Influence of Additives on the Fluctuation of Stiffness of Asphalt Concrete under Dynamic Stresses

Abstract

Monitoring the fluctuation of initial flexural stiffness of asphalt concrete, when, practicing dynamic flexural stresses can assess in understanding the failure mode of asphalt concrete mixture. An attempt has been made in the present investigation to assess the influence of implementing silica fumes and coal fly ash on the initiation of fatigue damage in asphalt concrete wearing course mixture. Control and silica fumes and fly ash treated mixtures have been prepared in the laboratory at optimum binder requirement. Beam specimens which were obtained from roller compacted slab samples of asphalt concrete, were subjected to dynamic flexural stresses under three constant strain levels of (750, 400, and 250) microstrain and 20℃ environment. The fluctuation in the percentage of initial flexural stiffness was monitored. It was observed that percent initial stiffness declines in a sharp trend under higher strain level as the loading proceeds, however, the fluctuation of the stiffness is restricted within 50 %. When silica fumes were implemented in asphalt concrete mixture, the fluctuation of the stiffness is restricted to (18-160) %. However, when coal fly ash was implemented in asphalt concrete mixture, the fluctuation of the stiffness is restricted to (10-180) %. On the other hand, implementation of fly ash and silica fumes additives was able to postpone the initiation of fatigue damage under (750, and 400) strain level by (5, and 3.1) folds and (1.5, and 1.6) folds respectively. The variation in the initiation of fatigue damage under 250 microstrain was not significant regardless of the additive type.