IS 456:2000 (Plain and Reinforced concrete code of practice)

Some Facts about IS 456:2000 ( Useful for Gate and ESE Exam)

• The pH value of water for making concrete shall not be less than 6
• Permissible limits of solids

                      Solids                                                  Permissible limits (mg/l)
                      Organic                                                       200

                      Inorganic                                                    3000

                     Sulphate (as SO3)                                        400

                      Chlorides (as Cl)                                         2000 for concrete not containing embedded                                                                                               steel and 500 for reinforced concrete work

                     Suspended matter                                          2000       

• Size of Aggregate: The nominal maximum size of coarse aggregate should be as large as possible within the limits specified but in no case greater than one-fourth of the minimum thickness of the member, provided that the concrete can be placed without difficulty so as to surround all reinforcement thoroughly and fill the comers of the form, For most work, 20 mm aggregate is suitable. Where there is no restriction to the flow of concrete into sections, 40 mm or larger size may be permitted.  
• Grade of concrete 

        Ordinary Concrete :        M10, M15, M20

        Standard Concrete:          M25 to M55

        High strength Concrete: M60 to M80

• Flexural strength of concrete (fcr)

                            Flexural strength (fcr)  = 0.7 √f_ck

       

where fck is the characteristic cube compressive strength of concrete in N/mm2 

• The short term modulus of elasticity of concrete can be computed as

                                     E_cs = 5000 √f_ck           

                      Ec is the short tern static modulus of elasticity in N/mm2 

• Actual measured values may differ by ± 20 percent from the values obtained from the above expression.
• The total shrinkage of concrete depends upon the constituents of concrete, size of the member and environmental conditions. For a given humidity and temperature, the total shrinkage of concrete is most influenced by the total amount of water present in the concrete at the time of mixing and, to a lesser extent, by the cement content.

• In the absence of test data, the approximate value of the total shrinkage strain for design may be taken as 0.0003 
• Creep of concrete depends, in addition to the factors listed above, on the stress in the concrete, age at loading and the duration of leading. 

• In the absence of experimental data the creep coefficient (Ɵ) can be computed as

                             Age at Loading                          Creep Coefficient

                                  7 days                                              2.2

                                  28 days                                            1.6

                                   1 year                                             1.1

• The long term young's modulus of elasticity (Ecl) can be computed as 

                                          Ecl  =     Ecs /1+  Ɵ       =  5000 √f_ck     /1+  Ɵ

                 Happy Learning