Concrete admixtures are crucial components in construction. Admixtures are designed to modify the properties of concrete mixes. These are usually powders or liquids that are specially made for mixing with concrete in small quantities. The exact dosage of mixing admixtures usually depends on the proportion of cement in the concrete mix. This is normally measured by ‘percentage by weight of cement’ or ‘%BWC’.
Admixtures used with concrete have a noticeable impact on hardened or fresh concrete. They can react physically and/or chemically and affect the rate of cement hydration. This way, the admixture can enhance or alter several properties of the concrete mix, according to specific construction requirements.
In this blog, we have detailed all you need to know about admixture in concrete, including their meaning, functions and types.
Different Types Of Admixtures
There are several different ways that admixtures are classified. Let’s look at the global way of classifying different types of concrete admixtures –
Plasticizer
Water reducing admixtures are also called plasticizers. This type of concrete admixture allows to reduce the proportion of water content in a concrete mix. However, the lower water content does not affect the concrete’s consistency. In fact, this helps to increase the flow, or ‘slump’ despite the lower water content.
Superplasticizer
High range water reducing admixture is also called superplasticizer. This type of admixture also allows using less water content in the concrete mix. It can increase the flow or slump noticeably without affecting the water content. Besides, high range water reducing admixture can also produce both effects at the same time.
Retarder And Water Reducing Admixture
Retarder is another commonly used water reducing admixture. This type of admixture normally combines the primary effect of water reducing admixture and the secondary effect of a water content retarder.
Retarder And Superplasticizer
The retarder and superplasticizer admixture has all the properties of a superplasticizer and water retarder too. Its primary effect mimics a superplasticizer while its secondary effect is that of a retarder.
Set Accelerator And Water Reducing Admixture
The set accelerator and water reducing admixture offers dual effects. Its primary effect is that of a water reducing admixture while its secondary effect is that of a set accelerating admixture.
Water Retaining Admixture
Water retaining admixture is also called stabilizer or viscosity modifying agent. This form of concrete admixture minimizes the loss of water by reducing bleeding of fresh concrete with excessive water content.
Air Entraining Agent
Air entraining agents are admixtures that produce evenly distributed air pockets or bubbles throughout the concrete. The tiny air voids are produced carefully using special air-entrapment techniques. These small air bubbles remain within the concrete when it hardens, making it lightweight yet strong.
Set Accelerator
Set accelerator is a type of concrete admixture that reduces the time for initial set. It also works to enhance the concrete’s initial strength level.
Hardening Accelerator
Hardening accelerator admixtures speed up the early strength development of concrete mixes. It may influence the final setting time of the concrete and affect the plastic properties of freshly mixed concrete.
Retarder
Retarder admixture is a type of admixture that prolongs the time of the initial set of concrete. It also extends the workability time and retardation of early strength development.
Water Resisting Admixture
Water resisting admixtures tend to reduce the capillary water absorption of hardened concrete.
Shrinkage Reducing Admixtures
Shrinkage reducing admixtures help to minimize early stage drying shrinkage of concrete mixes. This is helpful to prevent cracks from developing during the drying process.
Pumping Aid
Pumping aid admixtures are designed to make it easier to pump slushy concrete and to improve the overall stability of fresh concrete. This works especially well when using concrete with difficult aggregates and unfavorable grading curves.
Corrosion Inhibiting Admixtures
Corrosion inhibiting admixtures create a protective layer on the steel reinforcement to make reinforced concrete. This helps to delay the rate of corrosion which results in extending its durability too.
Surface Improving Admixtures
Surface improving admixtures are also called blowhole reducing admixtures. These types of concrete admixtures significantly lower the number of air bubbles in the fresh concrete. This helps to produce high-quality, smooth and stain-free concrete surfaces.
Admixtures To Control Alkali-Silica Reaction (ASR)
Admixtures to control alkali-silica reaction (ASR) minimize the unwanted expansion in concrete which results from the ASR process. This admixture helps to increase the durability and lifespan of the building.
Applications Of Admixtures
Admixtures are quick setting cement mixes and have the following functions –
- Improve the workability of concrete without reducing or increasing the water content in the cement mix.
- Accelerate setting time.
- Enhance the pumpability of the concrete mix.
- Improve the bond between new and existing concrete surfaces.
- Reduce segregation and bleeding of concrete during hardening.
- Lower the rate of slump loss in cement mixes.
- Enhance the bond to concrete to steel reinforcement.
- Increase water tightness.
- Decrease heat evolution.
Factors Affecting Admixture Performance
Following are some factors that affect the overall performance of admixtures in concrete –
- Type of admixture – The various types of admixtures are made to perform different functions, such as accelerating hardening time, diversifying workability, enhancing strength and improving the durability of the concrete. The type of admixture you choose will determine how well the admixture performs as each type contains different chemical components, with varying physical properties.
- Dosage – As admixtures modify the properties of concrete, the concrete’s functionality can be affected at varying levels by adding excess or an insufficient amount to the concrete. For instance, when the dosage of admixtures is not at the optimum level, it can cause bleeding or problems with segregation.
- Compatibility – The different types of cement produce different admixtures. The performance of the concrete also depends on the compatibility between the admixture and cement. Any incompatibility between these can impact the overall workability, durability, setting time and segregation properties of the concrete.
Conclusion
Admixtures are special chemical compounds used to influence the water content and hardening time of concrete mixes. Plasticizers and superplasticizer admixtures help to lower the water content without affecting the consistency of the concrete. It is highly recommended to buy admixtures from renowned brands, such as Sakshi Chem Sciences Pvt Ltd, India to get the strongest and most durable concrete structures.