Concrete Mix Design M-25

  Data Required for Concrete Mix Design

A) Design stipulations for M25

i) Characteristic  compressive strength required

in the field at 28 days

25 N/mm2
ii)  Max. size of aggregate 20mm
iii) Type of coarse aggregate Crushed
iv) Type of fine aggregate Crushed
v) Workability(Slump 25- 50 mm
vi) Degree of quality control Good
vii) Type of exposure Moderate
viii) Type or brand of cement A.C.C. ( PPC )
ix) Type of Admixture Sikka

(1)  Specific Gravity

i)

Cement 2.82

ii)

Coarse aggregate 2.67

iii)

Fine aggregate

2.60

iv)

Admixture Sikka

1.20

Coarse Aggregate

i)

20mm

0.50%
ii)

10mm

0.60%

Fine aggregate  

1.80%

Water Absorption

Coarse aggregate

i)

20mm 0.50%

ii)

10mm

0.60%

Fine aggregate  

1.80%

(3)   Free Surface Water

Coarse Aggregate
i) 20mm Nil
ii) 10mm Nil
Fine Aggregate Nil

Coarse Aggregate.

Table-I

Sieve size                 % passing
20mm
Fraction-1
10mm
Fraction-2
40mm 100 100
20mm 95.9 100
10mm 0 82.1
4.75mm 0 20.9

To satisfy the required grading of combined aggregates, the 20mm size and 10mm size

coarse aggregates are mixed in the following proportions.
Fraction -1 (20mm)          :   52 %

Fraction -2 (10mm)          :   48 %
The grading achieved of the blended aggregate is given is as under:-

  Sieve size % passing  observed

Required as per T-7

IS-383-2016

40mm 100 100
20mm 98 90-100
10mm 39 25-55
4.75mm 10 0-10

(ii)  Fine Aggregate: Sieve analysis of fine aggregate is given in table-2.
Table-2

Sieve size % passing Limits for zone –II
10.0mm 100 100
4.75mm 98.8 90-100
2.36mm 80.8 75-100
1.18mm 60.4 55-90
0.60mm 35.4 35-59
0.30mm   19.6 8-30
0.15mm   2.4 0-10

Fine aggregate belongs to Zone-II as per Table- 9 of IS 383-2016.

Procedure for Concrete Mix Design of M25 Concrete

A-0 — Determination Of Target Strength

Himsworth constant for 5% risk factor is 1.65. In this case standard deviation is taken from IS:456 against M 25 is 4.0.

ftarget = fck + 1.65 x S
= 25 + 1.65 x 4.0 = 31.60 N/mm2
Where,
S = standard deviation in N/mm= 4 (as per table -1 of IS 10262- 2009)
                          
For a tolerance factor of 1.65 and a standard deviation value of 4.0 the target mean strength
of concrete comes out to be equal to 31.60 N/mm2.
A-1    SELECTION OF WATER CEMENT RATIO
 
From table 5 of IS 456 on page no. 20, Maximum water-cement ratio=0.50
Based on experience, adopt water-cement ratio as 0.43,  for the target mean strength and required workability
0.43<0.50, hence O.K.
A-2    SELECTION OF WATER CONTENT
From Table 2 of IS 10262- 2009,
Maximum water content = 186 Kg (for Nominal maximum size of aggregate — 20 mm)

Table for Correction in water content

Parameters Values as per Standard reference condition Values as per Present Problem Departure Correction in Water Content
Slump 25-50 mm 25-50 mm Nil
Shape of Aggregate Angular Gravel with Crushed stone -20
Admixture Sikka Based on Experience -10.50
Total -30.50

So, estimated water content = 186 – 30.50 = 155.50 litre /m3
 
 
A-3   CALCULATION OF CEMENT CONTENT
               
Water-cement ratio    = 0.43
Corrected water content = 155.50 litre /m3
Cement content         = 155.5 = 361.63 say 362 Kg/m3
0.43
Minimum cement Content for moderate exposure condition = 300 kg/m3
362 kg/m3 > 300 kg/m3, hence, OK.
This value is to be checked for durability requirement from IS: 456.
In the present example against mild exposure and for the case of reinforced concrete the minimum cement content is 300 kg/m3 which is less than 362 kg/m3. Hence cement content adopted = 362 kg/m3.
As per clause 8.2.4.2 of IS: 456
Maximum cement content = 450 kg/m3.
A-4   PROPORTIONS OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT
From Table 3 of IS 10262:2009,
the volume of coarse aggregate per unit volume of total aggregate corresponding  to 20mm size aggregate and fine aggregate (Zone II)  for the water-cement  ratio of 0.43
The volume of coarse aggregate per unit volume of total aggregate is 0.634
Volume of fine aggregate is taken as 0.366
A-5   MIX CALCULATIONS
The mix calculations per unit volume of concrete shall be as follows:
a) Volume of concrete = 1 m3</sup
b) Volume of cement =              Mass of cement     x  1_
Specific gravity of cement     1000
= (362/2.82) x (1/1000)
= 0.1284 m3
c) Volume of water =             Mass of water     x   1_
The specific gravity of water     1000
= (155.5/1) x (1/1000)
= 0.1555 m3
d)   Volume of Chemical Admixture       = Mass of Chemical Admixture x   1
              Super Plasticizer @ 1.0% By         Specific gravity of admixture   1000
Mass of cementations material)
= (3.45/1.20) x (1/1000)
=0.0029
e) Volume of all in aggregate = [ a- (b + c + d) ]
= 0.7132 m3
f) Mass of coarse aggregate = 1207 Kg

g) Mass of fine aggregate = 679 Kg
A-6 (1)   MIX PROPORTIONS FOR TRIAL NUMBER 1

Water-cement ratio                           =   0.43

Quantity of cement                            =   362 Kg/m3

Quantity of Water taken                   =   155.5 Kg/m3

Quantity of Fine aggregate              =   679 Kg/m3

Quantity of Coarse aggregate          =   1207 Kg/m3

Quantity of Admixture @ 1.0%       =   3.45 Kg/m3

A-6 (2)  MIX PROPORTIONS FOR TRIAL NUMBER 2

Water-cement ratio                           =   0.45

Quantity of cement                            =   353 Kg/m3

Quantity of Water taken                   =   159 Kg/m3

Quantity of Fine aggregate               =    679 Kg/m3

Quantity of Coarse aggregate          =   1207 Kg/m3
Quantity of Admixture @ 1.0%       =    3.38 Kg/m3

A-6 (3)  MIX PROPORTIONS FOR TRIAL NUMBER 3  

Water-cement ratio                           =    0.46

Quantity of cement                           =    352 Kg/m3

Quantity of Water taken                  =    162 Kg/m3

Quantity of Fine aggregate              =    684 Kg/m3

Quantity of Coarse aggregate          =    1216 Kg/m3

Quantity of Admixture @ 1.0%       =    3.10 Kg/m3

The concrete cubes (150mm x 150mm) were cast with these mixes and the following results were obtained.

</table border=1> RECOMMENDATIONS.The 28 days compressive strength of trial mix no.3 fulfills the design criteria as per IS 10262:2009. Hence recommended being adopted for M-25 grade Cement concrete.
Quantities of Material for one cubic meter of concrete-Water                                    = 162 KgCement                                 = 352 KgSand                                     = 679 KgCoarse aggregate                 = 1207 KgFraction-1 (20mm)   = 603.50 KgFraction-2 (10mm)   = 579 KgQuantity of Admixture @ 1.0%     =  3.10 KgThe above concrete mix design holds good for the samples provided that the parameters taken for the mix design remain the same as taken and aggregates fall within close to their individual grading as mentioned above. The design was on saturated surface dry condition of aggregate when computing the requirement of mixing water, allowance must be made for free surface moisture content or for water absorption dry aggregate Necessary adjustment shall be made in the mass of aggregate. In actual execution, if there is a change in the grading of different materials, the proportions of mixing materials can be changed to achieve the required grading. Quantity of aggregates and water may please be adjusted according to the free moisture present in the aggregates at the time of mix preparations.

Mix No. Water Cement W/C Ratio Slump     (mm) 28-days Compressive

Strength. N/mm2.

1 155.5 362 0.43 45 31.11
2 159 353 0.45 51 32.89
3 162 352 0.46 55 33.33

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