Transcript Materials Selection Chapter 3

Materials Selection
Chapter 3
• Seal existing pavement
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More binder the longer the seal
will protect underlying HMA
• Bond to aggregate
• Bond to pavement
• Skid resistance
• Limit polishing
• Control abrasion
• Protects the binder from traffic
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Minimize risk of overheating
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Minimizing heat loss
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Seek advice from your supplier!!!
Aggregate Defines:
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Seal Type
Binder
Construction Procedures
United States
• Availability
• Transportation
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Method
Cost
Favor local sources
Emphasize Lower
Cost
Overseas
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Life Cycle Analysis
Transportation
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Up to 500 miles
Performance
Longevity
Emphasize Quality
• Grading / Particle Size:
Determines mixture physical characteristics
that affect fatigue resistance
• Cleanliness:
Dusty aggregates causes adhesion problems
in chip seal.
Hardness / Abrasion Resistance:
Must resist crushing, polishing,
degradation, and maintain skid resistance
Particle Shape and Surface Texture:
Cubical, not elongated for better interlock
and internal friction
Absorption:
Excessive absorption of binder can result in
raveling
If the seal coat is designed for chips in the
wheelpaths:
CHIP LOSS
CHIP LOSS
There is not enough binder in the non-traffic areas to
prevent traffic and snow plows from dislodging the chips.
If the seal coat is designed for chips in the
non- traffic areas:
There is not enough binder in the non-traffic areas to
prevent traffic and snow plows from dislodging the chips.
If the seal coat is designed for chips in the
non- traffic areas:
BLEEDING
There is too much binder in the wheelpaths after the flat
chips lay on their flattest side.
Dense Graded
Single Size
100
PERCENT PASSING
90
80
70
60
dense graded
single sized
50
40
30
20
10
0
0
0.1
0.2
0.3
0.4
SIEVE SIZE, inches
0.5
0.6
Advantages of Single Sizing
• More uniform height
• Weighs less per cubic foot
̶ 47% passing the #4 95.7 lbs/ft3
̶ 8% passing the #4 84.5 lbs/ft3
• More room for binder
̶ Increased Voids
Dense Graded (FA-3) $22.80 ton
• 18.5 lbs/yd2 needed = $0.21 per yd2
Single Sized
• 14.5 lbs/yd2 needed = $0.16 per yd2
Can pay $6.30 a ton more for single sized
aggregate at the same square yard cost
as dense graded aggregate.
Best Performance when:
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Single sized
Minimum fines
Clean
Free of clay
Cubical
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Crushed faces
Abrasion < 30%
Binder compatible
Damp for emulsions
Dry for hot binders
• Sieve Analysis: <1% passing No.200
• ASTM D3319: Polished Stone Value
(PSV) 44 to 48
• ASTM C131: LA Abrasion Test <30%
• Percent Fracture: 75% with at least 2
fracture faces.
Type
North America
AU, NZ, SA, UK
Limestone
37%
13%
Quartzite
13%
38%
Granite
35%
38%
Trap Rock
13%
25%
Sandstone
10%
25%
Natural Gravel
58%
25%
Greywacke, Basalt
4%
88%
• Asphalt must preferentially wet,
and bond to aggregate surface
• Poor compatibility leads to:
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Stripping
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Disintegration
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Stone loss
• No reliable chemical indicators
for stripping
• No bleeding when applied properly
• Fluid enough to cover surface
• Viscous enough to prevent puddling
or pavement runoff
• Develop adhesion quickly and
retain aggregate
• Standard Paving Asphalt
Aged Residue (AR) grade
• Asphalt Emulsion
(modified, unmodified, rejuvenating)
• Polymer-Modified Asphalts
Including PBA grades
• CMCRA
Chemically-Modified Crumb Rubber
Asphalt and Modified Binder (MB) grades
• Cutbacks
62%
Residual
85%
Residual
Influenced by:
• Surface Temperature
• Aggregate
• Construction Climate
• Performance Characteristics
Advantages
• Open earlier to traffic
• Appropriate for high
surface temperatures
• Good stone retention
• Can be reheated or stored
at high temperatures w/o
adverse effects
Disadvantages
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High temperatures
High energy consumption
Safety concerns
Sensitive to aggregate
moisture
“Emulsions lie between solutions and suspensions.
An asphalt emulsion is asphalt particles dispersed
in water. It is not a solution because the oil and
water are susceptible to separation. The oil is
stabilized with an emulsifier to keep it dispersed.”
“Breaking (curing) is used to describe the process
by which the asphalt expels the water and dries to
an integral film / layer on the aggregate.”
• Anionic • Cationic +
Particles begin to stick together (Flocculation)
Particles coalesce to form larger particles
Breaking Process
Emulsion
Step 1
Evaporation
Step 2
Evaporation
+
Drainage
Aggregate
Curing Process
Step 3
Fully Cured
Advantages
• Lower energy use
• Low application
temperatures
• Reduced emissions
• More amenable for use at
remote sites
• Lower cost per increase in
useful service life
• Suitable for treating a wide
array of distresses
Disadvantages
• Timing the “break” with
aggregate spreading
• Improper and prolonged
storage may result in phase
separation, coalescence
• Longer cure time than hot
applied cements
Temperature
• Flocculation and coalescence may
occur if too cool
• If too hot, water will evaporate
prematurely resulting in coalescence
and premature breaking
• Binder Suppliers are best source of
heating information!
• Circulate slowly at regular intervals
• Circulation frequency depends on
weather and storage time
• Flush pumps after use but not into
tank
• Warm lines and pumps as necessary
• Do not leave lines partially-filled
w/emulsion
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More “forgiving”
Allow for thicker residual asphalt film
Minimize asphalt runoff
Penetrate dust coatings (<5% fines)
Promote good bonding with
aggregate
• Good for situations where available
aggregate is very dirty
• Must be allowed to skin over
• Polymers typically utilized
• Reduce temperature susceptibility
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CRS-2 softening point 108º F
CRS-2p softening point 128º F
• Better adhesion
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Increased application rate by up to 15 %
• Increased stone retention / flexibility
• Early opening to traffic
• Recommended for high traffic roads
• Large molecules which
enhance performance
• Solid or liquid in form
• Properties
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Plastomeric (adds stiffness)
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Elastomeric (adds flexibility)
Properties Affecting Adhesion:
• Mechanical
(dust, aggregate porosity)
• Chemical
(moisture content, binder temperature)
• Electrostatic
(binder and aggregate should have
opposite charges)
Questions?