Determination of Binder Film Thickness for Bituminous Mixtures prepared with various Types of Fillers

Abstract

Roads form the lifeline of any country. It is considered to be an engineered structure and the pavement is expected to serve its designed life and meet the performance criteria for better economy. Various materials constitute the different layers of the pavement and their characterization becomes important for durability. In spite of these considerations however, many factors contribute to early pavement failure and improper material characterization is just one of them. The Bituminous mix which is used for the surface and binder courses is formed as a conglomeration of the binder, graded aggregates and voids which forms a stable mixture which can resist wear and tear as well as heavy wheel loads when used in the field. The bituminous mix needs to meet the volumetric requirements to attain stability. When bitumen is mixed with aggregates in a heated condition, the binder forms a coating around the aggregate particle which is termed as Asphalt film thickness (AFT) which is not measured but calculated. Bitumen due to its visco-elastic nature should be used at the optimum and the specified temperature to provide a minimum uniform film thickness to ensure proper bonding in the Bitumen mastic. Fillers play a major role in determining the properties and the behaviour of the mixture, especially the binding and aggregate interlocking effects. The filler has the ability to increase the resistance of particle to move within the mix matrix and/or works as an active material when it interacts with the asphalt cement to change the properties of the mastic. Mineral fillers serve a dual purpose when added to asphalt mixes, the portion of the mineral filler that is finer than the thickness of the asphalt film blends with asphalt cement binder to form a mortar or mastic that contributes to improved stiffening of the mix. In the present study the film thickness was determined by Hveem method by determining the total surface area and the effect of fillers thereon is discussed. The effect of types of fillers in varying percentage, in the performance of hot-mix-asphalt is also studied. Three types of fillers namely, Hydrated lime, Ordinary Portland Cement, and Fly ash were used as fillers in the present study. Their percentage by weight of aggregates was varied as 2%, 4% and 6% to study their effect on the mix prepared for BC Grade II. The optimum binder content was determined for the various fillers and moisture susceptibility of bituminous mixtures was evaluated.. The results of film thickness determination reveals that an average film thickness of 6 μm is obtained for all fillers which is necessary for durability of the mixes. The Fatigue results show that Lime at 4% can be used for enhanced performance and 2% is recommended, when cement or fly ash is used as filler material.