Abstract: To enhance the self-healing capability of cracked cementitious materials while promoting CO₂ sequestration, this study proposes a carbonation curing-assisted self-healing strategy and applies it to alkali-sulfate co-activated mortar prepared from multiple industrial solid wastes. Pre-cracked specimens were subjected to either standard curing and carbonation curing. Hydration heat test and X-ray computed tomography were used to investigate the hydration kinetics under carbonation conditions. A numerical model was established to quantify the respective contributions of carbonation and secondary hydration during the self-healing process. The results demonstrated that carbonation curing significantly enhanced crack closure by promoting calcite precipitation in cracks, particularly for cracks with initial widths below 300 μm. After 28 d of carbonation curing, the compressive strength recovery ratio of the specimens reached 81.5%−94.2%, representing an approximately 9.5% increase compared with the standard-curing group. Although high CO₂ concentration partially inhibited secondary hydration at the early stage by competitively consuming Ca²⁺, carbonate precipitation and hydrates coexisted to form a dense healing structure. The incorporation of desulfurization gypsum further enhanced both carbonation and hydration reactions, leading to an increased cumulative heat release. Crack healing in the near-surface region was primarily governed by carbonation, where secondary hydration gradually became the dominant healing mechanism with increasing crack depth. The synergistic effects of calcium silicate hydrates (C−S−H), ettringite, and calcite not only promoted crack closure but also improved the surface integrity of the healed cracks, resulting in a relatively stable crack depth healing ratio of 50%−80%. These findings provided new insights and theoretical guidance into sustainable self-healing strategies for alkali-sulfate co-activated materials under carbonation curing conditions.