Vibratory rollers should be carefully or, more precisely, consciously used. An additional condition for using vibration is maintaining the appropriate temperature behind the paver to enable the movement of particles during rolling. Applying vibration to a cool SMA mixture is a mistake that leads to the crushing of particles. Vibration is not an option when SMA is being placed in a thin layer (i. e., 20-30 mm), on a stiff base (e. g., concrete slabs or a brick or block pavement), or at too cold of a mixture. Compacting SMA with vibratory steel rollers is generally permitted, but high frequency and low amplitude vibrations are a must (Asphalt Review, December 2004).
Determining the correct type of vibratory roller to use from among the following is important when considering the use of vibration:
• Classic vibratory rollers—used when it is certain that the frequency and amplitude of vibrations do not threaten to crush particles or to squeeze mastic out on the layer surface.
• Vibratory rollers with other vibration techniques
• Oscillatory—marked by vibrations within a range of oscillations, compacting a shallower depth than classic vibratory rollers but sufficient for a wearing course
• Variable direction of vibration—features the possibility of amplitude direction control.
The use of vibration can be an acceptable method of compacting SMA layers; most producers of rollers currently have solutions to minimize the risk of crushing an SMA skeleton. Obviously using vibration does not apply to the aforementioned situations (thin layer, stiff underlayer, too cold of a mix), a priori limiting the possibility of using vibratory rollers.
