Influence of Constant Strain Levels on the Viscoelastic Properties of Asphalt Concrete

The viscoelastic properties of asphalt concrete pavement are highly susceptible to the flexural stresses applied by vehicular movement.The ability of the pavement to sustain the accumulated strain in the pavement structure is a good measure of its fatigue life. In the present work, asphalt concrete mixtures were prepared in the laboratory at optimum binder content and compacted in a slab mold using the roller compaction. Beam specimens of 5.6 Cm depth, 6.2 Cm width, and 40 Cm length; have been obtained from the slab samples and subjected to repeated flexural stresses at 20℃ using the constant strain mode of loading. Three levels of constant train have been tried as a target amplitude, (250, 400, and 750) while a loading frequency of 5 Hz was implemented. Test results regarding the viscoelastic properties were analysed and compared. It was observed that the phase angle at failure increases by (33.3, and 50) % when the constant strain level rises from 250 to 400 and 750 respectively.The cumulative dissipated energy at failure increased by (10, and 24) folds when the constant strain level changes from 750 to 400 and 250 respectively. However, thefatigue life of asphalt concrete was (6.1, and 141.8) folds higher for specimens practicing 400 and 250 constant strain levels respectively as compared with the specimen practicing 750 constant strain level. It was concluded that higher constant strain level exhibit sharper trend of decreases in the initial stiffness as compared with the other strain levels