An experimental study to select aggregate gradation for stone mastic asphalt

The present study evaluates the effect of aggregate gradation with different nominal maximum aggregate sizes on the stiffness, rutting, and fatigue performance of stone mastic asphalt (SMA). These performance parameters are important in mechanistic-empirical pavement design. Four SMA mixes with 4.75, 9.5, 12, and 19mm nominal maximum size of aggregate in aggregate gradation and a PG 58-22 asphalt binder were designed. Dynamic modulus, wheel tracker, and four-point beam fatigue tests were conducted at different temperatures. A regression model has been utilized using wheel tracker test data, which reveals that rut resistance of SMA increases with an increase of aggregate size in aggregate gradation. Beam fatigue testing and asphalt binder drain down testing indicate that increasing aggregate size in an aggregate gradation decreases fatigue life and increases binder drainage, respectively. This study also reports some relationships between dynamic modulus, wheel tracker rut depth and fatigue life of SMA. A relationship between fatigue coefficients (K-1 and K-2) obtained from the fatigue curves has also been proposed. Analysis of results indicates that stiffer SMA has lower fatigue life and rut values. Rut resistance and mix stiffness increase with an increase in aggregate size in an aggregate gradation.