The properties of bitumen and bituminous mixtures can be modified by the incorporation of certain additives. These additives are known as modifiers and the bitumen treated with modifiers is known as modified bitumen. The use of modified bitumen is now a fairly established practice. It covered under IS : 15462-2004.
Advantages With a careful selection of modifiers, it is expected that the properties of bitumen and bituminous mixtures will get considerably improved. Life of periodical maintenance and overlays gets enhanced by about 1.5 times, resulting in reduced frequency of maintenance renewals. The choice thus will ultimately be based on the life-cycle costing of the construction using conventional bitumen and modified bitumen.
The advantages of modified bitumen are: • Lower susceptibility to temperature variations • Higher resistance to deformation wear and tear • Better adhesion between aggregates and binder • Increase in fatigue life The bitumen modifiers/selected
polymers should be: • Compatible with bitumen • Blended with bitumen so that they disperse thoroughly with bitumen prior to use • Improve the temperature susceptibility of bitumen • Resist degradation at bitumen mixing temperature
• Capable of being processed by conventional mixing plants and laying machinery • Able to produce coating viscosity at application temperature • Maintain premium properties during storage, application and in service • Cost-effective considering life cycle cost
Handling of STP-Polymer Modified Bitumen During laying of various test stretches the experience has shown that a good circulation system is needed to ensure that modified bitumen retains its premium properties. Temperature of mixing and rolling should be slightly higher than conventional bituminous mixes. Requirement of temperature at different stages is given in table below:
Table: Requirements of Temperature Stage Temperature0C Binder at mixing 170 - 180 Mix at plant 145 - 155 Mix at site 120 - 140 Rolling at site 110 - 135 The hot mix construction using modified bitumen should be done when atmospheric temperature is above 150C.