Secondly, the water demand of concrete mix and the ratio of filling the empty space between the gravel grains by sand and cement paste is determined considering desired mobility level of the mixture. The higher the required mobility, the greater the volumes of sand, water and cement.
Example calculation Estimate the quantity of cement, sand and stone aggregate required for 1 cubic meter of 1:2:4 concrete mix. Ans. Materials required are 7 nos. of 50 kg bag of cement, 0.42 m 3 of sand and 0.83 m 3 of stone aggregate.
Below is an example of a sand to cement mix ratio recommendation from a cement manufacturer. Concrete - 1 part cement, 2 parts concreting sand and 3 parts 20 millimeter aggregate. Mortar - 1 part cement, 4 to 5 parts building sand. Alternatively, one can also use 1 part cement, 1 part lime and 4 to 5 parts building sand.
To determine the proportions you have to perform mix design, for this you have to find out the sp.gr. of cement, CA, FA, and water cement ratio, type of exposure, Maximum size of aggregate etc. Once the W/C ratio is determined use 186 kg water (for 20mm CA) to find out the qty. of cement per cum of concrete.
A concrete mixture ratio of 1 part cement, 3 parts sand, and 3 parts aggregate will produce a concrete mix of approximately 3000 psi. Mixing water with the cement, sand, and stone will form a paste that will bind the materials together until the mix hardens.
The closer you bring the ratio to an even one-to-one of sand to cement, the stronger the rating becomes. This principles works in the opposite direction as well. If you want to get a little more technical, some concrete experts recommend going for 26 percent sand, 41 percent gravel, 11 percent cement and 16 percent water.