compressive strength

[shazi1]

Recently I come across 2 concrete core test results (tested in different dates) where 28 days strength was lower by 10 MPa to 7 days... I do not have any justification to it, only reason can be honeycomb or air voids, or low quality aggregates used for concrete.. but this cases are not applicable as coring location is very near to each other.. 6 cores were taken from panel of 800*800 sq.mm.. (for 3,7 & 28 testing)_
Can anyone suggest any other reasons for such cases r had you ever encountered such situation.

 

[darthsoilsguy2]

perhaps the silt fence wasn't installed correctly.
(you're posting in the wrong forum shazi1)

 

[cvg]

you really cant compare cores to cylinder samples there may be no correlation if placement, finishing or curing was not done well. also, there are other reasons like improper curing of the slab, poor sample preparation for the core test or perhaps the core was cut through a crack in the slab