Cement Sand And Aggregate For Nominal Mix Concrete Grades 133a1k

Cement Sand and Aggregate for Nominal Mix Concrete Grades Following is a simple method to calculate cement, sand and aggregate for nominal mix concrete otherwise known as prescribed concrete mix.

Difference between Nominal mix concrete and Design mix concrete Nominal mix concrete is prepared by approximate proportioning of cement sand and aggregate to obtain target compressive strength. It is followed for easy volume batching in the site. Concrete grade up to M20 can be mixed using nominal mix method for ordinary construction purposes. Design mix concrete is prepared by proportioning materials based on codal procedure (in India it is IS 456 & IS 10262). Based on strength, concrete is classified into different grades like M5, M7.5, M10, M15 etc., M stands for Mix and the number stands for characteristic compressive strength(fck) of the concrete in 28 days in direct compression test. If the ratio for M20 concrete is 1:1.5:3 then 1 part cement, 1.5 part sand and 3 part aggregate (crushed stone) in volume is batched for mixing. Nominal Concrete Mix Ratio Table

GRADE

MIX RATIO

M5

1 : 5 : 10

M 7.5

1:4:8

M 10

1:3:6

M 15

1:2:4

M 20

1 : 1.5 : 3

Nominal mix concrete design for one cubic meter of M20 concrete It takes 1.52 cubic meter of total material to prepare one cubic meter of concrete because cement and sand fills the gaps between aggregate (coarse aggregate). If 40mm aggregate is used, total material required will be 1.57 cubic meter. Let’s design M20 grade concrete for 20mm aggregate. Ratio for M20 concrete is 1 : 1.5 : 3

Volume of = (cement / (cement + sand + aggregate)) x total cement material

= (1 / (1+1.5+3)) x 1.52

= 0.277 cu.m

Volume of sand = Volume of cement * Ratio of sand

= 0.277 x 1.5

= 0.415 cu.m

Aggregate = Volume of cement * Ratio of aggregate (20mm)

= 0.277 x 3

= 0.830 cu.m Corrections and Conversions 1. Cement is often bought in 50kg bags. Volume of a cement bag is 0.0347 cum. Bulk density of cement is 1440 kg/m3.

No. of Cement Bags needed

= 0.277/0.0347

= 7.98 bags

~ 8 bags or 400kg OR

Weight of Cement = 0.277 x1440

= 398.88 kg

~ 400kg or 8 bags Hence we require 7.98 bags of cement to prepare one cubic meter of M20 concrete. 2. In volume batching, presence of moisture in sand will increase the volume of sand( bulking of sand) hence, we may endup with less sand than calculated. Hence, always use dry sand or include the effect of bulking of sand in calculation. 3. Conversion of sand and aggregate to units may be necessary because sand and aggregate is often bought in units. 1 unit = 100 cubic feet, 1 cubic meter is 35.32 cubic feet.

Volume of Sand

= Volume of sand x 35.32

= 0.415 x 35.32

= 14.66 cft or 0.1466 unit of sand Hence we need 14.66 cubic feet or .1466 unit of sand to prepare one cubic meter of M20 grade

Volume of aggregate = Volume of aggregate x 35.32

=0.830 x 35.32

= 29.32 cft = 0.2932 unit of aggregate Hence we need 29.32 cubic feet or .2932 unit of aggregate to prepare one cubic meter of M20 grade concrete

QUANTITY

CEMENT

SAND

AGGREGATE

1 cu.m of M20

0.277 cu.m (400kg)

0.415 cu.m

0.830 cu.m

QUANTITY

10cu.m of M20

CEMENT

SAND

AGGREGATE

7.98 Bags

14.66 cft

29.32cft

7.98 Bags

0.1466 unit

0.2932 unit

79.8 Bags

1.466 unit

2.932 unit

Cement Sand and Aggregate required for M15, M10, M7.5, M5, M3 grade Using above procedure, materials required for different proportions are calculated and presented below.

For 20mm aggregate GRADE

CEMENT

SAND

AGGREGATE

M15

0.217 cu.m

0.434 cu.m

0.869 cu.m

6.25 Bags

15.34 cft

30.68 cft

0.152 cu.m

0.456 cu.m

0.912 cu.m

4.38 Bags

16.11 cft

32.21 cft

0.117 cu.m

0.468 cu.m

0.935 cu.m

3.37 Bags

16.52 cft

33.04cft

SAND

AGGREGATE

M10

M7.5

For 40mm aggregate GRADE

CEMENT

GRADE

CEMENT

SAND

AGGREGATE

M15

0.224 cu.m

0.449 cu.m

0.897 cu.m

6.46 Bags

15.84 cft

31.68 cft

0.157 cu.m

0.471 cu.m

0.942 cu.m

4.52 Bags

16.64 cft

33.27 cft

0.121 cu.m

0.483 cu.m

0.966 cu.m

3.48 Bags

17.06 cft

34.12cft

0.098 cu.m

.490 cu.m

0.981 cu.m

2.83 Bags

17.33 cft

34.66 cft

M10

M7.5

M5

Amount of water needed for mixing concrete Water/Cement ratio is a ratio of weight of water to weight cement. It changes based on the desired workability. Quantity of water needed per 50kg bag of cement in litres. (IS 456)

GRADE

WATER (L)

M5

60

M 7.5

45

M 10

34

GRADE

WATER (L)

M 15

32

M 20

30

Calculation of weight of sand and aggregate per bag of cement IS456 Code book recommends the following quantities of total aggregate per 50kg of cement to produce nominal mix concrete.

GRADE

TOTAL(F.A + C.A)

M5

800 kg

M 7.5

625 kg

M 10

480 kg

M 15

330 kg

M 20

250 kg

Note: General ratio of fine aggregate to coarse aggregate is 1:2. Ratio can be adjusted between 1:1.5 to 1:2.5 based on the grading of fine aggregate and size of coarse aggregate. Choose water from above table.

For M20 Grade Concrete Sand is confirmed to Zone II(average grading). From the above table we know 250kg of total dry aggregate is needed.

Sand per 50 kg bag = (1 / (1+2)) x 250 kg

=83 kg ~ 85 kg

Aggregateper 50 kg bag = (2 / (1+2)) x 250 kg

= 166 kg ~ 165 kg Note: Always use dry river sand because moisture in sand may increase its weight, mess up the water-cement ratio and causes bulking of sand.

CEMENT

SAND

AGGREGATE

per bag(50kg)

85 kg

165 kg

Sand and Aggregate per bag of cement – M5, M7.5, M10, M15, M20 Quantities are calculated according to above procedure with fine to coarse aggregate ratio as 1:2.

Grade

Total Agg.

Cement

Sand

Gravel

M5

800kg

1 bag

270kg

530kg

M7.5

625kg

1 bag

210kg

415kg

M10

480kg

1 bag

160kg

320kg

M15

330kg

1 bag

110kg

220kg

M20

250kg

1 bag

85kg

165kg

Quantities derived through nominal mix method and design mix method is different from each other. From experimentation, we find out that M15 grade concrete, batched through nominal mix method, has equivalent quantities of materials as M20 grade concrete batched by design mix method.