Sobhan, Khaled Dr.

With the growing environmental concerns related to the ever increasing
waste disposal problem in the US, the utilizing 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. The primary focus of this study was to
develop accelerated aging/testing protocols for predicting the durability of
recycled aggregate concrete (RAC), Type I Portland Cement, and up to 50% fly
ash replacement. Accelerated aging was accomplished by curing the specimens
at elevated temperatures regimes for specific durations. Stiffness-time master
curves were constructed using Time-Temperature Superposition (TTS) and
Stepped Isothermal Method (SIM) based on the Arrhenius Equation. All the
methods demonstrated that the stiffness decreased with time regardless of the
amount of fly ash. The Arrhenius method allowed stiffness prediction up to an
equivalent age of 14,000 hours developed from short-term tests lasting up to 144
hours. It was also found that SIM and TTS provide equitable results, potentially
reducing the number of specimens and testing time for durability prediction.

To better characterize the accumulation of permanent deformation in a granular material, 40 Consolidated Drained (CD) triaxial tests (14 static and 26 cyclic) were performed under various stress conditions. A Digital Image Correlation (DIC) technique was utilized in some Repeated Load Triaxial (RLT) tests to measure global and localized strains visually in a non-contact manner. Additionally, the experimentally determined resilient material properties were used in a finite element based pavement modeling software called MICH-PAVE. Under cyclic loading, the permanent strain accumulation was found to obey the relationship of the form epsilonp =aNb, and the Resilient Modulus was used to develop the nonlinear K-theta model for granular materials. The observed/measured permanent strains using DIC/LVDT techniques compared favorably with the values obtained by the finite element simulation, and the evaluation of granular material by multiple methods seems promising for improved pavement design.