Can Vibrating Concrete Screed Be Used for Vibrating Concrete?

Compacting Concrete

• When concrete is poured and spread, it has to be compacted to remove air pockets. Compacting is executed by vibrating the concrete as it's placed, while it's still in plastic condition. Vibrating liquefies the concrete, pushing the air out and forcing the concrete into all parts of the forms. For large flatwork projects, vibrating is done using a vibrating screed or internal vibrator. Mechanical screeding saves labor and results in quality work.

Vibrating Screed

• Screeding levels and compacts concrete slabs, and can be done manually or mechanically. The screeding operation involves resting a long metal or lumber board -- the screed -- on the forms, tilting it, and drawing it across the concrete. A mechanical screed is a gas-powered engine or electric motor, mounted at the center of a beam. It's a heavy piece of equipment, and usually requires a member of the crew at each end to pull it along.

Using a Vibrating Screed

• It's best if the slab can be engineered and laid out for a vibrating screed. Forms are laid out in equal widths, so the same length of beam can be used, and vertical elements, such as columns, are placed next to the forms so the screed can be lifted around them. The vibration speed is adjusted for the concrete mix and the length of beam -- drier mixes and longer beams need more vibrating speed.

Advantages of Compacting with a Vibrating Screed

• Mechanical screeding is better for compaction than manual screeding. It works quickly, and is less tiring than screeding by hand. It also allows for a low-slump mix (with less water) which makes stronger concrete, but lacks workability for manual screeding. The drier mix sets faster, allowing the concrete to be finished sooner. Mechanical screeding increases the density of concrete, making a durable wearing surface, and it reduces the need for hand tamping and bull floating.