Assessing the role of Additives in the Visco-Elastic Behavior of Asphalt Concrete

Asphalt concrete mixture for flexible pavement construction is designed to exhibit visco-elastic behaviour under vehicular loading. However, when mineral additives are incorporated into the mixture, a dramatic change in the failure mode is expected. In the present work, an attempt has been made to implement two types of additives (silica fumes and coal fly ash) for modification of asphalt binder using the wet process. Asphalt concrete mixtures were prepared with optimum binder requirements of 4.9 % and subjected to laboratory roller compaction in a slab Mold. Three constant strain levels (750, 400, and 250 microstrain) were used to assess the fatigue life of beam specimens that were taken from the slab samples under dynamic flexural loads in 20°C settings. The fluctuation in the initial flexural stiffness through the visco-elastic failure mode was monitored. It was observed that during the visco-elastic stage of failure, implication of coal fly ash additive for modification of asphalt concrete binder had extended the visco-elastic stage of failure of asphalt concrete by (1.8, 2.3, and 0.66) folds for (250, 400, and 750) microstrain levels respectively as compared with the control asphalt concrete mixture. However, modification of asphalt concrete binder with silica fumes had extended the visco-elastic stage of failure of asphalt concrete by (1.0, 1.0, and 0.25) folds for (250, 400, and 750) microstrain levels respectively as compared with the control asphalt concrete mixture. It was concluded that implication of additives as modifiers of the binder can support flexibility and extend the visco-elastic stage of failure of asphalt concrete.