Surface irregularities in concrete wall
Surface irregularities in concrete wall
(OP)
Hello All,
We are troubled with change in color of concrete in METRO tunnel wall. The wall is 30 m long and casted in multiple lifts 500-1000mm thick at one time. In this 6.5m meter wall, we see color layers have different colors, from light to dark grey. The concrete supplier says that it is due to varying color of flyash in the mix and the surface and color of formwork used.
what could be other possible reasons for such changes in color of concrete other than inconsistent W/C in different batches?
We are troubled with change in color of concrete in METRO tunnel wall. The wall is 30 m long and casted in multiple lifts 500-1000mm thick at one time. In this 6.5m meter wall, we see color layers have different colors, from light to dark grey. The concrete supplier says that it is due to varying color of flyash in the mix and the surface and color of formwork used.
what could be other possible reasons for such changes in color of concrete other than inconsistent W/C in different batches?





RE: Surface irregularities in concrete wall
I'd agree with the contractor; my first thought would be different colors produced by the fly ash used in each batch. Are you seeing the color change between each lift in a pour, between cold joints, and/or between form joints?
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/
RE: Surface irregularities in concrete wall
RE: Surface irregularities in concrete wall
RE: Surface irregularities in concrete wall
Also, I will respectfully disagree with hokie on one point; don't paint concrete! (Pet peeve of mine) It's a durable surface finish and that requires little to no annual maintenance for appearance; why replace it with a surface finish that requires regular attention to keep looking nice? Stamped or form lined concrete is a much better way if you want to break things up visually.
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/
RE: Surface irregularities in concrete wall
100% overkill but it's your wall, not mine.
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/
RE: Surface irregularities in concrete wall
We've used Nawkaw in Canada with excellent results; you might check to see if they have someone local. If not, there are likely many 'concrete staining' outfits that can do the work.
Dik
RE: Surface irregularities in concrete wall
I agree, looks good to me. I'd also worry about the integrity of any skim coating fix you may try. Might end up with more problems down the line.
RE: Surface irregularities in concrete wall
a. Variable rates of formwork oil application
b. Formwork surface
c. Difference in flyash color
d. Variable batch to batch w/c
Kindly share your views.
Thanks in advance
RE: Surface irregularities in concrete wall
RE: Surface irregularities in concrete wall
The discoloration definitely looks again like differential drying against the forms, no change from the previous thoughts we had.
However, what caused the broken surface finish in those photos? Did they pull the forms too early and peel chunks out of the concrete? That's definitely not something I would allow to go unrepaired.
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/
RE: Surface irregularities in concrete wall
RE: Surface irregularities in concrete wall
Regarding the above;
(a) seems most likely to me
(b) also likely but I'd rule out oil first
(c) & (d) seems less likely to be the main cause but that one section with the pour lines definitely had an issue with the mix or had too much time between pours.
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/
RE: Surface irregularities in concrete wall
Attached is another photo where one piece is totally light and uniform color than the rest of the wall !! The supplied concrete is same and all records are verified okay for w/c and flyash. Still this variation in shade is not understood. ANy ideas to share please
RE: Surface irregularities in concrete wall
Contractor A : a) Uses 5 different subcontractors for formwork & concreting operations b)formworks are not properly oiled by release agent. c) Flyash has slight color variations
Contractor B : a) Uses only one subcontractor for formwork & concreting operations b) workmanship is better in all forms c) Flyash has uniform color
RE: Surface irregularities in concrete wall
Post 30 Dec 17 07:43 seem to indicate in rather remarkable contrast that something in the composition or preparation of the form work is responsible for the color variation. Literally, one looks like it has been prepared with form oil, maybe even diesel fuel & the other with a chemical release agent. If not that then you have to look at the form face, itself. Aluminum, steel, plywood (species)?
Depending on ground water elevations, I'd be more concerned about the two cold-pour lines and the steady delivery of concrete during production & having enough vibrators to join the lifts, if there is a delay. That is really some haphazard placement.
RE: Surface irregularities in concrete wall
How can we get uniform color of concrete wall? My corrective actions would be,
1. Clean adhering dust coating or laitance from the formwork
2. Uniform application of suitable form release oil
3. proper placement and good vibration
RE: Surface irregularities in concrete wall
4. Use of one coloured flyash in all pours
RE: Surface irregularities in concrete wall
It is important to follow the Form Release manufacturers instruction. It has been a while since I have read up on them, so don't take my words as gold but some form release agents react chemically when the concrete is placed and too heavy an application is not good for the finish, other release agents, if I recall correctly rely on a weak hydrophobic action but again an uneven application can result in trapped water.
Are the forms faced with ordinary mdf plywood and if so, how old is it? Could it be swelling from water uptake & relaxing/distorting? Plywood that is past it good usage would also tend to make an even application of form release difficult to gauge since the open grain of the sheet will soak up the release agent and the denser grained areas will hold it at the surface.
RE: Surface irregularities in concrete wall
Please see latest photo (1) that shows dark and light shades. Why is this happening? any clues please...
1. too much release agent
2. too less release agent
3. no release agent
4. mix gradation issue
5. high slumps or variable w/c
6. different form face
7. vibrator near to surface/ over vibration / under vibration
8. flyash
9. reaction of form release with concrete
what???
RE: Surface irregularities in concrete wall
Please need your support to find the root cause...
RE: Surface irregularities in concrete wall
RE: Surface irregularities in concrete wall
Simple solution, get rid of the contractor that isn't performing the work sufficiently or get them to do the same things that the better contractor is doing (what epoxybot said).
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/