For a long time aggregate have been considered as inert material but later on particularly. After 1940s it can clearly brought out that the aggregate not fully inert. Some of the aggregate content reactive silica which react with alkali present in cement. I.e sodium oxide and potassium oxide.

Factors promoting the alkali aggregate reaction.

1) High alkali content in cement.

2) Availability of moisture.

3) Optimum temperature condition.

4) Reactive type of aggregate.

High alkali content in cement.

1) The high alkali content in cement is one of the most important factor contributing to alkali aggregate reaction. Since the time of recognition to the importance of alkali aggregate reaction phenomena, a serious view has been taken on the alkali content of cement.

2) Many specification restrict the alkali content to less than 0.6% there total amount expressed as Na2O equivalent (Na2O + 0.658 K2O)

3) A cement meeting this specification is designated as a low alkali cement.field experience has never detect serious deterioration of concrete through the process of alkali aggregate reaction when cement content alkali less than 0.6%.

4) In exceptional cases however cement with even lower alkali content have cause objectionable expansion.

Availability of moisture

1) Progress of chemical reaction involving alkali aggregate reaction in concrete requires the presence of water it has been seen in the field and laboratory that lack of water greatly reduce this kind of deterioration.

2) Therefor it is pertinent to note that deterioration due to alkali aggregate reaction will not occur in the interior of the mass concrete.

A temperature condition

1) Temperature for the promotion of alkali aggregate reaction is in the range of 10 to 38oC.

2) If the temperature condition is more than or less than the above,it may not provide and ideal situation for the alkali aggregate reaction.

Control of alkali aggregate reaction.

Alkali aggregate reaction can be control by the following method :

1) Selection of non aggregate reaction.

2) By the use of low alkali cement.

3) By the use of collective admixture such as pozzolanas.

4) By controlling the void space in cement.

5) By controlling moisture condition and temperature.