Alkali silica and pozzolanic reactions in concrete. Part 2: Observations on expanded perlite aggregate concretes

Abstract Alkali silica and pozzolanic reactions are examined on expanded perlite aggregate concretes by means of length change mechanical strength, water porosity measurements and SEM observations. Some experimental supports are supplied for the hypothesis concerning the reaction mechanism which was presented in the first part of this study. It is indicated that, even under very unfavorable conditions, once the concrete is made from reactive aggregates or from pozzolanic materials there is always a small amount of alkali silicate gel produced which may cause a subsequent slight expansion of which the magnitude is a function of the mechanical strengths of the concrete. It is also shown that only the formation of alkali silicate gel which has a bigger volume than original minerals can cause expansion.