Materials Used in Reinforcement Cement Concrete (R.C.C.) Work in Building Construction


Building-Building materials



Following Building materials are required for making the R.C.C. work in Building construction site:

(1) Cement

(2) Aggregates

(3) Steel

(4) Water.

 

(1) 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.

(2) Aggregates: These are the inert or chemically inactive materials that 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 Building 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 Building material used in Building construction 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 aggregates and hence reduces the strength of concrete.

(3) Steel: The steel reinforcement is generally in the form of round bars of steel. The diameters of bars vary from 5 mm to 40 mm. Sometimes the square bars or twisted bars or ribbed-tor steel are used as steel reinforcement n the building construction. For road slabs and such other constructions, the reinforcement may also consist of sheets of rolled of suitable thickness. The rib which is a steel lath may also be used as the 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 Building ingredients other than above are added in concrete to give it certain improved qualities or for changing different physical properties in its fresh 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 in the building Construction Industry:

Alum, aluminum sulfate, 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. For instance, when calcium chloride is added as an admixture, it absorbs water from the concrete and the water-cement ratio falls down and can even be brought down up to 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 detail of any admixture before its recommendation 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) the requirement of slump and retention,

(v) temperature 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 into the following five categories:

(i) accelerators,

(ii) air-entraining admixtures,

(iii) high range of water reducers or superplasticizers,

(iv) the normal range of water reducers or plasticizers, and

(v) retarders.

It may be noted that some admixtures may have the combined effect of the above individual activities. The popularity of various types of admixtures in concrete is increasing rapidly because of the following advantages available from their use:

(i) adjusting the final setting times of concrete,

(ii) higher early and ultimate strengths of the concrete

(iii) higher slump and self-leveling concrete,

(iv) increasing durability of concrete,

(v) lesser water-cement ratios used in the concrete

(vi) reducing quantity of cement,

(vii) reduction in the permeability of concrete,

(viii) time savings in terms of repair and maintenance, etc.

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