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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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    oceano california
    We epoxy installed the square dowels having the trick gizmo (from PNA) and the two rebar mats, the pic shows detailing at the (sawn) crack control joint to have the new concrete align the joints with the existing concrete.
    These are #4s at 12"oc and we use the grade 40s cause the modulus of 40 and 60 are the same, and we dont expect the rebar to ever Yield. That big blob at the end would normally have to go since it locks the concrete but that happened to be in the end portion of the Work and that section had to be hard dowelled since it is close/adjacent to the metal building frame.....from this point (where the rebars dive) to the other end at 80 foot away is where we will be dealt the cards that address the shrinkage, ergo the dowels.

    Faces of existing slab carefully ground to make sure no keys etc and being coated with some cure and seal as a bond breaker.
    Foam (felt) would probably be better but it makes the finish fugly at the joint .... after the pour on wet saw day we run the saw down the joint where the new meets the old and then (later) fill all the saw joints w semi rigid. That black felt was once good but is now lame: it falls apart w/i one year and it is the epitome of less than desired appearance.

    (Ronsii - when we removed the tape over the dowel holes we checked all the holes for any dust and there was none, clean as we left them LOL.....much nicer to drill when the excavation is empty than to wait until the end and fight the grade and the steel etc. My opinion.)

    Chairs are called Standees and we made em on a bender but they can be bought from others, simply spread the legs to change the ht. Goal is the standee is over a dobie. Lotta heavies walking on the upper mat.


    rebar at CJ w PNA dowels.jpg
     
  2. Ronsii

    Ronsii Senior Member

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    I think that is going to be plenty of bar to hold things together :)
     
  3. oceanobob

    oceanobob Senior Member

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    Quite a few folks were in complete agreement about the amount of rebar, but this is what happens when a Engineer is involved because they are required to invoke features that can be directly attributed to codes and standards, in this case: ACI. So named: temperature steel.
    ~
    The building is too low (25 feet peak) to utilize a boom pump, including the new fangled Z booms. Therefore we must compromise the mix a wee bit to use a trailer pump (ka Line Pump) but we call around to make sure one of the few with the 3" hose are available to do the pump. Note: 2-1/2" hose capable concrete can be titled a Courthouse Mix due to potential for excessive shrinkage (one of many neg issues). With the industry typical mix design philosophies/evaluator methods showing a workable and pumpable mix (coarseness factor, fineness factor, etc etc), but wanted more like all of us .....so mused to take a look to see how the concrete mix matched up to the Tarantula Curve - lo and behold it showed some room for improvement. The emphasis being improved workability without having to do the unspoken but oft employed ("give er a drink of water" or "add x" water). The Supe at the batch plant said the Tarantula Curve recommendations basically produced a boom pump mix. That name sometimes simply takes credit for the boom pump being able to pump most anything, rotten mixes not excluded LOL.
    But because of the predicted workability improvement it was worth a try and we did a 2 yard test pour yesterday w good success and today we placed the contents of the four ten yard trucks and we had to add no water on the jobsite, we had a nice 4 to 5 inch slump which made accurate rodding and skreeding possible, and the proof there was no excessive water was the minimal bleeding - of course, not forgetting to mention No Problems pumping 125'! And very good response to the vibrator.

    Let this be known as the day we got the boom pump mix through the line pump and line pump hose!!

    Pulling out a bit of sand as well as some pea aggregate made the percent rocks look formidable, but these tactics are well known to keep water demand low. Weird stuff this concrete, as it could seem a good dose of sand and some extra pea would make for easy placement - but all is not as it seems. Workability being the Driver for this effort
    Like the Man said: Well Graded is Magic

    Here is the finished placement: handworking those edges. Notice the sprayer with the Tea looking liquid, that is Fritz Control Finish which is mixed on the job, makes difficult concrete obey LOL:
    P9050224.JPG

    Tools for assuring flatness at the butt joint (this joint in about 2 weeks will be score saw cut to about 1" deep then filled with semi rigid MM80). Margin trowel and small 'burn' trowel at this point, big trowels cleaned and put away - need small surface area to affect outcome.

    P9050226.JPG

    What we are looking for, shiny concrete due to the seal cure 'membrane style'. Pail is way in the background. Stuff looks like milk but turns color then goes to clear. This pure wet look only for less than a day as it will be wet sawn tomorrow for crack control joints to match the existing slab CJ's (crack or construction joints).

    P9050228.JPG

    Trowel Stand for the 36" walk behinds and the pan. Easier to clean and able to test run as well. Can use forklift w some straps to move around or hoist onto B deck floor or lower down into a pit etc.
    I prefer the automatic clutch and the quick pitch but have used the hand crank on many jobs.

    P9050229.JPG
     
  4. Ronsii

    Ronsii Senior Member

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    Very nice job!!!

    I'm sure the customer will be more than satisfied :)
     
  5. oceanobob

    oceanobob Senior Member

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    As soon as we arrived at the job, we set up to cut the crack control joints. The thickness 18" indicates somewhere 'tween 4-1/2 to 6 inches depth (one fourth to one third the section thickness). Typically these joints are much less depth due to the slab is usually six inches thick, in that application - one saw pass gets the job done. Spalling is a big concern with cutting green and it was a 'try this, try that' to determine if we should do a guide cut and then the full depth pass, but the hazard of two passes is more spalling....the best solution was to accomplish the full cut depth in one slow steady pass. Some folks report good luck with the early entry dry cut but I have had good results with the 'first thing next day' wet saw.

    Good weather of course and the adjustment of the mix "recipe" - both can contribute to prevent random undesired cracks. I make a big effort to keep excessive water from the slab mix but provide for workability with the better admix chemicals (high range water reducers etc). Compared to previous experience line pump concrete mixes, this mix had a notable reduction in sand and pea gravel both providing less water demand. Deemed sufficient effort to reduce water thus no fancy chems on this job. Std water reducer was utilized as is common in this area unless high zoot chems are specified.
    Report card re: random cracks withheld for some time to tell LOL.

    Green concrete has a reputation for being hard on blades: this task was about 200 plus inch feet and the blade loss was maybe one eighth inch. Blade segment thickness minimally affected.

    IMG_1956.jpg
     
  6. oceanobob

    oceanobob Senior Member

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    On the second section on this slab, knowing the minimal cuts created an opportunity for the piece being removed to 'bite' the edge of the slab. On the first section we hammered a row to make a decent gap and the problem of chipped edge was greatly reduced.
    On this second section, we saw cut a third line and it was done at a non parallel direction (sort of like a saw tooth line)....this made the removal of the pieces for the gap quite easy to remove, in a way just like a morse taper on a lathe. Once the breaker cracked the piece, it literally slid along the gap which was ever wider in that direction. No more chipping.

    When the gap pieces were all removed, the remaining large pieces were lifted from the subgrade with the forks of the reach lift.
    IMG_1960.jpg
    IMG_1961.jpg
     
    Wytruckwrench likes this.
  7. oceanobob

    oceanobob Senior Member

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    Progress pics onto the second of the two foundations for the equipment: now that the concrete is gone, excavate to FF minus 22" and then bring Class II base for final depth of FF minus 19".
    Slab edge decidely improved with the modified removal technique.

    IMG_1966.jpg
    Diesel rammer to help with compaction, not req'd to overex as we need 1000psf and that is considered achievable w native uncompacted. Not thinking this building in 1980 ish time frame had overex and is performing absolutely fine. The big 2 yard trash bin can not be used for the spoils as it was deforming under load, am using a 1 yard cleanup and gravel bucket on the reachlift. So many trips but no time to fix the 2 yard trash bin for the chore - that is a future shop project.


    IMG_1969.jpg

    Getting some recycled but cert'd Class II road base into the ditch. Road base holds the dobies like no soil can, almost as good as a mud mat. Could have considered sand slurry but it seems like it takes a while to get tight enough so sticking with the Class II. Rammer first, then trim and smooth, then vibrating smooth drum roller.
     
  8. oceanobob

    oceanobob Senior Member

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    Occupation:
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    As to the concrete, last Friday (the day after placement) we 'crack joint' sawed it to one third the depth. Pls recall: Top mat of rebars were held out of the saw joint area and smooth dowels placed just below the saw depth. See Aug23 entry showing rebars.
    Here is a sketch showing activation progress of cracks in the five sawn crack control joints. Cleaned the saw joints with a pressure washer and inspected to observe.
    In summary, the 80 foot long strip has "divided itself" (at least the upper part of the slab) into thirds. Surprisingly the existing joint at the building center was a construction joint with a formed key, figured that point would have been one of the first to show effects of existing concrete and the style of the joint. So far, not so.

    img114.jpg