Stone Matrix Asphalt (SMA) is characterized by gap grading.

• A. Not characteristic
• B. True
• C. Sometimes
• D. False

Answer: (B)

Stone Matrix Asphalt is built around a gap-graded aggregate structure that creates a strong, interlocking stone-on-stone skeleton. By reducing or omitting certain middle-size aggregates, the mix forms deliberate gaps in the gradation. Those gaps allow the larger aggregates to lock together more effectively, giving high stiffness and excellent rut resistance. The asphalt binder, often used in higher percentage and sometimes with modifiers, fills the remaining voids and binds the skeleton into a durable matrix. Because this gap-graded design is a defining feature of SMA, the statement is true: SMA is characterized by gap grading. The other options would misrepresent SMA’s intentional gradation approach.