Fundamental properties of asphalts and modified asphalts, such as viscosity, elasticity, and temperature susceptibility, are critical in the modification processes. These properties guide the selection of additives, such as polymers or rubber, to enhance performance characteristics like durability, resistance to deformation, and aging. By understanding these properties, engineers can tailor the modification process to achieve desired outcomes, ensuring that the final product meets specific performance requirements for various applications in road construction and maintenance.