Proportioning of Materials of Concrete:

Concrete must be satisfactory in two states namely, plastic and harden. The choice of proportion is governed by both these conditions. In general cement, fine aggregate, coarse aggregate and water should be so proportioned that the resulting concrete has the following properties:

(a) Although fresh it is workable enough for economical and uniform placement, but not excessively fluid.

(b) When hardened, it has sufficient strength and ability for its purpose.

(c) Includes minimum cost for material and labour.

Once the quality of cement and aggregate is selected next is to decide the proportion of cement: fine aggregate: coarse aggregate. A proportioning of cement, sand and coarse aggregate is also termed as mix design; while proportioning these and water cement ratio, it must be kept in mind that the fresh concrete be workable enough for uniform placement and once hardened has sufficient strength and durability.

Factors governing a choice of mix proportion are:

(a)        Strength of concrete.

(b)       Quality control.

(c)        Durability and workability.

(d)       Water cement ratio.

(e)        Aggregate cement ratio.

(f)        Grading and type of aggregate.

(g)       Maximum or minimum size of aggregate.

There are several methods of mix design but there are also methods that give rough proportioning used in day-to-day works.