What is the limitation on the nominal maximum size of aggregate used in concrete?

The limitation on the nominal maximum size of aggregate used in concrete is crucial for ensuring that the concrete mix can be properly placed and consolidated within the forms. The correct answer states that the aggregate must not exceed the narrowest dimension of the forms. This guideline is significant because if the aggregate size is too large, it could prevent the concrete from flowing adequately into the formwork, leading to voids, honeycombing, or insufficient compaction.

In concrete applications, maintaining the correct aggregate size relative to the form dimensions helps optimize the performance and integrity of the hardened concrete. It facilitates proper mixing, pouring, and consolidation around reinforcing steel, which is vital for achieving the desired structural strength. This relationship between aggregate size and form dimension is especially important in narrower forms where larger aggregates would impede the filling process, hence compromising the overall quality of the concrete.

While other options imply certain considerations about size relationships within the aggregate, they do not specifically address the fundamental requirement that the aggregate's maximum dimension must fit within the form's dimensions to ensure effective concrete placement.