Impact of Constant Strain Level (CSL) and Additives on the Flow Number (FN) of Asphalt Concrete (AC)

Abstract

The flow number (FN) of asphalt concrete (AC) is the number of load repetition cycles at which the flow of aggregates within the AC structure begins, microcracking initiation, and permanent damage occur in the AC mixture. Such a flow of material constitutes an AC structure that can be differentiated by a significant variation from the linear trend relationship between the number of loading cycles and cumulative strain. Such permanent strain (PS) is unrecoverable. The FN is an important variable since it correlates well with the rutting potential of AC pavement. In this work, the influence of binder additives such as silica fumes (SF) and coal fly ash (CFA) on the FN of the AC mixture was investigated. Slab samples of roller compacted AC (control and modified) have been prepared with optimum binder requirements. AC beam specimens were obtained from the prepared AC slab samples and tested for fatigue life (FL) with the aid of a dynamic four-point flexural bending beam test under a moderate environment of 20°C. It was noticed that the implementation of coal fly ash into the AC mixture exhibits a significant decline in FN by (16.6% and 33.3%) for (400 and 750) CSL, respectively, when compared with the control AC mixtures. Implementation of silica fumes into the AC mixture exhibits a significant increase in FN at high constant strain levels by 77.7% for 750 constant microstrain levels when compared with the control AC mixtures; however, the variation in FN under (250 and 400) microstrain levels was not significant. Power mathematical models were obtained representing the rate of change in the FN of the AC mixture through FL due to the implementation of additives.