Abstract: X-ray computed tomography (CT) technology was adopted to analyze change rules of air void number, air void size and air void ratio of 1-10 slices in the concrete with the same aggregate gradation and scanning electron microscope (SEM) was used to analyze its mechanism. The results indicate that there are more air void numbers, larger air void size and higher air void ratio in the sides of the same concrete specimens, while they are the opposite in the middle. The highest air void ratio is 10.1%. The addition of ordinary Portland cement or the adoption of asphalt emulsion with optional dosage is helpful to decrease the air void ratio. There exists the lowest air void ratio, 3.9%, in the concrete when the dosage of asphalt emulsion and cement is 8.0% and 3.0% respectively. The air void distribution is inhomogeneous.

Key words: composite asphalt concrete, X-ray computed tomography (CT) technology, binders, air void characters