RHEOLOGICAL BEHAVIOUR OF BITUMINOUS BINDERS FOR INDIAN CONDITIONS

Abstract

India has large highways and road networks and the total length of the country's roads exceeds 3.31 million kilometers. The increase in India's road transport during the last two decades is likely to continue unabated in the coming years as well. The traffic on Indian highways ismixed and quite different in character as compared to many other countries. In India, about 98 percent of the roads are of flexible type, therefore bitumen as a binder plays a key role in the performance related properties of bituminous mixes. The failures of the bituminous pavements are not only due to increase in traffic butalso due to extreme climatic conditions prevailing in the country. There is a very high and very low pavement temperatures existed in some parts of the country. Thus climatic conditions play an important role in selecting the type of materials to be used in road construction. In order to increase the life of bituminous pavement, quality of bitumen needs to be enhanced. To achieve the improvement of binder, it is necessary to add the polymers to bitumen. By adding small amount of polymers to bitumen, the properties can be enhanced over wide range temperatures in road applications and the life span of the road pavement increases considerably. In India, the rheological characterization of bituminous binders is based on the properties such as penetration, softening point, ductility and absolute viscosity, which are usually inadequate to characterize the bitumen. Dynamic Mechanical Analysis (DMA) is the method already in use in developed countries to study the rheological properties of bituminous binder. Two types of polymer; Ethylene Vinyle Acetate (EVA), a plastomer; Linear Styrene Butadiene Styrene (SBS), an elastomer and Crumb Rubber (CR) were considered in the present study. The changes of rheological Abstract properties of 60/70 and 80/100 grades bitumen modified with different percentage of CR, EVA and SBS (3 to 9%) were studied. The rheological properties of the bituminous binders in terms of their complex modulus (G*), stiffness and overall resistance to deformation, storage modulus (G'), binder elasticity, loss modulus (G"), viscous behaviour and phase angle (5), viscoelastic behaviour were measured by using Dynamic Shear Rheometer (SR5 Ashphalt Rheometer). Testing was performed at temperatures ranging from 46°C to 82°C in increments of 6°C at a frequency of 10 rad/sec. Dynamic frequency sweep tests were performed at 60°C in the range from 0.1 to 100 rad/sec before and after ageing. Dynamic stress sweep test was also conducted at a frequency of 10 rad/sec and temperature 55°C before ageing. Short term ageing was simulated by Thin Film Oven Test. Rutting resistance (G*/sin 6) for different modified binders was also determined at different frequencies (1 rad/sec and 10 rad/sec) and 60°C. Crumb Rubber is the cheapest modifier and easily available in India. Therefore, the rheological property ofCR modified binder is also investigated in the present study. The results show that crumb rubber and polymer modification improve the complex modulus and elastic response of the bitumen at high temperatures. The complex modulus at 46°C increased 1.2 and 1.7 times by adding 3% CR to 60/70 and 80/100 bitumens respectively. It increases 1.8, 2.4 and 3, 4.8 times for 60/70, 80/100 bitumens modified with 3% SBS and EVA respectively. The complex modulus increases with increase in percentage of modifier and decreases with increase in temperature. However, phase angle decreases with increase in percentage ofmodifier and increases with increase in temperature. n Abstract The value of G*/sin 8 for EVA modified binders are found to be higher than CR and SBS modified binders at 1 rad/sec and 10 rad/sec and 60°C. It indicates that EVA modified binders have higher rutting resistance to deformation under loading as compared to CR and SBS modified binders at high temperature. The temperature susceptibility of the modified binders is lower than neat bitumen and increase in percentage of modifier decreases temperature susceptibility. It was observed that the rheological properties of bituminous binders were changed after ageing. There is an increase in complex modulus before and after ageing for CR and EVA modified binders. The complex modulus decreases after ageing at higher polymer content (7% to 9%) for SBS modified 60/70 bitumen and it increases up to temperature 58°C then decreases with above percentage for SBS modified 80/100 bitumen after ageing. In all cases, the aged modified binders showed better rheological properties than aged neat bitumens. The change in rheological properties of aged modified binders varied with polymer type, content and bitumen grades. The ageing index of the binders was also largely influenced by test frequency and temperature. Dynamic frequency and stress sweep tests were also conducted to characterize the bituminous binders in the present study. The results indicate that complex modulus increases with increase in the frequency and percentage of modifier. The EVA modified binders showlower phase angle for entire frequencies considered in the study as compared to CR and SBS modified binders. There is a significant decrease in dynamic viscosity for modified binders as compared to neat bitumens. The modified binders show lower strain as comparedto neat bitumens at the same stresses. It shows a substantial improvement in the resistance to permanent deformation of modified binders. in