Freeze-thaw resistance of concrete containing azodicarbonamide expansive agent

Abstract

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 investigates 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.