Interim Guidelines:The Design and Use of Foamed

Bitumen Treated Bases

Fenella Long

Road Pavements Forum13-14 November 2001

Outline

Objectives Projects Interim guideline document Timelines and deliverables Structural design procedure

Objectives

Synthesise – Available information

– Best practice

– Latest research results

Provide Interim Guidelines while further information and experience is gathered

Develop a structural design procedure for incorporation into the South African Mechanistic-Empirical Design Procedure

Similar work with bituminous emulsion treated bases

Projects and Funding

Laboratory Testing: Gautrans, C&CI, SANRAL HVS Testing: Gautrans Interim Guideline document

– Phase 1: Gautrans– Phase 2: SABITA, managed by the Asphalt Academy

Foamed Asphalt Working Group

Interim Guideline DocumentChapter 1. Introduction

Chapter 2. Selection Criteria

(Transportek)

Chapters 3-5. Mix Design Considerations

(Prof. Jenkins)

Chapter 6. Structural Design (Transportek)

Chapter 7. Construction Aspects (Transportek)

Chapter 8. Conclusions

Phase 1

Phase 2 Phase 1

Timelines and Deliverables

Phase 1– Draft completed June 2001– Currently incorporating comments

Phase 2– October 2001 – March 2002

Seminars run by the Asphalt Academy– May 2002

Structural Design

Design philosophy Mechanistic-empirical design procedure Based on HVS and laboratory tests Distress mechanisms, transfer functions

Design Philosophy

Adequate support Prevent overloading

– Materials very sensitive to overloading Optimize design for distress mechanisms Prevent moisture ingress

HVS Tests

Road P243/1, between Vereeniging and Heidelberg

Deep In Situ Recycled Base– 2% cement– 1.8% foamed bitumen or bituminous emulsion

2 HVS test sections per material 3 Wheel loads

Laboratory Tests

Unconfined compressive strength (UCS) Indirect tensile strength (ITS) CBR Static triaxial Dynamic triaxial Flexural fatigue beam Permeability Erodibility

Distress Mechanisms

Fatigue Permanent deformation

Fatigue Transfer Function HVS Tests

– Reduction in stiffness

409A4 and 409B4

0

500

1000

1500

2000

2500

3000

3500

0 300000 600000 900000 1200000 1500000

Repetitions

Ela

stic

Sti

ffn

ess

(MP

a)

409A4: MDD4

409A4: MDD12,409B4: MDD4

Traffic load 80kN

Traffic load 100kN

Fatigue Transfer Function HVS Tests

– Reduction in stiffness

411A4

0

500

1000

1500

2000

2500

3000

3500

0 300000 600000 900000 1200000 1500000

Repetitions

Ela

stic

Sti

ffn

ess

(MP

a)

MDD4

MDD8

MDD12

Traffic load 40kN

Traffic load 80kN

Fatigue Transfer Function

Effective fatigue life– Repetitions to 400 MPa stiffness

1000

10000

100000

1000000

10000000

100000000

0 20 40 60 80 100

Load (kN)

Eff

ec

tiv

e F

ati

gu

e L

ife

(r

ep

eti

tio

ns

)

Fatigue Transfer Function Laboratory test

– Four-point beam fatigue test

– Strain-at-break, b

0

100

200

300

400

500

600

700

800

900

1000

0.0 1.0 2.0 3.0 4.0 5.0Residual Binder Content (%)

Str

ain

- at

-bre

ak (

mic

rost

rain

)

2% CementFoam, 2% cementFoam, 1% cement

Fatigue Transfer Function Pavement structure Tensile strain at the bottom of the base,

Foamed bitumen

base

b

Strain ratio =

from laboratory test

Fatigue Transfer Function

Effective fatigue as a function of strain ratio

1000

10000

100000

1000000

10000000

0.0 1.0 2.0 3.0 4.0 5.0Strain Ratio (Strain/Strain-at-break)

Eff

ecti

ve F

atig

ue

Lif

e

All dataAverageTransfer function

1000

10000

100000

1000000

10000000

0.0 1.0 2.0 3.0 4.0 5.0Strain Ratio (Strain/Strain-at-break)

Eff

ecti

ve F

atig

ue

Lif

e

All dataAverageTransfer functioncemented cat Acemented cat Bcemented cat Ccemented cat D

Fatigue Transfer Function

Effective fatigue as a function of strain ratio

Permanent Deformation Transfer Function HVS Data

– Permanent deformation of base layer from MDD data

– NF,PD = f (wheel load, plastic strain)

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

0 20 40 60 80 100

Wheel Load (kN)

Rep

etit

ion

s

1% plastic strain

5% plastic strain

10% plastic strain

Permanent Deformation Transfer Function

Laboratory tests– Static and dynamic triaxial tests

– NF,PD = f (stress ratio, plastic strain, relative density, saturation, foamed bitumen and cement contents)

– Wider range of material conditions

Permanent Deformation Transfer Function

Pavement structure Stress ratio in the base layer, SR

Foamed bitumen

base

1

1allowable

Stress ratio =

from laboratory test

Permanent Deformation Transfer Function

Combine field and laboratory models Work in progress

Repetitions

Stress Ratio

Relative densitySaturationFoamed bitumen contentCement contentPlastic strain

Damage Factors

Effect of overloading Load equivalency

Fatigue– n 5.6

Permanent deformation– n 2.4

N =P

P80kN

n

Limitations

One material, ferricrete HVS tests

– 2.0% cement – 1.8% foamed bitumen

Laboratory specimen preparation

Conclusions

“Interim Guidelines for Foamed Bitumen Treated Bases” available March 2002

Includes structural design procedure for SA Mechanistic-Empirical Design Procedure

Industry feedback to gather experience and refine guidelines