GOOD VIBRATION FOR DYNAMIC COMPACTION

An account is given of a report made to the PIARC international congress in Sydney, Australia, concerning the performance of vibratory rollers on bituminous materials and comparing them to conventional types. Details are given of the types of roller popular in other countries and of their limited use in the United Kingdom. The factors determining the effectiveness of a vibratory roller depend on the frequency and amplitude of the dynamic force, the speed of rolling and number of passes, the workability of the mix, thickness of layer being compacted and the stiffness of the separating layer. Various trials are outlined and compared with the results obtained with static rollers. A number of factors are identified which give rise to unsatisfactory results and these may include cracking or decompaction caused by over-rolling, rolling at too high a speed or temperature. Despite an initial higher cost it is concluded that in comparison with conventional rollers total compaction costs are similar and that in certain conditions vibratory rollers are particularly suitable. (TRRL)