Development and evaluation of NO₂-– layered double hydroxides self-healing microcapsules for corrosion protection in cementitious composites

This study aims to synthesize a non-toxic, highly stable self-healing microcapsule and investigate its corrosion inhibition effect and crack repair performance in cementitious composites. Functionalized microcapsules(TO/SA microcapsules) were prepared via the sharp-hole-solid bath method using tung oil (TO) as the core and sodium alginate (SA) and NO₂ - -layered double hydroxides (LDHs) as hybrid wall materials. The microcapsules were characterized for their thermal stability, dissolvability, and corrosion inhibition capacity for steel bars in simulated pore solution. Their effect on the self-healing properties of cementitious composites was assessed by measuring the compressive strength recovery and crack healing rate of mortar specimens under dry curing, dry-wet cycling, and water curing conditions. The repair mechanism was further elucidated through microscopic analysis. Results indicated that the prepared microcapsules exhibited excellent thermal stability in cementitious environments. The cross-linking between SA and Ca²⁺ effectively suppressed excessive microcapsule swelling. The microcapsules' chloride ion adsorption capacity was 40 % higher than that of pure NO₂ - -LDHs, and their corrosion inhibition efficiency for steel bars reached up to 94.46 %. Image binarization analysis revealed that incorporating 2 % microcapsules significantly enhanced the strength recovery rate of cracked specimens and effectively sealed cracks through the autoxidative hardening of TO, secondary hydration of unhydrated cement, and calcium carbonate crystal deposition. Under dry curing conditions, the maximum strength recovery rate reached 78 %, while a crack healing rate of 96.95 % was achieved under water curing conditions. This study provides a valuable reference for developing high-efficiency self-healing materials suitable for reinforced concrete structures in harsh environments. • Fabrication of tung oil/sodium alginate microcapsules containing NO2 - - layered double hydroxides via the orifice solid bath. • TO/SA microcapsules effectively reduce the corrosion current density of steel reinforcement to achieve corrosion inhibiti. • TO/SA microcapsules can enhance the strength recovery rate of cracked cementitious composites and seal the cracks.