slump for low shrinkage concrete
slump for low shrinkage concrete
(OP)
The concrete contractor is going to pump the low-shrinkage concrete (0.02%) and questioned if the maximum slump limit of 4" indicated in the spec should be the slump at the point of placement, or at the point of delivery.
Does anyone has any comments or suggestions on this matter?
Thanks.
Does anyone has any comments or suggestions on this matter?
Thanks.





RE: slump for low shrinkage concrete
RE: slump for low shrinkage concrete
RE: slump for low shrinkage concrete
Designating the 4" slump as the limit at point of placement might entice the contractor to add too much water at the beginning and still meets the limit after the slump loss during the pumping. Designating the 4" slump as the limit at point of delivery might be over-restrictive as it might cause pump failure at point of delivery.
I am attempting to allow the 4" slump be the limit at the point of placement, if the concrete contains high-range water-reducing admixtures.
Do you think this a viable solution?
Thanks.
RE: slump for low shrinkage concrete
I don't think it is realistic to use a spec that says 100mm slump and then to say that the testing point is after pumping. The trial mixes will have to be carried out at a batching plant and won't have been through a pump so I just don't think the idea is workable.
I suggest that the slump value stated in the spec should be flexible enough to accommodate a change due to the mix design and delivery method. Therefore it could be modified to 100mm slump for delivery by crane/skip and 150mm for delivery by pump (which means 2 different mixes for the same strength grade).
RE: slump for low shrinkage concrete
RE: slump for low shrinkage concrete
RE: slump for low shrinkage concrete
This illustrates the problem with specifing slump. We as engineers really don't care what the slump is, only that the concrete perforems as required.
The design engineer should list the properties of the concrete that are required, such as shrinkage, maxiumum w/c ratio, air content, and strength. The contractor should tell the supplier what slump (at truck discharge) he needs to pump the concrete. The supplier should then supply a mix that meets all of these requirements.
If this system is followed, the slump should be checked at the point of discharge from the truck and the air content should be checked after the mix has been pumped.
Mike Lambert