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Tom,
Definetly seperate the two. I’ve been pouring concrete for the better part of 10 years and probably avg. 5-6 thousand c.y. a year. Pour the footing for the wall first. Then attach either redwood or 3/4″ black asphalt expansion board on grade to the footing and pour the walk. If the big one decides to take out the walk, it may spare the footing, but not if they are connected. just MHO.
Ron
Getting the details right for a wall assembly with the control layers to the exterior and lots of drying potential.
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Replies
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A monolithic pour? No way. You have two distinct pours or structures that need to be accounted for.
On the footer definitely re-bar. Also, 2" of clear space between the steel and the outside of the concrete would help in the long term durability of the footer and the block wall.
On the sidewalk, Why the re-bar or wire? 99% of concrete pavement used in the US, has no steel in it. The only steel used in concrete pavement are dowel bars at the joint location. If your not intending to drive a dump-truck over the walk, I would just pour as is. All be it, make sure that you groove or cut joints into the sidewalk at least every 5-6 feet. Some would also tell you to use fibers, these do help in small shrinkage cracking. The best advice, as little as possible water in the mix, a lot of water on it for curing. ( after hardening ). Also, drainage , drainage, and more drainage.
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I will be having done a 4 ft wide concrete path, next to a block wall. For this block wall, the city requires a footing that is 12" W & 24" Deep (for an "I" shaped footing). I intend to have rebar in both the walkway (about 4" thick) & the footing (rebar is mandatory in the footing, and vertically in the block, which will then be filled with grout).
Are there problems that could result from doing one pour to simultaneously form the walkway & footing ? or should the footing be poured first, with the walkway at a later time? should the rebar for walkway & footing overlap, or not?
the walkway is going to be right next to the house's concrete foundation, since the house is about 15 yrs old, hopefully the fill dirt next to the foundation has settled (sandy soil) by now.
*Tom,If you don't get an answer, explore a Masonry Organization. 10 yrs ago, a mason buddy showed me a manual from the Masonry Institute or some such organization. It had a detail for every Bar, Mix, Shape,footing design etc. I'm sure if you can find it, it'll have everything you'll need to know. If you want, email me and I'll contact my still mason buddy and ask him. Best of luck.
*Sure, it can be done. Except for one possibility: since you don't give any information about the block wall--other than to say it is a block wall and adjacent to a planned sidewalk--I think your bldg. dept. may have something to say about psi strength of the footing. This may differ from what the sidewalk requires. Other than that, be prepared to see some more elaborate formboards than typical. I mean, are the footing and the sidewalk even at the same elevation?
*If I understand what your asking, a 4" thick sidewalk above grade poured monolithic with a 24" deep footing, seems to me the walk will be subject to frost heave and probably crack at the walk to footing joint. I assume you have frost concerns given the 24" depth?I'm certainly no concrete expert but I'd pour the walk later and isolate the two with an expansion joint.Chuck
*Without seeing what you're talking about, it seems like you'd waste alot of concrete to connect a 24" deep footing to a 4" deep sidewalk. I'd say pour at the same time but I wouldn't bother to connect the two.Rebar or rewire in the sidewalk?
*being in So Calif, there is no frost problem, but 24" deep is the requirement for a narrow 12" footing, when building a 5-6 ft high wall (we are in a seismic zone, as well).The city requires 2000 psi concrete for the footing, which doesn't seem unreasonable for the pathway adjacent.#4 rebar is required in the footing, and vertical #4 on 24" centers in the blocks; all blocks filled with grout. For the adjacent pathway I'm inclined to use same #4 rebar on about 16-18" centers. Whereas "in theory" mesh might be OK, I hardly ever see mesh installed right. It's stepped on while pouring, sinks to the bottom, and loses all effectiveness. I have spreading cracks, with elevation shifts, in a 15 yr old drive way to prove it. in my situation, it seems that the footing & pathway could be at the same elevation - can't see a compelling reason otherwise... yet. I think I'm hearing most opinions, that probably OK to pour at same time, but may be a good idea to isolate the pathway & footing.
*Tom:Just as an FYI, around here we use a 2500 PSI mix for footings and 3000 - 4000 PSI for flatwork depending on the anticipated load and quality of substrate. Further I think you will find that for a relatively small pour the price difference between, say 2000 and 3000 PSI is a very small percentage of the overall project cost. I'm with Chuck when he says that the two elements will probably crack apart - unless you really do tie them together with more than a little steel, which in MHO would be way overkill. Even with no frost heave, some settling below the slab could cause the footer to tip & ultimately resulting in the "undoing" of your wall. By the way, what kind of a wall is this? - retaining wall? Garage wall? Whatever you do, be sure to pitch the walk away from the wall slightly to prevent channeling water into your wall foundation.
*Matt,the wall is just a "fence" between adjacent properties (replacing part of a deteriorating 40+ yr old block wall that has no visible mortar, just "dry set"). all new block walls in Calif have to be solidly built because of earthquake risk. I've seen pictures of older walls that just "flopped" over like dominoes, when the walls lacked sufficient vertical rebar (tied to the footing's rebar), or lacked solid footings. good inputs from everyone - I'm beginning to think the lowest risk approach is to keep the footing separate from the walkway, even if it does cost somewhat more.
*Tom, Definetly seperate the two. I've been pouring concrete for the better part of 10 years and probably avg. 5-6 thousand c.y. a year. Pour the footing for the wall first. Then attach either redwood or 3/4" black asphalt expansion board on grade to the footing and pour the walk. If the big one decides to take out the walk, it may spare the footing, but not if they are connected. just MHO.Ron
*Tom,I hope you heed the advice of both Chuck and Ron. Isolate the walkway from the footer. If tied together, your sidewalk will definately crack apart; only a matter of time. As for rebar in your foundation footer...YES. AS for rebar in your sidewalk....NO.Use the 6X6 inch welded wire mesh. Buy some "chairs", your concrete supplier will have some; or simply lay the mesh across some pieces of brick. This will be sufficient for keeping the mesh off the ground and set into the concrete. The "key" to keeping the concrete sidewalk from cracking too much later on is to prepare a solid, well packed base first. remove the grass sod, and looose dirt, and excavate down about 8 to 10 inches deep. Compact this ground, add about 4 to 6 inches of gravel(perferably) or sand overtop of this base and compact again. Then go ahead and pour your sidewalk.Good luck on the outcome.Davo.
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Rob H... right on... i would add.. make sure you have suitable material for your subbase (gravel) and...
compaction, compaction, compaction....