From 1984 several chipseal road surfacing trials have been carried out in New Zealand to examine the ageing behaviour of different bitumens. The New Zealand trial bitumens generally hardened rapidly for the first 3-4 years, after which the attained viscosity stabilised. In contrast, reports of Australian trials indicate that bitumens in that country continue to harden right up to the end of the seal lives. The concept of a critical binder viscosity above which a seal fails is therefore not appropriate in New Zealand, where ultimate seal failure may generally be from other causes. Laboratory high pressure oxidation of several bitumens revealed a variety of hardening relationships, some matching field behaviour and some not. The overall reaction mechanism was found to vary with temperature. Thus a valid test for estimating field performance needs to be as near to field temperatures as possible. Alternatively, it may be possible to develop extrapolation procedures for estimating field hardening from tests performed more rapidly at higher temperatures. (A)
Abstract