Portland Mixes

[bannerd]

Hey all,

Looking to mix some good ol cement with sand/gravel to make concrete. The yard has a pre-mix of concrete, I'm just worried about the ratios for this. Typically I would mix one part Portland, two parts sand and three parts gravel.

Would this mean I would mix one part portland and five parts to what the yard has to offer? I suppose I could get the concrete tested after but I would like to know what everyone uses for ratios.

 

[SGKent]

have you asked the yard what they recommend? They may have a chart based on strength and use.

 

[SteveCh]

I've been using 4:1 or 5:1 for decades. Friend of mine always uses 6:1, gets as good a result as I do.

Somewhere around here I have a concrete "textbook" someone now forgotten gave be back in the mid-seventies and is where I got my own ratio.

By the way, the "mix" I use is a premixed sand/gravel made around here by a gravel yard. They call it, wait for it, "concrete mix." I have also bought pure sand and loads of gravel and mixed it myself as I add it to the mixer. However, for the price and physical exertion, I now only go with the premixed. Last time I bought it, it was sold at either $12 a yard or $12 a ton, don't remember. But cheap....

 

[bannerd]

Yard said mixing is up to the customer, He wasn't sure how much gravel he puts in but it's more like a 1:2:2 one being portland.

Thanks SteveCh, that is what I was looking for. I was thinking 5:1 myself.

 

[SGKent]

https://structx.com/Material_Properties_011.html

 

[strutaeng]

First off, what are you pouring?

I've used the 4:1 ratio, but seems a bit too cement-rich. I want to say 5:1 to 6:1 worked well for me, but it's been a while. The more cement, the more shrinkage you will get. Probably doesn't matter for fence posts, but for slabs it might. Too little cement and hard to finish because of lack of cement paste.

My BIL's Dad is a master formwork guy and uses the 27 shovels to a 94 lb of portland cement. I've tried that before, but it is difficult to mix that much by yourself.

I'm talking sidewalks, pads and little projects like that. If you are thinking about testing, you are overthinking it or using the wrong mix (need to use ready-mix from truck.)

I had a small-ish project where the Contractor was going to infill a few small holes in elevated structural slab and could only use bagged pre-mixed concrete. The Owner only agreed if cylinders were taken, but even then was skeptical. Water was measured per instructions. It was a schedule driven project. On these projects it doesn't help because after 28 days they are wrapping up with finishes, etc. if cylinders don't meet specs.

28 days later, the numbers were in and it met specifications, but the deviation was all over the place.

 

[bannerd]

First off, what are you pouring?

I've used the 4:1 ratio, but seems a bit too cement-rich. I want to say 5:1 to 6:1 worked well for me, but it's been a while. The more cement, the more shrinkage you will get. Probably doesn't matter for fence posts, but for slabs it might. Too little cement and hard to finish because of lack of cement paste.

My BIL's Dad is a master formwork guy and uses the 27 shovels to a 94 lb of portland cement. I've tried that before, but it is difficult to mix that much by yourself.

I'm talking sidewalks, pads and little projects like that. If you are thinking about testing, you are overthinking it or using the wrong mix (need to use ready-mix from truck.)

I had a small-ish project where the Contractor was going to infill a few small holes in elevated structural slab and could only use bagged pre-mixed concrete. The Owner only agreed if cylinders were taken, but even then was skeptical. Water was measured per instructions. It was a schedule driven project. On these projects it doesn't help because after 28 days they are wrapping up with finishes, etc. if cylinders don't meet specs.

28 days later, the numbers were in and it met specifications, but the deviation was all over the place.

Doing footers for a small hunting camp in a remote area. About 8 yards of concrete so it’s going to be a fun day. Shouldn’t take too long. We’re dumping the cement mix at the start of the trail and going to use a tractor with a manure cart to get materials in. About 40 bags of Portland which we have on site. Nice place but off grid

 

[strutaeng]

Doing footers for a small hunting camp in a remote area. About 8 yards of concrete so it’s going to be a fun day. Shouldn’t take too long. We’re dumping the cement mix at the start of the trail and going to use a tractor with a manure cart to get materials in. About 40 bags of Portland which we have on site. Nice place but off grid

Yikes! 8 CUBIC YARDS?! That's a lot! How are you mixing it?

I just remembered we did a big pour years ago at my parents' place. Can't remember off the top of my head, but was about 6-10 yards.

We mixed it on a concrete driveway like in 3 batches. There was about 8 guys and took about 3 hours. Basically, you mix it like a giant cake mix, except you are casting stone, LOL.

 

[bannerd]

Yikes! 8 CUBIC YARDS?! That's a lot! How are you mixing it?

I just remembered we did a big pour years ago at my parents' place. Can't remember off the top of my head, but was about 6-10 yards.

We mixed it on a concrete driveway like in 3 batches. There was about 8 guys and took about 3 hours. Basically, you mix it like a giant cake mix, except you are casting stone, LOL.

We have a three point mixer for the tractor. Has a hydraulic pick up so we can back it in , pour the mix and just use the tractor. It holds half a yard so it shouldn't take to long. Just a lot of shoveling on our part. I don't mind shoveling at this point, after shoveling out the footers by hand