PLACING CONCRETE

LEARNING OBJECTIVE: Upon completing this section, you should be able to describe the proper placing procedures for well-designed concrete.

You cannot obtain the full value of well-designed concrete without using proper placing procedures. Good concrete placing and compacting techniques produce a tight bond between the paste and aggregate and fill the forms completely. Both of these factors contribute to the full strength and best appearance of concrete. The following are some of the principles of concrete placement:

Segregation - Avoid segregation during all operations, from the mixer to the point of placement, including final consolidation and finishing.

Consolidation - Thoroughly consolidate the concrete, working solidly around all embedded reinforcement and filling all form angles and corners.

Bonding - When placing fresh concrete against or upon hardened concrete, make sure that a good bond develops.

Temperature control - Take appropriate steps to control the temperature of fresh concrete from mixing through final placement. Protect the concrete from temperature extremes after placement.

Maximum drop - To save time and effort, you may be tempted to simply drop the concrete directly from the delivery chute regardless of form height. However, unless the free fall into the form is less than 4 feet, use vertical pipes, suitable drop chutes, or baffles. Figure 7-41 suggests several ways to control concrete fall. Good control prevents honeycombing and other undesirable results.

Figure 7-41.-Concrete placing techniques.