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HMA permanent deformation study: Progress report to the RPF 7 May 2008 Erik Denneman.

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Presentation on theme: "HMA permanent deformation study: Progress report to the RPF 7 May 2008 Erik Denneman."— Presentation transcript:

1 HMA permanent deformation study: Progress report to the RPF 7 May 2008 Erik Denneman

2 Slide 2 © CSIR Presentation structure Introduction HMA permanent deformation study, Background & objectives Methodology, Properties of standard mix, Permanent deformation phenomenon Results for Lab and APT testing on reference mix, Temperature, Loading, Age, compaction Conclusions and recommendations Preliminary results rut challenge mix

3 Slide 3 © CSIR HMA research programme State of the art surveyForensic study Determine scope Rut study (APT & Lab)Durability study (APT & Lab) Revised design guidelines

4 Slide 4 © CSIR Focus: Design for high demand situations

5 Slide 5 © CSIR Main objectives permanent deformation study Compare deformation APT to laboratory tests to: Identify appropriate tests for permanent deformation prediction, Develop protocols & acceptance criteria for selected tests. Test should reliably forecast deformation as function of: Mix composition Pavement structure Climate Traffic Research structure: First phase: standard ACM mix to provide benchmark (completed). Second phase: test purposely designed “rut challenge mixes”

6 Slide 6 © CSIR APT Study Field test devices: Heavy Vehicle Simulator (HVS), Model Mobile Load Simulator (MMLS). Objectives Assess relative effects of: Layer thickness Temperature Loading conditions (Short-term) asphalt ageing

7 Road R80

8 APT site

9 Slide 9 © CSIR Laboratory study Sources of material Aggregate from stockpiles and bitumen from tanks at asphalt plant Loose HMA mix sourced from truck Cores and slabs extracted from the test section Variables Method of preparation (source of material, compaction) Conditioning (unconditioned & short-term ageing) Binder content (optimum & high) Density (field & design) Layer thickness (25, 40 & 60 mm) Temperature Loading Mode of testing

10 Slide 10 © CSIR Overview of lab tests Compaction methods: Gyratory, Marshall, Modified Marshall, slab compaction, Kango Hammer. Wheel tracking tests: Hamburg wheel tracking test, Transportek Wheel Tracking Test (TWTT), Model Mobile Load Simulator (MMLS). General permanent deformation testing: Repeated Simple Shear Test at Constant Height (RRST-CH), Static creep, dynamic creep, Axial Load Slab test (ALS), resilient modulus (ITT). Binder Analysis: Penetration, softening point, viscosity, ductility, High Performance Liquid Chromatography (HPLC), Dynamic Shear Rheometer (DSR). Durability testing Lottman test, Beam fatigue. General testing BRD, MTRD, grading, binder content, ITS, Mashall stability & flow, constant head permeability, Marvil test, MRI scan, Rigden voids, ACV, Flakiness, 10% FACT, PSV, absorption, sand equivalent test.

11 Slide 11 © CSIR Reference mix aggregate properties Aggregate fractions used (all crushed/angular) Dolorite: 9.5 mm, 6.7 mm and crusher sand Dolomite: crusher sand Mine sand Aggregate properties Aggregate crushing value (ACV): 7 (25 max) 10% FACT: 344 kN (160 kN min) Water absorption: Coarse fractions: % (1.0% max) Fine fractions: % (1.5% max) Sand equivalent: (50 min) Flakiness index: 9-14% (50% max)

12 Slide 12 © CSIR Reference mix grading

13 Basic properties of standard mix: Marshall Binder type: 60/70 pen grade, PG 64 Optimum binder content: 5% PropertyTest ResultsSpecifications % voids in mix4.3%3 to 6% % VMA15%> 14% % VFB72%65 to 75% Filler-bitumen ratio to 1.5 Film thickness8.2 μm> 7 μm Marshall Stability~11 kN10 to 18 kN Marshall Flow~3.0 mm2 to 6 mm ITS~1 187 kPa> 800 kPa Static creep~242 MPa> 100 MPa Gyratory voids (300N)~2.4%>2.0% Dynamic creep modulus~ ~ 16.4 MPa15-20 MPa (medium - high)

14 Slide 14 © CSIR Permanent deformation (creep) of HMA Initial densification (volume change) Steady state shear deformation Shear failure

15 Slide 15 © CSIR 2006

16 Slide 16 © CSIR Effect of temperature Initial densification Steady state shear deformation Instable failure

17 Slide 17 © CSIR Increase of creep slope with temperature

18

19 MMLS re-run

20 Effect of loading condition

21 Effect of binder ageing

22

23

24 Slide 24 © CSIR Density of the test sections

25 Effect of Compaction

26 Slide 26 © CSIR Stresses and strains under various tests FEM Elastic displacement under MMLS in Laboratory

27 Slide 27 © CSIR Conclusions Objective: Identify appropriate tests Test methods that provide consistent trends with respect to variation in age, loading, temperature, compaction: Wheel tracking tests (TWTT, HWTT, MMLS) RSST-CH, and ITS, ITT. Test methods that did not provide consistent results: Marshall stability and flow, Dynamic creep, Axial loading slab test, and Static creep.

28 Slide 28 © CSIR (Main) Recommendations Include short term ageing in protocols of rutting tests, Slab compaction and gyratory compaction preferred over Marshall compaction Develop representable method for water permeability testing, Calibrate model for rutting prediction using HVS and RSST- CH results.

29 Slide 29 © CSIR Rut challenge mix Objective: assess performance of a mix with coarse aggregate skeleton Mix properties: 13.2 mm ACM Coarse graded (in Bailey terms 99% of CA LUW, and DASR 48.2 % porosity) 60/70 Pen grade binder

30 Slide 30 © CSIR Rut challenge mix

31 Slide 31 © CSIR Preliminary findings Sections constructed to the target density First lab test results (MMLS, RSST-CH) indicate performance similar to reference mix. HVS results (in 2 nd week of testing) start to indicate better performance of challenge mix Too early to tell!

32 Slide 32 © CSIR RSST-CH result reference & challenge Disclaimer: Individual test result do not derive conclusions!

33 The end… for now


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