02-Aggregate ( Highway and Airport Engineering Dr. Sherif El-Badawy )

1. 1
Aggregates
HMA Surface
Dr. Sherif El-Badawy
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

2. 2
Aggregates
In PCC:
• 60% to 75% by volume
• 79% to 85% by weight
In AC:
• Over 80% by volume
• 92% to 96% by weight
Aggregate Sources
Natural:
• Gravel pits.
• River run deposits.
• Rock quarries.
Manufactured:
• Slag waste from steel mills and expanded shale
and clays  Light weight agg.
• Styrofoam  Light weight agg.
• Steel slugs and steel ball bearings  Heavy
weight agg.
• Recycled Materials

3. 3
Gravel Pit in Germany
(From Wikipedia)
Quarry
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.

4. 4
Aggregate Terminology
• Aggregate
• Coarse Aggregate (CA)
• Fine Aggregate (FA)
• “Fines” (Mineral Filler: MF)
• Maximum Size
• Nominal Max. Size

5. 5
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
Mineral Filler
(Source: AASHTO M17)

6. 6
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

7. 7
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“.
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
Superpave defines nominal maximum
aggregate size as "one sieve size
larger than the first sieve to retain
more than 10 percent of the
material“.

8. 8
Maximum Size
• Maximum size can affect both AC and
PCC in several ways.
Grain Size Distribution Curve
• Semi-logarithmic  PCC and Soils
• Fuller Curve  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)

9. 9
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)
PercentPassing(byweight)
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

10. 10
(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)
%Passing
9.50
4.75
2.36
1.18
0.600
0.075
0.150
0.300
0.425
Max Density Line (FHWA
0.45 Power Curve)
d0.45
Aggregate Gradation) Max Size
Source: www.pavementinteractive.org

11. 11
Source: www.pavementinteractive.org
Gradation Types
Uniform
(poor)
Well (Dense)
graded
Gap Graded
Open Graded

12. 12
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).

13. 13
Particle Shape
Angular Rounded Flaky
Elongated Flaky & Elongated

14. 14
Particle Shape
Rounded
Angular

15. 15
Percent Fractured Faces
0% Crushed 2 or More
Fractured Faces
Surface Texture
Specs defines minimum percentage of
aggregates with fractured faces
Uncompacted Voids in Coarse Aggregate
(Coarse Aggregate Angularity)

16. 16
Uncompacted Voids in Coarse Aggregate
Uncompacted Voids in Coarse Aggregate

17. 17
Soundness and Durability
• Soundness or durability is the
resistance to weathering
(freeze/thaw).
• Most common methods
• Sodium or magnesium sulfate
• AASHTO T104
Soundness Test Method
• 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
• Conduct sieve analysis to determine change in gradation
due to weathering
Before After

18. 18
Deleterious Materials in Aggregates
Voids and Moisture Absorption
Oven Dry (Bone Dry)
Air Dry
SSD Moist
Permeable
Voids
Solid
Moisture

19. 19
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

20. 20
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.

21. 21
Stripping
43
Cairo – Alexandria Road, 2012

22. 22
Raveling
•Loss of bond between aggregates and asphalt binder.
•Typically begins at the surface of the HMA layer and progresses
downward.
Elsalwa Road,
KSA, 2007
Desirable Properties of Rocks for HMA
Source:Pavementinteractive