National Modified Bitumen (CRMB & PMB)
(Mfd. as per IS 15462:2004 & IRC: SP 53:2002)
Flexible pavements tend to become soft in summer and brittle in winter due to high temperature variations. Also early development of distress symptoms occurs duee to heavy traffic loads on such roads. In these circumstances ordinary bitumen is not sufficient to over come these symptoms.
Modified bitumens are formulated with additives to improve their service performance by changing such properties as their durability, resistance to ageing, elasticity and/or plasticity. Thus altering the physical properties allows bitumen to resist the stress caused by temperature variations, high traffic loads, thereby enhancing pavement life and reducing maintenance costs. The most important modifiers are polymers.
Modified Bitumens are generally categorised into two; Rubber Modified Bitumens and Polymer Modified Bitumens.
Rubber Modifed Bitumens are formulated by using Crumb Rubber or Synthetic Rubber Latex as additives. However Crumb rubber is commonly used.
Polymer Modified Bitumens are formulated by using polymers as additives. Polymers are categorised into two, Elastomeric & Plastomeric.
Plastomeric consists of Polyethylene (PE), Ethylene Vinyl Acetate (EVA),Ethylene Butyl Acrylate (EBA) and Ethylene Ter Polymer (ETP), etc. However Ethylene Vinyl Acetate is commonly used.
Elastomeric consists of Styrene Isoprene Styrene (SIS), Styrene-Butadiene Styrene (SBS) Block Copolymer, etc. However Styrene-Butadiene Styrene is commonly used.
Specification of CRMB ( E ) as per IRC SP 53 – 2002 & BIS I5462 – 2004
|Designation||Grades and Requirement||Test Method|
|CRMB 50||CRMB 55||CRMB 60|
|Penetration at 25°C||< 70||< 60||< 50||ISI 203 – 1978|
|Softening point, (R & B), C Min.||50||55||60||ISI 205 – 1978|
|Elastic Recovery of half thread in||50||50||50||ISI 5462 – 2004|
|Flash Point,°C Min||220||220||220||ISI 209 – 1978|
|Seperation difference in softening point,
(R & B)°C , Max
|4||4||4||ISI 5462 – 2004|
|Thin Film Oven Test (TFOT) on Residue|
|a. Penetration 25°C , Min % of original||60||60||60||ISI 203 – 1978|
|b. Increase in softening point,°C, Max||7||6||5||ISI 205 – 1978|
|c. Elastic Recovery of half thread in||35||35||35||ISI 5462 – 2004|
|Ductilometer at 25°C , % Min.|
Specification of PMB as per BIS I5462 – 2004
|Specification / Property||Grades and Requirement|
|PMB 40||PMB 70||PMB 120|
|Softening Point,°C (min)||< 60||< 55||< 50|
|Penetration at 25°C||30-50||50-90||90-150|
|Elastic Recovery of half thread, % ( min )||70||70||70|
|Seperation, Difference in softening point,°C ( Max )||3||3||3|