Repeatable self-healing with carbon sequestration function using ammonium bicarbonate

Repeatable self-healing at the same cracking site is one of the essential issues in self-healing concrete. The inorganic admixture ammonium bicarbonate (NH4HCO3) was proposed as the primary healing agent in this study to achieve repeatable self-healing. Among ammonium carbamate (NH2COONH4), NH4HCO3, ammonium acetate (CH3COONH4) and calcium hydroxide (Ca(OH)2), the molar ratio of precipitation reaction and the effect of calcium extraction were determined. Whether before or after the self-healing, ammonia water (NH3·H2O) invariably exists in the products and will be carbonised to regenerate NH4HCO3, which was verified by Fourier transform infrared (FT-IR). The proposed self-healing solution achieves a two-in-one strategy for calcium extraction and carbon sequestration in response to the global strategy for carbon neutrality. Self-healing experiments have been performed. The results suggested that the healing efficiency of the crack area of the tri-component (NH2COONH4, NH4HCO3 and CH3COONH4) is up to five times higher than that of the control group. Three cycles of self-healing in the simulated system and actual crack environment concluded that the regeneration potential of NH4HCO3 could be enhanced after the completion of more cyclic self-healing processes due to the increasing amount of NH3·H2O at the same cracking site.