What is the thin steel shell used in the placement of cast-in-place concrete piles called?

• A. Masonry Plate
• B. Nail Laminated
• C. Maintenance of Traffic
• D. Mandrel

Answer: (D)

A mandrel is the thin steel shell used as a temporary inner form or lining during the placement of cast-in-place piles. In bored or cast-in-place pile work, this shell provides a smooth interior surface, helps keep the bore open, and guides the concrete as it is poured, ensuring the pile takes and maintains its intended cross-section during construction. The mandrel may be removed after the concrete sets (or left in place, depending on the pile type), leaving the desired hollow or solid interior shape as designed.

The other terms listed don’t relate to pile forming: a masonry plate is a component used in masonry work, nail-laminated refers to a wood-based construction method, and maintenance of traffic concerns work-zone management rather than any structural form used in pile placement.