When it comes to concrete placing there are a few things to remember about preparations are:
- Have all placing equipment and manpower ready before the first ready mix truck arrives;
- Use the lowest slump concrete that can be properly placed, consolidated and finished;
- 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:
- Dump concrete into the face of concrete in place.
- Deposit concrete close to its final position and avoid moving it horizontally in the forms.
- Place concrete in layers that are no more than 1 and one-half or 2 feet deep.
- When placing concrete through a network of reinforcement or in deep forms, use a flexible drop chute.
- Don’t place concrete on cold or hot reinforcement. Don’t deposit all concrete through the tops of deep forms.
- Provide form ports along the sides with outside pockets that have a flat bottom.
- When placing concrete under water, use a tremie and high slump concrete with a high percentage of fines.
- 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:
- Match vibrators to the depth of the concrete layer and the slump of the mix.
- Insert vibrators heads deep enough into concrete layers to extend several inches into the previously placed layer, which should still be plastic.
- Insert them vertically, not at random angles in the concrete.
- Don’t depend on integral vibrators to consolidate concrete along intricate form faces.
- Use hand spading or puddling.
- Don’t over-vibrate, or attempt revibration without someone experienced with this technique on hand.
- And finally, don’t use form vibrators, as internal types can do the job as well.
