VIBRATION OF PAVEMENT CONCRETE

The effects of spud vibrators mounted on slipform pavers were examined on three paving projects. Slump and entrained air of the plastic concrete were measured and paver speed was deliberately varied. A total of 364 pavement cores were taken at various distances from the vibrators for determination of density, entrapped air content, aggregate distribution, and mesh embedment. Riding quality of the finished pavement was also measured. No aggregate segregation was found, and riding quality was not affected by the vibrators. The only appreciable effect on the reinforcing mesh was a slight increase in depth directly beneath the vibrators. Both density and entrapped air content provided measures of consolidation effected by the vibration applied to the concrete. Slump and air content of the plastic concrete affected pavement density because density of water and air is less than that of the other mix materials. However they had no appreciable effect on entrapped air content. Paver speed had some effects on density and entrapped air content, but these were small within a range of paver speeds up to 19 fpm. Vibrator frequency ranged from 7,000 to 11,000 vpm on the three projects, but no substantial differences in consolidation could be attributed to these differences. The greatest effects on density and entrapped air were related to distance of the concrete from the vibrator. The top of the pavement was consolidated better than the bottom, and substantial decreases in consolidation occurred only a few inches from vibrators.