Case Study: Dynamic Modulus Characterization of Naturally Occurring Bituminous Sands for Sustainable Pavement Applications

Abstract

──────────────── ─────── Abstract: Oil sand is a generic name given to naturally occurring deposits of bituminous sand materials that are mined for crude oil production. These materials are currently used as subgrade materials of temporary and permanent roads in oil sand fields. The presence of high bitumen content makes oil sand materials problematic for field operations of off-road haul trucks and shovels during the warm spring and summer months. The behavior of oil sand materials is primarily dependent upon stress states, temperature, and the rate of loading or frequency. To effectively account for temperature and loading frequency, dynamic modulus is the preferred material property to characterize bituminous materials. In this paper, dynamic modulus is determined for three types of oil sand materials with natural bitumen contents of 8.5, 13.3, and 14.5% by weight using cyclic load triaxial test procedure. All the three oil sand samples were compacted close-to-field densities and then tested at two temperatures and three loading frequencies (related to field trafficking speeds) at different stress states. Based on the test results, dynamic modulus was modeled as a power function of the applied stress states and temperature. Using all the test data obtained from the three oil sand samples, unified dynamic modulus characterization models were successfully developed to account for stress state, bitumen content, and temperature. The proposed model can be calibrated for field practical use to estimate modulus and deformation behavior of these oil sand materials for their sustainable use in pavement applications. 2 Oil sands, sometimes called as tar sands, are natural deposits of bituminous sand materials that are rich in bitumen content to the extent that oil can be extracted from these deposits. Oil sands are found worldwide. The largest and most thoroughly studied deposits are located in Canada, United States, and Venezuela. The Alberta Province in Canada has the world's largest deposit of oil sands. Oil sand surface mining involves excavation to remove the overburden and providing access to the mineral sands below it using haul trucks and shovels. In situ, the oil sand deposits are predominantly quartz sand surrounded by a thin film of water and fines, with bitumen filling the pore spaces between the sand grains. The quartz sand, silt, and clay, i.e., inorganic materials of the oil sand composition normally constitutes about 80% by weight, with bitumen and water constituting about 15 and 5%, respectively (1). Oil sand materials are currently used as construction materials of temporary and permanent roads in oil sand fields for operating large capacity haul trucks and shovels. These materials often exhibit stress dependent, viscoelastic, and plastic behavior under off-road construction and mining equipment. Field studies have shown that the modulus and deformation behavior of oil sands are primarily dependent upon the