If you mean the "fins" that are created when the water/fines in the concrete mix "ooze" out between joints in the forms, then most likely the mix is too "wet", the forms are poorly constructed, or both.
This is just a question from my friend. He said that they are constructing a mini-dam. During concrete pouring (I think) there is seepage flow on the concrete itself and at the base of dam.
Thanks.
if this is a "mini-dam" then it appears it may be a little late to control seepage at the base of the dam. correct procedure would be to address during foundation preparation for the dam by overexcavating a cutoff trench or installing some sort of cutoff wall or grouting etc. this being based on the geotechnical engineers recommendation after doing an foundation investigation. The seepage may continue and could cause failure of the dam. A possible retrofit might be to construct a toe drain, or place a buttress fill along the downstream toe to prevent a blowout caused by high exit pressures from your "seepage"
I think that, perhaps, EricM9 is talking about seepage (weepage) through the various layerings of the dam - i.e., at the contact between successive concrete pours (presumably roller compacted concrete) rather than basal seepage. cvg is correct if, in fact, it is basal seepage. There are ways to correct - and depending on how high the dam is, expensive - foundation grouting through the dam and perhaps directional grouting under the dam from the base of the dam.
Assuming it is the case of weepage between concrete layers, attention needs to be paid to the preparation of existing surface before placing the next one - keeping it moist, use of bedding concrete on all or part of the dam width (highly sanded mix with a bit more cement - some coarse agg - typically to achieve 150mm or so of slump. Cold joints (where successive layers are placed more than a day or so later need special treatment (air/water pressure spraying or wire brushing). Outer surfaces to be kept moist for say a month after placement. No curing compounds on the layering. Magazine: International Water Power and Dam Constrution, Feb 14 2006 has a feature story on RCC consturction for emergency spillway by USBR.
another way that is sometimes used for controlling seepage through the concrete is to use some form of waterstop in the joints, often in conjunction with some sort of a key which helps to lock the joint together.
I still don't understand what the problem is here. Just by the posts from EricM9 I think that what is being described is water migrating to the surface of the concrete shortly after casting. This could be a mix design problem, this would become more severe if the slumps are all approaching (or exceeding!) the maximum.
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