IS 73:2013 is the Indian Standard (BIS) for paving bitumen - specification. This standard specifies the physical and chemical requirements for paving bitumen used in highway construction and flexible pavements. The standard famously transitioned the Indian industry from penetration-based grading (e.g., 60/70, 80/100) to Viscosity Grading (VG-10, VG-20, VG-30, VG-40), which provides a more reliable indicator of field performance, particularly concerning rutting at high temperatures.
Specifies requirements for various grades of paving bitumen used in road construction and other civil engineering applications.
Key requirements for Viscosity Graded (VG) paving bitumen, including viscosity, penetration, softening point, ductility, and post-aging test limits.
| Reference | Value | Clause |
|---|---|---|
| Absolute Viscosity @ 60°C (VG 10) | 800 - 1200 Poise | Cl. 4.1 (Table 1) |
| Absolute Viscosity @ 60°C (VG 20) | 1600 - 2400 Poise | Cl. 4.1 (Table 1) |
| Absolute Viscosity @ 60°C (VG 30) | 2400 - 3600 Poise | Cl. 4.1 (Table 1) |
| Absolute Viscosity @ 60°C (VG 40) | 3200 - 4800 Poise | Cl. 4.1 (Table 1) |
| Kinematic Viscosity @ 135°C (VG 30)— Minimum value for Viscosity Grade 30. | ≥ 350 cSt | Cl. 4.1 (Table 1) |
| Kinematic Viscosity @ 135°C (VG 40)— Minimum value for Viscosity Grade 40. | ≥ 400 cSt | Cl. 4.1 (Table 1) |
| Penetration @ 25°C (VG 30)— 100g load for 5 seconds. | 50 - 70 (0.1 mm) | Cl. 4.1 (Table 1) |
| Penetration @ 25°C (VG 40)— 100g load for 5 seconds. | 40 - 60 (0.1 mm) | Cl. 4.1 (Table 1) |
| Softening Point (R&B) (VG 30) | ≥ 47 °C | Cl. 4.1 (Table 1) |
| Softening Point (R&B) (VG 40) | ≥ 50 °C | Cl. 4.1 (Table 1) |
| Flash Point (Cleveland Open Cup)— Minimum for all VG grades. | ≥ 220 °C | Cl. 4.1 (Table 1) |
| Solubility in Trichloroethylene— Minimum for all VG grades. | ≥ 99.0 % by mass | Cl. 4.1 (Table 1) |
| Ductility @ 25°C (VG 10) | ≥ 75 cm | Cl. 4.1 (Table 1) |
| Ductility @ 25°C (VG 30) | ≥ 40 cm | Cl. 4.1 (Table 1) |
| Loss on heating (Thin Film Oven Test)— Maximum for all VG grades. | ≤ 1.0 % by mass | Cl. 4.1 (Table 1) |
| Viscosity Ratio @ 60°C (Post-TFOT)— Ratio of residue viscosity to original viscosity. Max for all grades. | ≤ 4.0 | Cl. 4.1 (Table 1) |
| Retained Penetration (Post-TFOT)— Minimum for all VG grades. | ≥ 55 % | Cl. 4.1 (Table 1) |
| Ductility @ 25°C (Post-TFOT, VG 30)— Minimum ductility after aging. | ≥ 20 cm | Cl. 4.1 (Table 1) |
| Ductility @ 25°C (Post-TFOT, VG 40)— Minimum ductility after aging. | ≥ 15 cm | Cl. 4.1 (Table 1) |
IS 73 specifies paving bitumen — the binder used in flexible bituminous pavements (BC, DBM, BM, premix carpet, surface dressing) for highways, urban roads, parking lots, and airports. Bitumen is the asphalt-like binder; mixed with aggregate, it produces 'asphalt concrete' (the term bituminous mix is more correct in Indian usage).
Use IS 73 paving bitumen when specifying any of: - Flexible pavement layers — Bituminous Concrete (BC), Dense Bituminous Macadam (DBM), Bituminous Macadam (BM) - Surface treatments — premix carpet, surface dressing, fog seal - Road maintenance — patching, overlay - Airport runways and taxiways (with extra performance specs from IRC:37 and FAA) - Parking lots, internal estate roads, container yards
IS 73:2013 introduced the Viscosity Grading (VG) system for India, replacing the older Penetration Grading (S 35, S 65, S 90) used in IS 73:1992. VG grading is more rational because it ties grade to performance temperature directly.
Don't use IS 73 paving bitumen for: - Industrial bitumen (waterproofing, paint manufacturing) — use IS 702 - Cutback bitumen (RC, MC, SC for cold mixes) — use IS 217 - Bitumen emulsion (cold mix, prime/tack coat) — use IS 8887 for cationic, IS 3117 for anionic - Modified bitumen (PMB, CRMB) — use IS 15462 / IS 15469
IS 73:2013 specifies four grades by viscosity at 60 °C, the design service temperature for paving bitumen:
| Grade | Viscosity at 60 °C (poise) | Climate / use | |---|---|---| | VG-10 | 800-1200 (≈ 1000 nominal) | Cold climate, high-altitude (Ladakh, Himachal hills); also for emulsion manufacture | | VG-20 | 1600-2400 (≈ 2000) | Cold-to-temperate — Punjab, Delhi-NCR winter; Himalayan foothills | | VG-30 | 2400-3600 (≈ 3000) | Most of India — temperate plains, default for highway BC and DBM in average conditions | | VG-40 | 3200-4800 (≈ 4000) | Hot zones — Rajasthan, Gujarat, MP, peninsular India where pavement temperature regularly exceeds 35 °C; high-traffic / heavy-axle corridors |
Selection guidance (IRC:111 / IRC:37 cross-reference): - Annual mean pavement temperature (AMPT) ≤ 25 °C: VG-10 to VG-20 - AMPT 25-30 °C: VG-30 - AMPT > 30 °C OR commercial vehicle volume > 1500 CVD: VG-40
Most MoRTH and NHAI specifications now default to VG-40 for high-traffic corridors and VG-30 for general use.
Critical performance properties:
| Property | VG-10 | VG-20 | VG-30 | VG-40 | |---|---|---|---|---| | Absolute viscosity at 60 °C, poise (min) | 800 | 1600 | 2400 | 3200 | | Kinematic viscosity at 135 °C, cSt (min) | 250 | 300 | 350 | 400 | | Penetration at 25 °C, 0.1 mm (min) | 80 | 60 | 45 | 35 | | Softening point, °C (min) | 40 | 45 | 47 | 50 | | Flash point (Cleveland open cup), °C (min) | 220 | 220 | 220 | 220 | | Solubility in trichloroethylene, % (min) | 99 | 99 | 99 | 99 |
Tests after rolling thin film oven test (RTFOT) — short-term ageing simulation: - Viscosity ratio (after / before): ≤ 4.0 - Penetration ratio of residue (% of original): ≥ 55 % for VG-10 / VG-20; ≥ 45 % for VG-30 / VG-40 - Mass loss: ≤ 1.0 %
Tests after long-term ageing (PAV) — recommended for high-traffic design: - Viscosity at 60 °C: ≤ specified ceiling per project specification
Marking on supply: - Each tanker / drum: Grade (VG-10 / VG-20 / VG-30 / VG-40), supplier, batch number, manufacturing date, IS 73:2013
Sampling: - 1 sample per tanker on delivery - Tests: penetration, softening point, viscosity at 60 °C and 135 °C, flash point - Reject if any property outside spec — bitumen substitution at site is impossible
1. Specifying old penetration grade (S 35 / S 65 / S 90) on new contracts. The 1992 grading is obsolete; use VG grades. Penetration grade on a tender now is a documentation lapse. 2. Using VG-30 in Rajasthan summer. Pavement temperature can hit 65 °C; VG-30 ruts. Specify VG-40 for hot zones with significant truck traffic. 3. Mixing bitumen grades on site. Two grades are not equivalent — mixing changes viscosity unpredictably. One grade per project / per layer. 4. Hauling bitumen too far from depot to plant. Bitumen ages in transit (oxidation in tankers). Maintain temperature 150-170 °C in transit; minimise distance. 5. Heating bitumen above 165 °C in storage. Above 175 °C continuous, ageing accelerates and viscosity rises out of spec; flash hazard at 220 °C+. Storage tank thermostats must hold 150-160 °C. 6. No batch certificate from supplier. Refinery suppliers provide a per-batch test certificate; demand it. Spot-test on delivery is verification, not the primary acceptance. 7. Ignoring flash point on high-temperature mixes. Some tanker shipments can degrade if held too long; flash point < 220 °C is a fire hazard at the asphalt plant. 8. Testing bitumen at the plant after mix-design but not at site lay-down. Specifications require sampling at point of use, not just at the depot. Site lab should sample from each delivery. 9. Specifying PMB without justification. Polymer-modified bitumen is 2-3× more expensive than VG-40. Use only when traffic, climate, or pavement performance demand requires; routine highway BC does not need PMB unless IRC:111 or project-specific document calls for it.
Flexible pavement design and construction cascade:
1. Pavement design (IRC:37:2018) — traffic loading (msa), subgrade CBR, climatic factor → layer thicknesses (subgrade → granular sub-base → granular base / WMM → DBM → BC). 2. Mix design (IRC:111:2009) — Marshall mix design or Superpave; aggregate gradation, optimum bitumen content, stability, flow. 3. Materials procurement: - Aggregates per MoRTH Section 500 / IS 383 - Bitumen per IS 73:2013 (grade selected per IRC:37 climate guidance) - PMB per IS 15462 if specified 4. Mixing plant (batch or drum-mix) — accuracy ±2 % on aggregate, ±0.3 % on bitumen. 5. Lay-down: - Tack coat (bitumen emulsion per IS 8887) on prepared base - Mix delivered at 150-160 °C - Paver lay at 145-150 °C - Compaction in 3 passes: pneumatic-tyred → steel-wheel → final tyre roll 6. Compaction acceptance: density ≥ 92-94 % theoretical maximum density (TMD); segregation visual check 7. Surface acceptance: thickness, roughness (IRI), texture depth, skid resistance 8. QA records: per-tanker bitumen test, per-day mix design verification, per-section density, IRI at handover, riding quality at 6-month and 1-year follow-up
IS 73 enters the chain at step 3 (procurement) but its grade selection drives steps 1 (design temperature) and 2 (mix design) backwards.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Dynamic Viscosity @ 60°C | 240-360 Pa.s (for VG-30) | 240-360 Pa.s (for AC-30) | ASTM D3381/D3381M, AASHTO M 226 |
| Kinematic Viscosity @ 135°C | Min 350 mm²/s (for VG-30) | Min 300 mm²/s (for AC-30) | ASTM D3381/D3381M, AASHTO M 226 |
| Penetration @ 25°C, 100g, 5s | 50-70 dmm (for VG-30) | 40-90 dmm (for AC-30, ASTM D3381); 60-70 dmm (for Bitumen 60/70, EN 12591) | ASTM D3381/D3381M, EN 12591 |
| Softening Point (Ring & Ball) | Min 47 °C (for VG-30) | 48-56 °C (for Bitumen 60/70) | EN 12591 |
| Flash Point (Cleveland Open Cup) | Min 220 °C (for VG-30) | Min 232 °C (for AC-30, ASTM D3381); Min 230 °C (for Bitumen 60/70, EN 12591) | ASTM D3381/D3381M, EN 12591 |
| Solubility in Trichloroethylene | Min 99.5% (for VG-30) | Min 99.0% (for AC-30, ASTM D3381); Min 99.0% (for Bitumen 60/70, EN 12591) | ASTM D3381/D3381M, EN 12591 |
| Mass Loss (TFOT/RTFOT) | Max 0.7% (for VG-30) | Max 1.0% (for AC-30, ASTM D3381); Max 0.8% (for Bitumen 60/70, EN 12591) | ASTM D3381/D3381M, EN 12591 |
| Viscosity Ratio @ 60°C (after TFOT/RTFOT) | Max 4 (for VG-30) | Max 3 (for AC-30, ASTM D3381) | ASTM D3381/D3381M |