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Spalled the cut edge of the existing slab

Discussion in 'Demolition' started by oceanobob, Mar 9, 2019.

  1. oceanobob

    oceanobob Senior Member

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    In a 100' by 200' warehouse, have to cut two strips 8' by 80' of the existing 6" slab. Then excavate to 18" thickness and place new concrete for the future equipment.

    Made the cuts all the way through the concrete section. Pieces were cut at around four feet in order to handle and this also was a good spacing to work with the existing crack control joints.

    Needed to make a hole in the start of the job to find a place to hold the concrete saw slurry. First piece was removed with the reachlift forks and it spalled the edge of the concrete floor.
    Switched technique to the screw anchor and clevis figuring this allowed some freedom and it also caused spalling.
    Had to make a long hole (one area did the hammer and the other area the saw made more cuts) and then remove the panels with the chain tug to keep spalling to an absolute minimal.

    FYI the spalls were around two feet long and four inches wide, maybe 1/4 to 3/8 deep. Ugly and time consuming to patch.

    Never had this occur on the usual (admittedly narrower) trench cut for the usual pipes and or conduits?
    Must be the larger size of these panels.

    We tried all manner of wood wedges to soften the inevitable edge contact. And the lifting in all opinion is travelling flat and true but apparently at the time of raising is dragging that edge.

    P3080029.JPG P3080031.JPG P3080032.JPG
     
  2. oceanobob

    oceanobob Senior Member

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    We did some artist like rock stacking.
    P3080042.JPG P3080043.JPG
     
  3. Ronsii

    Ronsii Senior Member

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    Yeah, we've had that issue a few times.... one way to get around it is doublecut the borders but that takes more time and blade... Have also thought about angling the saw to give the cut a taper by putting 1 inch plywood down the inside of the cut for the saws' wheel.

    And as an added bonus to makes things more interesting we aren't allowed to overcut... so if you need an overcut is has to be inside the doublecut...
    doublecut-portside-21.jpg

    And sometimes the only way to get stuff out is breaking because there is so mush plumbing in the cut area... this was a bathroom remodel with at least a dozen penetrations in the slab. 6 inch slab... up to 10 inches in a lot of areas :(
    rubble-portside-05.jpg
     
  4. oceanobob

    oceanobob Senior Member

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    Once the concrete chain saw was invented, was that the end of the overcut? Have heard that a core drill can be implemented to make the cut at the corner by intersecting the circle into the corner cut lines (two point lineup).
    ~
    We didn't think to angle the sawcut (via the plywood which is a pretty good idea and that is indeed worth trying). This job ended up with the 'double cut method' [but only on one side so far] which burned up some blades and time of course. That second cut is laid out at a skew in plan view - the thinking is it will help the pieces pull/slide out in the direction of the floor plane.
    Likely will involve some hammer work as well.
     
  5. Ronsii

    Ronsii Senior Member

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    Another thing I have done when things were 'hilly' and hard to get a good straight vertical cut was run two blades(a lot slower) for a wider kerf cut... had sorta good luck with it... again it wears more and you have to remember to flip the blades now and then to keep em' wearing even.

    I see you took out some plumbing too... they always want us to avoid(if possible) any damage to existing plumbing, electrical, etc...

    Chain saws work great for corners... but.... there again more cost, time, etc.... the overcut rule is from way up corporate somewhere??? it applies to all diamond cutting: asphalt indoor/outdoor, concrete and anything else you might cut.... they also have a spec/rule for replacing the crete about 1/8" radius grind the cut edge where the new crete meets the old....
     
  6. oceanobob

    oceanobob Senior Member

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    Having seen many overcuts on seasoned concrete slabs I have yet to see a crack emanating from that location as a result of the overcut. Occurrence wise, more often the floors are overcut and as long as they are packed with concrete paste during the placement of the new concrete, there is not a comment. Left open and unfilled may bring a reaction / punchlist etc. Filling these maybe helps with raveling and could that be the issue?

    But on vertical concrete like tilt up or masonry walls, overcutting is a huge No No for structural concerns and the chain saw is one me$$y tool to help in that situation.

    Doubling diamond blades has been proposed as a solution for a wider cut but we heard that may require a thin spacer washer to allow for the fact the tooth is a hair wider than the disc .... but have not tried the doubling yet.

    When directed to feather grind the (e) edge to a small bevel, we have been allowed to instead butt the concrete new to existing (and sometimes we burn it in at the line with a power trowel) and then saw cut that line similarly to a shallow crack control joint and then clean it out and fill with flexible epoxy like MM80. Shave flush and a light local grind for a little profiling. This in lieu of the other has been determined satisfactory and is almost imperceptible to the forklift or other lift operator. This job may not get that clean up cut because there is no forklift wheel traffic on these patches; thinking is no potential for raveling. but for a fall back, could later use a hand grinder to make the clean up cut (goes way easier than compared to making a new cut line, almost as easy as crack chasing).

    Those pipes [in the pics] were abandoned conduits so we just yanked the slabs off them and of course they remained undamaged - whereas if wanted to 'keep those conduits safe' they would have broken or cracked.

    (Old to New) dowels must always be epoxied into the (e) concrete, sometimes we are allowed to use the square dowels - depends on the job.
     
  7. Ronsii

    Ronsii Senior Member

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    I forgot about the doweling... one of the co's we do a lot of work for now requires a special inspector for the epoxy... he checks dates on the epoxy, type, rebar size and condition, etc.... it has to be a specific type that no one in the area had so we went to a local concrete construction supply house(white cap) and they gave us a different brand that meets the same spec.... the inspector didn't like it :rolleyes:

    I never put a spacer/washer between the blades... just put two on and cranked it down :)

    When cutting openings in tiltup walls the guys we use just use the ring saw instead of a chain for cutting the corners.

    evercutter-43.jpg
     
  8. oceanobob

    oceanobob Senior Member

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    The ring saw - almost didnt consider that tool. Quite handy am sure.
    ~
    We tried a couple methods to extract the soil using the mini as opposed to a backhoe. The reachlift bucket is kinda small so we tried the warehouse forklift self dumping hopper. That was kinda marginal even when only one half full, so we swapped it onto the reachlift and filled it almost to the brim. That works real well, holds quite a bit and is very easy to load with the mini.
    Digging is in prototype mode while we are waiting for the breaker for a jumper circuit to heat up so we can pull the feeder we found under the slab.

    IMG_0935.jpg

    IMG_0934.jpg
     
  9. Ronsii

    Ronsii Senior Member

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    I like the tipper idea :)

    We usually do the mini-backhoe thing( painfully slow) if there is no ramp into the buildings, otherwise it's dump truck height permitting or dump trailer on a pickup.
     
  10. nycb

    nycb Active Member

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    I've done that a few times also, and ended up snapping a new line a few inches further after the first pieces were out of the way, then just cutting off a sliver that had all the busted edges on it.
     
  11. oceanobob

    oceanobob Senior Member

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    Looks like the tipper dump box idea/suggestion may be shortsighted, it seems the thin metal of the bottom and especially where the pivot is located has been moderately traumatized by the weight of the soil. Yes we did not pack the material in there, it was simply the weight.

    Correction Procedure to the deformation using a Industrial Massage Tool
    Massage deformation Tip Dump Bucket.jpg
    The pic was taken with the phone camera (7 model) and it is not as good as my basic pocket digital camera (for those occurrences when the lens is pointed toward the sunlight). I may have gotten the HD setting but it didn't relieve the contrast issue very much.
    Maybe about 10 or 15 blows with the perimeter supported on the warehouse lifts corrected the deformation.

    I wanted to update this post in the event others may also try such a contrivance.
    ~~~~~~~~~~~~~
    Here is how we finished the excavation for the footings:
    Alternate Version.jpg

    This reachfork bucket is made from thicker material. It has some forklift pockets but also due to it's smaller overall size maybe holds around a third of that tipper.
    Sidepoint: Being narrower than the carriage can be Ok for when trying to turn the reachforklift in tight spots.
    Other observations: If one uses care, it is possible to load gravel or sand into that bucket from a stock pile by easing and swiping it upward. Pushing straight in is the optimum practice to load a bucket generally, but that method places way more strain on everything including the reach fork.

    In this case where it is being loaded by the mini, it is simply dumping but I wanted to mention about loading it.

    Summary:
    The tipper container (shown above w the Massager and shown in previous posts in this thread) is clearly the way to go as far as productivity, but appears is in need of some reinforcement especially across the hinge zone.
    When that tipper container is full with excavated soil, it loads the 8k reachfork nicely.
     
  12. CM1995

    CM1995 Super Moderator

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    What we've done to help stop edge spalling is cut the perimeter then section the area to be demo'd and start in the middle. That way edge pieces can be carefully grabbed with a skid steer grapple bucket or mini with thumb and pulled away from the edge. Works pretty well.
     
  13. fast_st

    fast_st Senior Member

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    Looking at that edge, does anyone else think the top surface was overworked when the concrete was laid? I've clipped some edges by accident and it only takes out a small chip.
     
  14. Ronsii

    Ronsii Senior Member

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    I was just thinking about this thread yesterday :) Was cutting for some sidewalk replacement panels and wasn't getting through with the 16 inch blade in a lot of places so I went ahead and doublecut all the adjoining edges.
    abm-levee-doublecut.jpg

    Was a lot of glass surrounding the demo area so I strapped a rug around the hammer ;)
    abm-levee-breakerwrap.jpg

    Took an extra 30 minute to electric hammer the back side of the curb out, it was a monopour and goes 12 inches below the asphalt... and who knows how far out into it :eek: so we figured is was easier to just cut as deep as we could behind the curd and then chip down to grade...
    abm-levee-formed.jpg

    Turned out pretty good :) Glad we were able to save the curb as that would have been a lot more work and $$$
    abm-levee-finished.jpg
     
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  15. oceanobob

    oceanobob Senior Member

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    After the excavation, wanted to spread some Class II (recycle) to hold the dobies since the lower mat will be supporting upper mat and we will walk onto the upper mat. Probably the soil could hold the dobies but the base will be trimmable. A lot of jobs show a sand layer under the new concrete but a long while ago have gone away from that idea to just the Class II which isnt that much more costly.
    Bobtail came in handy to dump at the edge and the mini's blade to spread the material to save shovel time.
    The reachfork set it right in there cause jumping the edge or sliding down the loose pile were also considered but this method was straightforward. Was the first time having hoisted the machine. The TLB (backhoe) just sits in the yard because these two pieces work together so well. Especially for projects around these buildings as opposed to sight work on lesser improved areas.

    To fast_st - the upper surface indeed may have been "overworked" (term from ACI) using a vibrator.....based upon time of construction and the sizes of the joints, it is likely they invoked a large vibrating truss skreed. The joint in the center of the building is a construction joint with keyed to a form and the other crack control joints are sawn. All the joints have been filled with a trowellable floor aid such as flooring contractors utilize - this concrete slab was originally a surface for a cold storage (>32F), then became a dry goods storage with a showroom and the concrete was covered w VCT. They probably didnt want the joint telegraphing through the VCT. That VCT was (including adhesive) was easily removed when we started the project. Other than the edge chips from our demo operation the floor appears to be handling the service conditions with no adverse signs of the overworking. I don't think the surface was burned with a rider but likely whirlibirds used. Flatness folks don't like overworked cause the tolerance goes. Laser skreed, Pans on Riders, then burn with Rider is the preferred method these days.

    As to the new entry way by Ronsii - the carpet around the hammer is a very good idea. I would have probably stood plywood against the building.....but there are times where that hammer wrap will be The Solution. Good job on saving that curb.... that is typically trickier than it sounds as the concrete can be quite thick. Were there multiple parallel closely spaced cuts to aid in breaking it to depth?

    IMG_1828.jpg IMG_1827.jpg

    The plan for the chips is to place the concrete then address the chips.
    Immediately prior to the placement all the chips will be wirebrushed then the paste allowed to fill. May put some concrete adhesive in a spray bottle and brush work it into the spot. Concrete to match the edge and burned to suit (no edging). On saw day, wet saw across the new surface to match the existing joint spacing. Then will saw along the existing to new concrete (called riding the little black line).
    After the partitions (framing) is completed, will fill joints with semi rigid epoxy such as MM80. Will use joint filler via our sausage gun and home made trick nozzle and then next day shave the excess. Their SPF (stain preventer) helps removal of excess. Probably won't ever get to see which joints activate. Right before the semi rigid, apply the hammer test to the patches and if any are loose, then a patch with epoxy mortar to a sawn edge using a small wheel and the right angle. The bigger spalls will likely get loose (fail) due to the hammer test LOL.
     
  16. Ronsii

    Ronsii Senior Member

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    @oceanobob, I cut as deep as I could behind the curb ~6inches back from face then a second cut another 7-8 inches back from that... then I just used a bosch 65 pound electric hammer with a 1 inch chisel bit that I can get a bit more control with to take out chunks about every 8-10 inches along the curb... took probably half hour to get it all out cause there was #6 rebar running 5 spars including one right down the length of my edge cut on the sidewalk itself and since I did not overcut into the curb it survived in that corner :( almost spalled it when the boss tried to lift out the double cut and it was still connected at the curb :eek: which was my deciding factor in going with the electric hammer instead of putting the hydraulic hammer back on the mini....I think I made a good choice there ;)
    Here you can still see a foot of the rebar coming from the curb, it was running right into my doublecut pieces!
    sidewalkdemo-6bar.jpg

    Oh... and the carpet on the hammer :) worked out pretty good... next time I might slide it up a few inches as it was a little hard to see exactly where the tip was but all in all did what it was supposed to so I'm happy... especially since nobody remembered to bring any plywood or cardboard. I have actually wrapped cardboard around the breaker once before but it got beat up pretty bad in the first hour or so of use and was kind of useless after that :( so the carpet fared way better!!! another trick I've done in the past to limit projectiles from the hammer is to lay a CB sock down and punch through that works good for small limited area breaking, good for keeping cars clean that may be near to the impact zone ;)
     
    Last edited: Aug 14, 2019
  17. Bls repair

    Bls repair Senior Member

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    What I like to do is cut concrete on a slight angle towards the center of piece to be removed . What this does is make space between pieces of concreat as soon as you start lifting it out to stop binding and chipping edges

    Also help new slab from settling.
     
  18. Ronsii

    Ronsii Senior Member

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    Yeah a few times I've laid down a strip of 1/2 inch for one side of the saw... works ok for some things... It has some downsides though when we're trying to get max depth to prevent unwanted breaking when we know the slab is much thicker than our cut, and when there's lots of bar or very hard crete it can make the cut wander a lot!
     
  19. oceanobob

    oceanobob Senior Member

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    Gave some thought to kant on the saw, but was of the idea the shim thickness would be minimal, such as 1/4" (perhaps a old piece of bender board).

    As to squiggly cut lines, getting a more aggressive diamond has helped. The blades we bought at the universal low price supply house are too hard of a matrix, so we ruff up the cutting edges on asphalt. Not too much in the a/c cause it can undercut the blade. Just enough to remove some matrix and expose some of the diamonds. Having self propelled constant feed saw helps, but the shallow first cut then try for some progress on the subsequent passes....that process makes for the straightest cut lines. The more aggressive blades actually cost a bit less cause the labor is saved.

    Getting the base rock in the footing:

    IMG_1837.jpg IMG_1836.jpg

    The smooth vibrating drum (patch) roller does a decent job, never sure for compaction purposes if it is better than the giant plate compactor...some say the tangent line to a roller drum has the most force compared to that big plate. The plate compactor has a manual start diesel and it is an intriguing piece for sure.

    Notice all dowel holes are drilled and cleaned, then taped to keep em clean. The tape stays 'cause we spray some "77" aerosol contact cement on the concrete before we apply the duct tape. The duct tape isnt really duct tape made with the cloth, it is plastic tape which we call 'stucco tape' because the plasterers apply it on the window & door frames.

    The green hue is from the Metal Halide lights, the camera tends to exaggerate this 'special effect'. :D
     
  20. Ronsii

    Ronsii Senior Member

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    Yeah, I've seen the pros with deep cuts and they usually only take about 2 inches at a time, however when I have timed myself it goes a bit faster if I take more with this little saw I have :) need a bigger saw....but then I'd need a bigger truck... yada yada...

    I like to drill the holes very last but the boss tends to want to drill them earlier because it's 'easier'.... of course then you got to take precuations like you did or 'try' to clean all the rock and crud out of them after all the backfill is done....


    You always do some pretty nice looking work, bob :)
     
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