Interim Guidelines: The Design and Use of Foamed Bitumen Treated Bases Fenella Long Road Pavements Forum November 2001

Outline u Objectives u Projects u Interim guideline document u Timelines and deliverables u Structural design procedure

Objectives u Synthesise –Available information –Best practice –Latest research results u Provide Interim Guidelines while further information and experience is gathered u Develop a structural design procedure for incorporation into the South African Mechanistic- Empirical Design Procedure u Similar work with bituminous emulsion treated bases

Projects and Funding u Laboratory Testing: Gautrans, C&CI, SANRAL u HVS Testing:Gautrans u Interim Guideline document –Phase 1: Gautrans –Phase 2: SABITA, managed by the Asphalt Academy u Foamed Asphalt Working Group

Interim Guideline Document Chapter 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 u Phase 1 –Draft completed June 2001 –Currently incorporating comments u Phase 2 –October 2001 – March 2002 u Seminars run by the Asphalt Academy –May 2002

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

Design Philosophy u Adequate support u Prevent overloading –Materials very sensitive to overloading u Optimize design for distress mechanisms u Prevent moisture ingress

HVS Tests u Road P243/1, between Vereeniging and Heidelberg u Deep In Situ Recycled Base –2% cement –1.8% foamed bitumen or bituminous emulsion u 2 HVS test sections per material u 3 Wheel loads

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

Distress Mechanisms u Fatigue u Permanent deformation

Fatigue Transfer Function u HVS Tests –Reduction in stiffness

Fatigue Transfer Function u HVS Tests –Reduction in stiffness

Fatigue Transfer Function u Effective fatigue life –Repetitions to 400 MPa stiffness

Fatigue Transfer Function u Laboratory test –Four-point beam fatigue test –Strain-at-break,  b

Fatigue Transfer Function u Pavement structure u Tensile strain at the bottom of the base,  Foamed bitumen base bb Strain ratio = from laboratory test

Fatigue Transfer Function u Effective fatigue as a function of strain ratio

Fatigue Transfer Function u Effective fatigue as a function of strain ratio

Permanent Deformation Transfer Function u HVS Data –Permanent deformation of base layer from MDD data –N F,PD = f (wheel load, plastic strain)

Permanent Deformation Transfer Function u Laboratory tests –Static and dynamic triaxial tests –N F,PD =f (stress ratio, plastic strain, relative density, saturation, foamed bitumen and cement contents) –Wider range of material conditions

Permanent Deformation Transfer Function u Pavement structure u Stress ratio in the base layer, SR Foamed bitumen base  1  1 allowable Stress ratio = from laboratory test

Permanent Deformation Transfer Function u Combine field and laboratory models u Work in progress Repetitions Stress Ratio Relative density Saturation Foamed bitumen content Cement content Plastic strain

Damage Factors u Effect of overloading u Load equivalency u Fatigue –n  5.6 u Permanent deformation –n  2.4 N = P P 80kN n

Limitations u One material, ferricrete u HVS tests –2.0% cement –1.8% foamed bitumen u Laboratory specimen preparation

Conclusions u “Interim Guidelines for Foamed Bitumen Treated Bases” available March 2002 u Includes structural design procedure for SA Mechanistic-Empirical Design Procedure u Industry feedback to gather experience and refine guidelines