Evaluation the effects of nanoclay on permanent deformation behavior of stone mastic asphalt mixtures

In stone mastic asphalt (SMA) mixtures the binder phase has an important role in the integrity of the mixture and should withstand the applied shear forces. Due to platy structure of nanoclay particles and having a large length over width ratio, they have considerable effects in enhancing properties of bitumens. In this paper the effects of nanoclay on high temperature properties of two distinct categories of SMA mixtures namely those with fibers and polymers have been investigated. A 60/70 pen grade neat bitumen, limestone aggregates, cellulose fibers and Styrene Butadiene Styrene (SBS) polymer alongside different dosages of montmorillonite nanoclay particles in the range of 1-4 percent by the weight of bitumen were used. Performance characteristics of different asphalt materials were evaluated in terms of the storage stability of modified asphalt binders as well as Marshall stability and flow, creep properties and rutting resistance of SMA mixtures having different amounts of nanoclay particles. Results revealed that the nanoclay polymer asphalt binders have higher storage stability as well as better performance characteristics. SMA mixtures with polymer modified asphalt binder have better permanent deformation characteristics (higher rutting resistance). Moreover, the SMA mixture containing 3% of nanoclay has the highest rutting resistance.