1. Definition of Emulsified Asphalt
Emulsified asphalt is an oil-in-water (O/W) emulsion formed by dispersing asphalt (petroleum asphalt or coal tar pitch) in water with the help of an emulsifier. It has a brownish appearance and good fluidity. Simply put, it is a process that uses special technology to uniformly suspend asphalt in a water solution containing an emulsifier in the form of tiny particles.
The emulsifier is a crucial component of emulsified asphalt; it is a surfactant. Emulsifier molecules have hydrophilic and hydrophobic (lipophilic) groups. The hydrophobic groups bind to the asphalt particles, while the hydrophilic groups extend into the water solution, thereby reducing the surface tension between the asphalt and water, allowing the asphalt to be stably dispersed in the water. Simultaneously, to ensure the stability of the emulsion, stabilizers such as calcium chloride and ammonium chloride may be added.

2. Construction Application Scenarios
- Tack Coat Construction in Road Engineering
A tack coat is a structural layer placed on top of the base course (such as a cement-stabilized crushed stone base course) and below the asphalt surface layer. Emulsified asphalt tack coat application involves uniformly spraying diluted emulsified asphalt onto the base course surface. Its purpose is to allow the emulsified asphalt to penetrate the pores of the base course, sealing the surface, preventing moisture from rising to the surface layer, and enhancing the bond between the base and surface layers.
- For example, in new highway construction, after the cement-stabilized base course is completed, emulsified asphalt tack coat is evenly sprayed onto the base course surface using a distributor, typically at a rate of 0.7-1.5 L/m2. After the emulsified asphalt has penetrated and broken down (surface moisture has largely evaporated, and the asphalt begins to solidify), the asphalt surface layer is then laid.
- Tack coat application in road engineering
- Tack coats are mainly used for interlayer bonding in multi-layer asphalt pavement structures, such as between the upper and lower layers of asphalt concrete, or at the connection points between the asphalt pavement and structures like bridges and tunnels. By spraying emulsified asphalt tack coat, a tight bond is formed between the upper and lower asphalt structural layers, preventing interlayer slippage.
- For example, in urban road renovation projects, when adding a new surface layer to an old asphalt pavement, emulsified asphalt tack coat is sprayed onto the old pavement, typically at a rate of 0.3-0.6 L/m2, and then the new surface layer is laid immediately. This ensures good adhesion between the old and new pavements, improving the overall integrity of the road surface.
- Road sealing layer construction
- Sealing layers are divided into upper and lower sealing layers. The upper sealing layer is mainly used to protect the road surface from direct damage from natural and man-made factors such as rainwater erosion, sun exposure, and vehicle wear, while also improving the road surface's skid resistance. The lower sealing layer mainly protects the base layer from rainwater erosion.
- For upper sealing layers, emulsified asphalt slurry sealing is used on some mountain roads or tourist roads that are easily affected by natural factors. During construction, emulsified asphalt, aggregates, water, and additives are mixed in a certain proportion and then spread on the road surface using specialized equipment, typically to a thickness of 3-10 mm, forming a protective layer. For the under-sealing layer, after the construction of the new road base course is completed, an emulsified asphalt under-sealing layer is used to prevent the base course from being washed away by rainwater, laying a good foundation for subsequent pavement construction.
- Cold Mix Asphalt Mixture Construction
- Emulsified asphalt can be used to prepare cold mix asphalt mixtures, which can be mixed and applied at room temperature. It is mainly used for repairing road defects, such as potholes and ruts. It can also be used for the construction of some small roads or parking lots.
- For example, in the routine maintenance of urban roads, when small potholes appear, emulsified asphalt cold mix mixtures are used for repair. After mixing the emulsified asphalt, aggregates, and appropriate additives evenly at room temperature, it is filled into the potholes and compacted. The operation is simple and convenient, requiring no high-temperature heating like hot mix asphalt, and can quickly restore the smoothness of the road surface.