Repeatable self-healing with carbon sequestration function using ammonium bicarbonate.

• NH 4 HCO 3 possesses the capacity of extraction and precipitation towards calcium. • The regeneration of NH 4 HCO 3 realizes the catalyst effect and continuous supply. • The regeneration potential of NH 4 HCO 3 increased with the increase of NH 3 ·H 2 O. Repeatable self-healing at the same cracking site is one of the essential issues in self-healing concrete. The inorganic admixture ammonium bicarbonate (NH 4 HCO 3) was proposed as the primary healing agent in this study to achieve repeatable self-healing. Among ammonium carbamate (NH 2 COONH 4), NH 4 HCO 3 , ammonium acetate (CH 3 COONH 4) 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 (NH 3 ·H 2 O) invariably exists in the products and will be carbonised to regenerate NH 4 HCO 3 , 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 (NH 2 COONH 4 , NH 4 HCO 3 and CH 3 COONH 4) 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 NH 4 HCO 3 could be enhanced after the completion of more cyclic self-healing processes due to the increasing amount of NH 3 ·H 2 O at the same cracking site. [ABSTRACT FROM AUTHOR]