Slow Curing(SC), Medium Curing(MC) and Rapid Curing(RC) Cutback Bitumen

Asphalt cutbacks use petroleum solvents for dissolving asphalt cement. The solvents are variously called distillate, diluents or cutter stock. If the solvent used in making the cutback asphalt is highly volatile, it will quickly escape by evaporation. Solvents of lower volatility evaporate more slowly. On the basis of the relative speed of evaporation, cutback asphalts are divided into three types: rapid curing (RC), medium curing (MC) and slow curing (SC).

SLOW CURING (SC) CUTBACKS

Slow curing (SC) asphalt cement and oils of low volatility generally in the heavy distillate range (SC-70, 250, 800, 3000). 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.

Slow curing (SC) cutback asphalts are often called road oils and are used primarily in road-mixing and dust-laying applications. This term originated in earlier days when asphalt residual oil was used to give roads a low-cost, all-weather surface. SC cutback asphalts are also used for stockpile patching mixes, plant-mixed with graded aggregates and occasionally for priming.

MEDIUM CURING (MC) CUTBACKS

Medium curing (MC) asphalt cement uses medium diluents of intermediate volatility generally in the kerosene boiling point range (MC-30, 70, 250, 800, 3000).

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.

The medium setting grades are designed for mixing with aggregates. Because these grades do not break immediately upon contact with aggregate, mixes using them can remain workable for extended periods of time and lend themselves to cold mix stockpiles.

RAPID CURING (RC) CUTBACKS

Rapid curing (RC) 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.

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.

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.

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