The predominant pavement type used in New Zealand State Highways is an unbound granular sub-base and basecourse, with a chipseal wearing course. These pavements are very susceptible to the presence of moisture, which may induce both cracking and flushing of the surface under traffic and climatological stresses. It has been believed in the past that chipseals were impermeable providing there was at least 1.5 litres per square metre of bitumen. However, recent tests have suggested that water may gain access to the pavement undersurface by being forced through from the top of the chipseal by tyre pressure. This paper describes a laboratory study which duplicated the effect of tyres on wet roads. Core samples were taken from a selection of seals and the water permeability of these seals measured under pressure. The results support the proposition that water access occurs through the upper seal surface and may be a possible factor in causing chipseal distress. (a)
Abstract