Rutting characteristics of unbound aggregate layers

Abstract

With reference to the use of non-conventional aggregates in some developing countries particularly in the tropics, the objective of the research was to characterize unbound aggregates in respect of rutting or deformations under wheel passes. Artificially produced crushed brick aggregate and naturally occurring quartzite aggregate were compacted in an especially prepared container in order to measure rut depths. The TRRL wheel tracking device with modified vertical loads was used to run on the compacted aggregate surfaces. The factorial design technique considering the influence of four factors i.e. aggregate quality, grading, moisture content and wheel contact pressure, was used. Analysis of rut depths obtained for different combinations shows that initial grading and moisture are the most influential factors for the development of ruts on a compacted aggregate surface. For dense grading and dry conditions quartzite aggregate undergoes less rutting than brick aggregate, whereas for open grading, the performance of the brick aggregate was found to be better. It was found that the compacted surfaces of the unbound aggregate of both types will not undergo excessive rutting in surface or underlying courses provided the material is in dense grading and in dry condition.