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by Glynn Holleran Jeffrey Reed Monterrey, Mexico, Oct 1996 Back to VSS Technology Papers Library Contents Part 1 Understanding Emulsion Products Part 2 Advantages of Asphalt Emulsions Part 3 Applications of Asphalt Emulsions Part 4 Storage and Handling of Bitumen Emulsions Part 1: UNDERSTANDING EMULSION PRODUCTS Back to top 1. Introduction It is the purpose of this session to give a better understanding of the basics of emulsion physical chemistry so that problems in testing, handling or specification become less difficult. The information here should be read with the other publications on emulsions contained in the folder to fully understand their significance. 2. What is an Emulsion? If you know exactly what an emulsion is it is far easier to predict what it might do under certain circumstances. An emulsion is one phenomena that occurs when you mix two components together. At one extreme a solution results, in this the dispersed component takes up an elemental form, such as a molecule or an ion. At the other end of the scale a slurry or suspension forms in which the dispersed phase will fall out. Emulsions are somewhere in the middle. Common examples of emulsions are milk, margarine, butter, beer and paint. Emulsions are thus by definition made up of two components with one dispersed through the other. The dispersed component is not soluble in the continuous component. Because of this to maintain the dispersion requires some way of overcoming this lack of compatibility. The methods that have been found to work over many years are high shear and chemical treatment. An Asphalt emulsion is thus Asphalt dispersed through water and chemically stabilized as shown in figure 1.
3. Manufacturing Emulsions A schematic diagram of a typical emulsion system is shown in figure 2. The main features are, Molten Asphalt is sheared to fine droplets by a high shear system. In VSS we use a colloid mill designed for the purpose. (see figure 3) Within the colloid mill the Asphalt is brought into intimate contact with a chemical solution. This is the chemical stabilization. After discharge the emulsion consists of water with fine particles of Asphalt dispersed in it, all that is between the particles and each other is water and chemicals. Asphalt is not soluble in water and so to keep it dispersed in fine particles is a significant feat. It may be understood from this that the viscosity of the Asphalt when it enters the mill is important, hence the temperature of the Asphalt is important. Also the temperature of the soap is important. If either are too low the emulsion may become more coarse. If , on the other hand the temperatures are too high the emulsion may boil, lose water and cause coarsening.
4. Chemical Systems VSS manufactures three basic types of chemically stabilized materials: The last, clay, is the filled type and it's structure is rather different from the other two, and are mostly used for industrial applications such as roofing and underbody sealing and use an activated clay as the emulsifier system. They are essentially anionic emulsions. The other two categories get their name from the chemical type used to stabilize them. It is important to note that other chemicals may be added for specific effects but these do not change the basic chemistry, only modify it. 4.1 How Emulsifiers Work Emulsifiers of both the cationic and anionic type are based on salts of fatty long chain molecules, these may be synthetic or derivatives of fatty acids as found in oils and fats. a) Anionic emulsifiers are based on fatty acids, these are reacted with a base such as caustic potash or caustic soda (KOH or NaOH ) to form a salt. It is this salt that is the active emulsifier. Figure 4 shows a schematic of such a molecule. The non polar tail is hydrophobic and hence aligns itself inward to the Asphalt. The polar end is hydrophilic and hence provides the solubility in water. The emulsifier thus attaches itself to the Asphalt particle. The number and density of emulsifier molecules that do this will impart a charge to the surface of the Asphalt particle. This charge will be exactly balanced by the free charges in the water phase. This will be the sodium or potassium ion of the salt.
The products that are used for this process are usually mixtures of fatty acids, these will impart different levels of charge or Zeta Potential to the particles and give a balance of properties. Another emulsifier for slow setting emulsions worth mentioning is Vinsol. This is a wood resin. The emulsifying species is the salt of a long chain derivative of abietic acid. Figure 5 shows an anionic emulsified particle.
b) Cationic Emulsifiers are based on acid salts of amines prepared from fatty acids. These may be fatty diamines, fatty quaternary ammonium compounds or ethoxylated derivatives. The type of emulsifier determines the number of charges that are on the surface of the Asphalt. Thus they determine the zeta potential. Figure 6 shows a schematic of a cationic emulsifier. Again, commercial emulsifiers are mixtures and give a balance of properties.
Figure 7 shows a cationic emulsified particle.
c) Zeta Potential Zeta potential is an important concept to grasp as most emulsion properties flow from it or as a result of it. Zeta potential is the electrical potential between the surface of the Asphalt particle and the bulk solution. The zeta potential is determined by the emulsifier adsorbed onto the surface of the Asphalt. A double layer of ions and counterions exists in solution surrounding each particle of Asphalt. The form of the double layer depends on the concentration and ionic density of the emulsifier and the pH. A large zeta potential indicates a greater double layer, faster movement and greater repulsion between particles. Larger repulsion produces more stable emulsions. The pH affects the way in which the Asphalt adsorbs emulsifier and so is critical to the double layer and thus Zeta potential. Increasing the concentration of the emulsifier compresses the double layer; this in fact decreases zeta potential but the increased amount of surfactant increases stability by increasing colloidal protection. For this reason it is always better to choose the emulsifier for the application rather than attempting to slow break or make it more rapid by adjusting emulsifier concentration. In cationic emulsions it is often not possible to make a slow set using a rapid set emulsifier due to the very high zeta potential of such emulsifiers. 5. Properties of Emulsions All the properties of emulsions and their behaviour under various conditions may be directly related to the structure as discussed above. This goes for any application. If the structure is understood then everything else follows. 5.1. Breaking a) Anionic As anionic emulsions have a negative charge as does almost every mineral there can be no electrostatic attraction. So for an anionic emulsion to break requires that the particles get so close to each other that the repulsion forces are overcome by the attractive forces that exist between all things. This is a stepwise mechanism that involves coarsening into larger and larger particles until the particles are macroscopic (see fig 8 and 9). This is normally broken up into two steps of flocculation and coalescence. This can occur by forcing the particles together in any way. This may by an outside force such as pumping at high shear, taking away water by heating and boiling or pushing particles together by freezing. Breaking can also occur if the emulsion is packed into a smaller area by sedimenting or settling.
b) Cationic Cationic emulsions have a positive charge and hence a direct and very rapid reaction between the emulsion and an aggregate or pavement is possible (figure 10). The size of the charge, or the Zeta potential affects stability, ie. the larger the charge the greater the repulsion, but as the aggregate is negatively charged the higher the zeta potential the more rapid the reaction.
So it is possible to stabilize a cationic emulsion in the same way that makes it a more rapid break. The other mechanism of evaporation is available too but as the emulsion is stabilized this form of break becomes slower. Thus a balance must be struck. After the electrostatic part of the reaction is complete the emulsion will rely on flocculation and coalescence to complete break (figure 8, 9). After break is completed the water must still be completely evaporated for the residual Asphalt to achieve full strength. 5.2. Stability Stability may be understood in terms of the structure and the mechanism of break (figure 8, 9). Firstly, the density of all Asphalts is around one but always higher. Thus the emulsions will always settle unless this density can be adjusted below that of water or if the water is modified to a higher density (figure 12). In general it is not practical to do this aside from relatively small adjustments. Cutter is added for such an adjustment as is calcium chloride. The former changes the density of the Asphalt, the latter the density of the water. As the break down in storage of an emulsion is by flocculation and coalescence any measure to retard this or to begin the process at a finer particle size will increase stability. Also finer particles settle more slowly, if they are less than 3 microns they even have as sort of internal mixing called Brownian motion.
6. Conclusions Asphalt Emulsions are fine dispersions of Asphalt in water. Manufacturing is done by high shear in specially designed plants. The key features and considerations when choosing a system therefore are:
PART 2: ADVANTAGES OF ASPHALT EMULSIONS Back to top 1. Introduction: In part 1 the basics of emulsions were considered. Restated, Asphalt emulsions are dispersions of Asphalt in water and stabilized by a chemical system. All of the advantages of emulsions flow directly from this fact. As a way of comparison they will be compared to cutback Asphalts and to hot Asphalt. Keep in mind that the reason we use Asphalt in road applications is because it is waterproof and adheres to stone. To get it into a form that we can apply it requires the viscosity to be reduced. This may be done by:
2.1 Avoids waste of fuel Cutback Asphalts can contain anything up to 50% kerosene or gasoil. Asphalt emulsions contain 0-2%. Thus there is a significant saving in the use of valuable white fuel products. In a cutback the solvent is added merely to reduce viscosity of the Asphalt to a level where it can be poured and sprayed. It is expected that this will evaporate into the atmosphere, in fact if it does not then the Asphalt is too soft. In an emulsion the viscosity characteristics are determined by the water phase and hence the viscosity is low, only water will evaporate away. 2.2 Reduces Overall Energy Requirement (Source: US EPA REPORT 450/2-78-004 JANUARY 1978). Comparing an emulsion with a cutback of the same solids content: CUTBACK It takes about 700KJ to process a liter of Asphalt for paving according to the Asphalt Institute. Added to this is the energy of the cutter added. This is 40,000 KJ per liter. For a 60% cutback the total energy requirement is: 16,700 KJ= (700 + 0.4x 40,000) per liter. EMULSION 567 kj is required to produce a liter of emulsion. emulsifier energy requirement to produce 1 liter of emulsion is 584 KJ. This gives a total of 1151 KJ per liter of emulsion. compare to 16,700 KJ for cutback. Most of the energy is in the fuel lost! There is another saving however and that is in heating on the road. To spray a liter of emulsion at ambient requires 41 KJ per liter. To spray the cutback requires an extra 127 KJ per liter for heating. Before cutbacks were largely banned in the USA it was estimated that the energy loss was enough to fuel 588,000 cars for one year! (at 12 miles per gallon!) 2.3. Pollution Control Kerosene and gas oil fumes are green house gases. In a cutback they evaporate into the air and become pollutants. The cutbacks are designed this way. In an emulsion there is no such evaporation. 2.4. Safety Emulsions are water based. They have no flash point, they are not flammable or explosive. Drums of emulsion kept in the sun will not expand or burst. Being water based emulsions do not pose any health risk to workers and, being used cold they cannot cause burns. Spillages are of no environmental importance. If a spill occurs in a water way the emulsion will break and settle to the bottom, a harmless organic mass. Grass and other plant life can grow through it. A spill on the side of the road will actually encourage plant growth by keeping the moisture and warmth in the ground plants can simply break through. 3. Versatility Emulsions have many different applications. They can, with proper selection, be used for a wide range of applications. This will be discussed in a later session. But the same emulsion that is sprayed in large amounts for a sealing application can be used for small patching jobs. Because they can be stored in drums for long periods they can be used in remote areas. 4. Ease Of Use Application of emulsions for specialized applications will require specialized equipment such as a sprayer , however for small jobs the emulsion, being handled directly from the drum can be poured or spread by hand. For small patching jobs, crack sealing , small amounts of cold mix only the most basic of equipment is required. For example a watering can with a baffle and a shovel can be used to seal pathways and small areas such as school grounds etc. 5. Performance Asphalt emulsions are sophisticated chemical systems. This creates the opportunity of creating systems that suit the conditions of application and the materials available. The advantages compared to cutbacks or hot Asphalt are as a result of this. The performance advantages can be summarized as:
Aggregates can be classified by their mineralogical type, however when moisture is present all aggregates have a net negative charge. If a cationic emulsion is used the breaking mechanism is by a physio chemical reaction with the stone in which the emulsified particles electrostatically plate out on the surface of the stone. The greater the charge on the aggregate the faster the reaction. This can also be controlled by the emulsifier system. Thus the emulsion makes a strong chemical bond. The rest of the break is by flocculation and coalescence of the emulsion, that is the water evaporates and the particles come closer together and form groups of particles then ultimately become Asphalt. The fine nature of the Asphalt particles makes this process fast and even and the low viscosity makes the process able to happen at ordinary temperatures. AT THE END OF THE PROCESS THE RESIDUAL MATERIAL IS THE ASPHALT THAT YOU STARTED WITH. With a cutback the coating is purely physical and an adhesion agent is needed for aggregates of high surface charge. This is also true of hot Asphalt. With cutbacks the loss of kerosene is slow and can take years. This leaves a Asphalt that is soft and subject to bleeding in the summer. 5.2 Range Of Conditions Because an emulsion is water based the aggregates need not be dry for application. In fact it is an advantage if they are damp. Cutbacks will coat well wet aggregates because kerosene and water have a large surface energy difference. They do not mix. Hot Asphalt behaves similarly. At lower temperature conditions the viscosity to wet aggregate and form a bond depends on the viscosity and the ability to form a continuous film. An emulsions viscosity is low hence wetting can occur to temperatures well below 10C. For a cutback higher levels of kerosene are required (20-30%) and for Asphalt alone, higher temperature can be used. The drawbacks of higher cutter content is that the residual Asphalt is even softer virtually ensuring bleeding later on. For Asphalt the rate of temperature loss is such that the viscosity increases at a very rapid rate , and it has been estimated that the Asphalt will reach the road temperature in about 2.5 minutes. This gives little time for penetration or wetting to occur virtually ensuring stone stripping or patch disintegration in a short time. 5.3 Economy Of Materials A lower viscosity emulsion that has good adhesion will not only improve adhesion but will coat stone better than hot Asphalt or even a cutback. This means that less emulsion is required in many instances than hot Asphalt or cutback. This can be 5-10% depending on the situation. For example in penetration patching the emulsion will fill the voids more easily and not get hung up in the top layers. This can save Asphalt and create a patch that is not as soft or likely to bleed. In sealing the emulsion goes further up the sides of the stone creating a better bond. In residential streets this can save 10% on binder requirement. For highway work or remote areas other considerations will need to be taken into account. 5.4 Durability Emulsifiers in Asphalt are present in very small concentrations. However work has been carried out that shows that emulsifiers can have a positive benefit on the durability, that is resistance to oxidation of Asphalt. Also, it is relatively easy in an emulsion to incorporate additives to improve durability without affecting other properties. 6.CONCLUSIONS The major advantages of asphalt emulsion relate to their chemistry and physical properties. They are a handy way of storing, transporting and applying asphalt. They save energy and materials and are simple to use. In the next part some applications are considered. PART 3: APPLICATIONS OF ASPHALT EMULSIONS Back to top The advantages of Asphalt emulsions are related to their chemical and physical makeup, these advantages lead directly to the applications to the applications in which emulsions are used.
Asphalt emulsions are dispersions of small particles of Asphalt through a continuous water phase. This has some important benefits. The water phase means that the viscosity of the emulsion is lower than the base Asphalt, thus application will be at much lower temperatures than for Asphalt. In many instances the emulsion may be applied at ambient. This lower viscosity also means that Asphalt emulsions are less sensitive to weather conditions. Being water based an emulsion is less sensitive to damp stone or pavements as well as to dusty aggregates. The chemical surfactant system in the emulsion aids wetting of stone or pavement thereby improving the adhesive bond. this is especially true of cationic emulsions which effectively have an in built anti stripping system. There are many applications of emulsions in this section we will consider in detail the most important ones in detail being sealing, slurry surfacing ,patching and coldmix.. 2. Chip Sealing 2.1 Definition Spray sealing is the application of a sprayed film or membrane of an emulsion product with or without the application of aggregate. 2.2 Reasons For Chip Sealing
2.3.1 Prime Usually no aggregate. A layer of Asphalt to kill dust and bind the surface prior to another surface treatment. The main functions of a prime coat on a granular base are as follows:
Emulsions are discrete particles of Asphalt dispersed in water. The surfactant system plays an important part in the degree of penetration as it directly changes the surface tension of the emulsion. For this reason the penetration of most emulsions is extremely limited , especially on dry pavements. The pavement must be damped with water and a surfactant first, it should not be too tight. A better technique is to add the emulsion into the surface layer during pavement work up or by tyning the surface and mixing the emulsion into the loosened base. Application rates are around 0.8 Lt./m2 and a sand cover is required for trafficked areas. Suitable emulsions are CMS, SS-1, CSS. Invert Emulsions are available and achieve penetration equal to a cutback. It is the water phase in a standard emulsion that prevents the penetration into the pavement, one way of overcoming this is to make an emulsion where the Asphalt is the continuous phase. The solvent content of such emulsions is higher than a standard emulsion but lower than priming cutbacks. The water discrete phase reduces viscosity and allows cold application. Vprime is a suitable material. 2.3.2 Primer Seal The single coat sealing technique may be followed to seal directly on to a prepared pavement for the purpose of creating a temporary seal (12 months). This is done usually; to carry construction traffic, to hold a pavement over winter, or when the cost of a complete prime and seal is not an immediate option. An application with aggregate to provide a temporary running surface. Vprime 2, and CRS-2 or M-80 are suitable. 2.3.3 Final Seal This may take several forms:
Seals are designed according to a methodology based on filling voids between aggregate. This ensures a stable film (no bleeding), good adhesion and durability. This must take into account the traffic, the existing surface (punching effects, binder in the existing surface) and the weather. The ideal seal has about 2/3 of the ALD filled with Asphalt after compaction by traffic. Aggregates must be clean and single sized (graded may be used but care is required). Aggregates that are dusty should be precoated with a diluted CSS or special (adhesion promoter) emulsion. such as Coat. 2.5 Application 2.5.1 Surface Preparation The surface must be well compacted and sound repair potholes well before sealing (weeks). The surface must be free of clay, loose dirt and dust. Most often a prime will be required. Asphalt is non toxic, all weeds must be killed using a weedicide to prevent subsequent growth through the seal. If solvent based primers are used the full cure period recommended by the manufacturer should be allowed before application of emulsion. This is extremely condition dependent and will be much longer in the winter. The use of emulsion based primers can reduce this time. 2.5.2 Application of Emulsion The rate of emulsion application is determined by the aggregate and the surface to be sealed. This rate is based also on traffic type and frequency. VSS can provide a full design service or train local personnel in the appropriate methods. Emulsions of 60-80% Asphalt content are best sprayed at 30-85oC., especially when conditions are cool (12-15oC). Suitable emulsions are CRS-2, M-80 and the polymer modified versions of these materials. The selection is determined by existing surface traffic, weather and requirements for reopening the road. Standard emulsions may be used at pavement temperatures down to 10oC and when stone and pavement is damp. In general the weather subsequent to sealing should be dry for 4-12 hours, depending on the job and emulsion type used (cationic emulsions can withstand rain sooner than anionic ones). 2.5.3 Single Coat Surfacing of New or Previously Sealed Surfaces
Full cure will take 12-24 hrs but traffic may be allowed on subject to the above restrictions after rolling. For M-80 the cure times are considerable reduced. For standard emulsions a fog seal of diluted emulsion or a specialty product such as "chipset" may be used to lock the aggregate in place. 2.5.4 Two Coat Surfacing For New Or Previously Sealed Surfaces This technique is recommended for new constructions or where traffic is > 2000 VPD or has a high percentage of trucks. The surfaces must be tightly bonded and open textured. This may mean that the base needs to be stabilized with CMS emulsion first made from materials such as slate, gravel, lime rock etc.
On steep gradients the initial application of a 60% emulsion may need to be reduced, with a due allowance in the second application. If CRS-2 or M-80 are used this is not a problem. 2.5.5 Multiple Coat Surfacing Further coats may be added to a two coat seal. 2.5.6 Primer Sealing The single coat sealing technique may be followed to seal directly on to a prepared pavement for the purpose of creating a temporary seal (12 months). This is done usually; to carry construction traffic, to hold a pavement over winter, or when the cost of a complete prime and seal is not an immediate option. In some cases a single or two coat final seal may be directly applied to an unprimed pavement. This can save time and money. See VSS personnel for details. 2.5.7 Sand Seals The procedure is identical to that for single seal coats. Asphalt emulsion (preferably CRS or CMS is sprayed at 0.7- 1.0 Lt./m2 residual Asphalt and coarse sand is spread at 5-7 kg/m2. The sand is rolled well. On roadways excess sand should be swept off within 2-3 days. For bleeding pavements coarse sand may be spread directly onto the surface on a hot day and rolled in, a light coat of 0.3-0.5 Lt./m2 of residual binder in emulsion form may be sprayed to freshen the surface. 2.5.8 Penetration Macadam The low viscosity of emulsions allows excellent penetration and a graded aggregate may be used. Design is similar to a multicoat seal.
3. Slurry Surfacing The main types of Slurry surfacing are Slurry Seal, Cape Seal and Microsurfacing. 3.1 What Is Slurry Surfacing? Slurry surfacing is an application of a graded aggregate bound by a bituminous binder. It is essentially a cold mixed asphalt with a number of advantages related to the mix design and the manner in which the binder is applied. The material is mixed and applied in a mobile unit either self propelled or truck mounted. The binder applied is a quickset, or quick traffic emulsion. In most parts of the world this emulsion is a cationic type. This has a number of advantages over anionic types. These include rapid interaction of stone and binder, creating strong adhesive bonds, compatibility with a range of stone types and rapid setting. Slurry surfaces have low void contents and , being essentially self leveling have high stability, or deformation resistance. They can be made with different stone sizes and bitumen types that allow this property to be optimized. In thin layers slurry surfacings are very flexible, being relatively binder rich but the high surface area of the aggregate creates stable films and hence they will not bleed. 3.2 Definition Slurry surfacing is the application of a graded aggregate, a bituminous emulsion, fillers, and water with various additives to make a cold mixed material that cures quickly into a hard wearing surface. 3.3 Reasons For Slurry Surfacing Slurry surfacing provides:
The slurry surface is laid with a continuous paving machine that meters exact levels of bitumen emulsion, aggregate, additives and water. 3.4 Types of Slurry Surfacings 3.4.1 Slurry Seal A thin layer of slurry surfacing, about 1 to 1.5 stones thick used to resurface a pavement. Such materials may or may not be polymer modified. If they are the modification is usually in the form of a latex whose function is to Assist in creating early strength and to increase flexibility. Increases in softening point of the binder can also Assist in increasing softening point of the binder. Slurry seal mixes are based on smaller stones and limited to about 8mm thick (1.5 times top size). Slurry seals are used to:
A layer of slurry surfacing capable of correcting minor shape deformities and usually containing a modified binder. This type of material is able to be used as rutfilling. This may be laid in multiple stone thicknesses. These may be made with larger stone up to 10mm top size. The polymer modification allows the use of larger stone without the danger of raveling and the higher cohesion means that thicker layers can be supported without deformation. Polymer modification for such mixes can include EVA modification, this provides superior rut resistance. Layers of 50-75mm are possible. Such materials are usually very quick traffic, that is they build up cohesion very rapidly. These are not the only definitions in use in Australia and several brand names further cloud the issue, however by standardization it will be possible to produce a range of mixes based on application that all can understand. Microsurfacing is used for:
Mixes can be specified by application type as above This of course means that the contractor and the customer must agree on the problem at hand and the treatment chosen according to experience. 3.5 Cape Seal This is a method that combines the properties of a chip seal with that of a slurry. This method is referred to as Cape Seal. The desirable properties of chipseals are:
Thus a Cape Seal May be defined as the application of a chip seal followed by one or more layers of asphalt rich slurry seal (figure 15)
Cape seals have the following advantages: 3.6 Durability They are durable. Aging resistance is a function of voids content and film thickness. Cape seals reduce voids to 2-3%, increasing the durability, especially compared to a chip seal where void level is high. This can give seal durability of 12-15 years This is compared to seal lives of 5-8 years. 3.7 Skid resistance They are skid resistant. Figure 13 shows skid resistance for common road surfacings. The scrim results give a sideways coefficient of friction as 0.8 to 0.9 at 80 km/hr. This compares to a recommended minimum of 0.5- 0.6 for hot mix. 3.8 Cracking They can , with correct selection of binder alleviate cracking except alligator and block cracking. This is because these modes of cracking are normally due to structural problems in the base and cape seals add no structural strength. However basically sound pavements that are deflecting significantly can be treated with such seals as they can be designed to be flexible enough to move with the deflection. The fatigue resistance may be improved by the use of a highly modified PBA (3-5% polymer) in the chipseal and a latex modification in the slurry (2-5%). 3.9 Restoration They can be used to restore a weatherproof smooth surface caused by raveling or abrasion. 3.10 Noise Reduction. They have less noise than a chip seal (figure 14). 3.11 Cost Effective They are cost effective. In instances where the choice is a thin lift of hot mix or a slurry or chip seal they will give many of the benefits of the overlay at a lower cost. 4. Patching There are several methods of patching of existing surfaces where emulsions may be used. These may be classified as:
In areas of cracked or crazed pavement an overspray of 0.5 to 1.0 lt/m2 of or CRS may be sprayed or spread with a baffled watering can and the area gritted or sanded off. This applies to only fine cracks. Modified emulsion using latex is useful for this application. 4.2 Penetration Patching Potholes or areas of base failure or bad cracking may be repaired in this way.
This method may be used for large failed areas and potholes. Cold mix may be manufactured in dense or opengraded types using emulsions, VSS can supply technology and equipment for this application. CMS ,CSS and specialty emulsions are suitable, depending on the application. Cold mixes require design.
In this method (see figure 18) a specially manufactured machine is used to patch potholes and other depressions or disintegrated areas.
The DURAPATCHER unit can also crack seal. The SP-5 pavement maintenance testing done during the SHRP program determined that injection patching was the most effective method available. 4.5 Crackfilling Cracking takes many forms from small hairline cracks to very large ones. Large cracks or cracks caused by base defects may not be able to be treated in this way. In such instances the cracked area may need to be removed completely, the base reconstructed, or a membrane treatment used. For block cracking or other cracking caused by oxidation of binder or shrinkage an emulsion cracklfiller may be used. For small cracks CRS is suitable (low movement level). For greater movement polymer modified emulsions should be used. 4.6 Application
This is a method of road maintenance for sound surfaces that are aged. Or can be used to set chips in place in a chip seal as previously discussed. 5.1 Main Features.
Emulsion Cold mix may be used for arrange of patching jobs and small works. Increasingly in Europe cold mix is replacing hot mix, particularly in rural roads. VSS manufacture suitable equipment and have the emulsion and design technology to provide such systems. They are less expensive than hot mix and use simpler, less expensive equipment. 7. Tack Coating Tack coats are a priming coat of lightly sprayed, often diluted emulsion, that provides a bridge between a pavement and the next course of material. The principle use of tack coats is in Asphalt work and in patching of potholes. 7.1 Application 7.1.1 Patching The emulsion may be used neat for patching or diluted with an equal volume of water for asphalt work.(note:a special graded of low solids cationic emulsion is available for tack coating. This is available in a polymer modified form for higher shear strength, this is ideal for roundabouts and high shear corners). 7.1.2 Asphalt Apply the diluted emulsion (or the neat emulsion) at about 0.5 Lt./m2. Allow to break before overlay. Do not traffic tack coated areas. (newer rapid set tack coat emulsions are available for use with pavers with integral tack sprayers). Suitable emulsions for this application are SS-1,CRS,CMS and specialty tack coating emulsions. 8. Dust Laying The use of Asphalt emulsions to limit the loss of top soil in dry conditions can be an economic dust palliative. For stockpiles of finely divided material the deposition of a fine layer of Asphalt to form a surface crust is very effective.(e.g. mining tailings dumps). VSS have developed a special system based on asphalt and lignin- dope 30 for this purpose. This combines the flexibility of asphalt with the stiffness and strength of lignin for a harder wearing surface. 7.1 Application Either CMS or CSS is diluted with a compatible water at around 2-5 parts in a water cart or sprayer (remember, add the water to the emulsion not emulsion to water). The emulsion is then sprayed at around 0.5 Lt./m2 on the area to be treated. 8. Stabilization of Soils/Recycling In some cases gravels available for making road base are inadequate for the purpose. Emulsion stabilization can be used to increase load bearing capacity, resistance to weathering, cracking and waterproofing. This may be extended to recycling existing granular and asphalt pavements. In this process the material may either be dug up and processed in a central mixing plant or recycled or mixed on site. 8.1 Application The material is Assessed for grading and a mix design based on the CBR or the stiffness is made. The usual emulsion application is 3-5% by weight of residual binder. In some instances lime or cement works flue dust or cement may be added at 1-3%. In plant the material is mixed in a pugmill. The material is prewetted to optimum moisture content, the emulsion added and the mix made. It should be placed within 2-3 hours. In situ the material is pulverized using a travel mixer , rotary hoe or a recycling drum. For new material it may be simply windrowed with a grader. The material is wetted to OMC with a water cart. If lime is to be used or other additives it is spread now. If a recycler is to be used it is spread on the surface, if not it is windrowed with the rest of the material in the first stage. The emulsion is sprayed on the windrow or injected into the hood of the recycler. If a grader is used the emulsion is mixed by turning over the windrow. If the recycler is used then this does the mixing. Graders are used to spread. The finished course is rolled, extra water may be necessary at this point. Vibratory rollers are an advantage but finishing is with a multi tyred roller. For plant mix pavers may be used to lay and rolling is as above. 9. Water Proofing/Roofing/Home 9.1 Small works/Pathways Emulsions can be used to make pathways, play areas, or other small works using simple equipment. This is outlined in the appended brochure. 9.2 Waterproofing Asphalt emulsion may be sprayed directly on to concrete or earthen surfaces , or even on thatch or mud brick to form a waterproof finish. CMS emulsion may be used at 1.0 to 1.5 lt/m2 , sprayed on as two to three coats. For mud bricks 2-3 % emulsion by weight is added to the straw and mud mixture to create a waterproof brick. 9.3 Roofing A slurry of sand and Asphalt emulsion (SS-1 or CMS )can be prepared to the desired consistency and troweled or painted onto the surface. These slurries can be used for minor crackfilling (cracks to about 1-2mm width). For large roof areas the emulsion may be sprayed as above and a layer of sand sprinkled on. Allow 24 hours to dry. 10. Agriculture 10.1 Mulching The loss of soil by water or wind can be a serious problem in the construction of embankments and flat areas adjacent to highways or in farming land. The most common method of combating this is by vegetation. However, during the period between planting and germination the seeds may be washed away. Emulsion provides an inexpensive and effective way of combating this. Suitable emulsions are CMS and CSS. 10.1.1 Application There are two methods that can be used, in the first the emulsion is sprayed directly on to the seeded area forming a thin membrane cover. This cover holds the seeds in place, keeps in moisture, and has a hot house effect in promoting germination. As the young seedlings emerge they break up the surface. This can significantly improve yield. Application rate is 0.7-1.4 Lt./m2. depending on the soil. The soil should be dampened first. Emulsion may be used to anchor straw or hay mulch. First the hay is spread at 3-4 tonnes per hectare, then a mixture of seed and fertilizer is sprayed. Lastly around 0.5Lt./m2 of emulsion is sprayed. A second method involves blowing hay and spraying emulsion at the same time. 11. CONCLUSIONS Asphalt emulsions are versatile and can be easily used in any areas that a waterproofing, binding layer is required. They impart strength, flexibility and resist water. The unique properties are controlled by the chemistry and manufacturing techniques that VSS have developed internationally over many years and the application is ensured by the expertise in all aspects of roads that VSS has developed through its subsidiaries and customers around the world. PART 4: STORAGE AND HANDLING OF BITUMEN EMULSIONS Back to top 1. Introduction: We have seen in earlier parts what asphalt emulsions are and the advantages of using emulsions compared to hot bitumen and cutbacks. This part deals with the handling and storage of emulsions and covers the few simple rules for successful use. 2. Handling Handling of emulsions is not difficult. There are rules but they are simple if you can remember how emulsions are made. 2.1 Pumping Pumps are a way of doing work on an emulsion. They usually compress or shear the material that they pump. This results in the emulsion being compressed. If this happens too severely or often the emulsion will first become coarser by the mechanism of flocculation and coalescence and may even go back to bitumen. Pumps should be selected carefully. Centrifugal pumps and some types of positive displacement pumps may be used. Expert advice is available. 2.2 Temperature When materials get cold they shrink. In an emulsion this means that the bitumen droplets get closer together. This has a number of important results:
When materials get hot they expand, thus for an emulsion heating is a useful thing. However when water gets hot its evaporation rate increases enormously, if the water goes the droplets get closer together and can go back to bitumen by the flocculation coalescence mechanism. If any part of the emulsion gets hotter than 95oC. then localized boiling may occur with the droplets fusing back to bitumen. This has a number of important results:
The points made above equally relate to storage of the emulsion. When an emulsion is stored it has a finite lifetime. This lifetime is determined by the formulation, how it has been handled and how it is stored. Asphalt is heavier than water, the general movement must therefore be down. That is the emulsion settles. If the droplets pack in this way they can stick together, ie. flocculate and coalesce; eventually going back to bitumen. This may be controlled to some extent by formulation, ie. if the emulsion is fine enough to start with it will settle more slowly. If the emulsion is electrically unstable then it will flocculate and coalesce. This may not take it all the way back to bitumen but the large particles formed like this will settle faster. It is important to prevent settling by mixing. once an emulsion has coarsened remixing will not make it fine again. if it has coarsened too much then pumping may break the emulsion. The only way to prevent problems is to start with a very fine emulsion and keep it properly maintained. 3.1 Drums Drums should be stored in reference to the above principles of storage and handling.
For emulsions cleanliness is very important. A sloppy operation will produce problems. When an emulsion comes in contact with air it can begin to break. When a cationic emulsion comes into contact with metal it can begin to break. Thus if a pump is left without flushing it will clog. If lines are left part full of emulsion then they will clog. The higher the performance of the emulsion the more critical cleaning is. Cleaning should be done before storage of equipment and it should be done thoroughly. 4.1 Procedure
Emulsion is generally stable to transport. However a common problem is caused by the incorporation of air into the emulsion. This can cause particularly CRS to break in the bubbles of air. This can then seed the emulsion with larger particles causing settlement. The main transport requirements are to ensure that correct pumping is used, pumps are warmed in cool climates, clean tanks are used or switch load conditions are observed. Always pump into clean tanks and always transport full containers. 6. Application 6.1 Equipment Application of emulsions should always be through compatible equipment. Pumps should be of similar design to storage pumps. Sprayers are purpose built. However sprayers designed for bitumen spraying may be used. Jets should give appropriate application rates, this is about 4 gallons per minute. Configuration of jets may be slot or swirl. Emulsions may also be applied under air pressure or by pouring (depending on the application. VSS personnel will assist in equipment assessment or advice on purchase of new equipment. 6.2 Dilution Emulsions should never be diluted except where the method specifically calls for it, e.g. enrichment. Addition of water should always be to emulsion rather than the other way around. Compatibility should be checked by diluting a small amount first. Water can be made more compatible by the use of a non ionic detergent for cationic and anionic or by use of a compatible detergent for each individually. This is added at around 5Lt. to 5000 Lt. of water. 6.3 Contamination Emulsions are chemical systems, they should never be mixed with other types of emulsions, they should never be mixed with other chemicals. Rust, dirt, grass or other foreign material should be excluded. This is especially important for cationics as they can break by reacting with these materials. 7. Cationic V Anionic Many people ask which is the best, the answer is that it depends on what you want to do with the emulsion.
8. VSS EMULSIONS. 8.1 General VSS emulsions are formulated for local conditions. The technology is based on the worldwide technology of the VSS organization, a strong commitment to R&D. VSS has over 40 years of emulsion experience in most parts of the world. The products may be broken up into two categories.
8.2 VSS Standard Emulsion Products Standard products does not mean ordinary, VSS's emulsion products based on the products classed as standard, ie. the products that in name may be the same as a competitors are all performance enhanced, storage enhance and optimized to the best job. 8.2.1 Microfine emulsions VSS manufacture microfine all grades as microfine emulsions. This means mean particle size of 2-3um. When you consider that conventional emulsions are of the order of 8-10um it is obvious that there is a difference. CONCLUSIONS: EMULSIONS ARE VERSATILE AND COMPLEX PRODUCTS BUT WITH THE RIGHT TECHNOLOGY, CHEMICALS AND EQUIPMENT EMULSIONS CAN SOLVE MANY ROAD PROBLEMS IN AN ECONOMIC, SAFE AND ENVIRONMENTALLY FRIENDLY WAY. Back to VSS Technology Papers Library Copyright © 2000 Valley Slurry Seal Co All Rights Reserved. |
