Internal texture of road base as a measure of aggregate durability

Abstract

Research work done at the Australian Road Research Board and monash university (Melbourne, Australia) into the durability of crushed rock roadbase materials involved the comparison of material from roads with material subjected to repeated rolling loads under controlled laboratory conditions. The principal research method was the microscope examination of petrological thin sections prepared from undisturbed samples after impregnation with epoxy resin. It was observed that internal texture changes occurred as a result of the repeated loading. These were described and followed using a point counting procedure. It was postulated that the texture changes were related to rock durability on one hand, and to road condition on the other, thus providing a link between the geological characteristics of the rock and the in service performance and behaviour of the road built from these when crushed. The point counting method was adopted as a preliminary research method only and could be replaced by automatic image analysis techniques for routine examination of samples. The original research was done on a range of altered basaltic rocks but internal texture changes were later observed with schists and sandstones. Assessment of internal texture changes could be a basis for mathematically describing the relative durability of different rock types and for the indication of the remaining life of road pavements (a).