Experience and a review of practice indicate new paving materials and technology are being evaluated with empirical tests. The evaluations are comparative, usually including a familiar asphalt in binder tests or a favorite aggregate in paving mixture tests. Generally, at least one type of water sensitivity test would be applied in the evaluation. Rational tests such as creep modulus and fatigue tests are being used to some extent but meet resistance because of lack of equipment and experience, both with the tests and meaning of the results.

An attempt is made to supply background on both the empirical and rational tests that are used in evaluating modified asphalts or replacement binders for asphalt. The background discussion is considered timely for long-used empirical tests as well as newer rational tests because of the insight such discussion can offer in considering the potential changes facing the pavement industry today.

Drawing on the background discussion, test results on sulfur-extended asphalt, recycled asphalt, and polymerized asphalt are specifically included in the paper because they are materials currently undergoing evaluation in the United States and around the world.