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. Coarse Aggregate Angularity
• Historical
• Currently used or recommended
• Advanced topics
Aggregate Coarse Aggregates 3
4. Coarse Agg. Angularity
• Traditional and Newly Recommended
• Particle Index
• Flat and elongated
• Percent crushed faces
• Uncompacted voids
Aggregate Coarse Aggregates 4
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. Flat and Elongated Particles
• ASTM D4791
• Flat
• Elongated
• Total flat and elongated
• Superpave
• Flat or Elongated
• Maximum to minimum dimension
• 1:5
• 1:3
• 1:2
Aggregate Coarse Aggregates 6
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. 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
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 faces
Aggregate Coarse Aggregates 12
13. Percent Fractured Faces
ASTM D5821
0% Crushed 2 or More
Fractured Faces
Aggregate Coarse Aggregates 13
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 courses
Aggregate Coarse Aggregates 14
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. Uncompacted Voids
AASHTO TP 56
• Method A
Pass Retained 19 mm 12.5 m
19 mm 12.5 mm 1,740 -----
12.5 mm 9.5 mm 1,090 1,970
9.5 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
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 Index
Aggregate Coarse Aggregates 21
22. Toughness
Degradation 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 Compactor
Aggregate Coarse Aggregates 22
23. LA Abrasion
ASTM C131
• Step 1: prepare specific agg gradation
Passing Retained A B C D
37.5 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 --- --- --- 5,000
No. Steel Balls 12 11 8 6
Aggregate Coarse Aggregates 23
24. LA Abrasion
• Step 2: Rotate for 500 revolutions at 30 to 33 rpm’s
Aggregate Coarse Aggregates 24
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. 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. 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. 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 Amount
Pass Retained Retained Retained
19.0 16.0 mm 375 g ------
16.0 13.2 mm 375 g 375 g
13.2 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. Micro Deval Abrasion Test
Step 1: Dry, weighed sample with 2-L water
for 1 hour
Step 2: Sample and water with 5,000 g steel
balls into jar; roll at 100 rpms for 2 hours
Step 3: Wash sample and balls out of jar
over stacked 4.75 and 1.18 mm sieves
Step 4: Combine material from both sieves
and dry to constant mass at 110oC
Aggregate Coarse Aggregates 29
30. Micro Deval Abrasion Test
Steel jar
Small steel balls
Aggregate in water
Aggregate Coarse Aggregates 30
31. Micro Deval Abrasion Test
Step 5: Calculate loss
%Loss = (Orig. wt – Dry wt. after) x 100
Orig. wt
Aggregate Coarse Aggregates 31
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. 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
36. Soundness
• Evaluates coarse aggregate resistance
to weathering (freeze/thaw)
• Most common methods
• Sodium or magnesium sulfate
• AASHTO T104
Aggregate Coarse Aggregates 36
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. Soundness Test Method
AASHTO T104
• Aggregates prepared for soaking and
drying
Aggregate Coarse Aggregates 38
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. Soundness Test Method
AASHTO T104
• Aggregate rinsed at the end of the test
Aggregate Coarse Aggregates 40
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. Soundness Test Method
AASHTO T104
• Oven dry after rinsing
• Conduct sieve analysis to determine
change in gradation
Aggregate Coarse Aggregates 42
43. Soundness
AASHTO T104
Before After
Aggregate Coarse Aggregates 43
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. 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. 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. 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. Aggregate Durability Index
ASTM D3744
• Step 3: After 20 min of sedimentation,
level read and height of level used to
calculate the durability index
Dc = 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. Freezing and Thawing
(AASHTO T103)
• Aggregate washed, dried, and separated
into individual fractions
• 3 methods for saturation
Aggregate Coarse Aggregates 49
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. 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. Freezing and Thawing
(AASHTO T103)
• Method C
• Same as B except no alcohol is used
• 25 cycles typical
Aggregate Coarse Aggregates 52
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.
