Concrete questions

Hello all, getting retaining walls put in and then going to do a concrete patio and walk way. My brother said I want to get the concrete done in early may or wait for fall. He said the hot summer months make concrete more prone to crack when drying. He says he waits for fall to get all his concrete projects done. Area will be about 16'x20' plus a 3ft walkway 50-100 foot long all poured 4"

my concrete man makes two garantees with concrete. #1 it will crack #2 it wont blow away!
Have a great day!

I don't know the answer to your specific question, but when we had concrete poured a couple years ago someone told me make sure it's fresh in the truck if it's being delivered. If it's been in the truck too long (such as they left the yard early in the morn, went to another job, then your job) it might start to set up and not be (as) good causing cracks later. Knowing that now, it looks like we might have some areas that are suspect. Good luck.

When the temperatures are hot, concrete will hydrate too quickly, and there are problems associated with this, I have seen where the top layer spalls and exposes aggregate. I agree with the cooler, spring and fall weather, it definitely helps. However, concrete is still used commercially in all kinds of weather, for hot weather, on bridge deck jobs, you will see burlap and soaker hose used to keep the hydration process from happening too quickly, slow cure if you will which I believe is a good thing when it comes to concrete.

Yep, when I was in the concrete business I used to guarantee it 100% against fire and theft!

Pouring in the heat should not affect the strength of the concrete if it's laid right. Keep it wet for about 3 days with a sprinkler.

Concrete cures over several days,spray it with water/cover up with a tarp,it will crack if you get frost and its not sawcut to crack along freeze lines..if you are in a warmer climate where the ground never freezes don't worry about it,like the other poster said..it will crack..from weight or frost,never heard of heat and sun cracking it. If a crack appears there has been movement in the concrete's base from poor compaction of the gravel base..or frost/weight on top..it'll be fine! Good luck with it!

Also your concrete is guaranteed to get hard!
Brian

In Kansas that would be a gutsy concrete guy!

Have the concrete guy agree to leave his forms on for two days.

JohnDeereJimOhio,

If I was going to have that much concrete poured, I would want someone there that knew more than I do, which isn't much.
The cement I have had done by a professional, the veranda is scalding and wearing down to stone in less traveled areas.
Basement floor is cracking and you can see where water is coming up in spots not where it's cracked but soft areas.
Sorry to say I wasn't here when done.

I did see a cement truck adding Water From the Lake, just before he delivered it to a guy building a house down the road.

I would Tell the guy at the concrete office that you want a SLUMP TEST on site, Find out what you are paying for and what the test should read.

The standard for curing concrete calls for moist cure for 7 days. Temp to be above 40 F and below 80 F.
always specify the 28 day strength and maximum slump.
the lower the slump the least shrinkage.
Air entrainment is good if you have freezing weather as it reduces cracking and spalling.

As others have said below, just keep it wet with a sprinkler for a couple of days if it is too hot. There are additives to the concrete mix that assist in making it cure slow. I wouldn't worry about it personally, as long as you watch it. Bob

Concrete does not dry, it is called the hydration process, a chemical reaction between the water and cement. If the construction industry only placed concrete in the spring and fall, we in the midwest would never get concrete work completed. Spring the subgrade is wet and unstable, fall, days are shorter and low temps increase the cure time and potential for freezing. Concrete will crack at any temps, summer temps will increase this probability. So the use of control joints at 8 to 10 foot intervals will "cause a weak spot where the contracting or expanding concrete can relieve pressure and crack along your control joint cut. Cut must come within 24 hours of placing or as soon as cut can be made with out damaging the surface of the concrete and be approximately 1/3 the slab thickness. If this is a diy, do it in small bites, better to wait on the cure so your finish is what you desire, not fighting a flash set that you cannot catch up with. Do not add water to the surface to get a more workable concrete cream, it weakens the top 1/4 inch and will spall and durability and weather resistance will be compromised. orry for the long post, spent most of my working days around concrete. Buildings, bridges, roadways. Placed concrete in every month of the year. Just have to know what must be done to have the end result be a good product. I wish you well gobble

I would not pour it on 100 degree day, other than that just keep it damp for 3 days.

(quoted from post at 09:32:57 04/29/14) Hello all, getting retaining walls put in and then going to do a concrete patio and walk way. My brother said I want to get the concrete done in early may or wait for fall. He said the hot summer months make concrete more prone to crack when drying. He says he waits for fall to get all his concrete projects done. Area will be about 16'x20' plus a 3ft walkway 50-100 foot long all poured 4"

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There are only two kinds of concrete....that that is cracked, and that that is gonna crack.

They expansion joints that you put in about every 8 to 10 ft. You put them in while pouring the concrete the work great to stop cracking which is caused by expansion when hot. Ever drive on a concrete roadway in the hot summer the joints are pushed up and you get a real bumpy ride. Without these joints it would tear itself apart in no time.
Walt
Ps make sure that the concrete is hard to pour the more water in it the strength it will have.

Along with a slump test, also inform the appropriate parties that you are taking test cylinders for compressive strength testing. That usually keeps these outfits straight. From experience of building high rises in NYC, I can tell you any deviation or failure of the approved mix design is a disaster. Funny how when you consider residential work, the formalities of inspection, testing etc. are often skipped.

The mix design will have a specific water to cementitous material ratio, which if you deviate from and add more water than is called for, it will reduce the compressive strength. All the materials which make up a mix design are used in specific amounts, change that and you now have a different mix design, one that may or may not perform as what was called for, only way to find out is testing. That's why 03300 specifications, in division 1-16 usually or most likely call for an existing design, that has been tested and is using specific materials to the area or the batch plant, change any of that and the mix must be tested to prove it performs.

If a more flowable material is desired, its best ordered that way, ie; pump mix for a pump truck, or as called for in the specifications.

Most residential or similar users of this material will order 3000, 4000 psi, and the suppliers rarely hear about any testing unless its a big commercial job, so its good measure to mention the taking of test cylinders, very easy to do, local testing outfit should be helpful in obtaining test cylinders. Take 4 cylinders, fill one at a time, 1/3 at a time with concrete, use a 1/2" steel rod to "rod" that 1/3rd portion, 25x, repeat for the next 2/3rds, rod 25x each 1/3rd, then screed the top off evenly, make sure to mark the date on the cylinder, testing outfits use a metal tag from what I recall, then have a testing outfit break at 7,14,21,28 days. That's typical in commercial work, just an FYI for here though.

I got a ballpark estimate of $1500.00 to pour a 20 x 20 kennel. I called a Redi-mix plant to see what it would cost for just the concrete if I finished it myself--$1605.00. The first guy poured my walls and basement and a smaller 14 x 20 kennel so I trust his work.

Larry

20x20 four inches thick, not figuring thicker perimeter, would take 5 yards. $1605 for 5 yards?

Notice that Tom Turkey said "place" concrete, not "pour" My father used to say that concrete is not poured it is placed. If it is soupy enough to pour it is too weak.

There's a bunch of misnomers with Concrete, some people call it cement, but cement is the cementitous material that binds it together and gives it strength. Form, Place and Finish LOL !

Some call Masonry.... Masonary, we know what you mean, but if you want to be a stickler LOL!

Cinderblock, not sure where that was derived from, someone here must know, LOL ! In the industry its referred to as concrete masonry units, or C.M.U.

There is a specification for placing concrete that states it cannot free fall a certain distance, I think it was 8'-0", after that distance you have to use a chute or trunk, so with a deep form for a wall, I remember using chutes, basically a hopper with a flex tube attached to direct the "placement" (notice I said placement, not flow LOL !!!) then the vibration device to settle it in lifts, not all at once.

Its good to know the difference, most people know what you mean, but in the technical world of engineering one might sound a little inexperienced, then you might offend someone explaining why cement is not concrete LOL ! I'll kindly stay out of that one LOL !

The technical term is place,but here in the midwest everyone from the dispatcher at the redi mix plant to the drivers, to the the guys placing the concrete call it pouring concrete. I started tagging along with my Dad on the job sites over 50 years ago when I was 4 years old. Never in those 50+ years have I heard anyone but an architect or engineer say place concrete on a job site. Maybe it's a regional thing?

(quoted from post at 19:28:50 04/29/14)Cinderblock, not sure where that was derived from, someone here must know, LOL ! In the industry its referred to as concrete masonry units, or C.M.U.

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When blocks are made with ash, also known as cinders, the blocks are called cinder blocks...

Hey Billy.

Never heard of the 8' free fall rule however I have never heard of someone trying to do that.. You would need goggles with windshield wipers!!

On another note, I poured 2 identical walls for my shop: 40' x 4' x 2', 5000lb. One was poured at about 40 degrees with no calcium and the temperature dropped to I think about 10 degrees f.

The second wall was poured with hot water and calcium and both walls have 5/8 rerod cages and snap-tie forms were used.

Both walls are 20 years old with virtually no cracking.

The odd part is that the wall poured with the hot water and calcium rings when you hit it with a hammer while the other one gives the usual dull thud.

Just curious if you knew why.

Regards, Brad

Also the weather has broken here (finally) and I will be trying my hand at laying block soon. Will post the antics for the enjoyment of all.

I correct my wife on that all the time.

I tell her cement mixed with sand and water forms concrete.

She doesn't seem to listen too well.

Goose,
Next time tell her cement is an ingredient in concrete just like flour is an ingredient in bread. Might work but you never know.

That is interesting, lot of variables to consider, but they are different, one with an admixture, one without. Might be a chemistry thing, the difference, but the resonation difference, air entrainment different between the 2 mixes? There are tiny little voids, concrete does have capillaries, and is porous, perhaps the structures of these differ in size and each creates its own sound ? I've never really wondered about the acoustical qualities of concrete beyond the structure it forms except how sound attenuation is achieved with the architectural finishes used inside. One never thinks about the sound of concrete when struck. First guess would be density, or large aggregate which is source specific. Lightweight concrete specifications call for a lighter aggregate, such as Norlite, which is a specific shale mined just across the river from here. Its cooked, heated to a high temperature, expands and is porous, very light, kind of like sedimentary popcorn LOL ! I would bet a regular weight and the lightweight would sound very different when struck.

5000 psi is some strong material, and I forget where they are with the highest PSI concrete today, but recall years back in engineering news record where they had just reached 18,000 psi, which is hard to imagine, but has been achieved on WTC one.


Yes, its definitely in all the 03300 specifications on jobs I've done, you can't let it free fall past a certain distance. When in the excavation/foundation stage of a large job, or any for that matter, you have to be on the lookout for all these kinds of things with contractors. Put faulty material in these locations by mishandling and you have a real disaster on your hands once you put enough weight onto it. This material has a lot of rules to abide by.

So it goes with the name, will have to research that one, but people know what you mean its the household name for concrete block or concrete masonry units, CMU.

Billy--years and years ago block was made out of cinders as the course aggregate--it was readily available from coal burning plants,steam engines,etc. It was light weight so was easy to place the blocks, however was quite porous as compared to today's concrete blocks.
We had a cinder driveway when i was a kid--it was quite dirty!!