When concrete pumping is necessary, what slump rating is typically used?

In concrete pumping, a slump rating of S4 is typically used because it indicates a higher level of workability in the concrete mix. The S4 slump rating, which ranges from 100 to 120 millimeters, allows the concrete to flow more easily through the pump and reduces the risk of blockages, ensuring a smooth delivery to the pour site. This enhanced workability is crucial during pumping to maintain the integrity of the concrete and enable it to fill forms efficiently without leaving voids.

While S2 and S3 slumps can be used for general placements, they may not provide the same level of fluidity required for pumping, which can lead to inconsistent pouring or require additional effort to manage the flow. An S5 rating, which represents an even higher slump, can lead to excessive fluidity that might compromise the concrete’s strength and durability once it hardens. Thus, S4 strikes an optimal balance for pumping applications, making it the standard choice in these situations.