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4 Basic Rules of Concrete Mix Design

When a ready-mix concrete supplier supplies concrete to the job site, they should know the required compressive strength, maximum aggregate size and any other special requirements such as adding admixture, etc. Then they select a mix design based on the requirements.

But most often we mix concrete on site by mixture machine.  If you do so, you should understand the basic rules of concrete mix design yourself. So, in this post I'll discuss about that.

See: How to mix concrete with mixture machine?

The three main ingredients of concrete are cement, aggregate and water. Among them cement and aggregate provide volume stability, strength and durability. Mixing less or much quantity of any one of these ingredients can reduce the quality of concrete. So, mix design is done to balance the quantity of these ingredients without decreasing concrete quality.

See: Concrete ingredients.

The two most important factors of mix design are, proportion of dry ingredients and water-cement ratio. These two factors follow the following rules. Which are the basic rules of mix design.

4 Basic Rules of Concrete Mix Design

Rule-1: High cement and Low aggregate proportion
Concrete mixes with high cement content and low aggregate proportions produce sticky concrete.
Increasing cement content increases the cost of concrete.
Much cement in the mix also causes for shrinkage cracks in hardened concrete.
Cement and aggregate proportion should be balanced in mix-design.

Rule-2: Low cement & High aggregate
Concrete mixes with low cement content and high aggregate proportions produce poor workable and harsh concrete.
Cement quantity should not be lower in mix-design.

Rule-3: High Water-Cement  ratio
High Water-Cement  ratio causes for segregation thus reduces the strength of concrete. But it increases workability of concrete.

High water content increases porosity and permeability of cured concrete.
Water content shouldn't be much in mix-design.

See: How to calculate materials for different ratio concrete?

Rule-4: Low Water-Cement  ratio
Low water-cement ratio increases the strength and durability of concrete. But reduces the workability.

Workability is required for good quality concrete. So, water content and workability should be balanced.
Water content shouldn't be less in mix-design.

The purpose of mix-design is to produce most economical concrete product with desired strength. And that is done by tweaking the above rules. If required, chemical admixture can be mixed with concrete for not avoiding the rules.


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