Cutback Bitumen Description
Cutback Bitumen ( Liquid Bitumen ) is Bitumen that is dissolved in a solvent . Typical solvents include Naptha, gasoline and kerosene, white spirit, etc. The type of solvent controls the curing time while the amount determines the viscosity of the Cutback Bitumen.
The advantage Cutbacks have over Emulsions is a much higher residual Bitumen percent, typically over 80% compares with over 40-65% for Bitumen emulsions. The result I The ability to reshape is a great advantage the cutbacks have over the common penetration grade bitumen. It also requires less heat to liquefy which makes cutback grades easier to use at lower temperatures.s more Bitumen left on the roadway after curing, for the same volume of binder applied.
The benefit Cutbacks offer compared to Emulsions, is a much higher residual Bitumen percentage, usually over 80% while the rate for emulsions is around 40-65%. As a result, for the same volume of binder applied, more Bitumen is left on the roadway after curing.
The petroleum solvents used require higher amounts of energy to manufacture and are expensive compared to the water and emulsifying agents used in emulsified asphalts.
Cutback Classification
Cutbacks are divided into two classifications, Rapid-Curing (RC) and Medium-Curing (MC), and slow-curing ( SC) depending on the solvent used. They are further defined by a number that indicates the minimum kinematic viscosity (fluidity) of the cutback.
• Slow Curing often called “road oils,” are usually a residual material produced from the fractional distillation of certain crude petroleums. Traditionally any kind of aromatic, naphthenic, and paraffinic oils are used. Slow Curing liquid bitumen materials can be prepared by blending bitumen with an oily petroleum fraction.
• Medium Curing is a blend of Bitumen with lighter hydrocarbons such as kerosene.
• Rapid Curing products are prepared with light, rapidly evaporating diluents such as naphtha or gasoline.
Cutback Bitumen Application
Prime and Tack Coating
The process of priming involves applying a low viscosity binder to a prepared but usually unbound aggregate base. It is intended to be absorbed by the top layers of the base and provide a surface more easily ‘wetted’ by a subsequent bituminous covering. The primer will be able to carry traffic for a short time (although this practice is uncommon) and help control dust. Generally, primers are applied at rates between 0.5 and 1.4 L/m2. Cutback bitumens suitable for priming are also used for tack coats, which are applied to an underlying surface to help with the adhesion of the subsequent asphalt layers. A typical application rate is between 0.2 and 0.4 L/m2.
Prime Sealing
Where temperatures are too cool for an effective priming operation, or where traffic is likely to upset a primed surface before the final seal can be sprayed, a primer seal can be used to give adequate protection of the pavement for periods of up to 6 to 12 months. Cutback bitumens suitable for primer sealing can also be used in the manufacture of pre-mix asphalt, which is used in patch repairs.
Spray Sealing
Cutback bitumens are used extensively in sprayed sealing applications, particularly in cooler weather where they provide improved initial stone retention due to their lower viscosity. Typically, a single application of the appropriate cutback bitumen is sprayed onto the primed pavement onto which aggregate is laid.
Grades & Properties
| Grade | Curing Speed | Viscosity | Penetration of Residue |
| MC 30 | Medium | 30-60 | 120- 150 |
| MC 70 | Medium | 70-140 | 120- 150 |
| MC 250 | Medium | 250- 500 | 120- 150 |
| MC 800 | Medium | 800- 1600 | 120- 150 |
| MC 3000 | Medium | 3000- 6000 | 120- 150 |
| RC 70 | Rapid | 70-140 | 80- 120 |
| RC 250 | Rapid | 250-500 | 80- 120 |
| RC 800 | Rapid | 800- 1600 | 80- 120 |
| RC 3000 | Rapid | 3000- 6000 | 80- 120 |
