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

       

                                      



















































































                      

What is Pointing and its types.

POINTING :-

Brick wall  joints are raked for 20mm depth and it is cleaned and kept wet for 2 days.
Mix is generally made in requared proportion like 1:2 , 1:3.  after that we applied the mortar on raked brick wall. Extra mortar comes from joints during pointing is removed smoothly that it shows good appearance. And cured these for 7 days.


Types of Pointings :-


1). Flush Pointing :- This is the simplest pointing in this we press the mortar in the raked joints and level the mortar in the level of bricks edges.

2). Ruled Pointing :- In this pointing mortar is pressed in the clean and dry joint. A tool used to make a groove is made up of steel. Groove size should be 5-6mm deep along a center line joint.
Its mean joint shoud be V shaped. and same processes is applied in the vertical joint.

3). Trunk or Weather pointing :-  The mortar is pressed in the raked joint with with a tool so that the joint is sloping from top to bottom. and the vertical joints are filled like as Ruled Pointing.

4). Raised or Trucked Pointing :- In this pointing mortar pressed in the raked joint are in excess amount to make a Bands. Generally Band are 6mm raised and 10mm wide.

Removal time of Shuttering, props and formwork.

Removal time of Shuttering, Props, and Formwork :-

It is very necessary to remove the shuttering after gaining the strength.
stripping time of shuttering is given below according to IS code 456-2000

Type of Formwork                                                                         Minimum of stripping formwork

(a). Vertical formwork to column,walls,Beams                                                  16-24 hours

(b). Soffit formwork to slab ( Props to be refixed
        immediately after removal of formwork)                                                      3 Days

(c). Soffit formwork to Beams ( Props to be refixed

        immediately after removal of formwork)                                                      7 Days

(d). Props to salb :

      1). Spanning up to 4.5 mtrs                                                                         7 Days

      2). Spanning Over 4.5 mtrs                                                                         14 Days

(e). Props to Beams and Arches :

      1). Spanning up to 6.0 mtrs                                                                         14 Days

      2). Spanning Over 6.0 mtrs                                                                         21 Days

What is water cement ratio ?

Water Cement Ratio (w/c ratio) :-
 water cement ratio is the ratio of the weight of water to weight of cement. it is very neccesary to achive the desired WORKABILITY of concrete.
workability means how ease we use the concrete and it should be easy placed in structure.
Water cement ratio is the impotent factor of durability of concrete. it should be minimum as possible.
Generally Maximum water cement ratio is taken between 0.35 to 0.45 according to IS code 456-2000

 For Nominal Weight aggregate of 20mm, Minimum Cement content, Maximum Water cement ratio and Minimum Grade of concrete for different Exposer are given below :-

According to Environmental conditions water cement ratio is given below :-

Environmental condition                     Max. water cement ratio

(1). Mild                                                        0.45
(2). Moderate                                                0.40
(3). Sever                                                      0.40
(4). Very Sever                                             0.38                    
(5). Extreme                                                  0.35

Concrete covers in slab, Beam, Column and Footing,

What is concrete covers :- It is design depth of steel from the exposed surface of concrete. It is the dimension used in the design and indicated ion the drawing.
It should not be less then the Diameter of Bar.

Requirement of concrete cover :- It is provided to protect the steel bars from corrosion depends upon the quality of concrete.

Nominal cover in the COLUMN should not less then 40mm

Nominal cover in the FOOTING should not less then 50mm

Nominal cover in the SLAB should not less then 15mm

Cover in the BEAM is  should not less then the 25mm

The minimum Cover is depends upon the exposer condition of concrete.


  Exposure                    -        Nominal concrete cover in mm not less then

(1).  Mind                     -                                   20
(2).  Moderate              -                                   30
(3).  Sever                    -                                   45
(4).  Very sever            -                                   50    
(5).  Extreme                -                                   75

Note:-
(1). In Mild exposer rainforcement up to 12mm bars normal cover may e reduced by 5mm.
(2). Foe sever and very sever expose reduction of 5mm is made where grade of concrete is M35 and above.
  

What is shear force and bending moment diagrams ?

Shear force diagrames :- Theses are the diagrams those shows the value of shear force at various sections of the members.

Bending moment diagrams :- These are the diagrams those shows the value of the bending moment at various sections of the members.

(A). CANTILEVER BEAMS :- These beams are fixed from one Ends.

(1). Cantilever beams carry W concentrated load of length l.

Considering any section X from distance x from end B.
So     S.F.  at X=S=+W
        B.M. at X=M= -Wx

at x=0 then M=0 

if x=l then M= -Wl


(2). Cantilever beam of length l having uniformaly distributed load w

S.F and B.M at any section X will be

S= wx and M= -(wx^2)/2

if x=l Then
   M= -(wl^2)/2






(3). cantilever beam of length l carry uniformly distributed load w per unit length runs in whole length and have concentrated load W at free end.




S= wx+W
M= -{(wx^2)/2 +Wx}

if x= l then

S= (wl+W)
M= -{(wl^2)/2 +Wl}



(4). Cantilever beam of length l ccarry UDL w per unit length for a distance 'a' from the free end

Here, At x=0 S= 0   and   M= 0

Now section between A and D distance x from end B

S = +wa
M= -wa{x-(a/2)}

At x=a
M= -wa{l -(a/2)}





(B). SIMPLY SUPPORTED BEAMS :-


(1). SSB have concentrated load W at mid having span length l

S.F. at C point

S = -W/2
BM = M= Wl/4

hence BM increase uniformaly

from zero at A to  Wl/4 at C then decrease to zero at B.

(2). SSB have eccentric concentrated load on the span.

assume AD=a  and DB=b
Va and Vb are vertical reaction at the ends.

Vb = Wa/l    and Va = Wb/l

So, shear force between A and D  S = Va = +Wb/l  
      shear force between D nad B  S = Vb = -Wa/l

Bending moment at section between A and D at distance x from A.

M= + (Wb/l)x  at x=0 M= 0

if x= a  M= Wab/l




(3). SSB carry UDL w per unit length over whole span.




At x=0      S = wl/2    and M=0

At  x =l    S=  -(wl/2)    and    M = 0

At l/2        S = 0   and M =  + (wl^2)/8

Minimum area required for Rooms, W/C, Bathroom,

                                     Minimum Area For Rooms, W/C,  and Bathroom,


Before designing of any building we should know the minimum area required for the bathroom rooms and water closet, and the combined bathroom and water closet.

(1). Haritable Rooms :- Rooms may be bedroom, living room, or study rooms. The minimum Hight not be less then 2.74 meters. for row houses hight should be minimum 2.6 meters, and for air conditioner rooms 2.4 meters.
Area of single room should not be less then be 9.5 sqr mtr. with minimum width of 2.4 mtr.
In case of two rooms area of one room should be minimum 9.5 sqr mtr and other should be minimum qr 7.5 sqr mtr with minimum width 2.4 mtr.

(2). Water closet :- It does not includes the bathroom. minimum heigth should be 2,2 mtr and 1.1 sqr mtr minimum area.

(3). Bathrooms :- This place used for bathing whose area should not e less then 1.8 sqr mtr or 1.5x1.2 mtrs
and the hight should not be less then 2.2mtrs.

(4). Combined Lat-Bath :- Area should not be less then 2.8 sqr mtr with minimum width 1.2mtrs.