gieve the perfect ratio separately for walls, concretes..
I would use gravel and sand. For a 1 cubic yard concrete mix, use the following: 600 lbs cement 1250 lbs gravel 1650 lbs sand 45 gallons water (about 375 lbs) If you have to use all sand, then just use a 5:1 ratio and use a water to cement ratio of about .6 (6 lbs water to 10 lbs cement) This will put you at about 3000 psi. Don't add too much water as your strength will drop a bunch. Easier way: Just call the local concrete batch plant and ask for 3000 psi concrete. I would also call a local engineering firm to send someone out to take some concrete samples to make sure you get what you ordered. It'll cost a couple hundred bucks for the concrete tests, but it's worth it if you are building a house which will cost tens if not hundreds of thousands of dollars.
