Thursday, November 21, 2013


 Following materials are required for making the R.C.C. work :
1)      Cement
2)      Aggregates
3)       Steel
4)       Water.
1)      Cement : Before the introduction of ordinary Portland cement, the lime was used as a cementing materials. 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 a present. But other special varieties of cement  Such as rapid hardening cement and high alumina cement are used under certain circumstance. The cement should comply with all the standard requirements.
2)       Aggregates : These 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  together by means of cement The aggregates are classified into two categories : Fine and coarse :
      The material which is passing though BIS test sieve no. 480 is teemed 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 ad 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 bass such other constructions, the reinforcement may also consist of sheets of rolled steel of suitable thickness. The hyrax which is a steel lath may also be sued  used as  the steel reinforcement.
4)      Water : This is the least expensive but most important ingredient of concrete.  Impunities such as oils, alkali, acid etching  general the water which s fit for drinking should be sued of remaking, concrete.
It may be noted that sometimes the ingredients other than  above are added in concrete to give it certain improved qualities or for changing different physical properties admixture. 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, coat ash, common  salt, iron oxide, lime, mineral oils, organic oils, potassium chloride, silicate  cement ration falls done 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  concrete with reinforcing bars.

 It is necessary to know the complete detail of any admixture before the recommendation together with the following  factors :
I.Grading curves of aggregates and their respective properties,
II.Method of construction, quantity of cement  per m3 of concrete
III.Requirement f slump ad retention,
IV.Temperature variation,
V.Type and make of cement, and
VI.Water-cement ratio,
    Depending pun their respective activities in  the concrete mix, the admixtures and be classified in the following five categories.
1         Accelerators,
2          Air  entraining admixtures,
3          High range of water reduces or super plasticizers,
4          Normal range of water reducers of plasticizers, and 
5          Retarders.
It may be noted that some admixture 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.
1, adjusting the final setting times of concrete,
2 Higher early and ultimate strengths,  
3, higher slump and self-levelling concrete,
4 ,increasing durability of concrete,
5, lesser water-cement ratios,
6 ,reduction quantity of cement,
7 Reducing quantity of cement,
8 Reduction in the  permeability of concrete,
9 Lesser water-cement ratios,
10 Reducing quantity of cement,
11 Reduction in the permeability of concrete ,
12 Time savings in terms of repair and  maintenance, etc

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