Rapid self-sealing of macro cracks of cementitious composites by in-situ alginate crosslinking

Despite the development of several self-healing concrete techniques, only micro cracks can be effectively self-repaired. To achieve self-healing of macro cracks (>1 mm), a strategy by in-situ calcium alginate crosslinking within cracks was proposed herein. This strategy was accomplished by encapsulating sodium alginate in polyethylene glycol granules coated with epoxy resin and calcium sulphoaluminate cement as protective shells. The capsules can release alginates and leach calcium in water once broken and subsequently the gelation can be conducted, thereby generating hydrogels. By incorporating the capsules in mortar specimens, hydrogels were successfully formed through calcium alginate crosslinking after cracking, which led to closures of 1–4 mm wide cracks and significant reduction of water permeability mainly in 1 day. The crack sealing due to crosslinking generation was further simulated by a modified model in terms of hydrogel volume growth and the predicted crack sealing evolutions were consistent with the experimental results.