INFLUENCE OF ASPHALT FILM THICKNESS ON THE PERFORMANCE OF A BITUMINOUS MIX – A LABORATORY STUDY

Abstract

To offer a longer service life for sustaining the demands of the vehicular traffic, it is inevitable to design a durable paving mixture. Asphalt Film Thickness is one of the important parameter that needs to be significantly studied in order to design a durable performing pavement mixes. It is necessary to study the asphalt film thickness since it significantly affects the durability of the bituminous mix. A durable pavement should offer a long term resistance to aging of the binder throughout its design life without failures such as raveling or cracking. Several researchers recommended a film thickness value of 6 to 10 microns that can provide a flexible and durable paving mix. However, there exists inadequate researches that validates the existence of the recommended film thickness. Mixture with low film thickness generally tend to become brittle and are prone to durability problems. Also if the bitumen is in excess, then it will lead to rutting and shoving problems. A thicker film tends to be flexible and durable while a thinner film breaks, cracks and ravel excessively. A thin film also leads to water related problems. This study was aimed to review the literature available and determine the film thickness at various bitumen content for a bituminous concrete (BC) mix. Mixes were prepared at varying bitumen content ranging from 3% to 9% and the theoretical film thickness is found to be satisfying with the past researches. Also, most of the research has been theoretical and only a few attempts have been made to measure this property experimentally. Experimental measurements were also done on various bitumen contents using a Scanning Electron Microscopy (SEM) and experimental values of the film thickness was co-related with the theoretical values. Measurements done experimentally indicated that the validity of the theoretical film thickness does not exist since the film thickness was found to be highly irregular in shape having a thickness greater than 100 microns. Furthermore, several mixes at various film thicknesses were prepared and tested for performance deterministic parameters such as Fatigue and Moisture Susceptibility problems.