Nominal Mix Concrete Material CalculationHere you will find a simple method to calculate cement, sand and aggregate by volume and by weight for nominal mix concrete otherwise known as prescribed concrete mix . Proper relative proportioning of the materials is necessary to attain the targeted strength and quality for the intended use.DIFFERENCE BETWEEN DESIGN AND NOMINAL MIX

CONCRETE

For design mix concrete, materials are proportioned based on the rule and procedure given in the IS456 code book. For nominal mix concrete, there is a list of prescribed proportions to attain different grade of concrete. Nominal mix concrete is easy to follow in site, hence they are used for producing ordinary concrete (up to M20 grade) for construction.

UNDERSTANDING CONCRETE MIX RATIO

Based on strength, concrete is classified into different grades like M5, M7.5, M10, M15 etc., M stands for Mix and number stands for characteristic compressive strength of the concrete in 28 days in direct compressive 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.

GRADE MIX RATIO

M5 1 : 5 : 10

M7.5 1 : 4 : 8

M10 1 : 3 : 6

M15 1 : 2 : 4

M20 1 : 1.5 : 3

Ordinary concrete up to M20 grade can be designed by nominal mix concrete procedure. Standard and High strength concrete should be designed by standardized prescribed mix design procedure.

In most cases, ratio of fine aggregate to coarse aggregate is 1:2, but based on the size difference it shall be between 1:1.5 to 1:2.5.

NOMINAL MIX CONCRETE DESIGN FOR ONE METRE

CUBE OF M20 CONCRETE

It takes 1.5 cubic metre of total material to prepare one cubic of concrete, because cement and sand fills the gaps between the aggregate (crushed stone).

Let’s design M20 grade concrete.Ratio for M20 concrete is 1:1.5:3

CALCULATION FOR REAL-WORLD APPLICATION

Cement is often bought in 50kg bags and aggregate is bought in Units. So, convert the calculated quantity to bags and units.

Weight of cement needed = Volume of cement *Density of cement

= 0.273 cu.m * 1440 kg/cu.m

= 393.12 (approximately 390 kg)

No of bags = 390 / 50 = 7.8 bagsHence it takes nearly 8 bags of cement to prepare one cubic meter of M20 grade concreteAn Unit is 100cft (cubic feet) of material. 100cft is 35.32 cubic meter.

Unit of sand needed = Volume of sand / 35.32

= 0.409 / 35.32

= 0.0116 unit or 11.6 cft

Hence it takes 11.5 cft of sand to prepare one cubic meter of M20 grade concrete

Unit of aggregate needed = Volume of aggregate/ 35.32

= 0.0232 unit or 23.2cft

Hence it takes 23 cft of aggregate to prepare one cubic meter of M20 grade concrete

WATER REQUIREMENT FOR NOMINAL MIX CONCRETE

Water is added based on the quantity of content. Water/Cement ratio is a ratio of weight of water to cement. W/C ratio changes based on the desired workability of the concrete. IS456 code book suggest the following quantities for different concrete grades.

Grade of Cement Water per bag(50kg) of Cement

M5 60 litre

M7.5 45 litre

M10 34 litre

M15 32 litre

M20 30 litre

 QUANTITY REQUIRMENT PER BAG OF CEMENT

Gauge box is used for Volume batching in site. Volume of a gauge box is 0.035cu.m(1cft) which is a volume of 1 bag of cement. For M20 grade, use 1 bag of cement 1.5 box of sand and 3 box of aggregate.

Sand 0.035 * 1.5 0.053 cu.m 1.5 gauge box 1.5cft

Aggregate 0.035 * 3 0.105 cu.m 3 gauge box 3cft

M20 GRADE – MATERIAL REQUIREMENT BY VOLUME

Workability of the fresh concrete can be field tested by using slump cone test. Strength development of concrete should be tested by casting concrete in 15cm cube mould or cylinder mould and tested under compressive test machine on 3, 7, 14, and 28 days.

QUANTITY CEMENT SAND AGGREGATE

1 cu.m of M20 0.273cu.m 0.409cu.m 0.818cu.m

1 cu.m of M20 7.8 Bags 0.0116 Unit 11 cft 0.0232 Unit 23.2 cft

Per bag of Cement 1 1.5 cft 3cft

MATERIAL REQUIREMENT BY WEIGHT FOR 1 BAG

(50KG) OF CEMENT

IS456 Code book suggests the following quantities of total aggregate per 50kg of cement to produce nominal mix concrete.

GRADE TOTAL ( FINE+COARSE )

M5 800 kg

M7.5 625 kg

M10 480 kg

M15 330 kg

M20 250 kg

Note: General ratio of fine aggregate to coarse aggregate is 1:2, but it can be adjusted between 1:1.5 to 1:2.5 based on the grading of fine aggregate and size of coarse aggregate. Water is chosen from the above table.Lets find out the quantity needed to produce M20 grade by codal procedure. Sand is confirmed to Zone II – average grading. Ratio of fine to coarse aggregate is chosen as usual as 1:2. From the above table we know we need 250kg of total dry aggregate.

Weight of sand needed per bag = (1 / (1+2)) * 250 kg

= 83 kg ~ 85 kg

Weight of aggregate needed per bag

= (2 / (1+2)) * 250 kg

= 166 kg ~ 165 kg

MATERIAL REQUIREMENT BY WEIGHT TO PRODUCE 1

CU.M OF CONCRETE

Weigh batching is not used to prepare large volume of concrete by nominal mix concrete procedure. Weigh batching is the accurate form of batching. It includes the presence of moisture in aggregate, but in nominal mix concrete we ignore the moisture content provided we use dry aggregate while mixing

However, weight of materials needed can be calculated by multiplying BULK DENSITY of the aggregate with volume requirement from above calculation. Bulk density of fine aggregate varies from 1440kg/m3 to 1600kg/m3 and for coarse aggregate it varies from 1600kg/m3 to 1800kg/m3.

Bulk density depend on the moisture and compaction of aggregate. You better go for Design mix procedure if you want accurate results to suit your needs.