Influence of Additives on the Visco-Elastic and Visco-Plastic Behavior of Green Asphalt Concrete under Dynamic Flexure

Asphalt concrete mixture exhibit Visco-elastic behaviour under vehicular loading. In the present work, two types of additives (silica fumes and coal fly ash) have been implemented to modify asphalt binder. Asphalt concrete mixtures were prepared and subjected to laboratory roller compaction in a slab Mold. Beam specimens were obtained from the slab samples and tested for fatigue resistance under dynamic flexural stresses at 20℃ environment using constant strain level of 750 microstrain. The variations in the failure mode from Visco-elastic to Visco-plastic was monitored. It was observed that during the Visco-elastic stage of failure, implication of additives exhibits higher flexural stiffness as compared with the control mixture. However, the flexural stiffness declined by (66.6, 99 and 97) % for (control, fly ash treated, and silica fumes treated) mixtures respectively at 20 seconds of practicing the dynamic flexural stresses. However, after the 20 seconds of loading, the Visco-plastic stage of failure starts, and the flexural stiffness declined dramatically by (91.6, 98.7, and 95.8) % for (control, fly ash treated, and silica fumes treated) mixtures respectively. The deformation during the Visco-elastic stage increased by (6.8 and 5) % for (fly ash and silica fumes) treated mixtures respectively as compared with the control mixture. Through the Visco-plastic stage of failure, it can be noticed that at failure, the cumulative dissipated energy increases by (1.72 and 1.4) folds and the phase angle increase by (1.5, 1.25) folds for mixtures treated with fly ash and silica fumes respectively as compared with the control mixture.