Foundation, Concrete and Earthquake Engineering

How can Alkali-Aggregate Reaction of Concrete be Controlled with Admixtures?

Dear reader we have discussed about concrete cracking due to alkali-aggregate reaction. The product of this reaction is alkali-silica gel which is formed at location of reactive silica and takes its place in weak planes and surfaces of aggregate particles. The consequence of this is destroying bonds between aggregate particles and hydrated paste around them.

Different studies and report also available on the reduction of alkali-aggregate reaction under application of pozzolanas(Stanton 1950). The materials and admixtures that are used to reduce expansion potential of concrete due to ARS(alkali-silica reaction) are listed below:

Concrete cracking due to expansion(alkali-aggregate reaction)
 a. Soluble lithium salt

b. Soluble barium salt

c. Some types of air-entraining admixtures

d. Some types of water-reducing admixture

e. Some retarding admixtures

It is observed in laboratory that 1% inclusion of lithium salts results significant reduction of expansion. The same result is also found with inclusion of (2-7) % of some barium salts.

Now, have there a molar ratio that nullifies alkali-silica reaction?

Formation of alkali-silica gel in concrete
Yes, there have a particular molar ratio that can totally suppress expansion due to such reaction. It was reported (Stark, Ong 1993) that when molar ratio reaches 0.67 the expansion is totally suppressed. Inclusion 1% lithium salts and slight higher concentration of barium salts in concrete results significant reduction of expansion due to alkali-aggregate reaction.

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