January 11, 2022
Should structural engineers specify slump in the construction documents?….No, slump should be specified by the contractor and concrete producer.
Reasoning below:
1. Slump is not a good indicator of the quality of hardened concrete. This has always been true (as indicated in ASTM C143 – care should be taken in correlating slump results under field conditions to strength), but is even more true today with the widespread use of water reducing admixtures.
2. The National Concrete Ready Mixed Concrete Association (NCRMCA) recommends against it – “The engineer should avoid specifying a slump requirement as it might impact the ability to place the concrete” NRMCA Guide to Improving Specifications for Ready Mixed Concrete
3.. Not required by the building code. ACI 318 does not list slump as a required item to be included in the construction documents and ACI 301 indicates that slump selection should be by the contractor and documented in the submittal.