Micro Surfacing on Road Construction Applications
Difference Between Slurry seal and Micro Surfacing
Uses of Bitumen Emulsion in Prime Coat and Tack Coat of Road Construction
Bitumen Emulsion for Sand Seal
Bitumen Emulsion in Slurry Seal
Difference Between Anionic ss1 and Cationic css1 Bitumen Emulsion
Bitumen emulsion is bitumen dispersed in water as droplets half a micron to five microns across, held in suspension by an emulsifier that gives each droplet an electrical charge. That charge is not a technical footnote — it decides whether the binder bonds to your aggregate or strips off it. This guide covers what bitumen emulsion is, how the types are classified, which grade suits which job, and the storage rules that catch out buyers used to handling hot bitumen.
ZUMRUT INT Co. supplies cationic and anionic emulsion across the full grade range, shipped from Mersin, Jebel Ali and Bandar Abbas with a batch certificate of analysis before every shipment. Every grade linked below has its own specification page.
Bitumen is a thermoplastic: a thin liquid at high temperature and effectively solid at ambient. Most applications exploit that directly, working at 140 to 230 °C. But some jobs need a thinner film than hot application can achieve, or cannot tolerate the heat, the fumes or the fire risk.
Bitumen emulsion solves that. Hot bitumen is sheared into microscopic droplets and dispersed in water with an emulsifier — a surface-active agent that coats each droplet and gives it an electrical charge. Like charges repel, so the droplets stay apart instead of coalescing back into a single mass.
When the emulsion is sprayed or mixed, that stability is deliberately broken. The droplets coalesce, the water separates and evaporates, and what remains is a continuous film of the original binder. The industry calls this breaking, and you can see it happen: the emulsion changes from brown to black.
The property that matters commercially. Bitumen emulsion is applied cold or warm, typically 20 to 70 °C rather than 150 °C and above. That removes the heating plant, cuts fuel cost, eliminates most fume exposure and removes the burn risk. It also means the material can be applied where hot bitumen cannot — onto a damp surface, or in weather too cool for hot spraying.
This is where most specification errors happen, and where a lot of published information is simply wrong.
Mineral aggregate surfaces carry a natural electrical charge, and it depends on the mineralogy.
| Aggregate type | Examples | Surface charge | Emulsion to use |
|---|---|---|---|
| Siliceous / acidic | Granite, quartzite, sandstone, gravel with high silica | Negative | Cationic — positive droplets, opposite charges attract |
| Calcareous / basic | Limestone, dolomite, basalt | Positive | Anionic works well; cationic also performs |
| Mixed or unknown | Site-won material, recycled aggregate | Variable | Cationic — the safer default |
The principle is simple: opposite charges attract. A cationic bitumen emulsion carries positively charged droplets, so it bonds strongly to the negatively charged surface of siliceous aggregate. An anionic emulsion carries negatively charged droplets and bonds to positively charged calcareous surfaces.
Get it backwards and the binder does not grip. The visible result is stripping — aggregate shedding from the surface under traffic, often within the first winter. It looks like a construction fault and is usually a specification fault.
Cationic emulsion accounts for the large majority of global production, for two reasons. It adheres well to both siliceous and calcareous aggregate, so it is the safer choice when the aggregate source varies or is not fully characterised. And it breaks by chemical reaction with the aggregate surface rather than relying purely on water evaporation, which means it works in cooler and damper conditions where anionic emulsion struggles.
Anionic emulsion remains in use with limestone aggregate and in markets where it is the established specification. See our detailed comparison at SS-1 vs CSS-1, and the cationic and anionic overview pages.
The second classification is how quickly the emulsion breaks after application. This decides which jobs a grade can do.
| Class | Breaks | Can it be mixed with aggregate? | Typical uses |
|---|---|---|---|
| RS — rapid setting | Almost immediately on contact with aggregate | No — breaks before mixing completes | Surface dressing, chip seal, tack coat, penetration macadam |
| MS — medium setting | Minutes to tens of minutes | Yes, with coarse aggregate | Cold mix, patching material, stockpile mixes |
| SS — slow setting | Slowly — designed to resist premature breaking | Yes, including fine aggregate and filler | Prime coat, slurry seal, micro-surfacing, fog seal, soil stabilisation |
The logic follows from the chemistry. A rapid-setting emulsion is designed to destabilise the moment it touches aggregate — exactly what you want when spraying binder and dropping chippings onto it, and exactly what you do not want when mixing a stockpile.
A slow-setting emulsion resists breaking long enough to be mixed with fine aggregate, where the enormous surface area would break a rapid-setting grade instantly. That is why slurry seal and micro-surfacing always use SS grades.
Grades such as CSS-1h and SS-1h carry an "h" suffix, which stands for hard and refers to the base bitumen, not the emulsion. A CSS-1h is made from a harder penetration grade than a CSS-1.
That matters in hot climates. The residual binder left after the water evaporates is the base bitumen, and a softer base produces a residual film that can bleed or track in summer heat. Where ambient temperatures run high, the "h" grades are worth specifying.
| Grade | Setting | Bitumen content | Principal use |
|---|---|---|---|
| CSS-1 | Slow | 57% min | Prime coat on porous bases, tack coat, fog seal, soil stabilisation |
| CSS-1h | Slow | 57% min | As CSS-1 with a harder base binder — hot climates, slurry seal |
| CMS-2 | Medium | 65% min | Cold mix with coarse aggregate, patching, stockpile material |
| CMS-2h | Medium | 65% min | As CMS-2 with a harder base binder for warmer service |
| CRS-1 | Rapid | 60% min | Tack coat where paving follows quickly, light surface dressing |
| CRS-2 | Rapid | 65% min | Surface dressing and chip seal — the volume grade for this work |
| K1-40 | Rapid | 40% | Tack coat. European nomenclature, diluted grade |
| K1-60 | Rapid | 60% | Surface dressing, penetration macadam |
| K1-70 | Rapid | 70% | Heavy surface dressing where high binder content is specified |
| K2 | Medium | Varies | Cold mix and patching under European specification |
| K3 | Slow | Varies | Prime coat, slurry seal and fine-aggregate mixes |
The K-series follows European naming rather than ASTM. K1 is rapid setting, K2 medium, K3 slow, and the number after the dash is the bitumen content as a percentage. A K1-60 is a rapid-setting cationic bitumen emulsion at 60% bitumen. If your specification uses one system and your supplier quotes the other, confirm the equivalence before ordering.
| Grade | Setting | Bitumen content | Principal use |
|---|---|---|---|
| SS-1 | Slow | 57% min | Prime coat, tack coat, fog seal on limestone aggregate |
| SS-1h | Slow | 57% min | As SS-1 with a harder base binder for warmer service |
| RS-1 | Rapid | 55% min | Tack coat and light surface treatment |
| RS-2 | Rapid | 63% min | Surface dressing and chip seal on calcareous aggregate |
If you know the job but not the grade, work from here.
| Application | Grade | Application rate | Notes |
|---|---|---|---|
| Prime coat | CSS-1, SS-1, K3 | 0.8–1.5 l/m² | Slow setting so it penetrates the base before breaking |
| Tack coat | CSS-1, CSS-1h, CRS-1, K1-40 | 0.15–0.40 l/m² residual | Normally diluted 1:1 with water for even coverage |
| Surface dressing / chip seal | CRS-2, RS-2, K1-60 | 1.0–1.8 l/m² | Rapid setting. Chippings must follow within minutes |
| Slurry seal | CSS-1h, SS-1h, K3 | By mix design | Mixed with fine aggregate, filler and water on site |
| Micro-surfacing | CSS-1h, polymer modified | By mix design | Polymer modification is normally specified |
| Fog seal | CSS-1, SS-1 | 0.3–0.9 l/m² diluted | Heavily diluted, sprayed on an existing surface |
| Sand seal | CRS-1, RS-1 | 0.6–1.2 l/m² | Sand spread over the binder instead of chippings |
| Cold mix asphalt | CMS-2, CMS-2h, K2 | By mix design | Medium setting allows mixing and stockpiling |
| Pothole patching | CMS-2, CMS-2h | By mix design | Stockpile mixes remain workable for weeks |
| Soil stabilisation, dust control | CSS-1, SS-1 | Site dependent | Slow setting so it penetrates the soil profile |
| Crack sealing | CSS-1h | To fill | Multiple passes may be needed as water evaporates |
| Waterproofing, roof and basement | CSS-1, SS-1 | By coat | Two to three coats. Allow each to break fully |
Bitumen emulsion is the least forgiving bituminous product to store, and buyers used to handling hot bitumen or drummed penetration grade are routinely caught out.
| Risk | What happens | Prevention |
|---|---|---|
| Freezing | Ice crystals rupture the droplet films. The emulsion breaks permanently and cannot be recovered | Never let the temperature fall below 0 °C. The one failure with no remedy |
| Settlement | Droplets settle toward the bottom over weeks, leaving a concentration gradient | Recirculate or roll drums periodically. Do not draw from a static tank without mixing |
| Skinning | A film forms on the exposed surface in a partly full tank or drum | Keep containers sealed. Fill tanks below the inlet to avoid splashing |
| Overheating | Above roughly 85 °C the water flashes and the emulsion breaks | Store at 10–60 °C. Emulsion is never heated like hot bitumen |
| Contamination | Mixing cationic with anionic neutralises both and breaks them instantly | Dedicated tanks and lines per charge type. Flush thoroughly between products |
| Pump shear | Aggressive pumping shears the droplets and destabilises the emulsion | Use low-shear pumps. Avoid excessive recirculation |
Shelf life is months, not years. A well-stored bitumen emulsion keeps roughly three to six months depending on grade and conditions. Penetration and oxidized bitumen keep two to three years. If your project timeline is uncertain, order against the schedule rather than stockpiling — and test before use if material has been sitting.
Applied at ambient to 70 °C rather than 150 °C and above. No heating plant, lower fuel cost, faster mobilisation on small jobs.
Far lower burn risk and greatly reduced fume exposure compared with hot spraying.
Cationic emulsion breaks by reaction with the aggregate, so a slightly damp surface is tolerable where hot bitumen would fail.
Achieves film thicknesses that hot application cannot, which is why tack coats are almost universally emulsion.
No solvent evaporation, unlike cutback bitumen. Increasingly the regulatory preference.
No tank bottoms to dispose of, no material lost to cooling in lines and equipment.
Correctly charge-matched emulsion bonds chemically to the aggregate rather than merely coating it.
Medium-setting grades allow cold mix to be stockpiled for weeks, which hot mix cannot do.
| Bitumen emulsion | Cutback | Hot bitumen | |
|---|---|---|---|
| Carrier | Water | Petroleum solvent | None — heat only |
| Application temperature | 20–70 °C | 50–110 °C | 140–180 °C |
| Cures by | Breaking, then water evaporation | Solvent evaporation | Cooling |
| Emissions | Water vapour only | VOC — restricted in many markets | Fume at application temperature |
| Damp surface | Tolerated | Poor | No |
| Base penetration | Good with SS grades | Best — the traditional prime coat choice | Poor |
| Shelf life | 3–6 months | 12–24 months | 24 months in drums |
| Freeze risk | Destroyed by freezing | None | None |
The full comparison is in cutback bitumen vs bitumen emulsion.
Bitumen emulsion is specified under ASTM D977 for anionic grades, ASTM D2397 for cationic grades, and EN 13808 in Europe. The tests that matter on a certificate of analysis:
| Test | Method | What it tells you |
|---|---|---|
| Residue by distillation | ASTM D6997 | Bitumen content. The figure you are actually buying |
| Viscosity, Saybolt Furol | ASTM D7496 | Whether it will spray or pump correctly |
| Storage stability, 24 h | ASTM D6930 | How fast it will settle in the tank |
| Sieve test | ASTM D6933 | Oversized particles that will block the spray bar |
| Particle charge | ASTM D7402 | Confirms cationic identity |
| Penetration of residue | ASTM D5 | Hardness of the binder left behind — the "h" question |
The residue penetration is the test most often omitted from supplier certificates and the one that predicts how the finished surface behaves in summer. Ask for it.
| Packing | Volume | Notes |
|---|---|---|
| Steel drum | 200 kg | New drums with sealed bungs. Easiest for small and remote projects |
| IBC tote | 1,000 kg | Where handling equipment exists. Lower cost per tonne than drums |
| ISO tank / bulk tanker | 20–24 MT | For buyers with dedicated emulsion storage and recirculation |
| Flexitank | Up to 24 MT | Available on request. Single use, no tank cleaning |
Bitumen emulsion falls under HS 2715.00, bituminous mixtures based on natural asphalt or petroleum bitumen — a different heading from penetration and oxidized bitumen, which fall under 2713.20. Confirm the full national code with your customs broker. Shipment documentation is covered in our bitumen export documentation guide.
Route and season matter more for emulsion than for any other bituminous product. A shipment routed through a cold transhipment port in winter risks freezing, and a frozen emulsion is scrap. Tell us the destination and the schedule and we will flag any route where that is a genuine risk.
Bitumen dispersed in water as droplets typically 0.5 to 5 microns across, stabilised by an emulsifier that gives each droplet an electrical charge. Like charges repel, so the droplets stay suspended instead of coalescing. When applied, the emulsion breaks: the droplets merge, the water separates and evaporates, and a continuous film of the original binder remains.
Two classifications run in parallel. By electrical charge: cationic, anionic and non-ionic, with cationic dominating global production. By setting speed: rapid setting for surface dressing and chip seal, medium setting for cold mix and patching, slow setting for prime coat, slurry seal and fog seal. A grade name combines both, so CSS-1 is cationic slow setting and CRS-2 is cationic rapid setting.
The charge on the bitumen droplets. Cationic droplets are positively charged and bond to negatively charged siliceous aggregate such as granite, quartzite and sandstone. Anionic droplets are negatively charged and bond to positively charged calcareous aggregate such as limestone and dolomite. Opposite charges attract, which is the whole principle. Cationic dominates globally because it adheres to both aggregate families and works in cooler, damper conditions.
Cationic. Granite and other siliceous aggregates carry a negatively charged surface, so a positively charged cationic emulsion bonds to it strongly. Using an anionic emulsion on granite gives poor adhesion and typically shows up as stripping — aggregate shedding under traffic within the first season.
Rapid setting, medium setting and slow setting — how quickly the emulsion breaks after application. RS breaks almost immediately on contact with aggregate and suits surface dressing and chip seal. MS breaks in minutes and can be mixed with coarse aggregate for cold mix and patching. SS resists breaking long enough to be mixed with fine aggregate and filler, which is why prime coat, slurry seal and micro-surfacing all use SS grades.
Hard — it refers to the base bitumen, not the emulsion. A CSS-1h is made from a harder penetration grade than a CSS-1, so the residual binder left after the water evaporates is harder. That matters in hot climates, where a softer residue can bleed or track in summer heat.
K-series grades follow European rather than ASTM naming. K1 is rapid setting, K2 medium and K3 slow, and the number after the dash is the bitumen content as a percentage. A K1-60 is a rapid-setting cationic emulsion at 60% bitumen. If your specification uses one system and your supplier quotes the other, confirm the equivalence before ordering.
Prime coat and tack coat in road construction, surface dressing and chip seal, slurry seal and micro-surfacing, fog seal and sand seal, cold mix asphalt and pothole patching, soil stabilisation and dust control, crack sealing, and waterproofing for roofs and basements. The grade required differs for each — the selection table above gives the grade and application rate per job.
Roughly three to six months, depending on grade and storage conditions — far shorter than penetration or oxidized bitumen, which keep two to three years. Droplets settle over time and the emulsion needs recirculating or rolling before use. Order against the project schedule rather than stockpiling, and test material that has been sitting.
It is destroyed. Ice crystals rupture the emulsifier films around the droplets, the emulsion breaks permanently and it cannot be recovered by warming. This is the single failure mode with no remedy, and it is why route and season matter for shipments passing through cold ports in winter.
Onto a damp surface, generally yes — cationic emulsion breaks by reaction with the aggregate rather than relying purely on evaporation, which is one of its advantages over cutback and hot bitumen. In active rain, no: the emulsion is washed off before it can break. Plan spraying around dry windows.
Usually yes. Cationic slow-setting emulsions are commonly diluted around one part emulsion to one part water, so the required residual binder can be spread evenly at rates as low as 0.15 litres per square metre. Undiluted emulsion at tack coat rates is very difficult to distribute uniformly. Check whether your specification quotes residual or diluted volume before calibrating the distributor.
HS 2715.00, bituminous mixtures based on natural asphalt or petroleum bitumen. This is a different heading from penetration and oxidized bitumen, which fall under 2713.20. National tariffs add further digits, so confirm the full code with your customs broker.
100 MT. Packing options are 200 kg new steel drums, 1,000 kg IBC totes, ISO tank or flexitank. Mixed grades in one shipment are accepted provided each grade fills a container. Loading is from Mersin, Jebel Ali or Bandar Abbas on FOB, CFR or CIF terms.
Grade pages: cationic emulsion and anionic emulsion overviews, plus individual specifications for CSS-1, CSS-1h, CMS-2, CMS-2h, CRS-1, CRS-2, K1-40, K1-60, K1-70, K2, K3, SS-1, SS-1h, RS-1 and RS-2.
Application guides: prime coat vs tack coat, chip seal, slurry seal, micro-surfacing, slurry seal vs micro-surfacing, fog seal, sand seal, seal coating, emulsion in prime and tack coat and asphalt emulsion applications.
Comparisons: SS-1 vs CSS-1 and cutback vs emulsion.
Send us the application, the aggregate type and the quantity, and we will confirm the grade before you order. If your specification names a grade in a system you are not familiar with — ASTM against European K-series, for example — send the specification and we will confirm what matches it. Batch certificate of analysis with every shipment, third-party inspection accepted at loading.
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