Evolution of Pore Structure and Modification Mechanisms in Geopolymer-Stabilized Dredged Silt under Sulfate Attack: Low-Field NMR Study

Abstract

The use of fly ash-ground granulated blast furnace slag (FA-GGBS)-based geopolymer to stabilize dredged silt not only promotes the resource utilization of dredged silt, FA, and GGBS but also helps reduce cement consumption. In this study, dredged silt stabilized with FA-GGBS-based geopolymer was modified using nano - SiO 2 and LSS-1 ions. All specimens underwent strength and water stability tests, along with X-ray diffraction (XRD), scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS), and nuclear magnetic resonance (NMR) analyses during Na 2 SO 4 erosion. The mechanisms of modification by nano -SiO 2 and LSS-1, as well as the erosion mechanisms of Na 2 SO 4 , were investigated from a microstructural perspective. The results indicate that (1) the incorporation of nano -SiO 2 and LSS-1 improved strength, water stability, and sulfate erosion resistance, (2) LSS-1 ions promoted ion exchange, reduced the thickness of the diffuse double layer and interparticle repulsive forces, and facilitated the formation of larger soil aggregates, (3) the addition of LSS-1 and nano - SiO 2 enhanced geopolymerization, leading to increased formation of geopolymeric gels that filled pores and microcracks, (4) during an Na 2 SO 4 attack, SO 4 2− ions infiltrated the soil and reacted with C─(A)─S─H gels, forming expansive gypsum and ettringite; when the stress from these expansion products exceeded the tensile strength of the geopolymer matrix, cracking and structural failure occurred, and (5) the addition of nano - SiO 2 and LSS-1 limited the ingress of Na 2 SO 4 solution into the soil, reduced the formation of expansive corrosion products, delayed cracking, and thereby enhanced overall durability.