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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

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  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 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.