Mechanical properties and micro-mechanisms of geopolymer solidified salinized loess

Abstract

Salinized loess exhibits poor engineering properties, including low strength, salt migration, and instability, due to the combined characteristics of loess and saline soil. This poses serious threats to the safety and stability of buildings, roads, and other infrastructure. To address this issue, this study aims to solidify salinized loess using geopolymer produced through alkali activation of industrial waste, including slag powder and fly ash. An orthogonal experimental design was used to systematically investigate the mechanical properties, microstructural characteristics, and solidification mechanism of geopolymer solidified salinized loess. The tests included unconfined compressive strength (UCS), direct shear, pH, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) to evaluate the influences of different factors on the solidification effect. The results showed that the sodium silicate solution modulus was the primary factor affecting the strength of solidified salinized loess, followed by the amounts of fly ash and slag powder. The Baumé degree (°Bé) had the least impact. Under the optimal conditions (1 modulus, 35 °Bé, slag powder and fly ash ratio of 1:0), the UCS of the sample at 28 days reached 3204.06 kPa, which increased by 16.32 times compared with the unsolidified sample. Lowering the modulus and increasing the proportion of slag powder and the Baumé degree increased the sample pH. Micro-analysis revealed that the strength increase was mainly due to the bonding of soil particles by gel substances ($C-S-H$, $N-A-S-H$, and$C-A-S-H$) formed during alkali activation, as well as the filling effect of unreacted slag powder and fly ash. The findings of this study provide valuable theoretical and practical insights for treating salinized loess in engineering, offering essential references for optimizing geopolymer solidifier ratios.