The other thing the OP might want to know is cure time for optimum strength. Cover the pour with wet sacking, and allow to stay undisturbed for three days. Keep wet. Then remove the sacking, and allow to dry.
Carbon dioxide in the air reacts with calcium hydroxide in the wet cement. It's also known as slaked lime. That's where the bond strength of the cured concrete comes from.
The normal proportions for concrete are 4 parts of stone, 2 parts of sand, and one of cement. Good quality water should be used to avoid rebar corrosion, which will occur if the chloride content of the water is too high.
Corrosion of rebar results in spalling. At best, spalling is ugly. At worst, it is a risk to structural integrity.