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Browsing by Author "Yan, Tianhao"

Now showing 1 - 6 of 6
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    Cost Estimate of B vs. C Grade Asphalt Binders
    (Minnesota Department of Transportation, 2023-06) Yan, Tianhao; Marasteanu, Mihai; Turos, Mugurel; Barman, Manik; Manickavasagan, Vishruthi; Chakraborty, Manik
    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 lifecycle cost analysis (LCCA) is performed comparing the use of polymer-modified and unmodified binders for lowvolume 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.
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    Development of Superpave 5 Asphalt Mix Designs for Minnesota Pavements
    (Minnesota Department of Transportation, 2022-06) Yan, Tianhao; Marasteanu, Mihai; Le, Jia-Liang; Turos, Mugurel; Cash, Kristen
    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.
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    Experimental and Computational Investigations of High-Density Asphalt Mixtures
    (Minnesota Department of Transportation, 2019-10) Marasteanu, Mihai; Le, Jia-Liang; Hill, Kimberly; Yan, Tianhao; Man, Teng; Turos, Mugurel; Barman, Manik; Arepalli, Uma Maheswar; Munch, Jared
    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.
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    Experimental Investigation and Nonlocal Modeling of Compaction of Hot Asphalt Mixtures
    (2021-08) Yan, Tianhao
    Compaction is the most critical step in the construction process of asphalt pavements, which has a significant consequence on the durability of asphalt pavements. However, people’s understanding on compaction of asphalt mixture is still very limited. The objective of this thesis is therefore to explore physical mechanisms of the compaction of asphalt mixtures and to model the compaction process based on its physical mechanisms. Before exploring mechanisms of compaction, a statistical analysis of the field density data is performed to achieve a thorough understanding of the current situation of field compaction. Then, physical mechanisms are investigated in different length scales. In the length scale of the thickness of asphalt binder films (∼ 10 µm), the lubricating behavior of asphalt binder between rough aggregates is believed as the mechanism that affects the compactability of asphalt mixtures. A tribological test is developed to measure the lubricating effect of asphalt binder between rough surfaces. The results show a strong effect of asphalt binder lubrication on improving the compactability of asphalt mxitures. In the length scale of asphalt mixtures (∼ 10 cm), two mesoscopic mechanisms (aggregate rearrangement and aggregate-binder interaction) are proposed to explain the macroscopic phenomena observed in gyratory compaction process. Based on the mechanism of aggregate rearrangement, a 1D nonlocal model is then proposed to simulate the gyratory compaction process of asphalt mixtures. The results show that the model is able to simulate the compaction curve, the density profile, and the size effect observed in gyratory compaction tests. Lastly, the 1D nonlocal model is employed to study the effects of randomness in the initial density profile and compaction effort on the compaction process of asphalt mixtures. The results can explain some key features of the probability distribution of field density data. The results of this study have the potential to be used for the design of more compactable asphalt mixtures and the prediction of asphalt pavement compaction.
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    Investigation of Asphalt Mixtures Compaction Using a Novel Approach Based on Tribology
    (Center for Transportation Studies, University of Minnesota, 2020-12) Yan, Tianhao; Turos, Mugurel; Kumar, Ravi; Marasteanu, Mihai
    Compaction is one of the most important factors that affects the durability of asphalt pavements. Many studies have been focused on developing methods to improve compaction. Previously, the authors found that the addition of small percentages of Graphite Nanoplatelets (GNPs) significantly increase the compactability of asphalt mixture. Traditional viscosity test results show that the increase in compactability is not a result of viscosity reduction, which implies that other mechanisms are responsible for the increase in compactability of GNP modified mixtures. This study investigates the lubricating behavior of the binder. A new test method, referred to as a tribological test, is conducted to evaluate the lubricating behavior of binders modified with different percentages of GNP (0%, 3%, and 6%). To better simulate the roughness of the aggregate surface, the tribological fixture is modified using textured contact surfaces instead of smooth ones. The results of rough surface tribological tests show that the addition of GNPs increases the lubrication behavior of the thin film binder between rough surfaces. It is hypothesized that the increase in compactability can be attributed to the increase in the lubricating behavior of the binder due to the addition of GNP.
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    Investigation of Cracking Resistance of Asphalt Mixtures and Binders
    (Minnesota Department of Transportation, 2019-01) Marasteanu, Mihai; Turos, Mugurel; Ghosh, Debaroti; Matias de Oliveira, Jhenyffer Lorrany; Yan, Tianhao
    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.