Emulsion Classification Emulsions are divided into three grades for classification: cationic,anionic and non-ionic. In practice, only the first two are used in roadway construction and maintenance. The cationic and anionic designation refers to the electrical charge of the emulsifier surrounding the asphalt particles. Cationic emulsions have a positive (+) electrical charge surrounding the asphalt particles while anionic emulsions have a negative (-) electrical charge. Since opposite electrical charges attract, anionic emulsions should be used with aggregates having a positive (+) charge. Similarly, cationic emulsions should be used with aggregates having a negative (-) charge. Failure to use materials with opposite electrical charges may result in the materials repelling each other, causing failure.
Asphalt Emulsions Asphalt emulsions use surface-active agents or surfactants to suspend the asphalt particles in water. These surfactants or emulsifying agents are similar to soap, allowing the minute asphalt particles and the water to form a uniform mixture. When the asphalt emulsion is applied to the roadway, the asphalt cement and the water separate. This process is called breaking. The water then evaporates, leaving the asphalt cement and the emulsifying agents behind. Asphalt emulsions commonly used in road- maintenance operations are either anionic or cationic. The asphalt in the anionic type has a negative electrical charge while the cationic type has a positive electrical charge. Cationic emulsions are denoted by a letter “C” at the beginning of the emulsion type, and the absence of “C” denotes an anionic emulsion. The emulsions are classified by the letters, indicating the relative rate of curing. Rapid-setting (RS), medium-setting (MS), slow-setting (SS), and quick-setting (QS) are the designations. Emulsions are further classified by a number indicating viscosity “1” is more fluid than “2” and a letter for the hardness of the base asphalt (“h” for a harder grade and “s” for a softer grade). High float emulsions are designated with the letters “HF” preceding the emulsion grades.
MODIFICATIONS OF ASPHALT EMULSIONS High-Float Asphalt Emulsions High-float asphalt emulsions (HFEs) are being used more often. Usually, when an emulsion breaks, the remaining emulsifying agent has little effect on the asphalt. This is not so with an HFE. The high-float emulsifying agent creates a gel structure in the asphalt residue. The gel structure permits a thicker asphalt coating on the aggregate particles. The thicker film prevents raveling and is more resistant to oxidation from exposure to the atmosphere. The high-float residue is resistant to flow at high temperatures while not being affected as much by low temperatures. This allows a softer grade of the base asphalt to be used that will resist bleeding at high temperatures. The softer asphalt does not become as brittle at low temperatures and resists thermal cracking. HFEs are commonly used in hot arid environments with cold evenings. Polymer-Modified Emulsions Probably the most common modifier to asphalt emulsions is polymer additives. Polymers and polymer combinations are being modified constantly to enhance the various properties of the asphalt cement binder. Polymers can be used for any asphalt seal coat applications. Polymers generally used in the asphalt industry are either elastomeric (rubber like) or plastomeric (plastic like). The elastomeric polymers increase the elasticity and flexibility of the asphalt cement, while the plastomeric polymers improve the strength and the durability of the asphalt cement. Polymerized asphalt emulsions are effective in improving stone retention when construction conditions are less than ideal, such as in low air temperatures, shady areas, or sinuous alignment. Polymers can improve the performance of the asphalt binder in both cold and hot temperatures. Some polymers allow the emulsion to chemically break and do not depend on temperature to separate the asphalt cement from the water within the emulsion. This allows the emulsion to break at lower temperatures and provides a longer construction season in some areas or allows surface treatments to be done at night. Polymer modified binders usually cost more, but they increase the performance of the asphalt cement, often reducing life cycle costs. Rejuvenating Emulsions As pavement ages, asphalt cement becomes brittle and loses some of its binding qualities. Rejuvenating emulsions penetrate the asphalt pavement, soften the brittle asphalt, and improve the asphalt cement’s ability to bind with the aggregate. The rejuvenating agent is also known to heal small cracks in the pavement.
CRS-2P ~ “C”- Cationic emulsions “RS” - Rapid-setting 2 - viscosity “1” is more fluid than “2” “P” - Polymer-Modified Emulsions elastomeric (rubber like) or plastomeric (plastic like)
Apply the bituminous material above the minimum limits specified below: Bituminous Material Minimum Temperature Ideal Temperature CRS-2P [140° F]* [170-180º F] CSS-1h [100° F] * Intended for uniform lay down of emulsion.
Rolling Operations Complete the initial rolling within 2 minutes after applying the aggregate. Proceed at a recommended speed less than or equal to 5 miles per hour, to prevent turning over aggregate and so that the rollers do not pick up aggregates from the emulsified asphalt surface. Make a minimum of three complete passes over the aggregate. Roll the aggregate so the entire width of the treatment area is covered in one pass of all the rollers. The total compacting width of each pneumatic-tired roller shall exceed 5 ft. The function of the roller is to embed the aggregate into the binder and orient it into an interlocking mosaic. This is initially accomplished with pneumatic rollers, with final compaction applied by traffic, finishing the process. Rolling should be expedited in hotter weather to ensure proper embedment of the aggregate. Steel rollers are not normally recommended because they can crush the aggregate. Rolling shall be performed with a pneumatic-tired roller that remains immediately behind the spreader.
Contact pressure depends on the vehicle weight, the number of tires, tire size and rating, and the tire inflation pressure. Rollers that can be ballasted are very useful in assuring sufficient contact pressure. The ballasted weight should be 4 to 6 tons, with a corresponding tire pressure of 87 psi. Tires must have a smooth tread, should not vary more than 7 psi in pressure, and should not wobble during operation. Rollers should follow aggregate spreading by no more than 500 ft and should not be operated at more than 5 mph. The rolling pattern will depend on the number of rollers used. A minimum of two rollers should be used to cover the full width of the chip spreader. When two rollers are used, three passes are sufficient; one forward, one in reverse, and the final pass extending into the next section.
Following the application of the chip seal, the entire surface shall be carefully broomed to remove loose aggregate that could damage vehicles. This brooming shall be done as soon as possible without damaging the chip seal but no more than 18 hours following the application of the chip seal. Chipseal : 100% Clean – up before Fogging Paved Driveways: 100% Clean-up Do not use paved driveways for turning around.
Fog Sealing A fog seal consisting of a mixture of 50% CSS- 1H and 50% water shall be applied to the chip seal surface after all extraneous aggregates have been removed. The application rate of the CSS-1H/Water mixture is estimated to be 0.12 gallons per square yard. Apply the fog seal to minimize the amount of overspray. Do not allow traffic on the fog seal until it has cured.
CSS-1H ~ “C” - Cationic emulsions “SS” - Slow-Setting 1 - viscosity “1” is more fluid than “2” “H” - letter for the hardness of the base asphalt (“h” for a harder grade and “s” for a softer grade).
THE BENEFITS OF FOG SEALING There are numerous benefits resulting from a fog seal application. 1. The traveling public thinks it is driving on a new HMA surface rather than a chip seal. 2. The emulsion is diluted, which yields a very low viscosity that allows most, if not all of the additional asphalt binder to fill the chip voids increasing embedment by up to 15-percent with no bleeding. 3. The fog seal re-seals any chips that may have partially broken loose during sweeping operations. 4. Darkening the pavement surface with a light application of asphalt emulsion allows the pavement surface temperature to rise. The subsequent softening of the binder allows the chips to orient to their least dimension more quickly. This factor is very important where late season chip seal projects are more susceptible to failure due to colder weather conditions. 5. Fog sealing can provide a designer with a chance for a “re-do” of a chip seal application. If, after traffic has driven on the surface, it appears that embedment is low, an engineer can add additional binder to the chip seal by increasing the fog seal amount. In some cases, the amount of fog seal emulsion applied increased to over 0.20 gallon per square yard. 6. When a fog seal is applied, a reduced amount of paint is necessary to make pavement markings visible on the surface.