TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 324: Simulating the Effects of Hot-Mix Asphalt Aging for Performance Testing and Pavement Structural Design summarizes the results of an NCHRP effort that examined the limitations associated with provisional protocols on hardening potential of asphalt binders and mixes, and explored ways to enhance the predictive capabilities of these protocols. Detailed information on the conduct and results of these experiments was published as NCHRP Web-Only Document 113.