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Evaluation of Mechanical Performance of Asphalt Emulsion Stabilized Base Course Using Asphaltenes or Cement
- Author / Creator
- Uddin, Muhammad Misbah
Civilization has become highly reliant on the road industry in recent years for both commercial and personal purposes. A typical road's function is to promote traffic flow comfortably and safely. The pavement is a structure made up of natural ground with varying layers on top that can distribute loads over many years and millions of traffic loads. Pavement requires a fundamental understanding of materials to be designed and constructed. Once it is open to traffic loads, it gradually deteriorates with time, repeated traffic load, and climate conditions. An asphalt pavement consists of different layers, which include subgrade, subbase, base, and surface courses. The base layer is the pavement's core structure that distributes most of the load on the pavement and reduces the wheel load stresses to levels that the subgrade can handle. For the base course, various soils or granular materials are available. Still, they may have inadequate properties resulting in significant pavement deformation and reduced pavement life. Besides, the integrity of the underlying soils has a significant impact on the long-term performance of pavement structures. These layers must be able to withstand permanent deformation, shear load and prevent excessive deflection that could cause fatigue cracking in the layers.
Generally, unbound aggregate bases are used as a base layer in the flexible pavements. The effect of unbound base layers on overall pavement efficiency will thus be determined by the layer's depth from the surface as well as the stiffness properties of the layers underneath. The addition of stabilizing agents to untreated granular aggregates improves the stability of unbound bases by increasing aggregate interlocks and facilitating load transfer. Asphalt emulsion stabilization is one the most technically reliable, cost-effective, and environmentally friendly methods to improve the properties of the base layer. However, these mixes have some drawbacks, such as weak early life mechanical properties and high porosity compared to hot mix asphalt. Some researchers discovered that adding 1-2 percent cement to the asphalt emulsion stabilized mixes greatly improves the early mechanical properties as well as the strength and toughness. Nonetheless, the application of these materials causes shrinkage cracking and early brittleness in pavement layers, particularly in cold climates. Other significant disadvantages of asphalt stabilization with cement include high rigidity of the mixture after stabilization, cracking due to shrinkage, and negative environmental effects. These major drawbacks of cement stabilization lead to more research into new materials that can be used as an alternative to cement.
The objective of this research is to evaluate and compare the performance properties of the stabilized base layer with asphalt emulsion and two different additives: 1) asphaltenes which is a waste material obtained from Alberta-oil sand with no significant use in the pavement industry; 2) cement which is a commonly used additive for this type of mixes. A mix design was created for determining the optimum emulsion content (OEC), considering the optimum moisture content (OMC) needed to compact the samples into maximum density. For mixture modification, different proportions of asphaltenes and cement contents were added to the mixture and physical and mechanical properties of the mixes were determined. To investigate the permanent deformation, moisture sensitivity, tensile strength, and low-temperature properties of the modified mixtures, Marshall stability, indirect tensile strength (ITS), Hamburg wheel tracking (HWT), and creep compliance and strength tests were performed on modified and unmodified mixtures. Additionally, in order to better understand the cracking resistance of adjusted mixtures, cracking tolerance (CT) of the samples was determined using the indirect tensile asphalt cracking test (IDEAL-CT).
Results from the study indicate that modification with asphaltenes and cement improved the performance of mixtures significantly compared to the control samples. Overall, compared to asphaltenes, cement was more effective in enhancing the rutting resistance and moisture sensitivity of the mixes. At the same time, it increased the cracking potential of the modified mixes at both intermediate and low temperatures.
- Graduation date
- Fall 2021
- Type of Item
- Master of Science
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.