Concrete Mix Design for M25 grade as per IS 10262:2009

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1.STIPULATIONS FOR PROPORTIONING

a) Grade designation : M25 RCC

b) Type of cement :53 grade Ordinary Portland Cement conforming IS 12269

c) Maximum nominal size of coarse aggregate : 20 mm

d) Minimum amount of cement : 300 kg/m³ as per IS 456:2000

e) Maximum water-cement ratio : 0.50 as per Table 5 of IS 456:2000

f) Workability : 100 – 125 mm slump

g) Exposure condition : Moderate (For Reinforced Concrete)

h) Method of concrete placing : Pumping

j) Degree of supervision : Good

k) Type of aggregate : Crushed Angular Aggregates

l) Chemical admixture type : Super Plasticizer Normet

2.TEST DATA FOR MATERIALS

a) Cement used : Sagar 53 grade Ordinary Portland cement conforming IS 12269.

b) Specific gravity of cement :3. 15

c) Chemical admixture : Super Plasticizer conforming to IS 9103.

d) Specific gravity of

1) Coarse aggregate 20 mm : 2.799

2) Coarse aggregate 10 mm: 2.789

3) Combined Specific Gravity of aggregate

( 20 mm-45% & 10 mm -55% )=2.792.

4) Fine aggregate : 2.517

e) Water absorption:

1) Coarse aggregate 20 mm : 0.41 %

2) Coarse aggregate 10 mm : 0.59 %

3) Fine aggregate : 1.87 %

f) Aggregate Impact Value : 20.52 %

g) Combined Flakiness & Elongation Index : 27.57 %

h) Sieve analysis:

1) Coarse aggregate: Conforming to all in aggregates of Table 2 of IS 383

2) Fine aggregate : Conforming to Grading Zone III of Table 4 of IS 383

3 TARGET STRENGTH FOR MIX PROPORTIONING

f’ck =fck + 1.65 s

where

f’ck = average target compressive strength of concrete at 28 days,

fck = characteristics compressive strength of concrete at 28 days, and

s = standard deviation.

From table 1 of IS 10262 assumed Standard Deviation, s = 4 N/N/mm². Therefore, target strength of concrete = 25 + 1.65 x 4 = 31.6 N/mm².

But as per MORT&H 5th revision Table 1700.5 required target mean compressive strength = 25 + 11 = 36.00 N/mm² where 11 is the current margin.

4 SELECTION OF WATER•CEMENT RATIO

Based on the trial , adopted water cement ratio 0.38

From the Table 5 of IS 456 maximum Water Cement Ratio is 0.50

0.38 < 0.50 Hence ok.

As per MORT&H 5th revision Maximum Water Cement Ratio water cement ratio for moderate exposure is 0.45 , hence it is ok

5. SELECTION OF WATER CONTENT

From Table 2 of IS 10262:2009, maximum water content for 20 mm aggregate = 186 liter for 25 to 50 mm slump range but for an increase by about 3 percent for every additional 25 mm slump so here estimated water content for 125 mm slump = 186+(9/100) x 186 = 202 liter.

Water requirement if we are considering cement 360 kg & w/c ratio o.38 for concrete mix design ; calculated water will be 136.8 so net reduction in water while using super plasticizer = 100 – (136.8/202 x 100) = 32.28 %.

Now we had got reduction percentage of water , calculate of the required water = 202 – (202 x 32.28) % = 202 – 65.20 = 136.80 (For 75 mm slump increase 3% , for 100 mm increase 6% & increase 9 % for 125 mm slump)

6. CALCULATION OF CEMENT CONTENT

Adopted w/c Ratio = 0.38 then Cement Content = 136.80/0.38 = 360 kg/m³ ,from Table 5 of IS 456, minimum cement content for ‘moderate’ exposure conditions is 300 kg/m³ but taken 360 kg/m³ > 300 kg/m³ hence ok.

As per MORT&H 5th revision for moderate exposure with reference to Table number 1700-2 maximum water cement ratio 0.45 & minimum cement 340 kg/m³ is specified but we had taken 360 kg/m³ , hence ok

7. CALCULATION OF COARSE AGGREGATE AND FINE AGGREGATE PROPORTION

From Table 3 of (IS 10262:2009) Volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone III) for water-cement ratio of 0.50 =0.64 (a)

In the present case water-cement ratio is 0.38 therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content.

As the water cement ratio is lower by 0.12 , the proportion of volume of coarse aggregate is increased by= (0.12/0.05) = 2.4 times of 0.01 ,so 0.01 x 2.4= 0.024 (b)

Net required water cement ratio= a+b = 0.64 + 0.024 =0.66(at the rate of -/+ 0.01 for every ± 0.05 change in water-cement ratio) therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.38 = 0.66

NOTE – In case the coarse aggregate is not angular one, then also volume of coarse aggregate may be required to be increased suitably based on experience & Site conditions.

If we are doing concrete with pump , reduce upto 10% these value ,therefore volume of coarse aggregate =0.66 x 0.9 =0.59.

Actual reduced volume of fine aggregate content = 1 – 0.59 = 0.41.