EFFECT OF CARBON BLACK ON AGEING OF BITUMEN

Abstract

The ever increasing demands of traffic and temperatures imposed on the pavements tend to cause various distresses in the pavements. Simultaneously, ageing of bitumen causes the deterioration of asphalt pavements. Hence alternatives measures are essential to tackle such issues. Modification of the bituminous binders with various modifiers is one of the simplest and most effective techniques which has been used over years to increase the strength and life of pavements. Carbon black is one such modifier which has the potential to increase rutting resistance at high temperature and also reduces temperature susceptibility and cracking propagation at low temperatures. Therefore, both rutting and fatigue resistance are improved. The Dynamic shear rheometer (DSR) is used to determine the rheological properties of bitumen at a wide range of temperature and frequency and helps to get a better understanding of the behavior of the bituminous binders. In recent times, the Performance Grade (PG), Multiple Stress Creep and Recovery (MSCR) and Linear Amplitude Sweep (LAS) tests are used to characterize and evaluate the performance of bituminous binders. The present study deals with conventional and carbon black modified bituminous binders. The conventional and rheological properties of the binders are studied at a temperature range of 10 to 70C. The performance of the binders, before and after ageing, was analyzed in terms of rutting and fatigue. The base binder (VG-30) is modified with three different percentages (5, 10 and 15) of carbon black and the conventional and rheological properties of neat and carbon black modified binders were compared. The rheological properties were evaluated in terms of two parameters, i.e. complex modulus (G*) and phase angle (δ). The linear viscoelastic (LVE) limits were also evaluated for these binders. Both short term (Rolling thin film oven) and long term (Pressure ageing vessel) ageing conditions were simulated in the laboratory for neat and carbon black modified binders. The performance of the binders with respect to rutting and fatigue were evaluated using the MSCR and LAS test. The MSCR test was conducted at temperatures varying from 40 to 70C whereas in the case of LAS test the iv temperature range is 10 to 30C. The MSCR test was carried out on RTFO aged samples and the recovery behavior of the neat and carbon black modified binders was compared. The binders were also assigned their traffic rankings. LAS test was carried out on PAV aged samples and the fatigue lives of the neat and carbon black modified binders were ascertained. Based on the above studies the optimum content of carbon black to be used for modification is identified.