Five primary variables are under the control of the roller operator during the compaction process: roller speed, number of roller passes, rolling zone, rolling pattern, and vibration frequency and amplitude for vibratory rollers.
The faster a roller moves over a particular point on a new HMA pavement surface, the less time the weight of the roller dwells on that point. This means that less compactive effort is imparted to the mixture at higher roller speeds than at lower speeds. As asphalt roller speed increases, the density achieved with each roller pass decreases.
For static steel-wheel rollers and vibratory rollers that have a maximum frequency of 2,400 vibrations per minute (vpm), 21¦2 mph typically is accepted as the maximum speed a roller should travel. For a vibratory roller capable of applying compactive effort at a rate of 3,600 vpm, the roller can be operated up to 4 mph. For a pneumatic-tire roller, the maximum speed should also be 4 mph. Rollers can move faster or slower than the recommended speed, but compaction varies directly with roller speed.
