My question concerns the ratio for portland cement to sand/rock for concrete. Do I go by weight or volume? If so, what are the criteria? I have heard 3/2/1 mix of rock/sand/cement respectively. I could only get a rock/sand mixture, so the 3/2/1 thing is out of the question. Any ideas?
The PCA figures mixes by weight. Aggregate will vary in water content. After a rain it will most likely have excess moisture. To get consistent concrete mixes they must have the same ratio of water to cement and a gradation of aggregate. Usually the largest aggregate size is 1/3 of the narrowest width of the form where the pour will occur. However it must also go between the rebar.
Edited 2/22/2007 11:13 pm by gb93433
My rock/sand mixture looks good. The supplier said the usual weight of 1 cubic yard was 2000 pounds. Any idea how much portland would to mix with that?
cement 338 lbs 3000 psi
fly ash 85 lbs
sand 1434 lbs
stone 57 1650 lbs
water 250 lbs
air 4.0% 16.92 oz3000 pea gravelcement 550 lbs
fly ash 61 lbs
sand 1740 lbs
#8 pea gravel 1200 lbs
water reducer 42 oz
water 324 lbs
1 cubic yard was 2000 pounds27 cubic feet in a cubic yardcubic foot of concrete weigh from 140-150 lbs
140 x 27 = 3780 lbs
There is some good information at http://en.wikipedia.org/wiki/Water-cement_ratiohttp://www.cement.org/basics/concretebasics_concretebasics.asphttp://cee.engr.ucdavis.edu/faculty/kunnath/eci135/eci135-ho1.pdf.http://training.ce.washington.edu/WSDOT/Modules/05_mix_design/05-8_body.htm#water-cement_ratioTypically the optimum water to cement ratio is around 0.4. Basically that means for every 100 pounds of cement in the mix you will use 40 pounds of water. A higher water to cement ratio increases volume and workability but decreases compressive strength.The specific gravity of cement is 3.15. Therefore it would weigh 3.15 times the weight of water for the same volume. A cubic foot of water weight 62.4 pounds and a cubic foot of cement would weigh 196.56 pounds.The volume of one sack of cement equals: 94 ÷ (3.15 x 62.4) = 0.478 cubic feetNormal concrete weighs around 150 pounds per cubic foot. Concrete can be made to have compressive strengths of 2000 psi to 30,000 psi. The curing process and additives have a lot to do with that. The water to cement ratio is the biggest factor in determining concrete compressive strength.
OK guys,but let's suppose this poor guy just wants to mix some for a sidewalk repair in his yard. he doesn't have weighing equipment nor a calculator to figur how many gallons of water to make up a pound or vice verse. So how many spade fulls of sand/aggregate mix should he use with one of portland cement? I've heard anywhere from 3:1 to 9:1. His starting point sounds like 5:1. When I've done it, I've used 6:1Oh, we're off and running down that hill now!
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My projects have always used 5 shovels of 60/40 (60% agg/ 40% sand) to one of cement. The shovel of cement does seem a bit smaller than the others...
I took them mix and reduce to a cubic foot and it comes out Five gallon bucket of rock
3/4 bucket of sand
5/8 bucket of cement
1/4 bucket of water
For small amounts, speaking from practice experience measure by volume. Use a shovel or a bucket and a shovel. If you need more than a small amount, order a truck.