Masonry Magazine July 1978 Page. 14
Vertical cells of block to be filled with grout must be aligned so a continuous unobstructed opening is available for the full height of the grout pour. A minimum opening of 2" (5 cm.) x 3" (7.6 cm) is required in some codes.
Sizes and Shapes
With the evolution of reinforced concrete masonry, certain developments have occurred which result in more quality and efficiency of construction. Conventional "stretcher" blocks are generally 2-core units with plain ends. Thus, when units are laid up in center running bond, the cores are in alignment; and the cores are
Figure 1. Two-core units with plain, or square ends; when laid up in center running bond, continuous vertical cores are formed for easy placement of steel reinforcement and grout.
Figure 2. "Bond beam" unit for use with the block shown in Figure 1; the cores of this unit are open at the bottom, permitting vertical and horizontal reinforcing steel to extend through the unit.
Figure 3. Open end unit, or "A" - shaped block for use in reinforced concrete masonry walls where vertical steel reinforcement is required to be in place before masonry units are laid up in the wall.
Figure 4. Open-end bond beam unit for use with the unit shown in Figure 3.