Expansive deformation and mechanical properties of cementitious materials with azodicarbonamide expansive agent: influencing factors and mechanisms

Applying plastic expansive agent to solve the debonding and non-compacting problem in sealed structures (e.g. concrete-filled steel tube) caused by the deformation of concrete has become an important method. In this study, the effect of azodicarbonamide expansive agent (ADC) on the deformation, mechanical properties, hydration process, and pore structure of cement pastes and concrete was investigated. The results show that the low static yield stress and viscosity promote the formation and growth of bubbles, which are disadvantageous for their stabilization. The ADC reaction rate increases with the elevated temperature, which benefits for shortening the time to mitigate shrinkage. ADC has a limited effect on cement hydration but remarkably alters the pore structure. The balance between deformation and strength is considered to be the important criteria for determining the optimal dosage of ADC.