Medium Curing Cutbacks

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).

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.