Crumb Rubber Modified Bitumen

BYASHWANI KUMARNMIT,BANGALORE

Bituminous Pavements –Life Cycle Issue

AXLE LOAD

WATER

HEAT

BITUMEN Poor

susceptibility

Solution is

MODIFIED BITUMEN

MODIFIER BITUMEN

MODIFIERS

• Crumb rubberThe scrap tyre is shredded into small pieces by the help of mechanical blades up to sizes of 1mm-75µm.

NATURAL RUBBER

(25%)

WASTETYRE

CRUMB(75%)

MODIFIER(15% of bitumen)

CRMB Development

• Charles McDonald ,an engineer with City of Phoenix, Arizona, US developed in 1960s.

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.

Production method

• It is produced from discarded rubber by two methods:-

a) Ambient grinding

b) Cryogenic grinding

Ambient Grinding

• Processed at or above ordinary room temperature

• Produces irregularly shaped ,torn particles with relatively large surface area

Cryogenic Grinding

• This process uses liquid Nitrogen to freeze CR.

• It has relatively lower surface area.

Method of mixing of CR in Bitumen

a) Dry process

b) Wet process

Dry Process

• Introduced by two Swedish company

• Crumb rubber as a substitute for a part of mineral aggregate

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.

CR-interaction Process

Comparison

Characteristic VG 10 VG 30 VG 40 CRMB-50 CRMB-55 CRMB-60

Penetration at 25º C,(0.1 mm, 100g, 5 Sec.)

80-100 50-70 40-60 < 70 < 60 < 50

Softening Point, ºC(R&B), Minimum

40 47 50 50 55 60

Flash Point, COCºC, Min 220 220 220 220 220 220

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 .

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.

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.

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.

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.

Thank you