Cast-in-place concrete placement shall conform to ACI 318, and shall be placed in layers no greater than 16 in. Vertical construction joints for cast-in-place chimney shells shall not be used. Where used, horizontal construction joints for cast-in-place and precast concrete shall be approximately evenly spaced throughout the height of the chimney shell. Grout for setting precast sections shall have a specified compressive strength equal to or greater than the specified compressive strength of the set precast sections.