I need to place a 40 x 100 foot parking slab…it will be covered with a metal roof … metal building with no walls… metal posts on concrete piers…
no real weight will ever be on this slab… it will be high in the center (the long way) and slope out… prob 1″- 1.5″ max in 20 ft
very compacted hard base, no frost, no road salts ect…
is there any reason to be over 4″ thick? oh yeah and what pound mix?
thanks in advance
p
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Replies
Parking cars or heavy equipment?
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cars only... ceiling height only about 9ft... so no alot big could ever get in ... just covered parking for 20 cars (10 each side nose to nose) ... urban area... u know the loft type... subarus and small suvs :)
till somebody parks thier pickup similar to mine on it...
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P
Around here drive ways for car/pickup use are usually 4".
Doug
ponytl,
I would go 4", 3500#, #3 bar, 2' o.c. e.w.
Scored or cut into no larger than 10' sq. sections
"Poor is not the person who has too little, but the person who craves more."...Seneca
Edited 7/8/2007 11:50 am by dovetail97128
Everybody places 4 inches of concrete. The weight of the vehicle is sitting on four point. those four points are holding 1/4 the load. everybody place 4 inches. Everybody has cracked slabs. All concrete cracks, no just those that pour 4 inches. A slab will hold a car fine at 4 inches. what about the UPS truck or garbage truck, furniture delivery truck.I learned the hard way, I don't place under 6 inches.yes, its a lot. You going do what you want anyway. the extra 2 inches is not that much more and its insurance. It would be cheaper to place six inches than to buy the rebar for 4. After you lap and cross #4 bars you still only have Inch and a half of coverage over the bars. Six inches of concrete compared to 4 with bars are about equal.Then you got based problem. If you had the world perfect base, you could have a 1/inch of concrete with no problem. So the extra concrete bridges over any sub soil problem.Now if you could have 6 inches of concrete with rebar. That would be the ultimate. nothing under a 707 could screw that up.
"Six inches of concrete compared to 4 with bars are about equal"
I think you need to back that up with some sort of explanation before I believe it. How does the extra 2" act to strengthen the bottom of the slab in tension the way bar does?
this will be placed over what was a gravel parking lot not sure of the numbers but at the time i had 6" of the white rock with fines (road base) put down... that was over 6yrs ago and since everything from full redi mix trucks, full 20yd sand trucks and even my buddies 50ton crane have traveled the lot with none of them leave'n a mark... i mean zero... so i feel like i have a pretty solid compacted base...
not alot of ups or delivery trucks would fit under roof... (9ft max) prob closer to 8.5ft clearance...
it's covered parking I don't see it going anywhere ... pretty sure i will score & stain it... float it... knock it down with a power trowel... leave some "texture" and score in a simple pattern... 3 tone acid stain and seal...
deep score it on a 10x10 while green...
50% more material cost 4" vs 6" and i don't see me putting any steel into it at all ... i can see me doing the grade level and going from 5" thick in the center to 4" thick outer edge for some drainage... it will meet asphalt on 3 sides...
i was hope'n someone would swear by 3" thick... ( which is what i see them doing for most driveways around here ...)
p
I did my driveway 2x4 thickness , which is 3 1/2 and it cracking like crazy. all my other poured been six inches and doing good. all my driveway hold is a toyota
I was always taught that there be two types of concrete: already cracked, and going to crack. It don't make no matter how thick you make it.But what do I know?
Did only 3-1/2 " thick over a similarily compacted 6" base in 1992. 30 to 35 ft by about 60 ft, irregular shape.
6 to 8 ft square divisions.
Not a single crack yet, used 6 sack mix, kept the mix dry at 2 inch slump (hard to work*, but dry rich mix probably why no cracks)
What steel is in it is some old chain link fence and other scrap I wanted to get rid of.
* Finished 14 cu yards of it by myself one day, would not try that much alone now, was still under 50 YO then.
Edit - driveway/pad has had dozer and trailer on it more than a few times
Watched one of the mexican crews pour a drive and garage floor of 'soup' in a nearby subdivision, probably > 10" slump, no thicker than latex paint!! - that puppy's gonna crack first freeze we get next winter.
Edited 7/8/2007 9:28 pm ET by junkhound
man... dry mix and 14yds alone.... i don't care if ur 25 and a marine... thats killer...
at 46 i'm still wide open until i get home... then i'm done... use to be i'd be home shower and back out the door.... as it is my harley is covered in dust and hasn't been started this year... same for my boats & jetskis...
interest payments are the worst boss i've ever had
p
when you pour your slab, while it still wet, get a fish skeleton and press into the concrete, in a out of way place. then when you stain it, it will show up as a fossil, people be walking by, hey what that.
"pretty sure i will score & stain it... float it... knock it down with a power trowel"
I understand that some boys don't like their soon-to-be-acid-stained ceement worked with power trowels.
I like your plan of doing the stain, however.
you don't want a slick finish for acid stain (in most cases i did do it on my loft floors) but the "imperfections" are really what make the stain look "natural" or add effect... i poured 10,000 sf in one dat for my loft floors... the areas that i was most unhappy with... stained the best... including a few cat paw prints and some tennis shoe prints...
for a days work and $250 in material... i believe the acid stain will make the parking area much nicer... i have several sets of stamping mats and might do a stamped border... the mats are about 18" wide ... have em in a brick or cobble stone pattern that size... so... might be worth play'n with... alot of effect for few$$
kinda wish it wasn't 100 degrees out there for this pour... think'n 10 x 100 per pour since i have a 12ft power screed.... and doing 2 per day... full truck access.... only me & 3 guys.... so... the stamping might require a couple extra guys...
takes me a week or so to get a plan... might do a couple of my patios with the same stamped border first just as a trial run
p
If you really want to avoid the metal I'd start with 6". Load it with short fiber and pour a stiff mix, maybe 4000# mix at 2" slump. Score at 8-10' intervals. It WILL crack, but the individual scored sections should hold up fine. Be like 8' square pavers.
At the very least, make it 6" where cars enter and exit the slab. You might get away with 4-1/2" to 5" in the rest of it.
4" in the field, 6" front and back, (the transition from driveway to parking,) #5 rebar across the front and back, #4 on a 2' grid in the field.
Roof columns 18x18x9 with 1 #4 rebar ring and an X across the center. Have a 24x24 #4 ring you can drop on the field grid as soon as you pull the column forms.
5 sack mix.
SamT
Per the CRSI Handbook, 4-inch slab is ok for domestic or light commercial loads (less than 100 PSF). Do not go less than 4-inches thick. 6 x 6 8/8 minimum reinforcing. I'd go #4 rebar at 18-inch max spacing. I would suggest 3000 psi concrete if cracking and wearing is a concern, but 2500 psi is ok. For commercial loaded slabs I go 3000 psi minimum, and usually 4000 psi.
Cracking is really due to a number of causes. Mostly it's curing and Water/Cement ratio. I rarely see any contractor do a really decent job of curing.
thanks for the info... the only thing i do for curing is keep the surface wet for 10-20 days... first 48hrs just try to keep it damp then after i try to keep a light mist on it 24/7...
is there something better i could/should do?
on the very rare times i've used someone besides me to do my flat work... last time i see them is at the end of that job that day... pretty sure thats standard...
p
I've read that concrete hydrates for years. So keeping it moist for as long as you can really helps for cracking and overall strength as well.
Placing Visqueen on top works pretty well. There are also curing compounds that are wax-based that are just sprayed on. Basically, they put down a thin layer of wax to seal and cure the concrete.
Using a dryer mix probably helps more than anything. If you are not pumping the concrete, limit the slump to 4-inches.
I think someone else mentioned crack control as well. Put some sawcut or other type of control joint at 20-feet maximum for such a large slab.
Good luck.