Asphalt, also known as bitumen, is a sticky, black and highly viscous liquid or semi-solid form of petroleum. Asphalt is man's earliest organic engineering material. Its use as an adhesive and waterproof material dates back to the dawn of civilization. It is still used today largely for road building, roofing and various types of repair work where its water-proofing qualities are required, as well as in rubber and adhesive compounds.
Asphalt Cement and Emulsions
Asphalt cement is an asphalt that has been specially refined as to quality and consistency for direct use in the construction of asphalt pavements. This cement has to be heated to an appropriate high temperature in order to be fluid enough to be mixed and placed.
Emulsified asphalts are mixtures of asphalt cement, a surfactant and water that is used in preparing base courses for pavement. It is also used in cold laid mixes, mix-in-place and surface treatments. Asphalt emulsions must be perfectly homogeneous and able to withstand storage and shipping conditions. Most emulsions must not be subjected to temperatures below 0°C, 32°F because freezing of the aqueous solution will coagulate the asphalt particles.
Emulsified asphalt is produced at both refineries where the asphalt is produced and facilities solely built for the production of emulsified asphalt. Pumps are used to deliver asphalt and the aqueous solution to the mixer or colloid mill.
Asphalt viscosity is graded according to temperature and setting speed (once placed on the road, after aging due to the heating and mixing process). The following are general uses of some common grades of asphalt:
- RS-1 Low viscosity for penetration and surface treatment.
- RS-2 High viscosity for surface treatment.
- MS-1 Low viscosity for re-tread mixes with coarse aggregate.
- MS-2 Medium viscosity for plant mixers with coarse aggregates.
- SS-1 For fine aggregate mixes.
Asphalt Pump Selection
We recommend that you take the following into consideration when selecting a pump for asphalt cement applications:
- Steel fitted construction and extra clearances may be required, depending on viscosity.
- Bronze bushings can be utilized for temperatures up to 232°C (450°F). Carbon graphite is required for temperatures above 232°C. Note: High temperature graphite may be required for some pump sizes.
- Acceptable shaft seals include:
- Cartridge lip seal with quench
- Single metal bellows mechanical seal with hard faces and quench
- Double metal bellows mechanical seal with hard faces (inboard) and a pressurized barrier fluid
For help with selecting the right pump for your asphalt needs, contact a Viking Pump representative.