Activated sludge (AS) offers great potential for resource recovery considering its high organic and nutrient content. However, low recovery efficiency and high costs are directing the focus toward the high-valuable resource recovery. This study extracted 71.5 ± 5.9 mg/g VSS of alginate-like exopolysaccharides from AS (ALE/AS) and applied it to mortar as a novel biopolymer agent for crack self-healing. With a mortar crack of 120 μm, addition of 0.5 wt% ALE/AS yielded a high crack closure ratio of 86.5 % within 28 days. In comparison to commercial healing agents, marginal flexural strength reduction with ALE/AS addition (17.9 % vs 30.2–50.5 %) was demonstrated. The abundance of COO⁻ group in GG blocks of ALE/AS resulted in a higher cross-link capacity with Ca²⁺, while the reduction of hydrophilic residues (e.g., COO⁻ and OH) after complexation engendered a lower swelling capacity, which facilitated self-healing and flexural strength maintenance. Molecular dynamics (MD) revealed that lower Ca²⁺ diffusivity, arising from the stronger electrostatic interactions between the COO⁻ groups and Ca²⁺, resulted in a high Ca²⁺ concentration around the cracks, leading to CaCO₃ deposition and healed cracks. The outcomes of this study provided light on ALE-based mortar crack healing and presented a possibility for multi-level AS resource recovery.