentages of the stockpiles have been established, the combined aggregate specific gravities can also be calculated
- 19. NCAT 19 Combined Specific Gravities G = 1 P1 + P2 + ……. Pn 100 G1 100 G2 100 Gn
- 20. 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
- 21. NCAT 21 Blending of Aggregates • Numerical Method – Trial and Error – Basic Formula
- 22. 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
- 23. NCAT 23 Blending of Aggregates Agg. #2 Agg. #1 Blend Target Material % Passing % Passing % Used U.S. Sieve % Batch % Batch No. 4 No. 8 No. 16 No. 30 No. 50 No. 100 No. 200 3/8 “ 90 30 7 3 1 0 0 100 100 100 88 47 32 24 10 100
- 24. NCAT 24 Blending of Aggregates Agg. #2 Agg. #1 Blend Target Material % Passing % Passing % Used U.S. Sieve % Batch % Batch No. 4 No. 8 No. 16 No. 30 No. 50 No. 100 No. 200 3/8 “ 45 15 3.5 1.5 0.5 0 0 100 100 100 88 47 32 24 10 100 50 % 50 % First Try (remember trial & error) 90 30 7 3 1 0 0 50 90 * 0.5 = 45 30 * 0.5 = 15 7 * 0.5 = 3.5 3 * 0.5 = 1.5 1 * 0.5 = 0.5 0 * 0.5 = 50 0 * 0.5 = 0 100 * 0.5 = 50 80 - 100 65 - 100 40 - 80 20 - 65 7 - 40 3 - 20 2 - 10 100
- 25. NCAT 25 Blending of Aggregates Agg. #2 Agg. #1 Blend Target Material % Passing % Passing % Used U.S. Sieve % Batch % Batch No. 4 No. 8 No. 16 No. 30 No. 50 No. 100 No. 200 3/8 “ 80 - 100 65 - 100 40 - 80 20 - 65 7 - 40 3 - 20 2 - 10 100 45 15 3.5 1.5 0.5 0 0 100 50 50 44 23.5 16 12 5 50 50 % 50 % 90 30 7 3 1 0 0 50 95 65 47.5 25 16.5 12 5 100 100 100 88 47 32 24 10 100
- 26. NCAT 26 Blending of Aggregates Agg. #2 Agg. #1 Blend Target Material % Passing % Passing % Used U.S. Sieve % Batch % Batch No. 4 No. 8 No. 16 No. 30 No. 50 No. 100 No. 200 3/8 “ 80 - 100 65 - 100 40 - 80 20 - 65 7 - 40 3 - 20 2 - 10 100 45 15 3.5 1.5 0.5 0 0 100 50 50 44 23.5 16 12 5 50 50 % 50 % 90 30 7 3 1 0 0 50 95 65 47.5 25 16.5 12 5 100 100 100 88 47 32 24 10 100Let’s Try and get a little closer to the middle of the target values.
- 27. NCAT 27 Blending of Aggregates Agg. #2 Agg. #1 Blend Target Material % Passing % Passing % Used U.S. Sieve % Batch % Batch No. 4 No. 8 No. 16 No. 30 No. 50 No. 100 No. 200 3/8 “ 80 - 100 65 - 100 40 - 80 20 - 65 7 - 40 3 - 20 2 - 10 100 27 9 2.1 0.9 0.3 0 0 100 70 70 61.6 32.9 22.4 16.8 7 70 70 % 30 % 90 30 7 3 1 0 0 30 97 79 63.7 33.8 22.7 16.8 7 100 100 100 88 47 32 24 10 100
- 28. NCAT 28 Questions - ?
Editor's Notes
- #4: To specify gradation the HMA industry uses a .45 power graph. It is a modification of the Fuller’s curve used by geotechnical engineers - rather than use a power of 0.50 it uses a 0.45 for the exponent in the equation.
- #5: The maximum density gradation (line) represents a gradation in which the aggregate particles fit together in their densest possible arrangement. This is not the most desirable gradation for HMA because there would be very little aggregate space within which to develop sufficiently thick asphalt films for a durable mixture.
- #6: For HMA pavements these are the definitions for gradations.
- #7: To specify aggregate gradation, two additional features are added to the 0.45 chart: control points and a restricted zone. Control points function as master ranges through which gradations must pass. They are placed on the nominal maximum size, an intermediate size and the dust size. The restricted zone resides along the maximum density gradation between the intermediate size (either 4.75 or 2.36 mm) and the 0.3 mm size. It forms a band through which gradations should not pass. Gradations that pass through the restricted zone have often been called “humped gradations” because of the characteristic hump in the grading curve that passes through the restricted zone. In most cases, a humped gradation indicates a mixture that possesses too much fine sand in relation to total sand. This gradation practically always results in tender mix behavior, which is manifested by a mixture that is difficult to compact during construction and offers reduced resistance to permanent deformation during its performance life. Gradations that violate the restricted zone possess weak aggregate skeletons that depend too much on asphalt binder stiffness to achieve mixture shear strength. These mixtures are also very sensitive to asphalt content and can easily become plastic.
- #8: The term used to describe the cumulative frequency distribution of aggregate particle sizes is the design aggregate structure. A design aggregate structure that lies between the control points and avoids the restricted zone meets the requirements of Superpave with respect to gradation. Superpave defines five mixture types as defined by their nominal maximum aggregate size:
- #9: These are the five gradations developed for Superpave.
- #10: Several factors need to be considered in selecting a desirable aggregate gradation. The maximum size of the aggregate needs to be at a minimum less than one half of the planned lift thickness. Current construction practices with Superpave gradations indicate that this needs to be changed to less than one-third of the lift thickness. Larger maximum size aggregate gradations have several advantages such as improved aggregate interlock, improved skid resistance and improved rut resistance. Local availability of aggregates will usually dictate the largest size aggregate. Also, the larger maximum size gradations also tend to have more problems with gradation separation (segregation) during construction.
- #11: Target gradations are usually selected to meet an agency-specified gradation band. The selected gradation needs to meet the agency requirements as well as all other Superpave gradation and aggregate requirements. At the present time, there are 5 Superpave gradation bands. Each uses 4 sieve sizes to set upper and lower limits on the gradation. The restricted zone was originally included to help eliminate rounded natural sands. However, with the requirements on fine aggregate angularity, the need to stay out of the restricted zone is evaluated on a case by case basis (historical experience).
- #12: Once a target gradation or gradation band is selected, percentages of the aggregate stockpiles needed to produce an acceptable gradation are determined. This is usually accomplished using a spreadsheet and a trial and error approach.
- #13: The ability of a given set of aggregate stockpiles to meet particular gradation band requirements can be initially assessed by plotting the individual stockpile and gradation band requirements
- #14: If the individual gradations bracket the gradation band, then it is possible to produce a combined gradation which will be within the gradation band. Determining the percentages will be a trial and error process.
- #15: If the individual stockpile gradations are both either above or below the target gradation band, then there is no combination of the stockpiles which will produce an acceptable gradation.
- #16: If the individual stockpile gradations cross, then the any combination of these stockpiles will have that same percentage for that particular sieve size.
- #17: Once it has been established that an acceptable gradation can be prepared using the designated stockpiles, these steps need to be followed to determine the desired percentages of each stockpile.
- #18: Remember, two specific gravity tests are needed. The results from these two tests need to be combined to obtain the specific gravity of the composite.
- #19: This is the equation used for combining aggregate properties.
- #20: We blend aggregates for these reasons.
- #21: There are two methods for blending aggregates. The most common is trial and error. The basic formula is not used.
- #22: This is the basic formula for blending.
- #23: Example. Starting with two aggregates.
- #24: The first trial we will use 50% of each pile.
- #25: This worked but the No. 50 sieve and the No 100 sieve are low.