Discipline: Technology and Engineering
Subcategory: Civil/Mechanical/Manufacturing Engineering
Room: Exhibit Hall A
Elena Youngdale - Macalester College
Co-Author(s): Andrea Hernandez, California State Polytechnic University, CA
Average Hot Mixture Asphalt (HMA) consists of ~95% aggregate (stone, sand, or gravel) and ~5% asphalt binder. HMA Pavement costs the U.S. approximately $45 billion annually, the bulk of which goes to maintenance and repair. In previous applications and research, optimum dosages of recycled rubber tire (crumb rubber modifier CRM) and synthetic fibers like polyvinyl alcohol (PVA) fibers have each been mixed with HMA to enhance stiffness, strength, fracture toughness, and resilience. Dosage refers to the modifier’s percentage of a mixture?s total weight, so a 1% dosage takes up 1% of the mixture’s total weight. This study works to find optimum dosages of CRM (both coarse and fine grade) and PVA fibers when combined. In this study, a total of 10 mixtures are created and tested for maximize bending stress (strength) and fracture energy (toughness) through a ramping load, semi-circular bending beam test. Midpoints for the tested range of dosages for PCA and CRM are based off preliminary tests. Three mixtures act as control samples with one mixture free of modifiers, one without CRM, and one without PVA. To test how PVA and CRM interact with each other, all other 7 mixtures contain either 0.05% PVA fiber or a 1% coarse and 1% fine CRM dosage. Four variables were tested: First, PVA fibers with dosages of 0%, 0.05%, and 0.1%. Second, mixed CRM with a set 50/50 coarse-fine ratio at 0%, 1%, 2%, and 3% dosages. Third, coarse to fine ratio with total CRM content set to 2%, varying the coarse-fine rubber ratio as 0/100, 50/50, and 100/0. Fourth, fine CRM at 0%, 1%, and 2% dosages with no coarse rubber. From 0% to 0.1% PVA fiber dosage, the maximum bending stress decreased from 185->132Kpa with fracture energy decreasing 77->57 Kpa*cm2. Varying the coarse-fine grade rubber ratio from 100% fine rubber to 50/50 coarse-fine to 100% coarse rubber decreased 178->122Kpa bending stress and 73->50Kpa*cm2 fracture energy. At a set 50/50 coarse-fine ratio, increase in rubber dosage decreased both mechanical properties tested. When testing fine CRM for 0%, 1%, and 2% dosages, bending stresses rose then fell [188->196->178]Kpa while fracture energy gave [84->85->73] Kpa*cm2. In conclusion, PVA fiber and coarse CRM decrease bending stress and fracture energy while an optimum 1% dosage of fine CRM increases both mechanical properties. In preliminary tests, PVA and CRM samples were mixed at different temperatures with lower grade asphalt binder so mixing temperature and binder require further research. Fatigue testing is also required to better understand the bounce-back (resilience) of fiber and rubber mixtures since both modifiers should increase elasticity. References: Ye Q, Wu S, Li N. Investigation of the dynamic and fatigue properties of fiber modified asphalt mixtures. Int J Fatigue 2009; 31:1598-602. Kaloush K et al., Cracking characteristic of asphalt rubber mixtures. In: Proceedings of the Fifth International Rilem Conference, PRO 37, Limoges, France; 2004. p. 485-92.
Funder Acknowledgement(s): I thank M. Reza Bhuyan, A. Das, and S. Rahman for help in and out of the lab. I also thank primary investigator Dr. Jamal Khattak, professor at the University of Louisiana, Lafayette, for guidance in both the lab and logistic support. Funding was provided by the National Science Foundation.
Faculty Advisor: Mohammed Jamal Khattak, email@example.com
Role: My part of the research included all creating and handling of the samples with software skills such as running tests and analyzing results. I prepared, heated, mix, compressed, cut, painted, and tested each sample with my lab partner. After testing I compiled results and ran analysis to be interpreted by both my advisor and I. For mix designs, 8 were pre-determined but 2 were decided on by my lab partner, advisor, and I based on time and other results.