What is the maximum allowable nominal aggregate size for a 6-inch slab?

For a 6-inch slab, the maximum allowable nominal aggregate size is determined by the guidelines set forth in concrete standards. Specifically, one common rule is that the maximum nominal aggregate size should not exceed one-fifth of the slab thickness. For a 6-inch slab, one-fifth of that thickness is 1.2 inches, which means that the aggregate size should not exceed this value to ensure proper mixing, compaction, and strength of the concrete.

While 2 inches is provided as an option, it exceeds the one-fifth limit and may pose challenges regarding the concrete's workability and the potential for insufficient compaction in thinner sections. Therefore, the correct answer reflects a more appropriate aggregate size consistent with industry standards, ensuring durability and structural integrity in the slab's design. The other choices do not adhere to the criteria for aggregate size in relation to slab thickness, which is why they are less suitable.