When would a construction joint typically not be used?

A construction joint is generally utilized in scenarios where different sections of concrete are poured separately, either to manage the curing process, control cracking, or accommodate the expansion and contraction of the material. The proper understanding of when these joints are employed is critical in achieving structural integrity and longevity of concrete structures.

When the entire slab is being poured at once, it reduces the risk of cracking and eliminates the need for a construction joint. A continuous pour allows for a monolithic structure where the concrete can bond throughout the newly placed material without interruption. This method generally results in a stronger, more cohesive slab because there are no points of weakness introduced by joints.

In contrast, when concrete is poured in sections, construction joints are essential to account for the differences in set times and to help manage shrinkage and cracking. They are also needed to handle thermal expansion and contraction over time, which is vital for maintaining the integrity of a structure as temperatures fluctuate. Thus, using a construction joint in a situation where the entire slab is poured simultaneously is unnecessary, making it the correct answer in this context.