Wet curing concrete.

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New driveway poured. 5 inch pour, 6 bag, 4000 psi, wire mesh... The concrete truck guy said keep it wet for at least three days then you can drive on it. Concrete crew said wait 48 hours then whatever I wanted. My dad (retired old school contractor) said to wet for two weeks and wait a month to drive on it.

I currently have 2 sprinklers keeping the whole surface evenly wet. I was going to water for three days. I read that at this point it's going to have 80% it's compression strength and already be stronger than letting it air dry.

Any concrete experts lurking around here?
 
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Longer it takes to cure less Air bubbles. 3 days is a good time for the air to work it's way out.
 
Originally Posted By: dja4260
My dad said to wet for two weeks and wait a month to drive on it.


That surely isn't right.
 
My dad was a concrete expert and always said leave it wet for a long time and it cures much stronger. Nowadays they try to cure too fast and the concrete cracks much easier and the surface tends to break up much easier.
 
My father owned a small concrete construction firm. I worked for the business for 6 summers while in HS and college. If you poured a true 5 inches and used a 4,000 mix and steel wire, that's a pretty stout combination. When we did driveways, we used a 3,500 mix. I wouldn't obsess with keeping it wet, but I suggest not driving on it for a week.
 
General contractor here. Keep wet 7 days (you can cover it with plastic sheeting over the water and that will keep the moisture in it...in the old days we used burlap bags and kept them wet). The idea is for it to not dry out too fast and try to keep it cool.

I think 28 days before you drive on it is good advice due to the heavy loading. If it were a sidewalk it would be ok after 3 days...
 
3 days and keep it wet. You should be fine. My father worked concrete for 35 years. I helped him for far to long.
 
Good advice here but 28 days is a bit excessive, I worked many years on Bridge and Highway construction all over Michigan Ohio Indiana and Florida . The secret is to let it dry very slowly and keep it cool. After 3 days you are good to go unless you are going to bring a semi truck loaded with gold bars to your house. After 3 days you are good to go. Trust me. If you are still unsure, inbox me and I will get you connected with a competent engineer fluent in the curing process.

Originally Posted By: bcossa2001
General contractor here. Keep wet 7 days (you can cover it with plastic sheeting over the water and that will keep the moisture in it...in the old days we used burlap bags and kept them wet). The idea is for it to not dry out too fast and try to keep it cool.

I think 28 days before you drive on it is good advice due to the heavy loading. If it were a sidewalk it would be ok after 3 days...
 
This is one of those old myths that keep getting new life just like Pennzoil is made out of Bees wax and will sludge up your engine. Unlike rising bread, concrete does not make bubbles unless it gets to a boiling temp. Everyone knows what temp it takes to get water to make bubbles? OK back to concrete. There is a product called "Air Entrained Concrete" . This product contains billions of air bubbles per cubic foot. Bubbles can be a good thing. Just sayin....
Originally Posted By: Dyusik
Longer it takes to cure less Air bubbles. 3 days is a good time for the air to work it's way out.
 
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My Pop said keep it wet, plastic cover for three days, wait 7 days. Good to go for pickup's/cars. Drive way(6 bag mix, poured super wet, no wire) at his old house is 30 some years old, still no cracks.
 
Originally Posted By: Blueskies123
Eight replies eight different suggestions.


I spoke to the concrete crew, concrete delivery guy, and my dad. All three gave me different answers.

Concrete is expensive and I'd rather be safe than sorry. I'll water it through the weekend and stay off of it until the end of the week.

I'd like to be able to park in my new garage!

I've read alot on wet curing and it seems that after three days my concrete will be 30+% stronger than your typical air dried pour. Water is cheap, concrete isn't. Not sure why more people don't do this.

I'm also going to seal the driveway with HD39 Densifier in a few weeks.
 
I'm amazed every time I see a concrete foundation being poured down here, in the heat of Summer, with no sprinkler.

When mix cures, it gives off heat, which can dry it out. Like epoxy, a slow cure is stronger. With that much mass, it takes time. Water serves as a coolant + keeping it from drying out too fast.

So patience now + some water are well worth the wait.
 
I wouldn't worry about keeping it wet. Saw cut it in 24 hours. We have poured building slabs with 4000 psi and they were on it the next day with forklifts. The most important thing with slab concrete especially driveways is the subgrade. Compaction of the subgrade is so important to a long driveway life with no cracks.
 
Be gentle with your watering, else you might get some cement wash-out/aggregate separation.

Covering avoids this risk.

Covering with something permeable (hessian, newspaper) avoids this risk and allows you to water through it.

If that was going to happen, though, it probably already would have.
 
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28 days is the "design" strength time for the concrete, not that date at which it can be used...you will likely be at 75% after only a few days.

When I was project manager of the new Coal Handling Plant at Wallerawang in the late 90s, some of the structures needed to be utilised early to maintain programme, so the structural/cicil guys would overspecify the concrete strength, knowing that it would reach "design" in a week or thereabouts...it was ultimately way stronger than needed, but shortened the programme over waiting.

Two days in, the majority of your heat production will be gone, so you are keeping it wet for the hydration reaction to continue.

http://www.boral.com.au/brochures/ordering/PDF/DS2006Curing.pdf?pdfName=DS2006Curing.pdf

Keeping it wet longer is better.
 
Rule #1: concrete curing is a lot like paint drying, in that a lot of people do this work but very few understand or bother to educate themselves about the science behind it.

Rule #2: the cool go-to guy in the neighborhood's opinion always overrides the scientifically-correct answer.
 
Wet curing is fine. Keep that up for three days, and then normal car traffic can use it after about a week.

The other option (neither here nor there at this point) is to seal the concrete with a curing compound. Avoids the whole keep it wet for so many days issue, etc... That's how my driveway was done several years ago. 5" pour with 4500 psi concrete and rebar. Sawcut joints. Holding up well - though as others pointed out the main part of that was getting the subgrade done right more than anything. I waited two weeks before driving the truck on the driveway.

Early in my career I did a lot of concrete testing and sampling. Typically, we'd take three cylinders. Smash one at day 7, and another at day 28. The timeframe is completely arbitrary, but the idea was the concrete needed to be past its "design strength" at 28 days. Normal concrete mixes will generally test out somewhere above 65% of the design strength in a 7 day test, and over 90% in a 14 day test. We'd test at day 7 to catch any major errors early.
 
Considering the strength of conc., (4000 psi), and using wire wire mesh, I would do the following:
1. Keep the concrete damp for about 3 days, (moisture is required for proper curing). You can put light traffic on your driveway in about 5 days. (Conc. will reach most of its strength in 21 days)

This driveway will out last you! (34 years DOT highway engineer, retired.)
 
Originally Posted By: Shannow
Two days in, the majority of your heat production will be gone, so you are keeping it wet for the hydration reaction to continue.


Yeah especially in a slab where there is a large surface area compared to the thickness. I remember calculating the heat transfer for the Hoover Dam in a differential equations class, that dam would have taken over a century to cure had they not installed cooling pipes (which were later grouted).
 
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