This is an isolated footing in a semi raft foundation and they are prepare to install reinforcment and then cast the raft slab
I am a trainee and I would like some help identifying What is the purpose of these cuts? Is it a "concrete repair using grouting" because i think it too much cuts here .. and what is the red and blue marks is about ?
They intentionally roughened the top so that there is a mechanical interlock with the slab.
Yes, I know about surface roughening. My question is: is cuts considered part of roughening?
Hard to tell without asking directly but I believe you have the right idea. I would not consider these cuts as "1/4" amplitude roughening" because they are too narrow for the aggregate to lock in. The crew should use a chipping hammer to roughen this up
Could be cutting to make it easier to chip, but even still RFI. We have no idea if it was supposed to be roughened.
I am in an university internship they are roughning the surface for the raft slab and I actually asked my supervisor but he halfheartedly said the cuts for concrete repairing .. i just want to make sure it is the correct answer and there is no other purposes for these cuts..
Perhaps there were cracks in the top of the concrete and they used a grinder to chase them out so they will hopefully be filled with cement in the next pour? The cuts seem a bit straight to be chasing out cracks though. Also, they aren’t wide enough to get any aggregate in there so i imagine would be of limited use anyway
RFI with pictures to the SEOR
Trainee or not, this should be the answer. That guy needs to be involved or at least made aware.
You’re getting some good answers and feedback here. All very useful to read and try understand as a student/trainee engineer.
Just a note that those column stirrup spacings seem very large to provide any reliable confinement against buckling.
Just fiber wrap later. It’ll look cool!
Pretty sure you're seeing only the vertical dowels extending from the footing, and not the lapped bars of the column cage, where the ties will be installed. The one tie you're seeing at the top here is likely just for fabrication purposes to keep the dowels in alignment.
Hmm, from what I understand, it looks like they are doing a topping pour to form the second stage of the pad. This pour would mean the column vertical bars need to be adequately confined with stirrups within the beam-column joint region (i.e within the pad) - regardless of any laps. Perhaps they haven’t put in all the reinforcement like you say. But it also stood out to me. I work in a seismically sensitive region and these details are critical for our design - and often forgotten.
When he said "semi raft" foundation I am assuming there is a mat slab to be poured now, maybe 12-14" thick or so, with these thickened areas as needed for bearing area / punching shear at the columns.
You're saying because this is a separate pour, that the column vertical bars need to be confined within the pad? Can you share a code section (if in the US) that states this? I don't know why that would be a requirement simply because of the secondary pour for an interior column like this.
Just in case it isn't clear what I meant in that post, this picture may explain. This is a small concrete column with 4-#8 or #9 vertical dowels extending up from the footing, with a compression lap to the column vertical bars that extend up to the deck. It is in this full-height assembly where the column ties actually go. This is what I think might not be installed in OP's picture, and I don't think it would need to be installed until after the mat slab is poured.
https://preview.redd.it/9al3a7jny7ag1.jpeg?width=2988&format=pjpg&auto=webp&s=1512ae886bf3b85381b99eae8f6ec0a765861779
I had a contractor do some BS like this once as “roughening the surface to 1/4” amplitude” and it made me hate ACI so much. What good is specifying amplitude if you don’t specify the wavelength or frequency? My guy bc carved 5 cuts in a 7ft wide footing and claimed it was kosher and I couldn’t challenge him. From then on I specified concrete CSP values, but I wish ACI would be specific so we’d have something concrete (hehe) to hang our hats on.
From the sound of things you definitely could have. Unless that contractor is brand new to the point of being incompetent, they're just seeing what they can get away with to save costs.
How can you challenge “Roughen to 1/4” amplitude” without specifying wavelength?
What I would have said to the contractor you were working with is "the surface isn't rough... the surface is still generally smooth and you've cut some lines in it".
There's definitely degrees of roughness, I'll give you that, but what you've described with a few cuts and flat space in between isn't surface roughness, especially if they've just saw cut not done with percussive tools.
No harm in spec'ing
amplitudewavelength going forwards though. Eurocodes have that built in, for example.I hear you man, but imagine trying to defend that in court. “Isn’t this cut (show photo) of 1/4” depth or amplitude?” There is no way to enforce additional cuts without a change order. Our contractors are litigious as shit, I hate this the most about our industry.
"yes but they've not roughened the surface in general, in fact the cuts provided roughen only ~5% of the surface with these individual cuts. We specified that the surface be roughened, not ~5% of the surface." ...would be the defence.
unless this applies to a significant amount of footings or there's already a lawsuit for other parts of the project, I'd be surprised if this was worth the contractor litigating, let alone taking to court. Court is expensive. Source... worked for 2y as a forensic structural engineer writing expert witness reports for lawyers.
Shame is a good tool to use as a last resort in situations like this. "It's not explicitly stated, even in ACI, because it's industry norm to do a better job than this" or "I've never seen a slab roughened this poorly". Show them pictures from previous jobs. Include the owner in the communications.
Are you sure we are just roughening for bond here? Because this looks like how we’d remove material when the entire thing was cast too high.
Score with a diamond blade throughout to approximate depth, then come in with a chipping gun or bushing bit, depending on the severity.
The cuts are relief cuts that help establish elevation consistency and provide somewhere for concrete to break to. If I had to guess I’s say the spray paint is spot checks on elevation (blue low enough, red too high).
This is a very different operation than simply establishing 1/4” amplitude.
Source: I’m a recovering concrete contractor turned mega commercial GC.
Worth calling the builder to ask all these questions.
If I had to guess... their forman sprayed a few red lines and told a labourer "saw cut here and that'll help you scabble it easier"... and then they've scabbled some of those saw cuts. They maybe went a bit too deep with them as well.
As for if they're a problem, that's tricky to say without knowing how deep the cuts are, what reinforcement they've cut through (if any) and how hard the footing is working. If they're really deep they may not fill with concrete when you pour the slab, which may or may not be a problem. Likely fine as long as they're fairly shallow. If they're hundreds of mm deep they could reduce the shear capacity of the pad a bit. As long as the pads aren't shear governed, they're probably ok. Could just check them for a reduced depth in shear to be 100% certain.
I don't know if shear friction is the goal here, and I'd have to double check this, but in order to count the reinforcement in the shear friction calculation, it had to be developed on both sides of the critical plane (in this case, the top of footing).
It doesn't look like the bent rebar extends up enough to be fully developed in the future slab. The bars that just extend up 6" with no bend are surely nowhere near developed in the slab. So I'm curious what the roughened surface is actually for.
In terms of actually being "roughened," other than a few patches that are relatively smooth, it appears to be successfully roughened. You could probably account for only the roughened surface area here and determine how much steel can be counted (there are limits on max As %) and you would likely still be able to count all the perimeter dowels. Again the issue would be whether they're developed or not.
Like others said, I wouldn't be surprised if the saw cuts were made to help later chip out some amount of the entire top of footing down to grade level or something.
Exposing aggregate deeply embedded in mortar matrix with 1/4 amp is code, this is not that, they didn’t achieve that. The method shown is not industry standard.
This is poor workmanship. In order to get a key the aggregate should be showing, this can be done with a scabbler or retarder on surface and wash next day
the chasing is not considered correct either, unsure why anyone would do that.
To repair this, I would request the surface be scabbled back Before the next pour.
With the cracks, they should get filled on the next pour with the grout .
To actually answer your question... The spray lines appear to be marking locations of cracks in the concrete surface that are to be chased out before the next pour. In general cracking is remediated by drilling a hole at each end of the crack, to prevent propagation, and chased out to a width and depth of the specified repair material, usually 10mm wide by 10mm deep or similar. In YOUR case, these cracks will be caused by shrinkage during curing of the concrete, usually caused by bleed (water escaping the mixture through the surface while still malleable) usually a problem in self compacting mixes. Or by getting too hot and evaporating water, this is a Larger issue and is rare other than In large pours in hot countries.
The saw cuts are absolutely not enough to be a fix for the cracking, as you have to have grout reliably fill the crack, nominally openings should be to 2.5 * the maximum diameter of specified aggregate wide. But also, it is not a huge issue as they are very localized and construction defects are accounted for in the factors applied during design - if you wanted a hill to dye on though, people have done more for less.
As for the roughening, generally this surface will have a retarding mixture applied to the curing concrete, then jet washed off while the mixture is still green (usually within 24 hours). This is to expose approx 1/3 to 2/3 of the aggregates diameter in depth.
In an un related note, the concrete that is currently on the starter bars is not acceptable and will significantly affect its bond to the next pour, this should be cleaned as well as possible.
Also, mention this to your supervisor, if on a large site, it's good to mention this to supervisor, or ganger for the team - there might be a reason for doing things and snitching to your managers without communicating with the team can undermine your integrity as an engineer. Often teams can be doing stuff wrong for decades and change is hard to accept, so speaking to them (with permission from your organisation) and their team is always the best way to learn, if you intend to escalate, just mention it to the ganger or black hat so that they are aware you consider the defect to be non rectified, and give them a chance to either explain or start remedial work.
Forgot to mention, your role at this stage will be to observe and report. Unless explicitly told to do so by your supervising engineer NEVER EVER, EVER INSTRUCT WORK. This is to say don't EVER tell anyone to do anything other than instruction in writing, addressed to you from someone within your organisation.