Using compressive strength and mass change to verify the calcium oxychloride threshold in cementitious pastes with fly ash

Abstract Calcium oxychloride (CAOXY) formation is a deterioration mechanism known to cause joint damage in concrete pavements. The accepted CAOXY mitigation threshold in paste is 15 g/100 g paste; however, this limit was developed using flexural strength testing of pastes. This investigation seeks to verify this threshold using compressive strength and mass change testing. Cementitious pastes were cast with portland cement and fly ash (up to 50% mass). Specimens were stored in a 30% mass CaCl2 at 5 °C to accelerate deterioration. Visual observations, thermogravimetric analysis, low-temperature differential scanning calorimetry, mass change, and compressive strength results were recorded. Partial replacement of cement with fly ash reduces the Ca(OH)2, CAOXY, and damage levels. Using mass change, a threshold at which no damage occurs is established at 20 g/100 g paste, indicating that the current threshold is conservative. For compressive strength, while increasing the amount of fly ash reduces damage, damage is noted in all specimens tested; however, strength loss noted in this work is similar to the research which established the current threshold. Therefore, the compressive strength results generally validate the CAOXY threshold level of 15 g/100 g paste. Careful correlations between paste and concrete damage are needed in order to further verify the threshold value.