Freeze-thaw resistance of concrete containing azodicarbonamide expansive agent

Azodicarbonamide expansive agent (ADC) and air-entraining agent (AEA) have similarities in introducing pores into concrete and can both be applied in constructions served in severe cold environments. This paper in-vestigates the effect of ADC on the freeze-thaw resistance of concrete and compares the differences between ADC and AEA in the anti-freezing mechanism. The results show that ADC improves the freeze-thaw resistance of concrete, while its effect is weaker than that of AEA. The non-hydrophobic bubble shell formed by ADC cannot reduce the freezing temperature and delay freezing time as well as the shell consisted of hydrophobic calcium salt formed by AEA. A rosette-shaped pore structure and non-dense shell of air voids formed by ADC have both positive and negative effects on freeze-thaw resistance: they release hydraulic pressure to improve freezing resistance, while they reduce the suction force resulting in weakened freezing resistance. The air-void spacing factor instead of the air content at fresh stage is more suitable for assessing the freeze-thaw resistance of concrete with ADC.