Introduction to Bitumen Stabilised Materials BSMs

Transcription

1 Introduction to Bitumen Stabilised Materials BSMs Kim Jenkins SARF Course on BSMs Assagai, Shongweni 14 and 15 July 2015 tellenbosch

2 Hot In Place In Plant Cold

3 Rut resistant 3% 2% What defines a BSM? Strongly cemented Lightly cemented Less economical FBS (Aus)? Quick Lime Cement 1% Unbound Crushed stone / gravel / soil BSM (RSA) FBS (NZ)? HMA Stress 0% dependent 1% 2% 3% 4% Bitumen 5% Fatigue resistant

4 1. BSM Binder Type BITUMEN EMULSION Surfactants Colloidal Mill Acid or Caustic Soda Hot bitumen FOAMED BITUMEN Expansion chamber Wat Water Bitumen Water Air Mill 5 microns

5 2. Bitumen Dispersion Microscopic Analysis BSM-emulsion BSM-foam

6 Type of Dispersion Painting BSM-emulsion Spot-welding BSM-foam

7 Nature of BSMs (cold) BSM-foam (sand) 0.5mm Bitumen dispersion: Non-continuously bound

8 BITUMEN DISPERSION Thin bitumen Tiny bitumen film around pieces steam ± 20 C ± 100 C Particles < mm (# 200 sieve)

9 3. Aggregate Types Recycled Materials Natural Gravel CBR>25% 100% RAP Crushed Gravel CBR>45% Graded Crushed Stone 50% RAP + GCS

10 4. Grading requirements Cumulative % passing Foam Emulsion Sieve size (mm)

11 Optimisation of grading curve Indirect Tensile Strength (kpa) Emulsion 3.3% bitumen Foam 3.5% bitumen Without blending With 10% fines blend

12 Moisture: Durability FOAMED BITUMEN EMULSION Poorly graded Well graded Well graded

13 5. Bitumen content BSM Class Aggregate Bitumen (%) BSM 1 >75% RAP + Crush agg BSM 1 >25% RAP + Crush agg BSM 1 <25% RAP + Crush agg BSM2 Natural Gravel (CBR>45%) BSM 3 Natural Gravel (CBR>25%) (Wirtgen Recycling Manual, 2012)

14 Aggregate Mixing Temperature Foam > 25ºC Foam 15ºC Emulsion 10ºC OK Foam <15ºC Emulsion<10ºC X

15 Aggregate Temperature vs Particle coating (BSM-foam) Maximum Particle Size (mm) Practically no coating Partial coating Complete coating Aggregate Mixing Temperature (degc) Jenkins, 2000

16 7. Moisture Regime (mix & compact) EMULSION FOAMED BITUMEN Bitumen coating (thin films) Bitumen dispersion selective Some partial coating Partial coating Optimum Fluids Content 70% to 90% of OMC

17 MOISTURE DURABILITY HVS Cape Town on BSM PERMEABILITY Water introduction into 2.3% foamed bitumen stabilised base

18 8. Behaviour = Granular type Resilient Modulus of BSM-foam (BC = 2%) Resilient Modulus Mr (MPa) Sum of Principal Stresses q (kpa) s3 12kPa 24kPa 48kPa 72kPa

19 Stress dependency (triaxial) Resilient moduli 75C-0 blend Resilient modulus [MPa] % cem 0% cem Not main purpose BSM-emulsion BSM-foam Mix: A-75C-0 B-75C-0 C-75C Bulk stress [kpa]

20 Visco-elastic properties of BSM-foam HMA HW Fatigue cracks Tref = 20C BSM Rutting Equiv HOT T or Slow Traffic Equiv COLD T or Fast Traffic

21 Validation (100% RAP Foamed Mix) ºC 50ºC Repeated Load Triaxial σ1 Permanent axial strain σ2 60C 40C 50C ºC Number of load repetitions [-]

22 10. Active Filler: Purpose? Improve adhesion PRIMARY Improve dispersion REASONS Modify plasticity Increase stiffness & strength Accelerate curing Emulsion Foam Breaking time Dispersion! Improve workability

23 Influence of Active Filler BSM Strain-at-break εb Strength and flexibility Foamed bitumen, Strain Cement, Strain* Foamed bitumen, UCS Cement, UCS* Cement < 1%? Unconfined Compressive Strength (kpa) Cement : Foamed Bitumen Ratio CSIR

24 Can 1.5% cement work? BSM-foam + 1.5% cem using cracked CTB 2 years of traffic

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26 Stress (kpa) strength Mix Design Testing A1 Cemented Strain Bituminous Compressive Tensile Shear It s undeniable: More cement = more strength!

27 Stress (kpa) strength Dissipated Energy A2 A1 Cemented Strain Bituminous W = 0.5 σε Compressive Tensile Shear It s undeniable: More cement = more strength!

28 11. Time Dependency Mr (field) versus cure PSPA N7 PSPA M r Analysis ove r 7 M onths B1-B3 B4-B6 Poly. (B4-B6) Mr (MPa) Mr Moisture Tim e (days)

29 BITUMEN STABILISED MATERIALS TG2 : 2nd EDITION Published in South Africa by Asphalt Academy (CSIR / SABITA) May 2009

30 Conclusions Many combinations of aggregates can be used (continuous grading) BSMs = / asphalt BSM is granular with higher cohesion and shear strength Flexibility is NB! Active filler content needs to be restricted

31 Thank you Roads & Enviro!