Asphalts and Bitumens

· Cutback Asphalt :

Cutback Asphalts are made from a base asphalt of selected hardness or viscosity which is dissolved in a solvent of high, medium or low volatility to provide distinct differences for construction purposes among the types. ASTM D 2399 is a standard for the selection of cutback asphalts for various paving and related road construction uses. Thirteen different grades are defined based on rate-of-cure and on viscosity.

Slow-curing asphalt cutbacks are liquid asphalts, sometimes also called road oils, and may also be produced directly by distillation. They contain a low-volatility fuel oil type of solvent and require the longest curing periods. Four grades are defined in ASTM D 2399. The properties of slow-curing type cutback asphalt are detailed in ASTM D 2026.

There are five grades of medium-curing type cutback asphalts. They contain a less-volatile kerosene-type of solvent which evaporates more rapidly than the slow-curing types and provide a medium hardness base asphalt. ASTM D 2027 is the specification for medium-curing cutback asphalts.

Four grades of rapid-curing cutback asphalts contain highly-volatile naphtha type solvents which tend to evaporate quickly and provide a harder base asphalt. Test specifications are given in ASTM D 2028 for rapid-curing cutback asphalts.

The various grades of cutback asphalts are summarized as follows:

Cutback Asphalts for General Paving Use, ASTM D 2399
Kinematic Viscosity at 60 ° C (140 ° F), mm 2 /s or cSt	Slow-Curing ASTM D 2026	Medium-Curing ASTM D 2027	Rapid-Curing ASTM D 2028
30 to 60		MC-30
70 to 140	SC-70	MC-70	RC-70
250 to 500	SC-250	MC-250	RC-250
800 to 1600	SC-800	MC-800	RC-800
3000 to 6000	SC-3000	MC-3000	RC-3000