Oxidized Bitumen 115/15: Specification, Applications and Handling

The designation is a pair of measured values rather than a range. The first number is the ring and ball softening point in °C to ASTM D36. The second is the needle penetration at 25 °C in tenths of a millimetre to ASTM D5, using a 100 g load for 5 seconds. The trade convention of roughly ±5 on each figure puts the softening point between 110 and 120 °C. Older British project documents write the same grade as R115/15, a survival from the withdrawn BS 3690-2. In Europe two framework standards sit over this part of the market: EN 13304 for oxidised bitumen and EN 13305 for hard industrial bitumen. A grade made by air blowing falls under EN 13304 on the face of it, but hard blown material is quoted against both in practice, so confirm which document your project actually references before either is written into a contract. The naming convention itself, which buyers misread more often than any other in the trade, is explained in full on the oxidized bitumen hub page.

The penetration band deserves attention before anything else on the page. Published data sheets do not agree: some producers publish 115/15 with a penetration of 10–20 dmm in line with the ±5 convention, while others open the band downward and publish 5–20 dmm. A batch at 6 dmm and a batch at 19 dmm are both legitimately 115/15 under the second convention, and they will not behave the same way in a filled compound. Do not treat the grade name as the specification. Decide what penetration band your formulation needs, write that band into the contract, and check the measured figure on the batch Certificate of Analysis.

The hardest grade in ordinary commercial trade

The blown range runs from around 75/25 at the soft end up to specialty products such as 135/10 and 150/5. In practice 115/15 is where routine export volume stops. Grades above it are made to order in small quantities for narrow industrial uses, carry long lead times, and are worked at temperatures that push against the flash point of the material itself. If your requirement can be met at 115/15, it should be, and if a formulator is asking for something harder it is worth confirming that the problem is genuinely flow rather than something a filler loading would solve.

How the numbers moved to get here

Compare the steps through the family and the character of this grade becomes clear. Moving from 85/25 to 90/15, the softening point rises about 5 °C while the penetration roughly halves — that step buys hardness. Moving from 90/15 to 115/15, the penetration band stays in the same region while the softening point climbs about 25 °C. That step buys heat resistance, and it is bought by driving the blowing reaction far further: more of the maltene fraction has been converted to asphaltenes, and the gel structure that holds the material together at high temperature is much more developed.

The arithmetic shows up in the penetration index. Calculated from softening point and penetration by the Pfeiffer and Van Doormaal relationship, the nominal 115/15 pair gives a PI of about +5, and the corners of the band give roughly +3 to +6. For comparison the same calculation gives about +3.3 for 85/25 and about +2.9 for 90/15. 115/15 is the least temperature-susceptible grade in the family — its consistency changes less for a given change in temperature than any of the softer blown grades.

Low temperature susceptibility is not flexibility

This is the point at which specifications go wrong. A high penetration index describes the slope of the consistency curve, not its level. 115/15 starts hard and stays hard: it is a brittle solid at 5 °C, it is still a brittle solid at 40 °C, and it is still a stiff paste at 170 °C. The flat curve does not give the material any capacity to absorb strain at low temperature — it simply means the material does not soften much on the way up. Reading a high PI as evidence of a wide plastic range will put this grade onto a substrate that moves, and the coating will crack.

PI is nevertheless the fastest integrity check you can run on a Certificate of Analysis. Take the measured softening point and the measured penetration, calculate the index, and confirm it lands in the +3 to +6 region. Material labelled 115/15 whose measured pair calculates to a PI near zero has not been blown to this grade, whatever the drum says, and the check takes under a minute.

Why not a hard straight-run bitumen instead

Bitumen can also be made hard by distillation rather than by blowing. Hard paving grades under EN 13924-1, such as 10/20, reach a penetration in the same region as 115/15, and they are considerably cheaper. They are not a substitute. Hardness achieved by stripping light ends is not the same as hardness achieved by enlarging the molecules, and a hard straight-run grade at 10 to 20 dmm commonly softens somewhere in the 60 to 75 °C region — forty to fifty degrees below 115/15. A substitute of that kind will pass a hardness check on a laboratory bench in an air-conditioned room and then flow off a sun-heated pipe in a coating yard. If a supplier offers a hard paving grade against a 115/15 enquiry, ask for the softening point before you look at the price.

What 115/15 is not

It is not a roofing asphalt. ASTM D312, the North American standard for roofing asphalt, stops at Type IV: softening point 99 to 107 °C, penetration at 25 °C 12 to 25 dmm. A 115/15 softening point of 110 to 120 °C sits above every D312 type, and the material has none of the flexibility a roof membrane needs. It should not be offered against a D312 requirement and should not be accepted against one. For hot-climate roofing the correct grades are 95/25 and 85/25; where slope and mechanical loading also matter, 90/15.

What the material is like in the hand

At 5 to 20 dmm this is a hard, dense, glassy solid. It is not tacky. It does not mark your glove. A block dropped on a concrete floor does not deform — it fractures, often into a shower of angular fragments and dust with edges sharp enough to cut. This matters commercially before it matters technically: a consignment that has been double-handled, dropped from a tail-lift or thrown across a container floor arrives with a significant proportion of its contents broken down into fines. Fines are not a quality defect in themselves, but they are awkward to charge into a melter, they generate more airborne dust than a buyer expects, and in a bagged shipment they concentrate at the bottom of the pallet.

It has effectively no capacity to accommodate movement

This is the single design rule for the grade. A 115/15 film has almost no strain capacity at ambient temperature. If it is bonded to something that moves — a substrate that expands and contracts through a daily thermal cycle, a structure that settles, a panel that flexes under load — the film will crack, and it will crack through its full thickness rather than crazing on the surface. Cold weather makes it worse, and so does thermal shock: pouring material at 210 °C onto a cold steel surface generates a steep temperature gradient through the film as it sets, and the resulting internal stress can crack a coating before it has been put into service at all.

The consequence is that 115/15 belongs in applications where the material is loaded, confined and supported: filled to a heavy loading with mineral filler, reinforced with a glass-fibre or fabric carrier, poured into a cavity that constrains it on all sides, or applied to a rigid substrate that will not move. It does not belong anywhere it is expected to bridge a joint, absorb structural movement, or survive as an unreinforced free film. Where movement is part of the specification, either move several grades softer or move to a polymer-modified system, which is what most modern flexible-membrane specifications now call for.

Why there is no ductility figure — and what to use instead

Ductility to ASTM D113 stretches a briquette of bitumen at 5 cm/min at 25 °C until it breaks. A 115/15 briquette breaks almost immediately. A contractual ductility minimum on this grade is therefore not a demanding requirement — it is an unmeetable one, and its presence in a purchase specification is a reliable sign that the specification was copied from a paving-grade document. Its absence from the table above is correct rather than an omission.

If you genuinely need a low-temperature control parameter, there are better instruments. The Fraass breaking point (EN 12593) measures the temperature at which a thin film cracks under a standard bend and is the recognised low-temperature test for hard and blown binders; agree a limit with the producer rather than assuming one, since published limits for this grade are not standardised. Alternatively, and often more usefully, test the finished compound rather than the base binder — a bend or flexibility test on the actual filled and reinforced product tells you what will happen on site, which the base binder alone cannot.

Adhesion is not automatic

Blown bitumen wets steel, concrete and mineral surfaces less readily than a straight-run binder, and the harder the grade the less readily it wets. At 115/15 a compatible bituminous primer on a properly prepared surface is not an optional refinement, it is part of the system. Applying hot 115/15 directly to mill scale, flash rust, dust or a damp substrate produces a coating that looks correct on the day and disbonds later, and disbonded coating on a cathodically protected structure is worse than no coating at all because it shields the steel from the protective current.

The storage advantage

There is one place the hardness helps rather than costs. A softening point of 110 to 120 °C makes 115/15 the most stable grade in the family in storage and transit. Blocks and bags will not fuse into a single mass in a container standing on a quay in the sun, which is a genuine problem with 75/25 and 85/25 in tropical ports. The trade-off is the brittleness described above, so the packing question for this grade is about protecting against impact rather than against heat.

Pipeline coating enamel for warm and hot-climate lines

Hot-applied 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 — which raises the softening point of the finished enamel above that of the base bitumen, cuts sag, reduces thermal expansion so the coating moves less than the steel it protects, and gives the material enough body to build thickness in one pass. The full coating system, its standards and its failure modes are set out on the 90/15 page and on the bitumen enamel grade page; what follows is only what changes when the base grade is 115/15 instead.

Three conditions push a coating specification from 90/15 up to 115/15. The first is product temperature in the line. Where the fluid being carried is warm, the coating sits permanently at an elevated temperature, and a base grade softening at 85 to 95 °C leaves too little headroom once the enamel is also absorbing solar gain at the crown. Softening leads to disbondment, and disbonded coating shields the steel from cathodic protection current — the failure is doubly serious because it disables the backup system at the same time as the primary one. The second is the coating yard and the stockpile. Coated pipe in the Gulf, South Asia or equatorial Africa is routinely stacked outdoors for months; the crown of a dark pipe in direct sun runs far above shade temperature, and enamel that slumps or marks where pipes bear on each other has failed before the line is laid. The third is soil and backfill loading on buried lines, where a harder base resists indentation from stones and clods for the design life of the coating.

What changes operationally is the heat. Enamel blended from a 115/15 base is mixed and applied hotter than enamel from 90/15, which is precisely why pipe-coating plants use closed, indirectly heated, agitated vessels with mechanical extraction rather than the open kettles used on roofs. It also sharpens the field-joint problem that every hot-applied system has: welded joints are coated in the ditch, in worse conditions than the yard, and a material this hard and this hot is far less forgiving of a poor joint procedure than a softer grade. Specify the field-joint system explicitly and do not leave it to be improvised. As always, confirm which document you are buying against — European projects reference EN 10300 and older Middle East, South Asian and African projects still reference BS 4147, and both are formulated-coating standards covering the enamel, the primer and the reinforcement together, not the base bitumen.

Battery sealing compounds

Bitumen-based sealing compounds are used to seal the cover to the container and to seal around the terminal posts in hard-cased batteries. Modern automotive batteries in polypropylene cases are heat-sealed and use no compound at all, so this application now sits mainly in industrial, traction and stationary batteries, in hard-rubber and composite-cased designs, and in rebuild and repair markets — a fact worth knowing before you size an order against optimistic demand estimates.

Where it is used, the requirement set is specific and 115/15 meets it for reasons no softer grade can. The compound must resist dilute sulphuric acid in contact and in vapour. It must remain rigid at elevated temperature, because a battery compartment in service runs hot and a compound that creeps will open the seal or allow the cover to lift. It must tolerate vibration without cracking, which is why the compound is always filled and its formulation carefully balanced rather than being the neat base grade. And it must contain no free water. The base grade is one input to that formulation; the acid resistance, the filler system and the thermal cycling performance are properties of the finished compound, and they must be qualified on the compound rather than assumed from the bitumen specification.

Cable jointing, filling and potting compounds

Bitumen-based filling compounds are poured hot into cable boxes, joint boxes, sealing ends and similar enclosures to exclude moisture and provide insulation. The electrical requirement is straightforward — high volume resistivity, no conductive contamination, and above all no water — but the physical requirement is what makes this application difficult, and it is the point most buyers miss.

Bitumen contracts substantially as it cools. Between a pouring temperature around 200 °C and ambient, the volume reduction is on the order of ten percent. In an open pour that is invisible; in a filled enclosure it means the compound pulls away from the walls and from the conductors and leaves voids and a shrinkage cone at the surface. Voids fill with moist air, moisture condenses in them, and a dielectric failure follows months later at a point nobody can inspect. The countermeasures are formulation and procedure together: a heavy inert filler loading to reduce the shrinkage, pouring in stages with top-up after each stage has cooled, avoiding overheating the compound so it does not enter hotter than it needs to, and pre-warming the enclosure so the compound does not chill against a cold wall and skin over before the void closes.

Two further points belong in the enquiry. First, the base grade designation says nothing about ash content or water content beyond the general specification, and electrical work is sensitive to both — agree limits, name the test methods (ASTM D482 for ash, ASTM D95 for water) and require them on the Certificate of Analysis. Second, much modern electrical practice has moved to epoxy and polyurethane resin systems, so bitumen filling compounds today are largely a question of maintaining existing installations and of markets and equipment designs where the bituminous system remains the specified one. If your requirement is a new installation, confirm with the equipment manufacturer that a bituminous compound is still what the design calls for.

Hard sealing compounds and high-temperature industrial work

The remaining uses share the same logic. Hot-poured sealants and jointing compounds for joints that do not move, tank base and tank chime mastic, chemical-resistant floor jointing in plant areas, protective coatings and linings where ambient or process temperature is elevated, and heavy filled mastics generally. In all of these the material is confined by the geometry it is poured into or is supported by a rigid substrate, and the requirement is a hard, flow-resistant, moisture-excluding solid that will not extrude under load. Where the joint does move, this is the wrong material and no amount of filler will fix it. Formulators also buy 115/15 simply as a hardening fraction, blending it into a softer binder to lift the softening point of a compound to a target the softer grade cannot reach alone.

Do the margin arithmetic before the first vessel is lit

The minimum specified flash point is 250 °C by Cleveland open cup. The working range is 200 to 225 °C. That is a margin of 25 to 50 °C in normal operation, and only 10 to 15 °C at the 235 to 240 °C ceiling. On a grade that melts slowly, in a yard that is behind schedule, that margin is spent by a single failed thermostat, an unread thermometer or a burner left high while a charge comes up. Fit a working temperature readout on every vessel, verify it against a reference thermometer, and do not light a vessel that does not have one. Where the certificate gives the flash point as a measured value above the minimum, use that figure; where it gives only a limit, plan on the limit.

The second ceiling is the producer's finished blowing temperature. Heating blown bitumen above the temperature at which it was manufactured begins to reverse the blowing reaction: the softening point falls, fume rises steeply, and the material darkens and thins. On a hard grade the pressure to exceed it is greatest, because the material takes the longest to become workable.

Water and foam-over remain the leading cause of serious incidents

One volume of water becomes roughly 1,700 volumes of steam. Introduced beneath bitumen at 210 °C it flashes instantly and ejects the contents of the vessel across the working area, and the ejected material is above the temperature at which it will ignite on a hot surface. The routes in are all avoidable: rain into an open vessel, standing water in a drum rim or on a block, condensate in a transfer line, a damp block lowered below the surface of an existing melt, and — the route specific to this grade — damp mineral filler. Filler stored in paper sacks in a humid yard is a routine moisture source that goes straight into the middle of the melt during blending. Store it under cover, confirm it is dry and add it gradually to an agitated melt.

Never use a water jet on a bitumen fire. Keep dry powder or foam extinguishers rated for flammable liquids within reach of every vessel, keep lids closed except when charging, and site vessels on a level non-combustible base clear of the building line, escape routes, combustible storage and gas cylinders. Where local regulation requires hot-work permits and a fire watch after completion, treat those requirements as the minimum rather than the target.

Thermal burns

Hot bitumen adheres to skin and continues to transfer heat after contact, so the injury develops after the splash rather than during it — and material at 210 to 225 °C carries substantially more heat into the tissue than a roofing grade at 180 °C. Cool immediately with copious clean cold running water for at least 20 minutes and continue cooling on the way to medical care. Do not peel, scrape or solvent-strip adhered bitumen from skin. Once cooled it forms a sterile covering, and removing it in the field takes skin with it; removal is a clinical decision. Obtain medical attention for anything beyond a very small splash, and always for burns to the face, hands or eyes.

Fume, dust and exposure control

Fume generation rises steeply with temperature, so a grade worked at 200 to 225 °C generates considerably more than one worked at 180 to 200 °C. 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. That is a reason to control exposure properly rather than to avoid the material. Work upwind, hold the temperature at the low end of the workable range, and use mechanical extraction as standard rather than as an upgrade — enamel blending, compound pots, battery and cable filling and any enclosed pouring operation all concentrate fume in the operator's breathing zone. Wash exposed skin with an approved bitumen hand cleaner rather than solvent.

This grade adds a second exposure route the softer grades do not: dust. Breaking brittle blocks generates fine airborne particulate, so break material outdoors or under extraction and use respiratory protection appropriate to the task. Hydrogen sulphide can also accumulate in the vapour space of any heated bitumen vessel; treat tanks, pits and melters that have held hot product as confined spaces, gas test before entry, and enter only under permit.

Personal protective equipment

• Heat-resistant gauntlets long enough to cover the wrist and forearm, worn outside the sleeve so a splash runs off rather than into the glove.
• Face shield over safety glasses for charging, pouring, decanting and block breaking — this grade fragments as well as splashes.
• Cut-resistant gloves when handling broken blocks, whose fracture edges are sharp.
• Long-sleeved cotton or flame-retardant clothing, loose at neck and cuffs, with no synthetic base layers that melt onto skin.
• Trouser legs worn outside boots, never tucked in.

Storage, packing and container loading

Storage is the easy part of this grade. A softening point of 110 to 120 °C means blocks and bags will not fuse in a container standing in the sun, which is a real problem with the softer blown grades in tropical ports. The packing question is instead about impact: brittle material generates fines when it is dropped, so specify packing that protects against handling rather than against heat, and inspect for excessive breakdown at the point of discharge. Keep packages under cover, off the ground and clear of standing water, and reject any package that has been standing in water — moisture in the packing becomes moisture in the melt.

Typical export packing and loading figures: 25 kg kraft paper bags with a meltable liner, palletised, give roughly 20 MT in a 20-foot container; 25 kg cartons give about 18 to 20 MT; new steel drums of 180 kg net give about 80 drums and 14.4 MT; drums of 150 kg net give about 80 drums and 12 MT; 1 MT jumbo bags give about 20 bags and 20 MT. Exact counts vary with unit dimensions, pallet configuration and destination weight limits. Specify new steel drums explicitly — reconditioned drums are the most common source of contamination disputes, and residue from a previous cargo can put a solubility or ash result out of specification, which matters more here than usual because electrical buyers test for it. Confirm in the contract that drum tare weight is excluded from the invoiced net weight. 115/15 is not moved in bulk tankers: the discharge and tank-heating temperatures a softening point this high would require are beyond what destination terminals are equipped for, and blown material must never share storage with paving bitumen.

The supplier Safety Data Sheet governs in every case, and local hot-works, industrial and confined-space regulations may impose stricter requirements than anything on this page. Read the SDS before the first delivery is opened.