Admixtures in Concrete

Admixtures in Concrete

admixture in concrete

Admixtures are those ingredients in concrete other than portland cement, water, and aggregates that are added to the mixture immediately before or during mixing (Fig. 6-1). Admixtures can be classified by function as follows:

 

Admixtures in Concrete

Air-entraining admixtures
Water-reducing admixtures
Plasticizers
Accelerating admixtures
Retarding admixtures
Hydration-control admixtures
Corrosion inhibitors
Shrinkage reducers

Air-entraining admixture in Concrete

Air-entraining admixtures are used to purposely introduce
and stabilize microscopic air bubbles in concrete. Air-
entrainment will dramatically improve the durability of
concrete exposed to cycles of freezing and thawing (Fig.
6-2). Entrained air greatly improves concrete’s resistance to
surface scaling caused by chemical deicers (Fig. 6-3). Fur-
thermore, the workability of fresh concrete is improved
significantly, and segregation and bleeding are reduced or
eliminated.
Air-entrained concrete contains minute air bubbles
that are distributed uniformly throughout the cement
paste. Entrained air can be produced in concrete by use of
an air-entraining cement, by introduction of an air-
entraining admixture, or by a combination of both meth-
ods. An air-entraining cement is a portland cement with
an air-entraining addition interground with the clinker
during manufacture. An air-entraining admixture, on the
other hand, is added directly to the concrete materials
either before or during mixing.
The primary ingredients used in air-entraining ad-
mixtures are listed in Table 6-1. Specifications and meth-
ods of testing air-entraining admixtures are given in

[gview file=”http://www.ce.memphis.edu/1101/notes/concrete/PCA_manual/Chap06.pdf” profile=”14″]
  •  
  •  
  •  
  •  
  •  
  •  
  •  
  •  
  •  
  •