Repeated load triaxial testing is used in mechanistic-empirical pavement design procedures as the best means to determine resilient modulus properties of unbound aggregate base and subbase materials. Although the test has become more embraced by industry in the last decade, the results do not always link to expected aggregate layer rutting performance in the field. There is a need to develop a rapid and reliable quality assurance method to predict engineering properties and expected performance of aggregate materials from different sources. To gain a better understanding of the factors governing long-term performance of aggregate layers used in roadway construction, a series of laboratory tests were performed on aggregate samples from different sources for comparison. The laboratory testing program consisted of resilient modulus, repeated load permanent deformation testing, and quick shear and aggregate image analysis. The influence of geogrid on base-course engineering properties was also evaluated in the test program. Results from this laboratory research program demonstrated the positive effect of geogrid on quick shear and permanent deformation testing. This work demonstrated that the use of several techniques may be necessary to quantify the behavior of unstabilized and mechanically stabilized aggregate layers.