• MICP grouting significantly reduces pore size and connectivity in reef limestone, transforming the pore network from a loose, connected type to a dense, isolated one.
• The treatment enhances mechanical properties, with elastic modulus increasing from 3.27 GPa to 6.21 GPa and peak strength approximately doubling.
• Failure mode transitions from brittle to brittle–ductile, accompanied by a shift in acoustic emission energy and frequency characteristics.
• A novel constitutive model incorporating a structural densification factor effectively captures the MICP-induced strengthening behavior.