The Effect of Sodium Chloride as an External Alkali Source for Alkali-Silica Reaction in Aged Concrete

Alkali-silica reaction (ASR) is a deterioration mechanism in concrete through which reactive silica from the aggregates react with alkalis in the pore solution to form an expansive, hygroscopic gel, producing internal pressures within the concrete pores. The expansion caused by ASR may continue and reach a plateau upon full consumption of the reactants; alkalis or silica. Concrete expansion and damage caused by ASR may be promoted when exposed to an external alkali source. Sodium chloride (NaCl), commonly applied to concrete as a deicing salt, may act as an external alkali source and promote ASR-induced damage. This paper investigates the effects of NaCl on aged concrete, which has previously reached an expansion plateau caused by ASR. The expansions of aged concrete prisms, containing different aggregate and cementitious materials, exposed to NaCl solution were examined. Considerable expansions after NaCl exposure were observed in aged concrete made with non-boosted alkalis (0.99% \({{\text{Na}}}_{2}{{\text{O}}}_{{\text{e}}}\) per mass of Portland cement) in comparison to concrete with boosted alkalis (1.25% \({{\text{Na}}}_{2}{{\text{O}}}_{{\text{e}}})\), likely due to the presence of locations of unreacted silica. Moreover, aggregates of high reactivity provided greater late ASR expansions. The use of supplementary cementitious material was effective in limiting further ASR-induced expansion within the first year of testing.