Efficacy of Aluminum Hydroxides as Inhibitors of Alkali-Silica Reactions

Abstract

A comparative study of amorphous and crystalline forms of commercial aluminum hydroxides as inhibitors of alkali silica reactions in Portland cement mortars has been performed. It was found that at dosages of 1% to 3%, amorphous aluminum hydroxide can efficiently inhibit alkali-silica expansion of Portland cement compositions. High inhibiting activity of amorphous Al(OH) 3 additives may be explained by their ability to actively bind Ca(OH) 2 formed by the hy dration of silicate phases of cement, to form ettringite (with participation of gypsum). Crystalline Al(OH) 3 additives that do not possess the ability to interact with Ca(OH) 2 even after additional grinding, however, demonstrate week proper ties to inhibit alkali-silica expansion. This may indicate that the inhibitory effect of Al(OH) 3 at least — partly, may be given by its influence on the concentration of Al 3+ ions in the pore solution. Some expansion of the samples with ad mixtures of Al(OH) 3 observed during the alkaline expansion accelerated test procedure is not associated with the forma tion of ettringite and is only due to alkali-silicate reactions.