Medium Curing Cutbacks
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).
Medium-curing (MC) cutback asphalt cement is a combination of medium diluents of intermediate volatility, typically in the kerosene boiling point range, and asphalt cement. Medium-curing cutback grades include MC-30, MC-70, MC-250, MC-800, and MC-3000.
The degree of fluidity developed in each cutback’s case depends principally on the ratio 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 ambient 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 curing grades are designed to be mixed with aggregates. Because these grades do not break immediately upon contact with aggregate, mixes using medium-setting cutbacks can remain workable for extended periods of time and will lend themselves to cold mix stockpiles.