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CONCRETE MIX PROPORTIONING - GUIDELINES (M-20,A-20)

Test data required for different kind of material :-

Specific gravity ofProperty

Coarse

aggregate

Fine

aggregate1) Cement = 3.152) Mineral admixture = N.A. Water absorption (by mass) 0.5 % Nil

3) Coarse aggregate = 2.6 Free (surface) moisture (by mass) Nil 2.0 %

4) Fine aggregate = 2.6 Type of aggregate Graded 20 mm Zone-III

CALCULATION FOR MIX PROPORTION :-

Calculation of Target mean compressive strength ( f ’ck )

[as per IS-10262:2009 clause 3.2, Table-1; IS-456:2000 Table-2]

f ’ck = f ck + 1.65 s = 20 + 1.65*4 =26.6 N/mm2

Calculation of water cement ratio [as per IS-456:2000 Table– 5 ]

Maximum free Water cement ratio = 0.55

Based on experience adopt water cement ratio 0.5 < 0.55 Hence ok

Calculation of Water content [as per IS-10262:2009 Table-2]

Water content (Wc)= 186 lit.

Correction in water content for slump= (S l-50)*3/(100*25)*Wc = (100-50)*3/(100*25)*186 =11 lit.

Corrected water content (W’c)= 186+11=197 lit.

Calculation of Cement content [as per IS-456:2000 Table-5 & 6]

Water cement ratio = 0.5

Stipulations for proportioning (considering practical data) :-

Grade designation M20 Conforming to IS-456:2000 (Table 2)

Type of cement O.P.C.- 43 As per relevant IS Code (for OPC IS-8112)

Type of mineral admixture (optional) N.A. Conforming to IS-3812 (Part I)

Maximum nominal size of aggregate 20 mm Conforming to IS-383 (Table 2)

Exposure condition Mild Conforming to IS-456:2000 (Table 3)

Minimum cement content 300 kg/m3 Conforming to IS-456:2000 (Table 5 & 6)

Maximum free water cement ratio 0.55 Conforming to IS-456:2000 (Table 5)

Workability (by slump) (Sl) 100 mm Conforming to IS-456:2000 (Clause 7)

Method of concrete placing (optional) Pumping

Degree of supervision Good Conforming to IS-10262:2009 (it affect ‘s’

of table 1)Type of aggregate Crushing

angular

Conforming to IS-10262:2009 (Clause 4.2)

Maximum Cement content 450 kg/m3 Conforming to IS-456:2000 (Clause 8.2.4.2)

Chemical Admixture type Superplasticizer Conforming to IS-9103

5) Water = 1

6) Chemical admixture = 1.145



Cement content = water content/0.5 = 197/0.5 = 394 kg/m3

>Min. Cement content =300 kg/m3 Hence ok

Calculation of volume of Coarse Aggregate [as per IS-383 Table-4, IS-10262:2009 Table-3]

Volume of Coarse aggregate per unit volume of total aggregate = 0.64

[ For Zone III Fine aggregate & 0.5 water cement ratio ]

Calculation of volume of Fine Aggregate

Volume of Fine aggregate per unit volume of total aggregate = 1-0.64 = 0.36

Mix Calculation

Volume of Concrete = 1 m3

Volume of Cement = 394/(3.15*1000) = 0.125 m3

Volume of Water content = 197/(1*1000) = 0.197 m3

Volume of All in Aggregate = 1-(0.125+0.197) = 0.678 m3

Mass of Coarse Aggregate = 0.678*0.64*2.6*1000 = 1128 kg

Mass of Fine Aggregate = 0.678*0.36*2.6*1000 = 635 kg

Mix Proportions (For Trial Number 1)

Ingredients Quantity (per m3)

Cement 394 kg

Water 197 lit

Fine Aggregate 635 kg

Coarse Aggregate 1128 kg

Water Cement ratio 0.5

CORRECTIONS :-

1) Correction for Chemical Admixture & placing of concrete

[As per clause 4.2 of IS-10262:2009 :- water reducing admixture & super plasticizing admixture reduce water

content 5%-10% & ≥20% respectively]

As super plasticizer is used, the water content can be reduced 20% and above.

Here, we consider 29% reduction of water

Therefore reduced water content = 197*(1-0.29) =197*0.71 = 140 lit.

Water cement ratio = 0.5

Cement content = water content/0.5 = 140/0.5 = 280 kg/m3 <Min. Cement content =300 kg/m3

Hence, consider Cement content = 300 kg/m3 Hence ok

Now, Water cement ratio = 140/300 = 0.47 <Maximum free Water cement ratio = 0.55 Hence ok

Volume Of Coarse Aggregate [as per IS-383 Table-4, IS-10262:2009 Table-3]

Volume of Coarse aggregate per unit volume of total aggregate = 0.64

[ For Zone III Fine aggregate & 0.5 water cement ratio ]

Volume of Coarse aggregate per unit volume of total aggregate =0.64 +(0.01/0.05)*(0.5-water content)

[ For Zone III Fine aggregate & 0.47 water cement ratio ] =0.64 +(0.01/0.05)*(0.5-0.47) =0.64 + 0.006=0.646

For pumpable concrete these value should be reduced by 10%



Now, volume of Coarse aggregate per unit volume of total aggregate = 0.646*(1-0.1) = 0.581

Volume Of Fine Aggregate

Volume of Fine aggregate per unit volume of total aggregate = 1-0.581 = 0.419

Mix Calculation

Volume of Concrete = 1 m3

Volume of Cement = 300/(3.15*1000) = 0.095 m3

Volume of Water content = 140/(1*1000) = 0.14 m3

Mass of Chemical Admixture = @ 2% by mass of cementitious material = 300*(2/100) = 6 kg

[ For Super plasticizer]

Volume of Chemical Admixture = 6/(1.145*1000) = 0.005 m

3

Volume of All in Aggregate = 1-(0.095+0.14+0.005) = 0.76 m3

Mass of Coarse Aggregate = 0.76*0.581*2.6*1000 = 1148 kg

Mass of Fine Aggregate = 0.76*0.419*2.6*1000 = 828 kg

Now,

2) Correction on daily basis for Water absorption & Free (surface) moisture of aggregate

Corrected water content = Water content + Correction for water absorption ( Wca & Wfa )

- Correction for Free (surface) moisture ( Mca & Mfa )

=140+(5.74+0.00)-(0.00+16.56)=129.18 lit

Corrected Coarse Aggregate = Coarse Aggregate - Correction for water absorption of C.A. ( Wca )

+ Correction for Free (surface) moisture of C.A. ( M ca )

=1148-5.74+0.00=1142.26 kg

Corrected Fine Aggregate = Fine Aggregate - Correction for water absorption of F.A. ( W fa )

+ Correction for Free (surface) moisture of F.A. ( Mfa )

=828-0.00+16.56=844.56 kg

Now,

Mix Proportions (For Trial Number 1)Ingredients Quantity (per m

3)

Cement 300 kg

Water 140 lit



Chemical admixture 6 kg


Mix Proportions (For Trial Number 1)

Ingredients Quantity (per m3)

Cement 300 kg

Water 140 lit



Chemical admixture 6 kg




TRIAL MIXES

The calculated mix proportions shall be checked by means of trial batches.

- Trial Mix No. 1

Workability of the Trial Mix No. 1 shall be measured. The mix shall be carefully observed for freedom

from segregation and bleeding and its finishing properties. If the measured workability of Trial Mix No. 1

is different from the stipulated value, the water and/or admixture content shall be adjusted suitably.

- Trial Mix No. 2

With this adjustment in Trial Mix No. 1, the mix proportion shall be recalculated keeping the free water-

cement ratio at the pre-selected value.

- Trial Mix No. 3 & 4

Trial Mixes No. 3 & 4 shall be made with the water content same as Trial Mix No. 2 and varying the free

water-cement ratio by +/-10% of the preselected value.

Mix No. 2 to 4 normally provides sufficient information, including the relationship between compressive

strength and water-cement ratio, from which the mix proportions for field trials may be arrived at.

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