AGGREGATES.pptx

 Materials Engineers
◦ Responsible for the selection, specification, and
quality control of materials to be used in a job
 Classes of Criteria (Ashby and Jones 2005)
◦ Economic factors
◦ Mechanical Properties
◦ Non-mechanical properties
◦ Production/construction considerations
◦ Aesthetic properties
◦ Environmental quality

 Economic Factors
◦ Availability and cost of raw materials
◦ Manufacturing costs
◦ Transportation
◦ Placing
◦ Maintenance

 Mechanical Properties
◦ The mechanical behavior of materials is the
response of the material to external loads
◦ The specific response of a material depends on its
properties, the magnitude and type of loads, and
the geometry of the element
◦ Loading conditions
 Static loading
 Dynamic loading – generate shock or vibration and can
be periodic, random, or transient

◦ Stress-Strain Relations
 Materials deform in response to loads or forces
 Hooke’s Law
◦ Elastic Behavior
 If a material exhibits true elastic behavior, it must have
an instantaneous response (deformation) to load, and
the material must return to its original shape when the
load is removed
 Young’s modulus of elasticity
 Poisson’s Ratio

 For materials that do not display linear behavior, there
are four options in finding the Young’s modulus of
elasticity
 Initial tangent modulus – slope of the tangent of the
stress-strain curve at the origin
 Tangent modulus – slope of the tangent at a point on the
stress-strain curve
 Secant modulus – slope of a chord drawn between the
origin and an arbitrary point on the stress-strain curve
 Chord modulus – is the slope of a chord drawn between
two points on the stress-strain curve

 The selection on which modulus to use for a nonlinear
material depends on the strain level at which the
material typically is used
 When determining the tangent, secant, or chord
modulus, the stress or strain levels must be defined
 Several factors affect the modulus, such as the curing
level and proportions of the components of concrete
or the direction of loading relative to the grain of wood

◦ Elastoplastic Behavior
 For some materials, as the stress applied on the
specimen is increased, the strain will proportionally
increase up to a point
 After this point, the strain will increase with little
additional stress – the material exhibits linear elastic
behavior followed by plastic response
 Plastic behavior indicates permanent deformation of
the specimen
 Elastic response – the atomic bonds stretch
 Plastic response – the atoms slip relative to each other

 Strain or work hardening – process of loading and
reloading the material to increase the stress required
to cause plastic deformation
 Strain hardening is beneficial in some cases in that it
allows more stress to be applied without permanent
deformation
 In the production of cold formed steel framing
members, the permanent deformation used in the
production process can double the yield strength of
the member relative to the original strength of the
steel

 Materials that do not undergo plastic deformation
prior to failure, such as concrete, are said to be brittle
 Materials that display appreciable plastic deformation
such as mild steel, are ductile
 Three concepts of stress-strain behavior
 Proportional limit – transition point between linear and
nonlinear behavior
 Elastic limit – transition between elastic and plastic
behavior

 Methods of identifying the elastic limit
 Offset method – a specified offset is measured on the
abscissa, and a line with a slope equal to the initial
tangent modulus is drawn through this point to locate the
offset yield stress
 Extension method – the extension yield stress is located
where a vertical projection, at a specified strain level,
intersects the stress-strain curve

◦ Viscoelastic Behavior
 Materials exhibit both viscous and elastic responses,
i.e. asphalt and plastic
 Time-dependent response
 Viscoelastic materials have a delayed response to load
application – deformation lags the load
 The amount of time delayed of the deformation depends
on the material characteristics and the temperature
 The delay in the response of viscoelastic materials can be
simulated by the movement of the Slinky toy in the hand
of a child
 Mechanisms associated with time-dependent deformation
– creep and viscous flow

◦ Temperature and Time Effects
 The mechanical behavior of all materials is affected by
temperature
 Ferrous metals, including steel, demonstrate a change
from ductile to brittle behavior as the temperature
drops below transition temperature
 This change from ductile to brittle behavior greatly
reduces the toughness of the material
 Viscoelastic materials are not only affected by the
duration of the load, but also by the rate of load
application

◦ Work and Energy
 Modulus of resilience – area under the elastic portion
of the stress-strain curve
 Toughness – amount of energy required to fracture a
specimen
◦ Failure and Safety
 Failure occurs when a member or a structure ceases to
perform the function for which it was designed
 Modes of failure
 Fracture- brittle material typically fractures suddenly;
ductile materials fracture due to excessive plastic
deformation

◦ Failure and Safety
 Modes of failure
 Fatigue – repeated stresses cause material to fail;
endurance limit
 General yielding – failure in ductile material
 Buckling – long and slender members subjected to axial
compression
 Excessive deformation – (elastic or plastic)

 Non-mechanical Properties
◦ The properties of the material, other load response,
that affect selection, use and performance
◦ Density and Unit Weight
 Specific gravity
◦ Thermal expansion
 Coefficient of thermal expansion
◦ Surface Characteristics
 Corrosion and degradation
 Abrasion and wear resistance
 Surface texture

 Production and Construction
◦ Production considerations include
 Availability of the material
 Ability to fabricate the material into desired shapes
and required specifications
◦ Construction considerations
 Factors that relate to the ability to fabricate and erect
the structure on site – availability of trained work force
and specialized equipment

 Aesthetic Characteristics
◦ Refers to the appearance of the material
◦ A mix of artistic and technical design skills makes
the project acceptable to the community
◦ Engineers must understand that there are many
factors beyond the technical needs that must be
considered when selecting materials and designing
public projects

 Sustainable Design
◦ Sustainable design is the philosophy of designing
physical objects, the built environment and services
to comply with the principles of economic, social,
and ecological sustainability
◦ Green Building Council – Leadership in Environment
and Energy Design (LEED) building rating system
◦ Rating Areas of LEED
 Sustainable sites  indoor environmental
 Water efficiency quality
 Energy and atmosphere  innovation in design
 Materials and resources  regional priority

 Sustainable Design
◦ Materials and Resource Area
 Storage and collection of recyclables
 Building reuse – maintain existing walls, floors and
roof, interior walls and non-structural elements
 Construction waste management
 Materials reuse
 Recycled content
 Regional materials
 Rapidly renewed materials
 Certified wood

 Material Variability
◦ Engineering materials are inherently variable
◦ Three types of variance
 Inherent variability of the material
 Variance caused by the sampling method
 Variance associated with the way the tests are
conducted
◦ Error and blunder
◦ Precision and accuracy
◦ Bias – systematic error between a test value and the
true value

 Mass of crushed stone, gravel, sand, etc.,
predominantly composed of individual
particles, but in some cases including clays
and silts
 Largest particle size in aggregates may have a
diameter as large as 150 mm (6”) and the
smallest particle can be as fine as 5 to 10
micron

 Fine aggregate or sand
◦Not larger than 4.75 mm (3/16”)
in size (passing No. 4 ASTM
sieve)
 Coarse aggregate
◦At least 4.75 mm (3/16” ) in size

 Maximum aggregate size
◦ The smallest sieve through which
100% of the aggregates pass
 Nominal maximum aggregate
size
◦The largest sieve that retains not
more than 10% of the aggregates

 Maximum aggregate size
◦ One sieve size larger than the
nominal maximum aggregate size
 Nominal maximum aggregate
size
◦One sieve size larger than the
first sieve to retain more than
10% of the aggregates

 Natural sources
◦ Gravel pits
◦ River-run deposits
◦ Rock quarries
◦ Lightweight aggregates
 Pumice, scoria, volcanic cinders, tuff and diatomite
 Manufactured aggregates
◦ Slag waste from iron and steel mills
◦ Expanded shale and clays
◦ Steel slag and bearings
◦ Styrofoam beads

 Civil Engineers select aggregates for their
ability to meet specific requirements rather
than their geologic history
 Due to quantity of aggregates required for a
typical civil engineering application, the cost
and availability of the aggregates are
important when selecting an aggregate
source

 One of the primary challenges facing the
materials engineer on a project is how to use
the locally available material in the most
cost-effective manner
 Potential aggregate sources are usually
evaluated for quality of the larger pieces, the
nature and amount of fine materials, and the
gradation of the aggregates
 Price and availability

 Underlying material for foundations and
pavements
◦ Add stability to a structure
◦ Provide a drainage layer
 Ingredients in portland cement and asphalt
concrete
◦ 60 -75% of the volume or 79 – 85% of the weight of
the concrete is made up of aggregates
◦ Act as filler to reduce the amount of cement paste
needed in the mix
◦ Improves the quality and economy of the mix

 Ingredients in portland cement and asphalt
concrete
◦ 70 – 75% of the volume or 92 – 96% of the mass of
asphalt concrete
◦ Asphalt cement acts as a binder to hold the
aggregates together but does not have the strength
to lock the aggregate particles into position
◦ The strength and stability of the asphalt concrete
depends mostly on inter-particle friction between
the aggregates and, to a limited extent, on the
binder

 Defined by the characteristics of both the
individual particles and the characteristics of
the combined material
 PHYSICAL PROPERTIES
1. Particle shape and surface texture
 Determine how the material will pack into a dense
configuration
 Determines the mobility of the stones within the mix
 Considerations in the shape of the material –
angularity and flakiness
 Crushing rocks produces angular particles with sharp
corners and rough texture

 Due to weathering, the corners of the aggregates
break down creating sub-angular particles and
smooth texture
 When the aggregates tumble while being transported
in water, the corners become completely rounded
 Angular and rough textured aggregates produced
bulk materials with higher stability than rounded,
smooth-textured aggregates
 Angular aggregates will be more difficult to work
into place than rounded aggregates

 Particle shape of coarse aggregates
 Angular, rounded, flaky, elongated, flaky and elongated
 Flakiness describe the relationship between the
dimensions of the aggregate (ASTM D4791)
 Aggregates retained on the 9.5 mm (3/8”) sieve are
evaluated
 Flat particle is one where the ratio of the “middle
dimension” to the smallest dimension of the particle
exceeds 3:1
 Elongated particle is one where the ratio of the longest
dimension to the middle dimension exceeds 3:1

 Flat and elongated if the ratio of the largest dimension
to the smallest dimension exceeds 5:1
 Texture of Coarse Aggregates
 The roughness of the aggregate surface plays an
important role in the way the aggregate compacts and
bonds with the binder materials
 Aggregates with rough texture are more difficult to
compact into a dense configuration than smooth
aggregates
 Rough texture generally improves bonding and
increases inter-particle friction

 Since the stability of Portland cement concrete is mostly
developed by the cementing action of the cement and by
aggregate interlock, it is desirable to use rounded and
smooth aggregate particles to improve the workability
of the fresh concrete during mixing
 The stability of asphalt concrete and base courses are
mostly developed by aggregate interlock, thus, angular
and rough particles are desirable
 Flaky and elongated aggregates are undesirable for
asphalt concrete since they are difficult to compact
during construction and are easy to break

 To meet the needs of angular aggregates with high
texture, many specifications for coarse aggregates used
in asphalt concrete require a minimum percentage of
aggregates with crushed faces as surrogate angularity
and texture requirement
 ASTM D5821 – to evaluate the angularity and surface
texture of coarse aggregate, the percentages of particles
with one and with two or more crushed faces are
counted in are presentative sample

 Particle shape and texture of fine aggregates
 The angularity and texture of fine aggregates have a
very strong influence on the stability of asphalt concrete
mixes
 ASTM C1252 (Test Method for Uncompacted Void
Content of Fine Aggregate)
2. Soundness and Durability
 Ability of the aggregate to withstand weathering
 ASTM C88 (Soundness Test) – soaking the aggregate in
either a sodium sulfate or a magnesium sulfate solution
; five cycles of 16 hours soaking

2. Soundness and Durability
 AASHTO T103 (Soundness by freeze/ thaw)
 ASTM D4792 (Potential Screening from Hydrated
Reactions)
 ASTM C666 (Durability of aggregates in portland cement
concrete by rapid freezing and thawing
 ASTM C671 (critical dilation by freezing)
 ASTM C682 ( Frost resistance of coarse aggregates in
air-entrained concrete by critical dilation
3. Toughness, Hardness and Abrasion Resistance
 Ability of the aggregates to resist the damaging
effect of loads is related to the hardness of the
aggregate particles and is described as toughness or
abrasion resistance
 Los Angeles abrasion Test (ASTM C131,C535)

4. Absorption
 Four moisture condition states
 Bone Dry
 Air dry
 Saturated surface dry
 Moist or wet
 Absorption – moisture content in the SSD condition
 Moisture Content – weight of water / dry weight

4. Absorption

5. Specific Gravity
w
i
w
p
i
p
w
p
i
V
V
V
W
V
V






)
(V
W
Water)
to
Accessible
Not
(Volume
Dry Weight
Gr.
Sp.
Apparent
)
(V
W
Volume)
Particle
(Total
Weight
SSD
Gr.
Sp.
SSD
Bulk
)
(V
W
Volume)
Particle
Total
(
Dry Weight
Gr.
Sp.
Dry
Bulk
s
s
w
s
s
w
s
s
w













5. Specific Gravity
ASTM C127 – Specific Gravity and Absorption of
Coarse Aggregate
)
100
(
A
A
-
B
(%)
Absorption
C
-
A
A
Gr.
Sp.
Apparent
C
-
B
B
Gr.
Sp.
SSD
Bulk
C
-
B
A
Gr.
Sp.
Dry
Bulk




Where A = dry weight
B = SSD weight
C = submerged
weight

5. Specific Gravity
ASTM C128 Specific Gravity and Absorption of
Fine Aggregates
)
100
(
A
A
-
S
(%)
Absorption
C
-
A
B
A
Gr.
Sp.
Apparent
C
-
S
B
S
Gr.
Sp.
SSD
Bulk
C
-
S
B
A
Gr.
Sp.
Dry
Bulk







Where
A = dry weight
B = weight of pycnometer
filled with water
C = weight of pycnometer
filled with aggregate and
water
S = SSD weight of the
sample

6. Bulk Unit Weight and Voids in Aggregates
ASTM C29 Determination of Bulk Unit Weight
If the bulk dry specific gravity, Gs, of the aggregate is
known, the percentage of voids between the
aggregate particles can be determined as follows:
V
Ws
b 

s
w
s
b
s
b
b
s
s
s
V
Voids
x
G
x
x
W
W
x
V
V
V
%
100
%
100
100
100
100
%














7. Strength and Modulus
tensile strength – 0.70 MPa to 16 MPa
compressive strength – 35 MPa to 350 Mpa
AASHTO T292 – Resilient Modulus Test
8. Gradation
- Particle size distribution of the aggregate
- Large aggregates are economically advantageous
in Portland cements and asphalt concrete, as they
have less surface area however they are more
difficult to work into place

8. Gradation
 Sieve Analysis
 ASTM C136, E11
 Gradation results are described by the cumulative
percentage of aggregates that either pass through or are
retained by a specific sieve size

8. Gradation
 Maximum Density Gradation
 The density of an aggregate mix is a function of the size
distribution of the aggregates
 Fuller (1907) established the relationship for determining
the distribution of aggregates that provides the
maximum density or minimum amount of voids
 n = 0.50 (Fuller)
 n = 0.45 (Federal Highway Administration)
n
i
i
D
d
P 





100
Pi = percent passing sieve of size di
D = maximum size of aggregates

A sieve analysis test was performed on a sample of fine
aggregates and produced the following results:
Sieve , mm Amount Retained, g
4.75 (No. 4) 0
2.36 (No. 8) 33.2
2.00 (No. 10) 56.9
1.18 (No. 16) 83.1
0.60 (No. 30) 151.4
0.30 (No. 50) 40.4
0.15 (No. 100) 72.0
0.075 (No. 200) 58.3
Pan 15.6
Total 510.9

Sieve Size ,
mm
Amt
Retained, g
Cumulative
Amount
Retained, g
Cumulative
Percent
Retained
Percent
Passing
4.75 0 0 0 100
2.36 33.2 33.2 6.5 93.5
2.00 56.9 90.1 17.6 82.4
1.18 83.1 173.2 33.9 66.1
0.60 151.4 324.6 63.5 36.5
0.30 40.4 365 71.4 28.6
0.15 72.0 437 85.5 14.5
0.075 58.3 495.3 96.9 3.1
Pan 15.6 510.9

Sieve Size , mm
4.75 100
2.36 73
2.00 68
1.18 53
0.60 39
0.30 29
0.15 21
0.075 15
Pan
  45
.
0
100 D
d
P i
i 

0
20
40
60
80
100
0.01 0.1 1 10
Percent
Finer
Sieve Opening (Particle Size), mm
Sample
0.45 Power

◦ Fineness Modulus
 Measure of the fine aggregates’ gradation, and is used
primarily for Portland cement concrete mix design
 It is the sum of the cumulative percentage weight
retained on the 0.15-mm, 0.3-mm, 0.6-mm, 1.18-
mm, 2,36-mm, 4.75-mm, 9.5-mm, 19.0-mm, 37.5-
mm, 75-mm, and 150-mm (No. 100, 50, 30, 16, 8,
and 3/8-in., ¾-in., 1 ½-in., 3-in., and 6-in.) sieves
divided by 100
 Fineness modulus for fine aggregates should be in the
range of 2.3 to 3.1 with a higher number a coarser
aggregate

Effect of Amount of Fines on the Relative Properties of Aggregate Base
Materials
Characteristic No Fines (Open
or Clean)
Well graded
(Dense)
Large Amount of
Fines (Dirty or
Rich)
Stability Medium Excellent Poor
Density Low High Low
Permeability Permeable Low Impervious
Frost
Susceptibility
No Maybe Yes
Handling Difficult Medium Easy
Cohesion Poor Medium Large

ASTM Gradation Specifications for Fine Aggregates for
Portland Cement Concrete
Sieve Percent Passing
9.5 mm (3/8”) 100
4.75 mm (No. 4) 95 – 100
2.36 mm (No. 8) 80 -100
1.18 mm (No. 16) 50 – 85
0.60 mm (No. 30) 25 – 60
0.30 mm (No. 50) 10 - 30
0.15 mm (No. 100) 0 - 10

Aggregate Grading Requirements for Superpave Hot Mix Asphalt
(AASHTO MP-2)
Sieve
Size, mm
Nominal Maximum Size (mm)
37.5 25 19 12.5 9.5 4.75
50 100 - - - - -
37.5 90 -100 100 - - - -
25 90 max 90-100 100 - - -
19 - 90 max 90-100 100 - -
12.5 - - 90 max 90-100 100 100
9.5 - - - 90 max 90-100 95-100
4.75 - - - - 90 max 90-100
2.36 15-41 19-45 23-49 28-58 32-67 -
1.18 - - - - - 30-60
0.075 0-6 1-7 2-8 2-10 2-10 6-12

 Blending of Aggregates to Meet Specifications
◦ A single aggregate source is generally unlikely to
meet gradation requirements for Portland cement
or asphalt concrete mixes
◦ Blending of aggregates from two or more sources
would be required to satisfy specifications

◦ Determining a satisfactory aggregate blend with the
graphical method according to The Asphalt Institute
(1995)
1. Plot the percentages passing through each sieve on
the right axis for aggregate A and on the left axis for
aggregate B.
2. For each sieve size, connect the left and right axes.
3. Plot the specification limits of each sieve on the
corresponding sieve lines.
4. Connect the upper- and lower-limit points on each
sieve line.

(1995)
5. Draw vertical lines through the rightmost point on
the upper limit line and the leftmost point on the
lower limit line. If the upper- and lower-limit lines
overlap, no combination of the aggregates will meet
specifications.
6. Any vertical line drawn between these two vertical
lines identifies an aggregate blend that will meet the
specification. The intersection with the upper axis
defines the percentage of aggregate B required for
the blend. The projection to the lower axis defines
the percentage of aggregate A required.

(1995)
5. Projecting intersections of the blend line and the
sieve lines horizontally gives an estimate of the
gradation of the blended aggregate.

9. Cleanliness and Deleterious Materials
Substance Harmful Effects on Portland Cement
Concrete
Organic Impurities Delay settling and hardening, may
reduce strength gain, may cause
deterioration
Smaller than 0.075 mm
(No. 200)
Weaken bond, may increase water
materials requirements
Coal, lignite, or other
low-density materials
Reduce durability, may cause pop-outs
or stains
Clay lumps and friable
particles
Pop-outs, reduce durability and wear
resistance
Soft particles Reduce durability and wear resistance,
pop-outs

 Aggregates must handled and stockpiled in
such a way as to minimize segregation,
degradation, and contamination
 Sampling aggregates
◦ In order for a test to be valid, the sample of
material being tested must represent the whole
population of materials that is being quantified with
the test
◦ Aggregate samples are taken from the top, middle,
and bottom of the stockpile and then combined
◦ Before taking samples, discard the 75 mm to 150
mm materials at the surface

◦ Samples are collected using a square shovel and are
placed in sample bags or containers and labeled
◦ Sampling tubes 1.8 m long and 30 mm in diameter
are used to sample fine aggregate stockpiles; at
least five samples should be collected from random
locations in the stockpile and then combined
◦ Field sample sizes are governed by the nominal
maximum size of aggregate particles (ASTM D75)
 Larger sized aggregates require larger samples to
minimize segregation errors

◦ Field samples are typically larger than the sample
needed for testing
 Sample splitter
 Quartering (ASTM C702)

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