Polymer modified bitumen
Polymer modified bitumen (PMB) are mixtures produced from:
in which the polymers change the visco-elastic behavior of the bitumen and thus make this binder more suitable for different stresses.
Polymers can successfully improve the performance of asphalt pavements at low, intermediate and high temperatures by increasing mixture resistance to fatigue cracking, thermal cracking and permanent deformation.
The most commonly used polymer for bitumen modification is styrene–butadiene–styrene (SBS) followed by other polymers such as styrene–butadiene–rubber (SBR), ethylene–vinyl-acetate (EVA), and polyethylene. SBS block copolymers are classified as elastomers that increase the elasticity of bitumen.
Selected polymer or a blend of two or more modifiers shall have the following properties:
- Compatible with bitumen
- Resist degradation at mixing temperature
- Capable of being processed by conventional mixing and laying machinery
- Produce required coating viscosity at application temperature
- Maintain premium properties during storage, application and in-service
ADVANTAGES AND USAGE OF MODIFIED BITUMEN:
Properties of modified bitumen depend upon type and quantity of modifier used and process adopted for their manufacture. The advantages of modified bitumen can include one or more of the following for road works:
- Lower susceptibility to temperature variations
- Higher resistance to deformation at high pavement temperature
- Delay of cracking and reflective cracking
- Better age resistance properties
- Better adhesion between aggregates and binder
- Higher fatigue life of mixes
- Overall improved performance
According to these, polymer modified Asphalt needs much less maintenance work and Cost rather than a conventional Hot Mix Asphalt (HMA).
Polymer modified asphalt is mainly used in :
- Main Roads & Highways
- Roads with heavy traffic
- Toll roads
- Bus Lanes
Homogeneity is very important for desired performance of polymer modified binders. Hence, these should be prepared by appropriate industrial process and plant having high shear device. In high shear mixing, polymer particles are physically reduced in size by mechanical and hydrodynamic shear in a rotor-stator combination accompanied by significant input of heat energy to the mix. The polymer concentration up to the conditions and the polymer type may vary (e.g. SBS content is about 1%-7%).
The act of mixing base binder with polymer occur at elevated temperature (Min 160°C – Max 220°C) and the most appropriate temperature is about 180°C-200°C. also the shear rate is more than 2500 rpm. The time required to achieve a homogeneous blend of the polymer and the asphalt will vary with the type of polymer, its molecular weight, and (for thermoplastic rubbers) with the chemical composition of the polymer. A higher molecular weight will give rise to longer blending times.
|1203||30 to 50||50 to 90||90 to 150||Penetration at 25°C, 0.1 mm,100 g, 5 s|
|1205||60||55||50||Softening point (R&B), °C, Min|
|9381||-12||-16||-20||FRAASS breaking point, °C, Max|
|1209||220||220||220||Flash point, COC,°C, Min|
|–||70||70||70||Elastic recovery of half thread in ductilometer at 15°, percent, Min|
|–||3||3||3||Separation difference in softening point (R&B), °C,Max|
|1206||3-9||2-6||1-3||Viscosity at 150°C, poise|
Thin film oven test and test on residue
|9382||1.0||1.0||1.0||Loss in mass, percent, Max|
|1205||5||6||7||Increase in softening point, °C, Max|
|1203||35||35||35||Reduction in penetration of residue, at 25°C, percent, Max|
|–||50||50||50||Elastic recovery of half thread in ductilometer at 25°C, percent, Min|
POLYMER MODIFIED BITUMEN Specification