bituminous cold-mix technology and pavement design
TRANSCRIPT
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Bituminous Cold-Mix Technology and Pavement Design
TRB WORKSHOP 153SOUTH AFRICAN HIGHWAY TECHNOLOGY AND PRACTICE
Dr Fritz JoosteDirector
Modelling and Analysis Systems
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Topics of this Presentation:
• Some history, project background• Motivation of development approach
(focus on structural design)• Materials classification task details• Structural capacity assessment details• Conclusion
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Some History…
• Recycling with emulsion and foam was done from the early 1970’s
• Initially fairly primitive & often applied to less highly trafficked roads by experienced designers
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Some History…
First deep cold-in place recycling with Emulsion in 1994
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Some History…
CIPR with Foam from 1996 onwards
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Existing Cold-Mix Guidelines• Emulsion materials
�Sabita Manual 14 (1993)�Sabita Manual 21 (1999)
• Foamed bitumen materials�TG2 Interim Guideline (2002)
Guidelines widely used, but need to• Modernize & Improve• Place foam and emulsion on equal footing• Create a single, combined guideline• Address need for paradigm shift in SA
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Bituminous Cold-Mix Guidelines• Project initiated in 2005 to address
deficiencies in existing guidelines• Focus on mix design and structural design
elements
• Limited time-frame: short term deliverable� Somewhat novel structural design approach
adopted
Findings and methods will be incorporated into a larger, on-going pavement design development project (SANRAL sponsored)
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Project Constraints• Reasonable knowledge base of performance
(long-term and accelerated loading), but …• Not very detailed information, no fundamental
material properties• Current M-E design method has deficiencies
�Adopted a Heuristic or Knowledge-basedpavement design approach
�Simplified design method, more emphasis on correct materials assessment, mix design and construction
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Field Testing &
Assessment
Design Inputs & Rules of Design
Material Behaviour
Models
Response Models & Capacity
Prediction
Design Feasibility Appropriate
Spec’s
Practitioner/Human Domain
Research/Software Domain
Pavement Design Elements
Practitioner/Human Domain
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Field Testing &
Assessment
Design Inputs & Rules of Design
Design Feasibility Appropriate
Spec’s
Practitioner/Human Domain
Research/Software Domain
Material Behaviour
Models
Response Models & Capacity
Prediction
Pavement Design Elements
Practitioner/Human Domain
Traditional ME Research Approach: Focus mainly on model and software development. Determining inputs, implementation and knowledge transfer is often neglected
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Field Testing &
Assessment
Design Inputs & Rules of Design
Material Behaviour
Models
Response Models & Capacity
Prediction
Design Feasibility Appropriate
Spec’s
Practitioner/Human Domain
Research/Software Domain
Pavement Design Elements
Practitioner/Human Domain
Vision for Medium Term Outcome: Develop a practical design method that combines the best elements of current design methods, and incorporates best practice elements of mechanistic analysis, field testing and construction
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Knowledge Based Approach
• Gather all available field performance data• Distil best elements of mechanistic analysis• Validate and refine for robustness• Develop clear, strong linkage to field testing and
specifications
To Date:• 23 Field sites with construction, maintenance & performance info
• 7 HVS Sites (22 test sections) with construction & performance
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The Design Process
LAB
DCP
Visuals
Test Pits
FWD
Materials Classification
Capacity Assessment
Specifications
CBR 7-15%
200 mm BSM 1
130 mm C4
> 200 mm G6
Mix Design• Shear Strength
• Durability
• Flexibility
Adopt aspects of Certainty Theory
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DCP Penetration (mm/blow)
Materials Classification Using Certainty Theory
Material Class
Class 1 Class 2 Class 3 Class 4Available Information
Rule certainty = 0.3
C(Hypotesis|DCP Info) 0.1 0.47 0.23 0.0
Grading 0.1 0.2 0.0 0.0
Systematic way of combining diverse types of evidence to reach a consistent, rational conclusion. Also teaches young engineers the key factors affecting materials.
Plasticity Index 0.1 0.35 0.1 0.0
Backcalc. Stiffness 0.1 0.59 0.30 0.0
Refusal 1.5 3.0 6.0
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The Design Process
LAB
DCP
Visuals
Test Pits
FWD
Materials Classification
Capacity Assessment
Specifications
CBR 7-15%
200 mm BSM 1
130 mm C4
> 200 mm G6
Mix Design• Shear Strength
• Durability
• Flexibility
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Development Approach
CBR 7-15%
> 200 mm G6
130 mm C4
200 mm BSM 1
Design Parameter for Layer
� Range of Traffic Accommodated
� Rut situation, RQ situation
� Cracking situation
� Need for rehabilitation
System Performance Indicators
Reps to Failure ??
Reps to Failure ??
Reps to Failure ??
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Development Approach
CBR 7-15%
> 200 mm G6
130 mm C4
200 mm BSM 1
� Range of Traffic Accommodated
� Rut situation, RQ situation
� Cracking situation
� Need for rehabilitation
Area = Shear Potential “Fingerprint”
System Performance Indicators
System BehaviourIndicator ???
Octahedral Shear Strain
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Capacity Assessment Example
CBR 7-15%
1. Material Classes
3. Subgrade LTES
100 MPa
2. Subgrade Class
4. Adjust for region & subgrade cover
97 MPa
150 mm G6
150 mm C4
150 mm BSM2
150 mm G7
5. Assign modular ratio’s and Maximum Emods
MR = 1.8, EMax = 325
MR = 3, EMax = 450
MR = 4, EMax = 550
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Capacity Assessment Example
97 MPa
175 MPa
450 MPa
550 MPa
6. Determine Effective LTES for each layer
Octahedral Shear Strain
∑∑∑∑ = 3.77
Linear Elastic Theory
Vertical Compressive Strain on Subgrade = 237 microstrain
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Handling Reliability
30 mesa
10 mesa
3 mesa
Pavement Number
Axles Accommodated
Category A Roads (95% Reliability)
Category B Roads (90% Reliability)
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CONCLUSION
• Project is ongoing, 90% of technical work to be completed in March, 2008
• Efforts dedicated to Mix Design not covered, but this is a significant component (Project Leader: Prof Kim Jenkins)
• Aspects of the methodology to be incorporated in the broader revision of the SA Pavement design method
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Thank you very muchfor your attention!
TRB WORKSHOP 153SOUTH AFRICAN HIGHWAY TECHNOLOGY AND PRACTICE