RTFOT Viscosity Grade Bitumen (AR-Grades), in which the Viscosity of bitumen (asphalt) is measured at 60 centigrade degrees (140 degrees F) after the roll on thin film oven test. Viscosity grade bitumen have  thermoplastic properties which causes the material to soften at high temperatures and to harden at lower temperatures. This unique temperature/ viscosity relationship is important when determining the performance parameters such as the adhesion, rheology, durability and application temperatures of bitumen.