An emulsion is not a chemically different bitumen. It is ordinary paving bitumen torn into microscopic droplets and kept apart in water by a surfactant, so that a material which is effectively solid at ambient temperature can be sprayed cold.
Take a paving binder such as bitumen 60/70. At 25 °C it will not pour, will not spray and will not coat an aggregate. Three routes make it usable, and each buys fluidity in a different currency. Thermal energy: take the binder up to hot-mix temperature and pay for the fuel, the plant and the fume control. Solvent: thin it with a petroleum distillate that must later evaporate to atmosphere, which is a cutback bitumen. Water: tear the binder into droplets and float them in a water phase, which is an emulsion. Only the third route uses a carrier that is free, non-flammable and harmless when it leaves the pavement, which is why emulsion has taken over most cold-applied work.
In an emulsion the continuous phase is water and the bitumen is the dispersed phase. The droplets are typically 1 to 20 micrometres across, with most of the volume between 1 and 10 µm — small enough that gravity alone separates them only slowly. What stops them merging is the emulsifier, a surfactant molecule with a hydrocarbon tail that buries itself in the bitumen droplet and a charged head that sits out in the water. Every droplet ends up wearing the same electrical charge, and like charges repel. That mutual repulsion is the only thing holding the product together, which is the single most important fact about handling it.
The bitumen fraction — the residue — is normally 55 to 70 % by mass depending on grade. The rest is water, a fraction of a percent to a few percent of emulsifier, an acid or an alkali to activate the emulsifier, and in some grades a small oil distillate fraction. Because the fluid is mostly water it has roughly the density of water, a viscosity anywhere between that of thin cream and thick paint, and no meaningful fire risk in its own right.
An emulsion does its job by failing in a controlled way. When it is sprayed onto a road surface or mixed with aggregate, the emulsifier is stripped off the droplets and adsorbed onto the mineral surface, the electrostatic repulsion collapses, and the droplets coalesce into a continuous bitumen film. That is breaking, and it is visible from the truck: the material turns from brown to black.
Water is then expelled from the film and evaporates, and the binder develops its cohesion and its bond to the substrate. That is setting or curing, and it is what actually produces strength. The two are often confused in the field, with expensive results. A chip seal can break within seconds and still not be ready for traffic for an hour or more. A slurry seal can look black long before the water has gone. Break tells you the emulsion has committed; cure tells you the pavement is ready.
The distinction also separates an emulsion from a cutback. A cutback cures only — the solvent evaporates over hours to weeks and becomes an atmospheric hydrocarbon emission. An emulsion breaks chemically first and then loses water vapour. That is why emulsions have displaced cutbacks in most modern specifications: the carrier is free, non-flammable and environmentally inert.
Bitumen at roughly 120–150 °C and a water phase — the soap solution, water at roughly 30–70 °C carrying the emulsifier plus acid or alkali — are metered together into a high-shear colloid mill. A rotor turning at several thousand rpm inside a fixed stator, with a clearance of a fraction of a millimetre, shears the bitumen stream into droplets while the emulsifier stabilises each new surface as it is created.
The controlling constraint is temperature. The two feed streams have to be balanced so that the mill discharge stays below the boiling point of water, typically below about 90 °C, or the product flashes to steam in the mill. Where a hard base binder or a polymer-modified binder forces a higher bitumen temperature, the system is run under back pressure so the discharge can exceed 100 °C without boiling.
Grade designations such as CRS-2 or CSS-1h are performance envelopes, not recipes. Within the same designation a manufacturer chooses the base binder hardness, the emulsifier chemistry and dose, the acid dose and final pH, the water quality, the mill gap and the throughput. Two compliant CRS-2 emulsions from two plants can break at noticeably different speeds on the same aggregate. This is why an experienced contractor runs a trial section with the actual emulsion and the actual aggregate before committing a day's production, and why the manufacturing date and batch number on the Certificate of Analysis matter more for emulsion than for any other bitumen product.
Everything about an emulsion — which aggregate it will stick to, what metal you can store it in, and what it must never be mixed with — follows from the sign of the charge on the droplet.
In a cationic emulsion the droplets carry a positive charge. The emulsifier is a fatty amine — a diamine, an amido-amine, an imidazoline or a quaternary ammonium compound — neutralised with hydrochloric acid, so the finished emulsion is acidic, typically around pH 2 to 4.
Most road aggregates are electronegative in water: granite, quartzite, siliceous river and pit gravels, and most crushed hard rock present a negatively charged surface. Opposite charges attract. The positively charged droplet is pulled onto the aggregate, the emulsifier anchors there, and the break is driven by chemistry rather than by waiting for water to evaporate. Two things follow. The break is fast and predictable, and the bond that results is resistant to stripping by water — which is precisely the failure mode that ruins surface treatments in wet climates.
Cationic emulsions also work acceptably on limestone and other basic aggregates, so they are the safer default whenever the aggregate source is not fully known in advance. That combination of speed, water resistance and tolerance is why cationic emulsions dominate world trade and why almost every modern national specification is written around them.
The acidity has a practical consequence that catches out buyers with second-hand tankage: a cationic emulsion attacks zinc, aluminium and copper alloys. Tanks, pipework, pumps, valves and drums must be mild steel or stainless steel. Galvanised fittings, aluminium couplings and brass valves will corrode, and the dissolved metal ions will destabilise the emulsion in the process.
In an anionic emulsion the droplets carry a negative charge. The emulsifier is a fatty acid — tall oil fatty acid is the classic example — saponified with sodium or potassium hydroxide, so the emulsion is alkaline, typically around pH 10 to 12.
Negatively charged droplets bond well to electropositive aggregate: limestone, dolomite and some basic igneous rock. On siliceous aggregate both surfaces are negative and they repel each other, so the break depends far more on evaporation than on chemistry. That makes anionic emulsions slower, more weather-dependent and more vulnerable to rain shortly after application. They remain in use where limestone aggregate dominates the local supply, in high-float cold-mix work, and wherever a long-standing project specification names them.
Never mix the two families. Adding a cationic emulsion to an anionic one — or simply pumping one through a line that still holds a film of the other — neutralises both charges and coagulates the bitumen instantly. Changing charge type means flushing every tank, line, pump and hose properly first, not rinsing them.
An emulsion grade name is a compact technical description. Read it in four parts:
Two further markers appear on anionic products. HF in HFMS-2 and similar means high float — the emulsion contains a gelling agent that leaves a thicker, more temperature-tolerant binder film, verified by the float test. A trailing s, as in HFMS-2s, indicates the grade contains a solvent fraction.
The ASTM designation is not universal. Under EN 13808, a European cationic emulsion is described in the form C60B4: C for cationic, 60 for the binder content in percent by mass, B for bitumen (BP where the binder is polymer modified), and the final digit for the breaking-behaviour class determined by EN 13075-1, running from rapid to slow. In India, IS 8887 covers cationic emulsions with its own rapid, medium and slow setting designations. AASHTO M208 mirrors ASTM D2397 and AASHTO M140 mirrors ASTM D977. These are parallel classification systems, not translations of each other — a CRS-2 does not automatically satisfy a specification written as C69B3, and where a project names a European or Indian designation, buy against that standard.
The eleven grades below cover the great majority of traded emulsion. The first six are cationic under ASTM D2397, the last five anionic under ASTM D977. The dilution column matters commercially: a grade that is normally diluted on site goes further, since a drum cut 1:1 with water yields roughly twice its own volume of sprayable material — but it also delivers only about half as much binder per litre sprayed, so the application rate has to be doubled to put the same residue on the road.
| Grade | Standard | Charge | Setting speed | Typical application | Normally diluted? |
|---|---|---|---|---|---|
| CRS-1 | ASTM D2397 | Cationic | Rapid | Light chip seals, sand seals, and spray work where a very fast break is needed | No |
| CRS-2 | ASTM D2397 | Cationic | Rapid | Chip seal, single and double surface dressing — the principal spray-seal grade worldwide | No |
| CMS-2 | ASTM D2397 | Cationic | Medium | Cold plant mix and stockpile patching with coarse, open-graded aggregate | No |
| CMS-2h | ASTM D2397 | Cationic | Medium | As CMS-2 where a harder residue is wanted for hot climates or heavier traffic | No |
| CSS-1 | ASTM D2397 | Cationic | Slow | Tack coat, fog seal, prime on tight surfaces, soil and granular base stabilisation | Yes — commonly 1:1 with water |
| CSS-1h | ASTM D2397 | Cationic | Slow | Tack coat and slurry seal; the default slurry-seal and tack-coat grade in hot climates | Diluted for tack coat; used neat for slurry seal |
| RS-1 | ASTM D977 | Anionic | Rapid | Sand seals and light surface treatment on electropositive aggregate | No |
| RS-2 | ASTM D977 | Anionic | Rapid | Chip seal and surface dressing where limestone or basic aggregate is used | No |
| MS-2 | ASTM D977 | Anionic | Medium | Cold plant mix and patching mixes with coarse aggregate | No |
| SS-1 | ASTM D977 | Anionic | Slow | Tack coat, fog seal, dust control and soil stabilisation | Yes — commonly 1:1 with water |
| SS-1h | ASTM D977 | Anionic | Slow | Tack coat and slurry seal where a harder residue is specified | Diluted for tack coat; used neat for slurry seal |
These are the typical published requirements for each grade under ASTM D2397 (cationic) and ASTM D977 (anionic), together with the test method that produces each value. The Saybolt Furol test temperature is not the same for every grade, so it is stated in the cell rather than in the heading.
| Grade | Saybolt Furol viscosity, SFS (ASTM D7496) | Residue by distillation, min wt % (ASTM D6997) | Residue penetration at 25 °C, dmm (ASTM D5) | Sieve, max wt % (ASTM D6933) | Defining identity test |
|---|---|---|---|---|---|
| CRS-1 | 20–100 at 50 °C | 60 | 100–250 | 0.10 | Particle charge positive (ASTM D244); demulsibility min 40 % |
| CRS-2 | 100–400 at 50 °C | 65 | 100–250 | 0.10 | Particle charge positive (ASTM D244); demulsibility min 40 % |
| CMS-2 | 50–450 at 50 °C | 65 | 100–250 | 0.10 | Particle charge positive; coating ability and water resistance |
| CMS-2h | 50–450 at 50 °C | 65 | 40–90 | 0.10 | Particle charge positive; coating ability and water resistance |
| CSS-1 | 20–100 at 25 °C | 57 | 100–250 | 0.10 | Particle charge positive; cement mixing max 2.0 % (ASTM D6935) |
| CSS-1h | 20–100 at 25 °C | 57 | 40–90 | 0.10 | Particle charge positive; cement mixing max 2.0 % (ASTM D6935) |
| RS-1 | 20–100 at 25 °C | 55 | 100–200 | 0.10 | Demulsibility min 60 % with 0.02 N calcium chloride (ASTM D6936) |
| RS-2 | 75–400 at 50 °C | 63 | 100–200 | 0.10 | Demulsibility min 60 % with 0.02 N calcium chloride (ASTM D6936) |
| MS-2 | min 100 at 25 °C | 65 | 100–200 | 0.10 | Coating ability and water resistance (ASTM D244) |
| SS-1 | 20–100 at 25 °C | 57 | 100–200 | 0.10 | Cement mixing max 2.0 % (ASTM D6935) |
| SS-1h | 20–100 at 25 °C | 57 | 40–90 | 0.10 | Cement mixing max 2.0 % (ASTM D6935) |
An emulsion Certificate of Analysis is short, and every line on it protects against a specific failure. These are the tests worth insisting on, and what each one is really telling you.
A measured sample is distilled in an iron still and taken to 260 °C, held for 15 minutes, and the residue is weighed. The result does two jobs. It tells you what proportion of the tonne you bought is actually bitumen, and it produces the residue itself so that penetration, ductility and solubility can be run on the binder that will end up in the road.
This is the most commercially important line on the certificate. You are buying the residue, not the water. A CRS-2 delivered at 60 % rather than the 65 % minimum means five percent more water in every tonne and a spray rate that must be corrected upward to put the same residual binder on the road. If the correction is not made, the seal is under-binder and it will lose chippings. Where the emulsion is polymer modified, note that distillation at 260 °C degrades the polymer, so a low-temperature evaporative recovery is used instead and the recovered binder is tested for elastic recovery and softening point. ASTM D6934 residue by evaporation is the alternative route for unmodified products.
The time in seconds for 60 mL of emulsion to flow through the Furol orifice, reported as Saybolt Furol seconds. The test temperature depends on the grade: 25 °C for the lighter grades such as CSS-1, SS-1, RS-1 and MS-2, and 50 °C for heavier bodied grades such as CRS-1, CRS-2, RS-2, CMS-2 and CMS-2h.
Viscosity is what determines whether the emulsion sprays as a uniform fan and stays where it lands. Too thin, and it runs off the camber, streaks and pools in the wheel paths. Too thick, and the spray bar atomises badly and lays a ropey, striped pattern that shows through the finished surface. Viscosity is also the first property to shift when an emulsion has been stored badly, so an out-of-range result on an aged drum is a warning about the whole consignment.
The emulsion is washed through an 850 µm (No. 20) sieve and the retained material is weighed; the limit is a maximum of 0.10 % by mass. What it detects is coagulated bitumen — droplets that have already merged into lumps. Those lumps block spray-bar nozzles, filters and pumps, and the presence of any significant quantity means the emulsion has already begun to break, whether from freezing, overheating, contamination or simple age.
It is the cheapest test on the list and the fastest way to find out whether drums that have been standing on a quay for two months are still usable. Run it before you plan a day's spraying, not after the bar has blocked.
Two electrodes are placed in the emulsion and a direct current is passed between them. If the bitumen migrates to and deposits on the cathode, the droplets are positively charged and the result is reported as positive — the emulsion is cationic. It is the test that proves the product is the family the label claims, and it is the one to insist on when buying from a new source. For anionic emulsions the corresponding identity check is pH, also covered by ASTM D244; an alkaline result is expected.
Two related measurements, both comparing the residue content at the top and the bottom of a graduated cylinder: five-day settlement, typically limited to a maximum of 5 %, and 24-hour storage stability, typically limited to a maximum of 1 %. Bitumen droplets are slightly denser than water and will drift downward given time, and these tests predict what will happen to a tank or a stack of drums that stands unagitated at the destination.
Be aware that both ASTM D2397 and ASTM D977 allow the five-day settlement requirement to be waived by agreement when the emulsion is to be used within a short period after delivery, so it is a line that quietly disappears from some certificates. For an export shipment it is exactly the line you should insist on, because the material may sit for weeks between loading and use. Ask for the result on the batch certificate rather than the generic figure from the technical data sheet.
A destabilising chemical solution is added to a measured quantity of emulsion and the proportion of bitumen that coagulates is measured. It quantifies how eagerly the emulsion breaks. For the cationic rapid-setting grades the reagent is 35 mL of 0.8 % sodium dioctyl sulfosuccinate solution and the requirement is a minimum of 40 %; for the anionic rapid-setting grades it is 35 mL of 0.02 N calcium chloride solution with a minimum of 60 %.
A high demulsibility is exactly what a chip seal requires and exactly what a cold mix must not have. Reading demulsibility on an MS or SS grade certificate makes no sense — the corresponding checks there are the coating tests and the cement mixing test.
Applied to slow-setting grades. The emulsion is mixed with high-surface-area Portland cement and the coagulum retained on a 1.4 mm sieve must not exceed 2.0 %. It is the direct proof that the emulsion is stable enough to be mixed with very fine material, which is the property that makes slurry seal and micro-surfacing possible at all. If a CSS-1h fails cement mixing, it will flash-set in the slurry machine.
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 at 25 °C 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. Further reading on all of these is on the bitumen test methods page.
Emulsion covers almost every bituminous operation that is not hot mix. Each application demands a different setting class, and using the wrong one is the most common cause of failure on site.
A thin bond film sprayed between an existing surface and a new asphalt layer. Slow-setting grades — CSS-1h, CSS-1, SS-1h, SS-1 — diluted with water so a very light residual rate can be spread uniformly. A missing or over-applied tack coat is a leading cause of premature delamination and slippage cracking.
Applied to a compacted granular base to bind the surface fines and promote adhesion to the layer above. Emulsion primes use diluted slow-setting grades or purpose-formulated penetrating primes. On very tight bases a kerosene-cut MC grade still penetrates better, which is why cutback prime survives in specifications where emulsion has replaced everything else.
The classic emulsion job. CRS-2 is sprayed on the road, chippings are spread and rolled into the binder while it breaks, and traffic is returned once it has cured. Fast break is essential, aggregate must be clean and dry, and the emulsion must be used neat — dilution ruins the binder film thickness.
A cold mixture of graded aggregate, water, filler and slow- or quick-setting emulsion, spread by a paving box in a thin layer. CSS-1h is the standard slurry-seal grade; micro-surfacing uses a polymer-modified quick-setting cationic emulsion so the mat carries traffic within an hour and can fill ruts.
CMS-2 and CMS-2h coat coarse open-graded aggregate and stay workable long enough to be stockpiled, transported and placed weeks later. This is the material for pothole repair, shoulder work and maintenance in locations far from a hot mix plant.
A heavily diluted slow-setting emulsion sprayed over an oxidised surface to seal fine cracks, restore surface binder and arrest ravelling. The same principle at heavier dilution binds dust on unsealed roads, haul roads and shoulders.
The figures below are typical starting points used to plan quantities and to sanity-check a specification. Actual rates come from the project specification, the condition and texture of the surface, and a trial section run with the material that will actually be used.
| Operation | Usual grades | Dilution | Typical application rate | Typical spray or mix temperature |
|---|---|---|---|---|
| Tack coat | CSS-1h, CSS-1, SS-1h, SS-1 | Commonly 1:1 with water | 0.20–0.60 l/m² of diluted emulsion, giving roughly 0.06–0.18 kg/m² of residual binder | 20–60 °C |
| Prime coat | CSS-1, SS-1 or a penetrating prime emulsion | 1:1 or as specified | 0.70–1.50 l/m² depending on how open the base is | 20–60 °C |
| Fog seal | CSS-1, SS-1 | 1:1 up to about 1:3 | 0.30–0.90 l/m² of diluted emulsion | 20–60 °C |
| Chip seal / single surface dressing | CRS-2 (CRS-1 or RS-2 for light work) | Never diluted | 1.0–2.0 l/m² of emulsion with roughly 8–14 kg/m² of chippings for nominal 6–14 mm aggregate | 50–85 °C |
| Slurry seal | CSS-1h, SS-1h | Never diluted | Emulsion roughly 6.5–16 % by mass of dry aggregate depending on ISSA type — about 10–16 % for the fine Type I and 6.5–12 % for the coarse Type III; mixture spread roughly 3–16 kg/m² over the same range of types | 10–60 °C |
| Micro-surfacing | Polymer-modified quick-setting cationic emulsion | Never diluted | Mixture typically 8–20 kg/m² depending on layer and whether ruts are being filled | 10–60 °C |
| Cold mix and stockpile patching | CMS-2, CMS-2h | Never diluted | Emulsion typically 4–7 % by mass of aggregate, set by mix design | 50–85 °C |
An emulsion is a metastable product. It is held together by nothing more than electrostatic repulsion between droplets, and freezing, overheating, the wrong metal or a violent pump will overcome that repulsion permanently. These rules are not conservative advice — they are the difference between usable and scrap.
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 on thawing what you have is a layer of coagulated bitumen under a layer of dirty water. The change is irreversible — no amount of heating, stirring or recirculation will restore it.
The practical floor is not 0 °C but about 4 °C, because the coldest part of a consignment is never the part you measure. A drum on the windward side of a stack, the top of a partly filled tank, the outer container in a stow: these run colder than the bulk. Emulsion consigned to a winter destination needs insulated or heated storage arranged before the cargo arrives, and it should not be left standing on an open quay in a cold month. This is the single most common way an emulsion shipment is lost, and it usually happens after the material has been accepted.
Above roughly 85 °C water begins to flash off at the surface, a skin forms, the emulsion thickens and eventually it breaks. Typical recommended storage ranges are:
Heat only with low-intensity, fully submerged hot oil or steam coils. Never use a direct flame against a tank or drum wall, and never use a bare electric element. A high surface loading boils the water film against the coil, and the emulsion breaks locally and cakes onto the heating surface, which then heats even harder. Circulate gently before applying heat so hot spots cannot develop, and follow the tank builder's stated maximum coil surface loading.
Bitumen droplets are slightly denser than water, so an emulsion left standing for weeks develops a richer bottom and a leaner top. Gentle recirculation every few days keeps it uniform. The word gentle is doing real work here. High-shear pumping, cavitation, and returning the emulsion into the tank above the liquid level all entrain air and shear droplets, and both destabilise the product. Return lines must discharge below the liquid surface. A centrifugal pump run against a closed valve will break a tank of emulsion in minutes.
Emulsion is not a flammable liquid the way a cutback is, but it carries hazards of its own and they are frequently underestimated.
Emulsion is normally packed in nominal 200 litre steel drums with headspace left for expansion, in 1000 litre IBCs, or shipped in road tankers and insulated ISO tank containers. Density is close to 1.0 kg/l, but the drum is deliberately not filled to the brim, so a nominal 200 litre drum normally carries around 180–195 kg net rather than a full 200 kg. A 20-foot container takes about 80 drums, as it does for any drummed bitumen; confirm the exact net fill weight on the packing list and check it against the container payload limit before booking. Bitumen emulsions are commonly not classified as dangerous goods for sea freight, but the classification follows the specific formulation — confirm it against the Safety Data Sheet for the grade you are buying before you book the shipment, particularly for solvent-containing medium-setting grades.
Be realistic about shelf life. Drummed penetration grade bitumen stays serviceable for years; an emulsion does not. Its practical life is weeks to a few months, and it shortens with every temperature excursion. Plan the voyage and the destination storage so the material is used soon after arrival, insist that the manufacturing date and batch number appear on the Certificate of Analysis, and run a sieve test before committing an aged consignment to a day's spraying.
It is paving bitumen broken into droplets of roughly 1 to 20 micrometres and suspended in water, with a surfactant emulsifier on each droplet to keep them apart. Because the continuous phase is water, the product sprays and pumps cold. When it contacts aggregate the emulsifier is adsorbed onto the mineral surface, the droplets coalesce and the emulsion breaks; the water is then expelled and evaporates, leaving a continuous bitumen film. Bitumen content is typically 55 to 70 % by mass, measured as residue by distillation to ASTM D6997.
The sign of the charge on the droplets. Cationic emulsions (ASTM D2397) use an amine emulsifier neutralised with acid, the droplets are positively charged and the product is acidic at around pH 2 to 4. Anionic emulsions (ASTM D977) use a saponified fatty acid, the droplets are negatively charged and the product is alkaline at around pH 10 to 12. Most road aggregates are electronegative, so the positively charged cationic droplet is attracted to the aggregate and bonds quickly and water-resistantly. That is why cationic emulsions dominate the world market. Anionic emulsions work best on limestone and other electropositive aggregate. The two must never be mixed or run through the same unflushed equipment.
They are setting speeds: rapid setting, medium setting and slow setting. Rapid-setting grades break almost on contact and are meant to be sprayed, not mixed — chip seals and surface dressing. Medium-setting grades are stabilised enough to be mixed with coarse aggregate and to sit in a stockpile — cold mix and patching. Slow-setting grades are the most stable, tolerate mixing with fine material and cement, and are the only class normally diluted with water — tack coats, fog seals and slurry seals. A fourth class, QS or quick setting, is used for micro-surfacing.
The C means cationic; without it the grade is anionic. The trailing h means a harder base binder, so the residue penetrates 40 to 90 dmm at 25 °C instead of the 100 to 250 dmm a standard cationic grade leaves (100 to 200 dmm for the anionic grades under ASTM D977). The number, 1 or 2, indicates the viscosity and residue level, with 2 grades thicker and higher in bitumen content. So CSS-1h reads as cationic, slow setting, lower viscosity, hard residue — the standard tack-coat and slurry-seal grade for hot climates.
A slow-setting grade — CSS-1h or CSS-1 if cationic, SS-1h or SS-1 if anionic. Use the h version where summer pavement temperatures are high. Tack coat is normally diluted, commonly 1:1 with clean potable water, because the target residual binder rate is very low and dilution is the only practical way to spread that little binder uniformly across the width of the spray bar. Add the water slowly into the emulsion under gentle agitation at similar temperatures; do not pour emulsion into water and do not use hard water.
CRS-2 is the principal grade worldwide. It is a cationic rapid-setting emulsion, heavy bodied, with a minimum residue of 65 % by distillation, and it is designed to break within seconds of the chippings being spread so that traffic can be returned quickly. It is never diluted — diluting it thins the binder film and the seal will shed chippings. Where limestone aggregate dominates, RS-2 under ASTM D977 is the anionic equivalent.
Keep it above about 4 °C at all times. The carrier is water, and freezing grows ice crystals that rupture the emulsifier films around the droplets. The bitumen coalesces and the damage is permanent — heating and stirring will not recover it. Set the floor at 4 °C rather than 0 °C because the coldest part of a stack or a tank is always colder than the point you measure. Upper limits are grade-dependent: roughly 50 to 85 °C for CRS and CMS grades, and about 10 to 60 °C for CSS, SS and MS grades.
In most cases, emulsion. It carries no solvent, presents no flammable-liquid fire risk in the slow-setting grades, releases no hydrocarbon to the atmosphere, and is permitted where air quality regulation has restricted or banned cutbacks. The exception is priming a tight granular base, where a kerosene-cut MC grade still penetrates more deeply than an emulsion prime, which is why MC-30 and MC-70 remain in many specifications for that one job. If the specification allows either, the operational and regulatory case for emulsion is strong — but plan for its shorter shelf life and its freezing sensitivity, which cutbacks do not share.
This page covers what an emulsion is and how it breaks. Two neighbouring pages take it further.
Send the grade you need — CRS-2, CSS-1h, CMS-2 or another designation — along with quantity, packing, destination port and Incoterm. Tell us the aggregate type and the operation the emulsion is for, and the expected storage conditions at destination, so the grade and the shipping arrangement can be checked against the job before pricing.