Whether mixed using polypropylene fiber and air-entraining agent can further improve the macro and micro durability of concrete in cold and sulfate regions

Abstract

To explore the influence of mixed using polypropylene fiber (PF) and air entraining agent (AEA) on the durability of concrete in cold and sulfate regions, compressive strength, mass change, ultrasonic velocity and interface transition zone (ITZ) of samples with different admixtures were studied. In addition, the interaction between these two additives was explored. Results indicated that both PF and AEA can enhance the durability of concrete under freeze-thaw cycles and sulfate attack. Among which, AEA was more effective. However, mixed using these two additives cannot further improve the durability of concrete. On the macro level, samples with the best dosage of PF or AEA can resist 240 or more than 300 freeze-thaw cycles, respectively. Samples added both PF and AEA (AEPF) can also resist more than 300 cycles, but their strength and compactness were worse than that of the samples only added AEA (AE2). On the micro level, interpenetrating cracks formed at the ITZ of PF modified samples. Large numbers of ettringite generated, filled the cracks and presented a specific growth direction. Only some randomly distributed cracks formed at the ITZ of AE2 and AEPF. Ettringite also generated in these cacks but had no specific growth direction. However, more crystals were observed at the ITZ of AEPF compared with AE2. The interaction indicated that PF and AEA suppressed each other. PF reduced the proportion of surfactants responded for the formation and stability of air voids in AEA, and AEA reduced the connection effect between the fiber and mortar. These studies were meaningful for exploring and enhancing the durability of concrete in cold and sulfate regions.