What is the maximum slump that concrete should have if it is to be used for a floor slab?

The maximum slump for concrete used in floor slabs is typically recommended to be around 4 inches. A slump of this magnitude ensures that the concrete mixture has sufficient workability for placement and compaction without being too fluid, which could compromise the strength and stability of the slab.

Concrete with a 4-inch slump is considered to have the right consistency to flow and fill forms effectively while still maintaining enough paste to bind the aggregate. This is critical for creating a durable and long-lasting floor slab, as excessive water content can lead to problems such as segregation, shrinkage, and reduced strength.

Using concrete with a higher slump, such as 5 inches or more, may introduce excess water into the mix, leading to increased porosity and reduced durability. Similarly, lower slump levels like 2 or 3 inches might make it challenging to properly place and finish the concrete, risking incomplete compaction and surface issues. Therefore, the 4-inch slump strikes a balance that supports both ease of work and the structural integrity of the final product.