Tar vs Bitumen Difference
Last updated: 2026-09-29
Tar vs Bitumen Difference
Tar and bitumen are chemically different materials: bitumen is a heavy petroleum fraction (CAS 8052-42-4) with 40–60% asphaltenes, while tar is a distillate of destructive coal or wood pyrolysis (CAS 65996-93-2) containing 60–80% aromatics and known carcinogens. Bitumen softens at 45–60°C with penetration grades from 20/30 to 160/220 (0.1 mm), whereas coal tar pitch softens at 70–120°C and delivers 2–4× higher benzo[a]pyrene content. In global trade, bitumen moves 100–120 million tonnes per year at $300–550/tonne, while refined coal tar clears at $350–900/tonne with shipments typically 5,000–30,000 tonnes per parcel.
Chemical Composition: Two Different Feedstocks, Two Different Molecules
The single decisive difference is origin. Bitumen is produced from crude oil through vacuum distillation of the residue from atmospheric distillation, and can be air-blown to raise softening point. Tar is produced from organic materials — coal, wood, peat, or biomass — via destructive distillation at 900–1,100°C for coal or 400–600°C for wood.
| Parameter | Bitumen (Pen Grade 60/70) | Coal Tar / Tar Pitch |
|---|---|---|
| Feedstock | Crude oil residue | Bituminous coal, wood, biomass |
| Primary process | Vacuum distillation, air blowing | Destructive distillation / pyrolysis |
| Solubility in CS₂ | >99% | 70–85% (free carbon insolubles) |
| Aromatic content | 25–40% | 60–80% |
| Asphaltene content | 40–60% (coal tar pitch) | 15–25% |
| Sulfur | 2–6% (Middle East crudes) | 0.5–1.5% |
| Benzo[a]pyrene | <1 ppm (typical) | 5,000–15,000 ppm in pitch |
| Boiling range | 350–750°C | 200–500°C distillate range |
| CAS number | 8052-42-4 | 65996-93-2 (coal tar pitch) |
The presence of free carbon — typically 8–20% quinoline-insoluble matter in coal tar pitch — is the fingerprint that distinguishes tar from bitumen in laboratory testing (ASTM D2318 for bitumen has no equivalent pass in pitch).
Key takeaway for buyers: if a supplier cannot produce a vacuum residue certificate of origin or a crude slate declaration, the material may be blended tar-bitumen, which behaves unpredictably in hot mix plants.
Physical Properties and Performance: Grade Data That Drives Specification
Bitumen is graded by penetration at 25°C (ASTM D5) or by performance grade (PG) under AASHTO M320. Tar is graded by softening point (ASTM D36 ring-and-ball) and by viscosity classification for road tar (RT-1 to RT-12 under older BS 76 / ASTM D490).
| Property | Bitumen 60/70 | Bitumen 40/50 | Coal Tar RT-10 | Tar Pitch (binder) |
|---|---|---|---|---|
| Penetration @25°C (0.1 mm) | 60–70 | 40–50 | n/a (viscosity graded) | n/a |
| Softening point (°C) | 49–56 | 52–60 | n/a | 70–120 |
| Viscosity @60°C (Pa·s) | 160–240 | 280–400 | 100–200 (equi-viscous temp) | >1,000 |
| Specific gravity @25°C | 1.01–1.05 | 1.02–1.06 | 1.15–1.25 | 1.25–1.35 |
| Ductility @25°C (cm) | >100 | >100 | Low (brittle) | Very low |
| Flash point (°C) | >230 | >240 | 90–150 | 150–200 |
| Service temperature range (°C) | -10 to +70 | -5 to +75 | -20 to +50 | 0 to +60 |
- Bitumen is thermoplastic and self-healing at ambient-to-moderate temperatures, which is why it dominates 85–90% of global paved road surfaces.
- Tar is more brittle, more temperature-sensitive at low end, and has superior resistance to fuel spillage and organic solvents, but this comes at the cost of flexibility and worker safety.
- Blending: up to 10–15% tar can be blended into bitumen to improve fuel resistance, but this is banned or restricted in many jurisdictions because of PAH emissions during laying.
Trade relevance: European and North American road authorities typically specify EN 12591 or ASTM D946 bitumen grades. Tar for road use must meet EN 13924-2 or legacy BS 76, and is now rare — global coal tar road binder volumes have fallen below 500,000 t/y versus 100+ Mt/y for bitumen.
Applications and Market Data: Where Each Material Is Actually Used
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