What is the specified thickness of gyratory specimens?

• A. 90 ± 5 millimeters
• B. 95 ± 5 millimeters
• C. 100 ± 5 millimeters
• D. 85 ± 2 millimeters

Answer: (B)

Understanding how tall a gyratory specimen should be is about controlling its volume. In asphalt mix testing, the gyratory compactor produces cylindrical specimens with a fixed cross‑section and a target height so that the amount of air voids and the density can be compared across samples and laboratories. The specified thickness is 95 millimeters with a tolerance of ±5 millimeters because this height provides a practical, representative volume while keeping the geometry such that density, stiffness, and performance measurements stay reliable and comparable. The tolerance allows small molding variations without pushing the specimen into ranges where the air void content would drift outside the acceptable band. If the specimen were significantly thinner or thicker, the density and mechanical response would change, leading to inconsistent results. Therefore, 95 ± 5 millimeters is the standard choice.