Title: Vibration Of Concrete
Author(s): W. R. Johnson
Publication: Journal Proceedings
Appears on pages(s): 429-431
The selection of a vibrator to be used on a job is dependent on the type of form in which the com- crete is being batches ranging fr laced, Large open forms, using rom 2 to 6 cu yd, with aggregate graded up to 9-in. maximum size require a two-man vibrator. Thin walls and heavily reinforced sections should use internal vibrators operated by one man. Form vibrators are used where internal vibrators cannot be used, such as tunnel linin pipe. One vibrator will effectively handle concrete from 12 to 36 cu yd per hr. Formwork need not be changed but should be made as tight as possible to prevent leakage. Drier concrete can be used when placing with vibration; sand in the mix can be reduced 2 to 4 percent. Determining the end point of vibration is a matter of experience which is soon acquired the foreman or inspector. For measuring the the by effectiveness of equipment, work two or more vibrators of different type in the same form at the same time. Lower costs of vibrated concrete are due to saving in cement which amounts to one-half to one bag of cement per cu yd of concrete. The higher quality of concrete placed by vibration is due to drier mixes used, which means less free water, lower water-cement ratios, and less volume change.