VG-40 is the hardest of the four viscosity grades in IS 73:2013. It is defined by absolute viscosity at 60 °C — nominally 4000 poise, with an accepted band of 3200 to 4800 poise.
VG-40 does not describe a needle test. It describes flow. A sample of binder is held at 60 °C and drawn through a vacuum capillary viscometer under a controlled vacuum, and the time it takes to pass between two etched marks is converted into absolute viscosity, reported in poise. If the result falls between 3200 and 4800 poise, the material is grade VG-40. The method is IS 1206 (Part 2), the same procedure as ASTM D2171. The number 40 is the nominal centre of the band expressed in hundreds of poise: 4000 poise, with a tolerance of plus or minus 800.
That distinction changes what a buyer has to check. A penetration grade can be verified with a needle, a stopwatch and a water bath — equipment every road laboratory owns. A viscosity grade cannot. Absolute viscosity at 60 °C needs a vacuum capillary system and a bath held to a tight tolerance, and a good many laboratories that issue bitumen certificates do not run the test at all. A certificate reporting penetration and softening point but silent on viscosity has not evidenced VG-40 in any meaningful sense. It has evidenced consistency and applied a label.
Sixty degrees is a deliberate choice: it approximates the temperature a dark asphalt surface reaches in service in a hot country. Grading the binder there means the grade limit speaks directly to the property that governs rutting — stiffness under load when the pavement is at its hottest. Penetration is measured at 25 °C, which is neither a service temperature nor a construction temperature. It is a laboratory convenience inherited from the earliest days of the industry. That is the argument that moved India away from penetration grading, and it is why the Indian standard is built around a viscometer rather than a needle.
The second viscosity line — kinematic viscosity at 135 °C, minimum 400 cSt — covers the other end of the binder working life. One hundred and thirty-five degrees approximates mixing and pumping conditions, so this measurement tells the plant whether the binder will coat aggregate, move through a line and discharge at realistic temperatures. Two temperatures, two different jobs: 60 °C describes how the pavement will behave, 135 °C describes how the plant will behave. A single-point penetration reading gives you neither.
The standard contains four grades — VG-10, VG-20, VG-30 and VG-40 — running from soft to hard in that order. Penetration grading was withdrawn from the Indian standard in the 2006 revision and IS 73:2013 is the edition in force. VG-30 carries the bulk of Indian paving tonnage. VG-40 sits above it as the heavy-duty grade, specified where high pavement temperature combines with slow, heavy or standing traffic and permanent deformation, rather than cracking, becomes the dominant failure mode.
3200 to 4800 poise is a spread of fifty percent. Two cargoes can both be honestly certified VG-40 and still differ by half again in stiffness at service temperature, the one at 3300 poise behaving much closer to a VG-30 than to the one at 4700. Nothing about that is improper — it is how the standard is written. But it is why a buyer running repeat shipments into one project should record the measured viscosity from every batch Certificate of Analysis rather than filing the grade name, and why an unexplained drift from one end of the band to the other is worth raising before the next cargo loads.
These are the requirements IS 73:2013 sets for grade VG-40, restated as they appear on a typical export technical data sheet, with the test method that produces each value.
| Property | Test method | Unit | Min | Max |
|---|---|---|---|---|
| Absolute viscosity at 60 °C | IS 1206 (Part 2) / ASTM D2171 | poise | 3200 | 4800 |
| Kinematic viscosity at 135 °C | IS 1206 (Part 3) / ASTM D2170 | cSt | 400 | — |
| Penetration at 25 °C, 100 g, 5 s | IS 1203 / ASTM D5 / EN 1426 | dmm (0.1 mm) | 35 | — |
| Softening point, ring & ball | IS 1205 / ASTM D36 / EN 1427 | °C | 50 | — |
| Flash point, Cleveland open cup | IS 1448 (P:69) / ASTM D92 | °C | 220 | — |
| Solubility in trichloroethylene | IS 1216 / ASTM D2042 | wt % | 99.0 | — |
| Viscosity ratio at 60 °C, on RTFOT residue | IS 9382 / ASTM D2872, then IS 1206 (Part 2) | ratio | — | 4.0 |
| Ductility at 25 °C, 5 cm/min, on RTFOT residue | IS 1208 / ASTM D113 | cm | 25 | — |
Eight lines define VG-40. Each closes off a specific failure, and two of them — the pair measured after the rolling thin film oven test — are the ones most often missing from a weak certificate.
3200 to 4800 poise by IS 1206 (Part 2) or ASTM D2171. This single line is the grade. Everything else in the table is a supporting requirement that stops a binder of the right viscosity from being unacceptable for some other reason. If this value is absent from a certificate, nothing else on that certificate can establish that the cargo is VG-40, however good the other numbers look.
Minimum 400 cSt by IS 1206 (Part 3) or ASTM D2170. It is a minimum, not a maximum, which surprises buyers who expect a workability limit to cap viscosity rather than set a floor. The logic is that the 60 °C band already stops the binder being too stiff overall; the 135 °C minimum guards against a binder that is unusually temperature-susceptible — acceptably stiff at service temperature but thinning out too far at mixing temperature, which is the signature of an over-fluxed or blended product. Read the two viscosity lines together. The relationship between them says more than either alone.
Minimum 35 dmm by IS 1203, the same test as ASTM D5 and EN 1426. This is the line that most often confuses buyers arriving from the penetration-grade market, because IS 73:2013 sets no upper limit on penetration for VG-40. A binder testing at 36 dmm and one testing at 48 dmm can both be VG-40, provided each lands inside the viscosity band. It follows that VG-40 does not correspond to any single penetration grade, and that no penetration figure on its own can qualify or disqualify a cargo against the standard. The minimum exists to exclude material that is hard because it has been over-processed rather than because it is genuinely a heavy paving binder.
Ring and ball, IS 1205 or ASTM D36. Fifty degrees is three degrees above the VG-30 minimum of 47 °C, and on a certificate it is the practical marker of the harder grade. Read alongside penetration it is also the cheapest authenticity check available. A sample reporting a penetration close to the 35 dmm floor together with a softening point far above 50 °C is not a superior VG-40; it is a signal that the material may have been air-blown rather than produced as a straight-run paving binder. Blown residue can imitate the consistency figures of a hard paving grade and behave nothing like it in a mix.
Cleveland open cup, IS 1448 (P:69) or ASTM D92. Buyers cross-shopping Indian and Middle East material notice this line immediately, because export data sheets for penetration grades routinely quote a minimum of 250 °C and ASTM D946 sets 232 °C. The difference is not a quality gap. IS 73:2013 applies a single 220 °C minimum across all four viscosity grades as a safety floor, and production material normally tests well above it. The number to act on is the measured value on the batch certificate, not the floor in the standard, because the measured value is what your terminal operator, your insurer and the Safety Data Sheet will work from.
IS 1216 or ASTM D2042. This is the anti-adulteration line. At least 99 % of the sample must dissolve, confirming the product is genuine bitumen and has not been extended with mineral filler or inert material. It is an inexpensive test and there is no legitimate reason for it to be missing from a certificate.
India uses the rolling thin film oven test — IS 9382, equivalent to ASTM D2872 — rather than the older static thin film oven test, and then measures two things on the residue. Both are described in the test methods reference.
Viscosity ratio at 60 °C, maximum 4.0. The residue is re-tested for absolute viscosity and the result divided by the original value. A ratio of 4.0 means the binder is permitted to become four times stiffer during simulated plant mixing. The limit is elegant because it is expressed in the same units as the grading parameter: it tells you directly how much of the binder service-temperature stiffness will be ageing rather than design. A cargo arriving at 3300 poise that ages by a factor of 3.8 leaves the mixer stiffer than a cargo arriving at 4700 poise that ages by a factor of 2.5. What the pavement eventually experiences is the aged binder, not the delivered number.
Ductility at 25 °C on the RTFOT residue, minimum 25 cm. Measured by IS 1208 or ASTM D113, stretching a briquette at 5 cm/min until the thread breaks. Twenty-five centimetres is the lowest residual ductility requirement of the four viscosity grades — VG-30 requires 40 cm and VG-10 requires 75 cm — and the relaxation is deliberate, because a harder binder legitimately has less elongation left after ageing. Buyers comparing a VG-40 certificate against a VG-30 certificate sometimes read the lower figure as a defect. It is not. What is a defect is a result below 25 cm, which points to a binder that will be brittle in service.
Every one of the eight lines above, with a measured number against each and the test method named beside it. Two are most often absent: absolute viscosity at 60 °C, because the equipment is less common, and the RTFOT pair, because the test takes time and consumes sample. A certificate showing only penetration, softening point and solubility is a penetration-grade certificate wearing a viscosity-grade name. Ask for the missing lines before shipment rather than after, and on a significant project have sampling carried out by an independent inspector at load port, with sealed retained samples held by both parties so that any later test result can be traced back to the cargo it came from.
All four grades in IS 73:2013 side by side. Reading down the columns shows how each requirement tightens or relaxes as the binder gets harder, which is the quickest way to see what VG-40 is actually buying you.
| Requirement | VG-10 | VG-20 | VG-30 | VG-40 |
|---|---|---|---|---|
| Absolute viscosity at 60 °C, poise | 800–1200 | 1600–2400 | 2400–3600 | 3200–4800 |
| Kinematic viscosity at 135 °C, cSt, min | 250 | 300 | 350 | 400 |
| Penetration at 25 °C, dmm, min | 80 | 60 | 45 | 35 |
| Softening point, ring & ball, °C, min | 40 | 45 | 47 | 50 |
| Flash point, Cleveland open cup, °C, min | 220 | 220 | 220 | 220 |
| Solubility in trichloroethylene, %, min | 99.0 | 99.0 | 99.0 | 99.0 |
| Viscosity ratio at 60 °C after RTFOT, max | 4.0 | 4.0 | 4.0 | 4.0 |
| Ductility at 25 °C on RTFOT residue, cm, min | 75 | 50 | 40 | 25 |
| Typical role in Indian practice | Spray applications, and feedstock for emulsions and cutbacks | Paving in cooler regions and lighter traffic | The general-purpose paving grade across most of the country | Highly stressed areas and high-temperature heavy-duty pavements |
VG-30 is the default across most paving work written to Indian standards. Moving up to VG-40 is a deliberate decision taken on evidence, and the two grades sit closer together on paper than the grade names suggest.
VG-30 is specified at 2400 to 3600 poise and VG-40 at 3200 to 4800 poise. Between 3200 and 3600 poise a binder satisfies the grading parameter of both grades at once. What separates them in that overlap are the supporting lines: VG-30 requires penetration of at least 45 dmm where VG-40 requires only 35, the softening point minimum rises from 47 °C to 50 °C, the kinematic viscosity floor rises from 350 to 400 cSt, and residual ductility after RTFOT falls from 40 cm to 25 cm. A binder measuring 3400 poise with a penetration of 41 dmm is a legitimate VG-40 and fails VG-30 outright, because it sits below the VG-30 penetration minimum. That asymmetry is worth understanding before anyone assumes a VG-40 cargo can be offered against a VG-30 specification, or the reverse.
IRC guidance keys grade selection to two things: the highest daily mean air temperature at the site, and the volume and character of commercial traffic. VG-40 is indicated where the climate is hot and the loading is heavy, and it is called for specifically at the locations where traffic stops or crawls. That is why the standard application list is a list of places rather than a list of road classes — toll plazas, intersections, bus bays. On a corridor otherwise built with VG-30, these are the spots that deform first, and they deform because loading time, not load, is what a viscous binder resists poorly.
A laden truck at highway speed applies its axle load to any one point for a fraction of a second. The same truck queuing at a toll booth applies it for minutes, in the same wheel path, all day, at the hottest part of the afternoon. That is the condition VG-40 answers, and the reasoning holds equally in any market that writes its specifications against Indian standards rather than only within India.
Everything upstream runs hotter. Mixing typically moves into the 160 to 175 °C region and the aggregate has to reach the mixer hotter still, which means more burner fuel, more load on the dryer and, on a humid day when the dryer is already the constraint, reduced throughput. The binder also ages harder during that mixing — which is precisely the effect the viscosity ratio limit of 4.0 exists to bound, and the reason it deserves attention on a VG-40 certificate more than on any softer grade.
The more expensive consequence is on site. The mat leaves the paver hotter but stiffens faster, so the temperature below which further rolling achieves nothing sits roughly ten degrees above where a VG-30 crew is used to working. Long hauls, night work, wind, thin lifts and hand-laid areas around ironwork all compress that window further. An under-compacted VG-40 mat is a worse pavement than a well-compacted VG-30 mat, because the air voids left behind admit water and oxygen to a binder that had less flexibility in reserve to begin with.
The honest summary is that VG-40 buys resistance to deformation and pays for it in cracking risk, construction difficulty and fuel. Where the deformation problem is real and documented, that is a sound trade. Where it is not, VG-30 is the better pavement.
Indian practice concentrates VG-40 in the locations where traffic is slow, heavy or stationary and the pavement surface is hot. These are the places a corridor built in a mid-range grade fails first.
Queuing and stationary heavy vehicles apply load to the same wheel path for minutes at a time, at the hottest part of the day. This is the textbook case the grade exists for, and the approach lanes usually need it more than the booths themselves.
Braking and accelerating traffic imposes horizontal shear on top of vertical load. Distress appears as shoving and corrugation ahead of the stop line long before the open carriageway shows anything at all.
Buses stop in almost exactly the same position thousands of times a day on a heavy rear axle. A bay built in the same binder as the running lane is normally the first part of a route to deform.
Binder and wearing courses on heavy-traffic corridors in hot regions, where the mix design calls for a stiffer binder to raise mixture modulus and spread wheel load into the layers beneath.
Very high wheel loads at manoeuvring speed, plus laden equipment standing for long periods on an unshaded surface. Loading time here is measured in minutes rather than milliseconds.
Corridors where the highest daily mean air temperature keeps a mid-range binder working near the top of its useful range for the whole summer, and where commercial vehicle volumes are high.
Buyers regularly need to show an engineer, or a customs authority, how VG-40 relates to a specification written in another classification system. These are the nearest counterparts and what each one actually requires.
| System | Standard | Nearest counterpart to VG-40 | What that actually means |
|---|---|---|---|
| Viscosity grading (US) | ASTM D3381 / AASHTO M 226 | Grade AC-40 | The closest thing to a direct match. AC-40 is specified at 4000 poise plus or minus 800 at 60 °C, the same 3200–4800 window as VG-40. The supporting requirements are written differently, so it is a match on the grading parameter rather than on the whole standard |
| Penetration grading (US) | ASTM D946 / AASHTO M 20 | Grade 40-50, the hardest grade the standard contains | Not equivalent. D946 fixes a penetration band and says nothing about viscosity at 60 °C, while IS 73:2013 fixes a viscosity band and applies only a penetration minimum of 35 dmm. A 40/50 cargo does not automatically pass VG-40. Note that 30/40, which trade practice often mentions alongside VG-40, is not an ASTM D946 grade at all — D946 runs 40-50, 60-70, 85-100, 120-150 and 200-300 — and it is not an EN 12591 grade either. Do not quote it as a D946 counterpart |
| Penetration grading (Europe) | EN 12591 | 35/50, with 30/45 below it | EN 12591 grades on penetration and softening point and contains no absolute viscosity requirement at 60 °C, so there is no true counterpart. Treat it as an indication of consistency only |
| Old Indian penetration grades | IS 73:1992 (withdrawn) | S-35 / A-35 | The grade VG-40 effectively replaced when India moved to viscosity grading. Still quoted in older project documents and legacy tender language |
| Performance grading | AASHTO M 320 | Commonly compared with a PG 70 high-temperature grade, source dependent | Cannot be inferred from viscosity. Requires DSR on original, RTFO and PAV residue plus BBR at the low-temperature end. Where a project names a PG grade, only PG test data satisfies it |
A hard viscosity grade is unforgiving of temperature error in both directions: too cool and it will not coat or compact, too hot and the viscosity ratio budget is spent before the binder reaches the mixer. These are the typical operating windows.
| Operation | Typical range | What goes wrong outside it |
|---|---|---|
| Storage, short term | 155–170 °C | Below the range the binder moves slowly and lines run at pressure; above it, oxidative hardening accelerates and the binder ages before it ever reaches the mixer |
| Storage, long term | below 155 °C | Prolonged hot storage stiffens the binder. A VG-40 already sitting near 4800 poise has very little room before it leaves the band entirely |
| Pumping and circulation | 145–170 °C | Below roughly 145 °C viscosity climbs steeply, line losses rise and pumps begin to cavitate |
| Aggregate at the mixer | 160–180 °C | Cold aggregate chills the binder film on contact and leaves fines uncoated, which surfaces later as stripping and ravelling |
| Mixing with aggregate | 160–175 °C | Complete coating has to be achieved at a higher binder viscosity than a VG-30 mix requires; short mixing time shows up as dry, brown-looking mix |
| Delivery at the paver | above 150 °C | This is the number to verify, not the plant discharge temperature. Haul distance, sheeting and wind decide whether the mat is still compactable when it arrives |
| Compaction, start | 145–160 °C | Rollers must be on the mat immediately. A VG-40 mix stiffens faster than a crew accustomed to VG-30 expects |
| Compaction, cut-off | above 100–110 °C | Below this the mat is locked in as laid, and further passes add roller marks rather than density |
| Absolute ceiling | do not exceed 180–190 °C | Rapid oxidation, heavy fuming and an approach to the flash point. This limit belongs to the product, not to the grade |
VG stands for viscosity grade and 40 is the nominal absolute viscosity at 60 °C expressed in hundreds of poise. Under IS 73:2013 a VG-40 binder must measure between 3200 and 4800 poise at 60 °C by IS 1206 (Part 2), the Indian equivalent of ASTM D2171. It is the hardest of the four grades in the standard, above VG-30, VG-20 and VG-10, and Indian practice specifies it for highly stressed and high-temperature pavements.
IS 73:2013 requires a minimum of 35 dmm at 25 °C by IS 1203 and sets no upper limit at all. Penetration is a supporting requirement in a viscosity-graded standard rather than the grading parameter, so its job is only to exclude material that is hard because it has been over-processed. In practice VG-40 usually tests somewhere between the mid-thirties and the mid-forties, which is why it is loosely associated with 30/40 and 40/50 in trade conversation. Do not treat a penetration figure as proof of grade in either direction: the cargo is VG-40 if and only if the absolute viscosity at 60 °C falls inside 3200 to 4800 poise.
By the failure mode the site is exposed to. VG-40 is the answer where high pavement temperature combines with slow, heavy or standing traffic and permanent deformation is the risk: toll plazas, intersections, bus bays, container yards and heavy-freight corridors in hot regions. VG-30 is the better pavement almost everywhere else, and specifically where nights are cold, layers are thin, the substrate is cracked or the crew cannot reliably hold compaction temperature. Note also that the two viscosity bands overlap between 3200 and 3600 poise, so the practical differences sit in the supporting lines: VG-30 demands penetration of at least 45 dmm and 40 cm of residual ductility, VG-40 demands only 35 dmm and 25 cm but a higher softening point and a higher kinematic viscosity floor.
No. They are graded by different tests and the relationship only works one way at a time. VG-40 is defined by absolute viscosity at 60 °C, which penetration grading never measures, so a 40/50 or 30/40 cargo cannot be certified VG-40 unless the viscosity test has actually been run on that batch and the result falls inside 3200 to 4800 poise. The nearest counterpart in another standard is ASTM D3381 grade AC-40, which grades on the same window of 4000 poise plus or minus 800 — but that is a match on the grading parameter alone. D3381 writes its supporting requirements differently, so an AC-40 certificate is not automatic evidence of IS 73:2013 compliance and any substitution needs the engineer's written approval. Where an Indian or IS-based project names VG-40, ship VG-40 and put the 60 °C viscosity result on the certificate.
Eight measured values with the method named beside each: absolute viscosity at 60 °C, kinematic viscosity at 135 °C, penetration at 25 °C, softening point, flash point, solubility in trichloroethylene, and the two results taken on the rolling thin film oven residue — viscosity ratio at 60 °C and ductility at 25 °C. The two most commonly missing are absolute viscosity, because the vacuum capillary equipment is less widely held, and the RTFOT pair, because the test takes time and consumes sample. A certificate showing only penetration, softening point and solubility does not evidence a viscosity grade at all.
Because it is a different standard, not a different quality level. IS 73:2013 applies a single Cleveland open cup minimum of 220 °C across all four viscosity grades, while typical Middle East export sheets for penetration grades quote 250 °C and ASTM D946 sets 232 °C. Production material normally tests comfortably above the IS floor. What matters operationally is the measured value on the batch certificate, since that is the figure your terminal, your insurer and the Safety Data Sheet will use to set storage and heating limits.
The binder is aged in a rolling thin film oven to IS 9382 or ASTM D2872 to simulate what happens during hot mixing, the residue is re-tested for absolute viscosity at 60 °C, and the aged value is divided by the original. IS 73:2013 allows a maximum of 4.0, meaning the binder may become up to four times stiffer through mixing. A result close to the limit tells you the binder will reach the pavement considerably harder than the delivered figure suggests, which matters most for a grade that is already at the hard end. A result above 4.0 is a rejection, and it usually points to a binder that will be brittle and prone to cracking in service.
Mixing typically moves to about 160 to 175 °C with aggregate hotter still, which raises burner fuel consumption, loads the dryer and can cut throughput on a hot humid day. On site the compaction cut-off temperature sits roughly ten degrees higher, so the window between laying and locked-in density is shorter, and long hauls, wind, night work and thin lifts shrink it further. Roller patterns and haul scheduling normally need adjusting rather than merely tightening. If the cargo arrives in drums, allow noticeably more time and a properly sized melting unit, because a hard grade melts out slowly and forcing it with direct flame is the most common way a good cargo is ruined after arrival.
Tell us the tonnage, the packing, the discharge port and the Incoterm — and confirm the one thing specific to this grade: whether the Certificate of Analysis has to carry the measured absolute viscosity at 60 °C and the rolling thin film oven results, because a certificate without them does not evidence VG-40. If a project specification applies, attach it; the offer will be checked against it before pricing, and any point where the typical export values differ from IS 73:2013 will be flagged to you rather than left for the certificate to reveal.