After tack coat is applied, what must be done until it has sufficiently cured?

The correct answer emphasizes the importance of protecting the tack coat from traffic until it has sufficiently cured. Tack coat serves as a bonding layer between two asphalt surfaces, ensuring a strong adhesive bond and a smooth overlay. If traffic is allowed on a freshly applied tack coat, it can disrupt the curing process, resulting in an inadequate bond, which ultimately could lead to the failure of the asphalt overlay. This protection from all traffic is crucial to maintaining the integrity of the tack coat, ensuring that it can fully cure and provide the necessary adhesion for the subsequent layers.

In contrast, the other options do not adequately address the need for protection after application. Covering it with concrete is impractical since tack coat is specifically designed to bond asphalt surfaces to one another, not to be covered with other materials. Testing for adhesion is generally done after the tack coat has cured rather than during this waiting period. Opening the tack coat to light vehicle traffic could compromise the curing process, leading to bond failures. Thus, ensuring that the tack coat remains free from traffic until it is properly cured is essential for the longevity and effectiveness of the roadway surface.