Which of the following indicates an overheated HMA mixture?

The presence of blue smoke is a clear indicator of an overheated Hot Mix Asphalt (HMA) mixture. When HMA is overheated, it typically results in the degradation of the asphalt binder and can lead to the production of vapors, which manifest as blue smoke. This smoke may indicate not just overheating, but also a potential loss of performance characteristics due to binder oxidation or burning.

Understanding the context of blue smoke helps identify the overall quality of the asphalt mixture being used. If observed, this smoke suggests that care must be taken to monitor the temperature of the HMA during production and placement to ensure it remains within optimal limits for performance.

In contrast, segregation is related to the uneven distribution of aggregates within the mix and does not directly indicate overheating. The presence of mica typically relates to the mineral composition and not temperature. A stiff appearance in the truck could be due to various factors, including low temperatures or insufficient mixing, but it is not solely indicative of overheating. Thus, blue smoke is the most definitive sign of an overheated mixture.