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CUTBACK BITUMEN
Cutback Bitumen is made by reducing the viscosity of ordinary bitumen by adding mostly petroleum-type solvent. Cutback Bitumen is used because its viscosity is lower than that of neat asphalt and can thus be used in low-temperature applications. After a cutback is applied the solvent evaporates away and only the Bitumen is left. Cutback bitumen is said to cure as the petroleum solvent evaporates. Cutback bitumen is typically used as prime coats and tack coats. Generally are divided into three groups depending on the volatility of the solvent added
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
are 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.
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 pavem
