Crumb Rubber Modified Bitumen (CRMB) is hydrocarbon binder obtained through physical and chemical interaction of crumb rubber (produced by recycling of used tyres) with bitumen and some specific additives.
7. Source of Crumb Rubber
• Crumb rubber is obtained from truck or automobile tyres .
• Whole truck tyres contain 18 % natural rubber compared to 9
percent in automobile tyre.
8. Production method
• It is produced from discarded rubber by two methods:-
a) Ambient grinding
b) Cryogenic grinding
9. Ambient Grinding
• Processed at or above ordinary room temperature
• Produces irregularly shaped ,torn particles with relatively large
surface area
10. Cryogenic Grinding
• This process uses liquid Nitrogen to freeze CR.
• It has relatively lower surface area.
12. Dry Process
• Introduced by two Swedish company
• Crumb rubber as a substitute for a part of mineral
aggregate
13. Wet Process
• Thoroughly mixing crumbs of CR with bitumen and allowing
it to react for a period of 45min-1 hour.
• High temperature should be maintained.
17. Waste tyre crumb for roads
• Globally over 15 million tones of waste tyres are
generated, annually.
• India also contributes approx. 1 million tyres annually.
• If Waste tyre crumb is to be used with bitumen for
wearing course, an approx. 250 no's of tyre waste can be
consumed in roads every day or 100,000 no's of waste tyre
annually .
18. Advantages
• Lower susceptibility to daily & seasonal temperature
variations.
• Higher resistance to deformation at elevated pavement
temperature.
• Better adhesion between aggregates & binder.
• Prevention of cracking & reflective cracking.
• Overall improved performance under heavy traffic conditions.
19. Disadvantages
• The bitumen-rubber materials must be properly selected ,
designed & produced .
• Construction is more challenging as temperature requirement
are more critical.
• It is not possible to store CR-MB at elevated temperature
without equipping storage tanks with augurs.
20. Quality control requirements
• CRMB producer must obtain the viscosity curve for mix if the
source of bitumen and/or crumb rubber changes.
• It should be agitated continuously.
• Compaction of asphalt mix containing CRMB should begin
promptly to adequate compaction of pavement.
• Pneumatic- tyred rollers tend to pick up the asphalt mix
containing CRMB and therefore , should not be used.
21. References
• “A Study on the Performance of Crumb Rubber Modified Bitumen
by Varying the Sizes of Crumb Rubber” by Nabin Rana Magar.
• “Quality control requirement for using crumb rubber modified
bitumen(CRMB) in bituminous mixtures” by Prithvi Singh kandhal.
• “Recycled tyre rubber modified bitumens for road asphalt mixtures
:A literature review” by Davide Lo Presti.
• “Laboratory comparison of the crumb-rubber and SBS modified
bitumen and hot mix asphalt” by Baha Vural Köka , Hakan Çolak.