The objective of this study is to establish a satisfactory method of determining maximum density of cohesionless material, such as subbase, that will provide compaction criteria for these materials and be compatible with current methods of density determinations in the field. To establish a procedure for determining the maximum density of a subbase material, three different methods of tests are employed. These tests include the standard AASHO impact test methods (Methods C and D), a vibrating table type of compactive effort (ASTM Test for Relative Density of Cohesionless Soils (D 2049-69)), and a rectangular mold vibrated from the surface.
The effects of mold size, amplitude, surcharge pressure, and duration of vibration are investigated and analyzed. In addition, three types of subbase materials—gravel, limestone, and slag—are used in this study to examine the effects of subbase type on maximum density.
It is concluded that the interaction effects of aggregate type, mold size, amplitude, surcharge pressure, and duration of vibration are statistically significant on maximum dry density. The impact tests consistently produce higher densities with the investigated subbase materials than the vibratory methods. There is a very high degree of correlation between the densities obtained from the impact methods and the vibratory method where the subbase materials are vibrated at 0.030-in. amplitude and a surcharge pressure of 1 psi is applied. Estimating equations are developed for predicting maximum density of subbase material from the vibratory test data.