@article{malladi_ayyala_tayebali_khosla_2015, title={Laboratory Evaluation of Warm-Mix Asphalt Mixtures for Moisture and Rutting Susceptibility}, volume={27}, ISSN={["1943-5533"]}, DOI={10.1061/(asce)mt.1943-5533.0001121}, abstractNote={AbstractSince its introduction, warm mix asphalt (WMA) has garnered a lot of attention and interest from the pavement industry as a promising technology to replace the conventional hot mix asphalt (HMA). Despite its many benefits, including reducing emissions and fuel usage, definitive answers on the feasibility of replacing HMA pavements with WMA are yet to be answered. A major concern for WMA is susceptibility to moisture-induced damage. In this research study, mixtures prepared using three WMA technologies- viz. Sasobit, Advera WMA and the Foamer were evaluated for their moisture susceptibility and permanent deformation in comparison with an HMA mixture. Tensile strength ratio (TSR) and asphalt pavement analyzer (APA) tests were conducted on these mixtures. Results show that moisture-based WMA technologies (Advera and Foamer) are more susceptible to moisture damage. However, rut depths evaluated using APA, even for moisture-conditioned specimens, indicated WMA performance on par with that of HMA. Even ...}, number={5}, journal={JOURNAL OF MATERIALS IN CIVIL ENGINEERING}, author={Malladi, Haritha and Ayyala, Dinesh and Tayebali, Akhtarhusein A. and Khosla, N. Paul}, year={2015}, month={May} }
 @inproceedings{ayyala_malladi_khosla_tayebali_2014, title={Evaluation of warm mix asphalt technology for surface mixtures}, DOI={10.1201/b17219-88}, abstractNote={Economic, environmental, and engineering benefits led to the rapid implementation of Warm-Mix Asphalt (WMA) during the past decade. While WMA technologies are generally performing well to date, development of standard mix design protocols continues and performance questions remain. This study evaluated laboratory conditioning protocols for WMA to simulate early life when they are more moisture susceptible and proposed 2 hours at 116°C for mix design and reheating to this temperature for quality assurance for all WMA technologies except foaming which requires reheating to 135°C. Next, WMA was shown to be more moisture susceptible as compared to Hot-Mix Asphalt in the early life based on a comprehensive analysis of three standard laboratory tests (wet and dry indirect tensile strengths and resilient modulus and their ratios and Hamburg Wheel Tracking Test stripping parameters) from four field projects that included nine WMA mixtures. Finally, an evaluation of performance evolution showed that WMA can overcome this vulnerability to moisture after a summer of aging and proposed 5 days oven aging at 85°C to capture this effect in the laboratory. Proposed conditioning protocols, aging protocols, and criteria for the tests utilized are provided for WMA mix design and analysis to preclude moisture susceptibility.}, booktitle={Asphalt Pavements, vol 1}, author={Ayyala, D. and Malladi, H. and Khosla, N. P. and Tayebali, A. A.}, year={2014}, pages={701–708} }
 @article{khosla_ayyala_2013, title={A Performance-Based Evaluation of Superpave Design Gyrations for High Traffic Surface Mixes}, volume={104}, ISSN={["1877-0428"]}, DOI={10.1016/j.sbspro.2013.11.103}, abstractNote={The number of design gyrations (Ndes) is an extremely important parameter in the asphalt concrete mix design procedure using the Superpave method. The choice of Ndes is a function of total traffic during the pavement service life, expressed in ESALs. Asphalt concrete mixes for higher traffic levels are compacted to a higher Ndes as a denser mix resists rutting more effectively. However, this leads to a lower design asphalt content, which decreases fatigue performance of the mix. Therefore, a performance-oriented approach to determine Ndes was developed that optimizes mix performance with respect to both rutting and fatigue cracking. In this paper, the research methodology adopted to compare the relative performance of surface mixes with 12.5 mm nominal maximum aggregate size is presented, along with recommended Ndes values for C and D-level mixes, designed to handle traffic levels of 3-30 Million and greater than 30 Million ESALs, respectively. Asphalt concrete mixes were designed at Ndes levels of 50, 75, 100 and 125 gyrations to determine asphalt content using Superpave design method. Dynamic modulus (E*) was measured at design asphalt content for different gyration levels using the Asphalt Mixture Performance Tester device. The E* data and corresponding binder properties were used as input in the AASHTO Darwin-ME software to predict rutting and fatigue performance of the mixes by assuming a model pavement section and appropriate traffic levels. Relative performance indicators were developed for both rutting and fatigue, and plotted against the asphalt content to determine optimum Ndes. For both surface mixes, the optimum Ndes value was determined to be 85 gyrations.}, journal={2ND CONFERENCE OF TRANSPORTATION RESEARCH GROUP OF INDIA (2ND CTRG)}, author={Khosla, N. Paul and Ayyala, Dinesh}, year={2013}, pages={109–118} }