ASPHALT REINFORCEMENT

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ASPHALT REINFORCEMENT
DESIGN GUIDELINES FOR
SOUTHERN AFRICA?
PHILIP JOUBERT STEWART SCOTT
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BACKGROUND

• Based on SAT Seminar (Pretoria)
• Presentations by
• Products
• Cobus Venter Geotrac
• Garth James Kaytech
• Nicholas Reck African Gabions
• Application
• Mynhardt Augustyn VKE
• Philip Joubert Stewart Scott
• Analytical Techniques
• Dr Fritz Jooste Modelling Analysis
  Systems
• Innovation Planning
• Joop van Wamelen Agrément SA

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WHY GUIDELINES?

• Products and Purpose
• Applications
• Theory (Modeling)
• The Road Forward

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WHY REINFORCE ASPHALT?

• Normally during rehabilitation action
• Grids/fabrics laid between old (distressed)
  and new asphalt overlay
• To Provide Increased Resistance to
• Reflective Cracking
• Fatigue Cracking (strengthen pavement)
• Deformation (Rutting)
• Moisture/Fines Movement

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PRODUCTS

• Paving Fabrics Geotextiles (Sealmac)
• Glass Fibre Grids Glassgrid / Glasstex
• Polymer Grids Polypropolene (AR - Grid)
• Steel Grids Wiremesh (Road Mesh)
• Composites Grid plus Fabric

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PAVING FABRIC
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GLASS FIBRE GRID
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STEEL GRID
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COMPOSITE GRID / FABRIC
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PURPOSE
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WHY GUIDELINES?

• Products and Purpose
• Applications
• Theory (Modeling)
• The Road Forward

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RIGHT APPLICATION
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TYPICAL APPLICATIONS
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GLASS GRID FULL WIDTH
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GLASS GRID FULL WIDTH
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Percent Crack Reflection by length
GLASS GRID FULL WIDTH
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GLASS GRID STRIPS
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USE OF INTERLAYERS
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GRID AND FABRIC INTERLAYER
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GRID AND FABRIC INTERLAYER
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GRID AND FABRIC INTERLAYER
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GRID AND FABRIC INTERLAYER
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CONCRETE SLABS OVERLAY
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CONCRETE SLABS OVERLAY
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CONCRETE SLABS OVERLAY
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GLASSGRID - SETTLEMENT CRACKS
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GLASSGRID - SETTLEMENT CRACKS
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PAVING FABRIC
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PAVING FABRIC
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POTENTIAL PROBLEMS
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POTENTIAL PROBLEMS
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POTENTIAL PROBLEMS
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WHY GUIDELINES?

• Products and Purpose
• Applications
• Theory (Modeling)
• The Road Forward

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WHY MODEL?

• To investigate effects of
• changing pavement parameters on pavement response

• Given Effect X,
• what is Strain-Y in Asphalt?

• How will asphalt perform at Strain-Y?

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MICRO EFFECTS UNCRACKED
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MICRO EFFECTS UNCRACKED

• Thickness and anisotropic effects distort
  calculated strains

• Strain unlikely to be reduced by Reinforcement
• UNLESS
• Reinforcement considerably stiffer than Asphalt,
  and
• there is zero slip

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Micro Effects Cracked-Behaviour
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WAY AHEAD?

• Expert Panel / National Interest Group,
• develop code of practice for Southern Africa,
• follow approach Euro committee/ TRB Group,
• formalise sound network management approach
• Product Performance Guarantee?
• Vast potential matrix of operating conditions,
• Difficult to follow this line of approach
• Agrément Certification?
• Standard conformance testing
• Rutting, Beam Tests, Fatigue Testing (MMLS)
• product approval / application type, within
  boundary conditions

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MICRO EFFECTS CRACKED

• Some modelling is possible using FE

• Layered Elastic modelling not feasible

• Benefits of reinforcement are more obvious for
  cracked scenario

BUT Anisotropic effects still important and
likely to underestimate benefits of
reinforcement
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MODELLING POSSIBILITIES SUMMARY

• Routine modelling is likely to underestimate
  benefits of reinforcement

• Routine modelling does not appear feasible at
  this stage

Key Problem Impact on damage inhibiting and
crack retardation not evaluated at all
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WHY GUIDELINES?

• Products and Purpose
• Case Studies
• Theory (Modeling)
• The Road Forward

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WAY AHEAD

• Build Confidence Focus on field performance and
  validation (80 )

• Advanced modelling used mainly to identify key
  variables (5)

• Improve routine models to be able to accommodate
  transfer functions (15)

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PRODUCT X OVERLAYS gt 50 MM
Case Studies
BLI
Y-Max
lt 300
lt 95
A,B,C
300 - 600
95 - 130
D,E
F,G,H
gt 600
gt 130
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CASE STUDY INFORMATION

• Crack Type, Degree and Extent

• Maximum Deflection, Base Layer Index, Test Details

• Support Type and Thickness

• Traffic Volumes, Daily E80s

• Overlay and Construction Details

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PRODUCT X OVERLAYS gt 50 MM
Not Yet Cracked
Already Cracked
MESA
Base Layer Index
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REQUIREMENTS FOR GOOD PERFORMANCE

• Material Composition
• High tensile strength at low deformation
• Shear adhesion to maintain good bond
• Thermal and physically stable
• No creep deformation
• Recycle

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REQUIREMENTS FOR GOOD PERFORMANCE

• Geometry
• Sufficient cross-sectional grid area to redirect
  tensile stresses (slip over existing pavement)
• Mesh opening to achieve optimum shear adhesion
• Opening such to promote aggregate interlock
• Strip Width beyond crack

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REQUIREMENTS FOR GOOD PERFORMANCE

• Constructability
• Easy placement
• Remain secure during paving
• Roll width

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DESIGN GUIDELINES

• Structurally sound (e.g. no excessive movement)
• Evaluate condition (e.g. FWD, Crack Activity
  Meter)
• First address structural problems (e.g. potholes,
  slab replacement)
• Seal all large cracks
• Pave leveling course
• Overlay thickness (40mm deeper more effective)
• Tack coat (modify?)
• Consider potential for slippage
• Partial or full coverage (continuous better)

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SPECIFICATION GUIDELINES

• General description (e.g. glass fibre polymer
  covered
• Tensile strength (e.g. 50, 100, 200kN/m)
• Elongation at break (e.g. lt5)
• Melting point (e.g. gt200C)
• Mass per unit area (e.g. gt300g/m2)
• Storage (e.g. covered, dry, dust-free)
• Pavement preparation (e.g. cracks, levelling,
  clean, damp)
• Construction (e.g. tack, ripples, joints,
  roller, curves, paver/trucks)

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WAY AHEAD?

• Boundary operating conditions
• Minimum Joint Efficiency (Crack activity),
• Maximum surface deflections,
• Maximum vertical alignment for rutting)
• National Reinforcement Register
• Identifying solution,
• Anticipated outcomes,
• Design criteria,
• Validation approach
• Validation approach
• Crack mapping,
• Indices,
• TMH9 equivalent approach