Column discoloration 5

[khinz]

What is this discoloration in the lower part of the column? it's not honeycomb because I tried hammering it and there is no honeycomb. Anyone has encountered this? How do you fix it?

 

[BadgerPE]

Was fly ash used in the mix? If so, there may not be any way to fix the discoloration.

 

[khinz]

What's fly ash? why is it in the lower part of the column? I'm thinking whether it may be cause by some water leaking out leaving the cement behind (that's why it has color of cement, is this possible)? It's not honeycomb. No one has encountered this yet?

 

[dik]

What is the colour range? Can you post a photo that shows it?

Dik

 

[BadgerPE]

Fly ash is an admixture used to reduce the amount of cement needed. It is a byproduct of the coal power generating process and can reduce the cost of concrete significantly without reducing the strength significantly when portioned correctly. However, fly ash can cause streaking and discoloration of the concrete.

 

[khinz]

this is another column nearby with honeycomb.. note the same color pattern

the original picture has no honeycomb but has same color pattern as the honeycomb.. could it be lack of water in the concrete or in the verge of honeycomb?

About the picture above... hammering it appear it is only in the concrete cover.. is it serious enough to warrant removing the entire layer of the concrete and pouring new one? What have you experienced?

 

[PUEngineer]

When looking at the first picture I thought maybe it had some patching at the base, but the second picture doesn't agree with that thought.

Are you worried about structural issues? I wouldn't worry about structural issues, however I'd suggest that any loose material be removed and then the honeycombing should be patched; if it's truely just in the cover as you've stated. If you're still worried about structural issues, not exactly conclusive, but you could have the surface tested with a swiss hammer or something of the like.

 

[khinz]

How do you tell how deep it extends? I see solid concrete inside but not sure if there is micro honeycombs.. I don't want to keep hammering it because it can reach further inside.

When you use hammer on concrete.. is it supposed to be damaged significantly? how do I know if the hammer is removing honeycomb or normal concrete?

 

[PUEngineer]

Depends on the hammer; sounding hammer, framing hammer, sledge hammer, jack hammer, hammer scampi, etc. In my experience with a normal framing hammer; a good solid 'drive a nail in one swing' type of 'whack' shouldn't do much damage. That depends a little on how green the concrete is, it might dent the surface a little.

 

[khinz]

how long in your experience does the concrete stay green before it gets super hard? during green, it can be strike with hammer? i use a normal carpenter nail hammer

 

[khinz]

by the way.. in honeycombing pictures in the net, they honeycomb is same color as concrete (whitish).. but in the columns I saw, the honeycombs have color of fresh cement grout, the first picture has the same color but no honeycomb.. any theory where the colors come from especially in the first page picture?

 

[PUEngineer]

There have been questions about the use of fly ash, you haven't responded to that. What does the contractor or concrete supplier say about your concern? Was the slump high enough to cause segregation? What were the vibration techniques used?

 

[hokie66]

My guess for the discolouration would be that an excessive amount of form release oil was used. As to the honeycombing, leaky forms and/or inadequate consolidation.

 

[khinz]

The slump is 3/4 aggregates and it's 4000 psi concrete with only $2 difference to 3000 psi so admixture is probably used. The concrete supplier won't say what they use since it's company secret and they said they only supply concrete. But let's say it's ash fly, why is it at the bottom only? The contractor doesn't know either although the foreman said before concrete is pour, a liquid basin of grout cement is poured inside to seal any cement cracks in the surface of the previous lift at the floor level, could the discoloration at the bottom be from this liquid basin of grout cement? Vibrator technique is adequate as the hose is lowered all the way to the bottom and every sides and center vibrated.

Here's another picture of it at another angle. Is there no possibility it is caused by water leaking out of the cement rather than the honeycomb principle of cement leaking out of the aggregate?

 

[hokie66]

"Liquid basin of grout cement"? That could be your answer, and could present a bigger problem than discolouration. Why are you concerned about discolouration? This certainly does not appear to be architecturally exposed concrete.

 

[khinz]

but if you will note about the second picture (or again the following), the discoloration is half the height of the column in the location of the honeycombs. So it could be related to some liquid leaking. So i guess micro liquid leaking just cause the discoloration at bottom without honeycomb. More liquid leaking gives full fledge honeycomb. What do you think of this theory?

 

[Ron]

One of two reasons for discoloration...excessive form release or mortar "pig" from pump. Not likely fly ash as it would not segregate in that manner...too fine.

 

[khinz]

mortal "pig" from pump? what's that? no, the pump crete hose wasn't directly aimed inside the formwork but the column was filled up by aiming at a board on top of the column opening.


for the separate issue of honeycombing. Has anyone ever used epoxy in treating honeycomb? a worker suggested the honeycomb need not be removed but epoxy can be pumped thru the holes at high pressure filling up all spaces inside the honeycomb. has anyone ever used this technique? or is this never used?

 

[hokie66]

The mortar pig, as Ron called it, is the same no matter how it was placed, but the way you described will invariably lead to segregation.

Don't listen to that worker. You can't be sure of filling all honeycombing voids by injecting epoxy.

 

[khinz]

this is close up of the discoloration in the vicinity of the honeycomb (the left I hammer to see how deep it is, it's not deep enough is it).. haven't any of you guys ever encountered it before? it's only in the vicinity of the honeycomb so it must be related to leak or segregation problem. any other theories?