Abstract
The asphalt mixture performance tester (AMPT) requires an exhaustive examination of the factors that influence the dynamic modulus and flow number test results. Interlaboratory research conducted in NCHRP Project 9–29, Phase 4, showed that dynamic modulus test results were highly dependent on the testing laboratory and the preparation of the AMPT specimens. Factors could include the oxidative aging and the steric hardening of asphalt in the mixture specimens during storage in a laboratory. The Asphalt Institute, Lexington, Kentucky, performed an experiment in cooperation with FHWA to evaluate the effect of ambient laboratory sample storage on the mechanical properties of asphalt mixture specimens. A half-factorial test matrix with triplicate specimens was developed to evaluate the effect of the following factors on the dynamic modulus and flow number of a laboratory standard mixture: storage duration (1 to 84 days), binder type (PG 64–22 and modified PG 76–22), storage of the specimen in a bag, and the cutting and coring of the specimen after compaction or immediately before it was tested. The results showed that storage duration could affect significantly the properties of the mixture with neat binder. The bagging of specimens did not seem to prevent their stiffening. However, storage of specimens uncut and uncored seemed to delay the stiffening phenomenon.
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