PHILIP JOUBERT

STEWART SCOTT

Based on SAT Seminar (Pretoria)Presentations by:

• Products:Cobus Venter – GeotracGarth James – KaytechNicholas 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

BACKGROUND

Products and Purpose

Applications

Theory (Modeling)

The Road Forward

WHY GUIDELINES?

? 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

WHY REINFORCE ASPHALT?

Paving Fabrics: Geotextiles (Sealmac)

Glass Fibre Grids: Glassgrid / Glasstex

Polymer Grids: Polypropolene (AR - Grid)

Steel Grids: Wiremesh (Road Mesh)

Composites: Grid plus Fabric

PRODUCTS

PAVING FABRIC

GLASS FIBRE GRID

STEEL GRID

COMPOSITE : GRID / FABRIC

PURPOSE

Fabric Glass GridPolymer

GridSteel Grid Composite

MoistureBarrier

ReflectionCrack

FatigueCrack

Rutting

Products and Purpose

Applications

Theory (Modeling)

The Road Forward

WHY GUIDELINES?

RIGHT APPLICATION

TYPICAL APPLICATIONS

GLASS GRID FULL WIDTH

GLASS GRID FULL WIDTH

Percent Crack Reflection by length

48.4

29

21.4

7.30

20

40

60

% C

rack

ing

by

met

er

3 6 12 18 24 30 36 48 60 72

Time in Months

Fiberglass grid - long. Control - long.Fiberglass grid - trans. Control - trans.

GLASS GRID FULL WIDTH

GLASS GRID STRIPS

USE OF INTERLAYERS

GRID AND FABRIC INTERLAYER

GRID AND FABRIC INTERLAYER

GRID AND FABRIC INTERLAYER

GRID AND FABRIC INTERLAYER

CONCRETE SLABS OVERLAY

CONCRETE SLABS OVERLAY

CONCRETE SLABS OVERLAY

GLASSGRID - SETTLEMENT CRACKS

GLASSGRID - SETTLEMENT CRACKS

PAVING FABRIC

PAVING FABRIC

POTENTIAL PROBLEMS

POTENTIAL PROBLEMS

POTENTIAL PROBLEMS

Products and Purpose

Applications

Theory (Modeling)

The Road Forward

WHY GUIDELINES?

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?

MICRO EFFECTS: UNCRACKED

-200

-100

0

100

200

300

400

500

0 200 400 600 800 1000 1200 1400 1600

Offset From Load Centre (mm)

Te

ms

ile

Str

ain

(m

icro

str

ain

)

Benchmark

14,000 MPaReinforcement

10 MPa Reinforcement

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

Micro Effects: Cracked-Behaviour

• 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

WAY AHEAD?

-450

-400

-350

-300

-250

-200

-150

-100

-50

0

50

0 200 400 600 800 1000 1200 1400 1600 1800

Sh

ear

Str

ain

(m

icro

stra

in)

No Reinforcement

With Reinforcement

MICRO EFFECTS: CRACKED

• Some modelling is possible using FE

• Benefits of reinforcement are more obvious for cracked scenario

BUT Anisotropic effects still important

and likely to underestimate

benefits of reinforcement

• Layered Elastic modelling not feasible

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

Products and Purpose

Case Studies

Theory (Modeling)

The Road Forward

WHY GUIDELINES?

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%)

Y-Max BLI Case Studies

PRODUCT X: OVERLAYS > 50 MM

< 300

300 - 600

> 600

< 95

95 - 130

> 130

A,B,C

D,E

F,G,H

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

Base Layer Index

ME

SA

PRODUCT X: OVERLAYS > 50 MM

Already Cracked

Not Yet Cracked

Material Composition:

High tensile strength at low deformation

Shear adhesion to maintain good bond

Thermal and physically stable

No creep deformation

Recycle

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

REQUIREMENTS FOR GOOD PERFORMANCE

Constructability:

Easy placement

Remain secure during paving

Roll width

REQUIREMENTS FOR GOOD PERFORMANCE

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)

DESIGN GUIDELINES

General description (e.g. glass fibre polymer covered

Tensile strength (e.g. 50, 100, 200kN/m)

Elongation at break (e.g. <5%)

Melting point (e.g. >200°C)

Mass per unit area (e.g. >300g/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)

SPECIFICATION GUIDELINES

• 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

WAY AHEAD?