Bitumen/asphalt emulsions contain a combination of three basic ingredients: bitumen, water and a small amount of emulsifier. In the same process, these components are introduced into a mechanism called a colloid mill, which breaks the bitumen into tiny droplets. An emulsifier is a surfactant that keeps bitumen droplets in a stable suspension and controls breakup times. The result is a liquid product with a consistency ranging from milk to heavy cream that can be used for cold processing in road construction and maintenance. Today, they are used in a variety of road construction and pavement protection projects. The emulsifying agent assists by imparting an electrical charge to the surface of the asphalt cement globules so that they do not coalesce. 
Emulsions are used because they effectively reduce asphalt viscosity for lower temperature uses. The emulsion product can be applied to aging pavement or immediately after road construction like a finish or sealer. This will enhance the surface’s durability, offering protection from sunlight and oxidation, protection from various chemicals, and improving weight bearing capacity. Generally, emulsions appear as a thick brown liquid when initially applied. When the asphalt cement starts to adhere to the surrounding material (aggregate, existing surface, etc.) the color changes from brown to black and the emulsion is said to have “broken”. As water begins to evaporate, the emulsion begins to behave more and more like pure asphalt cement. Once all the water has evaporated, the emulsion is said to have “set”. The time required to break and set depends upon the type of emulsion, the application rate, the temperature of the surface onto which it is applied and environmental conditions. Under most circumstances, an emulsion will set in about 1 to 2 hours. ASTM D 3628 contains guidance on selection and use of emulsified asphalt. Why use asphalt emulsions? Asphalt emulsion does not require a petroleum solvent to make it liquid and in most cases asphalt emulsions can be used without additional heat. Both of these factors contribute to energy savings. Additionally, asphalt emulsions offer great flexibility in their application since they offer the end-user a great variety of characteristics not found in other paving and maintenance materials. Asphalt emulsions are environmentally friendly. There are little or no hydrocarbon emissions created with their use. 
Are asphalt emulsions new? Asphalt emulsions were first prepared in the early part of the 20th century and today they are used all over the world. The use of asphalt emulsions is growing and 10-20% of all asphalt is used in the form of asphalt emulsions. How are asphalt emulsions classified? Asphalt emulsions are classified into three categories: anionic, cationic, or nonionic. The anionic and cationic classes refer to the electrical charges surrounding the asphalt particles. The absence of the letter “C” denotes anionic emulsions. Asphalt emulsions are further classified on the basis of how quickly they coalesce, i.e., revert to asphalt cement. The terms RS (Rapid Set), MS (Medium Set), SS (slow set), and QS (Quick Set) have been adopted to simplify and standardize this classification. Additionally, trailing numbers are used to delineate the relative viscosity if the emulsion and the letters “h” and “s” indicate whether a hard or soft base asphalt is used to make the asphalt emulsions. Thus, a CSS-1h is a cationic slow set emulsion with a relatively low asphalt emulsion viscosity made with a hard base asphalt. 
What Are the Different Types of Asphalt? As one of the most recycled and reused types of pavements on the market, asphalt is used on 94 percent of paved roads in America. However, not all asphalt is created equal. Chemical composition and other properties determine what type of asphalt you’re driving on. Types of Asphalt There are several types of asphalt paving available to homeowners and contractors. What type is right for your project? Learn about five common asphalt paving types below: Hot mix – A combination of approximately 95 percent stone, sand or gravel bound together by asphalt cement, hot mix is heated and poured at 300°F. Warm mix – Because it is mixed and shipped at lower temperatures, warm mix does not cool as fast as hot mix. It includes emulsions that make it easier to pour and spread. Cold mix – This formula doesn’t require heat and is the most affordable asphalt mix. It is used to repair potholes and pavement cracks. Cut-back – A combination of asphalt cement and petroleum solvent, cut-back asphalt is used for its decreased viscosity, or thickness. It contains volatile chemicals and is restricted in many areas. Mastic – A dense and durable formula, mastic asphalt is a waterproofing medium. It is a mixture of asphalt, stone filler and mineral powder that is heated and mixed at hot temperatures. 
Tack Coat is a thin layer of bituminous liquid asphalt emulsion that is applied between HMA (Hot Mix Asphalt) pavement lifts to promote adhesion. Adequate connection between construction lifts, particularly between existing pavement and overlay, is essential for the finished pavement structure to function as a single unit and to provide sufficient strength. If adjacent layers are not bonded to each other, they essentially behave as separate thin layers—none of them are designed to accommodate the bending stresses imposed by expected traffic. Inadequate adhesion between layers can lead to debonding, followed by cracks in the longitudinal wheel path, fatigue cracks, pits, and other problems. The tackle coat should be applied evenly over the entire pavement surface and achieve approximately 90% surface coverage. Do asphalt emulsions have any uses around the home? Driveway sealers, roofing repair materials, caulks and mastics may contain specially formulated asphalt emulsions. Uncommon Uses for Asphalt Many architects use asphalt in construction for dams, reservoirs, playgrounds and parks. Farmers use asphalt to line the bottom of retention ponds where they raise fish and in livestock containment pens. Asphalt is also an ideal solution for flood control and soil erosion. Auto makers rely on asphalt to prevent rust and road noise in fenders and hoods of cars.
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