Download PDF version (272.4k). The full text of this article is
available as a PDF document. Some precast/prestressed structures
require external vibration due to rebar congestion, a stiff mix
or a relatively thin cross-section. And internally vibrating
long prestressed products such as beams or girders is especially
labor-intensive. Many producers use external vibrators in
addition to internal vibrators to consolidate concrete more
quickly. Regardless of mounting, select a vibrator with high-
frequency, low-amplitude output to reduce form damage. (For
material-movement purposes, i.e., installation on aggregate bin
hoppers, a higher amplitude is acceptable.) Pneumatically
powered vibrators' vibrations-per-minute (VPM) capabilities are
greater than those of most electric vibrators. The hose diameter
regulates the amount of compressed air entering the unit, which,
in turn, regulates VPMs. It's important to match hose and
fitting diameter to prevent air-flow restriction and
insufficient vibration. Eccentric weigh