8 Common Types of Concrete Admixtures With Examples

Concrete admixtures are essential components in modern construction, introduced during the mixing phase to enhance the properties and performance of concrete. Serving diverse purposes, these additives play a pivotal role in achieving specific goals such as improved workability, durability, and resistance to environmental factors.

Understanding the necessity of concrete admixtures involves recognizing their ability to optimize concrete mixes and address challenges inherent in conventional formulations.

8 Most Common Types of Admixtures

  1. Water-Reducing Admixtures (WRAs)
  2. Retarding Admixtures
  3. Accelerating Admixtures
  4. Air-Entraining Admixtures
  5. Superplasticizers
  6. Corrosion-Inhibiting Admixtures
  7. Shrinkage-Reducing Admixtures
  8. Pozzolanic Admixtures

1. Water-reducing admixtures (WRAs)

Enhance the workability of concrete by reducing the water content without compromising its performance.

  • Composition: Typically based on lignosulfonates, polycarboxylates, or melamine-formaldehyde. These admixtures reduce the water content without compromising workability.
  • Effect on Concrete: Enhances workability, reduces water-cement ratio, improves strength and durability.
  • Usage: Suitable for high-strength concrete, precast applications, and situations requiring improved workability without excessive water.

Hoover Dam

Water-reducing Admixtures at Hoover Dam
Water-reducing Admixtures at Hoover Dam

WRAs were used in the concrete mix for the Hoover Dam, which is one of the largest dams in the world. The WRAs helped to reduce the water content of the mix, which in turn improved the strength, durability, and heat resistance of the concrete. 

2. Retarding Admixture

Slow down the setting time of concrete, allowing for extended workability and improved placement in challenging conditions.

  • Composition: Commonly contain lignosulfonates or organic acids.
  • Effect on Concrete: Delays setting time, beneficial for extended placement or transportation.
  • Usage: Useful in hot weather conditions, large construction projects, and situations where time-sensitive applications are necessary.

Burj Khalifa

Retarding Admixture at Burj Khalifa
Retarding Admixture at Burj Khalifa

Retarding admixtures were used in the concrete mix for the Burj Khalifa. The retarding admixtures helped to slow down the setting of the concrete, which allowed workers to have more time to place and finish the concrete in the hot desert climate. 

3. Accelerating Admixtures

Speed up the curing and setting process of concrete, is beneficial in situations where early strength development is crucial.

  • Composition: Often based on calcium chloride or non-chloride compounds.
  • Effect on Concrete: Speeds up setting time and early strength development, beneficial in cold weather or when rapid construction is required.
  • Usage: Cold weather concreting, emergency repairs, and projects with tight schedules.

Panama Canal Expansion

Accelerating Admixtures at Panama Canal Expansion
Accelerating Admixtures at Panama Canal Expansion

Accelerating admixtures were used in the concrete mix for the new locks of the Panama Canal expansion. The accelerating admixtures helped to speed up the setting of the concrete, which allowed the canal to be opened to traffic sooner. 

4. Air-Entraining Admixtures

Introduce microscopic air bubbles to enhance the durability and freeze-thaw resistance of concrete, particularly in cold climates.

  • Composition: Usually contains synthetic surfactants or natural wood resins.
  • Effect on Concrete: Introduces microscopic air bubbles, enhancing freeze-thaw resistance and workability.
  • Usage: Cold climates, high-strength concrete, and applications where improved durability is crucial.

Construction of roads and bridges in cold climates

Air-entraining admixtures used for Roads and Bridges in Cold Climates
Air-entraining admixtures used for Roads and Bridges in Cold Climates

Air-entraining admixtures are used in the concrete mix for roads and bridges in cold climates. The air-entraining admixtures help to create tiny air bubbles in the concrete, which help to prevent the concrete from cracking when it freezes and thaws. 

5. Superplasticizers

Improve the fluidity and workability of concrete by reducing water content, leading to higher strength and enhanced performance.

  • Composition: Based on sulfonated naphthalene formaldehyde, sulfonated melamine formaldehyde, or polycarboxylates.
  • Effect on Concrete: Significantly improves flow and reduces water content, enhancing workability and strength.
  • Usage: High-performance concrete, self-consolidating concrete, and situations requiring increased fluidity without compromising strength.

Burj Khalifa

Superplasticisers at Burj Khalifa
Superplasticisers at Burj Khalifa

Superplasticizers were integral in achieving the extraordinary pumpability, flowability, and strength required for the world’s tallest tower. They enabled the use of lower water-cement ratios, enhancing durability and ultimate strength.

6. Corrosion-Inhibiting Admixtures

Protect reinforcing steel in concrete from corrosion, extending the lifespan of structures in aggressive environments.

  • Composition: Often include calcium nitrite or organic corrosion inhibitors.
  • Effect on Concrete: Protects reinforcing steel from corrosion, enhancing durability.
  • Usage: Coastal environments, structures exposed to de-icing salts, and locations with aggressive chemical exposure.

Worli Sea Link

Corrosion-inhibiting Admixtures at Worli Sea Link
Corrosion-inhibiting Admixtures at Worli Sea Link

To mitigate the risk of rapid corrosion for the bridge exposed to seawater, high humidity, and elevated temperatures, project engineers added Sika FerroGard 901, a potent nitrite-based corrosion inhibitor, to the concrete mix. This admixture creates a protective film on the steel reinforcement, guarding it against chloride damage and postponing corrosion onset, thereby preserving the bridge’s structural integrity and lifespan.

7. Shrinkage-Reducing Admixtures

Mitigate shrinkage cracks in concrete by minimizing volume changes during the curing process, improving overall durability.

  • Composition: Can contain polymers, colloidal silica, or other specialized compounds.
  • Effect on Concrete: Mitigates drying shrinkage, reducing the risk of cracking.
  • Usage: Large slabs, restrained conditions, and applications where minimizing cracking is critical.

Millau Viaduct, France

Shrinkage-reducing Admixtures at Millau Viaduct, France
Shrinkage-reducing Admixtures at Millau Viaduct, France

This world-famous bridge features a 2.4 km long concrete deck exposed to diverse weather conditions. Shrinkage-reducing admixtures were crucial in minimizing internal stresses and preventing cracking, enabling the construction of this slender and aesthetically pleasing structure without compromising its structural integrity.

8. Pozzolanic Admixtures

Enhance the properties of concrete by incorporating supplementary materials that react with the cementitious components to improve strength and durability.

  • Composition: Utilise pozzolanic materials like fly ash, silica fume, or metakaolin.
  • Effect on Concrete: Enhances strength, durability, and workability.
  • Usage: Mass concrete, high-performance concrete, and situations where improved long-term performance is required.

The Itaipu Dam

Pozzolanic Admixtures at the Itaipu Dam
Pozzolanic Admixtures at the Itaipu Dam

Facing cost concerns and environmental impact, engineers incorporated fly ash, reducing costs, promoting sustainability, and improving workability. This byproduct of coal-fired plants enhanced concrete performance by increasing strength, and durability, and mitigating the heat of hydration. The use of fly ash resulted in substantial cost savings, lowered CO2 emissions, and contributed to the long-term success of the world’s second-largest hydroelectric power station.

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