Calculating concrete components

[Stan in Oly, WA]

This is not a math problem. I'm good at math, and anyway, calculating concrete volumes doesn't really rise to the level of math---it's just arithmetic.

What I need to know is the volume of dry components it takes to achieve a volume of 1 cubic yard of concrete, and how to adjust that to come up with a 6 sack mix. A standard general purpose mix is 1:2:3 but that doesn't tell anything about the amount of cement which will be in 1 cu yd of concrete at that ratio because 1 cu ft of cement, 2 cu ft of sand, and 3 cu ft of gravel will not produce 6 cu ft of concrete.

If I can't find some good formulas to work with, I can't think of anything else to do but to mix test batches to try to find out the ratio of dry ingredients to mixed concrete. I don't want to do that because it means having to mix concrete I won't be able to use---it's a waste of materials, and it's hard work.

Thanks, Stan

 

[Anonymous-0]

1850lb. stone, 1350lb. sand, 6- 94lb. sacks cement, approx. 34 gals. H2O = 1cyd concrete. about 4000 lbs.

 

[atlarge54]

A 6 bag per yard will give a nice strong mix, really good for nice flat work. Footers and below grade stuff doesn't need to be as rich. Limestone aggregate will allow you to get out on it sooner to float and trowel than a gravel mix.

 

[Jerry (KS)]

You might want to try here:
http://www.csgnetwork.com/constructionconverters.html
Maintenance, Construction And Remodel Converters and Calculators

 

[PJH]

Stan, before I retired I could have given that information to you. I worked for the IL D.O.T., and was around concrete most every day. The numbers have faded away now after 8 years of non use.

In our area, you could call the Materials lab at the nearest state highway office and they would send you charts for every mix you could possibly want. I'm assuming the DOT folks in your area are as friendly as they are here. Bear in mind, those charts are for the basic mix, and after testing, some tweaking is usually necessary. Then again, you probably aren't going to pour any bridge abutments, so the charts alone would do you well.

Paul

 

[Anonymous-0]

Do you have a concrete plant in your area, they may help you.

 

[Gun guru]

I am not a concrete expert either, but I thought that if someone says they have a 5 bag mix. Which standard for flatwork, or 6 bag. Then it was considered 1 80 lb bag X 6 bags in 1 yard of concrete. The other stuff in the 1 yard of crete is Water/sand/gravel.

And 1 60 lb bag is a 1/2 of a cubic foot (I think)

4 bag mix is 2500 psi concrete,
5 bag mix is 3000 psi concrete
and so on.

I could be way off on this, but I tried.
If I had the phone number to the guy that poured my house and garage footings I could ask him, but........He probably out of business now.

 

[david - or]

Below is a URL that bears directly on this question; it goes further and adjusts cement volume for size of the aggregate. In the process it provides the useful rule of thumb that the total volume of concrete is 2/3 the sum of the volume of all the components that go into it.

Concrete strength is determined by the amount of cement and by the water/cement ratio. The water cement ratio should be kept below 0.5 by weight to reduce problems with weathering and shrinkage cracking, lower is better (consistent with acceptable workability)
Dry mix volumes from cement.org

 

[Billy NY]

Can't add much to this Stan, good info has already been provided. Way back in school we used ASTM formulas to create a mix design, using local raw materials and portland cement.

We would then make the material from that design, put into 4 test cylinders, then perform 7, 14, 21, 28 day breaks, to see if the compressive strength matched the mix design based on ASTM criteria.

Like I have mentioned in the past and has been mentioned below, water cement ratio is a critical factor in regards to compressive strength.

If you are intent on knowing what you design, meets the compressive strength you want, you could make a small amount of material, get some test cylinders, fill each test cylinder in 3rds, ( 1/3 of the way full, pack with a steel rod 25x, then fill 2/3, rod 25x, then the last 1/3 cylinder is now full rod 25x & screed off the top neatly, then take em to a lab to have em broke by the machine, simple ASTM formula to convert to PSI and you have your answer. You could have a cylinder broke at 7 days or 14 days, and calculate the projected strength or wait the 28 days, test lab can advise you on that.

If in no hurry and to use the least materials you could make 1 cylinder, or 1 of each various mix design, have em broke and take it from there. Remember, once you establish the design, you must use the exact same raw materials for that mix or it may change the compressive strength, probably not enough to void the design, but it's industry standard. Make sure to mark,label, date each cylinder, test labs use thin metal tags.

I'm thinking if you use the typical ratios for mixing by hand, beef up the portland cement a bit and don't add too much water, the design will more than meet your requirements, just keep an eye on the slump, like was said, the more "plastic" the mix is, easier it is to work, but go to far ( water ) and you know what happens, find a happy medium and it will be good.

 

[Stan in Oly, WA]

Thanks everyone. Good, useful, pertinent information and advice. I think it shows a high degree of seriousness when the answers make it clear that respondents took the time to read and answer the question that was actually asked. That's frequently not the case. I'd say it was one of my pet peeves except that I'm generally as amused as irritated by it.

I'm going to be adding powdered dye to the mix, which presents another complication. The dye is in 5 lb bags and I don't have a scale accurate enough to measure out the 1/2 lb per batch that is called for. I could do it by volume (and probably will have to) but I hate to have to handle it any more than is absolutely necessary---to touch it is to be stained by it.

Thanks again, Stan