A LABORATORY STUDY ON SHORT TERM AND LONG TERM AGEING OF BITUMEN USING MODIFIERS (original) (raw)
The ageing of bitumen binder has an influence on how long is in service a road coating. Thus, it is important to have reliable methods to predict pavement behaviour with time. During its service period, bitumen suffers a gradual loss of its desirable properties due to continuous exposure of bitumen to environment and traffic. To determine changes of binder characteristics with respect to time, one must expose bitumen to the influence of external factors which results in oxidation, evaporation and exudation of bitumen components thus hardening of the bitumen. In the present study two modifiers i.e. Styrene Butadiene Styrene (SBS), an elastomer and Crumb Rubber, obtained from discarded tyres are used, to modify VG30 bitumen. The changes in conventional and rheological properties of VG30 modified with different percentages of SBS(5% to 7%) and Crumb Rubber(7% to 9%) before and after ageing are studied. The rheological properties of binders in terms of their complex modulus (G*) which depicts stiffness and overall resistance to deformation, storage modulus (G' = G*×cosδ) which measures energy stored during a loading cycle, loss modulus (G " = G* × sinδ) which measures the energy dissipated during a loading cycle and phase angle (δ), measures the viscoelastic character of bitumen are studied using Physica Smart Pave Asphalt Rheometer. The properties are tested at different temperature varying from 58˚C till failure at frequency 10 rad/sec. Short and Long Term ageing is simulated by Rolling Thin Film Oven Test and Pressure Ageing Vessel respectively. Conventional tests shows hardening of bitumen due to ageing and increase in viscosity and temperature susceptibility characteristics due to addition of modifiers. Complex Modulus G* increases with increase in % of modifier and test temperature, G* values are greater after RTFOT ageing which indicated hardening of bitumen and considerably greater after PAV ageing due to prolonged ageing. Rutting resistance (G*/sinδ) values are greater for modified bitumen indicating better rutting resistance. The third rheometer measurement Loss modulus (G* × sinδ) is carried out on PAV aged residue, to evaluate fatigue cracking property of binder.
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