Natural weathering of styrene-butadiene modified bitumen

This chapter reports on the long-term weathering of 12 bituminous sealants that contain thermoplastic elastomers, namely block copolymers of polystyrene and polybutadiene. The goal of the work was to determine the rate and mechanisms of sealant weathering so that future accelerated aging tests could be developed. By means of physico-chemical analysis, much weathering was found to occur in the early years of service. Weathering pathways were found to be mass loss, oxidation, and copolymer degradation. Specific mechanisms include the loss of aromatics with time, the formation of sulphoxides, sulphones, and their acids, ketones, and carboxylic acids. Block copolymer degradation occurs mainly through a scission between polystyrene and polybutadiene blocks, and the crosslinking of polybutadiene fragments. The chapter ends with a brief discussion of the suitability of current accelerated aging tests to simulate the natural weathering of elastomeric sealants.