Assessing Potential Reactivity of Aggregates in Presence of Potassium Acetate Deicer

The standard ASTM C1260 and ASTM C1293 test methods focus on identifying aggregate reactivity in the presence of alkali hydroxides. The sensitivity of these test methods to assess aggregate reactivity in the presence of deicing chemicals is unknown. Preliminary efforts to develop a test method to identify aggregate reactivity in the presence of deicing chemicals yielded a mortar bar test (EB-70 test) based on soaking the mortar bars containing the suspect aggregates in a 6.4 molar potassium acetate (6.4 M KAc) deicer solution, instead of a 1 normal sodium hydroxide (1 N NaOH) solution, as in the standard ASTM C1260 test. The EB-70 test method was effective in identifying highly reactive aggregates but erratic in assessing moderate, slowly reactive aggregates. Deficiencies in that method were attributed to the lack of a precise understanding of the mechanisms involved in high pH jump observed on interaction of KAc with alkali hydroxides and calcium hydroxide. The knowledge gained in recent studies in understanding the mechanism has provided a sound basis for making some modifications to the EB-70 test method. A revised EB-70 test method is presented: it uses a 1 N NaOH and 3 M KAc deicer as its soak solution. Evidence from testing 31 different aggregates with a range of aggregate mineralogy and reactivity indicated that the revised method was effective in characterizing a range of aggregate reactivity in the presence of deicing chemicals. Limited studies were conducted to evaluate a low-lime fly ash (Class F) in mitigating mortar bar expansions in the EB-70 test method. A low-lime fly ash was effective in controlling mortar bar expansion in the revised EB-70 test method.