- Cement:
Before the introduction of ordinary Portland cement, lime was used as a cementing material. Most of the cement concrete work in building construction is done with ordinary Portland cement at present. But other special varieties of cement such as rapid hardening cement and high alumina cement are used under certain circumstances. The cement should comply with all the standard requirements.
- Aggregates:
The aggregates are the inert or chemically inactive materials which form the bulk of cement concrete. These aggregates are bound together by means of cement. The aggregates are classified into two categories: fine and coarse.
The material which is passing through 4-7625 mm size B.S. test sieve is termed as a fine aggregate. Usually, natural river sand is used as affine aggregate. But at places, where natural sand is not available economically, finely crushed stone may be used as a fine aggregate.
The material which is retained on 4-7625 mm size B.S. test sieve is termed as a coarse aggregate. Broken stone is generally used as a coarse aggregate. The nature of work decides the maximum size of the coarse aggregate. For thin slabs and walls, the maximum size of coarse aggregate should be limited to one-third the thickness of the concrete section.
The aggregates to be used for cement work should be hard, durable and clean. The aggregates should be completely free from lumps of clay, organic and vegetable matter, fine dust, etc. The presence of all such debris prevents adhesion of aggregates and hence, reduces the strength of concrete.
- Steel:
The steel reinforcement is generally in the form of round bars of mild steel. The diameters of bars vary from 5 mm to 40 mm. Sometimes, square bars or twisted bars or ribbed-torsteel are used as steel reinforcement. For road slabs and such other constructions, reinforcement may also consists of sheets of rolled steel of suitable thickness. Hyrib, which is a steel lath, may be also used as steel reinforcement.
- Water:
This is the least expensive but most important ingredient of concrete. Water, which is used for making concrete, should be clean and free from harmful impurities such as oil, alkali, acid, etc. In general, water which is fit for drinking should be used for making concrete.
- Admixtures:
It may be noted that sometimes ingredients other than above are added in concrete to give it certain improved qualities. These ingredients or substances are known as admixtures. The addition of an admixture may improve the concrete with respect to its strength, hardness, workability, water-resisting power, etc.
Following are the commonly used admixtures:
Alum, aluminium sulphate, barium oxide, bitumen, calcium chloride, coal ash, common salt, iron oxide, lime, mineral oils, organic oils, potassium chloride, silicate of soda. Tar products, volcanic ashes, zinc chromate, etc.
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