Concrete drying time?

[dusterdoug]

I just poured my new driveway and i am trying to pin point an amount of time I need to let it dry before I drive on it, or park my race car enclosed trailer (10000 lbs) on it.

The concrete is 4"+ thick, 2500 pound mix with 3/4 rock and #4 rebar 2' on center.

Any opinions. I have been told 2 weeks for a car to drive on it. but don't park the trailer on it for 2-3 months?

 

[tcianci]

Not sure about the driveway but we frame houses on the green concrete the day after we strip the forms. Your best bet is to ask a local concrete contractor. My SWAG on the situation woud be less than a week

 

[csargents1546]

At work when we had the floor redone, we were setting up the hoist seven days later and using it, might have been a high strength mix though. For most cases a week is a good number unless it is really cold or wet, that can affect the cure time.

 

[V-10 Killer]

2 weeks for heavy trucks (delivery vehicles on jobsites) seems consistent with what I hear from concrete contractors around here. I'd think a few days would be fine for a car.
2-3 months for the trailer does seem a bit long, but if you disobey and it cracks, are you going to man up and accept it, or call the contractor to fix it? 10k lbs is no light load to be sure. I commonly hear "you can guarantee 2 things from concrete, it'll dry, and it'll crack" lol. If you don't care about a crack, then go for it. From what I've read, concrete is ~97-99% of its advertised strength by the end of its first month.

 

[6768rogues]

The design strength of concrete is its strength after 30 days. It will be at about 60 to 70 percent of strength after 7 days. If it were mine, I would go 2 weeks for a car and 4 weeks for the trailer you described.
If you were in a hurry, you could have bumped up the strength of the concrete so that it would be where you want it after 7 days.

 

[dusterdoug]

Thanks guys.

This was a high strength mix with the larger rock.
The concrete finishers said two weeks. but didn't specify about driving or parking the trailer.

Other contractor friends just cautioned about the trailer.

I can wait for the trailer to be parked it is stored elsewhere and that isn't the problem. I have stuff I want to move into the garage so i am concerned about driving on it.

 

[BlackLead]

The guy that's coming out Thursday to finish pouring the rest of my driveway, said no traffic for 7 days after it's poured. Especially my F250. So we'll be making an alternate route thru the yard for a week.

 

[tcianci]

The guy that's coming out Thursday to finish pouring the rest of my driveway, said no traffic for 7 days after it's poured. Especially my F250. So we'll be making an alternate route thru the yard for a week.[/QUO

Is that because of how much the F-250 weighs or how much it leaks?

 

[Falcon67]

Is that because of how much the F-250 weighs or how much it leaks?

Hey! I resemble that remark!

When my Fords stop leaking, that's when it's time to check the fluid levels.

I didn't think 2500# mix was very high strength? Most I hear about around here is 3000 or 3500.

 

[Horseshoe Jack]

I didn't think 2500# mix was very high strength? Most I hear about around here is 3000 or 3500.

It's not. 2500 psi is a 4-sack mix usually spec'd for low cost, less critical applications like driveways. 3500 to 4000 psi is getting into the high strength mix designs.

 

[Grape Ape]

The guy that did my 6" thick driveway said to stay off of it 28 days. It was a PITA for the four weeks but I think the inconvenience is a small price to pay for peace of mind.

 

[dusterdoug]

well just looked at the reciepts from the ready mix company and the mix was rated as a 6.5 sack mix. 2500lb mix.

Was told that for Driveways and streets this was normal in our area. Called 3 different Ready mix companies told them what I was doing with it including the 10000lb trailer. they all said the 2500 lb with 3/4" rock was perfect?

The strength comes from the aggregate/rock added. 3/4" rock is 2-3 times stronger than pea gravel mix.

 

[Chris Adams]

Yeah, the guys on here want 2 feet deep 10,000 pressure concrete to park their mopeds on...
Don't worry about it.
Keep it wet as much as you can.
I had about 700 square foot of 4 inch 2500 concrete put in last year, two pads, one in front of my 700 square foot shop, the other in the rear to park my Class A on.
The concrete guys were laughing when I showed them the recommendations on the forum.
They wanted to know, was everyone parking a D9 Cat or what?
Anyway, after a month we were driving an F350 over them regularly. That was 15 months ago. They look fine. Had a 13,000 Class A parked on one after 60 days, and I really didn't need to wait.

Do water the heck out of them. The more you water the stronger and less cracks.

None of mine has cracked yet, even with the usual quakes (I'm between the Landers and Big Bear faults, about 12 miles from the San Andreas in the Cajon.

 

[bczygan]

If no one mentioned it, concrete doesn't dry, it chemically cures. And keeping it wet slows the cure. Concrete continues to cure and harden forever. Concrete in massive structures (Like dams) will not cure sufficiently, because of the excess heat from the chemical curing process of adjacent concrete, so engineers run cooling lines through it.

 

[jclem40c]

spent 23 years working for county highway dept in birdge construction
department. conrete does not dry it cures and for 3000 psi general
purpose concrete it takes 28 days to reach 3000 psi and still continues
to cure for long after that. if you have the time I would recommend
going the full 28 days, just my 2cents.

John

 

[PAToyota]

If no one mentioned it, concrete doesn't dry, it chemically cures. And keeping it wet slows the cure.

Not exactly. Concrete cures and keeping it wet allows it to continue to cure. As soon as it dries out, it stops curing - the chemical reaction stops. So keep it moist to keep the curing process going.

As mentioned, concrete will reach approximately 75% of its 28-day strength in seven days. So if the 28-day strength is 2500#, then it is at 1875# after seven days - but only if it is kept wet and allowed to continue to cure. The problem is that if it dries out on the first day, it isn't even going to reach that 1875# number.

If you look at the following chart, you'll see why it is important to keep concrete damp for as long as possible and allow it to cure properly. In the example shown, the strengths of 4000# concrete are graphed (the 28-day strength when fully cured). If only allowed to air dry, the concrete makes it just over 2000# strength. If kept moist for seven days, it almost makes it to 4000# strength.

The other thing is that colder temperatures slow down the curing. Strength gain in colder temperatures slows down. 40℉ concrete will be 35% of its design strength in seven days as compared to 75% for 73℉ concrete.

More than you really want to know about concrete curing can be found here: http://www.tkproduct.com/Curing Concrete.PDF

 

[Gary S]

When I poured mine, I started walking on it the next day and building the garage walls. It took me another 3 or 4 weeks to get the building up enough so I could park my vehicles in it. The 3-4 weeks was enough. I haven't had any problems with the concrete.

 

[kywildcat]

Water it........water it........water it!!!!

 

[Holedgr]

What PA said.

It never ceases to amaze me how much bad informtion is out there.

Who's giving the warranty on the concrete?? Ask them.

If I placed it...and your instructions were for 14 days with out traffic (parked or driven over and I catch you on it (parked) or anything else, I take a picture, send it to you with a "WARRANTY VOID" letter. If you tell me, "your contractor buddy said a week is fine." I say, "You can do what you want, But NOT if you expect me to warranty it!"


Something to consider...

-T

 

[tman74]

The best thing to do, to late for you, is to have several test cylinders made during the pour. Then after 7, 14, 28 days have them broken and see how strong they are. Most of the time we poured 3,000 or 3,500# mix, and did a 7 day break they were over the designed strength. Most concrete suppliers "over build" the designs, that is the 2,500# mix in 28 days usually will break @ 3,000#+. It is easier to over build than run the risk of not getting enough. Concrete never finishes curing, if you look at a chart it reaches near horizontal, after 90 days +/-, it increases very little, but still does.
my $.01 worth..

 

[6768rogues]

I also noticed that the strength was lower than what is typically used in our area. Then I noticed your location and thought it was probably ok. In our climate, 2500# concrete will chip, spall, scale, crack and deteriorate from salt.

 

[dusterdoug]

Asked a close friend of mine his opinion on it. He was the main building superintendent for JC Penny's for 30 yrs.
He said that different companies and different states list concrete differently on reciepts.
For example: 2500 lb can be weight of mix wet not strength.
Some companies and states list it as PSI.

He said the sack mix and aggregate size meant more than any weight on the order form.
They would order 6-7 bag mix with 3/4 rock, 4-5" thick w/#4 rebar for the docks and driveways at the Penny's stores and they never had a problem even for the delivery Semi's.

By the way I checked the weight of the load and it comes out to 2500lbs of weight for a yard of ready mix.

Thanks everyone for your imput.

I have come to the conclusion that I will be fine, as long As a I wait and keep it wet to let it "Cure" properly.

 

[PAToyota]

He said that different companies and different states list concrete differently on reciepts.

Industry standard is that it denotes compressive strength in psi at 28-days. As I said, read the PDF in the above link to learn more than you ever wanted about concrete.

 

[Kevin54]

I've never went more than a week without parking on new concrete and have never had a problem with it. For a large item like a motorhome though I would wait considerably longer

 

[dxdexter]

By the way I checked the weight of the load and it comes out to 2500lbs of weight for a yard of ready mix.

:

Whoever told you that is highly uninformed. Depending on the size of the load, there may have 2500 pounds of powder in the entire load, if it was maybe a 4.5 yard load. A single cubic yard of concrete will have a mass much greater than 2500#. Most normal density concretes, regardless of compressive strength, have an approximate, unit weight of 3500 to 4000 pounds per cubic yard.

The standard (with some exceptions) is to specify concrete, firstly, by it's compressive strength (fc). In my area 2500 psi concrete is considered a "lean concrete" and normally used in mud mats to stabilize an excavation as a work surface for rebar and formwork placement prior to placement of the structural concrete.

An exterior parking slab concrete in my area would be specified as 4500psi to 5000psi air entrained. This is not to say that the loading would ever be near the specified compressive strength, but there are other considerations such as freeze/thaw resistance,low permeability, flexural strength, resistance to chemicals (ie salts), wear resistance.........etc.

A properly cured concrete should reach 70% to 80% of it's specified 28 day strength in seven days. If flyash has been used in the mix then the expected seven day strength could be down in the 60% to 75% range. Of course most residential concretes are placed at substantially higher slumps and almost never properly cured so I would wait the 14 days especially with the lean mix in order to protect any warranty that the contractor may have given.

 

[BlackLead]

The guy that's coming out Thursday to finish pouring the rest of my driveway, said no traffic for 7 days after it's poured. Especially my F250. So we'll be making an alternate route thru the yard for a week.[/QUO

Is that because of how much the F-250 weighs or how much it leaks?

This is what I get for not keeping up with the threads I post on.

 

[green.bubbly]

Ok, seems that we all agree that we must water water water. I will be pouring a house slab and a garage slab hopefully in the next two weeks if the rain stops.

So, I know I should water water water but when? How long after the slab is finished should I water it? 12 hours, 24 hours?

Should I keep it covered with plastic and just stick the hose under the plastic or should I just keep a sprinkler running on it all day?

Sorry for the stupid questions but while I always read to keep it wet, I never read anyone give the little details. And with the price of these slabs, I want to do whatever I can to love them and tend to their needs. Seriously, I have no problem sitting out there all night reading story books to them if it helps.

 

[jclem40c]

cover it with burlap, put a lawn sprinkler hose on it and water it for 28 days.
Look at any bridge they build on an interstate and thas how they do it and if those bridges have problems the contractor gets sued bigtime.

John

 

[jclem40c]

cover it with burlap, put a lawn sprinkler hose on it and water it for 28 days.
Look at any bridge they build on an interstate and thats how they do it and if those bridges have problems the contractor gets sued bigtime.

John

 

[jclem40c]

Double post, my bad, so sorry fat fingers

John

 

[mkdive]

Before I changed industries I was a redi-mix plant manager...(for about a decade).

The design strength of concrete is its strength after 30 days.

It has to at least meet the mix designs strength in a 30 day break....(that's not the design strength).

If you were in a hurry, you could have bumped up the strength of the concrete so that it would be where you want it after 7 days.

True statement.

This was a high strength mix with the larger rock.

The larger the aggregate, the higher the psi mud.

spent 23 years working for county highway dept in birdge construction department. conrete does not dry it cures

True.....amazing how many people get that wrong....including the nimrod Bob Vila.

and for 3000 psi general
purpose concrete it takes 28 days to reach 3000 psi and still continues
to cure for long after that. if you have the time I would recommend
going the full 28 days, just my 2cents.

John

I have to disagree.....our mud was meeting our mix design specs at 14 day breaks. Only about 10% of the time was it meeting between the 14 & 30 day break.

The best thing to do, to late for you, is to have several test cylinders made during the pour. Then after 7, 14, 28 days have them broken and see how strong they are. Most of the time we poured 3,000 or 3,500# mix, and did a 7 day break they were over the designed strength. Most concrete suppliers "over build" the designs, that is the 2,500# mix in 28 days usually will break @ 3,000#+. It is easier to over build than run the risk of not getting enough. Concrete never finishes curing, if you look at a chart it reaches near horizontal, after 90 days +/-, it increases very little, but still does.
my $.01 worth..

Very true our mud broke 25%-40% higher than the mix designs PSI ....also the statement about it never really stopping curing is true...years even many decades later it is still gaining strength! This is in a perfect world with out degrading environmental factors. Concrete is not as simple as most think it is.

 

[mkdive]

Did anyone mention a sealer for the top of a slab or driveway? (To help stop the loss of moisture from the mud during the hydration process)?

 

[mkdive]

As I said, read the PDF in the above link to learn more than you ever wanted about concrete.

I have half a book case full of 1"-3" thick books on concrete......that's more than Ill ever want to know!

The pdf does have good info for someone who might be new to concrete

 

[PAToyota]

I have to disagree.....our mud was meeting our mix design specs at 14 day breaks. Only about 10% of the time was it meeting between the 14 & 30 day break.

Often the case - easier to supply a "stronger" mix than be responsible for having to take it out and do it again if it doesn't meet the specifications.

Did anyone mention a sealer for the top of a slab or driveway? (To help stop the loss of moisture from the mud during the hydration process)?

Sealers are often used, but they are also often requested not to be used if there is going to be a finish on the concrete - such as epoxy.

I have half a book case full of 1"-3" thick books on concrete......that's more than Ill ever want to know!

Well, you're a special case...

 

[green.bubbly]

cover it with burlap, put a lawn sprinkler hose on it and water it for 28 days.
Look at any bridge they build on an interstate and thats how they do it and if those bridges have problems the contractor gets sued bigtime.

John

Thanks

 

[kywildcat]

I dont think you have to water it that long. I was framing my garage after about a week. I think the first 3 to 5 days of keeping it good and wet will surfice.