At present, the commonly used stabilizers for cold recycling of asphalt pavement are cement and emulsified asphalt, and foam asphalt has gradually become a research hotspot. The different characteristics of these three stabilizers determine their unique design methods, construction processes, and quality control standards during the cold regeneration process. Table 1 compares the advantages and disadvantages of the three different cold regeneration stabilizers mentioned above.
When cement is used as a stabilizer, there are two ways to add it: one is to mix solid powder cement with recycled materials, and the other is to mix it with recycled materials in the form of cement slurry.
When using cement as a stabilizer, the recycled structural layer is prone to shrinkage cracks, and the following aspects should be considered to minimize the degree of shrinkage cracking
Cement content. A large amount of cement results in a large shrinkage. To control shrinkage cracking, the dosage of cement stabilizer is 2% to 4%.
The nature of recycled materials. When certain materials are treated with cement, the shrinkage is particularly large; Some materials have significant volume changes and high plasticity indices when the water content changes. When the plasticity index of the material is greater than 10, cement should not be used alone for stabilization treatment. Lime must be mixed with cement or used alone to reduce the plasticity of the material.
The water content during construction compaction. The degree of shrinkage cracking is directly proportional to the amount of water that disappears after construction compaction and drying, but too low water content can easily cause compaction failure. It is generally recommended to control the water content during construction compaction to be 1%~1.5% lower than the optimal water content.
The rate of drying. Properly curing the structural layer material treated with cement to reduce the drying rate of the material and thus reduce shrinkage cracking. Within 7 days after the construction of the cement stabilized structural layer, it is necessary to sprinkle water for curing, or lay a temporary sealing layer and asphalt layer to avoid rapid evaporation of water on the surface of the structural layer, which may cause shrinkage and cracking of the structural layer. If a temporary sealing layer is not laid, the cement stabilized structural layer shall not be open to traffic for a certain period of time.
Cold regeneration of asphalt pavement using emulsified asphalt as stabilizer
Emulsified asphalt can be mixed with moist particles at room temperature to improve the strength of the material. Therefore, emulsified asphalt is a commonly used asphalt stabilizer. In general, mixing emulsified asphalt and cement can not only improve the water stability of the recycled mixture, but also improve its early strength. However, the amount of cement added must be controlled below 2% of the weight of the aggregate to avoid weakening the fatigue resistance of the mixture.