Air-entraining admixtures introduce and stabilize microscopic air bubbles in concrete to increase its resistance to freezing and thawing. They are used for exterior flatwork but avoided for interior structural concrete where a smooth finish is desired. Water-reducing admixtures increase workability without increasing water content, allowing for higher strengths with the same cement. Plasticizers or superplasticizers greatly reduce water needs while maintaining workability and enable the production of self-consolidating concrete. Accelerating admixtures speed the rate of setting and strength gain for applications requiring early use or where temperatures are lower.

1. 1.0 Air-entraining admixtures
The main purpose of adding air-entraining admixtures is to introduce and stabilize
microscopic air bubbles in concrete during mixing. The air bubbles are widely known
as entrained air. Air-entraining admixtures are normally added for exterior flatworks
such as, parking lots, sidewalks, driveways, and etc as these exterior flatworks are
normally subjected to thawing weather cycles. Air-entraining admixtures should be
avoided for interior structural concrete as a smooth finish of the structure is desired.
Main Examples of Air-entraining admixtures
 Abietic and pimeric acid salts
 Alkyl – aryl sulphonates
 Alkyl sulphonates
Advantages Disadvantages
 Increase resistance of concrete towards
thawing and freezing
 Reduce strength in high
cement content concretes
 Increase workability of concrete
 Reduce bleeding and segregation of concrete
mixtures
Photos:
Air-Entrained Concrete
(Source: http://www.theconcreteproducer.com/air-
entrainment/help-for-your-air.aspx)
Air-Entrained Concrete 2
(Source:
http://www.northernconcreteinc.com/blog/?p=1415)
Concrete with added air-entraining admixtures will have a rougher surface as they
have air bubbles with sizes varying from 10 to 500 micrometers in diameter and are
closely spaced.

2. 2.0 Water-reducing admixtures
Water-reducing admixtures are a type of material which is used to increase
workability of freshly mixed concrete without increasing the water cement ratio.
Water-reducing admixtures can reduce the water content of the mixture by 5% - 15%
(University of Memphis, n.d.). This type of admixtures are normally used to improve
the mixture’s workability at a given water cement ratio.
Main Examples of Water-reducing admixtures
 Lignosulfonic acids
 Nepthalene sulphonic acids
 Hydroxylated carboxylic acids
 Sulfonated melamine polycondensation products
 Inorganic material such as borates, phosphates, amines, and etc.
Advantages Disadvantages
 Increase workability of concrete  Aggravate the rate of slump loss with
time
 High strength can be obtained with
the same cement content
 Save up cement up to 10%
Photos:
Lignosulfonic Acid
(Source: http://www.indiamart.com/kakkat-drugs-
chemical/chemicals.html)
By adding water-reducing admixtures, it doesn’t really have any effect on the
aesthetic side of concrete mixture. However, it surely improves the workability of
concrete mixture at a fixed water-cement ratio.

3. 3.0 Plasticizers
Plasticizers are usually known as superplasticizers, which are a higher range of
water reducing admixture. These admixtures are added to concrete with a low-to-
normal slump and water-cement ratio to make high-slump flowing concrete. Flowing
concrete is a type of fluid but is a workable concrete that can be placed with little
vibration. Superplasticizers are able to reduce water requirement 12-25% without
causing any effect on the workability of the concrete (National Ready Mix Concrete
Association, 2001).
Main Examples of Plasticizer admixtures
 Sulfonated melamine
 Sulfonated naphthalene
 Polycarboxylate ether
Advantages Disadvantages
 Enhance concrete early strength  Loss of workability as a result of rapid
slump loss
 Produce flowing concrete to use in
heavy reinforced structure with
inaccessible areas
 Incompability of cement and
plasticizers
Photo:
Concrete A: Without admixture
Concrete B: With admixture
(Source: http://www.rhein-
chemotechnik.com/en/products/concrete-
admixtures/for-concrete-precast-industry/concrete-
plasticizers.html)
From the photo shown above, it can be seen that concrete with added plasticizer
admixtures has a smoother surface. As for the types of pasticizer, polycarboxylate
ether works differently from the sulfonate-based plasticizers. It provides cement
dispersion by steric stabilization, where the sulfonate-based plasticizers provide
cement dispersion by electrostatic repulsion. Steric stabilization has a more powerful
effect and gives an improved workability retention to the cement mixture.
A B

4. 4.0 Accelerating admixtures
An accelerating admixture is used to accelerate the rate of setting and strength
development of concrete at an early stage. These admixtures function by interacting
with Tri-calcium silicate component of the cement, thus increasing the reaction
between cement and water. Accelerating admixtures are most effective at lower
temperature. Accelerating admixtures are also used for urgent concrete repairs and
in sea defense work to ensure early stiffening of concrete in the tidal zone(Dransfield,
2012).
Main Examples of Accelerating admixtures
 Calcium chlorides
 Sodium thiocyanate
 Calcium formate
 Calcium nitrate
Advantages Disadvantages
 Shortens the setting time of cement  Might cause discoloration
 Reduce segregation and increase
density and compressive strength
 Potential corrosion of reinforcement
 Reduce water requirements  Increase in drying shrinkage
Photo:
Concrete with discoloration (Source:
http://www.nrmca.org/converted_pdfs/cip_23.asp)
Accelerating admixtures, especially calcium chloride, which is one of the most
common used accelerating admixtures, will cause discoloration which darkens the
concrete as shown in the photo above.

5. References
1. University of Memphis. (n.d.). Design and Control of Concrete Mixture. Admixtures
for Concrete. Retrieved April 20, 2014 from
http://www.ce.memphis.edu/1101/notes/concrete/PCA_manual/Chap06.pdf
2. Dransfield, J. (2012). Admixture Technical Sheet –ATS 4 Accelerating admixtures.
[Website] Retrieved April 20, 2014 from
http://www.admixtures.org.uk/downloads/ATS%204%20Accelerating%20admixtures.
pdf
3. National Ready Mix Concrete Association. (2001). CIP15-Chemical Admixtures for
Concrete. [National Ready Mix Concrete Association] Retrieved April 20, 2014 from
http://www.nrmca.org/aboutconcrete/cips/15p.pdf
4. Research Designs & Standard Organisation Indian Railways. (n.d.) Guidelines on
use of Admixture in Concrete. [Research Designs & Standard Organisation]
Retrieved April 20, 2014 from
http://www.rdso.indianrailways.gov.in/uploads/files/1296815485110-page_3.pdf
5. America’s Cement ManufacturesTM
. (2014). Finishing Air-Entrained Concrete.
[Portland Cement Association] Retrieved April 20, 2014 from
http://www.cement.org/for-concrete-books-learning/concrete-
technology/concrete-construction/finishing-air-entrained-concrete
6. Kakkat Drugs & Chemical Co. (n.d.). Lignosulfonic Acid. [Kakkat Drugs &
Chemical Co.] Retrieved April 20, 2014 from http://www.indiamart.com/kakkat-
drugs-chemical/chemicals.html#lignosulfonic-acid
7. Rhein Chemotechnik. (n.d.). Concrete Plasticizers. [Rhein Chemotechnik]
Retrieved April 20, 2014 from http://www.rhein-
chemotechnik.com/en/products/concrete-admixtures/for-concrete-precast-
industry/concrete-plasticizers.html
8. National Ready Mix Concrete Association. (1993). Discoloration. [National Ready
Mix Concrete Association] Retrieved April 20, 2014 from
http://www.nrmca.org/converted_pdfs/cip_23.asp