The resilient modulus of a soil or unbound aggregate material is the recoverable stress/strain relationship of the soil. The greater the resilient modulus of the soils is; the "stiffer" the soil will be, and the greater the strength will be for supporting transmitted wheel loads. This parameter is considered to be the best indicator of a subgrade's strength since the test replicates the dynamics of moving wheel loads. The new 2002 AASHTO Design Guide for Pavement Structures requires that the resilient modulus of the subgrade be used to design the pavement thickness for both asphalt concrete and PCC concrete pavements. Due to the complexity of the test, test results have been inconsistent. For example, data to date has shown that: · Two different laboratories testing split samples of the same soil or aggregate layer get widely different results. · Two technicians on the same equipment would also get widely different results. · Repeated tests on the same sample by one technician on the same equipment would not always produce consistent results.

This pooled fund study has two primary goals: 1. To reduce the variability currently associated with resilient modulus testing of unbound materials. 2. To conduct a precision and bias study of the test procedure.

See attached.

Approximate amount of funding requested per State is $50K.