If the viscosity of bitumen is reduced by volatile diluents like kerosene or oil, it is called:

Explanation:

Bitumen Viscosity Reduction

When bitumen's viscosity is reduced using volatile diluents such as kerosene or oil, it is referred to as cutback bitumen. This process involves adding a solvent to the bitumen to decrease its viscosity, making it easier to work with, especially in paving applications. The diluent evaporates after application, leaving behind the bitumen which then binds the aggregate particles together. Analyzing each option:

• Emulsion: Bitumen emulsion is a mixture of bitumen, water, and an emulsifying agent. It does not involve reducing viscosity with volatile diluents.

• Tar: Tar is a different substance, derived from the destructive distillation of organic materials like coal and wood, not by adding volatile diluents to bitumen.

• Asphalt: Asphalt is a broad term that can refer to both the natural and refined product used in road construction. It is not specific to the process of reducing bitumen viscosity with volatile diluents.

• Cutback: Cutback bitumen is indeed the correct term for bitumen whose viscosity has been reduced by volatile diluents like kerosene or oil.