What is a tack coat primarily used for in road construction?

A tack coat is primarily used in road construction to create a bonding layer on previously paved surfaces. This bonding layer is crucial for ensuring that the new asphalt layer adheres properly to the existing surface, which enhances the overall integrity and longevity of the pavement. When applying a new layer of asphalt over an old one, the tack coat helps prevent the new layer from sliding off or delaminating, which could lead to failures in the pavement structure.

In terms of the other options, while dust palliatives are important in managing surface dust, they do not pertain to the bonding of asphalt layers. Finishing concrete slabs requires different materials and techniques that are not related to tack coats. Controlling the temperature of asphalt is also not the function of a tack coat; instead, this involves techniques related to the heating and placement of the asphalt mix itself, rather than a bonding agent. Thus, the role of the tack coat is specifically focused on adhesion rather than any of these other functions.