Block 8 coarse aggregate 13


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  • This section covers aggregate tests related to the coarse aggregate fraction. This is typically the material retained on the 4.75 mm (no. 4) sieve. However, is certain instances, the coarse aggregate can be defined as retained on the 2.36 mm (no. 8) sieve.
  • Limits are placed on deleterious materials which are considered contaminates in the hot mix asphalt.
  • This section has been divided into three major groups. The first covers a brief background on older test methods used to determine coarse aggregate properties. The second covers tests either currently in use or soon to be implemented. The last section includes topics for more in-depth information and/or for use in graduate classes.
  • There are four tests that can be used to determine or estimate coarse aggregate shape. The Particle Index is an older method that is not commonly used at this time but is included in this section as background information. The two methods currently used in the Superpave mix design method are Flat and Elongated, and Percent Crushed Faces. Recent research from NCHRP 4-19 recommends using the uncompacted voids in coarse aggregate for evaluating shape.
  • One of the older test method standards used to characterize coarse aggregate shape is the Particle Index. This method uses measurements of the void space in between particles after compaction to represent shape and surface texture. The hypothesis is that the more angular or rougher textured the aggregate is, the more difficult it will be to obtain a dense packing. The first step is to separate the coarse aggregate into individual sieve sizes. Next, about a 1/3 of a particular mold (selected based on aggregate fraction) is filled, then compacted with 10 tamps over the surface, a second layer is added and tamped, followed by the last layer and tamping. The void volume is determined. The process is repeated using 50 blows per layer. The Particle Index is determined using the equation shown in this slide. The Particle Index for the entire coarse aggregate gradation is calculated using a weighted average based on the percent of each fraction in the coarse aggregate gradation.
  • Flat and elongated particles are undesirable since they have a tendency to break during construction and under traffic. If they do not break, they tend to produce mixtures with directionally-oriented material properties. Current recommendations for HMA aggregate are less than 10% passing the 1:5 ratio. There is some indication that a few agencies are considering 20% maximum passing the 1:3 ratio.
  • The longest dimension of an aggregate particle is used to set one end of the caliber. (pin is at the 1:5 ratio pivot point). The aggregate particle is removed without moving the caliper arm and the narrowest dimension is inserted into the other end. If the aggregate can be inserted without moving the arm, then the particle is flat and elongated at a 1:5 ratio.
  • Determining flat and elongated with the previous method at each of the ratios is extremely tedious and time consuming. In order to improve both the reliability and shorten the testing time, Martin Marietta has developed a semi-automated flat and elongated test jig. The first step is to select an aggregate particle, raise the foot, place the aggregate under the foot with the longest
  • This slide presents the steps needed to determine the flat and elongated ratio for each aggregate particle. dimension in the vertical direction. The foot is lowered until it contacts the aggregate then a foot pedal (not shown) is pressed by the operator. The digital caliper attached to the foot sends the measurement to an excel spread sheet (with macro – shown on next slide). The process is repeated for the minimum dimension. The computer screen indicates which ratio the aggregate particle meets. The aggregate particle is then placed in a bowl that corresponds to this ratio. Testing is repeated with the remaining particles. The percent of aggregate that meets each ratio is determined by weighing the aggregate is each bowl and dividing by the total weight of aggregate tested. The results are expressed as a percent.
  • This slide shows the initial excel macro work sheet that will be automatically filled in as testing proceeds.
  • This slide shows what a typical work sheet looks like as testing progresses. Note the color coding provides a simple means of letting the operator know the bowl in which to place the aggregate.
  • The third test that is used in the Superpave mix design method is the determination of the percent fractured faces. The test can be conducted so that the percent of aggregate with one or more crushed faces or two or more crushed faces are determined. A crushed face is defined as having a fracture that is at least 25% of the area.
  • This slide gives examples of how different levels of crushing look.
  • While Superpave defines the level of crushing based on both the depth in the layer and the traffic level, states have historically used a wide range of specification limits for this coarse aggregate property. This slide gives a couple of examples of the wide range of values used as late at 1995.
  • Uncompacted voids in coarse aggregate is the same as the uncompacted voids in fine aggregates except that the size of the equipment has been increased to accommodate the larger aggregate.
  • One of two standard gradations can be used for Method A. The gradation is selected based on the largest size of aggregate in the sample. A total of 5,000 grams is used, regardless of the aggregate size or the test method. 19 MM = ¾” 12.5 MM = ½” 9.5 MM = 3/8” 4.74 MM = 3/16”
  • This is the equipment needed for determining the voids in uncompacted voids in coarse aggregate. This is a way of using differences in the voids due to aggregate shape and texture to estimate angularity.
  • The first step in testing is to prepare the aggregate sample, which is then poured into the upper chamber. The bottom door is quickly moved out of the way and the aggregate flows freely into the unit weight bucket below.
  • The second step is to level off the top of the bucket, then weigh it to determine the mass of aggregate in the known volume.(bucket tare subtracted). The volume of voids is then computed from a standard mass/volume relationship.
  • Some research has been done that investigates the relationship between coarse aggregate shape and the value of the uncompacted voids. This figure shows that there is a good correlation between the uncompacted voids and the percent flat and elongated (3:1). This figure shows that for a given percent flat and elongated, crushed materials will have a greater uncompacted void volume than rounded gravels.
  • A number of researchers are trying a wide range of two and three dimensional imaging techniques for quantifying fine aggregate shape. One example is that currently being developed at the University of Arkansas. This method spreads the aggregate on a glass plate then uses a high resolution video camera to obtain the digital image. Digital imaging hardware and software is used to measure key aggregate shape properties. It this example, the University of Arkansas uses two parameters to characterize the fine aggregate shape: EAPP and Roughness Index. These parameters are discussed in the next two slides. There are a number of ways to obtain an image of fine aggregate. The key to characterizing shape factors is in the mathematics associated with refining and defining the image. Summarizing the various imaging methods and mathematical methods would be a good term paper research project for a graduate class. .
  • The ability of the aggregate to withstand the rigors of handling, construction processes and in-service loading without degrading is a measure of the aggregate’s toughness. This section discusses several test methods that can be used to assess toughness. The Los Angeles abrasion test is the most often run toughness test. The micro-Deval wet abrasion test has been recently recommended as either an alternative or replacement for the Los Angles abrasion test. Degradation during Superpave gyratory compaction (without asphalt) has also been used but remains as a research test at this time. Two tests used in other parts of the world include the British methods for Aggregate Impact Value and Aggregate Crushing Value.
  • The LA abrasion test uses one of four standardized gradations. The gradation required is defined by the largest size aggregate present in the gradation. The number of steel balls added to the steel drum is also based on the gradation used in the test. In general, the larger the aggregate, the more steel balls are added.
  • Once the gradation has been selected and the aggregate batched, the aggregate and steel balls are added to the steel drum. The drum is then rotated at 30 to 33 rpms for a total of 500 revolutions.
  • At the end of the test, the aggregate and steel balls are removed from the chamber, the steel balls removed from the aggregate, and the aggregate is separated on the 1.70 mm (no. 12) sieve.
  • The aggregate retained on the 1.70 mm (no. 12) sieve is then washed, dried to a constant mass, and the amount of aggregate lost due to the impact of the steel balls is determined.
  • This figure shows the results from NCHRP 4-19. Results were obtained for a range of aggregate types with a range of historical field performance. Note that almost all of the aggregates, with the exception of source 7, had LA abrasion values of less than 30%. There is no clear distinction between aggregates with good, fair, or poor pavement performance history.
  • The micro-Deval test is a smaller scale, wet abrasion test. Like the LA abrasion test, it uses prescribed gradations based on the top size aggregate.
  • The first step is to prepare a dry aggregate sample batched to meet the desired gradation, then soak it for one hour in 2 liters of water. Next, the sample and water along with the steel balls are placed in the jar. The jar is rotated at 100 rpms for 2 hours. At this time, the sample and balls are washed out of the jar onto a stack of 4.75 and 1.18 mm sieves. A magnet is used to remove the steel balls, then the aggregates from both sieves are washed out into a bowl that is then placed in the oven to dry.
  • The aggregate is soaked in water, then added to the stainless steel jar along with 5,000 grams of small steel balls. The jar is sealed and place on the stand. The jar is rotated at 100 rpms for 2 hours. The aggregate from the jar and drained over a nest of sieves. The material retained on both the 4.75 and 1.18 mm sieves is placed in a bowl and then in an oven. The aggregate is dried to a constant mass.
  • The last step is to calculate the micro-Deval loss. This is the amount of material lost, expressed as a percentage of the original weight.
  • This figure shows the results reported for NCHRP 4-19. Note that in most cases there is a clear difference between good, fair and poor performing aggregates. The one exception is the source 15 aggregate. As noted previously, its performance was rated as poor for rutting and bleeding problems. Since these problems are not usually associated with toughness problems, this source was discounted when setting recommended test method limits. For this test, a loss of less than 18% indicates an aggregate with acceptable performance properties.
  • The Ontario Ministry of Transportation has adapted this test to use standardized reference materials for calibration.
  • A standard gyratory compactor can be used to evaluate the degradation of an aggregate due to shearing action. This test can be used to evaluate only the coarse aggregate. It can also be used to evaluate the blended gradation or just the fine aggregate portion.
  • There are a number of gyratory compactors that are used throughout the country.
  • Another property that needs to be considered is the soundness, or resistance to weathering, of the coarse aggregate.
  • The first step is to separate the aggregate into prescribed sieve size fractions, then place each size in a container for the next series of steps. Old sieves can be used for this purpose. The Alabama Department of Transportation allows the use of cheese cloth with either a No. 40 or 50 sieve size equivalent.
  • The first step is to separate the aggregate into prescribed sieve size fractions, then place each size in a container for the next series of steps. Old sieves can be used for this purpose. The Alabama Department of Transportation allows the use of cheese cloth with either a No. 40 or 50 sieve size equivalent.
  • The first step is to separate the aggregate into prescribed sieve size fractions, then place each size in a container for the next series of steps. Old sieves can be used for this purpose. The Alabama Department of Transportation allows the use of cheese cloth with either a No. 40 or 50 sieve size equivalent.
  • After the required numbers of cycles of soaking and drying, the aggregate is rinse to remove any remaining salts.
  • The rinsing is continued and intermittently tested until the water remains clear. This ensures that all of the chemicals have been washed off of the aggregate.
  • The last steps are to dry the aggregate, determine the gradation, and then determine the change in gradation due to weathering.
  • This slide shows and example of how aggregate particles can be damaged with this type of testing.
  • This section includes brief discussions on other soundness, less commonly used, soundness tests.
  • This test combines a gentle agitation of aggregate in water with an evaluation of the type of fines that are produced by agitation. The sand equivalent solution is used for this evaluation of the type of fines.
  • This test method simply identifies three methods for determining soundness by actually freezing and then thawing the aggregate fractions. Each of these three methods are briefly outlined in the next several slides.
  • Block 8 coarse aggregate 13

    1. 1. Senior/Graduate HMA Course Coarse AggregatesAggregate Coarse Aggregates 1
    2. 2. Deleterious Materials ASTM C142• Mass percentage of contaminants such as clay lumps, shale, wood, mica, and coal• Test • Wet sieving agg. size fraction over specified sieves • Mass lost = % contaminants• Range from 0.2% to 10%, depending upon contaminant Aggregate Coarse Aggregates 2
    3. 3. Coarse Aggregate Angularity• Historical• Currently used or recommended• Advanced topicsAggregate Coarse Aggregates 3
    4. 4. Coarse Agg. Angularity • Traditional and Newly Recommended • Particle Index • Flat and elongated • Percent crushed faces • Uncompacted voidsAggregate Coarse Aggregates 4
    5. 5. Particle Index ASTM D3398• Vol. of voids between packed, uniform-size aggregate particles indicate combined effect of shape, angularity and surface texture • 203 mm (8 in), 152 mm (6 in), 102 mm (4 in), 76 mm (3 in), and 51 mm (2 in) diameter mold • Blows on each of three layers 50 mm above surface• Ia = 1.25 V10 - 0.25 V50 - 32.0• Particle index increases with angularity• Ia weighted on basis of % of each fraction Aggregate Coarse Aggregates 5
    6. 6. Flat and Elongated Particles • ASTM D4791 • Flat • Elongated • Total flat and elongated • Superpave • Flat or Elongated • Maximum to minimum dimension • 1:5 • 1:3 • 1:2Aggregate Coarse Aggregates 6
    7. 7. Flat and Elongated Particles Max : minAggregate Coarse Aggregates 7
    8. 8. Semi-Automated Flat and Elongated• Martin Marietta has developed semi-automated method Digital Height Caliber Computer for data acquisition and analysis program Handle for raising and lowering foot Foot and base plate Aggregate Coarse Aggregates 8
    9. 9. Nord Jaws• Place agg under foot in largest dimension • Step on foot pedal to enter data• Rotate agg to least dimension • Step on foot pedal again to enter least• Place aggregate particle in appropriate ratio bowl • Separates agg into 2:1, 3:1, 4:1, and 5:1 Aggregate Coarse Aggregates 9
    10. 10. Nord JawsAggregate Coarse Aggregates 10
    11. 11. Nord JawsAggregate Coarse Aggregates 11
    12. 12. Percent Fractured Faces ASTM D5821 • Retained on 4.75 mm (#4) • Fractured = min 25% of area • Clean, well-defined edges • Can specify • 1 or more fractured faces • 2 or more fractured facesAggregate Coarse Aggregates 12
    13. 13. Percent Fractured Faces ASTM D5821 0% Crushed 2 or More Fractured FacesAggregate Coarse Aggregates 13
    14. 14. Coarse Aggregate Angularity HMA 1995 1 Fractured Face: 30 States with requirements Range from 40 (Ohio) to 100 (Utah) 2 Fractured Faces: 13 States with requirements Range from 30 (all mixes, AZ) to 100 (Surface, IN)Usually designated for either high quality HMA or wearing coursesAggregate Coarse Aggregates 14
    15. 15. Uncompacted Voids AASHTO TP 56• Up-scaled version of the fine aggregate angularity test discussed in preceding sections • Two methods can be used • Standard gradation (Method A) • Each sieve size (Method B) Aggregate Coarse Aggregates 15
    16. 16. Uncompacted Voids AASHTO TP 56• Method APass Retained 19 mm 12.5 m19 mm 12.5 mm 1,740 -----12.5 mm 9.5 mm 1,090 1,9709.5 mm 4.75 mm 2,170 3,030• Method B • Uses 5,000 grams of each fraction, tested individually • A weighted average is used to combine results Aggregate Coarse Aggregates 16
    17. 17. Uncompacted Voids in Coarse AggregateAggregate Coarse Aggregates 17
    18. 18. Uncompacted Voids in Coarse AggregateAggregate Coarse Aggregates 18
    19. 19. Uncompacted Voids in Coarse AggregateAggregate Coarse Aggregates 19
    20. 20. Gravel Stone 53 Uncompacted Voids, % (Coarse 52 R2 = 0.8638 51 50 49 Agg.) 48 47 46 R2 = 0.8743 45 44 43 0 10 20 30 40 % Flat or Elongated (3:1)Aggregate Coarse Aggregates 20
    21. 21. Image Analysis• University of Arkansas • Aggregate spread on glass plate • High resolution video camera • Modern digital imaging hardware, analysis techniques and computer analysis used • Uses two parameters • EAPP • Roughness IndexAggregate Coarse Aggregates 21
    22. 22. ToughnessDegradation due to handling, construction, and in-service • Traditional or newly recommended • Los Angeles Abrasion • Micro-Deval • Advanced topics • Aggregate Impact Value • Aggregate Crushing Value • Gyratory CompactorAggregate Coarse Aggregates 22
    23. 23. LA Abrasion ASTM C131 • Step 1: prepare specific agg gradationPassing Retained A B C D37.5 mm 25.0 mm 1,250 --- --- ---25.0 mm 19.0 mm 1,250 --- --- ---19.0 mm 12.5 mm 1,250 2,500 --- ---12.5 mm 9.5 mm 1,200 2,500 --- ---9.5 mm 6.3 mm --- --- 2,500 --6.3 mm 4.75 mm --- --- 2,500 ---4.75 mm 2.36 mm --- --- --- 5,000No. Steel Balls 12 11 8 6 Aggregate Coarse Aggregates 23
    24. 24. LA Abrasion• Step 2: Rotate for 500 revolutions at 30 to 33 rpm’s Aggregate Coarse Aggregates 24
    25. 25. LA Abrasion (ASTM C131)• Step 3. Empty cylinder, remove balls, and make preliminary separation of agg on 1.70 mm (No. 12) sieve Steel balls need to be removed Aggregate Coarse Aggregates 25
    26. 26. LA Abrasion (ASTM C131)• Step 4: Wash material retained on No. 12 sieve, dry to constant weight, and determine dry (cooled) mass• % Loss = (original wt – final wt) x 100 original wt Aggregate Coarse Aggregates 26
    27. 27. LA Abrasion Loss, % 60 50 40 Good 30 Poor 20 10 Good Fair Poor 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Agg. Source No. Source 15 had poor performance due to rutting and bleeding This would not be related to toughness Aggregate Coarse Aggregates 27
    28. 28. Micro Deval Abrasion Test• One of two gradations can be used 19.0 to 9.5 mm 3.2 to 4.75 mm Sieve Size Amount AmountPass Retained Retained Retained19.0 16.0 mm 375 g ------16.0 13.2 mm 375 g 375 g13.2 9.5 mm 750 g 750 g 9.5 6.7 mm ------- 375 g 6.7 4.75 mm ------- 375 g Aggregate Coarse Aggregates 28
    29. 29. Micro Deval Abrasion TestStep 1: Dry, weighed sample with 2-L waterfor 1 hourStep 2: Sample and water with 5,000 g steelballs into jar; roll at 100 rpms for 2 hoursStep 3: Wash sample and balls out of jarover stacked 4.75 and 1.18 mm sievesStep 4: Combine material from both sievesand dry to constant mass at 110oC Aggregate Coarse Aggregates 29
    30. 30. Micro Deval Abrasion Test Steel jar Small steel balls Aggregate in waterAggregate Coarse Aggregates 30
    31. 31. Micro Deval Abrasion TestStep 5: Calculate loss %Loss = (Orig. wt – Dry wt. after) x 100 Orig. wt Aggregate Coarse Aggregates 31
    32. 32. 40 35 30Micro-Deval Loss, % 25 Good 20 Criteria = 18% Fair 15 Poor 10 5 Good Fair Poor 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Agg. Source No. Aggregate Coarse Aggregates 32
    33. 33. Micro Deval Abrasion Test• Ontario Ministry of Transportation (MTO) has: • Standardized equipment • Reference materials for calibration • 12% loss for 19 to 9.5 mm • 14.5% loss for 13.2 to 4.72 mm Aggregate Coarse Aggregates 33
    34. 34. Gyratory Compactor• 0.6 MPa (87 psi), 1.25o angle, 30 rpm/min • Can be use with just coarse, fine, or blend • Gradation before and after specified numbers of gyrations • Differences can be analyzed for given particle sizes • Research indicates changes in % passing 4.75 mm (No. 4) good indicator Aggregate Coarse Aggregates 34
    35. 35. Gyratory CompactorAggregate Coarse Aggregates 35
    36. 36. Soundness• Evaluates coarse aggregate resistance to weathering (freeze/thaw)• Most common methods • Sodium or magnesium sulfate • AASHTO T104 Aggregate Coarse Aggregates 36
    37. 37. Soundness Test Method AASHTO T104• Repeated immersions in sodium or magnesium sulfate• Followed by oven drying• Salts precipitate in permeable voids during drying• Salt expands and contracts with wet/dry cycling• Simulates in-service weathering of agg. Aggregate Coarse Aggregates 37
    38. 38. Soundness Test Method AASHTO T104• Aggregates prepared for soaking and drying Aggregate Coarse Aggregates 38
    39. 39. Soundness Test Method AASHTO T104• Aggregates soaked then transferred to oven to dry • 1 cycle = one soak + one dry• 5 cycles to 30 cycles used • 5 to 10 most common Aggregate Coarse Aggregates 39
    40. 40. Soundness Test Method AASHTO T104• Aggregate rinsed at the end of the test Aggregate Coarse Aggregates 40
    41. 41. Soundness Test Method AASHTO T104• The rinse water is checked to determine when salts are removed • Water is not cloudy when tested Aggregate Coarse Aggregates 41
    42. 42. Soundness Test Method AASHTO T104• Oven dry after rinsing• Conduct sieve analysis to determine change in gradationAggregate Coarse Aggregates 42
    43. 43. Soundness AASHTO T104 Before AfterAggregate Coarse Aggregates 43
    44. 44. Soundness• Advanced Topics • Aggregate Durability Index • ASTM C88 (AASHTO T210) • Soundness by freezing and thawing • AASHTO T103 • Canadian Freeze/Thaw Test Aggregate Coarse Aggregates 44
    45. 45. Aggregate Durability Index ASTM D3744• Resistance to producing clay-like fines when aggregates are subjected to mechanical agitation in the presence of water• Especially suitable for basalt type aggregates containing interstitial montmorillonite Aggregate Coarse Aggregates 45
    46. 46. Aggregate Durability Index ASTM D3744• Step 1: Washed and dried aggregate agitated in mechanical washing vessel for 10 min. (photo to be added) Aggregate Coarse Aggregates 46
    47. 47. Aggregate Durability Index ASTM D3744• Step 2: Wash water and minus 0.075 mm fines collected and mixed with stock calcium chloride solution Aggregate Coarse Aggregates 47
    48. 48. Aggregate Durability Index ASTM D3744• Step 3: After 20 min of sedimentation, level read and height of level used to calculate the durability indexDc = 30.3 + 20.8 cot(02.29 + 0.15 H)Test method provides table of solutions for H in increments of 0.5 mm Aggregate Coarse Aggregates 48
    49. 49. Freezing and Thawing (AASHTO T103)• Aggregate washed, dried, and separated into individual fractions • 3 methods for saturation Aggregate Coarse Aggregates 49
    50. 50. Freezing and Thawing (AASHTO T103)• Method A • Aggregates soaked in water for 24 hr • Samples remained completely immersed during freezing and thawing • 50 cycles typical Aggregate Coarse Aggregates 50
    51. 51. Freezing and Thawing (AASHTO T103)• Method B • Aggregates soaked and subjected to vacuum of not over 25.4 mm (1 in) of mercury • Penetration of water increased by using 0.5% by mass solution of ethyl alcohol and water • Sample frozen/thawed in alcohol-water solution • 6 cycles typical Aggregate Coarse Aggregates 51
    52. 52. Freezing and Thawing (AASHTO T103)• Method C • Same as B except no alcohol is used • 25 cycles typical Aggregate Coarse Aggregates 52
    53. 53. QUESTIONS?Aggregate Coarse Aggregates 53