A STUDY ON MODIFIED BINDERS FOR ROAD CONSTRUCTION

Abstract

Bitumen being a by-product of petroleum distillation process, can justifiably be considered as scarce material due to limited reserves of crude petroleum in the world. Thus to use bitumen binders efficiently sometimes it requires modification of bitumen using certain additives. Beside this, rapid industrialisation and urban development and construction of heavy duty pavements may also require modification of bitumen. In India, the modification process is often required due to inferior quality of bitumen derived from indigenous crude and also due to diverse climatic conditions. Of all the modifiers investigated by researchers, rubbers and polymers are found to be the most promising modifying agents due to their cost effectiveness and easy availability. Due to environmental problem of solid waste management, use of scrap tyre rubber as a bitumen modifier is more important. Use of rubbers and polymers enhances the performance based properties of bitumen and its mixes remarkably. Softening point, Theological characteristics like viscosity and flow value, temperature susceptibility, low temperature brittleness, durability, Marshall stability and tensile strength of mix, permanent deformation, fatigue, elastic recovery and creep characteristics are found to have greatly improved by using rubbers and polymers as bitumen modifier. It is also found that due to increased life of the pavement and lesser frequency of maintenance, use of rubbers and polymers as bitumen modifier may be a cost effective alternative. The modifiers used in the present study are waste tyre rubber or Crumb Rubber (CR) and Ethyl Venyl Acetate (EVA). Use of crumb rubber alone is found to have improved various properties of bitumen like low temperature ductility, elastic recovery, Marshall stability and water susceptibility. Use of EVA alone was found to have improved the properties like temperature susceptibility, low temperature ductility, viscosity at service temperatures, stripping and softening point. CR when added to bitumen, increases the fatigue strength of the mix 1.5 times. EVA however did not show any improvement in fatigue strength. When bitumen is modified with the various combinations of both CR and EVA their is an overall improvement in performance related properties of paving bitumen. The improvement is very much significant in case of low temperature ductility, water susceptibility, viscosity, elastic recovery, temperature susceptibility and fatigue strength of the mix. The results indicate that the modified bitumen blends can be used successfully in high temperature as well as low temperature regions. Due to low water susceptibility, the modified blends may be very useful in high rainfall regions. An increase in viscosity at medium service temperatures and higher softening point make these modified blends very useful for high temperature zones where the prime concern of highway engineers is always to prevent bleeding and permanent deformation. Increase in fatigue strength indicates longer service life and saving in maintenance cost of the pavement in high traffic intensity and axle load corridors.