Determination of air-void system and modified frost resistance number for freeze-thaw resistance evaluation of ternary blended concrete made of ordinary Portland cement/silica fume/class F fly ash

Use of fly ash (FA) in concrete subjected to freeze-thaw (F-T) cycles in a cold region has been limited because of its slow hydration and low scaling resistance. One of the solutions to increase the utilization of FA in this area may adopt ternary blended concrete to overcome the shortcoming of FA. In this paper, the F-T resistance of plain concrete, binary concrete, and ternary blended concrete mixtures made of ordinary portland cement (OPC), 5%-fixed silica fume (SF), and various Class F FA contents up to 45% as replacement of cement by weight were evaluated. Durability factor (DF), both frost resistance number (FRN) and modified FRN, and critical air void spacing factor (CAVSF) were determined to characterize the F-T resistance of all concrete mixtures. Except for non-air-entrained concrete containing OPC/5SF/15FA, air-entrained binary concretes containing OPC/0SF/35FA and OPC/0SF/45FA, and air-entrained ternary blended concrete containing OPC/5SF/45FA, all concretes had a good F-T resistance which exceeded DF of 60%. The critical air-void spacing factor for binary and ternary blended concretes for 60% DF was determined to be 198.2 μm and 305.2 μm, respectively. Moreover, ternary blended concretes resulted in higher FRN than plain and binary concrete mixtures. Finally, air voids under 300 μm size play a critical role in reducing the F-T damage of ternary concrete mixtures. Based on these results, it can be concluded that construction of the proper air-void system is required to ensure the F-T resistance of ternary blended concrete. Moreover, the modified FRN can be successfully used to evaluate the F-T resistance of ternary blended concrete.