What is the main role of a tack coat during the asphalt paving process?

The main role of a tack coat in the asphalt paving process is to enhance adhesion between layers. Tack coat is a thin layer of asphalt emulsion applied to the surface of a previously laid asphalt layer to promote bonding with the next layer that will be placed on top. This improved adhesion is crucial as it helps ensure the structural integrity and longevity of the pavement by preventing the new layer from slipping or separating from the existing layer.

The application of a tack coat is essential, particularly when there is a significant temperature difference between the layers or when the existing surface has been cold milled. Without proper adhesion, layers may delaminate over time, leading to premature failure of the pavement.

While the other choices mention roles that are important in the pavement process, such as sealing surfaces or controlling moisture, they do not specifically address the critical function of promoting bonding between asphalt layers, which is the primary purpose of a tack coat.