PERFORMANCE EVALUATION OF UNCRUSHED AGGREGATES IN UNSURFACED ROAD APPLICATIONS THROUGH ACCELERATED PAVEMENT TESTING

摘要

Design of low volume roads and unsurfaced pavements traditionally involves covering prepared subgradewith an aggregate layer of sufficient thickness such that traffic induced loads are adequately distributedand stresses on the subgrade can be tolerated. Aggregate gradation and field density requirements arecommonly the only considerations for constructing “acceptable” aggregate layers. Aggregate qualityaspects and properties are often not considered in detail while selecting aggregate sources with the lowestmaterial hauling and transportation costs. This approach based solely on economic considerations mayresult in the selection of locally available material for routine use as the primary pavement load bearinglayer. Full-scale test sections were constructed at the University of Illinois by placing aggregate materialsof different types and qualities over a weak subgrade of controlled strength and tested to failure using anaccelerated transportation loading assembly. Pavement performances under near-optimum and floodedaggregate moisture conditions were monitored through surface profile measurements. Moreover,transverse trench sections were excavated to identify different mechanisms contributing to failure.Accelerated testing of a pavement test cell constructed using an uncrushed gravel with high amounts ofnonplastic fines showed excessive rut accumulations through internal shear failure of the aggregate layerat near-optimum aggregate moisture conditions. Excavated trench sections clearly indicated thedevelopment of a shear surface within the gravel layer which caused a lateral offset in the subgradedeformation with respect to the wheel path. Under flooded conditions, excessive subgrade movement,however, was found to be the primary mechanism contributing to pavement failure.