Properties of Concrete : (Part-1) _ STRENGTH PARAMETER #1

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PROPERTIES OF CONCRETE

1. Properties in Strength Parameter:  #1

            
                    The following are the important properties of concrete in STRENGTH parameters and these should be noted by every civil designer.

    A. COMPRESSIVE STRENGTH / GRADE OF CONCRETE: It is the ability (or) strength of an individual structural member to carry Designed loads under compressive force. 

    • In the sense, the member should withstand to resist the cracks on the surface of a slab, even to resist deflection in the beam and of course to resist Buckling of the column also.
    • Shrinkage of a member happens only under compression. This is designated by fck.
  • The formula of Compressive Strength: It is the load applied to the face of the surface at the point of failure to the Cross-sectional area.
Compressive Strength =  Load (kN) / Cross sectioanl area (mm2)_ MPa (SI Units)
  • Compressive Strength of Concrete according to Age (Days): The following table shows the compressive strength gained by concrete after mentioned days. From the Table, 16 % of strength is gained in 1 day, 40 % of strength is gained in 3 days in the same way, 99 % of strength is gained in 28 days, like that.
          Compressive Strength of Different Grades of Concrete at 7 and 28 Days:


         The following table shows the Minimum at 7 days and Maximum(Specified) at 28 days compressive strength gained by concrete.


                From the above Table, for  M15 - 10 N/mm2 at 7 days, 15 at 28 days, M20 - 13.5 N/mm2 at 7 days, 20 at 28 days. In the same way, M40 - 27 N/mm2 at 7 days, 40 at 28 days.

           M20 - Stands for
                                          
                    M refers to Mix
                    20 refers to Characteristic Strength of 150 mm cubes at 28  days in N/mm2.            
  
           B. TENSILE STRENGTH: It is the ability (or) strength of a member to fight a Pulling Force which is a Tensile Force.

    • The value of Tensile Strength is less as compared to the Compressive Strength and even this value is not considered in any design of any structural element.
    • But, it is a very important property which affects the width of cracks in the structure. 
    • Elongation of a member happens only under compression. This is designated by fcr. 
  • The formula of Tensile Strength: The Tensile strength value can find out using the formula according to IS 456-2000 from Compressive strength is as follows.
Tensile Strength (fcr) =  0.7 x Square root of Compressive Strength (fck) _ MPa (SI Units)



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