Oxidized bitumen is not a harder distillation cut. It is a chemically altered material, and that distinction governs everything it is used for.
Oxidized bitumen — traded also as blown bitumen, blown asphalt, air-blown bitumen or oxidised asphalt — is bitumen whose molecular structure has been deliberately changed by reacting it with air at high temperature. A hard paving grade such as 20/30 is hard because more of the light fraction was stripped out under vacuum. An oxidized grade such as 95/25 is hard because the molecules themselves have been made larger. The two arrive at a similar penetration by completely different routes and they do not behave alike.
It is worth separating three things that get called the same name in trade conversation. Fully oxidized bitumen is blown to a defined softening point and sold as an industrial or waterproofing material. Air-rectified or semi-blown bitumen is lightly blown to nudge a paving binder into specification and is still sold and used as a paving binder. Hard industrial bitumen covered by EN 13305 is a hard grade that may or may not have been blown. Only the first of these is what a buyer means when the enquiry says oxidized bitumen 85/25.
Paving bitumen behaves as a sol. Asphaltene micelles are well dispersed and peptised in a maltene medium, and the material flows in an essentially viscous way — heat it and it thins predictably, cool it and it stiffens. Air blowing converts a large part of the maltene fraction into asphaltenes. As asphaltene content climbs, the micelles begin to associate into a loose three-dimensional network and the material shifts towards a gel structure. Finished oxidized bitumen feels rubbery rather than sticky, springs back partially when deformed, and resists flow at temperatures where a paving binder would run off a slope.
The commercially important consequence is a much wider plastic range. Temperature susceptibility is expressed as the penetration index (PI), calculated from penetration at 25 °C and ring-and-ball softening point using the Pfeiffer and Van Doormaal relationship. Straight-run paving bitumen sits between roughly −1 and +1. Run the same calculation on the seven grades in the table below and the answers land between about +2 for 75/25 and about +6 for 105/35 and 150/5. A higher PI means the material changes consistency less for a given change in temperature. Note that PI is calculated, not measured: if a Certificate of Analysis shows a softening point and penetration pair that works out near zero, the material has not been properly blown whatever the label on the drum says, and that is a check a buyer can run in a minute.
A worked comparison makes it concrete. Take a flat roof in a hot climate where the membrane surface reaches 75 °C in afternoon sun. A 60/70 paving binder, softening point 49–56 °C, is well past its softening point and will creep, slump and bleed. An 85/25 oxidized grade, softening point 80–90 °C, is still below its softening point and holds position. That single property — staying put on a warm slope — is why the roofing and waterproofing industries use blown bitumen and not paving bitumen.
Blowing is a controlled oxidation carried out in a converter, also called a blowing column or bitublower. The chemistry is simple to state and difficult to control, which is why grade consistency between suppliers varies.
The charge is normally vacuum residue or a soft base bitumen in the 180/200 to 200/300 penetration class. The asphaltene-to-maltene balance of the feed decides how far the material can be blown, how much air it takes to get there, and how the finished product behaves. Two refineries blowing to the same 85/25 target from different crude slates will not deliver identical material — which is why repeat buyers stay with one source.
The feed is heated to roughly 240–260 °C and charged to the converter. The reaction needs this temperature to proceed at a useful rate, but it is also exothermic once running, so the starting temperature is chosen with the heat release in mind rather than pushed as high as possible.
Air is introduced through a sparger or distributor at the base of the column. The design objective is small, well-distributed bubbles that rise slowly, because the reaction rate depends on the contact area between oxygen and hot bitumen rather than on the air volume alone. Excess air simply leaves unreacted and carries hydrocarbon vapour into the off-gas.
Oxygen abstracts hydrogen from the bitumen molecules. The hydrogen leaves as water vapour and the resulting free radicals recombine into larger, more condensed structures. In practical terms the maltene fraction is progressively converted to asphaltenes. Asphaltene content rises, molecular weight rises, softening point rises and penetration falls — all in the same direction, at rates that depend on the feed.
The reaction releases heat, and an uncontrolled exotherm is the classic failure mode of a blowing unit. Temperature is held by adjusting air rate and by quench or steam injection. The off-gas carries water vapour, light hydrocarbons and oxidation products and is routed to an incinerator or scrubber. Some units use a catalyst — ferric chloride, phosphoric acid or phosphorus pentoxide — to reach a given softening point faster and with a higher penetration retained at that softening point. Catalytically blown material is a legitimate product but it is not identical to straight-blown material, and a careful buyer asks which route was used.
Blowing is stopped when softening point and penetration reach the target window. The batch is sampled and tested before release. Record the temperature at which blowing was stopped — the finished blowing temperature, or FBT. It is the practical ceiling for every downstream heating operation, because heating the material above the temperature at which it was made begins to undo the reaction, dropping softening point and increasing fume. A proper technical data sheet states it.
This is the most common misreading in the industrial bitumen trade, and it produces wrong orders often enough to be worth stating bluntly.
In an oxidized bitumen designation such as 85/25:
So 85/25 describes a material with a softening point of about 85 °C and a penetration of about 25 tenths of a millimetre. It is not a penetration band running from 85 to 25 — which would be meaningless, because the numbers run backwards.
Because paving bitumen uses the opposite convention and most people meet paving bitumen first. In a penetration grade such as 60/70, 80/100 or 40/50, both numbers are penetration limits and the pair is an ascending range: minimum 60 dmm, maximum 70 dmm. Nothing in the written designation tells you which convention is in use, so buyers carry the paving habit across and read 90/15 as a range, or compare 85/25 against 80/100 as though the numbers were on the same scale.
One test settles it, and one common shortcut does not:
The industry convention is a nominal value with a tolerance of about ±5 on each number. On that basis 85/25 means softening point 80–90 °C and penetration 20–30 dmm, and 115/15 means softening point 110–120 °C and penetration 10–20 dmm. The convention is widely followed but it is not a standard. Individual refinery data sheets publish asymmetric bands, quote penetration as a maximum only, or quote softening point as a minimum only. Read the actual data sheet for the material you are buying rather than assuming the ±5 rule, and get the band you need written into the contract.
Buyers working from older project specifications will meet the same grades written as R85/25, R90/40 or 85/25 R. These come from BS 3690-2, the withdrawn British standard for bitumens for industrial purposes, in which the R denoted the oxidized series. Europe replaced it with EN 13304, the framework specification for oxidised bitumen, and EN 13305 for hard industrial bitumen. The standard went; the designation stayed. If your specification carries an R prefix you are looking at the same softening point / penetration convention described above.
State the grade in the 85/25 form, and add the softening point and penetration band you actually need if the project is tight on either. If the specification references ASTM D312, name the Type as well — Type I to Type IV — because the D312 bands do not map one-to-one onto the commercial grade names. If the material is for pipe coating or electrical work, say so, because those applications carry filler content, adhesion and dielectric requirements that a plain grade name does not cover.
The seven grades below cover effectively all commercial oxidized bitumen trade. Softening point and penetration bands follow the standard ±5 naming convention; individual refinery data sheets vary by a few degrees either way.
| Grade | Softening point, ASTM D36 | Penetration at 25 °C, ASTM D5 | Primary application |
|---|---|---|---|
| 75/25 | 70–80 °C | 20–30 dmm | Roofing felt saturation and impregnation, general waterproofing, mastics and adhesives in temperate climates |
| 85/25 | 80–90 °C | 20–30 dmm | The most traded grade — roofing membrane coating, building waterproofing, sealants, sound-damping compounds |
| 90/15 | 85–95 °C | 10–20 dmm | Hot-climate waterproofing, base for pipe-coating enamel, hard mastics and jointing compounds |
| 95/25 | 90–100 °C | 20–30 dmm | Roofing and membranes for hot climates, bituminous paint, industrial adhesives where flow resistance matters |
| 105/35 | 100–110 °C | 30–40 dmm | High softening point with retained flexibility — expansion joint filler, sealants, damp-proof coursing |
| 115/15 | 110–120 °C | 10–20 dmm | Pipe-coating enamel, electrical insulation compounds, hard industrial and foundry applications |
| 150/5 | 145–155 °C | 0–10 dmm | Very hard grade — cable jointing and potting compounds, battery and capacitor sealing, specialist binders |
Softening point and penetration are grade specific and are given in the grade table above. The properties below are common to the oxidized range and appear on most Middle East refinery data sheets.
| Property | Test method | Unit | Typical export requirement |
|---|---|---|---|
| Softening point, ring & ball | ASTM D36 / EN 1427 | °C | Grade specific — see the grade table |
| Penetration at 25 °C, 100 g, 5 s | ASTM D5 / EN 1426 | dmm (0.1 mm) | Grade specific — see the grade table |
| Flash point, Cleveland open cup | ASTM D92 | °C | min 250 (ASTM D312 roofing asphalt requires min 260) |
| Solubility in trichloroethylene | ASTM D2042 / EN 12592 | wt % | min 99.0 |
| Loss on heating, 163 °C / 5 h | ASTM D6 / IS 1212 | wt % | max 1.0 |
| Specific gravity at 25 °C | ASTM D70 / EN 15326 | — | 1.00–1.05 |
| Water content | ASTM D95 | vol % | max 0.2 |
| Spot test | AASHTO T102 | — | Negative |
ASTM D312 is the specification that governs asphalt used in built-up roofing in North America and in many projects that follow US practice. It classifies material into four types by softening point, and the type is selected by roof slope rather than by climate alone.
| Type | Softening point (ASTM D36) | Penetration at 25 °C, 100 g, 5 s | Maximum roof slope | Where it is used |
|---|---|---|---|---|
| Type I | 57–66 °C | 18–60 dmm | up to 1/2 in per ft (about 4 %) | Dead-level roofs. The softest type, with the best self-healing and cold-weather behaviour; it will flow on any real slope |
| Type II | 70–80 °C | 18–40 dmm | up to 1 1/2 in per ft (about 12 %) | Flat roofs. The general-purpose type for conventional built-up work |
| Type III | 85–96 °C | 15–35 dmm | up to 3 in per ft (about 25 %) | Steep roofs and hot climates, and the most widely supplied type. The commercial 90/15 and 95/25 grades sit near this softening point band, but neither is automatically D312 compliant: 95/25 can test above the 96 °C ceiling and 90/15 can fall below the 15 dmm penetration minimum |
| Type IV | 99–107 °C | 12–25 dmm | up to 6 in per ft (about 50 %) | Special steep roofs and the hottest exposures, where slump resistance outweighs flexibility |
Every application below exploits the same property: the material holds its consistency and stays where it was placed across a wide temperature range.
Used both to saturate the carrier and to coat it. A glass fibre or polyester carrier is impregnated and then coated with 85/25 or 95/25 filled with mineral filler, and finished with slate granules or sand. This is the largest single outlet for blown bitumen worldwide. See roofing bitumen.
Hot-applied asphalt mopped between plies of felt, with the ASTM D312 type chosen by roof slope. The work is done at high temperature on the roof itself, which makes kettle control and fire discipline part of the specification, not an afterthought.
Basement tanking, foundation and retaining wall protection, bridge deck waterproofing and wet-area membranes. Applied hot over a bituminous primer, often reinforced. See waterproofing bitumen.
Hard grades such as 115/15 are blended with inert mineral filler to make hot-applied enamel for buried and submerged steel pipe, applied over a primer and reinforced with glass fibre wrap. Adhesion, filler loading and cathodic disbondment matter as much as the base grade. See bitumen enamel grade.
Expansion and construction joint filler, roofing and flashing cement, tile and membrane adhesives, and sound-deadening compounds for vehicle floor pans. 105/35 is favoured where a high softening point has to coexist with movement tolerance.
The hardest grades, 115/15 and 150/5, are used as cable jointing and filling compounds, battery and capacitor sealing compounds and general potting media, where the requirement is a solid, void-free, moisture-excluding fill that will not soften in service.
Oxidized bitumen is worked hotter than paving bitumen and, in roofing, is worked uncomfortably close to its flash point. This section is not optional reading.
Treat 230 °C as the absolute ceiling for any kettle or melter handling a blown grade, and understand what that ceiling is protecting. Against a specification flash point of 250 °C minimum it leaves about twenty degrees of margin; a kettle that has been allowed to drift to 240 °C has about ten. A failed thermostat, a hot spot over an uncovered heating surface, or an operator chasing viscosity on a cold morning closes that gap in minutes. Roofing kettle fires are a recognised and recurring cause of serious building fires, and almost all of them are temperature-control failures rather than accidents.
Water is the most dangerous contaminant in any hot bitumen operation. One volume of water becomes roughly 1,700 volumes of steam at atmospheric pressure. If water is introduced beneath hot bitumen — rain into an open kettle, condensate in a transfer line, a wet drum interior, moisture at the bottom of a storage tank, a damp block dropped into the melt — it flashes instantly and throws hot material across the working area. Inspect drums for standing water before charging, drain and dry lines before use, charge blocks and drum contents gently and never below the surface of an existing melt, and cover kettles in wet weather.
Because it is applied hotter, oxidized bitumen generates more fume than paving bitumen. IARC reviewed the evidence in Monograph Volume 103 (2013) and classified occupational exposure to oxidised bitumens and their emissions during roofing as Group 2A, probably carcinogenic to humans — a step above straight-run bitumen emissions during road paving, which were placed in Group 2B. That classification is a reason to control exposure properly, not a reason to avoid the material.
Hydrogen sulphide can accumulate in the vapour space of heated bitumen tanks and tank containers even when the product itself carries very little. Treat any heated bitumen tank as a confined space with a potential H2S atmosphere: gas test before entry, ventilate, and do not gauge or sample over an open hatch without monitoring.
Hot bitumen adheres to skin and keeps transferring heat after contact, which is why bitumen burns are deeper than the splash suggests. Cool the affected area immediately with copious clean cold water for at least 20 minutes and continue cooling while the casualty is transported. Do not peel or solvent-strip adhered bitumen. Once cooled it forms a sterile covering; pulling it off takes skin with it. Removal is a decision for a burns unit, not for the site. For hot work, PPE means a face shield over safety glasses, heat-resistant gauntlets worn outside the sleeve so that a splash runs off rather than into the glove, non-melting cotton or treated overalls with no synthetic layers underneath, and boots without exposed laces.
By the direction the pair runs. An oxidized designation states softening point in °C first and penetration at 25 °C in dmm second, so it descends — 85/25, 90/15, 150/5. A penetration grade states a minimum and a maximum penetration, so it ascends — 40/50, 60/70, 85/100. Never judge from the first number alone: 85/100 is a soft paving binder and 85/25 is a hard blown grade, and they share a first number. Where a purchase order, drawing or specification is ambiguous, ask the seller in writing which property the first figure represents before the cargo is nominated.
No, and the naming convention is opposite. In a penetration grade such as 60/70 both numbers are penetration limits and the range ascends. In an oxidized grade the first number is a softening point and the second a penetration, so the pair descends. The materials are also chemically different: oxidized bitumen has been reacted with air, has a much higher asphaltene content, a far lower temperature susceptibility and much lower ductility. It is an industrial and waterproofing material, not a paving binder.
Vacuum residue or a soft base bitumen is heated to about 240–260 °C in a converter and air is blown through it via a distributor at the base. Oxygen strips hydrogen from the bitumen molecules, the hydrogen leaves as water vapour, and the resulting fragments polymerise into larger molecules. Maltenes convert to asphaltenes, so softening point rises and penetration falls. Blowing is stopped when the target softening point and penetration are reached, and the batch is tested before release.
It depends on roof slope and climate. 85/25 is the general-purpose roofing and membrane grade. For hotter climates or steeper slopes, 90/15 and 95/25 give more slump resistance and sit close to the ASTM D312 Type III softening point band — close to, not inside it, because a commercial grade name is not a certification against D312. If the project is written against that standard, order by Type and ask for a certificate issued against the Type, not a data sheet for the nearest grade. Type IV territory, above 99 °C softening point, is for special steep work only. A hotter grade than the slope requires buys nothing and costs low-temperature flexibility.
Softening point band and therefore slope capability. Type III is 85–96 °C and is suitable up to about 3 inches of rise per foot; Type IV is 99–107 °C and is intended for slopes up to about 6 inches per foot. Type IV resists slump better and is more brittle in cold weather and less able to self-heal. Type III is the more widely supplied of the two.
No, and it is worth being firm about because blown material is occasionally offered as a cheap hardener to stiffen a soft paving binder. It does not work that way. The gel structure that gives a blown grade its heat resistance is the same structure that leaves it with almost no ductility and poor fatigue behaviour under repeated wheel loading, and at plant temperatures it is too stiff to wet and coat aggregate. Blending it into a paving binder degrades that binder rather than upgrading it. The one legitimate overlap is air-rectified or semi-blown bitumen — very lightly blown to bring a paving grade into its specification band, still sold and tested as a paving binder, and a different product from a fully blown industrial grade despite the shared process step.
Most export volume moves in new steel drums of 150 kg or 180 kg net, roughly 12 MT and 14.4 MT respectively in a 20-foot container at about 80 drums. Hard grades are also supplied as 25 kg blocks in kraft bags or cartons, which suit kettle work because the block is charged whole. Bulk shipment is possible where the buyer has heating and a dedicated tank, but oxidized bitumen must not share storage with paving bitumen.
It requires controls. IARC Monograph Volume 103 (2013) classified occupational exposure to oxidised bitumens and their emissions during roofing as Group 2A, probably carcinogenic to humans. The practical controls are keeping the application temperature at the low end of the workable range, working upwind, using extraction in enclosed spaces, wearing correct PPE and washing with a bitumen hand cleaner rather than solvent. Hot bitumen burns and kettle fires are the more immediate hazards on any site, and both are addressed by temperature discipline and keeping water away from the melt.
Send the grade, quantity, packing and destination port with your Incoterm. If the project is written against ASTM D312 or an older BS 3690-2 designation, or if the material is for pipe coating or electrical work, say so and the offer will be checked against that requirement before pricing.