Aggregates Fine Aggregates 1

Fine Aggregates

Shape, Angularity, and Surface Texture

Cleanliness

Properties of Minus 0.075 mm (#200)

Senior/GraduateHMA Course

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Fine Aggregate Shape, Angularity and Texture

• General Concepts

• Particle Index

• Fine Aggregate Angularity

• Uncompacted Voids

• Image Analysis

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General Concepts

• Direct measurements

• Visual

• Indirect measurements

• Packing volume

• Flow

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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

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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

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Background (continued)

• Indirect methods

• Direct shear test

• Direct shear box used to determine angle of internal friction under different normal stress conditions

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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

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Fine Aggregate Angularity(ASTM C1252 or ASSHTO 304)

• Void volume indicator of shape, surface texture

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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

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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

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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

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Advanced Topics on Shape and Texture

• Image Analysis

• Microscopic Evaluation

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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

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Plastic Fines in Fine Aggregate

• Mineral Finer than 0.075 mm in Mineral Aggregate by Washing

• Sand Equivalent

• Plasticity Index

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Minus 0.075mm by Washing (ASTM C117)

• Only measures quantity not quality of minus 0.075 mm (#200).

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Clay Content

• Sand equivalent

• Plasticity index

• Methylene blue

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Plasticity Index

• Atterberg limits

• Used to determine

• Liquid limit

• Plastic limit

• Plasticity index

• LL - PL

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Plasticity Index

• Non-plastic for highway construction

• PI < 4 to 6

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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

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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

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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

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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

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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

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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)

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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

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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

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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

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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

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P200 and Sand Equivalent

0

20

40

60

80

100

Per

cen

t, %

WashedSands

CrushedGravels

CrushedStones

Pit RunSands

SE% P200, %

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Methylene Blue

• ISSA recommended method

• Quantifies amount

• Harmful clays (smectite)

• Organic matter

• Iron hydroxides

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Methylene Blue

• Step 1: 10 grams of Minus -0.075 dispersed in 30 grams distilled water

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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

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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

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Methylene Blue

• MB value is reported as the mg of methylene blue per gram of fine aggregate

• Example: MB value = 5.3 mg/g

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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

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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

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Properties of Minus 0.075 mm

• Traditional

• Size distribution by hydrometer

• New

• Laser evaluation

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Hydrometer Analysis

Add soil, shake

Let stand and test periodically

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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

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Laser Devices

• Step 1: sample preparation

• Step 2: Charge laser unit

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Laser Devices

• Step 3: Set unit up to run

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Laser Devices

Step 4: Run test and collect data on computer

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Properties of Minus 0.075 mm

Advanced Topics

• Rigden Voids

• German Filler

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Rigden Voids

• Void content regulated by:

• Shape

• Size

• Distribution (gradation)

• Surface structure

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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

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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

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QUESTIONS?