Types of Bitumen
Oxidised Bitumen
Air-blown grades with high softening points and low temperature susceptibility — for roofing, pipe coating and industrial work.
Oxidised or blown bitumen is produced by passing hot air through penetration grade bitumen at 240 to 300 °C. The oxygen drives dehydrogenation and polymerisation, building larger molecules and raising the asphaltene content. The finished product has a far higher softening point than its feedstock and changes much less across the temperature range.
Grades are written as two numbers: softening point over penetration. Bitumen 85/25 has a softening point near 85 °C and a penetration near 25.
Why it behaves differently
Straight-run bitumen softens steadily as it warms. An oxidised grade holds its consistency across a much wider band, which is exactly what a roof membrane needs when the surface temperature swings forty degrees between night and afternoon.
The trade-off is reduced ductility and adhesion compared with paving grades, which is why oxidised bitumen is used for sealing and coating rather than as a road binder.
Standard grades
- Bitumen 75/25 — general waterproofing and membrane manufacture
- Bitumen 85/25 — the most widely used roofing and sealing grade
- Bitumen 85/40 — softer variant where more flexibility is required
- Bitumen 90/15 — hard grade for pipe coating and high-temperature service
- Bitumen 95/25 — high softening point for hot-climate roofing
- Bitumen 105/15 and 115/15 — very hard grades for industrial and electrical use
- Bitumen 150/5 — extremely hard, near-solid grade for specialist applications
Applications
- Manufacture of torch-applied and self-adhesive roofing membranes
- Built-up roofing systems and roofing felt saturation
- External corrosion coating for buried and submerged steel pipelines
- Bitumen paints, mastics and jointing compounds
- Sound-deadening panels in automotive manufacture
- Electrical cable insulation and battery casing compounds
- Adhesives for tile, board and membrane bonding
Typical specification
| Softening point (ring & ball) | ASTM D36 — to grade |
|---|---|
| Penetration @ 25 °C | ASTM D5 — to grade |
| Loss on heating | ASTM D6 — 0.5% maximum |
| Flash point | ASTM D92 — 250 °C minimum |
| Solubility in trichloroethylene | ASTM D2042 — 99% minimum |
| Ductility @ 25 °C | ASTM D113 — 1.5 cm minimum |
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.
