Effect of aluminum sulfate on alkali-silica expansion of cement slurry compositions in solutions of sodium salts

The results of comparative tests of cement-sand mortars with a reactive aggregate in the solutions of sodium hydroxide (NaOH) and sodium salts (sulfate, chloride and nitrate) under conditions close to the accelerated procedure in accordance with GOST 8269.0 are presented in the paper. Both in salt solutions and solutions of NaOH, the samples of cement-sand mortars expand because of alkali-silica reaction, but the values of the strains towards the end of testing depend on the type of salt anion. In the case of solutions of NaCl and NaNO3, deformations reach the values comparable to those in conditions of NaOH solution at the end of the test, whereas in the sodium sulfate (Na2SO4) solution the expansion significantly exceeds the values for NaOH due to the additional input from ettringite crystallization. The addition of aluminum sulfate — Al2(SO4)3 — slows down the expansion of cement-sand samples both in NaOH solution and in solutions of sodium salts. At the end of the tests, the deformations of the samples with the additive were 2.5—3.0 times lower than those of additive-free samples exposed to the similar conditions.
Author: A.S. Brykov, N.S. Paritskaya

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