Construction of a working platform is often needed on soft, unstable soils to provide sufficient stability and adequate support for equipment mobility during paving operations without developing excessive rutting or sinkage of the equipment. One method of verifying the adequacy of such a layer is through conducting permanent deformation tests in the laboratory. This paper presents permanent deformation test results from an ongoing research project at the University of Illinois aimed at characterizing strength, stiffness, and deformation behavior of three different aggregate types commonly used in Illinois for subgrade replacement and subbase. Aggregate gradations were carefully engineered in the laboratory to study the effects of increasing amounts of both plastic and non-plastic type fines on permanent deformation behavior. Aggregate type or angularity, plasticity of fines and moisture conditions in relation to optimum water content were found to significantly affect the permanent deformation behavior.