Refining practice for bitumens in New Zealand has been reviewed over the years, and a range of bitumens of different temperature sensitivities may become available for roadmaking in New Zealand. Some of these bitumens may not be able to meet the requirements of the Transit New Zealand Specification for asphaltic bitumens, TNZ M/1:1995. Economic benefits may be possible if the requirements of TNZ M/1:1995 could be relaxed to permit a more temperature-sensitive bitumen.
Because of New Zealand's investment in chipsealing, an assessment of the sensitivity of chipseal performance to changes in the rheology (flow properties) of the binder was made. The bitumens studied between 1993 and 1996 were a 180/200 bitumen that is slightly outside the TNZ M/1:1995 specification and a 180/200 Heavy Iranian, and they were compared with a normal Safaniya bitumen used in chipseals. Both laboratory tests and field trials were performed to determine if the early life (first year) of chipseals constructed using these bitumens was significantly different from the Safaniya bitumen currently used.
The results show that chipseal performance could be affected using a more temperature-sensitive bitumen with an increased risk of chip loss in the first winter, and of chip rollover during periods of high pavement temperatures.