From the beginning of the construction to final touches of any building, The concrete is the most used material in construction projects all over the world. As a civil engineer its your responsibility to check the properties of concrete and sometimes it needs to be altered as per requirement and thus concrete admixtures comes into the picture.
The concrete admixture is a material mixed with sand, cement, aggregate and water to enhance the properties of concrete such as setting time, strength, retardation time etc. In this blog, you will understand what is concrete admixture is used and there types with application.
Concrete Admixture : Types, Benefits, and Applications.
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What is a Concrete Admixture?
Concrete admixture are specialised ingredients with a blend of chemical added to the concrete mix along with the basic material like cement, sand, aggregate and water to enhance certain properties. From making it stronger to increasing its workability, admixtures are used for various purposes.
Different types of Concrete Admixtures :
There are different conditions when we pour a concrete into the form work. Different regions has different varieties of temperature and geographical conditions, hot weather, cold weather etc. based don these conditions types of concrete admixtures are used.
Chemical admixtures are used to improve the quality of concrete during mixing, transporting, placement and curing. They fall into the following categories;
1. Accelerating admixture (accelerator) :
As the name suggests, accelerators speed up the setting and hardening process of concrete and helps in;
- Increased heat of hydration,
- Quickens concrete setting time,
- Useful in cold weather to prevent delayed setting time of concrete mix,
- Boots early concrete strength,
- Quicker formwork removal after pouring,
- These admixture often include calcium chloride as a base material.
2. Retarding admixture ( retarder) :
Retarders work oppositely to accelerators, slow down the setting time of concrete. These are helpful when the concrete needs to travel long distances in special mixers or when it is hot outside.
- Slow down concrete setting time,
- Helpful in high temperature,
- Extends concrete workability,
- Allow for intricate job demands,
- Commonly uses sugar or lignosulfonate,
- Increas surface finishing in hot weather.
3. Water reducing admixture :
These are the types of admixtures that enable the reduction of water content in the concrete mix without compromising its workability. It increases the flow ability of concrete so it can be placed easily and can be pumped to the required place where it is not easily possible like in high rise buildings.
- Enhance concrete workability,
- Lower water content, improve strength,
- Improved durability, increased strength,
- Enhances concrete pumpability,
- Facilitate easier placement, compaction,
- Polycarboxylate ether are commonly used.
4. Air entraining admixture :
When the nature conditions is several cold, concrete casting may be difficult due to freezing condition and water in the concrete may freeze, these admixtures introduce microscopic air bubbles into the concrete mixture during mixing.
By modifying the surface tension of the mixing water, they enable the formation and even distribution of air bubbles throughout the concrete. These bubbles enhance the concrete’s durability by increasing its resistance to freeze-thaw cycles, reducing bleeding, and improving workability.
- Introduces micro bubbles for durability,
- Enhance freeze thaw resistance in concrete,
- Improves workability, durability and cohesion,
- Used in extreme cold places,
- Boosts resistance to sulfate attack,
- Fatty acids salts are widely used.
5. Super plasticiser admixture :
Super plasticisers are advanced water-reducing agents that greatly enhance the workability of concrete without increasing water content.
They significantly improve the flow characteristics of concrete, allowing for easier placement in congested reinforcement areas. They are used to make self compacting concrete where less compaction or no compaction required.
- Minimize water demands up to 30%,
- Low workability extreme high strength,
- Avoids things like bleeding segregation,
- Compaction or little compaction required,
- Used in highly reinforced members.
Uses of Concrete Admixtures :
A concrete admixture is a quick-setting ingredients that can be used for following various functions :
- To improve the workability of the concrete without increasing or reducing the water content,
- To accelerate or retard its setting time,
- To enhance the pumpability of the concrete mixture,
- To enhance the bond between existing and new concrete,
- To reduce segregation and bleeding of the concrete,
- To increase the bond of concrete to steel reinforcement,
- To decrease heat evolution and increase water tightness.
Factors affecting the Performance of Admixtures in Concrete :
- Different types of admixtures are designed to improve workability, setting time, strength, or durability of concrete.
- The chosen type of admixture affects its performance in concrete due to varying chemical and physical properties.
- The amount of admixtures must be optimal, as excess or insufficient amounts can affect the concrete’s functionality.
- The type of cement used influences the results of the admixture, impacting the concrete’s performance.
- Compatibility between admixture and cement is crucial for optimal workability, segregation, durability, and setting time.
- Ambient temperature affects the performance of the admixture, with higher temperatures increasing saturation.
- The mix composition, including water, coarse aggregates, fine aggregates, and cement, influences the performance of admixtures.
The overall efficiency of admixtures depends on the proper balance of all mix components, type of admixture, grade of concrete and many more. It’s your responsibility as an engineer in charge to take care of everything.
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