Types of Bitumen
There are six major classifications of petroleum bitumen produced by the refining and manufacturing process:
Paving Grade BitumenPaving grade bitumen (or asphalt cement in the USA) is the most widely used bitumen and is refined and blended to meet road engineering and industrial specifications that take into account different climatic conditions. Paving grade bitumen may also be considered as the parent bitumen from which the other forms are produced.
Cutback BitumenCutback bitumens consist of bitumen that has been diluted in solvent (cutter or flux) to make it more fluid for application. The fluidity of cutback bitumens (or cutbacks as they are known) depends on the degree of hardness of the bitumen and the proportion of diluent. Cutbacks are classified according to the time it takes for them to cure, or become solid due to the evaporation of the diluent. Classifications are rapid curing (RC), medium curing (MC) or slow curing (SC). A cutback varies in behaviour according to the type of cutter or flux used as the diluent with white spirit commonly used for RC grades, kerosene for MC and diesel for SC.
Bitumen EmulsionsBitumen emulsions are dispersions of bitumen in water. Hot bitumen, water and emulsifier are processed in a highspeed colloid mill that disperses the bitumen in the water in the form of small droplets. These droplets or particles of bitumen are normally in the 5-10 micrometre size range but may be even smaller. The emulsifier assists in forming and maintaining the dispersion of fine droplets of bitumen. Bitumen emulsions normally comprise between 30% and 80% bitumen by volume. If the bitumen starts to separate from the water solution in storage, the emulsion can usually be easily restored by gentle agitation to redisperse the droplets.
Bitumen emulsions have a low viscosity compared to the bitumen from which they are produced and can be workable at ambient temperatures. Their application requires controlled breaking and setting. The emulsion must not break before it is laid on the road surface but, once in place, it should break quickly so that the road can be in service again without delay.
The development of bitumen emulsions is an area where technological progress is still being made to meet current and emerging engineering demands. The first emulsions were the anionic types. They are currently less favoured than the cationic types because the positively charged globules of bitumen in cationic emulsions better coat the majority of aggregate types and result in greater adhesion. Use of cationic emulsions is therefore preferred in most applications.