ROAD AGGREGATES 01
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This document provides information on pavement materials, specifically road aggregates. It discusses aggregate characterization, including maximum aggregate size, gradation, and other properties like toughness, specific gravity, particle shape, durability, and cleanliness. It describes methods for determining aggregate size distributions and developing target gradations. Graphs and equations for 0.45 power gradations are presented. The document also covers testing methods for aggregate properties like crushing value, impact value, Los Angeles abrasion, and soundness. It provides guidance on blending aggregate stockpiles to achieve design gradations.
ROAD AGGREGATES 01
- 2. PAVEMENT MATERIALSPAVEMENT MATERIALS ENGINEERINGENGINEERING (CE-862)(CE-862) Lec-10 Fall Semester 2016 Dr. Arshad Hussain arshad_nit@yahoo.com , Office Room#111, Tel: 05190854163, Cell: 03419756251 National Institute of Transportation (NIT) School of Civil & Environmental Engineering (SCEE) National University of Science and Technology (NUST) NUST Campus, Sector H-12, Islamabad
- 3. ROAD AGGREGATESROAD AGGREGATES (Cont..)(Cont..)
- 4. AGGREGATE CHARACTERIZATIONAGGREGATE CHARACTERIZATION Aggregate Physical Properties Maximum Aggregate Size Gradation Other Aggregate Properties Toughness and Abrasion Resistance Specific Gravity Particle Shape and Surface Texture Durability and Soundness Cleanliness and Deleterious Materials
- 5. AGGREGATE CHARACTERIZATIONAGGREGATE CHARACTERIZATION Maximum Aggregate Size Maximum size The smallest sieve through which 100 percent of the aggregate particles pass. Nominal maximum size The largest sieve that retains some of the aggregate particles but generally not more than 10 percent by weight.
- 6. Aggregate Size DefinitionsAggregate 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 100100 100100 9090 7272 6565 4848 3636 2222 1515 99 44 100100 9999 8989 7272 6565 4848 3636 2222 1515 99 44
- 7. AGGREGATE GRADATIONAGGREGATE GRADATION Use 0.45 Power Gradation Chart Blend Size Definitions ◦ maximum size ◦ nominal maximum size Gradation Limits ◦ control points ◦ restricted zone
- 8. Example:Example: 4.75 mm sieve plots at (4.75)4.75 mm sieve plots at (4.75)0.450.45 = 2.02= 2.02 Sieve Size (mm) Raised to 0.45 PowerSieve Size (mm) Raised to 0.45 Power 00 2020 4040 6060 8080 100100 00 11 22 33 44 Percent PassingPercent Passing 0.45 Power Grading Chart0.45 Power Grading Chart
- 9. 0.45 Power Grading Chart0.45 Power Grading Chart 0 .075 .3 .6 1.18 2.36 4.75 9.5 12.5 19.00 .075 .3 .6 1.18 2.36 4.75 9.5 12.5 19.0 Sieve Size (mm) Raised to 0.45 PowerSieve Size (mm) Raised to 0.45 Power 00 2020 4040 6060 8080 100100 maximum density linemaximum density line Percent PassingPercent Passing maxmax sizesize
- 12. Calculation of the Max Density CurveCalculation of the Max Density Curve n D d P = where P = % finer than the sieve d = aggregate size being considered D = maximum aggregate size being used n = parameter which equals 0.45—represents the maximum particle packing
- 13. 100100 00 .075.075 .3.3 2.362.36 4.754.75 9.59.5 12.5 19.012.5 19.0 Percent PassingPercent Passing control pointcontrol point restricted zonerestricted zone max density linemax density line maxmax sizesize nomnom maxmax sizesize Sieve Size (mm) Raised to 0.45 PowerSieve Size (mm) Raised to 0.45 Power
- 14. Superpave Aggregate GradationSuperpave Aggregate Gradation 100100 00 .075.075 .3.3 2.362.36 12.512.5 19.019.0 Percent PassingPercent Passing Design Aggregate StructureDesign Aggregate Structure Sieve Size (mm) Raised to 0.45 PowerSieve Size (mm) Raised to 0.45 Power
- 15. Superpave Mix Size DesignationsSuperpave Mix Size Designations SuperpaveSuperpave Nom Max SizeNom Max Size Max SizeMax Size DesignationDesignation (mm)(mm) (mm)(mm) 37.5 mm37.5 mm 37.537.5 5050 25 mm25 mm 2525 37.537.5 19 mm19 mm 1919 2525 12.5 mm12.5 mm 12.512.5 1919 9.5 mm9.5 mm 9.59.5 12.512.5
- 16. 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
- 17. TARGET GRADATIONTARGET 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
- 18. BLENDING STOCKPILESBLENDING 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
- 19. BLENDING STOCKPILESBLENDING 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
- 20. TRIAL AND ERROR STEPSTRIAL 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
- 21. Blended Aggregate Specific GravitiesBlended Aggregate Specific Gravities Once the percentages of the stockpiles have been established, the combined aggregate specific gravities can also be calculated
- 22. COMBINED SPECIFIC GRAVITIESCOMBINED SPECIFIC GRAVITIES G = 1 P1 + P2 + ……. Pn 100 G1 100 G2 100 Gn
- 23. BLENDING OF AGGREGATESBLENDING OF AGGREGATES Reasons for Blending Obtain desirable gradation Single natural or quarried material not enough Economical to combine natural and process materials
- 24. BLENDING OF AGGREGATESBLENDING OF AGGREGATES Agg. #2Agg. #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
- 25. BLENDING OF AGGREGATESBLENDING OF AGGREGATES Agg. #2Agg. #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
- 26. BLENDING OF AGGREGATESBLENDING OF AGGREGATES Agg. #2Agg. #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
- 27. BLENDING OF AGGREGATESBLENDING OF AGGREGATES Agg. #2Agg. #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.
- 28. BLENDING OF AGGREGATESBLENDING OF AGGREGATES Agg. #2Agg. #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
- 29. Other Aggregate PropertiesOther Aggregate Properties Aggregate Crushing Value Aggregate Impact Value Los Angeles Abrasion Soundness Sand Equivalent
- 30. AGGREGATE CRUSHING VALUEAGGREGATE CRUSHING VALUE • Metal measure • Tamping rod Below mentioned are its specifications: • Three sizes 75mm dia for 1/8 to 1/4 Size aggregate, 150mm dia for 3/8 to 3/4 Size aggregate 300mm dia for 1in to 2in size aggregate The aggregate crushing value indicates the ability of an aggregate to resist crushing. The lower the figure the stronger the aggregate, i.e. the greater its ability to resist crushing.
- 31. AGGREGATE CRUSHING VALUE Aggregate passing IS sieve 12.5 mm and retained on 10 mm sieve is generally used. Oven dried aggregates are filled in the measuring cylinder of 11.5cm dia. & 18.0cm height in 3 equal layers, each layer being subjected to 25 tamps with a tamping rod of 16mm dia and 45 to 60mm long.
- 32. AGGREGATE CRUSHING VALUE The crushing test apparatus consist of a 15cm dia open ended heavy steel cylinder, plunger and a base plate. Compression testing machine a load of 40 tonnes is applied in 10 min. crushed aggregate Sieved through 2.36 mm sieve.
- 33. Agg crushing value > 35 weak for pavement. Agg crushing value < 10 exceptionally strong. For majority of aggregates the impact value and crushing value are numerically similar. Rock group Crushing value Impact value Basalt 14 15 Granite 20 19 Lime stone 24 23 Quartzite 16 21 AGGREGATE CRUSHING VALUE
- 34. AGGREGATE IMPACTVALUE A base, which helps in supporting the columns to form a rigid framework around the quick release trigger mechanism for ensuring the effective free fall of the hammer during test. The hammer is offered with locking arrangement and the free fall can be easily adjusted through the 380+ 5mm. cylindrical cup, with the metal measure 75 mm dia x 50 mm high and tamping rod. Satisfactory resistance to crushing under roller during construction. Adequate resistance to surface abrasion under traffic.
- 35. IMPACT VALUE Due to traffic loads the road stones are subjected to impact. IS sieves 12.5 mm,10 mm & 2.36 mm. Cylindrical steel cup of dia 10.2 cm & depth 5 cm. Metal hammer of weight 13.5 to 14 kg. Height of fall 38 cm. Cylindrical measure with internal dia 7.5 cm & depth 5 cm. Metal tamping of 1 cm dia.23 cm long. < 10 % exceptionally strong. 10 - 20 % strong. 20 - 30 % satisfactory. > 35 % weak.
- 36. ELONGATION & FLAKINESS INDEXELONGATION & FLAKINESS INDEX When the length is more than 1.8 of the mean dimension, then the aggregate particles are considered elongated. The aggregate particles are to be flaky, if the thickness is less than the 0.6 of their mean dimension.
- 37. LOS ANGELES ABRASION TEST Start with fraction retained on No. 12 sieve
- 38. Sample submerged in magnesium or sodium sulfate—causes salt crystals to form in the aggregate pores SOUNDNESSSOUNDNESS TESTTEST
- 39. SAND EQUIVALENTSAND EQUIVALENT SE = (Height of Sand/Height of Clay)100 This is a test to determine the amount of clay in fine aggregate. Aggregate passing a No. 4 sieve is agitated in a water-filled transparent cylinder. Liquid is water and flocculating agent. After settling, the sand separates from the flocculated clay. Measure each.
- 40. ThanksThanks
Editor's Notes
- #7: For HMA pavements these are the definitions for gradations.
- #9: 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.
- #10: 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.
- #12: This illustration shows linear lines for six different maximum aggregate sizes. Aggregate gradations that conform to one of these lines has the maximum packing of particle sizes. On the next image, the equation for calculating these lines is shown.
- #14: 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.
- #15: 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:
- #17: 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.
- #18: 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).
- #19: 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.