Yan, Tianhao

Polymer-modified binders (PMB) have been shown over the decades to improve the mechanical properties of asphalt mixtures compared to unmodified binders. Considering the higher initial cost of PMB, selecting the best alternative is very important, especially for local agencies given their limited budgets. A challenge in the materials selection process for low-volume roads is the limited information available, which could allow engineers to determine whether using PMB is cost-effective. In this research, we investigate the use of PG 58H-34 PMB binders (grade C) and PG58S 28 unmodified binders (grade B) for low-volume roads in Minnesota. Historical pavement performance data are analyzed to compare the field performance of modified and unmodified mixtures. Laboratory experiments are performed to compare the low-temperature cracking properties of polymer-modified and unmodified binders and mixtures commonly used in Minnesota. Based on the experimental results, a life-cycle cost analysis (LCCA) is performed comparing the use of polymer-modified and unmodified binders for low-volume roads in Minnesota. The results show that using PMBs for new construction is expected to extend the pavement service life by 6 years, and that using PMB is more cost-effective than using unmodified binders for low-traffic roads.

High field density is desired for improving the durability of asphalt pavements. This research aims to develop Superpave 5 mixtures (more compactable than traditional Superpave mixtures) by using locally available materials to improve the field density in Minnesota. First, previous projects in Minnesota were investigated. The mean and standard deviation of field density in Minnesota were about 93.5% Gmm and 1.5% Gmm, respectively. Significant correlations were identified between field density and mix design indices, i.e., Ndesign, NMAS, and fine aggregate angularity (FAA). Four traditional Superpave mixtures were then selected and modified to Superpave 5 mixtures by adjusting their aggregate gradations while maintaining the asphalt binder content. Laboratory performance tests were performed to check the mechanical properties of the modified mixtures. The results showed it was feasible to design Superpave 5 mixtures (more compactable mixtures) by adjusting aggregate gradations, and the improved compactability of the mixtures did not adversely affect the performance of the mixtures for rutting, stiffness, and cracking resistance. Therefore, Superpave 5 mixtures can increase field density as well as other performances of asphalt pavements if implemented.

Compaction of asphalt mixtures represents a critical step in the construction process that significantly affects the performance and durability of asphalt pavements. In this research effort; the compaction process of asphalt mixtures was investigated using a combined experimental and computational approach. The primary goal was to understand the main factors responsible for achieving good density and was triggered by the success of a recently proposed Superpave 5 mix design method. First; a two-scale discrete element method (DEM) model was developed to simulate the compaction process of asphalt mixtures. The computational model was anchored by a fluid dynamics-discrete element model; which is capable of capturing the motion of aggregates in the viscous binder. The model was then calibrated and validated by a series of experiments; which included rheological tests of the binder and a compaction test of the mixture. It was concluded that the compaction process was significantly influenced by the rheological properties of the fine aggregate matrix and by the sphericity of the coarse aggregates. Finally; the mechanical properties of two high-density mixtures were determined and compared with mechanical properties of mixtures used for MnROAD 2017 National road Research Alliance (NRRA) test sections. It was found that the properties of high-density mixtures as a group were not significantly different compared to the properties of conventional mixtures.

In this study; the viability of using three test methods for asphalt mixtures and one test method for asphalt binders are investigated. These test methods are: Bending Beam Rheometer (BBR) for creep and strength of asphalt mixtures; low temperature Semi Circular Bend (SCB) test for fracture energy of asphalt mixtures; Dynamic Modulus (E*) test of asphalt mixtures using the Indirect Tensile Test (IDT) configuration; and BBR strength test of asphalt binders. The materials used in the experimental work were used in MnROAD cells constructed in the summer of 2016 as part of the MnROAD Cracking Group (CG) experiment; a 3-year pooled-fund project. The results show that the testing methods investigated provide repeatable results that follow trends similar to the one observed using traditional methods. The results also show that the properties are highly temperature dependent and the ranking observed at one temperature can change at a different temperature. In addition; it is observed that materials with similar rheological properties; such as complex modulus absolute value E*; creep stiffness S; and m-value; do not necessarily have the same fracture resistance. These results confirm one more time the need for a fracture/strength test for correctly evaluating cracking resistance of asphalt materials.