Introduction to Bitumen Stabilised Materials BSMs Kim Jenkins SARF Course on BSMs Assagai, Shongweni 14 and 15 July 2015 tellenbosch
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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
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
2. Bitumen Dispersion Microscopic Analysis BSM-emulsion BSM-foam
Type of Dispersion Painting BSM-emulsion Spot-welding BSM-foam
Nature of BSMs (cold) BSM-foam (sand) 0.5mm Bitumen dispersion: Non-continuously bound
BITUMEN DISPERSION Thin bitumen Tiny bitumen film around pieces steam ± 20 C ± 100 C Particles < 0.075 mm (# 200 sieve)
3. Aggregate Types Recycled Materials Natural Gravel CBR>25% 100% RAP Crushed Gravel CBR>45% Graded Crushed Stone 50% RAP + GCS
4. Grading requirements Cumulative % passing 100 80 60 40 20 0 Foam Emulsion 0.08 0.15 0.3 0.6 1.18 2.36 4.75 6.7 9.5 13.2 Sieve size (mm)
Optimisation of grading curve 700 600 Indirect Tensile Strength (kpa) 500 400 300 200 100 0 Emulsion 3.3% bitumen Foam 3.5% bitumen Without blending With 10% fines blend
Moisture: Durability FOAMED BITUMEN EMULSION Poorly graded Well graded Well graded
5. Bitumen content BSM Class Aggregate Bitumen (%) BSM 1 >75% RAP + Crush agg 1.6 2.1 BSM 1 >25% RAP + Crush agg 1.8 2.5 BSM 1 <25% RAP + Crush agg 2.0 3.0 BSM2 Natural Gravel (CBR>45%) 2.2 3.5 BSM 3 Natural Gravel (CBR>25%) 2.5 4.0 (Wirtgen Recycling Manual, 2012)
Aggregate Mixing Temperature Foam > 25ºC Foam 15ºC Emulsion 10ºC OK Foam <15ºC Emulsion<10ºC X
Aggregate Temperature vs Particle coating (BSM-foam) Maximum Particle Size (mm) 40 35 30 25 20 15 10 5 0 Practically no coating Partial coating Complete coating 35 45 65 85 Aggregate Mixing Temperature (degc) Jenkins, 2000
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
MOISTURE DURABILITY HVS Cape Town on BSM PERMEABILITY Water introduction into 2.3% foamed bitumen stabilised base
8. Behaviour = Granular type Resilient Modulus of BSM-foam (BC = 2%) Resilient Modulus Mr (MPa) 1350 1150 950 750 550 350 150 0.0 200.0 400.0 600.0 800.0 1000.0 Sum of Principal Stresses q (kpa) s3 12kPa 24kPa 48kPa 72kPa
Stress dependency (triaxial) Resilient moduli 75C-0 blend Resilient modulus [MPa] 10000 1000 1% cem 0% cem Not main purpose BSM-emulsion BSM-foam Mix: A-75C-0 B-75C-0 C-75C-0 100 100 1000 10000 Bulk stress [kpa]
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
Validation (100% RAP Foamed Mix) 10.00 9.00 8.00 60ºC 50ºC Repeated Load Triaxial σ1 Permanent axial strain 7.00 6.00 5.00 4.00 3.00 σ2 60C 40C 50C 2.00 40ºC 1.00 0.00 0 200000 400000 600000 800000 1000000 Number of load repetitions [-]
10. Active Filler: Purpose? Improve adhesion PRIMARY Improve dispersion REASONS Modify plasticity Increase stiffness & strength Accelerate curing Emulsion Foam Breaking time Dispersion! Improve workability
Influence of Active Filler BSM Strain-at-break εb 800 700 600 500 400 300 200 100 Strength and flexibility Foamed bitumen, Strain Cement, Strain* Foamed bitumen, UCS Cement, UCS* Cement < 1%? 4000 3500 3000 2500 2000 1500 1000 500 Unconfined Compressive Strength (kpa) 0 0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 Cement : Foamed Bitumen Ratio CSIR
Can 1.5% cement work? BSM-foam + 1.5% cem using cracked CTB 2 years of traffic
Stress (kpa) strength 1800 1600 1400 1200 1000 800 600 400 200 0 Mix Design Testing A1 Cemented 0 0.1 0.2 0.3 0.4 0.5 0.6 Strain Bituminous Compressive Tensile Shear It s undeniable: More cement = more strength!
Stress (kpa) strength 1800 1600 1400 1200 1000 800 600 400 200 0 Dissipated Energy A2 A1 Cemented 0 0.1 0.2 0.3 0.4 0.5 0.6 Strain Bituminous W = 0.5 σε Compressive Tensile Shear It s undeniable: More cement = more strength!
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) 4000 3500 3000 2500 2000 1500 1000 500 0 Mr Moisture 0 50 100 150 200 250 Tim e (days)
BITUMEN STABILISED MATERIALS TG2 : 2nd EDITION Published in South Africa by Asphalt Academy (CSIR / SABITA) May 2009
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
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