Dynamic behavior and microstructural mechanisms of nano–MgO modified cement–stabilized dredged sludge under cyclic loading

Large volumes of dredged sludge (DS) are generated in waterway and port engineering, yet its direct utilization is limited by high water content and poor mechanical properties. Cement stabilization improves strength but fails to ensure long–term stability under cyclic loading, where stiffness degradation and cumulative deformation remain critical issues. This study evaluates the dynamic performance of nano–magnesium oxide (NM) modified cement–stabilized dredged sludge (CDS) through unconfined compressive strength (UCS) and cyclic triaxial tests, supported by X–ray diffraction (XRD) and scanning electron microscopy (SEM). Results show that incorporating 2% NM increases the 28–day UCS by ∼97% compared with cement–only samples, reduces cumulative plastic strain by nearly two–thirds, and delays dynamic modulus degradation by more than 20%. A dual mechanism of “σ3 enhancement–σd amplification” is proposed to describe the confining pressure effect. Microstructural analyses reveal that NM promotes the formation of magnesium silicate hydrate (M–S–H) and Mg(OH)2 gels while inhibiting AFt, leading to a denser pore structure and improved fatigue resistance. The findings provide mechanistic understanding and practical guidance for the sustainable reuse of dredged sludge in coastal road and railway subgrades subjected to traffic– and wave–induced cyclic loads.