In 1986, a main arterial forestry road in Kaingaroa Forest was sealed using public highway design procedures. However, as the majority of traffic on this forestry road was off-highway trucks with axle loads up to two times greater than on public highways, premature flushing occurred. Since 1989, various small trials of new chip seal designs have been undertaken in an attempt to remedy the flushing. The result of this research led to the establishment of 40 chip seal trial sections in January, 1994. The variables were: (i) level of stress (straight level road versus adverse gradient); (ii) type of bitumen (PMB 100, Emoflex, 80/100 and 180/200 bitumens); and (iii) residual bitumen rate (five rates for each type of bitumen). rates for each type of bitumen). These trial sections are being monitored, with the aim of developing a suitable chip seal design procedure for arterial forestry roads carrying single axle loads up to 16 tonnes. A primary criteria for defining performance is the change in surface texture. Thus far, the Emoflex sections are performing the best, followed closely by PMB 100, 80/100 and then 180/200, though the 180/200 grade bitumen on the sloping sections had all severely flushed. The results confirm that chip seals can be designed to perform satisfactorily under such heavy axle loads and high stresses. (A)
Abstract