Bitumen Emulsion Grades: Naming, Master Table and Acceptance Limits

The bitumen emulsion overview covers what an emulsion is, how a colloid mill makes one, and why breaking and curing are two different events. This page starts one step later, at the moment a buyer or an engineer has to turn a job into a grade name that a laboratory can test against.

Position 1 — the charge prefix

A leading C means cationic: the emulsifier is a fatty amine neutralised with acid, the droplets carry a positive charge and the finished product is acidic. A designation with no leading letter is anionic: a saponified fatty acid emulsifier, negatively charged droplets, an alkaline product. So CRS-2 and RS-2 are not variants of one another. They are opposite-charge products from two different specifications, they suit different aggregates, and mixing them — even by pumping one through a line still wet with the other — neutralises both charges and coagulates the bitumen on the spot.

This single letter also governs your metallurgy. A cationic emulsion is typically in the region of pH 2 to 4 — a characteristic of the product family rather than a value either ASTM specification puts a limit on — and it attacks aluminium, zinc, galvanised coatings and copper alloys. Mild steel or stainless steel only, from the tank through the pump and valves to the coupling.

Position 2 — the setting class

The setting class states how quickly the grade is formulated to break, and therefore what operation it belongs to:

• RS — rapid setting. Minimally stabilised, designed to break on contact with mineral surfaces. These are spray grades. A rapid-setting emulsion put into a pugmill will break in the mixer.
• MS — medium setting. Stabilised enough to be mixed with coarse, open-graded aggregate and to survive in a stockpile for weeks. These are cold mix grades.
• SS — slow setting. The most heavily stabilised class. Tolerates fine, high surface area material including Portland cement, and is the only class routinely diluted with water. These are tack coat, fog seal and slurry grades.
• QS — quick setting. A fourth class used mainly for micro-surfacing and quick-traffic slurry, where the mixture must stay workable in the machine and yet be trafficable quickly — commonly within about an hour, which is ISSA micro-surfacing practice and a project requirement where it is written in, not a figure set by any ASTM emulsion specification. QS grades sit outside ASTM D977 and ASTM D2397 and are bought against agency or ISSA documents instead.

Position 3 — the grade number

The digit is an index of body and binder content, not a percentage and not a quality ranking. A 2 grade is more viscous and carries more residue than the corresponding 1 grade of the same family. CRS-2 is required to hold a minimum 65 % residue by distillation against 60 % for CRS-1, and its Saybolt Furol viscosity band at 50 °C is 100–400 s against 20–100 s. That is the difference between a binder that stays on a camber under chippings and one that runs off it.

Position 4 — the trailing letter

• h means a harder base binder. The residue of a standard grade penetrates 100–250 dmm at 25 °C under ASTM D2397, or 100–200 dmm under ASTM D977; the residue of an h grade penetrates 40–90 dmm under both. Nothing else about the grade changes — a CSS-1h has the same viscosity band, the same residue minimum and the same cement mixing limit as a CSS-1. Only the binder left on the road is stiffer.
• s, seen on HFMS-2s, indicates a grade containing a solvent fraction.
• HF, placed before the setting class on anionic grades, means high float: a gelling agent produces a thicker, more temperature-tolerant binder film, verified by the float test on the residue.
• P, L or similar trailing letters in agency specifications indicate polymer or latex modification. Neither ASTM D977 nor ASTM D2397 covers modified emulsions, so a designation such as CRS-2P is bought against AASHTO M316 or against the agency specification that defines it.

Two worked examples

CMS-2h reads as cationic, medium setting, the heavier-bodied number 2, harder residue. In plain terms: a positively charged cold-mix emulsion for coarse aggregate, carrying at least 65 % binder, leaving a 40–90 dmm residue suited to a hot climate or heavier traffic. HFMS-2s reads as anionic, high float, medium setting, number 2, solvent-containing — a cold-mix grade with a thick temperature-tolerant film and a solvent fraction that brings a flash point with it.

The trap that catches importers

The prefix rule is an ASTM rule, not a universal one. Under the Indian standard IS 8887, which specifies cationic bitumen emulsions for roads, the grades are written RS-1, RS-2, MS, SS-1 and SS-2 with no C prefix at all — every grade in that standard is cationic by definition of the standard’s scope. An RS-2 on an Indian project document and an RS-2 on an ASTM D977 certificate are opposite charges. Whenever a grade name arrives without a standard number beside it, ask which standard it is written against before you price it.

The division of labour

ASTM D977, Standard Specification for Emulsified Asphalt, covers the anionic family. ASTM D2397, Standard Specification for Cationic Emulsified Asphalt, covers the cationic family. Their AASHTO counterparts are M140 and M208 respectively, and the requirement tables mirror each other closely enough that a laboratory can work from either.

Each specification is built around one requirement table, and that table is split into two halves that answer two different questions.

• Tests on the emulsion — Saybolt Furol viscosity, storage stability, settlement, sieve, demulsibility or cement mixing according to class, particle charge on the cationic side, oil distillate where a solvent fraction is permitted, and residue by distillation. These describe the fluid in the drum: whether it will spray, whether it will separate, and how much binder you are actually buying.
• Tests on the residue from the distillation test — penetration, ductility, solubility, and the float test for the high-float grades. These describe the binder that will still be on the road after the water has gone.

The second half is the one buyers most often skip, and it is the half that decides pavement performance. An emulsion can pass every fluid test and still leave a residue outside the penetration band the specification calls for.

What the standards deliberately do not cover

Neither specification states a storage temperature, a shelf life, an application rate, a dilution ratio or an aggregate compatibility. Neither covers polymer or latex modified emulsions, and neither covers the quick-setting class used in micro-surfacing. Those belong to other documents: AASHTO M316 for polymer-modified cationic emulsified asphalt, and the ISSA recommended performance guidelines — ISSA A105 for slurry seal and ISSA A143 for micro-surfacing — for the surfacing systems themselves. If a purchase order simply says to ASTM D2397 and the job is micro-surfacing, the order is incomplete.

The clause that quietly disappears from certificates

Both standards allow the five-day settlement requirement to be waived by agreement where the emulsion will be used within a short period after delivery. That is a reasonable provision for a domestic supply chain and a poor one for an export shipment, where the material may sit for weeks between load port and site. Settlement is precisely the property an export buyer needs measured. State on the purchase order that the five-day settlement result is required on the batch Certificate of Analysis, and check that it is there rather than assuming the standard supplied it.

Ordering language that works

A complete emulsion order names four things: the grade, the standard and its current edition, the tests required on the batch certificate including any the standard permits to be waived, and the manufacturing date. The last one matters more for emulsion than for any other bitumen product, because emulsion is the one product family whose properties move measurably while it sits in a drum. Sampling for all of it is covered by ASTM D140, and an emulsion sample must be protected from freezing on its way to the laboratory or the result describes the courier, not the cargo.

Reading a grade against a foreign specification

Where a project is written to EN 13808, the emulsion is described by binder content and a breaking-behaviour class rather than by an RS/MS/SS label, and the supporting European test methods are different documents again — EN 1430 for particle polarity, EN 1429 for residue on sieving, EN 1431 for recovered binder and oil distillate, EN 12846 for efflux time in place of Saybolt Furol, and EN 13075-1 for the breaking value that sets the class digit. A CRS-2 tested to ASTM methods does not automatically demonstrate compliance with a C69B3 line in a European bill of quantities. Buy against the standard the engineer will accept.

Most road aggregate is negatively charged in water

Granite, quartzite, rhyolite, siliceous river and pit gravels and most crushed hard rock are siliceous. In contact with water the silanol groups at the mineral surface lose protons, and the surface carries a net negative charge across the whole range of pH values encountered on a road job. Carbonate rock — limestone and dolomite — behaves differently and presents a surface that is electropositive or close to neutral.

A cationic emulsion droplet carries a positive charge. Presented to a negatively charged aggregate surface, it is electrostatically attracted to it. The amine head of the emulsifier is adsorbed onto the mineral, the charge that was holding the droplets apart is stripped away, and the droplets coalesce onto the stone. An anionic droplet presented to the same stone is negatively charged as well, and like charges repel: nothing pulls the binder onto the aggregate, so the break has to wait for water to leave by evaporation.

Three consequences follow, and all three are commercial

• Speed and predictability. A chemically driven break happens in seconds to minutes and is far less dependent on humidity, wind and ambient temperature. An evaporation-driven break is a weather forecast. On a chip seal, that difference decides whether traffic returns the same afternoon.
• Resistance to stripping. The bond formed by an adsorbed cationic emulsifier survives water far better than a bond that formed only because the water dried out. Stripping — loss of adhesion between binder and aggregate in the presence of water — is the dominant durability failure of surface treatments in wet climates, and it is the reason the adhesion and anti-stripping question sits behind every emulsion selection.
• Tolerance. Cationic grades work acceptably on limestone and basic aggregate as well, and they cope better with stone that is damp or lightly dusty. Anionic grades are more particular. Where the aggregate source is not fully known in advance — a common situation on export projects — the cationic grade is simply the lower-risk purchase.

Where anionic grades still belong

Anionic emulsions retain a real place. Where limestone or dolomite dominates the local supply, the charge argument reverses and an anionic grade bonds well. The high-float HFMS family has properties — a thick, temperature-tolerant binder film verified by the float test — that have no direct cationic equivalent, which keeps them in cold-mix and seal-coat specifications in some markets. And a long-standing project specification that names SS-1 or RS-2 should be supplied as written, not substituted because the cationic version is more available.

Two things the charge argument does not mean

First, a cationic emulsion is not an anti-stripping additive. The charge chemistry works at the emulsion-to-aggregate interface in a cold-applied operation; it does nothing for the adhesion of a hot binder in a hot mix, which is a separate problem solved with a separate product. Second, charge affinity does not excuse dirty stone. Clean, correctly graded aggregate is still the first requirement of any seal, and dust on the chippings will defeat a cationic emulsion as reliably as it defeats an anionic one.

The equipment consequence

Because the cationic family is acidic, everything the emulsion touches must be mild steel or stainless steel. Aluminium couplings, brass valves, galvanised fittings and zinc-coated pipework corrode, and the dissolved metal ions destabilise the emulsion as they go — so the first symptom is often a failed sieve test rather than a visible leak. Buyers commissioning second-hand tankage for their first emulsion consignment should audit the wetted materials before the cargo arrives, not after the first batch coagulates.

Residue by distillation — ASTM D6997, and the binder you are actually buying

A measured sample is distilled in an iron still to 260 °C and held there, and the residue is weighed. The test does two jobs at once: it reports what proportion of the delivered mass is actually binder, and it produces the residue on which penetration, ductility and solubility are then run.

This is the most commercially significant line on the certificate, and it deserves arithmetic rather than a glance. A 20 MT parcel of CRS-2 at the 65 % minimum contains at least 13.0 MT of binder. The same 20 MT of CSS-1 at the 57 % minimum contains at least 11.4 MT. That is 1.6 MT of binder difference on one container, before anyone discusses price per tonne. On the road the same arithmetic decides spray rate: an emulsion delivered at 60 % residue against a specified 65 % puts roughly eight percent less binder down at the same litres per square metre, and a chip seal short of binder loses chippings.

Where the emulsion is polymer modified, distillation at 260 °C degrades the polymer and the residue is no longer representative. ASTM D7497, the low-temperature evaporative recovery practice, is the alternative, and ASTM D6934 covers residue by evaporation for unmodified products where the specification permits it.

Saybolt Furol viscosity — ASTM D7496, and why the test temperature changes with the grade

The time in seconds for 60 mL of emulsion to flow through the Furol orifice. The test temperature is grade specific: 25 °C for the thinner grades — CSS-1, CSS-1h, SS-1, SS-1h, RS-1 and MS-2 — and 50 °C for the heavier-bodied CRS-1, CRS-2, RS-2, CMS-2 and CMS-2h. Viscosity governs whether the emulsion sprays as an even fan and stays where it lands. Too thin and it runs off the camber and pools in the wheel paths; too thick and the bar atomises badly and lays a ropey striped pattern. It is also the first property to shift when an emulsion has been stored badly, so an out-of-band result on an aged consignment is a warning about the whole lot.

Sieve test — ASTM D6933, the one limit that is identical for every grade

The emulsion is washed through an 850 µm (No. 20) sieve and the retained coagulum is weighed against a maximum of 0.10 % by mass for every grade in both standards. What it finds is bitumen that has already merged into lumps: material that blocks nozzles, filters and pumps. It is the cheapest test on the list, it takes very little time, and it is the correct first check on drums that have stood on a quay or in a yard. Run it before you plan a day’s spraying, not after the spray bar blocks.

Particle charge — ASTM D244, the test that proves the leading C

Two electrodes, a direct current, and an observation of which one the bitumen deposits on. Migration to the cathode means positively charged droplets and the result is reported positive: the product is cationic. It is the only test that proves the family, and it is the one to insist on from a new source, because the difference between CRS-2 and RS-2 is invisible in the drum and catastrophic in the tank. ASTM D7402 is the corresponding practice for identifying cationic emulsified asphalts. For anionic products the equivalent identity check is pH, which should come back alkaline.

Settlement and storage stability — ASTM D6930, and the clause an export buyer must reinstate

Both measurements compare residue content at the top and the bottom of a graduated cylinder: 24-hour storage stability, typically limited to 1 %, and five-day settlement, typically limited to 5 %. Bitumen droplets are slightly denser than water and drift downward given time, so these results predict what a stack of drums or an unagitated tank will look like at destination. Remember that the settlement requirement can be waived by agreement in both standards; for export it should be reinstated on the purchase order.

The three tests that define the setting classes

• Demulsibility (ASTM D6936) quantifies how eagerly a grade breaks, and it is the defining test of the rapid-setting class. The cationic rapid grades are tested with sodium dioctyl sulfosuccinate solution against a minimum of 40 %; the anionic rapid grades with 0.02 N calcium chloride solution against a minimum of 60 %. Demulsibility on an SS grade certificate is meaningless — the property is not required and not wanted.
• Cement mixing (ASTM D6935) is the defining test of the slow-setting class. The emulsion is mixed with high surface area Portland cement and the coagulum retained on the sieve must not exceed 2.0 %. It is the direct proof that the grade can survive contact with fines, which is what makes slurry seal and micro-surfacing possible. A CSS-1h that fails cement mixing will flash-set in the slurry machine.
• Coating ability and water resistance (ASTM D244) is the medium-setting class check: whether the grade coats reference aggregate, and whether the coating survives a water wash. It is what separates a genuine cold-mix grade from a spray grade with the wrong label.

The tests run on the recovered residue

These describe the binder that will actually be in the pavement, and they are the lines an engineer will look at first. Penetration at 25 °C to ASTM D5 is what separates a standard grade from an h grade, and it is the number to check when the specification calls for a harder residue in a hot climate. Ductility to ASTM D113, minimum 40 cm, confirms the residue has the cohesion to tolerate pavement movement. Solubility in trichloroethylene to ASTM D2042, minimum 97.5 %, confirms the binder is genuine bitumen rather than extended material. The float test to ASTM D139 applies only to the high-float grades under ASTM D977 and is the requirement that gives the HF family its name. Where the emulsion is polymer modified, softening point by ASTM D36 and elastic recovery on the recovered binder are normally added, since the polymer is the reason for the premium. Further detail on each of these sits on the bitumen test methods page.

The rule that admits no exception: it must never freeze

The continuous phase is water. Below 0 °C ice crystals grow through the emulsion and mechanically rupture the emulsifier films around the droplets. The droplets merge, and what thaws is a layer of coagulated bitumen under a layer of dirty water. The change is irreversible. No amount of heating, stirring or recirculation restores it, and no grade — cationic or anionic, rapid or slow, 1 or 2, h or standard — is exempt.

The practical floor is not 0 °C but about 4 °C, and the reason is measurement rather than chemistry. The coldest part of a consignment is never the part anybody measures: the windward drum in a stack, the top of a part-filled tank, the outer container in a stow and the drum standing on cold concrete all run below the bulk. A four-degree margin covers the gap between the thermometer and the worst-off drum.

Because the rule is absolute, it is a grade-selection question as well as a logistics one: there is no colder-climate grade to switch to. Insulated or heated storage for a winter destination is arranged before the cargo sails. The handling and hazard detail for emulsion generally — heating equipment, agitation, contamination and the physical risks — is set out on the emulsion overview and is not repeated here.

Upper limits differ by grade, and the grade name tells you which window applies

Above roughly 85 °C the water begins to flash off at the surface, a skin forms, the emulsion thickens and eventually breaks. The heavier-bodied rapid and medium grades are formulated to be handled warm and tolerate the top of the range; the thinner slow-setting grades are not. Typical recommended storage windows, which are manufacturer guidance and common practice rather than requirements of ASTM D977 or ASTM D2397:

• CRS-1, CRS-2, RS-2, CMS-2, CMS-2h — about 50 to 85 °C
• RS-1 — about 20 to 60 °C
• CSS-1, CSS-1h, SS-1, SS-1h, MS-2 — about 10 to 60 °C
• Every grade without exception — never below about 4 °C

Confirm the window against the supplier’s data sheet for the grade actually delivered. Where the two disagree, the data sheet governs.

The two storage points that are grade-driven rather than general

• Warming a heavy grade is normal; warming a thin one is not. The 50 to 85 °C window belongs to the rapid and medium grades that are formulated to be handled warm. Applying it to a CSS-1h or an SS-1 because the tank happens to be set that way will skin and thicken the product. The grade name tells you which window applies, so check the label before you set the thermostat.
• The cationic family dictates the metallurgy of the whole storage train, as set out under the charge chemistry above: mild or stainless steel from tank to coupling, and never a shared tank, line or pump with an anionic grade. This is the one storage decision that changes when the grade prefix changes.

Heating equipment, coil surface loading, agitation practice, contamination and drum stacking apply identically to every grade and are covered on the emulsion overview and the bitumen storage tanks page.

Two hazards that the grade designation itself warns you about

• Any grade discharged into a hot vessel is a steam hazard. The carrier is water and water flashing to steam expands more than a thousandfold. Emulsion of any designation pumped into a tank, line or tanker still above 100 °C, or onto a residue of hot binder, can eject the contents through the hatch. Confirm every receiving vessel is cool, drained and free of hot bitumen before transfer, and never steam-clean a line into a live emulsion tank.
• The medium-setting grades carry a flash point; the slow-setting grades do not. Because ASTM D2397 permits up to 12 % oil distillate by volume in CMS-2 and CMS-2h, and up to 3 % in the CRS grades, those designations contain a solvent fraction and bring a vapour and fire hazard with them. Read the flash point on the batch documentation and the Safety Data Sheet before heating a CMS product, and treat it as you would a solvent-containing material: no open flame or hot work at the tank, and bonded and earthed transfers. An anionic HFMS-2s carries the same warning in its trailing s.

Every storage abuse shows up in a test you already have

This is the practical value of the acceptance test list: it doubles as a diagnostic set. If a consignment behaves badly on site, the tests tell you what happened to it.

• A sieve result (ASTM D6933) that has climbed since the batch certificate means droplets have already coalesced — from freezing, from overheating, from contamination or simply from age.
• A viscosity result (ASTM D7496) that has moved out of band points to water loss at the surface or the beginning of a break.
• A settlement result (ASTM D6930) outside limits means the material has stood unagitated too long; gentle recirculation may recover it, and a failed sieve test alongside it means it will not.
• A particle charge result (ASTM D244) that contradicts the label means the wrong product was loaded, or the tank or line held the other family.

Shelf life is not a grade property

Neither ASTM D977 nor ASTM D2397 sets a shelf life, and no grade in either standard is formulated to last longer than another. Practical life depends on how the material was kept rather than on which designation is on the drum, which is why the manufacturing date belongs on the certificate and a fresh sieve test belongs on any aged consignment. The product-family view is on the shelf life and storage page.

Application rates: what can and cannot be stated in advance

Rates belong to the project specification, the surface condition and a trial section, not to a supplier page. Two points are established industry practice rather than specification requirements, and they are safe to plan against: slow-setting grades for tack coat and fog seal are commonly diluted 1:1 with clean potable water, and rapid-setting grades for chip seal are never diluted. The arithmetic that follows from dilution is worth doing before the truck arrives. Take a CSS-1h at its ASTM D2397 minimum of 57 % residue: cut 1:1, the diluted material carries roughly 28 to 29 % residue, and emulsion density is close to 1.0 kg per litre. Spraying it at 0.40 litres per square metre — a mid-band figure from typical tack-coat practice, used here purely to demonstrate the calculation and not as a rate for any particular job — therefore places in the order of 0.11 kg of residual binder per square metre. Work in residual binder, agree the rate with the engineer, and confirm it on a trial section with the actual emulsion and the actual surface. Indicative spray rates by operation are tabulated on the bitumen emulsion overview, and the tack-versus-prime decision is covered on prime coat vs tack coat.

• CRS-2 — the workhorse of chip seal and surface dressing, and what makes the break succeed or fail
• CSS-1 and CSS-1h — the slow-setting counterpart, dilution arithmetic, and where tack coats go wrong
• Surface dressing and chip seal — where the rapid-setting grades are used, and why the setting speed is the whole design
• Slurry seal and micro-surfacing — where the slow-setting and quick-setting grades go, and what micro-surfacing adds