Low temperature fracture properties of polymer-modified asphalts relationships with the morphology

A methodology for studying the relationships between fracture behavior and morphology of polymer-modified asphalts used as binders was developed by us ing the linear elastic fracture mechanics (LEFM) method and confocal laser scanning and environmental and cryo-scanning electron microscopies. Differe nt types of polymers were used as modifiers: (i) copolymers from ethylene a nd methyl acrylate (EMA), butyl acrylate (EBA) or, vinyl acetate (EVA); (ii ) diblock or star-shape triblock styrene-butadiene copolymers (SB or SBS*). The 4 to 6 wt. % blends display an heterogeneous structure with a polymer- rich dispersed phase based on the initial polymer swollen by the aromatic f ractions of the asphalt. The fracture toughness of the blends is higher tha n for the neat asphalt even if Klc of blends remains low compared to usual polymer blends due to the brittleness of the asphalt matrix. The fracture b ehavior which is strongly dependent on the nature of the polymer is discuss ed from the toughening mechanisms given for the filled polymers and the pol ymer blends. The EBA, SB, and SBS-based blends compared to the EMA and EVA- based ones display a higher KIc due to the elastomeric behavior of the poly mer phase leading to a more efficient energy dissipation during crack propa gation. The sample prepared with 4% crosslinked SB (Styrelf) and the corres ponding physical blend (non-crosslinked) display the better fracture proper ties. (C) 2001 Kluwer Academic Publishers.