Experimental evaluation of durability enhancement in nano-silica modified plastic concrete: Physical and impermeability properties under long-term seepage-dissolution action

This study investigates the durability evolution of nano-silica (NS) modified plastic concrete (NSPC) under long-term seepage-dissolution conditions. Nine groups of NSPC with varying NS dosages were exposed to an accelerated dissolution environment (0.2 MPa seepage pressure and 6 mol/L NH₄Cl solution) to evaluate their mass loss rate, Ca 2+ leaching amount, porosity, permeability coefficient, microstructure, and phase composition. The results reveal the mechanism by which NS suppresses the degradation of physical and impermeability properties of plastic concrete during prolonged seepage-dissolution processes. The results indicate that with increasing dissolution duration, the mass loss rate, Ca 2+ leaching amount, porosity, and permeability coefficient exhibit a time-dependent trend characterized by an initial rapid increase followed by a gradual slowdown and eventual stabilization. Among all tested specimens, NSPC containing 3% NS exhibited the best durability, whereas excessive NS (e.g., 6%) resulted in reduced durability. Further scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analyses revealed the modification mechanism of NS: an appropriate NS content fills capillary and micro-pores, while the pozzolanic reaction transforms soluble calcium hydroxide (CH) into more stable calcium silicate hydrate (C-S-H). This process significantly increases the matrix density and enhances the dissolution resistance of the material. Conversely, excessive NS tends to agglomerate, forming micron-scale defects that offset its beneficial effects. The findings of this study provide valuable guidance for material design and durability improvement in plastic concrete underground impermeable structures. • This study investigates the physical, permeability, and microstructural properties of NSPC subjected to seepage-dissolution processes. • This study systematically examines the influence of NS content on the durability performance of NSPC under seepage-dissolution conditions. • The study identifies an optimal NS dosage of 3%, which enhances the durability of plastic concrete and reduces dissolution. • The findings reveal the mechanisms by which NS inhibits seepage-dissolution-induced deterioration in plastic concrete at both the macro- and micro-scales.