REQUIREMENTS OF BITUMEN

The describable properties of bitumen depend on the mix type and the construction. The general problems while using bitumen in paving mixes are:

1. Mixing.
2. Attainment of desired stability of the mix.
3. To maintain the stability under adverse weather conditions.
4. To maintain sufficient flexibility and thus avoid cracking of bituminous surface. 
5. To have sufficient adhesion with the aggregates in the mix in. presence of water.

Keeping above problems in view the bitumen should possess the following desirable properties,

1. The viscosity of the bitumen at the time of mixing and compaction should be adequate. This is achieved by heating the bitumen and aggregate prior to mixing or by use of cut backs or emulsions of suitable grade.
2. The bituminous material should not be susceptible too much to temperature. Bituminous material should not become too soft during the hottest weathers of the region. Similarly it must not become too hard and brittle during cold weather which may cause cracking of the bituminous surface. The material must be durable.
3. Bitumen should not strip off from the aggregate in presence of water.
4. Affinity and adhesion between the bitumen and the aggregate used, in the mix should be adequate.

INTRODUCTION OF BITUMINOUS MIXES

Bituminous mixes are most commonly used all over the world in pavement construction. Under normal circumstances, conventional bituminous materials if designed and executed properly perform quite satisfactorily. But for special applications like roundabouts or where traffic is extremely heavy, stiffer mixes are required which can have larger fatigue life and more resistance to permanent deformation. It has been found from many researches that the strength of the paving mixes can be enhanced by use of a binder formed by modifying available bitumen with certain additives like sulphur and organic polymers. The modified polymers also improve temperature susceptibility and viscosity characteristics and help alleviating some common problems like bleeding of binder during peak summer temperature and stripping of aggregate in moisture prone areas. The polymers used for modification of bitumen for paving purposes are generally styrene­-butadiene-styrene copolymer, styrene-butadiene rubber, latex, ethylene vinyl acetate copolymer, polyethylene, polypropylene, etc. Most of these polymers, besides being costly, are not available very commonly. Due to these reasons reclaimed rubbers mainly in the form of used tires have been found to perform satisfactorily for years. Keeping the above things in mind, it was felt that an effort can be made to use some material which besides being available easily, is very cheap, or even better, if it is waste material. From this point of view, low density polyethylene carry bags have been used for modification of bitumen in the present investigation. Moreover another reason for choosing this topic is that very little papers are found published with this theme.