Types of Bitumen
Bitumen Emulsions
Bitumen dispersed in water with an emulsifier — applied cold, with no solvent, and no heating on site.
A bitumen emulsion is a suspension of fine bitumen droplets in water, held apart by an emulsifying agent that gives each droplet an electrical charge. The result is a brown, free-flowing liquid that can be sprayed at ambient temperature and that breaks on contact with aggregate, leaving a continuous bitumen film behind as the water drains and evaporates.
Emulsions have steadily displaced cutbacks across much of the world. They carry no flammable solvent, they release no hydrocarbon vapour, and they need a fraction of the energy that hot binder application demands.
Cationic and anionic
Cationic emulsions carry a positive charge on the bitumen droplets and are the dominant type worldwide. Most mineral aggregates carry a negative surface charge, so the attraction is immediate and adhesion is excellent even on damp stone and with siliceous aggregates.
Anionic emulsions carry a negative charge and bond best with electropositive aggregates such as limestone. They remain in use in specific markets and applications but account for a much smaller share of supply.
Breaking speed grades
- CRS-1 and CRS-2 — cationic rapid setting, for surface dressing and chip seals
- CMS-2 and CMS-2h — cationic medium setting, for open-graded cold mixes
- CSS-1 and CSS-1h — cationic slow setting, for slurry seals, tack coats and dense cold mixes
- RS, MS and SS — the anionic equivalents of the three setting speeds
- The h suffix indicates a harder base bitumen in the emulsion
Applications
- Tack coats between asphalt layers — the single largest use
- Prime coats on granular bases as an alternative to MC cutback
- Surface dressing and single or double chip seals
- Slurry seal and micro-surfacing for preventive maintenance
- Cold in-place and full-depth recycling of existing pavement
- Fog seals to rejuvenate an oxidised surface
- Crack sealing and pothole repair with stockpiled cold mix
Storage and handling
Emulsions are stable but not indefinitely. Keep them above 10 °C — freezing destroys the emulsion irreversibly — and below 85 °C. Circulate stored material gently to prevent settlement, avoid contact with galvanised or aluminium surfaces, and never mix cationic with anionic product, which will break the emulsion immediately.
Typical specification
| Bitumen content | ASTM D6997 — 57 to 70% by mass |
|---|---|
| Saybolt Furol viscosity @ 50 °C | ASTM D7496 — to grade |
| Particle charge | ASTM D7402 — positive for cationic |
| Sieve test | ASTM D6933 — 0.10% maximum retained |
| Storage stability, 24 h | ASTM D6930 — 1% maximum |
| Residue penetration @ 25 °C | ASTM D5 — 100 to 250 |
Values are indicative and given for guidance. Contract specification is agreed in writing and certified per batch on the certificate of analysis issued with each shipment.
