Transformations in cementitious compositions with alkali-free accelerators during accelerated alkali reactivity tests

The paper describes phase-chemical transformations in cement pastes and cement-sand mortars with the addition of aluminum and iron sulfates in accelerated tests of the effects of alkaline environment according to GOST 8269.0–97. It was established that sulfoaluminate phases (ettringite and calcium monosulfoaluminate) formed in the pastes and mortars in the beginning of the tests, disintegrate almost immediately after the samples are placed in a hot NaOH solution with the formation of a hydrogarnet phase. After testing all samples of cement-sand mortars (additive-free and with sulfate additives) showed destructive changes in the particles of the reactive aggregate, but the linear deformations of the samples with additives were 5-10 times lower than in additive-free samples. It is possible that lower deterioration due to alkali-silica reaction (ASR) in the presence of aluminum and iron sulfates is due to the influence of the latter on the phase composition of the samples and on the chemical composition of the alkali-silica hydrogel formed as a result of the ASR and, as a consequence, a decrease in its destructive properties.

Author: A.S. Brykov, M.Ye. Voronkov, N.S. Paritskaya

Section: Science and production

Keywords: Portland cement, alkali-free accelerators, alkali-silica reaction, ASR, phase conversions.