advances and challenges in asphalt paving
TRANSCRIPT
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Advances and Challenges in Asphalt Paving
Jenny Liu, Ph.D., P.E. Sheng Zhao, Ph.D.
Center for Environmentally Sustainable Transportation in Cold Climates University of Alaska Fairbanks
February 12, 2015
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Outline • Background • Material & design • Construction • Maintenance,
preservation, and assessment
• Summary
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• Paving industry are constantly seeking to – Improve pavement performance, increase
construction efficiency, conserve resources and advance environmental stewardship
• Innovations are continuously being developed • Issues arising:
– Performance, durability and compatibility – Material design, cost analysis, specifications and
quality control
Background
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• High RAP/RAS content
Materials & Design
Recycled Asphalt Pavement (RAP)
Recycled Asphalt Shingle (RAS)
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NAPA 2009-2013 survey
RAP Averaging Usage - State Practice
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NAPA 2009-2013 survey
RAS Usage -State Practice
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• Cracking resistance – Aged and stiff RAP binder can cause fatigue
damage and low-temperature brittleness • Water susceptibility
– Generally positive: RAP aggregates already covered with asphalt; less chance of water penetration
– However, if RAP already has a stripping problem, it can be transferred to new mix
• Rutting Resistance – Aged and stiff RAP binder improves rutting
resistance
Performance of High RAP Mix
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• Pavements using RAS can be successfully produced – With RAS alone – In combination with: WMA, RAP, GTR and SMA
• Meet state agency quality assurance requirements • Good rutting and fatigue resistance (four-point
beading beam) • No statistical change in Low temperature fracture
resistance, with fibers that can be beneficial
Performance of HMA containing RAS
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• Field performance after two years – No signs of
• Rutting • Wheel path fatigue cracking • Thermal cracking
– Transverse reflective cracking were observed from the underlying jointed concrete pavement
• More cracks for pavement containing coarsely ground RAS • Controversial observations:
– Non-RAS pavement showed similar or more cracking: IA, IN, IL and WI – RAS pavement showed similar or more cracking: MS and CO
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• Due to construction costs and environmental issues • WMA with high RAP/RAS can be successfully
produced and placed • Mutual benefits
– WMA: less aging, more workable – High RAP/RAS: increased rutting and moisture resistance
• Nation-wide study – Completed: NCHRP 9-46 (high RAP), NCHRP 9-47
(WMA) – Active: NCHRP 9-49 9-53 (WMA), NCHRP 9-55 (WMA-
RAS)
WMA containing High RAP/RAS
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• Aged binder property – Recycled binder is too stiff, especially RAS – Cracking concerns still exist
• Blending efficiency – How much and how well the old and new binders blend? – Rejuvenators for RAS mixture seems necessary
• RAP aggregate – Excessive fines can be generated by milling and crushing,
thus affecting further mix design
Challenges for Use of High RAP/RAS
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• NCHRP 9-46 “Mix Design and Evaluation Procedure for High RAP Content in HMA” (Completed, Report 752) – Develop mix design and analysis procedure for High
RAP mix – Propose changes to existing specifications
• However, state practices may vary – Texas, balanced RAP/RAS overlay mix design and
performance evaluation system was proposed • More experience needed for Mix design of RAS
Mix
Challenges – Mix Design
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• Intelligent compaction (IC) Construction
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• Benefits of IC – Improved compaction
quality of asphalt pavements
– Increased quality control and reduced maintenance cost
– Money-savings – Safer operations
Why Use IC ?
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How IC Works? • GPS based compaction
Photo credit: Ammann America, Texas DOT
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How IC Works?
Photo credit: Ammann America, Texas DOT
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• 12 DOTs had demonstrated 16 field IC projects before 2011
Current Status
NCHRP 21-09, for subgrade soils
Transportation Pooled Fund #954, for embankment subgrade soils, Aggregate base and asphalt pavement material
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• Extensive professional training required • Data standardization: parameters of each
section may affect the IC data results • Moisture content measurements and variation • Poor correlation between density and
modulus/stiffness
Challenges in Implementation of IC
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Pavement Preservation - “Strategy including all activities to provide & maintain serviceable roadways”
$1 for preventive maintenance here
Costs 6-10 times or more when it’s done as rehab
Con
ditio
n
Cost
Maintenance, Preservation & Assessment
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• Crack Sealing • Patching • Fog Seals • Chip Seals • Slurry Seals • Microsurfacing • Bonded Wearing
Courses
• Interlayers • Thin Overlays • In-place Recycling • Other treatments • Asphalt Surface
Treatment/ Bituminous Surface Treatment (AST/BST)
Types of Pavement Preservation Treatments
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• Pre-cut technique - control thermal cracks/build “better” thermal cracks
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Preservation treatment
Estimated life, years
Estimated cost, $/yd2
Crack Seals 3-8 -- Fog seals 2-5 0.40 to 0.60 Chip seals 3-10 2.00 to 4.00 Slurry Seals 3-7 1.00 to2.00 Microsurfacing 3-9 1.50 to 3.00 Thin HMA Overlays 5-12 3.00 to 6.00
Typical Lives and Costs of Treatments
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• The right treatment on the right pavement at the right time
• Perception: the public will not support pavement preservation, but prefer the "worst-first" strategy
• Other issues than cost effectiveness speak for pavement preservation concept: sustainability, green products and technologies and traffic safety
Issues
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• Life cycle assessment (LCA) of asphalt pavement
Quantify the environmental impacts over the full life cycle of asphalt pavement
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• Identifying opportunities to improve the environmental performance of asphalt pavement in its life cycle.
• Informing and guiding decision makers • Developing appropriate indicators of
environmental performance of asphalt pavement; for example, if using RAS is environmental-friendly
Purpose of LCA for Asphalt Pavement
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• Data collection – Availability of readily accessible and applicable data – the cost of data collection – A number of uncertainties in the data
• Data quality – Establishment of standards is required
• Issues with impact assessment methods – Can it be exclusive to pavement?
• Issues with weighting of impacts in decision-making – Different impact categories give conflicting impact
rankings? – Which impact(s) is (are) more important?
Challenges of LCA
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• Advance innovative sustainable materials and design
• Effective design, management and preservation strategies during construction, operations and preservation
• Life cycle assessment
Summary
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• International Symposium on Systematic Approaches to Environmental Sustainability in Transportation, August 2-5, 2015, Fairbanks AK – http://cem.uaf.edu/cesticc/symposium.aspx – Contacts
• Jenny Liu: [email protected] • Sheng Zhao: [email protected]
Upcoming Events
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Question ?