# Do You Make These 6 Common Concrete Mix Design Mistakes?

According to Indian Standard: 456-2000 and Indian Standard 1343-1980, the most important factors affecting the design of concrete mix are: (Must read)

### Factors affecting Concrete Mix Design

According to Indian Standard: 456-2000 and Indian Standard 1343-1980, the most important factors affecting the **design of concrete mix** are:

Factors affecting Concrete Mix Design |

- Grade of Concrete
- Type of Cement
- Maximum nominal size of aggregate
- Grading of combined aggregate
- Maximum water/cement ratio
- Workability
- Durability
- Quality Control

### 1. Grade of concrete

**Concrete Mix**is categorised by its grade which indicates it’s comprehensive strength at a 28 day

- It’s the most important factor which highly influencing the mix design of concrete

- The grade M25 denotes crushing strength (fck) of 25 N/mm^2

- Depending upon the degree of quality control, materials, the technology available at the site, the mix design of concrete has to be designed for a target mean comprehensive strength (fck) with applying suitable standard deviation

### 2. Type of cement

- Category of cement highly affected the rate of development of compressive/crushing strength of concrete

- If you use high strength cement than low cement content needed

- The use of 43 grade of cement and 53 grade of cement, provide savings in the use of cement-like as 15 per cent and 25 per cent respectively, as compared to 33 grade of cement

- It is suitable to use 43 or 53 grades of cement of reputed brands because the good fineness of 43 and 53-grade cement help in increases the Workability of the concrete mix

### 3. Maximum nominal size of aggregate

- A
**sieve analysis test**is carried out for determining the maximum size of C.A. because**reinforcement spacing**control by aggregate size which alternatively control the size of the structural member

- IS 456:2000 and IS 1343:1980 provided detail guidelines about the nominal size of aggregate

- The maximum nominal size of coarse aggregate should not be greater than one-fourth of the minimum thickness of the element

- For heavy reinforced concrete element members in the case of the rib of the main element, the nominal maximum size of the coarse aggregate should generally be
**limited**to less than the minimum clear distance between the main reinforcement bars or 5 mm less than the minimum cover. For steel reinforcement,**whichever is smaller**

- The
**workability**of mixing concrete increases with increasing the maximum size of aggregate but the smaller size of the aggregate offers a more surface area that is much more responsible for the bonding with the mortar matrix which gives higher strength

### 4. Grading of combined aggregate

- In a concrete mix design, the relative proportions of the fine aggregate and the coarse aggregate are among the most important factors that greatly influence the strength of concrete

- It is necessary that the aggregates (fine aggregate and coarse aggregate) are well graded

- In the case when aggregates taken from natural sources do not conform to the specified grading in such a situation, a ratio of more than two aggregates becomes necessary

- Their ratio should be such that the combination provides specified grading

### 5. Maximum water/cement ratio

- Abram's water/cement ratio law states that for any test condition, the strength of
**green concrete**depends only on the w / c ratio. The lower the water/cement ratio, the higher the compressive strength and vice versa

### 6. Workability

- The
**workability of green concrete**determines the ease with which the concrete mixture can be mixed, transporting, moulding, condensing, and separating and finishing capacity withoutand bleeding*segregation*

- A concrete mix that is hard to place and compaction will not only
**increase the cost**of handling but will also have poor strength and durability

- The cost of concrete not only increase if it is hard to place and compaction but will also result in poor strength and durability

- On the other hand, a concrete mixture that has separation and bleeding are more expensive to repair and will produce less durable concrete

- Thus, workability can affect both the quality and the cost of concrete

### 7. Durability

- The ability of concrete to withstand adverse environmental conditions is called concrete durability

- The durability of concrete required a lower
**water/cement ratio**

- Generally, it is achieved not by increasing the cement quantity, but by lowering the water quantity at a given cement content

- You can control water demand by taking care of aggregate grading and also by using water-reducing admixtures

- This reduces the chances of cracking due to high heat of hydration and drying shrinkage