Admixture – Advantages And Disadvantages, Explained

By Author: Shruti Tripathi
Total Articles: 5
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Admixture is a material other than cement, water, and concrete added to batches before mixing or during mixing to modify the properties of ordinary concrete & to make it more suitable for the essential condition.
Organic or inorganic materials are added in small quantities to modify the properties of the concrete, which is fresh/hardened state as per the concrete admixture manufacturers.
Here we will learn about admixture, types of admixture, merits & demerits of admixtures used in concrete.
INTRODUCTION TO ADMIXTURE
Admixtures are materials used in concrete to modify its properties.
The effects of using admixture depend on the properties of concrete. Sometimes it is difficult to predict the effect and result because of changing the cement brand, aggregate grading, mix proportions using a rich mix.
Sometimes, many admixtures affect the property of concrete and adversely affect the desirable properties.
Functions of Admixture
To accelerate the initial set of concrete, i.e. to accelerate the rate of strength development at an early age.
To dim the initial set i.e. ...
... to keep the concrete in a working position for a longer time for placement.
Also, to enhance workability.
Construction material manufacturers states that to improve the penetration (flowability) and permeability of concrete.
Moreover, to reduce the separation in grout and concrete mixtures.
Increasing the strength of concrete by decreasing the water content and increasing the density of concrete.
To increase the durability of concrete.
Also, to reduce the capillary flow of water through concrete and increase its imperviousness.
To control alkali-aggregate expansion or alkali-silica reactivity (ASR).
Prevents corrosion of reinforcement in concrete.
Also, increase resistance to the chemical attack.
To reduce the heat of hydration.
To increase the bond between old and new concrete surfaces.
Also, to enhance the bond of concrete to the steel reinforcement.
To decrease the weight of concrete per cubic meter.
ADVANTAGES OF ADMIXTURE
Admixtures reduce the required amount of cement and make concrete economical.
They enhance the practicality of concrete.
Admixtures provide initial strength in concrete.
It reduces the initial heat of hydration and overcomes the problem of thermal cracking in concrete; if there is excess heat of hydration, the cracks can spread to the fresh concrete.
Admixtures improve the resistance against the freeze-melting effect on concrete.
Concrete mixtures maintain maximum stability by bringing waste products into use.
The mixing of concrete can accelerate the setting time.
Some enzymes work as an antibacterial agent.
There are mixtures of concrete that reduce the initial strength but increase the strength of hardened concrete compared to normal concrete stated by construction chemical suppliers.
DISADVANTAGES OF ADMIXTURE
This increased drying shrinkage.
This provides less resistance to sulfate attack.
CaCl2 high risk of corrosion of steel – not allowed in reinforced concrete.
It is more expensive and less effective.
Proper admixture use provides beneficial effects such as improved quality, acceleration or retardation of time, and improving frost and sulfate resistance performance.