What is used to create penetrations in concrete before it is poured?

The process of creating penetrations in concrete before it is poured typically involves the use of sleeving. Sleeves are tubes or casings made from materials such as plastic or metal that are placed in the formwork ahead of the concrete being poured. They allow for pipes, cables, or other utilities to pass through the concrete structure once it has cured. This is critical in ensuring that penetrations are clean and properly aligned, which enhances both the structural integrity and functionality of the installation.

Formwork is primarily used to contain the concrete while it is being poured and helps shape the final structure, but it does not create the penetrations. Reinforcement bars, or rebar, are used to strengthen the concrete but do not serve the purpose of making holes or openings. Wooden inserts may be employed to provide a structure for future fixings but are less common for making penetrations since they can complicate the removal process and might not provide the desired hole specifications for utilities. Thus, sleeving is the correct choice as it effectively facilitates the necessary overpass for utilities in concrete structures.