Conventional bitumens, being thermoplastic materials, have restricted service temperature ranges. With special manufacturing techniques, bitumens can be produced that offer a wider temperature service range than standard pen grades. SBS thermoplastic elastomers can extend the limits even further. Although the increase in service temperature range is suggested by traditional, empirical tests generally in use for the characterisation of conventional bitumens, these tests do not necessarily give a true reflection of the actual performance in asphalt mixes. Dense asphaltic mixes have been subjected to rutting experiments in a laboratory test track and to thermal cracking experiments in a restrained cooling test where crack initiation and propagation were studied with the aid of an acoustic emission technique. Depending on the formulation and type of base bitumen, the service temperature can be significantly extended at both the high and low temperature ends. In terms of traditional gradings the performances at high and low temperatures correspond to conventional bitumens with penetrations that are different by an order of magnitude. The polymer-modified bitumens can thus be applied in climates with extreme temperature variations. (A)
Abstract