Abstract
NCHRP is in the final stages of developing and implementing a new mechanistic-empirical pavement design guide (MEPDG) to be used by all state highway agencies for layer thickness design. Once adopted, it will become the national procedure required on all federally aided projects. A key material property to be used in the design will be the resilient modulus value, which either can be obtained from laboratory testing or can be backcalculated from deflection data collected with falling weight deflectometers. It is important that realistic design moduli values be used. The standard test method for resilient modulus of subgrade soils and untreated base and subbase materials is AASHTO T307-99. However, the setup for this procedure is both difficult and time-consuming, and the equipment required to run this test is expensive. With the low strain levels used, it is likely that accurate instrumentation will be problematic for most state departments of transportation. The free-free resonant column test is a simple, nondestructive laboratory test method for determining the seismic modulus of pavement materials; it takes approximately 5 min to setup and complete. The equipment costs less than $4,000. For the tests conducted, it appears that the seismic modulus device is a better and more repeatable test for estimating the resilient modulus of stabilized materials, and it shows great potential for acquiring reasonable resilient modulus input values for the new AASHTO MEPDG.
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