Concrete Bleed Water Staining

[Gammyleg]

Hi,

Can anyone confirm what the black material is on the attached photo.

Photo taken after finishing of basement floor slab. It's a blended CEM1 & GGBS F5 flow mix which, upon inspection of the placement records, was regularly in excess of maximum flow limits and hence exhibited excessive bleed characteristics.

I have seen the same black substance streaking on high consistence mixes elsewhere and also in the lab when we have blown mixes by adding too much superplasticizer &/or water.

My suspicion is that it is one of the constituents of either the CEM1 or the GGBS, but which?

Thanks

 

[Ron]

First...the finish is atrocious! Very poor control on concrete.

The staining appears to be black. That is not consistent with GGBFS....that would be a greenish-blue color until oxidation. Black particles are generally associated with fly ash. This is extreme. The durability of this concrete will suffer!!

 

[darthsoilsguy2]

Looks like it rained in the middle of the pour.... if so, could be fly ash washing out of the mix.

 

[Gammyleg]

Thanks for the replies.

No fly ash in the mix, almost none existent in UK nowadays since all coal power generation has ceased. Also no microsilica, so as far as powder addition goes it's OPC + GGBS only.

We have had instances on this project where lignite has been present in the dredged concrete aggregates but this is usually in the form of small 'stones' rather than the fine powder seen in the photo.

As I mentioned, we have also noticed this phenomena in the laboratory pan mixer when we've overcooked the mix with either superplasticiser &/or water and where there has been no lignite contamination, so my guess is it one of the OPC constituents that is bleeding out.

Wondering whether anyone has seen OPC under the microscope to confirm different coloured particles are present.

 

[bimr]

Perhaps it is concrete dye. Some of the dye could have been become trapped in the concrete mixer from a previous concrete delivery.

 

[Ingenuity]

The black staining is loose surface-based material, right?

If so, I have seen similar 'staining' resulting from wash-out of fine basalt sand aggregate from OPC mixes, due to heavy rain during placement - however, usually the resulting finish has a more 'exposed aggregate look, that what appear in your photo.

Looks like there is a good sized 'bird-bath' where the water/stain is 'flowing'/draining to the lower-left of the photo.

Petrographic analysis will give you some good info on the as-constructed concrete constituent properties, but such microscopic analysis is not cheap.

 

[epoxybot]

There seem to be some other incidences where black particles turned out to be carbon but that was from flyash, still not to be dismissed for blast furnace slag. Kept in suspension in the mix it behaves much like silica fume. If it is carbon then it could also be coming from a water source.

 

[dik]

Can you take a small core and drag it down to a lab?

Dik

 

[Gammyleg]

Thanks for the input,

Having researched the major constituents of both GGBS & CEM1 the only thing that comes close colour-wise is the Iron Oxide in the cement. Once the concrete goes off, the black staining seems to disappear.
The finished surface looks very dusty which ties in with the excessive bleed water bringing up the fine paste/grout.

The water visible on the photo is all bleed water.

It didn't rain that day and I'm told the shutters were dry before the pour started.

 

[bimr]

Although there are number of methods for coloration of concrete, iron oxide pigments are the most commonly used by the construction industry.