Rapid curing cutback bitumen is a type of bitumen that is blended with another substance in order to improve its curing time. In this case, the correct substance that is blended with bitumen to produce rapid curing cutback bitumen is petrol.

Petrol, also known as gasoline, is a flammable liquid mixture that is primarily used as a fuel in internal combustion engines. It is derived from crude oil through a refining process. Petrol has a low viscosity and a high volatility, making it an ideal additive for bitumen to enhance its curing properties.

Below is a detailed explanation of why petrol is used as a blending agent to produce rapid curing cutback bitumen:

1. Enhances Volatility: Petrol has a high evaporation rate due to its low boiling point. When blended with bitumen, it increases the overall volatility of the mixture. This enhanced volatility helps in the rapid evaporation of the petrol component, which accelerates the curing process of the bitumen.

2. Reduces Viscosity: Bitumen is a highly viscous material at room temperature, which makes it difficult to handle and apply. By blending it with petrol, the viscosity of the mixture is reduced, making it easier to work with. The lower viscosity also aids in the rapid penetration of the bitumen into the pavement surface, leading to faster curing.

3. Improves Adhesion: The addition of petrol improves the adhesion properties of the bitumen. It helps in better bonding between the bitumen and the aggregate particles, resulting in improved pavement performance. The enhanced adhesion also contributes to the rapid curing of the bitumen.

4. Provides Cost-effectiveness: Petrol is readily available and relatively inexpensive compared to other blending agents such as kerosene, benzene, or diesel. This makes it a cost-effective choice for producing rapid curing cutback bitumen.

In summary, petrol is used as a blending agent in the production of rapid curing cutback bitumen due to its high volatility, ability to reduce viscosity, improved adhesion properties, and cost-effectiveness. The addition of petrol enhances the curing time of bitumen, making it a suitable choice for various road construction and maintenance applications.