In this emerging world of modern design of structures, concrete acts as the backbone of civil engineering. A structural engineer’s first and foremost objective is to build an efficient and durable concrete structure that is also aesthetically pleasing. Here comes the role of a concrete designer. When the aim is to build a concrete structure that is efficient and durable, this demands to follow the concrete mix design steps as per IS codes
If the mix design is incorrect, the mix may not have the desired strength, durability, or workability, which can lead to problems such as cracking and reduced resistance to external factors such as weather, fire, and impact.
For example, if too much water is used in the mix, the mix will be too wet and will have a lower strength. On the other hand, if too little water is used, the mix will be too dry and will be difficult to work with.
In short, the mix design determines the final quality of the concrete, and it is essential to follow mix design procedures and standards (IS- 10262 : 2009 and IS- 456 : 2000) to ensure that the mix meets the desired strength and performs as intended.
Before reading this post just go and check "Concrete mix design procedure as per IS 10262:2009 & IS 456:2000"
What are the different design stipulations for the concrete mix design ?
This post will help you to have a brief idea of the different parameters required and will also make you aware of the different exp. data required to do the mix design. The different design stipulations required for the desired mix are shown in the table below
| Stipulations for proportioning | |
|---|---|
| Type of Concrete | PCC |
| Grade Designation | M15 |
| Shape of Particle | Angular |
| Slump | 85 mm |
| Water- Cement Ratio | 0.40 |
| Exposure Condition | Mild |
| Concrete Placement | By Hand |
| Degree of Supervision | Good |
The different experiemental data required for the desiered mix are shown in the table below
| Sieve analysis | |
|---|---|
| Fine Aggregate | Zone 1 |
| Coarse Aggregate | 20 mm |
| Chemical Admixture | |
|---|---|
| Volume ( By mass of cement) | 2% |
| Water Content Reduction | Zero |
| Test data for materials | |
|---|---|
| Standard Deviation | 3.50 MPa |
| Specific Gravity of Fine Aggregate | 2.74 |
| Specific Gravity of Coarse Aggregate | 2.74 |
| Specific Gravity of Cement | 3.15 |
| Specific Gravity of Admixture | 1.145 |
| Water absorption of Fine Aggregate | 1.0 % |
| Water absorption of Coarse Aggregate | 0.5% |
| Free Surface Moisture of Fine Aggregate | Zero |
| Free Surface Moisture of Coarse Aggregate | Zero |
Step by step procedure for concrete mix design of M15 grade as per Indian standards
The detailed step by step procedure for concrete mix design of M30 grade, according to IS – 10262:2009 and IS- 456:2000 is given below:
Mean compressive strength: Calculate the target mean compressive strength at 28 days
| target mean compressive strength | characteristic strength + 1.65 X Standard Deviation |
| target mean compressive strength | 15 + 1.65 X 3.50 = 20.78 N/mm2 |
Where sufficient test results for a particular grade of concrete are not available, the value of standard deviation could be taken from Table 1 of IS-10262.
- Water cement ratio: In this step we select maximum water/cement ratio, which should be selected as per Table 5 of IS – 456: 2000.
| Maximum water-cement ratio | 0.60 |
| Adopted water-cement ratio | 0.40 |
- Entrapped air: For the maximum size of aggregate used the air content is estimated.
- Water content and fine to total aggregate ratio: The selection of water content is based on Table 2 of IS:10262:2009. Maximum water content for 20 mm aggregate and a slump value of 25 to 50 mm = 186.0 l. But in our problem the value of slump is 85 mm, so we need to alter the water content.
| Estimated water content | 186 + 4./100 X 186 = 193.81 litres |
- Cement content: The cement content per unit volume of concrete is computed sing Table 5 of IS:456:2000:
| Minimum cement content for mild expossure condition | 220 kg/ m3 |
| cement content | 194/0.40 = 485 kg / m3 |
- Aggregate content: Volume of coarse aggregate per unit volume of total aggregate corresponding to 20 mm maximum size and zone I of fine aggregate = 0.60 – Table 3 of IS- 10262:2009.
Correction on volume of different ingredients
| Based on water cement ratio | 0.02 |
| Based on placement | 0.00 |
Hence Volume
| Coarse aggregate | 0.62 |
| Fine aggregate | 0.38 |
$$
V=\left[W+\left(C / S_{c}\right)+(1 / P) \cdot\left(f_{a} / S_{f a}\right)\right] \times(1 / 1000)
$$
$$
C_{a}=1- P / P \times f_{a} \times S_{ca}/ S_{fa}
$$
| Mass of Coarse aggregate | 1108.24 kg / m3 |
| Mass of Fine aggregate | 679.25 kg / m3 |
Computation of actual quantities required for a concrete mix – Trial mix
Water Correction
Extra quantity of water to be added
| Coarse aggregate | 5.54 kg |
| Fine aggregate | 6.79 kg |
| Mix Design | |
| Cement | 485 kg / m3 |
| Water | 206 kg / m3 |
| Fine Aggregate | 672 kg / m3 |
| Coarse Aggregate | 1103 kg / m3 |
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In order to check the efficiency of the designed concrete mix we shall prepare different trial mixes and the same are tested to check the strength and workability of designed concrete mix. If the designed concrete mix fails to meet the desired properties then minor adjustment is done in the water cement ratio and aggregate quantities, then again the trial mixes are prepared.
The nominal mix for M15 grade is (1:2:4). The quality of concrete depends on a number of factors and the standard mix just gives us a rough estimate of the quantities of material required, this is exactly where a design mix procedure is required as it is evident from the results that for the same mix proportion when exposure and material properties are changed mix proportion also changes. Therefore, standard mixes may be used only for very small jobs.
Hope this post helped you to learn the step by step procedure for concrete mix design using IS code ( IS – 10262: 2009 and IS – 456: 2000)
Concrete Mix Design
- Calculate cement, sand and aggregate quantity in concrete.
- Calculate the number of premix bags required for your project.
- Option to set your own size and rate of premix bags.
- Calculate the volume of concrete required for slabs, walls, footings and columns.
- Calculate the weight of ingredients required for preparing the calculated volume of concrete.
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