Balanced Mix Design and Construction of Red Coloured Asphalt Bus Rapidways with Enhanced Cracking and Rutting Resistance

摘要

A balanced mix design methodology was utilized to design a red coloured surface asphalt mix with enhanced rutting and cracking properties for use in a dedicated bus rapidway project. In the past, coloured asphalt mixes have experienced early fatigue cracking in heavy traffic applications. Increased sulfoxide oxidation product formation was noted in binders recovered from mixes after laboratory aging when the mixes contained iron oxide colouring. While impacts of iron oxide based colouring on real world pavement aging were unknown, the design accounted for this potential by using a PG 70-34 binder with improved low temperature cracking properties compared to the originally specified PG 70-28. PG 64-34 was also considered but rejected as mixture rutting results did not meet performance criteria. Longitudinal joints were eliminated between lanes when feasible by using echelon paving. Stringent compaction requirements at the longitudinal joint between the red and black coloured lanes were achieved by milling the low density unconfined edge of pavement of the conventional black mix prior to placement of the red mix. The newly created vertical face served to confine the red coloured asphalt when it was placed and rolled in order to achieve required joint compaction.