Cold mix design based on current understanding of the breaking of bitumen emulsions
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The document discusses the current understanding of breaking bitumen emulsions and its implications for cold mix design in road construction. It highlights the environmental benefits of cold mixes but notes their limited application due to technical challenges and the need for specific testing methods. The authors emphasize the importance of standardizing practices and developing reliable design procedures to aid in evaluating cold mix performance.
Cold mix design based on current understanding of the breaking of bitumen emulsions
- 1. A RATIONAL APPROACH BASED ON THE CURRENT UNDERSTANDING OF THE BREAKING OF BITUMEN EMULSIONS Didier Lesueur & Juan José Potti COLD MIX DESIGN: EATA 2004 – Nottingham – 6th July 2004
- 2. Introduction › Cold mixes are Environmentally Friendly Construction Technologies reduce energy spending (no aggregate drying) lower particle and fume emissions › But still used in a narrow application range mostly on secondary roads France ~ 200 kt slow setting emulsions for ~ 2 500 kt of bitumen for hot mixes › Why is that so? In part because they are thought to be highly technical and therefore risky
- 3. Hot and cold mixes › Hot Mix aggregates bitumen air voids › Cold Mix aggregates bitumen air voids water
- 4. COLD MIX The emulsion is not the final binder Water at a time-dependent amount Proportion not sufficient: Is the bitumen in the form of droplets? COLD MIX The emulsion is not the final binder Water at a time-dependent amount Proportion not sufficient: Is the bitumen in the form of droplets? Final density difficult to measure and control COLD MIX The emulsion is not the final binder Water at a time-dependent amount Proportion not sufficient: Is the bitumen in the form of droplets? Final density difficult to measure and control Depends on the breaking process COLD MIX The emulsion is not the final binder HOT MIX QUALITY CONTROL Quality of constituents Proportion of constituents Final density will ensure good performance WORKABILITY Depends on temperature Hot and cold mixes (2)
- 5. Hot and Cold Mixes (3) › 1st Consequence: Cold mixes need specific testing methods to measure what is usually not taken into account for hot mixes › 2nd Consequence: Workability is controlled by the breaking of the emulsion How do we do that?
- 6. The breaking of bitumen emulsions › The stability of emulsions (from Schubert, AIChE 2000)
- 7. -500 -250 0 250 500 0 5 10 15 20 interparticle distance (nm) interactionenergy(kT) ATTRACTION -500 -250 0 250 500 0 5 10 15 20 interparticle distance (nm) interactionenergy(kT) REPULSION ATTRACTION The breaking of bitumen emulsions (2) -500 -250 0 250 500 0 5 10 15 20 interparticle distance (nm) interactionenergy(kT) REPULSION ATTRACTION
- 8. The breaking of bitumen emulsions (3) › The Van der Waals attraction is inevitable and essentially independant of bitumen origin › The electrostatic repulsion can be tuned by: The choice of emulsifier The ionic environment
- 9. -100 -50 0 50 100 0 2 4 6 8 10 12 14 pH zetapotential(mV) The breaking of bitumen emulsions (4) STABLE UNSTABLE: BREAKING
- 10. The breaking of bitumen emulsions (5) › The breaking scenario of an unstable bitumen emulsion (after Bonakdar et al., Coll. Surf. A176,2001) t= 0 t= 1 h e u r e t= 2 h e u r e s 10 µ m10 µ m10 µ m
- 11. The breaking of bitumen emulsions (6) › The breaking can be induced by the aggregates Ca2+ M g2+ K+ Na+ Cl- SO4- 0 500 1000 1500 2000 2500 concentration(mg/l) local water - pH = 7,7 GE - pH = 7,1
- 12. The breaking of bitumen emulsions (7) › Consequences: Two possible scenarios when an emulsion is mixed with aggregates › 1: The ionic environment is not modified and the emulsion remains essentially stable › 2: The ionic environment is highly modified and the emulsion becomes unstable
- 13. The breaking of bitumen emulsions (8) No emulsion destabilisation (non- reactive aggregates) Emulsion destabilisation (reactive aggregates): gelling Evaporation kinetics (days) A. FILM FORMING Contraction kinetics (min) B. GEL CONTRACTION
- 14. Designing cold mixes › Consequences: The mix design needs to take into account the breaking kinetics › Also, emulsifier choice will guarantee good coating › In all cases, the mix design needs to give a reasonable estimate of the long term properties › Water content is not indicative of the breaking of the emulsion (except when almost all is gone) › Inside the mix, breaking may not be homogeneous
- 15. Designing cold mixes (2) › The mix design shall confirm that the emulsion breaking will permit laying down and compaction › It is not necessary to use complicated laboratory tests on the emulsion as long as the corresponding property can be directly measured on the mix How can we measure it on the mix?
- 16. Designing cold mixes (3)
- 17. Designing cold mixes (4) › Adapting the emulsion reactivity through workability (after Eckmann et al., RGRA 802, 2002) NOT WORKABLE curing time (hours)
- 18. Designing cold mixes (5)
- 19. 0 10 20 30 40 50 60 70 1 10 100 1000 number of rotations totalvolume(heightinmm) water total porosity Designing cold mixes (6) › Need to take into account the presence of water onset of water drainage ~ 10 % ~ 2 %
- 20. Designing cold mixes (7) › There exists appropriate tools to estimate workability (laying down) › Not clear yet how compaction can be predicted at the laboratory scale › Long term mechanical properties can be measured with current means (curing procedure 14 days, 35ºC, 20 % RH representative of 1-3 years in the field - see Serfass et al., RILEM 2003) › What about short term? Fatigue?
- 21. Designing cold mixes (8)
- 22. Conclusion: Key Messages › Cold mixes are not that technical: We (almost) know what´s going on › Still, they sometimes need specific testing methods (compaction, curing) › Time to standardize the practices standardize the accepted practices do the necessary pre-normative research develop a reliable design procedure allow the road network managers to evaluate the product on a sound basis