Tar is the viscous liquid produced when natural organic materials such as coal, petroleum, wood, etc., are carbonised. Depending on the material from which tar is obtained, it is called as wood tar or coal tar. Coal tar is used mostly for road work because of its superior quality. Road tar is produced by undergoing three stages, viz., carbonisation of coal to produce coal tar, refining or distillation of crude tar and blending of distillation residue with distillate oil fraction.
There are five grades of road tar, viz., RT-1 to RT-5 based on their viscosity and other properties. Uses of different grades of road tar are given below.
RT-1: Used for surface painting under adverse cold conditions.
RT-2: Used for standard surface painting under normal weather conditions.
RT-3: Used for surface painting, renewal coats, pre-mixing chips for top course and light carpets.
RT-4: Used for pre-mixing tar macadam in base course.
RT-5: Used for grouting.
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