RE : concrete mixes

I just wanted to update people on the mixing project.I moved over here from tool talk because now that it is a working mixer, it is going to be tractor related. Through more internet searching, I found a break-down by weight to mix a one yard, 4000# mix. I adjusted the weights to 5-gal buckets, ended up with 50# cement, 120# sand, and 130# 3/4" crushed stone.Trial mix made a 2'x3'x 3.5" pad.I may adjust a little more to get a 4500# mix and add color.We are going to do my cousins sidewalks first though. I'll try to post photos as we go? Thanks Jeff

Dad and I always used 3 shovels gravel, 2 shovels sand and 1 shovel cement. He and mom used that mix when they poured the concrete for the holding area and through the barn and on side and ends- They did it at night, because dad worked as a carpenter during the day, and of course, had to milk the cows, too. That would have been about 65 years ago, and the concrete is still in good shape. I was too young to help then, but worked with him later. I'd add the water to the mixer, and I don't think he ever failed to say "don't drown the miller."

It has been said on here many times before you can get close on home made concrete, the way you are doing it the moisture content of the sand is the big variable. A five gallon bucket of dry sand can weigh a lot less that a 5 gallon bucket of wet sand. Can change the strength of your concrete real quick.

For that you need a cast iron fry pan,scale and a hot plate,done it many times.

If you want to really prove the strength of the mix, get 4 concrete test cylinders and fill them properly.

Filling them is as follows: fill 1/3, using a steel rod, tamp 25 times. Repeat for the next 2/3rds. Screed off the top and take to a test lab. Typically 4 are taken for breaks at, 7 day, 14 day, 21 day and 28 days. (Break = test ) It is a way to see in advance, if the concrete is rising to the mix designs compressive strength, as you need to wait 28 days for it to fully cure, after that the strength may still rise, but very very slowly, it's almost irrelevant.

Moisture content, specific gravity etc. etc. all play a role in this, the mix design procedure is reference-able in ASTM. ASTM C39 is for: "Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens"

Reason I mention any of this is because there is a lot that goes into developing and proving a concrete mix design to a certain compressive strength. While the information you may have researched may be a guideline, you have no way of knowing without testing. If someone here or elsewhere got the wrong idea and used it for a critical structural component, an unproven mix design, it could easily fail catastrophically.

The fun part of this material is learning it. I never thought the ASTM or ACI reference material was too difficult to understand and practice, heck we even learned how to calibrate a concrete plant. We designed our mixes, we did all the breaks, made beams and tested those as well from mixes we designed. Prior to creating a mix design, the basis was testing all the aggregate and determining how much of each sieve size was used in the mix.

Now, there is also another way to test in place concrete, it's called a Windsor Probe. Look it up on the web, might be easier, but we typically take test cylinders of the mix before it's placed.

Hi
Would a two port hydraulic diverter valve be able to operate a tipping trailer
Thanks

As a younger man, I remembered the 3-2-1 ratio also. Billy, I would love to take test cylinders, not sure where I could have them tested? The first job is just sidewalks, not too worried about the # mix.More worried about keeping a consistent mix? We weighed the buckets with the wife's scale.They say a happy wife leads to a happy life, last night was not a happy life.Yes , our sand was wet, I'll have to get a weight when dry. I'm trying to attach a photo, says disabled?

the windsor probe usually gave false readings on the higher side--a core sample from the hardened concrete was much more accurate---but taking test cylinders was by far the most simple

Twelve years ago I was listening to a quality control employee at a concrete batch plant. He said that he knew that the government job only tested every fifth truckload of concrete. So they shorted the cement in the concrete mix for four loads then made the correct strength for the fifth load that was goin to be tested. How many time have you and I been shorted on the strength of the concrete?

concrete company were fools if they really did do that,on state jobs I've been on the inspector might test any load and will test any load that they don't like the looks of.plus there is a state inspector in the batch house while any big pour is going on and they can read the computer print out of what went into the mix.
I'll say at least 90% of non inspected concrete I have seen poured was out of spec in some way,most common was too much water added by the finishers which kills the strength.

Finishers like that water, easy to move that soup and like you say sure cuts the strength of the finished product.

Exactly, I'd prefer test cylinders.

Yea I used to joke with the finishers on jobs told them on every concrete finisher's tombstone it should say "Five more gallons".

I only mix concrete my hand for very small jobs.
I put sand/gravel mix form gravel pit in front end of
10k dump trailer. Then put cement bags in. Last goes
the cement mixer. That way all the mess stays in the
dump trailer. Back up to where I want the concrete,
mix and dump. The strength of your mix is also dependent on water. Too much water and that will weaken mix.
My arms are hurting just talking about mixing
concrete.
geo.

Who is going to shovel the aggregate way up in the air like that?

I always put the stones in first, then the water. If I put the water in first some of it would slop out. Then 1/2 bag of cement, then the sand. I poured a big patio, a 24'x 24' parking area and a sidewalk over 80' long plus another walk about 60' long. Used 2x4 forms for walkways and 2x6 forms for patio and parking area. After each project I swore I would never mix concrete by hand again. But then, I'd start all over again and lay down more concrete. These projects were all with a 3:2:1 mix. No re-rod. Finally, when I was 74 years old, I put up a 60'x 88' Morton shed. I did the prep work leveling, packing, etc. and then called a concrete contractor. Two days of concrete laying (13 mixer loads) five man crew, I had a concrete floor 5 1/2" thick and then finished and jointed and sealed. Six bag mix. W/Re-rod. Not a crack anywhere including my 50 year old parking area, patio, walkways or the 10 year old shed floor. I'm happy. (;>))