VG-30 vs VG-40 Bitumen:
Choosing the Right Grade for Bihar Road Projects

Bitumen is the binder that holds road surfacing aggregates together — and using the wrong viscosity grade in Bihar's climate leads to premature road failure. The two grades most commonly specified on Bihar PWD, Rural Works Department, and PMGSY contracts are VG-30 and VG-40. Here is what distinguishes them and when each is correctly used.

From Penetration to Viscosity Grades

Until 2006, Indian road contracts specified bitumen by penetration grade (60/70, 80/100). The Bureau of Indian Standards then shifted to Viscosity Grade (VG) designation under IS 73:2013, which better describes bitumen's performance at high temperatures — critical for India's climate. Penetration grade 60/70 broadly corresponds to VG-30; penetration grade 30/40 broadly corresponds to VG-40. However, IS 73 specifications are tighter and should always take precedence over the old penetration equivalents.

Comparison: VG-30 vs VG-40

VG-30 — Standard Grade for Bihar Roads

VG-30 is the standard bitumen grade for most Bihar road contracts — Rural Works Department, PMGSY rural roads, and many district-level PWD roads. Bihar's average pavement temperature (typically 40–50°C in peak summer) is within the comfort zone of VG-30 for low to medium traffic roads.

For rural roads, village link roads, and PMGSY-funded works carrying agricultural and light commercial traffic, VG-30 provides adequate rut resistance at acceptable cost. The higher ductility of VG-30 (compared to VG-40) also provides better performance in Bihar's winter months when pavements cool and become brittle.

VG-40 — For Heavy Traffic and National/State Highways

VG-40 has higher viscosity and a higher softening point — it resists permanent deformation (rutting) better under heavy, slow-moving loads and high pavement temperatures. It is specified on contracts carrying heavy truck traffic such as state highways, national highways, industrial approach roads, and mining haul roads.

Some Bihar PWD state highway contracts and all NHAI (National Highways Authority of India) works in Bihar specify VG-40 for wearing course layers. If your contract drawings and BOQ specify VG-40, do not substitute VG-30 — even with approval from a junior site engineer. The specification is a contract condition and material test certificates will reveal the substitution.

Quality Checks on Bitumen Delivery

Bitumen quality is hard to verify visually. The key tests are:

• Penetration test (IS 1203) — measures hardness. VG-30 should penetrate 45–79 units at 25°C
• Softening point (IS 1205) — ring-and-ball test. VG-30 min 47°C, VG-40 min 51°C
• Viscosity at 60°C (IS 1206 Part 2) — the defining VG test
• Flash point (IS 1209) — safety requirement, min 220°C for both grades

On government road contracts, bitumen samples are taken from each tanker delivery. Retain a sealed sample (1 litre in a tin can) from each delivery for potential re-testing. Ensure the delivery challan states the grade, tank number, refinery source, and date.

Storage and Handling

Bitumen must be stored in insulated tanks and heated to 150–165°C for pumping and spraying. Never heat above 175°C — oxidation occurs, hardening the bitumen and dropping its ductility below specification. The hot mix plant temperature must also be controlled: aggregate temperature at 155–165°C, mix temperature at 130–160°C at the point of laying, and compaction completed before the mix cools below 100°C.

Bihar's monsoon season (June–September) makes bituminous surfacing impractical — wet aggregate and rain on fresh bitumen cause stripping of the binder from aggregate. Plan your road surfacing works for October–May.