Follwing materials are required for making the RCC work:
(2) Aggregates (4) Water
(1) Cement
Before the introduction of ordinary portland cement, the lime was used as 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 is done with ordinary Portland cement and high alumina cement are used under certain circumstances. The cement should comply with all the standard requirement.
(2) Aggregates
These are the inert or chemically inactive material 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 BIS test sieve no.480 is termed as a fine aggregate usually, the natural river sand is used as a fine aggregate. But at places,where natural sand is not available economically, the finely crushed stone may be used as a fine aggregate.
The material which is retained on BIS test sieve no. 480 is termed as a coarse aggregate.The 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 the cement concrete 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.
(3) 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 the square bars or twisted or ribbed-tor steel are used as steel reinforcement. For road slabs and such other constructions, the reinforcement may also consist of sheets of rolled steel of suitable thickness. The hyrib which is a steel lath may also be used as the steel reinforcement.
(4) Water
This is the least expensive but most important ingredient of concrete.The water, which is used for making concrete, should be clean and free from harmful impurities such as oil, alkali, acid, etc. In general the water which is fit for drinking should be used for making concrete. It may be noted that sometimes the ingredients other than above are added in concrete to give and hardened stages. These ingredients or substances are known as the 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 calcium chloride, coal ash, common salt, iron oxide, mineral oils, potassium chloride, silicate of soda, tar products, volcanic ashes ,zinc chromate, etc. For instance, when calcium chloride (CaCl2) is added as admixture, it absorbs water from the concrete and water-cement ratio falls down and can even be brought down upto the limit of 0.25. Thus it gives quick setting concrete. However the use of calcium chloride is not suitable for concrete with reinforcing bars.
It is necessary to know the complete details of any admixture before its recommendations together with the following factors:
(i) grading curves of aggregates and their respective properties,
(ii) method of construction,
(iii) quantity of cement per M3 of concrete,
(iv) requirement of slump and retention,
(v) temperature and variation,
(vi) type and make of cement, and
(vii) water-cement ratio.
Depending upon their respective activities in the concrete mix, the admixtures can be classified in the following five categories:
(i) accelerators,
(ii) air entraining admixutres,
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