What method must be used to consolidate concrete with a slump of less than 1 inch?

When dealing with concrete with a slump of less than 1 inch, vibration is the appropriate method for consolidation. This is because low-slump concrete is typically very stiff and may not flow easily. Vibration effectively reduces the air voids within the mix and helps the concrete settle into place, ensuring uniformity and strength in the finished product.

Vibration helps achieve better compaction by shaking the particles closer together without adding additional water, which can compromise the concrete's integrity. As a result, this ensures that the final structure achieves the desired density and durability.

In contrast, other methods like hand tamping can be labor-intensive and less effective with such stiff mixes. Water saturation could negatively affect the concrete's properties, and mechanical stirring is generally not suitable for final consolidation as it may not adequately remove entrained air or create the necessary density in low-slump mixes.