A comparison of potential healing agents for vascular-based self-healing concrete

Vascular self-healing concrete is an innovative technology that can potentially improve the durability and longevity of concrete structures. However, limited research is available concerning this type of self-healing compared to intrinsic or capsule-based healing. As the rheology and curing properties of a healing agent can dictate the optimal design configuration of a vascular network, a series of testing procedures for evaluating healing agents is further explored. In this study, the suitability of various commercially available healing agents is considered using a vascular network system in mechanical loading and water absorption test set-ups. In this particular configuration, high sealing efficiencies were obtained for most of the healing agents used, and the polyurethanes and epoxy resin that were studied showed high load regain values. This work provides a testing methodology to select a healing agent in terms of its mechanical load regain, sealing efficiency, rheology, and curing properties, and can be used to determine a suitable healing agent for vascular healing applications

Repair of concrete in environments with chlorides or subjected to freeze-thaw scaling

Crack formation further decreases the durability of structures when chloride ions associated with freezing temperatures are present. Therefore, preventing the entry of aggressiveness is imperative to guarantee the service life. Repair actions might recover the liquid-tightness when cracks occur. A water repellent agent (WRA) and a sodium silicate (SS) solution were applied to self-repair cracks in the current research. The repair occurred by manual injection of cracks to obtain a proof-of-concept for the possible self-healing efficiency. Two extreme conditions have been assessed after the healing period, the first referring to continuous immersion in a chloride solution, and the second applying freeze-thaw conditions with de-icing salts. Chloride ingress was evaluated through the colour change boundary test. In addition, optical microscopy analysis was used to measure the crack width and to observe differences before and after exposure. SS prevented the chloride ingress through the crack in both conditions. However, the method used to verify chloride ingress did not give consistent results for the WRA due to its hydrophobicity. Microscopic analysis showed that both agents could avoid chloride ingress in the cracks. For the samples exposed to freeze-thaw cycles, only chloride ingress measurement could indicate the healing performance as the scaling destroyed the surface

Comparison of different types of self-healing concrete under extreme conditions

Extreme environments are aggressive for concrete structures, hence a performance-based design is crucial to guarantee the durability during the service life. Nonetheless, there is a knowledge gap regarding the influence of cracks on standard and self-healing concrete. This research focuses on monitoring cracked self-healing concrete with two commercial healing agents: a bacteria-based healing agent (BAS) and a crystalline admixture (CA). After crack formation and a healing process of three months in wet/dry conditions (4 days/3 days), several extreme conditions were considered: (1) submerged in artificial seawater, (2) submerged in a solution with 33 g/L sodium chloride and (3) freeze-thaw (FT) cycling with de-icing salts. Microscopic images were used to quantify the healing efficiency of the two different healing agents, while chloride ingress and scaling were measured to determine durability. The results of the microscopic measurements indicated significant healing efficiency for both healing agents after the healing regime reaching 72% for CA, and 67% for BAS. After exposure to a marine environment, this efficiency increased to 95% and 92%, respectively. The uncracked BAS samples achieved a scaling reduction of 93% under FT exposure relative to the uncracked REF samples, while this was 49% for the CA samples. In cracked samples, scaling was reduced by 50% for BAS and 24% for CA, relative to the cracked REF samples. In all tested conditions, the BAS samples partially prevented the chloride ingress through the crack, while CA samples showed a great reduction. Overall, both healing agents reduced the degradation and could decrease the chloride ingress