portland cement mix

[mwkellner]

I have only used ready mix in the past, but was given a few bags of portland cement and need some quick help from your knowledge and experience. How much mortar sand and gravel would I need to get to mix 1 92lb. sack of cement? I was guessing .5 yards of sand, but I dont know. Another question -- Does the gravel add strength, of just filler. Thank you all so much for your help.

 

[Bus Driver]

Your 92 pound bag is one cubic foot of Portland cement powder. Makes it easy to get correct proportions with the other materials.
Mix

 

[Billy NY]

Yes, you want the proportions to be correct and uniform for every batch.

Portland is the cementitious material that bonds the aggregate together, more portland will increase the compressive strength of the material, more water will reduce it, so it's very important to use measured amounts based on a good design mix, or ratio like what you were inquiring about. Make sure to keep that water/cement (portland) ratio correct, and use a sound ratio for portland to fine aggregate, coarse aggregate, I forget what the common rule of thumb is on ratios by the shovel full, but hand mixing ratios have been around a long time and usually work well, just remember to keep that water/cement ratio correct, it's the easiest way to screw up this material, more portland is stronger, but you can overdo that too.

 

[Rst277]

The standard ratio is

1 part cement
2 parts sand
3 parts gravel

There is 27 cubic feet per yard so you can divide from there. Keeping the concrete cool/moist while it dries, a longer drying time, contributes to its final strength. So cover it with a tarp or spray with water if you can. Cool wet weather is the best time to pour concrete.

 

[Stan in Oly, WA]

Hi mwkellner,

Actually 94 lbs unless cement is going the way of plywood thickness (i.e. 23/32" instead of 3/4").

Because I've been working in a place where a truck can't get close, and I can't afford to get a pump out time after time, I mix a lot of concrete by hand, either in a cement mixer or, frequently, in a wheelbarrow. Here are some tricks I've developed to make it easier to get a consistent mix.

1. I welded sides on a shovel so that it will hold a reasonable amount of gravel.

2. A 5 gal plastic bucket holds .71 cu ft when filled to the rim.

3. Measure the volume of cement you want to use and put it into a container before you add it to your mix. Then use the container to always get the same amount. This allows you to keep the amount constant. Same with the water, except that the water requirement changes as you get deeper into your sand pile where the sand has more water in it.

4. Keep your sand pile covered with a tarp to prevent cats from adding organic matter to your mix. They ALWAYS do. Gravel is okay uncovered.

5. Calculating concrete volumes is not straightforward. Sand fills the space between the rocks of the gravel, cement fills the space between the grains of sand. 3 cu ft of gravel, 2 cu ft of sand, and 1 cu ft of cement will make between 4 and 5 cu ft of concrete. If it's critical, you have to measure the concrete which results from measured components. If it's not so critical, best efforts are good enough.

6. There's not much reason not to use a rich mix (6 or more 94 lb sacks of cement per yard of concrete.) Cement is relatively cheap compared to the value of what you make with it.

Best of luck with it, Stan

 

[pat sublett]

1,2,3 is right easy to remember, the larger the diameter of the ingredient the higher the proportion. 1-cement 2-sand 3-gravel.