Aggregates
Aggregates
 Objectives of this Chapter is to Expose Students to the
• Definition of Aggregates
• Sources of Aggregates
• Uses of Aggregates
• Aggregate Properties and Tests to Measure
 Particle Shape and Surface Texture
 Fine Aggregate Angularity
 Soundness
 Cleanliness and Deleterious Materials
 Clay Lumps and Friable Particles
 Gradation
 Specific Gravity
• Fineness Modulus
• Common Problems Associated with Aggregates
Aggregates
Mass of Crushed Stone, Gravel, sand, etc.,
Predominantly Composed of Individual
Particles, but in some cases Including Silts
and Clays.
 Largest
Size 150 mm (6 in.)
 Smallest Size 5 to 10 microns
Aggregates

Natural Sources
• Gravel Pits
• River Run Deposits
• Rock Quarries (Crushed Stones)

Manufactured Sources
• Slag Waste from Steel Mills (Lightweight)
• Steel Slugs and Bearing (Heavyweight)
• Styrofoam Beads (lightweight )
Aggregates

Geological Classification:
• Igneous
• Sedimentary
• Metamorphic

Suitability from a Given Source:
• Physical
• Chemical
• Mechanical and
• Mineralogical Examination
Aggregates
 Extensive
Geologic Information is not Required
for Highway Construction
 Physical
Properties are important rather than
Chemical properties
 Continuous
 Cost
Sampling & Testing is Essential
and Availability Important Consideration
 Challenge
is to Use Local Material in Cost
Effective Manner
Aggregates
 Aggregate
Primarily Uses:
• Underlying Material for Foundations and Pavements
 Stability to a Structure
 Provide Drainage Layer
 Protect from Frost Damage
Aggregates
 Aggregate
Primarily Uses (cont.):
• Ingredient in Portland Cement Concrete
 60 to 70% by Volume or 79 to 85% by Weight
 Filler to Reduce Cement Requirement
 Better Volume Stability than Cement
 Maximizing Improves the Quality and Economy
Aggregates
 Aggregate
Primarily Uses (cont.):
• Ingredient in Asphalt Concrete
 More than 80% by Volume or 92 to 96% by Wt.
 Asphalt Cement Acts as a Binder to Hold Aggregates
Together
 Does not have Enough Strength to Lock Aggregate
Particles Together
 Strength of Asphalt Concrete Depends on
Interparticle Friction and to a Limited Extent on
Binder
Aggregate Properties
 Characteristics
 Further
of Individual and Combined
Described by Physical, Chemical
and Mechanical Characteristics
 Table
5.1
Angular
Flaky
Rounded
Elongated
Flaky and
Elongated
Relative Importance of Basic
Aggregate Properties
Physical
PCC
AC
Base
Particle Shape (angularity)
M
V
V
Particle Size -Distribution
M
V
M
Unit wt. , Void
V
M
M
Soundness
V
M
M
Relative Importance of Basic
Aggregate Properties
Chemical
PCC
AC
Base
Surface Charge
U
V
U
Reactivity to Chemicals
V
U
U
Volume Stability
V
M
M
Coatings
M
M
U
Relative Importance of Basic
Aggregate Properties
Mechanical
PCC
AC
Base
Compressive Strength
M
U
U
Toughness
M
M
U
Abrasion Resistance
M
M
M
Mass Stability
U
V
V
Aggregate Properties
 Particle
Shape and Surface Texture:
• Shape of Individual Particle  Packing
• Shape of Individual Particle  Mobility
• Two Considerations in Shape of Material:
 Angularity
 Flakiness
Crushing
River Gravel
Partially Crushed
River Gravel
Aggregate Properties
 Particle
Shape and Surface Texture:
• Crushing Rock Produces Angular Particle with
Sharp Corners
• Weathering Creates Subangular
• Transportation Makes Rounded
• Angular Particle Difficult to Work Than
Rounded
Aggregate Properties
 Particle
Shape and Surface Texture:
• Texture Affects Compaction and Bonding
• Rough More Difficult to Compact than Smooth
• Rough Bonds Better than Smooth
• Rounded and Smooth Aggregates for PCC
• Rough and Angular for AC
Surface Texture
Coarse Aggregate
Percent
by weight of aggregates larger
than 4.75 mm with one or more crushed
faces
A
fractured face is any fractured
surface that occupies more than 25% of
the area of the outline of the aggregate
particle visible in that orientation.
Percent Crushed
Fragments in Gravels
Quarried materials always 100% crushed
 Minimum values depended upon traffic
level and layer (lift)
 Defined as % mass with one or more
fractured faces

Percent Crushed Fragments in
Gravels
0% Crushed
100% with 2 or More
Crushed Faces
Coarse Aggregate Angularity
Criteria
Traffic
Depth from Surface
Millions of ESALs < 100 mm
> 100
mm
< 0.3
--/-55/-<1
--/-65/-<3
50/-75/-< 10
60/-85/80
< 30
80/75
95/90
< 100
95/90
100/100
100/100
100/100
 100
First number denotes % with one or more fractured faces
Second number denotes % with two or more fractured faces
Fine Aggregate Angularity
 Fine
aggregate at a specified gradation is
allowed to flow freely into a 100 cm3
cylinder.
 Knowing
the specific gravity of the
aggregate, the voids between aggregate
particles can be determined
 The
more angular the aggregate, the higher
the void content
Fine Aggregate Angularity
Natural sands:
typically < 45
Manufactured sands:
typically > 42
Fine Aggregate Angularity Criteria
Traffic
Depth from Surface
Millions of ESALs < 100 mm
> 100mm
< 0.3
<1
<3
< 10
< 30
< 100
 100
-40
40
45
45
45
45
--40
40
40
45
45
Soundness

Estimates resistance to weathering .

Simulates freeze/thaw action by successively
wetting and drying aggregate in sodium
sulfate or magnesium sulfate solution
• One immersion and drying is considered
one cycle

Result is total percent loss over various sieve
intervals for a prescribed number of cycles
• Max. loss values typically range from 10
to 20%per 5 cycles
SOUNDNESS
SULFATE SOUNDNESS
Sodium or magnesium is used
 Sample submerged for 18 hrs in solution @
70 F
 Removed and dried @ 230 F
 Process is repeated four or five times.

Soundness by Freeze–Thaw
Rapid Freeze Thaw Process
 Method A involves Freeze-Thaw
in Water
Method B involves Freezing in Air
and Thawing in Water
 ASTM C666

Soundness
Cleanliness and Deleterious
Materials
• Sand equivalent test
• Clay lumps and friable particles
• Plasticity test
Sand Equivalent Test
* ASHTO T176, ASTM D2419
- Used to estimate the relative proportions
of fine agg. and clay-like or plastic fines
and dust.
SE =
Sand Reading
Clay Reading
*100
Flocculating
Solution
Clay Reading
Sand
Reading
Suspended
Clay
Sedimented
Aggregate
Bottle of Solution on Shelf
Above Top of Cylinder
Hose and
Irrigation Tube
Measurement Rod
Marker on Measurement Rod
Top of Suspended Material
Top of Sand Layer
Clay Content Criteria
Traffic
Millions of ESALs
< 0.3
<1
<3
< 10
< 30
< 100
 100
Sand Equivalent
Minimum, Percent
40
40
40
45
45
50
50
Clay Lumps and Friable
Particles
ASTM C 142
Dries a given mass of agg., then soaks for 24
hr., and each particle is rubbed. A washed
sieve is then performed over several screens,
the aggregate dried, and the percent loss is
reported as the % clay or friable particles.
Sampling
• Why Sampling Is Important
– To evaluate the potential quality of a proposed
aggregate source.
• Does new source meet aggregate
specifications?
– To determine compliance with project
specification requirements.
• Do current aggregates meet specifications?
Sampling from Stockpile
Sampling from Fine
Aggregate Stockpile
Sampling from Conveyor
Aggregate Properties
Gradation
Types of Gradations
* Uniformly graded
- Few points of contact
- Poor interlock (shape dependent)
- High permeability
* Well graded
- Good interlock
- Low permeability
* Gap graded
- Only limited sizes
- Good interlock
- Low permeability
Aggregate Gradation
• Use 0.45 Power Gradation Chart
• Blend Size Definitions
– maximum size
– nominal maximum size
• Gradation Limits
– control points
– restricted zone
0.45 Power Grading Chart
Percent Passing
100
80
60
Example:
40
4.75 mm sieve plots at (4.75)0.45 = 2.02
20
0
0
1
2
3
4
Sieve Size (mm) Raised to 0.45 Power
0.45 Power Grading Chart
Percent Passing
100
80
max
size
60
40
20
maximum density line
0
0 .075 .3 .6 1.18 2.36
4.75
9.5 12.5
19.0
Sieve Size (mm) Raised to 0.45 Power
100
100
90
72
65
48
36
22
15
9
4
Aggregate Size Definitions
• Nominal Maximum Aggregate
Size
– one size larger than the first sieve
to retain more than 10%
• Maximum Aggregate Size
– one size larger than nominal
maximum size
100
99
89
72
65
48
36
22
15
9
4
Percent Passing
100
max density line
restricted zone
control point
0
.075
.3
2.36
4.75
9.5
nom
max
size
max
size
12.5
Sieve Size (mm) Raised to 0.45 Power
19.0
Superpave Aggregate Gradation
Percent Passing
100
Design Aggregate Structure
0
.075 .3
2.36
12.5
19.0
Sieve Size (mm) Raised to 0.45 Power
Superpave Mix Size
Designations
Superpave
Designation
37.5 mm
25 mm
19 mm
12.5 mm
9.5 mm
Nom Max Size
(mm)
37.5
25
19
12.5
9.5
Max Size
(mm)
50
37.5
25
19
12.5
Gradations
* Considerations:
- Max. size < 1/2 AC lift thickness
- Larger max size
+ Increases strength
+ Improves skid resistance
+ Increases volume and surface area of agg
which decreases required AC content
+ Improves rut resistance
+ Increases problem with segregation of particles
- Smaller max size
+ Reduces segregation
+ Reduces road noise
+ Decreases tire wear
Target Gradation
• Acceptable gradation band specified
• Mix design selects a job mix formula (JMF) which falls
within band and meets design criteria
• Superpave
– 5 nominal sizes (37.5, 25, 19, 12.5, and 9.5 mm)
– Four sieve sizes used to set upper and lower limits
– Staying out of the restricted zone in suggested to minimize
problems with natural sands
Blending Stockpiles
• Basic formula for combining stockpiles to
achieve a target gradation is:
p = Aa + Bb + Cc + ….
where:
p = percent of material passing given sieve size
A, B, C, .. = percent passing given sieve for each agg.
a, b, c, … = decimal fraction of A, B, C, … to be used
Blending Stockpiles
• Plot individual gradations
• Plot specification limits
• Can be used for initial assessment
– Can blend be made from available
materials?
– Identification of critical sieves
– Est. trial proportions
All possible combinations fall between A and B
Percent Passing, %
100
90
80
70
60
50
40
30
20
10
0
Gradation B
Control points for
12. 5 nominal max. size
Gradation A
0.075 0.3
1 .18
4.75
Sieve Size, mm
9.5
12.5
19
No poss. combination of A and B will meet spec.
Percent Passing, %
100
90
80
70
60
50
40
30
20
10
0
Gradation B
Gradation A
Control points for
12. 5 nominal max. size
0.075 0.3
1 .18
4.75
Sieve Size, mm
9.5
12.5
19
All poss. combinations pass through cross-over point
Blends containing more A than B will be closer to A
Percent Passing, %
Gradation A
100
90
80
70
60
50
40
30
20
10
0
Gradation B
Control points for
12. 5 nominal max. size
0.075 0.3
1 .18
4.75
Sieve Size, mm
9.5
12.5
19
Trial and Error Steps
• Select critical sieves in blend
• Determine initial proportions which will
meet critical sieves
• Check calc. blend against specification
• Adjust if necessary and repeat above
steps
Blended Aggregate Specific
Gravities
• Once the percentages of the stockpiles
have been established, the combined
aggregate specific gravities can also be
calculated
Combined Specific Gravities
1
G=
P1
+
100 G1
P2 + ……. Pn
100 G2
100 Gn
Blending of Aggregates
• Reasons for Blending
– Obtain desirable gradation
– Single natural or quarried material not enough
– Economical to combine natural and process
materials
Blending of Aggregates
• Numerical Method
– Trial and Error
– Basic Formula
Blending of Aggregates
· P = Aa + Bb + Cc + ….
– Where:
• P = % of material passing a given sieve for
the blended aggregates A, B, C, …
• A, B, C, … = % material passing a given
sieve
for each aggregate A, B, C, …..
• a, b, c, …. = Proportions (decimal fractions)
of aggregates A, B, C, … to be
used in
Blend
Blending of Aggregates
Material
Agg. #1
Agg. #2
Blend Target
% Used
U.S. Sieve
%
Passing
3/8 “
No. 4
No. 8
No. 16
No. 30
No. 50
No. 100
100
90
30
7
3
1
0
100
100
100
88
47
32
24
No. 200
0
10
%
Batch
%
Passing
%
Batch
Blending of Aggregates
Material
Agg. #1
Agg. #2
% Used
50 %
50 %
U.S. Sieve
%
Passing
%
Batch
%
Passing
3/8 “
No. 4
No. 8
No. 16
No. 30
No. 50
No. 100
100
90
30
7
3
1
0
50
45
15
3.5
1.5
0.5
0
100
100
100
88
47
32
24
No. 200
0
0
First Try
(remember trial & error)
Blend Target
%
Batch
100 * 0.5 = 50
90 * 0.5 = 45
30 * 0.5 = 15
7 * 0.5 = 3.5
3 * 0.5 = 1.5
1 * 0.5 = 0.5
0 * 0.5 = 50
10 0
* 0.5 = 0
100
80 - 100
65 - 100
40 - 80
20 - 65
7 - 40
3 - 20
2 - 10
Blending of Aggregates
Material
Agg. #1
Agg. #2
% Used
50 %
50 %
Blend Target
U.S. Sieve
%
Passing
%
Batch
%
Passing
%
Batch
3/8 “
No. 4
No. 8
No. 16
No. 30
No. 50
No. 100
100
90
30
7
3
1
0
50
45
15
3.5
1.5
0.5
0
100
100
100
88
47
32
24
50
50
50
44
23.5
16
12
100
95
65
47.5
25
16.5
12
100
80 - 100
65 - 100
40 - 80
20 - 65
7 - 40
3 - 20
No. 200
0
0
10
5
5
2 - 10
Blending of Aggregates
Material
Agg. #1
Agg. #2
% Used
50 %
50 %
U.S. Sieve
%
Passing
%
Batch
3/8 “
No. 4
No. 8
No. 16
No. 30
No. 50
No. 100
100
90
30
7
3
1
0
50
45
15
3.5
1.5
0.5
0
No. 200
0
0
Blend Target
%
%
Passing Batch
100Let’s Try
50
100 and get
50
a little closer
100
50
to
88the middle
44 of
the target values.
47
23.5
32
16
24
12
10
5
100
95
65
47.5
25
16.5
12
100
80 - 100
65 - 100
40 - 80
20 - 65
7 - 40
3 - 20
5
2 - 10
Blending of Aggregates
Material
Agg. #1
Agg. #2
% Used
30 %
70 %
Blend Target
U.S. Sieve
%
Passing
%
Batch
%
Passing
%
Batch
3/8 “
No. 4
No. 8
No. 16
No. 30
No. 50
No. 100
100
90
30
7
3
1
0
30
27
9
2.1
0.9
0.3
0
100
100
100
88
47
32
24
70
70
70
61.6
32.9
22.4
16.8
100
97
79
63.7
33.8
22.7
16.8
100
80 - 100
65 - 100
40 - 80
20 - 65
7 - 40
3 - 20
No. 200
0
0
10
7
7
2 - 10
Questions - ?