Why oil is used in the viscosity of asphalt test?

Oil is used in the viscosity of asphalt test primarily to simulate the conditions under which asphalt will be used in real-world applications, such as road construction. By incorporating oil, the test can more accurately measure the flow and deformation characteristics of asphalt when subjected to temperature changes and mechanical stress. This helps in evaluating the performance and durability of asphalt mixtures, ensuring they meet specific engineering standards. Additionally, oil can help reduce the viscosity of asphalt for easier handling and mixing during testing.