Oxidized Bitumen 90/15: Specification, 85/25 Comparison and Export Supply

Read the designation as two separate laboratory results joined by a slash. It is not a range, and it is not a quality rating. The ninety is a ring and ball softening point in °C, determined by ASTM D36. The fifteen is a needle penetration at 25 °C in tenths of a millimetre, determined by ASTM D5 under a 100 g load applied for five seconds. Trade practice tolerates about ±5 on each figure, which is why a cargo sold as 90/15 is contracted and tested against 85–95 °C and 10–20 dmm rather than against 90 and 15 exactly. Older British project documents write the identical material as R90/15, a survival from the withdrawn BS 3690-2; the European framework specifications are EN 13304 for oxidised bitumen and EN 13305 for hard industrial bitumen. All of these describe the same material — the naming conventions are explained in full on the oxidized bitumen hub page.

The five degrees are not the point

Buyers comparing this grade with oxidized bitumen 85/25 usually fix on the first number and conclude that 90/15 is the same product with 5 °C more heat resistance. That reading is wrong in a way that costs money, because it points buyers at the wrong grade for the wrong reason.

Compare the pairs properly. Softening point moves from 80–90 °C to 85–95 °C, a shift of five degrees at the nominal value — roughly six per cent on the number that governs heat resistance. Penetration moves from 20–30 dmm to 10–20 dmm: at the nominal pair the needle sinks fifteen tenths instead of twenty-five, about 40 % less, and between the unfavourable corners of the two bands the gap widens to threefold. Consistency, not heat resistance, is where the two grades genuinely part company. The change you are buying is a step change in stiffness that happens to come with a modest gain in heat resistance, not the other way round. If heat resistance alone is what you need, the grade that delivers it without sacrificing movement capacity is 95/25, which lifts the softening point to 90–100 °C while keeping penetration at 20–30 dmm. Choosing 90/15 when 95/25 was the right answer is the single most common grade error in this part of the range.

What the extra hardness buys, and what it costs

At 10 to 20 dmm the material is a genuinely hard solid at ambient temperature. It fractures rather than deforms when a block is dropped, it does not feel tacky, and it holds an edge. In service that translates into resistance to indentation and creep: a coating on buried steel pipe that must survive backfill stones and the weight of soil, a joint compound that must not extrude under a slab edge, an enamel that must not slump off the crown of a stacked pipe standing in the sun in a coating yard.

The cost side is equally direct. Low-temperature flexibility is worse, because the same asphaltene network that resists flow at 90 °C has very little capacity to absorb strain at 5 °C. The material is harder to melt, needs more heat and more time in the kettle, and is unsuitable for any job that depends on the binder wetting and impregnating a fibrous carrier. Adhesion also needs help: like all blown grades it wets steel, concrete and mineral surfaces less readily than a softer binder, which is why a primer is part of the system rather than an optional extra.

Penetration index: the counterintuitive part

The penetration index (PI), calculated from softening point and penetration by the Pfeiffer and Van Doormaal relationship, expresses how much the consistency changes for a given change in temperature. Straight-run paving grades sit near 0; properly blown grades sit well above it. Run the arithmetic on the nominal pairs and 85/25 calculates to about +3.3 while 90/15 calculates to about +2.9. Worked across the four corners of the 90/15 band the figure runs from about +1.6 at 85 °C with 10 dmm to about +4.0 at 95 °C with 20 dmm, so a batch anywhere in the band can legitimately return a PI between roughly +1.5 and +4.

In other words, the harder grade does not have a wider plastic range than the softer one. Both are correctly blown gel-structure binders with a comparable PI; 90/15 has simply been moved along the hardness scale. This matters commercially because PI is the check you run on a Certificate of Analysis to confirm the material was actually blown rather than blended or filled. A 90/15 COA whose measured pair calculates to a PI near zero is not blown material, whatever the label says, and that check takes under a minute.

How it differs from a hard straight-run bitumen

A straight-run paving bitumen can be distilled to a similar penetration, but it will soften roughly 20 to 30 °C lower than a blown grade at the same consistency, because hardness achieved by stripping light ends is not the same thing as hardness achieved by enlarging the molecules. That gap is the whole commercial reason blown grades exist, and it is why 90/15 must never be substituted with a hard paving grade of matching penetration — the substitute will hold its shape on a bench and flow off a sun-heated surface.

Start by separating two requirements that buyers routinely merge. Heat resistance is the ability to stay in place at service temperature and is governed mainly by softening point. Rigidity is the ability to resist indentation, creep and extrusion under mechanical load and is governed mainly by penetration. A hot flat roof needs heat resistance. A buried pipe coating needs rigidity as well. Once you know which of the two is actually driving the specification, the grade choice becomes almost mechanical.

Five questions that settle it

• What temperature will the material reach in service, not what is the air temperature? Dark membrane on an exposed flat deck in the Gulf, in South Asia or on the equatorial African coast will sit at 65 to 80 °C through a summer afternoon. That surface figure, not the shade reading, is what the softening point has to clear — and it typically runs 25 to 30 °C above the temperature anyone quotes from a forecast.
• What is the geometry? Flat deck, moderate slope, steep slope, vertical upstand, parapet, pipe penetration, buried cylinder. Gravity acts on a vertical detail all year; on a flat deck it barely acts at all.
• How much movement must the material tolerate? A deck that cycles thermally, a structure that settles, a pipeline that expands — all of these strain the coating, and strain capacity is the property 90/15 gives up.
• How cold does it get, and when? A binder at 10–20 dmm is brittle at low temperature. If installation or service will see near-freezing conditions, the low-temperature side of the decision outranks the hot side.
• What does the specification actually name? A grade name, an ASTM D312 type, an EN reference, or nothing at all. If it names something, that is the answer and the rest of this section is background.

Application by application

Roofing membrane coating in a hot climate. 85/25 remains the default, and in most cases the correct fix for a marginal case is not a grade change but a batch request: ask for material testing in the upper half of the 80–90 °C band and require the measured value on the COA. Move up when the deck geometry or the exposure genuinely demands it. Between the two grades above 85/25, 95/25 is usually the better roofing answer because it adds softening point without removing flexibility. 90/15 belongs on a roof when the detail is steep or vertical, when the coating must resist foot traffic and mechanical damage, or when the formulation is being filled and the base needs to start hard.

Felt and carrier saturation. Not 90/15, in any climate. Saturation depends on the binder flowing into and wetting the fibre, and at 10–20 dmm the material cannot do it at any sensible application temperature. Attempting it produces a poorly impregnated carrier that delaminates later.

Industrial and below-grade waterproofing. Tanking, foundation and retaining-wall protection, plant-room and wet-area work, tank base mastic, and waterproofing under screeds and hot process floors. This is a good fit for 90/15 wherever the membrane is confined and loaded rather than exposed and moving, and wherever the substrate reaches elevated temperature in service. Always over a bituminous primer.

Pipe coating and corrosion protection. The clearest case for 90/15 — covered in detail in the next section.

Hard mastics, joint filling and industrial compounds. Expansion and construction joint filler in hot climates, sound-deadening and anti-drumming compounds, insulating and filling compounds. These formulations want a hard, flow-resistant base, and 90/15 is the usual starting point before the specification pushes into 115/15 territory.

Cold and temperate climates. Prefer 85/25 or softer. A 90/15 membrane installed on a deck that will see near-freezing temperatures depends entirely on its reinforcement carrier to survive thermal contraction, and hot-applied blown systems in cold climates are increasingly replaced by polymer-modified membranes for exactly this reason.

The ASTM D312 Type III trap

Projects written to North American practice specify ASTM D312 Type III for steep and hot-climate built-up roofing: softening point 85–96 °C, penetration at 25 °C 15–35 dmm. The 90/15 softening point band of 85–95 °C sits inside it, and that near-fit is why 90/15 is so often offered against a Type III requirement. Note, though, that the lower edge of the grade band rests exactly on the Type III minimum: a batch at the bottom of its own grade is simultaneously at the bottom of the standard, with nothing in hand.

The penetration band does not. A 90/15 batch is permitted anywhere from 10 to 20 dmm, and everything below 15 dmm fails the Type III minimum. Half the legitimate 90/15 band is out of specification for the standard it is being offered against. If your project is written to D312 Type III, do not accept a grade name as evidence of compliance: require the measured penetration on the batch Certificate of Analysis, require it to be 15 dmm or above, and write that floor into the contract. This is the most common technically valid rejection we see on this grade, and it is entirely avoidable at the enquiry stage. Note also that the current edition of D312 carries further requirements this page does not reproduce: penetration limits at 0 °C and 50 °C as well as at 25 °C, a minimum flash point, a solubility minimum and a ductility minimum. A data sheet quoting flash point as ‘min 250 °C’ does not by itself demonstrate compliance with the D312 flash point requirement, so check that line too rather than assuming it passes. D312 is the binding document for any project written against it, and the current edition is the one that counts.

When 90/15 is not enough

If the finished compound still slumps, the next step is not more of the same. 115/15 raises the softening point to 110–120 °C at a comparable nominal penetration of 15 dmm, and is the grade for the hardest pipe-coating enamel, electrical and foundry work. Note that its published penetration band is usually wider than 90/15's — typically 5–20 dmm — so the hardness step can be larger than the shared nominal figure suggests, and the band is worth agreeing contractually. If instead the problem is cracking, the answer is to move softer or to a polymer-modified system, not harder. Reading the failure mode correctly — flow versus fracture — points at opposite ends of the range, and getting it backwards is expensive.

What hot-applied bitumen enamel actually is

Bitumen enamel is not the base grade applied neat. It is the blown bitumen blended hot with a heavy loading of inert mineral filler — slate dust, limestone or talc are the usual choices. The filler is not an extender bought to reduce cost. It raises the softening point of the finished enamel above that of the base bitumen, cuts flow and sag at service and stockyard temperatures, reduces thermal expansion so the coating moves less than the steel it protects, improves resistance to indentation from backfill and rock, and gives the material enough body to build coating thickness in a single pass.

The commercial consequence is one that trips up buyers regularly: the enamel specification and the base grade specification are two different documents, and the finished enamel will not test at 85–95 °C softening point. If a project specifies a coating standard, you are being asked for a formulated enamel; if it specifies 90/15, you are being asked for the base bitumen that a formulator will turn into enamel. Establish which one you are buying before you compare prices, because the two are not comparable.

Which standards apply

Hot-applied bitumen coatings for onshore and offshore pipeline steel are specified in Europe under EN 10300; older projects, particularly across the Middle East, South Asia and Africa, still reference the British BS 4147 for bitumen-based hot-applied coating materials for iron and steel. Both are formulated-coating standards covering the enamel, the primer and the reinforcement together. Coal-tar enamel is a parallel hot-applied system with its own standards and its own health controls; it is a different material and a project written for one should not be supplied with the other. Where the requirement is a general industrial coating rather than a pipeline system, the framework specifications for the base bitumen are EN 13304 and EN 13305. See also the bitumen enamel grade page.

Why the base grade is 90/15 rather than 85/25

Three service conditions drive the choice, and none of them is roof-like.

• Soil load and backfill. A buried coating carries the weight of the fill and takes point loads from stones and clods for the life of the line. A softer base allows the coating to be indented, thinned at the point of contact and eventually breached at exactly the place a corrosion cell will start.
• Stockyard temperature before the line is even laid. Coated pipe is commonly stacked outdoors for months in hot climates, and the crown of a black pipe standing in the sun runs far hotter than the shade temperature. A coating that softens will sag, slip against its wrap and mark where the pipes bear on each other. Heat resistance here is a storage requirement as much as a service requirement.
• Operating temperature and cathodic protection. Where the product in the line is warm, the coating must not soften and disbond, because disbonded coating shields the steel from the cathodic protection current that was supposed to be the second line of defence. Where the specification demands more than 90/15 can give, the step up is 115/15, not a filled version of a softer grade.

The system, not the material

A bitumen coating fails at its weakest interface, and that interface is almost never the enamel itself. Buyers who specify only the grade and leave the rest to the coating yard are specifying the least important part of the system.

• Surface preparation. Adhesion is decided on blast-cleaned steel to the cleanliness and profile the coating standard requires. Enamel applied over mill scale or flash rust will disbond regardless of grade.
• Primer. A compatible bituminous primer is applied to the prepared steel and allowed to dry before enamel. Blown bitumen wets steel poorly on its own; the primer is what makes the bond.
• Inner reinforcement. A glass-fibre inner wrap is embedded in the hot enamel to reinforce it and prevent sag on the pipe crown while it cools.
• Outer wrap. An outer wrap or rock shield takes the mechanical abuse of handling, lowering-in and backfill.
• Holiday detection. The finished coating is spark-tested over its full length before the pipe is lowered in. A holiday found in the yard costs minutes; the same holiday found by a corrosion survey costs an excavation.
• Field joints. Welded joints are coated separately, in the ditch, under worse conditions than the yard. They are the recurring weak point of every hot-applied system and deserve their own procedure.

Beyond pipelines

The same reasoning puts 90/15 into other corrosion-protection work: tank base and tank chime coatings, buried structural steel and pile protection, coatings on the outside of buried vessels and culverts, and heavy-duty protective mastics where the coated element is confined rather than free to move. In each case the requirement is a thick, rigid, moisture-excluding film that stays where it was applied under load and elevated temperature. Wherever the element must instead flex, choose a softer grade or a modified system.

What to put on the enquiry

State whether you are buying base bitumen or formulated enamel. If base bitumen, give the softening point and penetration bands you need and any floor on penetration your coating standard imposes. If you are formulating, say what filler you intend to use, because filler type and loading change the finished softening point substantially. Name the coating standard the project is written to, and say whether the line is buried, immersed or above ground — those three cases carry different reinforcement and thickness requirements.

Work out your margin before the first vessel is lit

Do this arithmetic once, on paper, and post the answer at the vessel. The specification guarantees a flash point of no less than 250 °C by Cleveland open cup. Normal working for 90/15 is 190 to 210 °C. The gap in ordinary operation is therefore 40 to 60 °C, and at the 230 °C never-exceed ceiling it has narrowed to 20 °C. A hard grade in a cold melter, on a shift already running late, is precisely the circumstance in which a gap that size gets spent: a stuck thermostat, an unread dial, or a burner left on high while the charge comes up will close it inside a few minutes. Where the Certificate of Analysis reports a measured flash point above the minimum, plan against that figure; where it reports only the limit, plan against the limit and assume nothing better.

A second ceiling sits alongside the first and is frequently the lower of the two: the finished blowing temperature at which the producer actually made the material. Take blown bitumen above it and the blowing reaction begins to run backwards — softening point falls away, fume output climbs steeply, and the material visibly darkens and thins. The pull to cross that line is strongest on hard grades, precisely because they are the ones that keep a crew waiting.

Moisture is what actually hurts people

Water expands roughly 1,700-fold on turning to steam. Trapped beneath a hot melt it converts in an instant and hurls the vessel contents across the working area, and every route by which it gets there is preventable: rain falling into an uncovered kettle, water pooled in a drum rim, condensate left in a transfer line, a damp block pushed under the surface of a melt already running. To that list 90/15 adds a route of its own — damp mineral filler. Enamel and compound work means sacks of slate dust, limestone or talc, commonly stored in a yard, commonly in paper, commonly in a humid climate, and every kilogram of it is introduced directly into the middle of a melt at around 200 °C. Keep filler covered, satisfy yourself that it is dry, and feed it in slowly against agitation instead of tipping it.

If a fire does start, water is not the answer and a jet will make it dramatically worse by ejecting burning material. Keep dry powder or foam units rated for flammable liquids at arm's reach of every vessel. Keep lids shut except while charging. Site vessels level, on non-combustible ground, and well away from the building line, escape routes, stored combustibles and gas cylinders. Where local rules require a hot-work permit and a fire watch after work stops, treat those as the floor rather than the target.

Burns from this material behave differently

Bitumen sticks to skin and goes on delivering heat after it lands, so the damage keeps developing once the splash itself is over. Get clean cold running water onto it immediately and keep the water running for 15 to 20 minutes as a minimum, then carry on cooling all the way to medical care. Adhered bitumen must not be peeled, scraped or dissolved off in the field. Once cooled it forms a sterile covering, and pulling it away takes skin with it — whether and when it comes off is a clinical judgement, not a site one. Anything beyond a trivial splash needs medical attention, and burns to the face, hands or eyes need it without exception.

Fume, dust and what to do about them

Fume output climbs steeply with temperature, so the 190 to 210 °C that 90/15 requires produces measurably more of it than the 180 to 200 °C a softer roofing grade needs — one of the less obvious costs of moving up a grade, and worth stating in a method statement. In Monograph Volume 103 (2013) IARC assessed occupational exposure to oxidised bitumens together with the emissions given off during roofing, and placed them in Group 2A, probably carcinogenic to humans. That conclusion argues for controlling exposure, not for avoiding the material. Stand upwind. Hold the melt at the bottom of the workable range rather than the top. Treat mechanical extraction as standard equipment for enamel blending, compound pots, pipe-coating plant and any enclosed or indoor pouring, rather than as an upgrade. Clean skin with a proprietary bitumen hand cleaner, never with solvent. There is a particulate route as well: reducing brittle blocks throws fine dust into the air, so do that work in the open or under extraction, with respiratory protection matched to the job. Separately, hydrogen sulphide collects in the vapour space above heated bitumen: any tank, pit or melter that has held hot product counts as a confined space, to be gas-tested before entry and entered only under permit.

Personal protective equipment

• Gauntlets rated for heat, long enough to reach well past the wrist, and worn over the sleeve rather than under it so that a splash sheds outward instead of running into the glove.
• A face shield over safety glasses for charging, pouring, decanting and block breaking — this grade throws fragments as readily as it throws liquid.
• Cut protection on the hands whenever broken material is handled; fractured 90/15 leaves edges sharp enough to open a glove.
• Cotton or flame-retardant long sleeves, closed loosely at neck and cuff, and no synthetic base layer of any kind, because synthetics melt into the wound.
• Boots worn with the trousers outside them, never tucked in.

Storage, stacking and packing

Storage is the easy half of this grade. At 85 to 95 °C softening point, blocks and bags will not fuse into a single mass in a container standing on a tropical quay, which is a real and expensive problem with softer blown material such as 75/25 or 85/25. What replaces heat as the packing problem is impact. Brittle material breaks down into fines under repeated dropping, and a consignment that has been handled roughly arrives with a measurable proportion already reduced to crumb — awkward to charge, dusty to break, and easy to argue about on discharge. Specify packing that protects against handling rather than against heat, inspect for breakdown at the point of discharge, and store packages covered, off the ground and away from standing water. Reject anything that has been sitting in water, because moisture in the packing becomes moisture in the melt.

Container loading runs to familiar figures, all of them approximate and all subject to the destination's weight limits. Palletised 25 kg kraft paper bags with a meltable liner load about 20 MT into a 20-foot container, and 1 MT jumbo bags reach the same 20 MT at roughly 20 bags. Cartons of 25 kg come in a little lower, around 18 to 20 MT. In steel drums the figure is set by the drum: 80 drums at 180 kg net gives 14.4 MT, and 80 drums at 150 kg net gives 12 MT. Unit dimensions and pallet configuration move all of these by a tonne or so either way. Two contract points repay the effort of writing them down. Insist on new drums in words — reconditioned drums are the single most common origin of contamination claims, and residue from whatever the drum carried previously can drag a solubility result below the 99.0 % line. And state that drum tare is excluded from invoiced net weight before the invoice is raised rather than after. Expect packaged cargo rather than bulk. Very few destination terminals can hold and discharge at the temperatures a softening point in this range would demand, and in any case blown material and paving bitumen must never occupy the same storage tank.

Everything above is general practice. The supplier's Safety Data Sheet takes precedence over it in every case, and national hot-works and roofing regulations may be stricter still — permit systems, mandatory fire watch periods after work ceases and restrictions on where a vessel may be sited are all common. The time to read the SDS is before the first package is opened.