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Tips on preparations for concrete construction placing

When it comes to concrete placing there are a few things to remember about preparations are:

  1. Have all placing equipment and manpower ready before the first ready mix truck arrives;
  2. Use the lowest slump concrete that can be properly placed, consolidated and finished;
  3. Use concrete with a lower water content at the top of deep members and progressively increased toward the bottom to equalize water content when bleeding occurs.

For tips on placing:

  1. Dump concrete into the face of concrete in place.
  2. Deposit concrete close to its final position and avoid moving it horizontally in the forms.
  3. Place concrete in layers that are no more than 1 and one-half or 2 feet deep.
  4. When placing concrete through a network of reinforcement or in deep forms, use a flexible drop chute.
  5. Don’t place concrete on cold or hot reinforcement. Don’t deposit all concrete through the tops of deep forms.
  6. Provide form ports along the sides with outside pockets that have a flat bottom.
  7. When placing concrete under water, use a tremie and high slump concrete with a high percentage of fines.
  8. And finally, when bonding is desired, scrub a grout or mortar coat into hardened concrete to roughen the surface before casting a new layer.

Use vibrators wherever practicable to achieve denser, more durable concrete. When using vibrators remember to:

  1. Match vibrators to the depth of the concrete layer and the slump of the mix.
  2. Insert vibrators heads deep enough into concrete layers to extend several inches into the previously placed layer, which should still be plastic.
  3. Insert them vertically, not at random angles in the concrete.
  4. Don’t depend on integral vibrators to consolidate concrete along intricate form faces.
  5. Use hand spading or puddling.
  6. Don’t over-vibrate, or attempt revibration without someone experienced with this technique on hand.
  7. And finally, don’t use form vibrators, as internal types can do the job as well.


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Dennis Ayemba
Country/ Features Editor, Kenya


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