slump test without additives 2

[chekre]

Hi guys,
i had an inspection on a site where they were pouring a concrete Slab. The concrete is C35/45. The concrete slump is reaching 21 cm although no superplasticizer has been added to the mix. it is too much since the allowable for slabs as i know is around 14 cm.
What is weird is that the cube tests are giving very good results. The recommnended is 45 and they are reaching 55Mpa.
any ideas ?

 

[JAE]

Sometimes the testing lab takes samples, then the foreman adds water to the truck.



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[shazi1]

Cube sampling was done before discharge for start of placing concrete in structure? if that's the case then its clear indication of water added to truck after sampling of concrete.
Such high slump is not possible without plasticizer.. anyways its hand mix or RMC.. nowadays nearly all mix are design with additives

 

[TXStructural]

Slump is a poor predictor of strength, in fact there is almost zero correlation EXCEPT between otherwise identical mixtures.
Slump is an indicator of variation between batches, no more, no less. Also, why would slump be tested at a different time from taking strength samples unless slump is done first, then strength samples taken AFTER admixtures have been added?

Without details, I would predict excessive shrinkage of the slabs. High slump (without water reducer) with high strength usually indicates a high cement content which usually leads to greater shrinkage. Shrinkage in slabs usually means curling, and curling means cracking.

 

[Ron]

TXS is correct. Slump determines consistency....in two forms. First is consistency as related to the viscosity of the mix (an indicator of workability), while the second is as TXS described....the consistency of batch to batch similarity.

High slump concrete can be produced with high strength....it is the water-cement ratio that determines strength.

 

[bb29510]

or you just got a good hot mix that can handle water

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