How to design M25 grade concrete

Mix grade is the method to find out the proportion of cement sand and aggregate for getting the desired strength of concrete. Actually Nominal mix is done on the basis of volumetric batching which is more costly for higher grades.


                      CONCRETE MIX DESIGN M-25 - RCC

A-1):-  Design stipulation :-

(a). Grade of concrete  =   M25

(b).Characteristic compressive strength of concrete at 28 days   =   25 N/mm2

(c). Maximum size of Aggregate  =  20mm anguler

(d). Degree of Workability and Slum  =   75-125mm  ( MORT&H table 1700-4 )

(e). Type of Exposer =  Normal

(f). Degree of Quality Control  =   Good

(g). Concreting Method =   Pump able concrete.

(h). Target Mean strength of concrete =  36 N/mm2


A-2):-  Tested data for materials :-

(1). Type of cement and grade :- Ultratech OPC 43 Grade

(2). Specific Gravity of cement =   3.15

(3). Specific Gravity of 10mm Aggregate =   2.524

(4). Specific Gravity of 20mm aggregate =   2.539

(5). Specific gravity of Fine aggregate(sand)  =    2.512

(6). Water Absorption of  20mm  =    1.24%

(7). Water Absorption of 10mm  =   1.30%

(8). water Absorption of fine aggregate(sand).  =    1.67%

(9). Specific gravity of Admixture  =  1.062  ---( Fosroc Auramix 300 )



A-3) :-  Target Mean Strength  :- 

                       Ftarget = Fck + 1.65xS        -----(from IS 10262-2009 Table -1  Clauses 3.2.1.2)
                              
                                   = 25 + 1..65x4 =  31.6 N/mm2
Target mean strength as per table 1700-5 of  MORT&H

  Hence, Target mean strength is Adopted.


A-4) :- Slection of water cement Ratio :- 

Maximum allowed w/c as per MORT&H is =  0.50
Based on trail Adopted water water cement ratio as =    0.45

0.45 <  0.50  hence,  OK

A-5). :- Selection of water content 

 From IS 10262-2009 Table-2
Maximum water content  for 20mm aggregate  =    186 kg  ( for 25-50mm slum range )

Estimated water content for 50-75mm slum we add the 3% extra   ---( from IS 10262-2009, clause 4.2 )

so, corrected Water content =  186 + (3/100)x186  =   191.58 ltrs

As super plasticizer is used , water content can be reduced up to 20% and Above.

Based on trial with super plasticizer , water content reduction of 18.27% has been achieved.

Hence, the arrived water content = 191.58 - 35.00  =  156.58 ltrs
                                                                      says   =   157 ltrs


A-6).  :- Selection of Cement content :-

             Water cement ratio                                                                                           =    0.45

             Hence, Cement content                                                              =  157/0.45    =    349 kg/cum
          
             Minimum cement content ( from MORT&H 1700-3)                 = 330 Kg

                  Hence, Cement content is O.K.


A-7). Proportion of volume of coarse aggregate and fine aggregate. :-


    Therefore,  volume of coarse aggregate  =          0.60 x 100     =      60.00 %

                    volume of Fine aggregate       =          0.40 x 100     =      40.00 %



A-8). Mix calculation :-


          (a). Volume of Concrete :-      

          (b). Volume of Cement   =  mass of cement/(specific gravity of cement x1000)

                                                = 349/3.15 x 1000

                                                = 0.1108 cum

           (c). Volume of Water   =  mass of water/(specific gravity of water x1000)

                                                 = 157/(1 x 1000)

                                                 = 0.157 cum

           (d). Volume of admixture   =  mass of admixture/(specific gravity of admixture x1000)

                                                   = 3.49/(1.062 x 1000)

                                                   = 0.0033 cum

           (e). Volume of All aggregate   =  a- (b+c+d)

                                                         = 1- (0.1108+0.157+0.0033)  

                                                         =  0.729 cum

           (f). Mass of 20mm coarse aggregate  = 0.729 x 0.60 x 0.60 x specific gravity of 20mm x 1000

                                                         = 0.729 x 0.60 x 0.60 x 2.539 x 1000

                                                         = 666.30 Kg

          (g). Mass of 10mm coarse aggregate  = 0.729 x 0.60 x 0.40 x specific gravity of 10mm x 1000

                                                         = 0.729 x 0.60 x 0.40 x 2.524 x 1000

                                                         = 441.60 Kg

          (h). Mass of Fine aggregate(sand)  = 0.729 x 0.40 x specific gravity of sand x 1000

                                                         = 0.729 x 0.40 x 2.512 x 1000

                                                         = 732.50 Kg

A-9). Mix proportion :-

(a). Cement                                                           =   349 Kgs

(b). Coarse aggregate 20mm                                =  666 Kgs 

(c). Coarse aggregate 10mm                                =  442 Kgs

 (d). Fine aggregate(sand)                                   =  733 Kgs

(e). Water                                                              =  157 ltrs

(f). Admixture ( 1% by weight of cement )          =   3.49 Kgs

A-10). Trial Observations :- 

The slum shall be measured and the water content and dosage of admixture shall be adjusted for achieving the required slum based on trail. If required the mix proportion shall be reworked for the actual water content  and checked for durability requirements. 

        Time                12.15PM                12.45PM             1.15PM                    Remarks

        Duration             1/2 hours                1 hour                   11/2                                  Cohesive mix

       slum (mm)           110mm                    90mm                    65mm