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I have an existing basement slab-on-grade, approx. 2-years…

I have an existing...

I have an existing basement slab-on-grade, approx. 2-years old. There are portions of slab that have settled, cracked and require replacement. The original building is going to remove these sections and re-pour. The correct method is in question. Slab is approx. 3.5" thick, non-reinforced, 6-mil vapor barrier. I would assume the builder will saw-cut small portions to be removed. Diamond Dowel and epoxy. I am considering an independent testing agency to determine the existing compaction rate as a "Baseline". Ultimately the builder and Eng or record shall determine the corrective action, I will be observing, and want to make sure work is proper. I looked throught IRC and ACI, and was not able to find specific means & methods.

Tutor's Assistant: OK. Is there anything else important you think the Structural Engineer should know?

Any details and/or guidelines is greatly appreciated. Thanks Joe Burke

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3/12/2018
walkereng
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Customer reply replied 1 month ago
I would have to see if I have any photo's. The home builder, structural engineer, building department and so forth are engaged. Over this time period, it is concluded that structural deflection, shift, etc. is not the cause. I believe basement slab settlement is due to poor compaction / workmanship. two locations are around the sump-pump pit and at the base of the precast stair. Control joints have little with creep. Based on this, I just wan to see how the replacement concrete should tie at the slab to remain, should it be doweled, float, tie to perimeter foundation wall. Once the sections of the slab is removed, I might be able to see the sub-base soil material as well. If compaction is poor, should compaction grouting, or expansive foam injection be added? Don't think any aggressive compacting should be applied.
Thanks
StructuralEng
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If your contractor is going to sawcut the sections that have cracked, you will want to check the existing compaction under the removed areas, then you will want to recompact the areas in question with mechanical compaction methods (you do not need compaction grouting, etc.). You should provide dowels into the existing slab to tie the new into the existing. The best method for your dowels would be to dowel the rebar into the holes drilled into the existing slab with epoxy. Epoxy dowels are better than mechanical expansion anchors.

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Customer reply replied 1 month ago
Hi
I didn't receive a recommendation.
thanks
I responded above at 22:51, do you see it?
walkereng
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Customer reply replied 1 month ago
hi,
Sorry Have another question on same topic; as outlined below.
This message is not letting me attached a file; The construction documents details are vague and limited; the engineering drawings detail appears that the design intend is that the foundation wall (8") is seated on the footer. It seems the basement floor slab could possibly seat on top of the footer (Not a monolithic pour). Detail does not show a turndown rebar for interconnection of the basement slab to footing.
So, the my final questions are:
1) If the bottom-side of slab is seated at the top of the footer, and no turndown rebar installed, should dowels be installed to tie the slab to the footer? Or just float?
2) Should they be inserting dowels where the replacement basement slab-on-grade meets the existing foundation wall or float at this point?
3) Should heavy tar paper be placement between the replacement slab and existing foundation wall. Keep in mid that the vapor-barrier must be maintained.
4) Any suggestion of the dowel size for a 3.5" think slab? I assume dowel spacing should be 12" on center, with insertion depth a min. of 8", any thoughts?
5) How they installed the 6-mil vapor barrier will be interesting. I would expect to find the vapor barrier to be continuously up the perimeter foundation to the top edge of the slab, then the abutted edge epoxy sealed.Your help and input is much appreciated, It well exceeds my expeditions.
Thank you!

1. No, not necessary.

2. Floating is fine.

3. Yes, you can use the tar paper as a bond breaker.

4. 3/8" diameter rebar, 12" long +/-, with 6" doweled into the existing concrete areas and 6" into the new pour area. You can space these at 18" o.c.

5. That can work, I would leave that up to the contractor as to the most practical way to install.

I hope this helps.

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Customer reply replied 1 month ago
Just awesome!
Thanks

Good Luck with your project!

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