Cutback bitumen is created by reducing the viscosity of standard bitumen through the addition of petroleum-type solvents, mainly petroleum-based. Cutback bitumen is valued for its lower viscosity compared to neat asphalt, making it suitable for use in lower-temperature applications. After application, the solvent evaporates, leaving only the bitumen behind. Cutback bitumen is considered to cure as the petroleum solvent gradually evaporates. It is commonly used as prime coats and tack coats in various applications.
There are three primary groups of cutback bitumen based on the volatility of the added solvent:
- Slow Curing, often referred to as “road oils,” typically consist of residual materials obtained from the fractional distillation of specific crude petroleums. These traditionally include aromatic, naphthenic, and paraffinic oils. Slow Curing liquid bitumen materials are created 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 a light, rapidly evaporating diluent like naphtha or gasoline.
It’s worth noting that the use of different solvents or a combination of solvents and additives can further enhance the performance of cutback asphalt, including antistripping effects.
Each of these three types of liquid asphalt materials comes in six standard grades. The prefix indicates the type: SC for Slow Curing, MC for Medium Curing, and RC for Rapid Curing. The suffix, or grade number, indicates the consistency range of the material. In each type, grade 0 is the most liquid, while grade 5 is the most viscous, with intermediate grades progressing consistently in consistency. Grade 0 materials resemble heavy cream at room temperature, while grade 5 materials have the consistency of heavy molasses in cold conditions. These products cure through the evaporation of the petroleum diluent.
Cutback asphalts were previously favored for their lower paving temperature, but today, they are primarily used as prime coats and tack coats.
In prime coat applications, cutback asphalt is sprayed onto the surface of untreated subgrade or base layers to fill voids, protect against water penetration, stabilize fines, and promote bonding to subsequent pavement layers.
When used as a tack coat, cutback asphalt is applied between hot mix asphalt pavement lifts to ensure proper bonding, which is essential for the pavement structure’s strength and longevity. Inadequate bonding can lead to various pavement distresses.
Applications of Cutback Bitumen in Bituminous (Asphalt) Pavement Construction and Maintenance include:
- Prime and Tack Coating: Priming involves applying a low-viscosity binder to a prepared aggregate base, aiding subsequent bituminous layer adhesion. Tack coats are used for adhesion between asphalt layers.
- Prime Sealing: In cooler conditions or high-traffic situations, primer sealing offers temporary pavement protection.
- Spray Sealing: Cutback bitumens are extensively used in sprayed sealing, particularly in colder climates, enhancing initial stone retention due to their lower viscosity.
These versatile materials play a crucial role in various asphalt pavement applications, ensuring durability and performance.
BituPlus offers products within this bitumen category, classified into the following subcategories:
Cutback Bitumen Rapid Curing (RC)
Cutback Bitumen Medium Curing (MC)
Cutback Bitumen Slow Curing (SC)