Concrete mix design is the method for finding the precise amount of materials to achieve the specified strength, concrete is a composite mixture consisting of cement, sand and aggregates.
Accurate concrete mix design makes concrete construction more economical.
In large constructions such as bridges, dams requires a large amount of concrete, using it in correct amount makes the structure economical.
To calculate or find the correct quantity of cement, sand and aggregate required in 1 m3 concrete.
Objectives of concrete mix design:
- They are designed to attain the specified functionality within the plastic phase.
- To realize the desired minimal energy within the rigid phase.
- Also, for achieving desired practicality with durability in given environmental situations.
- To provide concrete as economically as possible.
Types of Concrete mix design
Previously, concrete specifications determined the ratio of cement, fine and coarse aggregates.
These mixtures of fixed cement-aggregate ratios guarantee sufficient power called as nominal mixes.
These provide simplicity under normal conditions, with a margin of power greater than specified.
However, the nominal concrete for given workability varies extensively in strength because of the variability of the mix design materials.
2. Standard mixes:
Nominal mixtures of fixed cement- aggregate ratio (by volume) vary extensively in strength and should result in fewer or over content mixtures.
For this reason, minimal compressive strength included in many features, these mixes are known as standard mixtures.
On this concrete mix design, the letter M specifies the quantity which is the specified 28-day cubic energy of the mixture in N/mm2.
The Mixture grades M10, M15, M20 and M25 roughly correspond to mixing ratios (1: 3: 6), (1: 2: 4), (1: 1.5: 3) and (1: 1: 2).
3. Designed Mixes:
In these mixes, the efficiency of the concrete is specified by the designer, although the mix ratio is determined by the manufacturer of the concrete, in addition the minimum cement content can be maintained.
This is essentially the most rational strategy for the selection of mixing ratios with particular materials, considering roughly distinctive characteristics.
The strategy results in the manufacturing of concrete with economically suitable properties.
However, the designed combination does not function information because it doesn’t guarantee the correct mixing ratio for the prescribed efficiency.
Nominal or standard mixing for concrete with under handing efficiency can be used for very small projects, where the 28-day strength of concrete does not exceed 30 N / mm2.
There is no control test required dependence on the mass of the material.
Factors affecting concrete mix design:
Grade designation of concrete compressive strength requirements is the major issue affecting the mix design.
Primarily based on the degree of management available on site, the concrete mixture is to be designed for the target mean compressive strength.
Type and Grade of Cement:
The selection of the kind of cement is dependent upon the required price of power development.
Within the case of prestressed concrete constructions, the excessive power OPC of grades 43 and 53 are used.
In conditions where an initial strength improvement is required, rapid hardening Portland cement is preferable.
Maximum nominal size of aggregate:
The workability will increase with a rise in the dimension of the mixture.
Concrete mix design with an excessive water-cement ratio, larger maximum size could also be helpful.
Grading of Mixed Aggregate:
The relative ratio of fine and coarse aggregates in concrete mixtures is a vital issue affecting the strength of concrete.
For dense concrete, it is necessary that coarse and fine aggregates are nicely categorized.
The compressive power of concrete at a certain age at regular temperature primarily depends on the water-cement ratio.
The water-cement ratio is minimized by compressive strength and vice versa.
Desirable performance depends on two factors:
- The size of the segment, the quantity and spacing of the reinforcement.
- The method of condensation to use.
Insufficient workability resulting from incomplete compaction can have a serious impact on the strength durability and floor finish of concrete.
The durability of concrete might be defined as resistance to deteriorating influences that reside contained in the concrete or in aggressive environments.
The strength of concrete varies from batch to batch depending on the variation in material quality, variation in mixing ratio, variation in batching and mixing equipment, etc.
Advantages of Concrete Mix Design:
1.Required ratios of each component:
2.Quality Concrete Mix:
Aggregates with good strength, size, specific gravity and free of organic material are used.
3.Economical Concrete Mix:
This saves the cost of the project and an economical concrete mix can be obtained.
4.uses of locally available ingredients:
This allows the use of locally available materials such as coarse aggregates, fine aggregates, etc.
5.Desired Properties of Mix:
Concrete obtained through mix design has desired properties such as working capacity, durability, setting time, strength, etc.
Disadvantages of Concrete Mix Design:
- It requires high initial cost.
- Also, require skilled labout.
- Also, requires specific attention.
Water, cement, fine aggregate, coarse aggregates, in suitable ratio of penetration into concrete with efficient guidance.