Which method is recommended for consolidating concrete where stay-in-place forms are used for a foundation?

The recommended method for consolidating concrete when using stay-in-place forms for a foundation is internal vibration. This technique involves inserting a vibrating device directly into the wet concrete mixture. Internal vibration effectively reduces air pockets and voids, ensuring a denser and more uniform concrete structure, which is particularly important when forms are not meant to be removed. It facilitates deeper penetration of vibration, resulting in optimal consolidation at various depths.

By utilizing internal vibration, workers can effectively consolidate areas that might be difficult to compress using external methods due to form constraints or concrete placement practices. This method also minimizes the risk of damaging the forms, which might occur if external vibration is used too aggressively. The internal vibration helps achieve a high-quality finish and adequate strength of the foundation.

Considering the other consolidation methods, hand tamping can be labor-intensive and ineffective in achieving full compaction in larger forms, while external vibration may not adequately reach the lower depths of the concrete, potentially leaving weaknesses in the structure. Mechanical compaction, while useful in some scenarios, is not practical for consolidating concrete in stay-in-place forms, as it can be disruptive to the formwork and overall alignment. Thus, internal vibration is the most efficient and effective choice in this context.