Design and Performance Evaluation of Road Base Courses Comprised of Asphalt Emulsion and Asphaltenes Derived from Alberta Oil sands
Creators: Kamran, Farshad
Publisher: name: University of Alberta Library
Year: 2023

<p>Stabilization of granular base course materials has proven to be an effective method for enhancing the performance of pavement structure. Among the various methods used in this field, asphalt emulsion stabilization stands out as a widely employed technique that offers several benefits, including the production of high-quality base courses with reduced energy consumption, carbon footprint, and natural material usage. This method leads to increased strength, stability, bearing capacity, and overall mechanical properties compared to granular base layer. However, it comes with certain drawbacks, such as decreased moisture and rutting resistance, early-life performance issues, and longer curing times. Researchers have proposed solutions to address these deficiencies, although not comprehensive enough to eliminate further disadvantages. The addition of cementitious materials as active fillers in asphalt emulsion stabilization yields significant benefits. It leads to higher early-strength gain, increased stiffness, improved rutting resistance, enhanced moisture resistance, and shorter curing and breaking times compared to unmodified layers. These advantages contribute to enhanced structural integrity, load-bearing capacity, and overall performance of the stabilized layer, making it a valuable and effective technique in road construction. A review of existing literature reveals several disadvantages in base layer stabilization, including the low performance properties of base layers stabilized with asphalt emulsion, negative effect of the rigidity of alternative cementitious materials used for stabilization, the lack of proper information regarding the impact of temperature on pavement base layers in current guidelines. In addition, using widely available residue materials like asphaltenes and reclaimed asphalt pavement (RAP) as additives in road construction can improve these layers and reduce the carbon footprint. Integrating these materials into the design process leads to more sustainable and environmentally friendly practices. In this study, to enhance the performance of the base layer, two different mixtures consisting of natural aggregates or RAP are selected to be stabilized with asphalt emulsion, with the addition of asphaltenes as an additive. Additionally, Portland cement was added to same gradation of aggregates selected and the performance properties were compared to asphaltenes modified mixes. The asphaltenes used in this study are derived from Alberta oil-sands bitumen without any application in industry. The design process of the mixtures is determined based on available guidelines, utilizing tests such as Indirect Tensile Strength (ITS), Tensile Strength Ratio (TSR), and Marshall stability. The performance properties of the mixtures are investigated at high-temperatures with Hamburg wheel tracking, intermediate-temperatures using ITS and TSR, and low-temperatures using creep compliance and strength, and indirect tensile test at low temperatures. Binder testing, and field emission scanning electron microscopy (FESEM) are conducted to analyze the properties of the binders. Additionally, dynamic modulus tests are performed on the mixes to predict the viscoelastic properties of the samples. Furthermore, an analysis of variance (ANOVA) is employed to evaluate the significance of asphaltenes modification. The results of this research demonstrate a significant improvement in the high-temperature properties of both aggregate and RAP layers with addition of asphaltenes and Portland cement. Intermediate-temperature properties also show improvement, and in some cases, the mixes meet the minimum requirements suggested by guidelines after modification. However, no significant changes are observed in the low-temperature properties, indicating that the addition of asphaltenes do not adversely affect the performance in low-temperature conditions, as indicated by the results from ANOVA. However, cement increased the brittleness of the mixes at low-temperatures. The dynamic shear rheometer (DSR) test results also show that addition of asphaltenes results in stiffening the base binder with FESEM indicating that asphaltenes interact. However, cement does not interact with binder. The dynamic modulus test results demonstrate that both the stabilized base layer and recycled materials exhibit viscoelastic behaviour, with varying moduli at different frequencies and temperatures. This finding indicates that these layers, are viscoelastic materials rather than granular materials in pavement design. The dynamic modulus results of cement modified mixes exhibit elastic behaviour which highlights the unique impact of asphaltenes on the material&#39;s viscoelastic properties, providing valuable insights for pavement design and performance. Comparing the positive effects of both cement and asphaltenes at high- and intermediate-temperatures with adverse behviour of mixes with cement with respect to asphaltenes modified mixes, ultimately, suggested the potential replacement of Portland cement with asphaltenes in asphalt emulsion-stabilized mixes to achieve improved performance in base layers.</p>