Mix ratios for M30 Grade concrete?

Answer 1

Grade of Concrete : M35
Characteristic Strength (Fck) : 35 Mpa
Standard Deviation : 1.91 Mpa*
Target Mean Strength : T.M.S.= Fck +1.65 x S.D.
(from I.S 456-2000) = 35+ 1.65×1.91
= 38.15 Mpa

Test Data For Material:
Aggregate Type : Crushed
Specific Gravity
Cement : 3.15
Coarse Aggregate : 2.67
Fine Aggregate : 2.62

Water Absorption:
Coarse Aggregate : 0.5%
Fine Aggregate : 1.0 %

MIX DESIGN

Take Sand content as percentage of total aggregates = 36%

Select Water Cement Ratio = 0.43 for concrete grade M35

(From Fig 2. of I.S. 10262- 1982)

Select Water Content = 172 Kg

(From IS: 10262 for 20 mm nominal size of aggregates Maximum Water Content = 186 Kg/ M3 )

Hence, Cement Content= 172 / 0.43 = 400 Kg / M3

Formula for Mix Proportion of Fine and Coarse Aggregate:

1000(1-a0) = {(Cement Content / Sp. Gr. Of Cement) + Water Content +(Fa / Sp. Gr.* Pf )}

1000(1-a0) = {(Cement Content / Sp. Gr. Of Cement) + Water Content +Ca / Sp. Gr.* Pc )}

Where Ca = Coarse Aggregate Content

Fa = Fine Aggregate Content

Pf = Sand Content as percentage of total Aggregates

= 0.36

Pc = Coarse Aggregate Content as percentage of total Aggregates.

= 0.64

a0 = Percentage air content in concrete (As per IS :10262 for 20 mm nominal size of

aggregates air content is 2 %) = 0.02

Hence, 1000(1-0.02) = {(400 /3.15) + 172 +(Fa / 2.62 x 0.36)}

Fa = 642 Kg/ c*m

As the sand is of Zone II no adjustment is required for sand.

Sand Content = 642 Kg/ c*m

1000(1-0.02) = {(400 /3.15) + 172 +(Ca / 2.67 x 0.64)}

Hence, Ca = 1165 Kg/ c*m

From combined gradation of Coarse aggregates it has been found out that the proportion of 53:47 of 20 mm & 10 mm aggregates produces the best gradation as per IS: 383.

Hence, 20 mm Aggregates = 619 Kg

And 10 mm Aggregates = 546 Kg

To obtain slump in the range of 150-190 mm water reducing admixture brand SP430 from Fosroc with a dose of 0.3 % by weight of Cement shall be used.

Hence the Mix Proportion becomes:

Cem


W/C


Water


Sand


20mm


10mm


Admix

400


0.43


172


635


619


564


1.2

1




0.43


1.6


1.547


1.36


0.003

Units – Kg/ M3

Cement : Sand: Coarse Aggregates = 1 : 1.6 : 2.907

We are thankful to Er. Ishan Kaushal for this valuable information.
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