3 aggregate ( highway engineering dr. sherif el-badawy )

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Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Aggregates

HMA Surface

Dr. Sherif El-Badawy Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

http://www.pavementinteractive.org


Aggregate

Definition: • A mass of crushed stone, gravel, sand, …. Etc.

• Composed of individual particles.

• May include clays and silts.

Uses: • Underlying materials for pavements:

• (Base & Subbase).

• Ingredient in PCC and AC


Aggregates

In PCC: • 60% to 75% by volume

• 79% to 85% by weight

In AC: • Over 80% by volume

• 92% to 96% by weight

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Aggregate Sources Natural:

• Gravel pits. • River run deposits. • Rock quarries.

Manufactured:

• Slag waste from steel mills and expanded shall and clays Light weight agg.

• Styrofoam Light weight agg. • Steel slugs and bearings Heavy weight agg. •

• Recycled Materials


Geological Classification Igneous -- cooled from molten magma

• Intrusive • High density granite, cooled slowly below ground

• Extrusive • Basalt (lava) cools rapidly above ground

• Large air pockets may form creating low density cinder &

pumice

Sedimentary • Disintegrated minerals moved by gravity, wind, water, or ice and

deposited as sediment in nearly horizontal layers

• These deposits may eventually be compressed into sandstone,

limestone, shale, conglomerate, gypsum

Metamorphic • Minerals are changed by heat and pressure

• Crystals partially melt & grow into quartzite, marble, slate, etc.

Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Aggregate Terminology

• Aggregate

• Coarse Aggregate (CA)

• Fine Aggregate (FA)

• “Fines” (Mineral Filler: MF)

• Maximum Size

• Nominal Max. Size

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Sieve Designation • Sieve Opening: for sieves greater than ¼ in.

• Number of Openings per Linear Inch.

Sieve Designation Sieve Opening (in.)

75 mm 3 in. 3.0

37.5 mm 1 ½ in. 1.5

19.0 mm ¾ in. .75

12.5 mm ½ in. .5

6.3 mm ¼ in. .25

4.76 mm No. 4 .187

2.36 mm No. 8 .0937

1.18 mm No. 16 .0469

0.6 mm No. 30 .0234

0.3 mm No. 50 .0117

0.15 mm No. 100 .0059

0.074 mm No. 200 .0029

CA

FA

MF


Definition of Gravel and Crushed Stone

Gravel - Natural Particles No. 4

to 3 in. Size and the Particles tend to be Smooth and Rounded.

Crushed Stone - Artificially

Crushed Rock, Boulders, or Large Cobbles. Most or All of the Surfaces are from Crushing, and the Particle Edges tend to be Sharp and Angular.


• Gradation

• Particle Shape and Surface Texture

• Hardness

• Toughness

• Soundness

• Deleterious Materials

Aggregate Characteristics


Maximum and Nom. Max. Aggregate Size

• Nominal Maximum Aggregate Size. The largest sieve that retains some of the aggregate particles but generally not more than 10% by weight.

• Superpave defines nominal maximum aggregate size as "one sieve size larger than the first sieve to retain more than 10 percent of the material“.

• Maximum Aggregate Size: The smallest sieve size through

which 100% of the aggregate sample particles pass.

• Superpave defines the maximum aggregate size as "one sieve larger than the nominal maximum size“.

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Grain Size Distribution Table

sieve #

Sieve size (mm)

% Passing

3/4 ″ 19.00 100

3/8 ″ 9.50 100

4 4.750 95

8 2.360 84

16 1.180 74

30 0.600 53

40 0.425 41

50 0.300 31

100 0.150 14

200 0.075 3.80

Pan --- 0.00

Maximum Aggregate Size = 9.5 mm

Nominal Maximum Aggregate Size =4.75 mm


Grain Size Distribution Curve

• Semi-logarithmic for PCC and Soils

• Fuller Curve for HMA (hot mix asphalt aggregate gradation)

Pi = 100(di/D)n

Pi = % passing a sieve of size di di = sieve size i D = Maximum size of aggregate n = 0.5 (Fuller), n = 0.45 FHWA (0.45

gradation chart)


Semi-logarithmic Grain Size Dis. Curve

0

10

20

30

40

50

60

70

80

90

100

0.0001 0.001 0.01 0.1 1 10

Grain Size (mm)

Percent Pa

ssing

(by we

ight)

Silica Sand

Piedmont Silt

Plastic Kaolin

CLAY SIZE SILT SIZE SAND SIZE GRAVEL

0.075 mm

Fine-Grained Soils Coarse-Grained Soils

Grain Size (mm)


Grain Size Distribution Curve (0.45 Power Gradation Table)

sieve #

Sieve size (d) (mm)

% P of the aggregate

(d)0.45

pi = 100(di/D)0.45

(FHWA Max Density Line), %

3/8 9.5 100 2.754 100(9.5/9.5)0.45 =100

4 4.75 95 2.016 100(4.75/9.5)0.45 =73

8 2.36 84 1.472 53

16 1.18 74 1.077 39

30 0.6 53 0.795 29

40 0.425 41 0.680 25

50 0.3 31 0.582 21

100 0.15 14 0.426 15

200 0.075 3.80 0.312 11.3

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Grain Size Distribution Curve (FHWA 0.45 Power Gradation Chart)

0

10

20

30

40

50

60

70

80

90

100

0.00 0.50 1.00 1.50 2.00 2.50 3.00

Sieve Size (mm)

% P

assin

g

9.5

0

4.7

5

2.3

6

1.1

8

0.6

00

0.0

75

0.1

50

0.3

00

0.4

25

Max Density Line (FHWA 0.45 Power Curve)

d0.45

Aggregate Gradation) Max Size


Gradation Types

Uniform

Well (Dense) graded

Gap Graded

Open Graded


Gradation Types

• Dense (well-graded): a gradation that is near the FHWA’s 0.45 Power Curve for maximum density.

• Gap Graded: a gradation that contains only a small

percentage of aggregate particles in the mid-size range. The curve is flat in the mid-size range.

• Open graded: a gradation that contains only a small percentage of aggregate particles in the small range. This results in more air voids. The curve is near vertical in the mid-size range, and flat and near-zero in the small-size range.

• One Sized: a gradation with the majority of aggregates passing one sieve (vertical line).

• Uniformly Graded. a gradation that contains most of the

particles in a very narrow size range. (almost vertical line).


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Particle Shape

Angular Rounded Flaky

Elongated Flaky & Elongated Mansoura University - Faculty of Engineering – Public Works Engineering Dept.

Particle Shape

Rounded

Angular


Percent Fractured Faces

0% Crushed 2 or More Fractured Faces

Surface Texture

Specs defines minimum percentage of aggregates with fractured faces


Voids and Moisture Absorption

Oven Dry (Bone Dry) Air Dry

SSD Moist

Permeable Voids

Solid

Moisture

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Absorption Oven Dry (Bone dry)

• Zero moisture in voids

Air Dry • Some moisture in voids (equal to atmospheric

humidity)

Saturated-Surface Dry (SSD) • Voids totally filled with moisture but surface of

particles are dry

Moist • Voids are filled and some surface moisture exists

• We want SSD for concrete so that mix water is not absorbed

and is available for workability and hydration

• We want dry aggregate for asphalt

• Some asphalt absorption is good for bonding and locking

• But, this uses a little more asphalt in the mix which is

slightly more costly


Aggregate Specific Gravities


• All matter has mass and occupies space.

• Volumetrics are the relationships between mass and volume.

• Superpave mix design based on aggregate and mixture volumetrics

Volumetrics


Specific Gravity, G

• Ratio of the mass to volume of an object to that of water at the same temperature

Mass Solid

Volume

Mass Water

Volume

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Densities

• Density is the unit weight of a material

lb/ft3 or kg/m3

Unit weight = g w G

gw = 1.000 g/cm3

gw = 1000 kg/m3

gw = 62.4 lb/ft3


Gsb = Mass, oven dry

Bulk Specific Gravity, Dry

Vol of agg, + surface voids

Vol. of water-perm. voids

Surface Voids


Bulk Specific Gravity, SSD

Gs, ssd =

Mass, oven dry agg + mass water

Vol of agg, + surface voids

Vol. of water-perm. voids

Surface Voids


Gsa =

Mass, oven dry agg

Apparent (true) Specific Gravity

Vol of agg

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Specific Gravity Tests for Aggregates

• Two tests are needed:

• Coarse aggregate (retained on the 4.75 mm

sieve).

• Fine aggregate (passing the 4.75 mm sieve)


Coarse Aggregate Specific Gravity





• ASTM C127 • Dry aggregate

• Soak in water for 24 hours

• Decant water

• Use pre-dampened towel to get SSD condition

• Determine mass of SSD aggregate in bucket

• Determine mass under water

• Dry to constant mass

• Determine oven dry mass

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• A = oven dry mass in air

• B = SSD mass

• C = mass under water (submerged mass)

Gsb = A / (B - C)

Gs,SSD = B / (B - C)

Gsa = A / (A - C)

Water absorption, % • Absorption % = [(B - A) / A] * 100

Calculations

Mass (=Volume) of water displaced by the aggregate

1 gm water = 1 cc water


Fine Aggregate Specific Gravity





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• ASTM C128 • Dry aggregate

• Soak in water for 24 hours

• Spread out and dry to SSD

• Add 500 g of SSD aggregate to pycnometer of known volume

• Pre-filled with some water • Add more water and agitate until air bubble have been

removed

• Fill to line and determine the mass of the pycnometer, aggregate and water

• Empty aggregate into pan and dry to constant mass

• Determine oven dry mass



• A = oven dry mass in air • B = mass of pycnometer filled with water • C = mass pycnometer, SSD aggregate and water • S = mass SSD aggregate

Gsb = A / (B + S - C) Gs,SSD = S / (B + S - C) Gsa = A / (B + A - C) Water absorption, %:

• Absorption % = [(S - A) / A] * 100

Calculations

Mass (=Volume) of water displaced by the aggregate

1 gm water = 1 cc water


Adhesion of Aggregate to Bitumen

• Some aggregates have an affinity for water over asphalt (hydrophilic). • These aggregates tend to be acidic and suffer from

stripping after exposure to water.

• Some aggregates have an affinity for asphalt over water (hydrophobic). • These aggregates tend to be basic and do not suffer from

stripping problems.

• Mineralogy and chemical composition of the aggregate are important contributing factors to the stripping problem.

• Additionally, an aggregate’s surface charge when in contact with water will affect its adhesion to asphalt cement and its susceptibility to moisture damage.


Stripping •Loss of bond between aggregates and asphalt binder •Typically begins at the bottom of the HMA layer and progresses upward.

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Raveling

•Loss of bond between aggregates and asphalt binder. •Typically begins at the surface of the HMA layer and progresses downward.

3 aggregate ( highway engineering dr. sherif el-badawy )

Engineering

aggregate particles

aggregate definition

aggregate sources natural

mf maximum size nominal

definition of gravel

crushed rock

largest sieve

clays light weight agg