Selected In-Track Applications and Performances of Hot-Mix
Transcript of Selected In-Track Applications and Performances of Hot-Mix
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Selected In-Track Applications and Performances of Hot-Mix Asphalt Trackbeds
Dr. Jerry G. Rose, P.E.
Professor of Civil Engineering
261 Raymond Building
University of Kentucky
Lexington, KY 40506
859-257-4278
www.engr.uky.edu/~jrose
Joint Rail Conference -- 2013 Track 1 Railroad Infrastructure Engineering -- JRC2013-2525
University of Tennessee – Knoxville April 15 -17, 2013
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Classic All-Granular Trackbed
Typical Thickness (mm)
250-300
100-150
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Asphalt Underlayment trackbed without granular subballast layers
Asphalt Combination trackbed containing both asphalt and subballast layers
Ballastless trackbed containing thickened asphalt and subballast layers
Typical Thickness (mm) 300
150
Typical Thickness (mm) 300
150
100
Typical Thickness (mm) 300
150
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United States Applications
• Short Maintenance—Road Crossings, Turnouts, Rail Crossings, Tunnels, Bridge Approaches, WILDS, etc.
• Capacity Improvement—Double Tracking, Line Changes, etc.
Since 1981
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SW Durham Rd. May 15-16, 2010
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Trackbed Measurements & Evaluations
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Geokon Pressure
Cell
Ballast
Subballast/HMA
Wooden Tie
Subgrade
Geokon Pressure
Cell
Tekscan Sensor
Tekscan Sensor
Geokon Earth Pressure Cell
Tekscan Sensor
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• Geokon Model 3500-2
• 9 in. Diameter
• Strain Gage
• Snap-Master
• Thermistor
Pressure
Cell
Cell
Placement
on Asphalt
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P-Cell 209 on 5 in. HMA Layer
0
5
10
15
20
7 8 9 10 11 12 13 14 15 16 17
Time (s)
Pre
ss
ure
(p
si)
4 6-Axle Locos
Initial 5 Cars
Empty Coal Train at Conway
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05
1015
202530
2 3 4 5 6 7 8 9 10
Time (s)
Str
ess (
psi) 8 in. HMA surface
Subgrade surface
Reduction of Dynamic Stresses
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View of Tekscan Sensors
Tekscan
Measurement
Configuration
•Matrix-based array of
force sensitive cells
•Silver conductive electrodes
•Pressure sensitive ink –
Conductivity varies
•Crossing of ink – strain gauge
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Scale in PSI
This represents a typical pressure distribution between a machined steel tie plate and the rail with an included rubber bladder.
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0
100
200
300
400
500
600
700
10 T
ies Bef
ore
Sen
sor
8 Tie
s Bef
ore
Senso
r
6 Tie
Bef
ore
Sen
sor
4 Tie
s Bef
ore
Senso
r
2 Tie
s Bef
ore
Senso
r
Dire
ctly A
bove
Sen
sor
2 Tie
s Pas
t Sen
sor
4 Tie
s Pas
t Sen
sor
6 Tie
s Pas
t Sen
sor
8 Tie
s Pas
t Sen
sor
10 T
ies Pas
t Sen
sor
Lead Wheel Position
Avera
ge P
ressu
re (
psi)
Positioning of Lead Wheel with Respect to Sensor
Snapshot of the Lead Wheel Directly above the Sensor
Lead Wheel Over
Sensor F = 25372 lbf, P = 529 psi
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Core Drilling
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Subgrade Findings/Discussion
• In-situ Moisture Contents
– Remain Consistent Over Time
– Compare Favorably With Optimum
• Assume Unsoaked, Optimum Condition
• Bearing Capacity Remains At or Near Optimum
• Wide Range of Subgrades Evaluated
• Minimum Loading Induced Stress on Subgrade.
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Asphalt Findings/Discussions
• Resilient Modulus Values are Intermediate in Magnitude-Typical of Unweathered Asphalt Mixes
• Asphalt Binders do not Exhibit Excessive Hardening (Brittleness), Weathering, Deterioration or Cracking
• Asphalt is Insulated from Environmental Extremes • Asphalt Experiences Minimal Loading Induced
Stress • Conditions Influencing Typical Failure Modes
Experienced by Asphalt Highway Pavements don’t Exist in Asphalt Railroads Trackbeds.
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International Applications Italy France
Japan Spain
Germany
Austria
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Italy
• Rome-Florence: 252 km (1977-1986)
• Debated between cement and asphalt
• Asphalt – designated on all future high-speed passenger lines
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• Prevents rainwater from infiltrating the layers below the embankment
• Eliminate high stress loads and failures of the embankment
• Protect the upper part of the embankment from freeze/thaw actions
• Gradually distribute static and dynamic stresses caused by trains
• Eliminate ballast fouling Buonanno, 2000
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Typical Cross Section
• 12 cm of asphalt with 200 MPa modulus
• 30 cm of super compacted subgrade with 80 MPa modulus
• 35 cm of ballast on top
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Policicchio, 2008
Teixeira, 2005
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Japan
• Widely Used
• High Speed/Regular
• Firm Support for Ballast
• Reduce Load Level on Subgrade
• Facilitate Drainage
Momoya and Sekine, 2007
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• Performance Rank I: Concrete roadbed or asphalt roadbed for ballastless track – Concrete base thickness = 190 mm
– Asphalt base thickness = 150 mm
– Stone base thickness = 150 mm
• Performance Rank II: Asphalt roadbed for ballasted track – Ballast thickness = 250-300 mm
– Asphalt base thickness = 50 mm
– Stone base thickness = 150-600 mm
• Performance Rank III: Crushed stone roadbed for ballasted track
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Ballastless Cross Section
• Mainly used for viaducts and tunnels
• Proposed a low noise solid bed track on asphalt pavement
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Ballasted Cross Section
• Asphalt Thickness:
5 cm
• Well-Graded Crushed Stone Thickness:
15-60 cm
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France
• Paris to Strasbourg high-speed line
• 3 km asphalt subballast
• 574 km/hr (357mph) (test)
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Comparative Cross-Sectional Profiles
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• Reduces overall cross-sectional thickness by 36 cm
• Reduces quantity of fill material by
5,000 cubic meters/ kilometer
Bitume Info, 2005
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Testing
• Conduct tests for 4 years (2007-2011)
• Temperature sensors continuously recording air temperature
• Pressure Sensors and Strain Gages checked twice a year
• Accelerometers
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Spain
• Madrid – Valladolid
• Barcelona – French Border
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Germany
• Utilize several alternatives to conventional ballast design
• German Getrac A1/A3 – ballastless slab consisting of asphalt
• Concrete ties are anchored to the asphalt
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Austria
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Reasons for Implementing Asphalt Layers
How to install an Asphalt Layer?
drainage effect for raining water hindering it penetrating the substructure
avoiding the pumping up of fines into the ballast delivering a certain amount of elasticity homogenising the stresses affecting the substructure
to allow road vehicles running on the sub-layer during construction phase independently from weather and sub-soil situation
clear separation of sub- and
superstructure during the whole service life
Targets of an Asphalt Layer
Advantages
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Long Term Experiences Jauntal, Carinthia
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Conclusions Asphalt layers improve the quality of track in defining a clear and long lasting separation between superstructure and sub-structure. This separation results in less maintenance demands of track and (thus) longer service lives.
These benefits must be paid by an additional investment of 10€/m² within the initial construction.
Life cycle cost analyses show that it is worth to implement asphalt layers on heavy loaded lines (> 15,000 gt per day and track), as then the annual average track cost can be reduced by 3% to 5%.
However, implementation of asphalt layers cannot be proposed for branch lines carrying small transport volumes. Asphalt Layers must be understood as an additional investment in quality, then it pays back its costs. It must not be implemented in order to reduce quality in sub-layers, by for example reducing the thickness of the frost-layers.
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Due to the long interruption of operation installing of asphalt layers are not proposed within track re-investment and maintenance operations.
Implementation Consequently asphalt layers of 8 cm to 12 cm form a standard element for new high capacity and high speed lines in Austria.
Picture a to c: new Koralm link
Picture d: Schoberpass-line, built in 1991
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Closure
• Represents Current Practices
• Not All-Encompassing
• Typical Activities