The process of selection of relative proportions of cement, sand, coarse aggregate and water to obtain a concrete of desired quality is known as proportioning the concrete. There are various methods for determining the volumetric proportions of various components, like the arbitrary method, fineness modulus method, minimum voids method and maximum density method.
The recommended mixes of concrete for various types of construction are given in the following table. The maximum sizes of aggregates are also mentioned in the table. The proportions are by volume.
| Proportion of concrete mix | Maximum size of aggregate | Nature of work |
|---|---|---|
| 1:1:2 | 12–20 mm | Heavily loaded RCC columns and RCC arches of long span |
| 1:2:2 | 12–20 mm | Small precast members of concrete, such as poles for fencing telegraphs, long piles, watertight constructions and heavily stressed members of the structures. |
| 1:1½ :3 | 20 mm | Water-retaining structures, piles, precast products, etc. |
| 1:2:3 | 20 mm | Water tanks, concrete deposited under water, bridge construction and sewers |
| 1:2½:3½ | 25 mm | Footpaths and roadworks |
| 1:2:4 | 40 mm | For all general RCC works in building, such as stair, beam, column, weather shed, slab and lintel, machine foundation subjected to vibration and RCC piles. |
| 1:3:6 | 50 mm | Mass concrete works in culverts, retaining walls, etc. |
| 1:4:8 or 1:5:10 or 1:6:12 | 60 mm | Mass concrete work for heavy walls, foundation, footings, etc. |
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