Post on 16-Jul-2015
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
New Trends in HMA Mixes
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
The GOAL of Mix Design
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Getting this to
Carry this without
To much of This.
The GOAL is…
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
• Design of an asphalt-aggregate mixture
consists of…
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1 • Select the type and gradation of
aggregate
2 • Select the type and grade of asphalt
binder, with or without modification
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• Select the amount of asphalt binder to satisfy the project-specific requirements…
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Properties of a Good
Asphalt-Aggregate Mixture
Stiffness
Durability
Stability
Fatigue Resistance
Fracture Resista
nce
Low Skid
Permeability
Work-ability
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Special HMA Mixes
• SuperPave
• Reclaimed Asphalt Pavement (RAP)
• Warm Mix Asphalt (WMA)
• Stone Matrix Asphalt (SMA)
• Open Graded Friction Course (OGFC)
• Pervious Pavement
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Gyratory Compaction
• Gyratory compaction of specimens in mix design is one of the key differences with the Marshall method.
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
• Simulate field densification • traffic
• climate
• Accommodate large aggregates
• Measure compactability
Goals of Lab Compaction
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
• 150 mm diameter • Up to 37.5 mm nominal
size
• Height recordation
Superpave Gyratory Compactor
150 mm
diameter
ram pressure
600 kPa
1.25 degrees 30 gyrations
per minute
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
SGC Types
Troxler Pine Brovold Interlaken
4141
4140
AFG1A
AFGC125X GYR-001 HM-293
Rainhart
144
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
SGC Compaction Curve
% Gmm
Log (Gyrations)
10 100 1000
The increase in density
(%Gmm) with each gyration
is used to graph this
compaction curve.
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Hot-Mix Asphalt (HMA) Recycling
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Hot-Mix Asphalt (HMA) Recycling
Hot-Mix Asphalt Plant
Milling an Asphalt Pavement
Reclaimed Asphalt Pavement (RAP)
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Why Recycle Asphalt?
• Pavement Benefits
• Economic Payoff
• Energy Savings
• Natural Resource Conservation
Milling (Cold Planing) of an Asphalt Pavement
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Benefits of Milling
• Removes cracked and aged
pavement layers
• Improves pavement
smoothness and cross-slopes
• Maintains curb heights,
drainage inlets, and bridge
clearances
• Creates a rough texture that
bonds better with the overlay
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Materials savings will depend on...
• Virgin binder cost
• Asphalt content of the mix design
• Aggregate cost
• RAP cost
• Asphalt content of the RAP
• Percentage of RAP
Economics of HMA Recycling
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Recycling Economics Example
• Aggregate: LE 60.00/ton
• Asphalt: LE 3000.00/ton
• Mix Design AC Content: 5.0%
LE 60 x .95 = LE 57
LE 3000 x .05 = LE 150
Total Mix LE 207
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Recycling Economics Example
• Aggregate: LE 60.00/ton
• Asphalt: LE 3000.00/ton
• RAP: LE 40.00/ton (5% AC in RAP)
• Mix Design • AC Content: 5.0%
• RAP content 20% (19% rock, 1% AC)
LE 60.00 x .76 = LE 45.60
LE 3000.00 x .04 = LE 120.00
LE 40.00 x .20 = LE 8.00
Total Mix LE 173.6
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Recycling Economics Example
• Virgin Mix: LE 207.0/ton
• Recycled Mix: LE 173.6/ton
@20% RAP: Savings = 16.1%
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Current Practices
for HMA Recycling
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Surface Mixes: % RAP Allowed
0%
10%
15%
20%
25%
30%
n/a
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Base Mixes: % RAP Allowed
0%
10%
15%
20%
25%
30%
n/a
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Testing RAP
• General properties:
asphalt content
aggregate gradation
aggregate bulk specific gravity
fine aggregate angularity
fractured face count
flat & elongated percentage
deleterious materials
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Current Superpave Guidelines for Selecting the Virgin Binder Grade
• Tier 1: Up to 15% RAP
• use the normal binder grade
• Tier 2: 15%-25% RAP
• use one binder grade lower, e.g., PG
58-28 instead of PG 64-22
• Tier 3: Over 25% RAP
• use blending charts to determine
required binder grade
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Warm Mix Asphalt
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Q. Which project is which?
A: Hot-Mix Asphalt (HMA)?
B: Warm Mix Asphalt (WMA)?
Project No. 1 29
Project No. 2
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
What is WMA?
• Process or additive that allows for the production and compaction of asphalt pavements at temperatures lower than traditional HMA
• Reduced mixing temperature
can range between 135 - 85°C
• Different mixes and technologies dictate mixing temperature
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Three General Categories for
WMA
• Foaming • Example, double Barrel Green
• Organic Additive
• Example, Sasobit
• Chemical Additive
• Example, Evotherm
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept. Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Benefits of WMA
• Energy savings
• Reduced emissions
• Extended paving season
• Increased haul distance
• Less oxidized binder • Less brittle, may be more resistant to cracking
• Softer binder may be better for high RAP content mixes
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Similarities With HMA
• Same plants, just modified in many
cases
• Same hauling and laydown equipment
• Same compaction equipment
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Concerns About WMA
• Moisture susceptibility
• Rutting
• Coating of aggregate
• Drying aggregate
• Use with RAP and RAS binder
• Compatibility with polymer modified binder
• Expense
• One more material/process to control
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
How Are The Concerns Being
Addressed?
• Moisture susceptibility
• Anti-stripping agents
• Monitoring of pavement performance
• Checking moisture content of mix
• To date no issues with moisture damage in the
field
• Rutting
• Binder is less oxidized but lab and early field
results indicate it is not an issue
• To date no issues with rutting in the field
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
How Are The Concerns Being
Addressed?
• Mixing with RAP and RAS binders
• Field and laboratory studies underway
• Evaluating blending of virgin and RAP binder for HMA and WMA
• Compatibility with polymer modified binder
• Test sites constructed
• May require higher temperature than unmodified mixes
• So far no observed problems
• Expense
• Offset by energy savings
• Seems feasible to use higher RAP
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Stone Matrix Asphalt
(SMA)
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
SMA
• Stone mastic asphalt (SMA), also
called stone-matrix asphalt, was developed
in Germany in the 1960s.
• It is:
• Deformation resistant,
• Durable surfacing material,
• suitable for heavily trafficked roads.
• Good skid resistance
• Noise reduction
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
SMA and Conventional AC
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Introduction • SMA Has Been Used >30 Years in Europe
• First Project in U.S. ~ 1991 in Wisconsin
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Results of the 1996 Survey study:
• Over 70% with rutting < 2 mm
• 25% with no measurable rutting
• No thermal or reflective cracking
• No evidence of raveling
SMA Performance in USA
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
How is SMA Different?
• Gradation
• Asphalt Content
• Dust Content
• Stabilizing Additives
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Asphalt Contents
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Dust Content
Superpave
2 to 10 percent
SMA
8 to 12 percent
Mansoura University - Faculty of Engineering – Public Works Engineering Dept. SMA & OGFC
Increased Film Thickness
SMA has 25% thicker film coating than conventional dense-graded mix.
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Additives
• Polymers
• Mineral Fillers
• Fibers
• Hydrated Lime
• Liquid Anti-Strip
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Stabilizing Additives
– Cellulose:
0.3% to 0.5%
– Mineral fiber:
0.4 to 0.5%
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
SMA Mixtures
• Consists of two parts
– Coarse aggregate
matrix
– Binder rich mortar
Typical SMA:
• 70−80% coarse aggregate,
8−12% filler,
• 6.0−7.0% binder,
• and 0.3 per cent fiber.
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
SMA Mixtures
• Mix properties
– 50 blow Marshall or
100 gyrations SGC
– VTM - 4%
– VMA - 17% Min.
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Disadvantages
• Increased material cost associated with
higher binder and filler contents, and fiber additive.
• Increased mixing time and time taken to add extra filler,
may result in reduced productivity.
• Possible delays in opening to traffic as the SMA mix
should be cooled to 40°C to prevent bleeding.
• Initial skid resistance may be low until the thick binder
film is worn off the top of the surface by traffic
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Open-Graded Friction Courses
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
History of OGFC
• First use in 1944
• FHWA design procedure in 1974
• Stripping of underlying layer
• Quick failure mode (raveling)
• Needed improvements
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Mix Design Method
• FHWA procedure – 1974
• Modified Marshall design
Mansoura University - Faculty of Engineering – Public Works Engineering Dept. SMA & OGFC
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Estimated Average Service Life
Based on 1998 Survey
Per
cen
t of
Sta
tes
Mansoura University - Faculty of Engineering – Public Works Engineering Dept. SM & OGFC
Use of OGFC
• 38% still use
• 38% discontinued use
• 8% do not use
• 16% did not respond
Based on 1998 Survey
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Advantages
• Provides water drainage
–Reduce hydroplaning
–Improve friction
• Improves visibility
–Reduce splash/spray
–Improve visibility of traffic stripes
–Reduce headlight glare
• Reduces noise
• Mitigate Urban Heat Island Effect
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Benefits of OGFC
Improved
Nighttime Visibility
& Friction
Reduced
Splash/Spray
and Hydroplaning
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept. SMA & OGFC
Texas Dense-Graded Mix
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
OGFC in France
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Accident Data: Travis County,
Texas
Year 2001 2002 2003 2004 %
Change
Total # Accidents 29 51 44 17 -58.9
Dry Weather Accidents 10 23 13 15 -2.2
Wet Weather Accidents 19 28 21 2 -91.2
Fatalities 0 1 5 0 -100
Total Injuries 25 16 21 0 -100
Annual Rainfall (in) 42.9 36.0 21.4 52.0 55.5
Total Rain Days 57 56 37 70 40.0
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Design Air Voids
at 18 – 22%
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Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Variation of Road Noise
to Surface Type
Cement Concrete
Asphalt Concrete
OGFC/Porous
72-79
76-85
67-77
72-79
68-73
69-76
65 70 75 80 85
Internal Noise
External Noise
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Noise Reduction - OGFC
Effect of -3dB(A)
Equivalent to 20% Speed Reduction
60 48
Equivalent to 1/2 the Intensity
Mansoura University - Faculty of Engineering – Public Works Engineering Dept.
Recommended Design Procedure
• Step 1 ~ Materials selection
• Step 2 ~ Selection of design gradation
• Step 3 ~ Determine opt. binder content
• Step 4 ~ Evaluate moisture susceptibility