Project on Concrete Mix Design for various grades of Concrete
CONCRETE MIX DESIGN FOR VARIOUS GRADES OF CONCRETE
AIM: Concrete mix design is the process of finding right proportions of cement, sand and aggregates for concrete to achieve target strength in structures.
INTRODUCTION: Concrete mix design can be stated as Concrete Mix = Cement:Sand:Aggregates. The concrete mix design involves various steps, calculations and laboratory testing to find right mix proportions. This process is usually adopted for structures which requires higher grades of concrete such as M25 and above and large construction projects where quantity of concrete consumption is huge.. Benefits of concrete mix design is that it provides the right proportions of materials, thus making the concrete construction economical in achieving required strength of structural members. As, the quantity of concrete required for large constructions are huge, economy in quantity of materials such as cement makes the project construction economical. Concrete mix design of M20, M25, M30 and higher grade of concrete can be calculated.
Concrete is a composite mixture which consists of Cement, Sand and Aggregate. Concrete mix design is the procedure for finding the right quantities of these materials to achieve the desired strength. Accurate concrete mix design makes concrete construction economical. Large constructions such as Bridges, dams requires huge amount of concrete, using the right quantity of constituents make the structure economical. In order to calculate or find the right amount of cement, sand and aggregate required in 1m3 of concrete; you need to know about different grades of concrete.
As per IS456:2000, Different grades of concrete are classified into M5, M7.5, M10, M15 etc., whereas M stands for Mix and the number behind M stands for Characteristic Compressive strength(fck) of the concrete in N/mm2 @28 days when checked with 15cm×15cm×15cm cube in direct compression test.
Concrete Mix design of M25, M30 and higher grades of concrete is calculated as below:
The procedure for finding the different grades of concrete mixes are same. The below mentioned method can be applied to any grade of concrete by changing the values. To make ease in understanding we are finding the Concrete mix design of M20 grade concrete.
The Concrete mix ratio for M20 grade of concrete is 1:1.5:3 that mean 1 part of cement, 1.5 part of sand (fine aggregate) and 3 parts of aggregate (crushed stone) in volume and then batched for mixing. To know the Concrete Mix Design follow below:-
Mix Design (M) = Cement: Sand :Aggregate
The following Steps Should be followed to calculate Concrete Mix Design:
Step 1: Determining the Target Strength of Concrete
Step 2 : Determining Water-Cement ratio
Step 3: Selection of Water Content and Cement Content for Mix
Step 4: Estimation of Coarse Aggregate Proportion for Mix
Step 5: Correction for Absorption and Concrete Trail Mixes
Different grades of concrete :
Different grades of concrete has different Concrete Mix proportions which means different concrete mix ratios. As Per IS456:2000, the Concrete mix design has the following concrete mix proportions :-
| Type of Concrete | Concrete Grade | Mix Ratio | Characteristic Compressive strength of Concrete @28Days in N/mm2 |
|---|---|---|---|
| Ordinary concrete | M5 | 1:5:10 | 5 N/mm2 |
| M7.5 | 1:4:8 | 7.5 N/mm2 | |
| M10 | 1:3:6 | 10 N/mm2 | |
| M15 | 1:2:4 | 15 N/mm2 | |
| M20 | 1:1.5:3 | 20 N/mm2 | |
| Standard Concrete | M25 | 1:1:2 | 25 N/mm2 |
| M30 | Design Mix | 30 N/mm2 | |
| M35 | Design Mix | 35 N/mm2 | |
| M40 | Design Mix | 40 N/mm2 | |
| M45 | Design Mix | 45 N/mm2 | |
| M50 | Design Mix | 50 N/mm2 | |
| High Strength Concrete |
M55 | Design Mix | 55 N/mm2 |
| M60 | Design Mix | 60 N/mm2 | |
| M65 | Design Mix | 65 N/mm2 | |
| M70 | Design Mix | 70 N/mm2 |
Different types of Concrete mixes:
Concrete Mixes are primarily divided into the two different types :
Nominal Mix:
Nominal Mix is generally adopted for small scale constructions. In this type of mix, the mix ratios and concrete constituent proportions are prefixed and specified. Eg: M20(1:1.5:3); the quantity of cement, sand and aggregate is batched in volume as per the fixed ratio 1:1.5:3. From the above table till M25 grade, the concrete proportions are called as Nominal mix concrete.
Design Mix:
Design mix concrete is adopted for high rise constructions. In this type of mix, the mix ratios are decided by an Engineer after analysing the properties of individual ingredients of concrete. Like, cement is tested for Fineness modulus and Specific gravity of cement in the lab while deciding the Design mix ratio. There is No Pre-fixed ratio, and ingredients are are batched in weight. From the above table, concrete grades more than M25 falls in Design mix.
Data Required for Mix Design
i. Design Data
(a) Characteristic compressive strength of concrete required at end of 28 days = M 25
(b) Nominal maximum size of aggregate used = 20 mm
(c) Shape of Coarse Aggregate = Angular
(d) Required workability at site = 50-75 mm (slump Value)
(e) Quality control is done by as per IS: 456
(f) Type of exposure Condition of concrete (as defined in IS: 456) = Mild
(g) Type of cement used = PSC conforming IS: 456 – 2000
(h) Method of placing Concrete on Site = pumpable concrete
(ii) Material testing data (determined in the laboratory)
(a) Specific gravity of cement = 3.15
(b) Specific gravity of FA = 2.64
(c) Specific gravity of CA = 2.84
(d) Aggregates are assumed to be having surface dry conditions.
(e) Fine aggregates are confirmed to Zone II of IS – 383
Mix Design of M25 Grade of concrete.
The following steps to be followed for concrete mix design calculation,
Step-1 Determining the Target Strength of Concrete.
Himsworth constant for 5% risk factor is 1.65 & standard deviation is taken from IS: 456 2000 for M – 25 Grade of concrete is 4.0.
ftarget = fck + 1.65 x S
= 25 + 1.65 x 4.0 = 31.6 N/mm2
Where,
S = Standard Deviation (N/mm2) = 4 (Refer: IS 10262- 2009 table -1)
Step-2 Determining Water-Cement ratio.
Refer: IS 456, (page no 20) Table 5
Maximum water-cement ratio taken for Mild exposure condition = 0.55
Assume water–cement ratio as 0.50 for experiment base
0.5 < 0.55, hence it is OK.
Step-3 Selection of Water Content for Mix.
Refer: IS 10262- 2009 Table 2
Maximum water content is taken = 186 Kg (maximum size of aggregate = 20 mm)Correction in water content is
Estimated water content for mix = 186+ (3/100) x 186 = 191.6 kg /m3
Step-4 Selection of Cement Content for Mix.
- Water-cement ratio = 0.50
- Corrected water content for mix = 191.6 kg /m3
- Cement content =
- Refer IS 456 – 2000, Table 5
- Minimum cement Content required for mild exposure condition = 300 kg/m3
- 383.2 kg/m3 > 300 kg/m3, hence, OK.
- This value is required to be checked for durability requirement from IS: 456 – 2000
- In this example for mild exposure and for the reinforced concrete the minimum cement content is 300 kg/m3 which are less than 383.2 kg/m3. Hence cement content adopted = 383.2 kg/m3.
- IS: 456: 2000, clause 8.2.4.2
- Maximum cement content for mix = 450 kg/m3.
Step-5 Estimation of Coarse Aggregate Proportion for Mix.
Refer IS 10262- 2009, Table 3
- For Nominal max. size of aggregate for mix = 20 mm,
- Zone of fine aggregate = Zone II
- And For w/c = 0.5
- The volume of coarse aggregate per unit volume Concrete = 0.62
Table for Correction in Estimation of Coarse Aggregate Proportion
(Note 1: For every ±0.05 increase or decrease change in w/c, the coarse aggregate proportion is to be changed by 0.01. If the w/c is less than 0.5, the volume of coarse aggregate is required to be increased to reduce the fine aggregate content in the mix. If the water-cement ratio is more than 0.5, the volume of coarse aggregate is to be reduced to increase the fine aggregate content. If the coarse aggregate is not of an angular shape, the volume of coarse aggregate is required to be increased suitably, based on experience-based.)
(Note 2: For pumpable concrete or congested reinforcement in structure the coarse aggregate proportion may be reduced up to 10%)
Hence,Volume of coarse aggregate per unit volume of total Volume of concrete = 0.62 x 90% = 0.558
Volume of fine aggregate in mix = 1 – 0.558 = 0.442
Step-6 Estimation of the Mix Materials.
Volume of concrete is taken = 1 m3
Volume of cement = (Weight of cement / Specific gravity of cement) x (1/100) = (383.2/3.15) x (1/1000) = 0.122 m3
Volume of water = (Weight of water / Specific gravity of water) x (1/1000)
= (191.6/1) x (1/1000) = 0.1916 m3
Volume of aggregates = a – (b + c ) = 1 – (0.122 + 0.1916) = 0.6864 m3
Weight of coarse aggregates = 0.6864 x 0.558 x 2.84 x 1000 = 1087.75 kg/m3
Weight of fine aggregates = 0.6864 x 0.442 x 2.64 x 1000 = 800.94 kg/m3
RESULTS :
Concrete Mix Proportions for Concrete Trial Mix -1
- Cement = 383.2 kg/m3
- Water = 191.6 kg/m3
- Fine aggregates = 800.94 kg/m3
- Coarse aggregate = 1087.75 kg/m3
- W/c = 0.5
- For trial -1 of concrete in lab & to check its properties.
- It will satisfy durability & economy.
- For making trial -1, mass of ingredients required will be calculated for 4 no’s cube assuming 25% wastage.
- Volume of concrete required for Making 4 cubes = 4 x (0.153 x1.25) = 0.016878 m3
- Wt. of Cement = (383.2 x 0.016878) kg/m3 = 6.47 kg
- Wt. of Water = (191.6 x 0.016878) kg/m3 =3.23 kg
- Wt. of Coarse aggregate = (1087.75 x 0.016878) kg/m3 =18.36 kg
- Wt. of Fine aggregates = (800.94 x 0.016878) kg/m3 = 13.52 kg
Mix Design of M30 Grade of concrete.
Step-1 Determining the Target Strength of Concrete.
Himsworth constant for 5% risk factor is 1.65 & standard deviation is taken from IS: 456 2000 for M – 30 Grade of concrete is 5.0.
ftarget = fck + 1.65 x S
= 30 + 1.65 x 5.0 = 38.25 N/mm2
Where,
S = Standard Deviation (N/mm2) = 4 (Refer: IS 10262- 2009 table -1)
Step-2 Determining Water-Cement ratio.
Refer: IS 456, (page no 20) Table 5
Maximum water-cement ratio taken for Mild exposure condition = 0.55
Assume water–cement ratio as 0.50 for experiment base
0.5 < 0.55, hence it is OK.
Step-3 Selection of Water Content for Mix.
Refer: IS 10262- 2009 Table 2
Maximum water content is taken = 186 Kg (maximum size of aggregate = 20 mm)Correction in water content is
Estimated water content for mix = 186+ (3/100) x 186 = 191.6 kg /m3
Step-4 Selection of Cement Content for Mix.
- Water-cement ratio = 0.50
- Corrected water content for mix = 191.6 kg /m3
- Cement content =
- Refer IS 456 – 2000, Table 5
- Minimum cement Content required for mild exposure condition = 300 kg/m3
- 383.2 kg/m3 > 300 kg/m3, hence, OK.
- This value is required to be checked for durability requirement from IS: 456 – 2000
- In this example for mild exposure and for the reinforced concrete the minimum cement content is 300 kg/m3 which are less than 383.2 kg/m3. Hence cement content adopted = 383.2 kg/m3.
- IS: 456: 2000, clause 8.2.4.2
- Maximum cement content for mix = 450 kg/m3.
Step-5 Estimation of Coarse Aggregate Proportion for Mix.
Refer IS 10262- 2009, Table 3
- For Nominal max. size of aggregate for mix = 20 mm,
- Zone of fine aggregate = Zone II
- And For w/c = 0.5
- The volume of coarse aggregate per unit volume Concrete = 0.62
Table for Correction in Estimation of Coarse Aggregate Proportion
(Note 1: For every ±0.05 increase or decrease change in w/c, the coarse aggregate proportion is to be changed by 0.01. If the w/c is less than 0.5, the volume of coarse aggregate is required to be increased to reduce the fine aggregate content in the mix. If the water-cement ratio is more than 0.5, the volume of coarse aggregate is to be reduced to increase the fine aggregate content. If the coarse aggregate is not of an angular shape, the volume of coarse aggregate is required to be increased suitably, based on experience-based.)
(Note 2: For pumpable concrete or congested reinforcement in structure the coarse aggregate proportion may be reduced up to 10%)
Hence,Volume of coarse aggregate per unit volume of total Volume of concrete = 0.62 x 90% = 0.558
Volume of fine aggregate in mix = 1 – 0.558 = 0.442
Step-6 Estimation of the Mix Materials.
Volume of concrete is taken = 1 m3
Volume of cement = (Weight of cement / Specific gravity of cement) x (1/100) = (383.2/3.15) x (1/1000) = 0.122 m3
Volume of water = (Weight of water / Specific gravity of water) x (1/1000)
= (191.6/1) x (1/1000) = 0.1916 m3
Volume of aggregates = a – (b + c ) = 1 – (0.122 + 0.1916) = 0.6864 m3
Weight of coarse aggregates = 0.6864 x 0.558 x 2.84 x 1000 = 1087.75 kg/m3
Weight of fine aggregates = 0.6864 x 0.442 x 2.64 x 1000 = 800.94 kg/m3
RESULTS :
Concrete Mix Proportions for Concrete Trial Mix -1
- Cement = 383.2 kg/m3
- Water = 191.6 kg/m3
- Fine aggregates = 800.94 kg/m3
- Coarse aggregate = 1087.75 kg/m3
- W/c = 0.5
- For trial -1 of concrete in lab & to check its properties.
- It will satisfy durability & economy.
- For making trial -1, mass of ingredients required will be calculated for 4 no’s cube assuming 25% wastage.
- Volume of concrete required for Making 4 cubes = 4 x (0.153 x1.25) = 0.016878 m3
- Wt. of Cement = (383.2 x 0.016878) kg/m3 = 6.47 kg
- Wt. of Water = (191.6 x 0.016878) kg/m3 =3.23 kg
- Wt. of Coarse aggregate = (1087.75 x 0.016878) kg/m3 =18.36 kg
- Wt. of Fine aggregates = (800.94 x 0.016878) kg/m3 = 13.52 kg