Сement Mortars with Alkali-Free Accelerators under Test Conditions for Alkali-Silica Reactions

Abstract

The results of long-term and accelerated tests of cement–sand mortars with a reactive aggregate and additives Al₂(SO₄)₃ and Fe₂(SO₄)₃, carried out under the conditions of the corresponding standardized techniques, indicate that these additives suppress the development of destructive expansion deformations of mortars and concretes caused by alkali-silica reaction. In all samples of cement–sand mortars, after accelerated and long-term tests, destructive changes occurring with particles of reactive aggregate were noted. Ettringite was found in samples after long-term tests (its content is higher in samples with additives of aluminum and iron sulfates), whereas in samples subjected to accelerated tests in NaOH solution, ettringite rapidly decomposes with the formation of a hydrogarnet phase. The results of an energy dispersive microanalysis of an alkali-silicate hydrogel formed as a result of an alkali-silica reaction do not allow explaining the ability of aluminum and iron sulfates to suppress expansion deformations by their influence on the chemical composition of the hydrogel and, accordingly, on its destructive properties. It can be assumed that the presence in the samples of other phases (ettringite and hydrogarnet phase), the formation of which is promoted by additives, can have a restraining effect on the dynamics of the development of destructive expansion deformations.