Aggregates Fine Aggregates 1
Fine Aggregates
Shape, Angularity, and Surface Texture
Cleanliness
Properties of Minus 0.075 mm (#200)
Senior/GraduateHMA Course
2Aggregates Fine Aggregates
Fine Aggregate Shape, Angularity and Texture
• General Concepts
• Particle Index
• Fine Aggregate Angularity
• Uncompacted Voids
• Image Analysis
3Aggregates Fine Aggregates
General Concepts
• Direct measurements
• Visual
• Indirect measurements
• Packing volume
• Flow
4Aggregates Fine Aggregates
Background• Direct Measurements
• US Corps of Engineers
• Flat and elongated particles in fine agg.
• Microscope evaluation
• length:width = 1:3
• Laughlin Method
• Developed for PCC
• Enlarged photographs
• Radii of curvature of particles and inscribed circle
• Roundness of particles then computed
5Aggregates Fine Aggregates
Background (continued)
• Indirect methods
• Ishai and Tons Method
• Relates flow test to geometric irregularities of particles
• Size of orifice depends on agg. size
• Specific rugosity by packing volume
• Flow test used as direct measurement of packing specific gravity of one-sized particles
6Aggregates Fine Aggregates
Background (continued)
• Indirect methods
• Direct shear test
• Direct shear box used to determine angle of internal friction under different normal stress conditions
7Aggregates Fine Aggregates
Particle Index ASTM D3398
• Vol. of voids between packed, uniform-size aggregate particles indicate combined effect of shape, angularity and surface texture
• 76, 51, and 38 mm diameter molds
• each of three layers tamped 50 mm above surface
• 10 blows/layer
• 50 blows/layer
• Ia = 1.25 V10 - 0.25 V50 - 32.0
• Particle index increases with angularity
8Aggregates Fine Aggregates
Fine Aggregate Angularity(ASTM C1252 or ASSHTO 304)
• Void volume indicator of shape, surface texture
9Aggregates Fine Aggregates
Fine Aggregate Angularity(ASTM C1252)
• Uncompacted voids in fine aggregate
• Method A (specific gradation)
• 44 g of 2.36 - 1.18 mm
• 57 g of 1.18 - 0.60 mm
• 72 g of 0.60 - 0.30 mm
• 17 g of 0.3 - 0.15 mm
• Method B
• Individual sieve sizes
• Method C
• As-received
10Aggregates Fine Aggregates
Fine Aggregate Angularity(ASTM C1252)
Method Type Agg. 95% Confidence Limits
A Natural 39.5 - 45.5Manufact. 42.8 - 53.4
B Natural 43.0 - 49.2Manufact. 46.8 - 57.0
Examples of Test Results
11Aggregates Fine Aggregates
Uncompacted Voids Results for Alabama Pit Run Sands
(Method A)
46.6*
46.443.6
44.946.1
47.2
46.1
44.1
40.1
43.2
46.0Unexpected state-wide variation
Problems with aggregates in south east part of state
May be due to other factors that shape and angularity
12Aggregates Fine Aggregates
Advanced Topics on Shape and Texture
• Image Analysis
• Microscopic Evaluation
13Aggregates Fine Aggregates
Image Analysis
• University of Arkansas
• Agg spread on glass plate
• High resolution video camera
• Modern digital imaging hardware, analysis techniques and computer analysis used
• Uses two parameters
• EAPP
• Roughness Index
14Aggregates Fine Aggregates
Plastic Fines in Fine Aggregate
• Mineral Finer than 0.075 mm in Mineral Aggregate by Washing
• Sand Equivalent
• Plasticity Index
15Aggregates Fine Aggregates
Minus 0.075mm by Washing (ASTM C117)
• Only measures quantity not quality of minus 0.075 mm (#200).
16Aggregates Fine Aggregates
Clay Content
• Sand equivalent
• Plasticity index
• Methylene blue
17Aggregates Fine Aggregates
Plasticity Index
• Atterberg limits
• Used to determine
• Liquid limit
• Plastic limit
• Plasticity index
• LL - PL
18Aggregates Fine Aggregates
Plasticity Index
• Non-plastic for highway construction
• PI < 4 to 6
19Aggregates Fine Aggregates
Clay Content (ASTM D2419)
• Percentage of clay in material finer than 4.75 mm sieve ASTM D2419 or AASHTO T 176
• Sand equivalent test method
20Aggregates Fine Aggregates
Clay Content (ASTM D2419)
• Step 1: Obtain a known volume of fine aggregate; if the sample is not dry, dry it to a constant mass before testing
• Step 2:
• Prepare working solution
• Add sample to cylinder
• Use wand to add solution to cylinder
• Step 3: Stopper the cylinder and agitate
21Aggregates Fine Aggregates
Bottle of Solution on Shelf Above Top of Cylinder
Hose and Irrigation Tube
Measurement Rod
• Step 4: Irrigate the sample to flush the fines into the solution
22Aggregates Fine Aggregates
Clay Content (ASTM D2419)
Marker on Measurement Rod
Top of Suspended Material
Top of Sand Layer
• Step 5: After 20 minutes, determine the height of the sand and suspended clay particles
23Aggregates Fine Aggregates
Clay Content (ASTM D2419)
Sedimented Agg.
Flocculating Solution
Suspended ClayClay Reading
Sand Reading
SE = Sand Reading Clay Reading *100
• Step 6: Calculate the sand equivalent
24Aggregates Fine Aggregates
Clay Content - Background
• Francis Hveem of Caltrans
• 1952
• Rapid field test to evaluate the effective volume of clay
• Measurements based on volume rather than weight (or mass)
25Aggregates Fine Aggregates
Development of Solution
• Strength of flocculating solution selected so that 5% of bentonite would give same SE reading as 25% of kaolinite after 20 minutes
• Not critical for natural soils
• Working sol’n of 0.05N CaCl2 adopted
• Small amount of glycerin for stabilizing
• Formaldehyde to prevent mold formation
26Aggregates Fine Aggregates
Suggested Limits (1952)
• Bituminous mixtures
• Original limit was 60
• Secondary limit of 50 proposed for slightly greater tolerance
• Bases
• Not less than 30
• PCC
• Minimum of 80 to 85
27Aggregates Fine Aggregates
Effect of Dust on SE Values
0
20
40
60
80
100
0 20 40 60 80 100
Percent Clay or Dust Mixed with Ottowa Sand, %
San
d E
quiv
alen
t, %
Bentonite
Kaolinite
Quartz Dust #1
Limestone Dust
Quartz Dust #2
28Aggregates Fine Aggregates
Effect of Percent Passing 0.075 mm Sieve
0
20
40
60
80
100
0 5 10 15
Percent Passing No. 200
Sand
Equ
ival
ent,
%
Crusher Dust
Natural Dust
Sand Equivalent
29Aggregates Fine Aggregates
P200 and Sand Equivalent
0
20
40
60
80
100
Per
cen
t, %
WashedSands
CrushedGravels
CrushedStones
Pit RunSands
SE% P200, %
30Aggregates Fine Aggregates
Methylene Blue
• ISSA recommended method
• Quantifies amount
• Harmful clays (smectite)
• Organic matter
• Iron hydroxides
31Aggregates Fine Aggregates
Methylene Blue
• Step 1: 10 grams of Minus -0.075 dispersed in 30 grams distilled water
32Aggregates Fine Aggregates
Methylene Blue• Step 2: 1 gram methylene blue in
distilled water and enough distilled water to make 200 ml of solution
• Step 3: Titrated in 0.5 ml aliquotes from burette• Fines solution stirred
33Aggregates Fine Aggregates
Methylene Blue
• Step 4: After 1 minute of stirring, drop removed with glass rod and placed on filter
• Step 5: End point is reached when a permanent light blue “halo” is observed in the clear ring
34Aggregates Fine Aggregates
Methylene Blue
• MB value is reported as the mg of methylene blue per gram of fine aggregate
• Example: MB value = 5.3 mg/g
35Aggregates Fine Aggregates
11.7
11.616.9
4.7*13.9
18.4
11.0
7.0*
2.0
7.3
1.1
Methylene Blue Results for Alabama Pit Run Sands
High MB for pit run sands indicate presence of clay
minerals
High MB are found in south ease, where potential for accumulation of smectite
greatest
36Aggregates Fine Aggregates
Methylene Blue
• General guidelines for methylene blue values
Methylene Blue Expected HMA Performancemg/g
5 - 6 Excellent 10 – 12 Marginally Acceptable 16 – 18 Problems or possible failure 20+ Failure
37Aggregates Fine Aggregates
Properties of Minus 0.075 mm
• Traditional
• Size distribution by hydrometer
• New
• Laser evaluation
38Aggregates Fine Aggregates
Hydrometer Analysis
Add soil, shake
Let stand and test periodically
39Aggregates Fine Aggregates
Hydrometer Analysis
• Examples of HMA specifications
• Michigan
• Not more than 60% nor less than 10% passing the 10 m
• Minnesota
Particle Size % Finer 20 m 35 - 100
5 m 10 - 40 1 m 1 - 25
40Aggregates Fine Aggregates
Laser Devices
• Step 1: sample preparation
• Step 2: Charge laser unit
41Aggregates Fine Aggregates
Laser Devices
• Step 3: Set unit up to run
42Aggregates Fine Aggregates
Laser Devices
Step 4: Run test and collect data on computer
43Aggregates Fine Aggregates
Properties of Minus 0.075 mm
Advanced Topics
• Rigden Voids
• German Filler
44Aggregates Fine Aggregates
Rigden Voids
• Void content regulated by:
• Shape
• Size
• Distribution (gradation)
• Surface structure
45Aggregates Fine Aggregates
Rigden Voids
Binder
Dust Solids
Binder
Dust Solids
Free Binder(asphalt)
Fixed Binder(asphalt)
Vs
Vt
Vdb
Vaf
Vdv = (Vdb - Vs) / Vdb
Vdb = (Vdb) / (Va + Vds)
Vaf = 1 - Vdb
Va
46Aggregates Fine Aggregates
German Filler
• Measures the amount of mineral filler needed to absorb 15 grams of hydraulic oil
• Steps:• Combine 15 g oil and 45 g filler, mix
• Form ball, if it holds shape, add 5 g more of filler
• Repeat until mixture loses cohesion• At this point, all of oil is fixed in voids of No.
200• Report amount of No. 200 added
• Related to Rigden voids
47Aggregates Fine Aggregates
QUESTIONS?
Top Related