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