Emulsified asphalt is a suspension of asphalt in water, stabilized by an emulsifying agent that imparts an electric charge to the asphalt particles, causing them to coalesce. Cutback asphalt, in contrast, is simply asphalt dissolved in petroleum solvent. The addition of emulsifying agent or petroleum solvent in these respective types of asphalt serves to lower its viscosity at lower temperatures, making it easier to apply and work with.
Initially, the emulsion used for tack coat appears brown upon application. As the asphalt particles bind to the surface and the water begins to evaporate, the color transitions to black, a process known as “breaking.” The emulsion is considered “set” when all the water has evaporated. Similarly, cutback asphalt is said to “cure” as the solvent evaporates.
However, cutback asphalts present several drawbacks compared to emulsified asphalt:
- Application Rate: Emulsified asphalt can be diluted with water, allowing for a lower application rate and potentially reducing material costs.
- Environmental Impact: The evaporation of petroleum solvents from cutback asphalt releases volatile organic compounds (VOCs) into the atmosphere, contributing to air pollution and environmental concerns.
- Production Cost: Petroleum solvents are generally more expensive to produce than emulsifying agents and water, making cutback asphalts less cost-effective.
These disadvantages highlight the advantages of emulsified asphalt as a more sustainable and economically viable option for tack coat applications. Its lower environmental impact and cost-effectiveness make it a preferred choice in many construction projects.