Difference Between Additives and Admixtures

Main Difference – Additives vs Admixtures

Additives and admixtures are chemical components that are added to other materials to improve their chemical and physical properties. Although both of them are components added to other materials, there are differences between additives and admixtures when it comes to cement and concrete mixtures. Additives can be food additives or any other substance added to something in small quantities to improve or preserve it. In this article, we will be discussing additives that are added to cement while manufacturing of cement. Admixtures, on the other hand, are components added to a concrete mixture while mixing. The main difference between additives and admixtures is that additives are added to cement during manufacturing to get new properties for cement whereas admixtures are added to concrete mixtures while mixing to get new properties.

Key Areas Covered

1. What are Additives
     – Definition, Different Additives with Examples
2. What are Admixtures
     – Definition, Uses, Different Admixture Types with Examples
3. What is the Difference Between Additives and Admixtures
     – Comparison of Key Differences

Key Terms: Accelerators, Additives, Admixtures, Alumina, Cement, Concrete, Dispersants, Retarders, Roasting, Silica

What are Additives

Additives are chemical components added to cement during manufacturing to get new properties for cement. The raw materials used in the manufacturing of cement are lime, silica, alumina and iron oxide. These material are ground into a fine powder and are mixed followed by roasting. Heating of this mixture to about 1500^oC will initiate a number of chemical reactions that give the final chemical composition of cement.

In order to obtain desired properties, various additives are added to cement while manufacturing.

Accelerators

Accelerators are added to reduce cement settling time and to speed up the development of compressive strength.

Retarders

Retarders extend the cement settling time. This helps the cement to have sufficient time for slurry placement in deep wells.   

Dispersants

Dispersants are added to reduce the viscosity of cement slurry and to ensure good mud removal during placement.

Fluid Loss Control Agents

Fluid loss control agents control water loss from the cement into the formation.

Some accelerators added to cement are calcium chloride (CaCl2), sodium chloride (NaCl), sea water and potassium chloride (KCl).

What are Admixtures

Admixtures are chemical components that are added to concrete mixtures while mixing to get new properties. Admixtures are the components in concrete other than cement, water and aggregates. Admixtures are added to cement immediately before or during mixing the concrete mixture.

Admixtures are added to:

• Intentionally entrain air
• Reduce water requirement
• Increase workability
• Adjust the settling time
• Adjust the strength

There are different types of admixtures classified as below with some examples.

• Air entraining admixtures – salts of wood resins, some synthetic detergents, salts of petroleum acids
• Plasticizers
• Water-reducing admixtures – lignosulfonates, hydroxylated carboxylic acids, etc.
• Accelerating admixtures – calcium chloride, sodium thiocyanate, etc.
• Retarding admixtures – lignin, borax, sugars, etc.
• Corrosion inhibitors, etc.

Difference Between Additives and Admixtures

Definition

Additives: Additives are chemical components added to cement during manufacturing to get new properties for cement.

Admixtures: Admixtures are chemical components that are added to concrete mixtures while mixing to get new properties.

Raw Material

Additives: Additives are added to cement.

Admixtures: Admixtures are added to concrete.

Addition

Additives: Additives are added to cement while manufacturing.

Admixtures: Admixtures are added to concrete before or during mixing.

Different Types

Additives: Different additives are classified as accelerators, retarders, dispersants, fluid loss control agents, etc.

Admixtures: Different admixtures are classified as air retaining admixtures, plasticizers, water-reducing admixtures, etc.

Conclusion

Additives are added to cement while manufacturing. Admixtures are added to the concrete mixture before or during mixing. The main difference between additives and admixtures is that additives are added to cement during manufacturing to get new properties for cement whereas admixtures are added to concrete mixtures while mixing to get new properties.

References:

1. “Cement Additives.” Wipertrip – Cement Additives (Function and definition), Available here.
2. “Cementing Additives.” Additives, Chemicals, Materials – Halliburton, Available here.

Image Courtesy:

1. “Stockage de ciments” By Oussama zrafi – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Addforce brand mobile self loading concrete mixer truck 1.5m3 3.5m3 diesel concrete mixer” By Addforce Machine – Own work (CC BY-SA 4.0) via Commons Wikimedia