Day to day we are concerned with our detrimental impact on the environment. With the ever increasing waste disposal problem in the US, the utilizing utilization of recycled materials in Civil Engineering construction has become an attractive option, which not only supports the concept of green buildings, but can also bring about economic savings by conserving natural resources and landfill spaces. However, the questionable long-term performance of recycled materials often hinders the widespread use in structural applications. This book explores the use of accelerated aging/testing protocols for predicting the durability of Recycled Aggregate Concrete (RAC), containing recycled crushed aggregate, Type I Portland Cement, and up to 50% replacement of cement with ASTM Class F fly ash. replacement. Accelerated aging was accomplished by curing the specimens at elevated temperatures regimes for specific durations. Stiffness-time master curves were then constructed using Time- Temperature Superposition (TTS) and Stepped Isothermal Method (SIM) based on the Arrhenius Equation.