Vibratory compaction of asphalt concrete

A total of 10 different roller models were used on 10 contracts-3 overlays and 7 new constructions. Discovery of two important operating parameters resulted in development of performance criteria applicable to any roller. These parameters the spacing of drum impacts and their magnitude can be controlled by adjusting forward speed, and drum amplitude. Impact magnitude was correlated with layer thickness to produce the ranges necessary for each lift. The force necessary for adequate compaction increased with lift thickness, but on lifts thinner than 3 in., the maximum force applied was found to be equally critical. If too great, roller rebound occurred, reducing densities. Vibratory rollers also compacted single-lift wearing and base courses-respectively 2 1/2 and up to 8 in.--more efficiently than conventional rolling. In sum, vibratory rollers when operated properly were found to be effective in compacting asphalt concrete. Also rather than accept or reject rollers individually, operating criteria were developed to determine the ability of any roller to compact a given lift thickness.