Date of Graduation
Bachelor of Science in Civil Engineering
PavementME Design is based on mechanistic-empirical principles, which take the properties of layer materials into account in predicting pavement responses and performance. Of these principles, dynamic modulus is one of the most important. Dynamic modulus measures strain in response to the applied stress, which mimics loads from traffic and the corresponding deformation of the asphalt pavement. The traditional test for dynamic modulus in the uniaxial configuration cannot be performed on field cores due to lift thickness. Owing to that, the Indirect Tension and torsion bar configuration were developed. This research will focus on the torsion bar, which requires specimens that are 10x12x50mm per ASTM D7552-09. The smaller size of torsion bar specimens is convenient for forensic evaluation. However, due to the small size of specimens, there are challenges with obtaining a sample that is representative of the global properties of the test material when the nominal maximum aggregate size, NMAS, is 12.5mm or greater.
The goal of this project is to determine if using aggregates of larger NMAS in asphalt concrete mixtures influences the shear dynamic modulus. Mixtures with a NMAS of 9.5mm and 25mm were tested. The results from the Torsion Bar test were used to generate master curves for each mix design using the time-temperature superposition technique. The results were analyzed by comparing test results from torsion bar test to other specimens of different NMAS and asphalt binders. Based on the analysis, the conclusion is the shear dynamic modulus from the torsion bar configuration is affected by the nominal maximum aggregate size used in asphalt concrete mixtures, `and the binder does not influence the results. RVE for torsion bar specimens falls between 9.5mm and 25mm, or even smaller.
Mahmud, Farida, "The Effects of Aggregate Size on Shear Dynamic Modulus from Torsion Bar" (2017). Civil Engineering Undergraduate Honors Theses. 37.