Compatibilizer role of styrene-butadiene-styrene triblock copolymer in asphalt

Polymer modified asphalt (PMA) was prepared from mixtures of triblock copol ymer poly (styrene-butadiene-styrene) (SBS) and asphalt. Physical and mecha nical properties of the mixtures were characterized by differential scannin g calorimeter (DSC), needle penetration and softening point methods, and te nsile strength measurement. The glass transition temperatures of both block s of SBS changed with the fraction of asphalt varied from 0 to 97%, which i ndicates the mixture system to be partially miscible at least. Maltene, the soluble fraction extracted from the asphalt by n-heptane, was found to int eract preferentially with the polybutadiene unit of SBS, whereas asphaltene , insoluble fraction interacted predominantly with the polystyrene unit. Fr action dependence of viscosity, penetration and tensile strength of the mix tures showed the threshold at low SBS concentration (e. g., 5-10%) to incre ase markedly. A microstructure model for the PMA system with lower SBS is p roposed. The small amount of SBS in PMA seem to act as compatibilizer and e mulsify the two components of asphalt to make a mechanically stable network .