What is Rapid Curing cutback Bitumen?
Rapid curing cutback asphalt cement is a combination of light diluents of high volatility, generally in the gasoline or naphtha boiling point range (RC-70, 250, 800, 3000), and asphalt cement.
Rapid curing cutback asphalt combinations are prepared to start from the lighter diluents, and even from the fluid of higher viscosity. The grades used for rapid curing cutback bitumen are RC-70, RC-250, RC-800, and RC-3000. Here, the value given by numbers 70, 250, 800, and 3,000 represents the kinematic viscosity of the bitumen given in centistokes. The solvent concentration of rapid curing asphalt is 15-45% of the volume of asphalt cement used.
Mainly two tests are conducted on cut-back asphalt and are given as 1) residue and 2) cutback test. The testing of residue focuses on examination of penetration, ductility, and solubility. The testing of cutback bitumen includes the distillation, viscosity, and flash point tests.
The degree of liquidity developed in each case depends principally on the proportion of solvent to asphalt cement. To a minor degree, the liquidity of the cutback may be affected by the hardness of the base asphalt from which the cutback is made. The degree of fluidity results in several grades of cutback asphalt—some quite fluid at ordinary temperatures and others somewhat more viscous. The more viscous grades may require a small amount of heating to make them fluid enough for construction operations.
Asphalt cutbacks use petroleum solvents for fluidifying asphalt cement. The solvents are called distillate, diluents, or cutter stock. If the solvent used in making the cutback asphalt is highly volatile, it will evaporate quickly, while solvents of lower volatility evaporate more slowly. Based on the relative speed of the solvent fraction’s evaporation, cutback asphalts are divided into three types: rapid curing (RC), medium curing (MC), and slow curing (SC).
Application
The rapid-setting grades are designed to react quickly primarily for spray applications, such as bond/tack coats, aggregate chips seals, sand seals, and similar surface treatments.
Rapid curing Cutback bitumen is typically used as prime coats and tack coats. Generally, Cutback Bitumen are divided into three groups depending on the volatility of the solvent added:
RC cutback bitumen
After an RC cutback is applied the solvent evaporates away and only the Bitumen is left. A rapid curing cutback bitumen is said to cure as the petroleum solvent evaporates.
Rapid Curing Cutback Bitumen is made by reducing the viscosity of ordinary bitumen by adding mostly petroleum-type solvent. Cutback Bitumen are used because their viscosity is lower than that of neat asphalt and can thus be used in low-temperature applications.
Properties and Features
Fluidity of RC cutback bitumen is defined mostly by the solvent-to-asphalt cement ratio. Its liquidity also depends on that of the base asphalt. RC cutbacks vary in viscosity in a way that some are very fluid at temperatures near or lower than ambient temperature, while others must be lightly heated to use effectively.
Some of the properties of RC cutback bitumen include:
- Speed of curing by rapid evaporation of solvents.
- Lower viscosity compared to standard asphalt cement, making it suitable for use in cold temperatures.
- Easy application without the need for massive heating.
- Strong aggregate adhesion, improving pavement longevity.
Conclusion
Rapid Curing Cutback Bitumen is an essential commodity in road building and maintenance that is highly workable and displays good adhesion. Its capability to cure very fast makes it ideal for application in spray-type applications such as tack coats and chip seals. Its use should, however, be well handled to balance its performance benefits with environmental concerns.
With the knowledge of its properties, testing, and applications, engineers and construction personnel can optimize the use of RC cutback bitumen to create durable and high-quality road surfaces.
