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**What Is Concrete Mix Design?**

**Concrete Mix Design** can be **defined **as the **method **of **calculating **a **suitable quantity **of **materials **of **concrete **and find out the **required proportions **with the **object **of **producing concrete **of certain **minimum strength **and **durability **as **economically **as **possible**.

**Mix Design of Concrete** is a **process **of **calculating **the **quantity **of **materials **like **cement, sand**, **aggregate**, **water**, and **admixtures** to **achieve **or make **specified strength **of concrete.

I**n simple words,** the method of **calculating materials quantity **that makes the **required **grade of **concrete**.

The **concrete mix design** is no easy task **considering **the widely **varying** **properties **of the **constituent **materials, the **conditions **that **prevail **at the site of work, in **particular **the **exposure condition**, and the **conditions **that are **essential **for different **construction **work for **which **the mix is **designed**.

**Design of concrete mix **demands **deep knowledge** of concrete **materials **properties; these **make **the **task **of **mix design **more **complex **and **difficult**.

**The design process of concrete mix **required deep **knowledge **of **material properties **and properties of concrete in **plastic condition**; it also needs **wider knowledge** and **experience **of **concrete**.

Even the **quantity **of **materials **of concrete **calculated **in the **laboratory requires **modification and **readjustments **to suit the **field conditions**.

The **advanced research **and **experiment **with deep studies of **properties **of **materials**, concrete is **becoming more **and more an **exact material **than in the **past**.

The **structural designer considers some minimum criteria for strength for design; and the concrete designer with the knowledge of the materials, site exposure conditions** and standard of **supervision** on **construction **site to achieve this **minimum strength** and **durability**.

Further, it’s the site **engineer’s responsibility **to make **concrete **at the **site **and for that, he has to closely **following **the **parameters suggested **by the **mix designer **to achieve the **minimum** **strength **specified by the **structural engineer**.

In **some cases**, **concrete mix ***design *calculation **parameters **have to **slightly modify** the mix **proportions **given by the **mix** **designer**.

There must be the **provision **of **casting concrete cubes **and **cylinders **in required **numbers **and **tests **them to **confirm **the **achievements **with respect to the **minimum specified strength**.

**Concrete Mix Design Calculation as per IS Code** means the **Government of Indian** releases **guidelines **for **concrete strength **and **quality control**.

**Indian standard code **gives **proper guidelines **and **methods **for **designing **concrete mix to get **proper strength **of **concrete**.

**Read More:** **Concrete – Its Materials, Properties, Tests & Cos****t**

**Concrete Mix Design**

The **Bureau **of **Indian Standards **recommended a set **procedure** for the **design **of **concrete mix **mainly based on the **work done **in **national laboratories**.

The **Concrete Mix Design **procedure is covered in** IS 10262 2019**. The **methods **can **utilize **for both **medium strength **and **high strength concrete**.

The **guidelines **for **concrete mix design** is **10262 is 2019 pdf**

** Data Required for Mix Proportioning**

**The following data is required for Concrete Mix Design Calculations of a particular grade of concrete.**

**Grade designation**- Type of
**cement**, and**grade**of cement (if applicable) **Maximum**nominal**size**of aggregate.- Minimum cement/
**cementitious materials**content and**maximum****water**–**cement**/cementitious materials ratio to be adopted; (Exposure conditions as per Table 3 and**Table 5 of IS 456**) **Workability required**at the time of**placement**- Transportation
**time** - Method of
**Placing** **Degree**of**site control**(good/fair) or**value**of established**standard deviation**, if any;- Type of
**coarse aggregate**(angular/sub-angular/**gravel**with some**crushed particles**/rounded gravel/manufactured coarse aggregate) - Type of
**fine aggregate**(natural sand/**crushed stone**or gravel sand/manufactured sand/ mixed sand); - Maximum
**cement content** - Whether a
**chemical admixture**shall or**shall not**be**used**and the**type of chemical admixture**and the**extent**of use; - Whether a
**mineral admixture**shall or shall not be**used**and the**type**of**mineral admixture**and the**extent**of use; and - Any other
**specific requirement**like**early age strength requirements**.

**Following are the steps to be followed for concrete mix design,**

**Concrete Mix Design for M – 20 Grade of Concrete**

**Following steps for concrete mix design procedure as per IS Code 10262 – 2019,**

**Step-1 Calculate Target Mean Strength of Concrete**

In order that not more than the **specified proportion **of **test results **are likely to **fall **below the **characteristic strength**, the **concrete mix **has to be **proportioned **for **higher target **mean** compressive strength f ’ck.**

**The Target mean characteristic strength is given by the following relation:**

**f’ck = fck + 1.65 S**

**or**

** f’ck = fck + X**

**whichever is higher.**

where,

**f’ck **= Target mean strength (compressive) at end of 28 days, in N/mm2;

**fck **= characteristic strength (compressive) at end of 28 days, in N/mm2;

**S **= standard deviation, in N/mm2 (see 4.2.1); and

**X **= Factor as per Grade of Concrete, as per Table 1.

**Table – 2 Assumed Standard Deviation**

**For M -20 Grade of Concrete,**

**Target Mean Compressive Strength (f’ck) = fck + 1.65 S**

** = 20 + 1.65 x 4 (S = 4.0 for M – 20)**

** = 26.6 N/mm****²**

**Target Mean Strength ( f’ck) = fck+ X**

** = 20 + 5.5**

** = 25.5 N/mm²**

**Always select a higher value. Therefore, for the **M-20 grade of concrete,** we will try to achieve 26.6 N/mm² strength.**

**Read More:** **How To Make Concrete – Batching, Concrete Mixing, Transporting & Placing**

**Step-2 Selection of Water-Cement Ratio**

It is stated for **concrete mix design **as per **is code **that in general **different types of cement**, aggregates of **various maximum size **and **supplementary cementitious materials**, **grading**, **surface texture**, **shape**, and other **characteristics **may produce concrete of **different compressive strength **for the same **free water**–**cement **ratio.

Therefore, a **proper relationship between **the water-**cement ratio **and the **strength **of **concrete **should preferably be **established **for the **materials actually **to be **used**.

In case such **data **is **not available**, related water-**cement ratio **(by mass) (w/c) **corresponding **to the** compressive strength at 28 days** may be selected from the **relationship **shown in Fig.1, for the **expected **28 days strength of **cement**.

**So, for the M – 20 Grade of concrete, we have a **target mean strength of **26.66 N/mm² and we have OPC – 53 grade of cement.**

**As per our cement grade OPC -53, we have to follow Curve 3.**

**From the graph, for 26.66 N/mm² concrete strength at 28 days bisect the curve 3 at 0.62 free water-cement ratios.**

Where **supplementary cementitious **materials are used, that is, **mineral admixtures**, the water **cementitious materials** **ratio **(w/cm) shall be calculated, in **accordance** with **T**able 5 of IS 456 and this** w/cm** shall be as per Table 3 and Table 5 of **IS 456** or as specified.

**So, we select water-cement ratio for M- 20 grade of concrete is 0.62.**

**Suggestion:**

Always prefer a **higher water**–**cement **ratio for your **concrete **because **IS code** tests and **studies **are done in a **controlled manner **in **laboratories **which **procedure **and care are **not possible **on **construction **sites. So, my **suggestion **is to select a higher **water-cement ratio **for your **concrete grade**. **(Higher means, for M -20 grade of concrete IS code indicates 0.62, select 0.5 less that is 0.55)**

**Step-3 Estimation of Air Content**

The **approximate** **volume **of **entrapped **air content to be **expected **in normal (non-air-entrained) concrete is given in Table 3.

**We have a nominal maximum size of aggregate of 20 mm.**

**From the **above table, the **approximate air content** as a percentage of the **volume **of **concrete **is **1 %.**

**Step-4 Selections of Water Content and Admixture Content**

The **water content **in **concrete **is **generally** affected by **various factors**, such as **aggregate size**, aggregate **shape**, aggregate texture, **workability**, water-cement ratio, **cement**, and **other supplementary **cementitious materials type and content, **chemical admixture**, and **environmental **conditions.

As **aggregate maximum size **increases, a **reduction **in **water**–**cement ratio **and **slump**, and the **use **of **rounded aggregate **and **water reducing **admixture will **reduce **the **water demand**.

On **another side**, if the **cement content**, slump, **water**–**cement ratio**, **aggregate **angularity, **temperature**, and a **decrease **in the **proportion **of the **coarse aggregate** to** fine aggregate **will increase **water demand**.

The **amount **of **water content **per unit **volume **of **concrete **may be **determined **from **Table 4.**

**The water content given in Table 4 is for angular coarse aggregate and for 50 mm slump.**

The **water content **given in Table 4 can be **reduced **by **approximately 10 kg** for **sub**–**angular aggregates**, **15 kg for gravel **with some **crushed** **particles**, and** 20 kg for rounded gravel** to produce the same **workability**.

So, if required more **workability **means **slump **value **more than 50 mm**, the required **water content** may be **increased **or **decreased **by about **3 percent for each increase or decrease of 25 mm slump** or may be **established **by **trial**.

We have a **nominal maximum** **size **of aggregate of** 20 mm**.

From the above table, the **water content for the nominal maximum size of aggregate is 186 kg (Liter). (Slump 50 mm)**

We want to **increase **the **slump **up to **100 mm**. so we have to **increase **it **twice **by **25 mm**. As per **IS code** we have **increase **water by about **3 percent** for every **additional 25 mm** slump so here **estimated **water content for **100 mm slump.**

**For one 25 mm (3%) and second 25 mm (3%). Total increase in water content is 6%**

**= 186 + 186x(6/100)**

**= 197.16 Liters**

**Note: Increase Water Content as per for following.**

Slump Value | Increase in Water in % |

50 mm | – |

75 mm | 3 % |

100 mm | 6% |

125 mm | 9% |

150 mm | 12% |

**For 75 mm slump increase 3% , for 100 mm increase 6% , increase 9 % for 125 mm slump, increase 12 % for 150 mm slump & increase 15 % for 175 mm slump.**

**Read More:** **Grade of Concrete – Their Ratio, Uses & Suitability**

**Step-5 Estimation of Cement Content**

We have **water content **and **water**–**cement ratio**. So, from this **data**, we can **calculate cement content **for **concrete**,

**Water-Cement Ratio = 0.62**

**Water / Cement = 0.62**

**197.16 / Cement = 0.62**

**Cement = 197.16/0.62**

**Cement = 318 Kg.**

**From Table 5 of IS 456, minimum cement content for ‘moderate’ exposure conditions is 300 kg/m³ but taken 318 kg/m³ > 300 kg/m³ hence ok.**

**Step-6 Estimation of Coarse Aggregate Proportion**

It is **essential **to use the **specified **nominal maximum size, **type **and **grading **will produce **concrete **of satisfactory **workability **when a given **volume **of **coarse aggregate **per **unit volume **of total aggregate is **used**.

**Approximate values **for this **aggregate volume **are given in Table 5 for a **water-cement/water cementitious** **materials **ratio of 0.5, which may be suitably **adjusted **for **other ratios**,

The **proportion **of the **volume **of **coarse aggregates **to that of total **aggregates **is **increased **at the **rate **of **0.01** for every decrease **watercement**/**cementitious materials **ratio by 0.05 and **decreased **at the rate of **0.01** for each **increase **in a **water-cement** ratio by **0.05**.

**Sometimes**, it is **required **more **workable concrete **such as when **placement **is by **pump **or when the **concrete **is **required **to be worked around **congested reinforcing steel**. In such a case, it is **desirable **to reduce **estimated coarse aggregate content determined **using Table **5 up to 10 percent**.

**We have a maximum size of aggregate = 20 mm and which confirming the zone – II.**

As per table number 5 of **IS 10262:2019** volume of coarse aggregate for **20 mm** **nominal size aggregate **and **fine aggregate **(Zone III) for having a **water**–**cement ratio **of 0.50 =0.62 (a)

In the **present case**, the **water**–**cement ratio **is 0.62. Therefore, the **volume **of **coarse aggregate **is required to be **decreased **to **increased **the fine **aggregate content**.

As the **water**–**cement ratio **is higher by **0.12.** the **proportion **of the **volume **of **coarse aggregate **is **decreased **by 0.014 (at the rate of -/+ 0.01 for every ± 0.05 change in the water-cement ratio).

**= 0.12/0.05 = 2.4 % decrease in coarse aggregate content**

**= 0.62 – 0.62 x(2.4/100)**

**= 0.62 – 0.014**

= 0.60

Therefore, the **correct proportion **of the **volume **of **coarse aggregate **for the **water**–**cement ratio** of 0.62 = 0.60

or **pumpable concrete **these **values **should be **reduced **up to **10%. **

**Therefore, Coarse aggregate Volume =0.60 x 0.9 =0.54**

**Fine Aggregate Volume = 1 – 0.54 = 0.46**

### Step-7 **Mix Calculation for 1 m³**

**Material quantity **calculation for concrete mix design as per **IS Code** – **10262 **: **2019**,

**A) Volume of concrete = 1 m³**

**B) Volume of Air Content wet concrete = 0.01m³**

**C) Volume of cement = [Mass of cement] / {[Specific Gravity of Cement] x 1000}**

**= 318/{3.15 x 1000} = 0.1 m³**

**D) Volume of water = [Mass of water] / {[Specific Gravity of water] x 1000}**

**= 197.15/{1 x 1000} = 0.197 m**³

**F) Volume of all in aggregate = [(A-B)-(C+D)]**

**= [(1-0.01)-(0.100+0.197)]= 0.99-0.297**

**= 0.693 m³**

**G) Weight of coarse aggregate= E x Coarse Aggregate Volume x Specific Gravity of coarse Aggregate x 1000**

**= 0.693 x 0.60 x 2.795 x 1000**

**= 1162.16 kg/m³**

**H) Weight of fine aggregate= E x Volume of Fine Aggregate x Specific Gravity of Fine Aggregate x 1000**

**= 0.693 x 0.46 x 2.517 x 1000**

**= 802.36 kg/m³**

**MIX Proportion by Volume**

**Cement **= 318 kg/m³

**Water** = 197.15 Liter/m³

**Fine aggregate **= 802.36 kg/m³

**Coarse aggregate 20 mm **= 1162.16 x 60 %= 697.29 kg/m³

**Coarse aggregate 10 mm ** = 1162.16 x 40 %= 464.86 kg/m³

**Water-cement ratio** = 0.62

**Weight of Materials for 1 Bag ( 50 kg) Bag of Cement**

We know that **volume **of **50 kg** bag of cement is **0.035 m³.** so if we **divide **the **weight of cement **by the **volume **of **1 bag of cement** we will get a **number **of **bags of cement** required for making** 1 cubic meter of concrete.**

**Cement = 318 kg / 0.035 = 11.13 Nos. of Bags**

Now divide all other **quantities **by 11.13 to get **materials quantity **for **50 kg or 1 bag of cement**

**Fine Aggregate (Sand) = 802.36 / 11.13 = 72.08 kg**

**Coarse Aggregate ( 20 mm) = 697.29 / 11.13 = 62.64 kg**

**Fine Aggregate (10 mm) = 464.86 / 11.13 = 41.76 kg**

**Water = 197.15 / 11.13 = 17.71 liter.**

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## FAQ:

**What is Concrete Mix Design?**

**Mix Design of Concrete** can be defined as the method of calculating a suitable quantity of materials of concrete and find out the required proportions with the object of producing concrete of certain minimum strength and durability as economically as possible.

### How many bags of cement make 1m3 of concrete?

For making 1m3 of concrete, approximately 25 to 30 bags of cement requires depends on the grade of concrete. As the grade of concrete increases nos. of cement bags also increased.

### What is the mix ratio for the M 20 grade of concrete?

For M20 grade of concrete mix, ratio is 1 part cement, 1.5 part sand(fine aggregate), 3 part gravel (Coase aggregate)

### What is IS code for concrete mix design?

The Bureau of Indian Standards recommended a set procedure for the design of concrete mix mainly based on the work done in national laboratories. The **Concrete Mix Design Calculation** procedure is covered in** IS 10262: 2019**.

### What are the requirements of concrete mix design?

Requirements of concrete mix design are listed below:

1. Characteristic compressive strength of concrete

2. Nominal maximum size of aggregate used

3. Shape of Coarse Aggregate

4. Required workability at site

5. Quality control is done by as per IS: 456

6. Type of exposure Condition of concrete

7. Type of cement used

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