Anchoring epoxy for rebars - how to estimate?

Old 08-01-17, 05:40 PM
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Anchoring epoxy for rebars - how to estimate?

I cut open my concrete slab in order to have access for plumbing repairs below. Now that I am done I have backfilled soil, compacted, termite treated etc...and I need to put in some rebars to tie to old concrete to the new concrete I am going to pour.

It's not a large area so I have drilled about 16 holes 3/4" in diameter and going to use 1/2" rebars.

I need to anchor the rebars into the existing concrete using those two part epoxy that comes in tubes that you inject with a caulking gun. I have never done that before so could use some pointers.

(1) First, I need to figure out how much of this epoxy I need, or what mileage I will get from one tube. Strangely I do not see any quantity on these tubes except like 8.6oz or 10.1oz in weight. That tells me nothing. Looking online I found this product 8.6 oz. Quikrete High Strength Anchoring Epoxy and in the product Q&A section their "expert" said "A 8.6 oz. tube of QUIKRETE® High Strength Anchoring Epoxy yields 15 cubic inches of epoxy. One tube can fasten 18 5/8” bolts into 3/4” diameter holes at 6” depth. Yields will vary based upon waste, nonuniform hole dimensions, etc." Well, if I do my calculation, the volume of a 3/4" diameter hole at 6" depth is 6*PI*(0.75/2)^2 = 2.65 cubic inches. If it yields 15 in^3 divided by 2.65 in^3 = 5.66 less then six holes. How did he get 18 holes? Or is he assuming you wouldn't fill up the entire hole with epoxy because the rebar takes up most of the room? But most videos I saw they bottom the nozzle into the hole and filled the hole, pushed the rebar in and the excess epoxy squeezes out as waste. In my case I have 3/4" holes as well, sixteen of them, 7" deep, and I am wondering if I can get away with one tube, or do I need two or more. I also read from another review that these epoxy tubes have a plunger inside that takes up half the height of the tube. In fact one review said all that came out was half a tube, about 4 oz, before they "bottomed". So I am more confused.

(2) What is a good product to use? I do NOT need it to be fast or rapid set. I can wait a few days before pouring concrete.

(3) Will a regular caulking gun work? Or do I need a powered one? I would prefer not to buy a new gun just to squeeze 1 to 2 tubes, but I also know once you opened these products you have minutes to work or it is wasted.

Thanks in advance for any comments or advice.
Old 08-01-17, 07:17 PM
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The stuff sets up fast and will also set up in your tube so if you go this route have everything ready to go in one pass. You will need a fairly strong caulking gun as you are squeezing two tubes at once and it goes in a zig zag pattern instead of straight out.

I don' even think you need the epoxy and can just shove some cement in the hole and then do your main pour and vibrate the mix to get some to go into the holes you drilled. Wet the concrete first or hit it with a leveling cement primer to promote adhesion and don't sweat it. The rebar is there to tie the slab pieces in for uniform vertical movement not to keep them from expanding and moving horizontally.
Old 08-01-17, 08:20 PM
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I tend to agree with Czizzi and think no epoxy is needed.
To me epoxy is for serious holding power such as this example of a seismic hold down. Around here, the holes and the epoxy application are inspected at the time of install.
That's serious business All you need is to tie your patch into the old slab.

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Old 08-01-17, 08:31 PM
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I agree with the others. I have seen numerous floor patches in industrial situations, including floors close to a foot thick, and the dowels (re-rods) were simply placed in the holes and the concrete poured. The only time I have seen epoxy used is when there was a definite load that might cause the rods (or more likely, bolts) to be pulled out of the concrete.
Old 08-02-17, 05:09 AM
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Our engineers called it forced fit; in other words, it may have to be pounded in. You don't want the bars to move. Can you get 3/4" bars? If not, maybe 1/2" bars and non-shrink grout. Epoxy sounds a little like overkill
Old 08-05-17, 04:07 PM
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In most cases as mentioned earlier epoxy is required to hold the bars in place of the existing concrete, a tight fit is all that's required. However, before asking advice you went ahead and drilled holes that are way too large, they are actually larger than what you would normally use even if you were using epoxy. Your best and probably cheapest route for you to take now is to drill new holes between the existing ones that the #4 rebar you now have would fit tightly into.

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