Alkali Aggregate Reaction(AAR) & Fineness Modulus OF Aggregate

Alkali-Aggregate Reaction(AAR) :

It is the reaction between active silica constituents of the aggregate and alkalis i.e.Na₂O  & K₂O present in the cement. The factors promoting the alkali-aggregate reaction are the reactive type of aggregate, high alkali content in cement, availability of moisture content and optimum temperature condition.

Fineness Modulus :

It is a numerical index of fineness of sand presenting the distribution of particles of sand in mass. It consists in dividing a sample of sand into fractions of different a sample of sand into a fraction of different sizes by sieving through a set of standard test sieve taken in order. The material retained on each sieve represents the fraction of aggregate coarser then sieve but finer than the sieve above. The sum of cumulative % retained on sieve divided by 100 gives fineness modulus.