Potential for inducing and accelerating alkali silica reaction in concretes exposed to potassium acetate deicer: Laboratory and field studies

Alkali acetate based deicers have been found to cause significant distress in airfield concrete pavements, allegedly by a mechanism similar to conventional Alkali-Silica Reaction (ASR). Prior research indicated that aggregates having a history of being susceptible to ASR may undergo active deterioration when exposed to alkali acetate deicers. Further, deicer exposure was suspected to cause changes in the CSH gel composition by formation of secondary reaction products. Preliminary laboratory investigations had shown that the conditions conducive to triggering ASR could mainly be attributed to a drastic increase (jump) in the pH of the deicing solution, which occurs when it comes in contact with calcium hydroxide. The focus of this study was to further investigate the interaction between potassium acetate deicer solution and concrete components in an attempt to gain a better perspective of the reaction mechanism and its relevance with respect to the distress observed in the field. Thus, the broad objectives of this study included a detailed laboratory-based investigation into the influence of deicers on concrete microstructure and also a forensic investigation of cores collected from selected airports whose deicing operations predominantly involved application of potassium acetate deicer. The fundamental part of the investigation involved utilizing techniques such as pore solution analysis and SEM-EDX to study the deleterious interaction of potassium acetate deicer solution on cementitious systems. In addition, experiments were conducted to verify the “pH jump” phenomenon, monitor mortar bar expansions and to study the influence of the deicer solution on the stability of siliceous aggregates. Based on the results of comparative experiments performed using reactive as well as non-reactive aggregates, it was concluded that in accelerated laboratory conditions the potassium acetate deicer could induce ASR in test specimens containing reactive aggregates. Further, microscopic evaluation revealed the formation of a calcium-bearing potassium sulfate phase as a result of the chemical interaction between potassium acetate deicer and hydrated cement paste. The forensic investigation component of the study comprised of a thorough microscopic investigation of field cores and determination of the profile of deicer penetration into the pavement. The results indicated more or less uniform level of damage throughout the depth of the pavement with no appreciable penetration of the deicer into the pavement. Consequently, this part of the study did not yield sufficient evidence to confirm the role of the deicer in inducing or heightening damage due to ASR in the pavement