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 Portland cement DIY question.
KRONIIK  [Member]
10/4/2010 10:38:54 PM
Anybody know how many (94 lb.) bags of Portland Cement it takes to make one cubic yard of concrete?
The directions on the bag say to mix one part PC to 3 parts of 3/4-inch aggregate gravel and 2 parts sand for general purpose concrete. (Back porch; footers for a block wall, in my case.)

But the bag doesn't seem to note the volume of its' contents...

I have only about a cubic yard to pour in total and it's pretty much inaccessable for a pre-mix truck, so I figured I'd just mix it myself. I have sand, water and gravel at the site and figured I'd get a stronger product and cheaper than the Sackrete stuff if I go the Portland route.

Also- will crushed limestone serve as the gravel portion or should I use round "river" rock? (I'm placing rebar in the forms, and shouldn't require any unusual strength, beyond that.)
Ranchitecture  [Team Member]
10/4/2010 10:40:51 PM
Use the rive rock. Are you using a mixer?

Posted Via AR15.Com Mobile
foxherb53  [Team Member]
10/4/2010 10:44:52 PM
7 sack mix would be a normal truck mix for a yard.
Tim_the_enchanter  [Team Member]
10/4/2010 10:45:22 PM
My old man was a bricklayer. I have mixed tons (literally) of Portland cement by hand. I have no idea how much makes a square yard though.
ragedracer1977  [Team Member]
10/4/2010 10:46:48 PM
Originally Posted By KRONIIK:
Anybody know how many (94 lb.) bags of Portland Cement it takes to make one cubic yard of concrete?


13.5 bags.

A 94# bag of portland makes 6 cubic feet of concrete. 3 cubic yards of concrete x 27 (cubic feet per yard) = 81 cubic feet; 81 / 6 (cubic feet of concrete per bag) = 13.5 bags.

(I stole this off the net, I don't know how accurate it is, but it sounds good. )
out-a-ammo  [Member]
10/4/2010 10:48:24 PM
The volume of a bag is about one cubic foot.

DzlBenz  [Team Member]
10/4/2010 10:49:02 PM
You'll need about 500 pounds of Portland Cement per cubic yard of concrete. That's based on 3000psi, 3/4" coarse aggregate.

Crushed rock will give you higher compressive strength than smooth, rounded river rock. However, for your application, that's not really very critical.
SuperJanitor  [Member]
10/4/2010 10:49:09 PM
6 or 7 bags depending on the strength you want. Aggregate don't matter, stone or gravel, as it's just filler anyway. Go with whatever is cheaper/easier to get.

ETA, you'll want it plenty wet with footers so it will work easier. A little more cement helps give a wetter mix more strenght. I used to haul to a contarcor who'd say "I want it so wet it seeks it's own level" whenever he was pouring footings.
DzlBenz  [Team Member]
10/4/2010 10:51:58 PM

Originally Posted By ragedracer1977:
Originally Posted By KRONIIK:
Anybody know how many (94 lb.) bags of Portland Cement it takes to make one cubic yard of concrete?


13.5 bags.

A 94# bag of portland makes 6 cubic feet of concrete. 3 cubic yards of concrete x 27 (cubic feet per yard) = 81 cubic feet; 81 / 6 (cubic feet of concrete per bag) = 13.5 bags.

(I stole this off the net, I don't know how accurate it is, but it sounds good. )

wut
DzlBenz  [Team Member]
10/4/2010 10:52:40 PM

Originally Posted By SuperJanitor:
6 or 7 bags depending on the strength you want. Aggregate don't matter, stone or gravel, as it's just filler anyway. Go with whatever is cheaper/easier to get.



You have no idea what you're talking about.
SuperJanitor  [Member]
10/4/2010 10:56:03 PM
Originally Posted By DzlBenz:

Originally Posted By SuperJanitor:
6 or 7 bags depending on the strength you want. Aggregate don't matter, stone or gravel, as it's just filler anyway. Go with whatever is cheaper/easier to get.



You have no idea what you're talking about.


It's footings. It don't make a damn bit of difference.

Just to satisfy you though, we always batched out concrete with 3/4 crushed limestone unless the customer asked otherwise.
DzlBenz  [Team Member]
10/4/2010 11:00:46 PM
If you want a good rule-of-thumb for concrete mix design, start with the tried-and-true 3:2:1 method - 3 parts coarse aggregate, 2 parts fine aggregate and 1 part Portland cement. You can use this by volume or weight and get decent results. Only add as much water as necessary. Most people put WAY too much water in concrete when they mix it, and the strength goes way down in a hurry. With excess water, you start to get segregation of material, and don't develop a good mechanical bond between the paste and the aggregate. Furthermore, with too much water, you get a lot of shrinkage, which is manifested in the form of cracks. Lastly, excess water leads to spalling of exposed concrete surfaces.
DzlBenz  [Team Member]
10/4/2010 11:01:35 PM

Originally Posted By SuperJanitor:

It's footings. It don't make a damn bit of difference.
Whatever you say; you're the structural engineer.

SuperJanitor  [Member]
10/4/2010 11:06:11 PM
Originally Posted By DzlBenz:

Originally Posted By SuperJanitor:

It's footings. It don't make a damn bit of difference.
Whatever you say; you're the structural engineer.



It's footings for a block wall on his back porch for crying out loud. No big deal. I've hauled a lot of concrete.

Next I suppose you'll want him to run a slump test.
DzlBenz  [Team Member]
10/4/2010 11:07:42 PM

Originally Posted By SuperJanitor:


It's footings for a block wall on his back porch for crying out loud. No big deal. I've hauled a lot of concrete.

Like I said, you're the expert.
zeekh  [Member]
10/4/2010 11:10:09 PM
Contents of the bag is 1 cubic foot. Add in the aggregate & sand and you have your answer
ragedracer1977  [Team Member]
10/4/2010 11:19:39 PM
Originally Posted By DzlBenz:

Originally Posted By ragedracer1977:
Originally Posted By KRONIIK:
Anybody know how many (94 lb.) bags of Portland Cement it takes to make one cubic yard of concrete?


13.5 bags.

A 94# bag of portland makes 6 cubic feet of concrete. 3 cubic yards of concrete x 27 (cubic feet per yard) = 81 cubic feet; 81 / 6 (cubic feet of concrete per bag) = 13.5 bags.

(I stole this off the net, I don't know how accurate it is, but it sounds good. )

wut


I guess that was a recipe for 3 yds? Like I said, I just typed it in google and grabbed the first answer. I even added the disclaimer.
CavVet  [Team Member]
10/4/2010 11:20:44 PM

Originally Posted By DzlBenz:
You'll need about 500 pounds of Portland Cement per cubic yard of concrete. That's based on 3000psi, 3/4" coarse aggregate.

Crushed rock will give you higher compressive strength than smooth, rounded river rock. However, for your application, that's not really very critical.

Correct on all three!


Originally Posted By DzlBenz:
If you want a good rule-of-thumb for concrete mix design, start with the tried-and-true 3:2:1 method - 3 parts coarse aggregate, 2 parts fine aggregate and 1 part Portland cement. You can use this by volume or weight and get decent results. Only add as much water as necessary. Most people put WAY too much water in concrete when they mix it, and the strength goes way down in a hurry. With excess water, you start to get segregation of material, and don't develop a good mechanical bond between the paste and the aggregate. Furthermore, with too much water, you get a lot of shrinkage, which is manifested in the form of cracks. Lastly, excess water leads to spalling of exposed concrete surfaces.

Listen to everything this guy says. Everything. 3:2:1 is a tried and true old school concrete that our Grandfathers Grandfathers knew. And you know what? Its as good today as it was then. In fact you will still find lots of it still performing quite nicely.




And if you have any questions, send him a PM and follow his advice. Seriously. I dont know what he does (or maybe my CRS made me forget), but he knows concrete very well.


KRONIIK  [Member]
10/4/2010 11:56:19 PM
Thanks for all the advice, Fellas!
I know what I need to get now.
alc1343  [Team Member]
10/5/2010 12:00:04 AM

Originally Posted By DzlBenz:

Originally Posted By SuperJanitor:
6 or 7 bags depending on the strength you want. Aggregate don't matter, stone or gravel, as it's just filler anyway. Go with whatever is cheaper/easier to get.



You have no idea what you're talking about.
I've got a concrete pour @ 6am...I can't wait to tell the engineer (if he shows his ass up) this and watch him shit his pants...

DzlBenz  [Team Member]
10/5/2010 12:02:52 AM

Originally Posted By alc1343:

I've got a concrete pour @ 6am...I can't wait to tell the engineer (if he shows his ass up) this and watch him shit his pants...


If you really want to watch his head explode, tell him you're going to water down the surface after it's poured. Tell him not to worry about the standing water; you plan on sprinkling cement over the top to soak up the water.
alc1343  [Team Member]
10/5/2010 12:04:54 AM

Originally Posted By DzlBenz:

Originally Posted By alc1343:

I've got a concrete pour @ 6am...I can't wait to tell the engineer (if he shows his ass up) this and watch him shit his pants...


If you really want to watch his head explode, tell him you're going to water down the surface after it's poured. Tell him not to worry about the standing water; you plan on sprinkling cement over the top to soak up the water.
Before or after it's troweled?

Because in their specs, the 3 approved curing methods are ponding, wet sand, or blankets...

DzlBenz  [Team Member]
10/5/2010 12:07:42 AM

Originally Posted By alc1343:

Originally Posted By DzlBenz:

Originally Posted By alc1343:

I've got a concrete pour @ 6am...I can't wait to tell the engineer (if he shows his ass up) this and watch him shit his pants...


If you really want to watch his head explode, tell him you're going to water down the surface after it's poured. Tell him not to worry about the standing water; you plan on sprinkling cement over the top to soak up the water.
Before or after it's troweled?

Because in their specs, the 3 approved curing methods are ponding, wet sand, or blankets...

Tell him you're going to water it down so that you can trowel it easier. (For reference, it's just about the worst thing you can do to the surface.)

KRONIIK  [Member]
10/5/2010 12:48:32 AM
Trowel?
I was just going to sort of level it off with the pressure washer!
A_Free_Man  [Team Member]
10/5/2010 1:19:13 AM
Since we're getting technical here...

The volume of the Portland cement DRY is 1 sack = 1 cubic foot = 94 lb. In bulk, it will fluff up a little over that if transferred pneumatically (blown through a hose into a tank), requiring about 1.3 cubic feet of tank capacity per cubic foot of cement to be blown in. Later it will settle and be a hair under 1 cft. But 1 cft per sack is a good guess.

When mixed with water, just Portland and water, nothing else, with maximum water (no "free water" excess to the reaction) it takes 5.2 gallons of water to mix at a density of 15.6 lb/gal, and 1.08 cubic feet of slurry per sack.

Now you add your sand and gravel to this. There are airspaces in the sand. So you can't just say, 1 cubic foot of sand plus 1 cft of cement = 2 cubic feet. You have to know the absolute volume of the sand (and gravel). And you will have to add a slight amount of extra water to wet the sand and gravel.

The "6 sack mix" is OK.
KRONIIK  [Member]
10/5/2010 6:26:21 AM
Originally Posted By A_Free_Man:
Since we're getting technical here...

The volume of the Portland cement DRY is 1 sack = 1 cubic foot = 94 lb. In bulk, it will fluff up a little over that if transferred pneumatically (blown through a hose into a tank), requiring about 1.3 cubic feet of tank capacity per cubic foot of cement to be blown in. Later it will settle and be a hair under 1 cft. But 1 cft per sack is a good guess.

When mixed with water, just Portland and water, nothing else, with maximum water (no "free water" excess to the reaction) it takes 5.2 gallons of water to mix at a density of 15.6 lb/gal, and 1.08 cubic feet of slurry per sack.

Now you add your sand and gravel to this. There are airspaces in the sand. So you can't just say, 1 cubic foot of sand plus 1 cft of cement = 2 cubic feet. You have to know the absolute volume of the sand (and gravel). And you will have to add a slight amount of extra water to wet the sand and gravel.

The "6 sack mix" is OK.

It's always more complicated than one first thinks, isn't it?
Thanks for the interesting info!
Ron

KRONIIK  [Member]
10/5/2010 6:29:16 AM
Originally Posted By Ranchitecture:
Use the rive rock. Are you using a mixer?

Posted Via AR15.Com Mobile


Yes, I'll probably borrow or rent a mixer.
SuperJanitor  [Member]
10/5/2010 9:56:06 AM
Originally Posted By alc1343:

Originally Posted By DzlBenz:

Originally Posted By SuperJanitor:
6 or 7 bags depending on the strength you want. Aggregate don't matter, stone or gravel, as it's just filler anyway. Go with whatever is cheaper/easier to get.



You have no idea what you're talking about.
I've got a concrete pour @ 6am...I can't wait to tell the engineer (if he shows his ass up) this and watch him shit his pants...


I don't care what you tell the engineer. We are talking about residential footings here, not prestressed bridge beams. You people are over complicating it.