Pavement Materials – Rapid-curing (RC) cutback bitumen Rapid-curing cutback bitumen is obtained by blending penetration-grade bitumen with which volatile diluent?

Introduction / Context:
Cutback bitumen is produced by dissolving bitumen in a volatile petroleum solvent so that the mixture has temporarily reduced viscosity at ambient temperature. Depending on solvent volatility, cutbacks are classified as rapid-curing (RC), medium-curing (MC), or slow-curing (SC). Selecting the correct solvent is important for setting time and early strength in road works such as surface dressing and patch repairs.

Given Data / Assumptions:

• Base binder is penetration-grade bitumen.
• Field application may require quick set and early opening to traffic.
• Solvent must evaporate readily to restore binder viscosity.

Concept / Approach:

Solvent volatility controls cure rate: RC uses highly volatile solvents, MC uses moderately volatile solvents, and SC uses low-volatility diluents. Petrol (gasoline) has a low boiling range and evaporates quickly, producing the “rapid-curing” behavior. Kerosene (for MC) and diesel/fuel oil (for SC) evaporate more slowly, which extends curing time.

Step-by-Step Solution:

Verification / Alternative check:

Standard highway specifications list RC binders (e.g., RC-70, RC-250) that use gasoline-range solvents; MC grades (MC-30, MC-70, etc.) use kerosene-range distillates; SC grades use diesel/fuel oil fractions.

Why Other Options Are Wrong:

Kerosene and diesel correspond to MC and SC cutbacks, respectively; benzene is not used for standard cutbacks due to toxicity and unsuitable properties; fuel oil is too heavy and slow evaporating.

Common Pitfalls:

Using inappropriate cutback in cold weather (leading to delayed set) or in hot weather (risk of bleeding), and not accounting for environmental restrictions on cutback use.

Final Answer:

Petrol (gasoline)