When used to produce flowing concrete, a superplasticizer can make placing and consolidating concrete much easier. Here are some of the guidelines the U.S. Corps of Engineers developed for placing flowing concrete.

HIGHER FREE FALL, THICKER LIFTS

Because properly designed flowing concrete does not segregate and is easy to consolidate, lift thicknesses and free fall limits usually can be increased. Architectural concrete can be placed in 3- to 4-foot lifts and structural concrete in 7-foot lifts.

HOW TO PLACE FLOWING CONCRETE

Use concrete pumps to place flowing concrete whenever possible. Pump pressures usually can be reduced significantly. If pumps are not available, use extra large buckets.

SOME VIBRATION STILL REQUIRED

Flowing concrete does require some vibration, about 25 percent of what is required to consolidate 2- to 4-inch-slump concrete. The frequency of the vibrator should be at least 7000 vibrations per minute, preferably close to 10,000 vibrations per minute.

SOME ADDITIONAL POINTS

If the mix is properly designed, flowing concrete will float and trowel much like normal slump concrete. However, if the mix is oversanded or the air content is too high or both, the surface of the concrete may dry before it sets, making it sticky and difficult to finish.

Column and wall forms must be designed to withstand a full liquid head. Form joints must be constructed tightly also. Flowing concrete will leak through even small cracks and leave surface defects.