Bitumen VG-30: IS 73:2013 Specification, Applications and Export Supply

The designation is an instruction to a laboratory, not a brand. VG stands for viscosity grade. The number is the nominal absolute viscosity at 60 °C expressed in hundreds of poise, so VG-30 is nominally 3000 poise, and IS 73:2013 accepts any batch between 2400 and 3600 poise. The test that produces that number is IS 1206 (Part 2) — a sample held at 60 °C and drawn through a capillary under controlled vacuum, the procedure written as ASTM D2171 in the American system. Contracts written in SI units state the same band as 240 to 360 Pa·s, one poise being 0.1 Pa·s.

The two temperatures used in the standard were not chosen for laboratory convenience. 60 °C represents the hottest condition the binder is expected to face inside a pavement in a hot climate, which is where rutting is decided. 135 °C sits inside the range where the binder is pumped, sprayed and mixed with aggregate, which is where workability and coating are decided. Grading the binder at 60 °C while also fixing a floor at 135 °C brackets the material across the two temperatures that actually determine whether a road performs and whether a plant can build it.

Why India replaced penetration grading with viscosity grading

Indian paving bitumen was previously classified by penetration under IS 73:1992, in grades written as S-35, S-45, S-65 and S-90 with a parallel A-series. That system was withdrawn in favour of viscosity grading, which was formalised in IS 73:2006 and carried into the current IS 73:2013 revision. Four arguments drove the change, and they are worth understanding because they explain every line in the specification table below.

• Penetration is measured at the wrong temperature. A pavement does not rut at 25 °C and is not mixed at 25 °C. Two binders can record an identical penetration at 25 °C and still differ substantially in viscosity at 60 °C, and it is the 60 °C figure that governs deformation under a loaded axle in summer.
• Penetration is an empirical index, viscosity is an engineering quantity. Tenths of a millimetre cannot be used in a calculation. Poise and Pa·s feed directly into pumping, spraying and mix-design work.
• Viscosity grading constrains temperature susceptibility. By fixing a band at 60 °C, a minimum at 135 °C and a minimum penetration at 25 °C, IS 73 pins the binder at three points on its viscosity–temperature curve. Penetration grading pins one point and says nothing about the slope.
• Traffic and pavement temperatures had both risen. Heavier axle loads and higher summer pavement temperatures made a system anchored at service temperature the practical answer for a national road programme.

There is a structural point in all of this that catches buyers out at the certificate stage. The 2400–3600 poise band is applied to the binder as supplied, never to a laboratory-aged residue, so the headline viscosity on a VG-30 certificate describes the material leaving the refinery rather than the material that will end up under a wheel. How much it hardens on the way there is a separate question, answered by the two RTFOT lines at the foot of the table. Read the grade line and the ageing lines as a pair; either one alone tells you half the story.

The 2013 revision uses RTFOT, not TFOT

The most consequential detail for anyone reading a VG-30 certificate is which ageing test produced the residue. IS 73:2013 requires the rolling thin film oven test — RTFOT, IS 9382, equivalent to ASTM D2872 — and then checks two things on that residue: the viscosity ratio at 60 °C must not exceed 4.0, and ductility at 25 °C must be at least 40 cm.

It is not the thin film oven test. The distinction is not cosmetic. RTFOT rolls a moving film of binder inside rotating glass bottles under a jet of hot air; TFOT heats a static film in a shallow dish. They expose different surface areas for different lengths of time and they age the binder differently, so a TFOT result is not an acceptable substitute line on an IS 73:2013 certificate. Certificates that report loss on heating and retained penetration instead are written in the older penetration-grade format. They may describe perfectly good bitumen, but they do not demonstrate compliance with the standard the buyer named, and an Indian consultant checking submittals will say so.

Where VG-30 sits in the viscosity family

IS 73:2013 defines four paving grades. Stiffness rises with the grade number, because the number tracks viscosity directly rather than inversely as penetration does:

• VG-10 (800–1200 poise) — the softest grade. Used for spray applications and surface dressing, in the coldest regions, and as feedstock for bitumen emulsion and cutback manufacture.
• VG-20 (1600–2400 poise) — paving work in cold climate zones.
• VG-30 (2400–3600 poise) — paving in hot climate and under heavy traffic. This is the volume grade of the Indian road programme.
• VG-40 (3200–4800 poise) — the stiffest paving grade, reserved for very heavily loaded and channelised locations such as intersections, toll plazas, bus bays and container yards.

VG-30 carries the bulk of Indian paving demand for a straightforward reason: it matches the climate and the traffic of most of the country at the same time. It is also the grade most often written into tenders in neighbouring markets that draft their specifications on Indian practice, and into projects elsewhere that are financed or engineered from India.

2400 to 3600 poise: the only two-sided limit in the table

Seven of the eight VG-30 lines are one-sided. This one is not, and that asymmetry is where a certificate should be read first. The band is 1200 poise wide about a nominal 3000, which means one honestly certified VG-30 can be half as stiff again at service temperature as another. For a single container that is academic. For a plant fed by repeat shipments it is not: a mix design tuned around a 2500 poise binder and then supplied a 3500 poise binder needs a different roller pattern, and the difference will show up in the density cores before anyone notices it on paper. Record the measured figure from each batch Certificate of Analysis and watch the trend across shipments rather than filing the grade name.

The two ends fail differently. Below 2400 poise the binder is out of grade and short of rut resistance in exactly the condition VG-30 was chosen for — a hot afternoon under a channelised heavy axle. Above 3600 poise the batch may well make a better summer pavement, but it is a harder one to build and it has less reserve on a cold night. Both are rejections against IS 73:2013, not matters of judgement.

350 cSt at 135 °C: the line that catches an over-fluxed blend

Kinematic viscosity is set as a minimum, which reads oddly if you expect a workability requirement to cap stiffness rather than raise a floor. The reason becomes clear once you ask how a batch could be brought into the 60 °C band without being the right material. A hard residue cut with a lighter stream can be dialled to almost any absolute viscosity at 60 °C. What such a blend cannot do is hold its viscosity once it is hot — the light fraction dominates at 135 °C and the reading collapses. The 350 cSt floor is where IS 73 stops it, and it is the reason the specification is not simply a single number at 60 °C.

The line also earns its place operationally. A VG-30 measuring close to 350 cSt sits at the thin end of what the standard allows at mixing temperature, so the temperature that delivers the target binder viscosity will be lower than a crew accustomed to a stiffer parcel expects. The two viscosity figures on the certificate are the two anchor points of that batch's own viscosity–temperature line; the handling table further down this page is a default to be replaced by that line, not a substitute for it.

45 dmm minimum penetration: the line VG-30 buyers misread most often

This causes more argument than the rest of the table combined, because it is where the penetration-grade world and the viscosity-grade world collide on the same cargo. IS 73:2013 sets 45 dmm as a floor for VG-30 and sets no ceiling of any kind. Typical VG-30 production lands in the fifties and sixties and it is entirely normal for a compliant batch to test above 70 dmm. A buyer who has spent a decade checking that cargoes sit inside a two-sided 60/70 band sees 74 dmm on a VG-30 certificate and opens a claim. There is nothing to claim. Unless the sales contract wrote a penetration ceiling in, that batch is in grade if the 60 °C viscosity is in grade.

The floor guards the opposite failure: a binder that reaches 3000 poise by being brittle rather than by being heavy. A parcel at 3000 poise and 38 dmm has a far steeper viscosity–temperature line than one at 3000 poise and 58 dmm, and it will crack earlier in service even though both satisfy the grading parameter. So the penetration figure on a VG-30 certificate is a susceptibility cross-check on the viscosity figure, never a hardness classification of its own. It is also set per grade rather than as an even ladder — 80, 60, 45 and 35 dmm from VG-10 to VG-40 — because a stiffer binder is legitimately expected to read lower.

47 °C softening point: a cheap consistency cross-check

Ring and ball to IS 1205 / ASTM D36, minimum 47 °C, no ceiling. A batch properly inside the VG-30 viscosity band normally lands in the low to mid fifties, so a result within a degree of the floor is worth a question rather than an automatic rejection. The value of this line is relational. Softening point and penetration both describe consistency near ambient temperature; when they tell a different story from the 60 °C viscosity — a high softening point beside a low penetration, or a softening point at the floor beside a viscosity at the top of the band — the production route deserves an explanation. A straight-run paving binder gives a coherent account across all three readings. A blended or partly air-blown one frequently does not, and on VG-30 that matters because the grade is traded in volume and is therefore the one most worth imitating.

Viscosity ratio 4.0 after RTFOT: the line that actually predicts the pavement

IS 73:2013 grades the binder unaged, then bounds how much it may harden in the plant. The residue from the rolling thin film oven test is re-tested for absolute viscosity at 60 °C and divided by the original value; the quotient may not exceed 4.0. Because the limit is a ratio rather than an absolute ceiling, two compliant cargoes can arrive at the mixer in reverse order of their delivered stiffness. A parcel delivered at 2500 poise that ages by a factor of 3.9 leaves the mixer near 9750 poise. A parcel delivered at 3500 poise that ages by a factor of 2.4 leaves it near 8400. The certificate that looked softer produces the harder mix, and nothing except the ratio line reveals it. What the pavement carries is the aged binder, so on VG-30 — the grade most often run through high-throughput plants on long production days — this is the number to read before the headline viscosity.

The consequence of exceeding it is not abstract. A mix that arrives at the paver already partly aged compacts short of target density, and the voids left behind admit water and oxygen to a binder that has already spent most of its ageing budget. That pavement cracks years ahead of design. The details of the test itself are set out in the test methods reference.

40 cm residual ductility: not the 100 cm on a penetration-grade sheet

A briquette of the aged residue is stretched at 5 cm/min at 25 °C to IS 1208 / ASTM D113 and must reach 40 cm before the thread breaks. The number is measured on RTFOT residue, not on original binder, and that single distinction generates a recurring error in VG-30 tender evaluation. Export data sheets for penetration grades quote a ductility minimum of 100 cm on unaged material; an evaluator setting 40 against 100 in adjacent columns concludes the viscosity grade is the weaker product. The two figures describe different samples and are not comparable in either direction. Within IS 73 itself the requirement is scaled to the grade, falling from 75 cm at VG-10 to 25 cm at VG-40, so VG-30's 40 cm is a middling demand made of a binder that has already been aged once.

220 °C flash point: a contract trap when VG-30 replaces 60/70

IS 73:2013 sets a Cleveland open cup minimum of 220 °C to IS 1448 (P:69) / ASTM D92, and it applies the same floor to all four viscosity grades. The figure is the basis for storage and heating limits, and it is what a terminal operator, an insurer and the Safety Data Sheet will work from. The trap is commercial rather than technical, and it appears most often on this grade precisely because VG-30 is what gets substituted into contracts originally drafted around 60/70. Those contracts routinely carry a flash point clause of minimum 250 °C. A cargo can satisfy IS 73:2013 in full and still breach it. Where a contract names IS 73 and also states its own flash point figure, the stricter number is the one that will be enforced — resolve the conflict when the contract is drafted, not when the cargo is at the discharge berth.

99.0 % solubility: the anti-adulteration line

Solubility in trichloroethylene to IS 1216 / ASTM D2042 confirms that what is in the drum is bitumen and not bitumen extended with mineral filler or insoluble heavy residue. It is inexpensive, it is quick, and there is no defensible reason for it to be absent from a certificate. On a viscosity-graded cargo it carries more weight than usual: an extender can pull a stiff residue down into a viscosity band without a needle test showing anything unusual, so on VG-30 the solubility line and the penetration line are doing complementary authenticity work rather than duplicating each other.