2 days ago, we poured a 3 in. thick, 3 ft. wide sidewalk in 40F weather (no precip).?

Question

The top surface color has already tuned light, but the sides are still dark indicating it hasn't completely cured. What is the best way to tell if it's ready to have 1/4 inch holes drilled on it, and anchor bolts put in? The holes will be 1 inch away from the sidewalk edge.

(Only experienced & well-informed answers only please)

Correction: It's 2 inches from the edge. Also, the bolts will only be used to support a bench, nothing heavy or tall. I have done this on another similar sized sidewalk before and it worked well, but then I had the luxury of time. This time, I'm on a tight sked and the bench needs to be put in ASAP (thus the curing time question).

Answer 1

I would try going to menards and getting their two part epoxy for concrete, metal, wood, etc..

Get a good deal of it. place the bench where you want it. outline it with a pencil. then, place some tape around the outline. Then, add mix the epoxy (make sure you add enough hardener). Add the epoxy to both the concrete and the bench.

put some boxes of tiles on top of the bench to add weight.

it should set in 4-6 mintues, and should cure in about a day.

If you ever need to remove the bench, just use a reciprocating saw. then gride away the glue with a grinder and should be good.

Answer 2

Everyone seems to agree that concrete cures and gains strength over time.
So, it seems to me, the sooner you drill the holes, the easier it would be to drill the holes. Then you could install the anchor bolts at a later time. And, all depends on if the concete was a 1-2-3 mix or just plain 1-2 (1 part cement & 2 parts sand). If you were drilling and hit a piece of gravel, the edge of the concrete might crack. You should have inserted 1/4" carrage bolts head first in the concrete as you were pouring and screeding. Oh well, maybe next time eh?

Answer 3

If you poured it off a truck, contact the vendor and take their recommendation. If you sacked it, contact the manufacturer and they will help you. If you don't have the sacks, go back to the store and get the Customer Service # or the website address off a sack in the store where you purchased it. If you don't follow the mfr's instructions, then you are taking a chance.

That having been said, concrete curing is a chemical process... not just the process of water evaporating off the top, etc... If part is in contact with the soil, and there is moisture in the soil, then it will take a tremendously long time for the lower parts to take on the same white cloudiness as the top already has. That's normal and doesn't necessarily indicate the concrete hasn't cured. Concrete can have moisture in it (gray) and be fully cured. If you go to your old sidewalk and spray it down with a hose, it turns gray. That just indicates the presence of moisture... not that it hasn't cured. Curing is really the chemical bonding process that takes place within the concrete. This chemical process produces heat.. and thus can evaporate the moisture out of the concrete. As with anything wet, perspiration and evaporation take place and concrete that's not in the rain always dries out... much as with anything: a piece of meet, soil, bread, whatever. Don't confuse the presence of moisture with a lack of curing.

True, as the concrete sits, curing is taking place at a similar rate as drying. But concrete will actually cure under water too... so, again, dryness is not a benchmark for curing.

Your anchors you are setting are small... but I would advise you to check w/ the manufacturer's info on THEM. The strength and stress an anchor provides is represented as a cone (pointy side down, and starting at the bottom of the anchor. The higher up the anchor you get, the wider the stress is exerted on the material it's anchored in.. then that is factored mathematically by the size of the anchor (and the implied resultant stress by selecting an anchor of a given size). I can pretty much guarantee that 1 inch is too close to the edge for that anchor. If you don't blow out the slab drilling for it (which seems pretty likely to me...), then I'd expect the slab to either blow out when you are tightening down the nut onto whatever you are fastening down... or worse, that once you get it installed it will topple either due to environmental stress or just normal expansion/contraction w/ temperature (especially if you say it's 40f there now...), and either the object you are anchoring will be damaged, or it will damage something else when it falls... or worse, hurt you or someone else.

Consider using Epoxy based anchors instead of plastic or wedge type... you have have better luck in NOT splitting out your slab at the edge.

Typically w/ concrete you would allow 1 day for foot traffic (but often less...), 7 days for normal road traffic (<10k#), and 30 days for heavy traffic (>10k#). That's just general rule, and I really think the placement of your anchors will determine the failure sooner than the curing time itself... but they do go hand in hand.

Good luck.

Answer 4

At 40 F concrete cures at a really slow rate. But, rest assured, that is an ideal temp to cure concrete at for max strength. Drilling holes one inch from Edge is really risky even in concrete cured for years. I would not drill a hole into concrete 1 inch from the edge. For sure it will crack and ruin your job. At 40F, the 5000 PSI concrete will not reach the 5000PSI strength untill 96 hours after a pour. That is an example, of course.

What you should have done is "cast a receiver type bolt" into the concrete positioning it with grip strut vertical rod driven into the ground.

Is there some way you can mount by drilling a hole into the "side" of the concrete midway of the 3 inch thickness? That would certainly work and not crack out that easily.

Answer 5

Sorry Gessen...sounds like you needed some experience and well informed advice before you poured the sidewalk. My hubby always told me..."if you fail to plan..then you have planned to fail." And with all the concrete we have poured, even I know you should have set the bolts before it was poured, and not just one inch from the edge. Ok, not trying to be smart *** here...really. But..is there any way you can build a small form along the edges of the sidewalk where the bolts will be more than an inch from the edge...and set your bolts ...then pour another round of concrete?(the fast drying kind) And what are you planning to use the bolts for? A fence or railing?

I truly wish you good luck with this project.

Answer 6

Well the people that gave you the tech info are right and the bolts even at two inches should have been cast in place.Don't use a hammer drill for sure.If poured off a truck call for the mix design it will be like 2500lb,3000lb and on and they can tell you what type of aggregate was used. probably pea-gravel used in most common bag mixes,so drill slow when you get to it.At 40 you could have used a calcium-mix and padded it to help it cure faster.Just info if you have to pour in colder weather again.

Answer 7

A woman discovered concrete... thus it takes 28 days to cure. I agree with the rest: do not drill a hole 1" from the edge of concrete unless your desire is to have it break off right about where you drilled the hole...

Answer 8

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Answer 9

I think it is too soon to be drilled, the vibration of the drill will break the edge off the sidewalk ,better wait a while longer than damage your work.

Answer 10

Drilling that close to the edge is going to be risky, not matter what, use a good bit and a hammer drill.
A simple test is to rap the concrete with a hammer...if it sounds dull, let it cure more...if it "rings" when you hit it, that's pretty good.