What kind of block has recessed end shells and is used to build columns or piers?

The choice of a double corner block is accurate because it is specifically designed with recessed end shells, which facilitate the construction of strong and stable columns or piers. The recessed ends enable better bonding with other masonry units, ensuring that the blocks interlock effectively, promoting structural integrity. This design is critical especially in applications where vertical loads are significant, as it provides the necessary strength and support required in such structures.

Other types of blocks have different configurations that may not provide the same functional benefits. U-shaped blocks, for example, are typically used to create forms for reinforced concrete structures rather than for building solid columns or piers. Half blocks serve to fill gaps and adjust course heights, while strap blocks, though useful in certain forms of masonry, do not focus on facilitating the creation of vertical elements like columns as effectively as double corner blocks do. Understanding these nuances in block design helps in selecting the appropriate materials for specific construction needs.