Abstract: To solve the issues of insufficient early strength of cement solidified muddy clay and high pollution, high energy consumption and high cost induced by the application of cement binder, the one-part slag-fly ash (SL-FA) based geopolymer was adopted as the binder to solidify the muddy clay. The effects of the ratio of slag to fly ash in silicon-aluminum (Si-Al) raw materials, the ratio of solid activator to Si-Al raw material and the ratio of water to binder on the mechanical properties of geopolymer solidified muddy clay were studied through the unconfined compression test. The micro-analysis (i.e., scanning electron microscope and energy dispersive spectrometer) was also conducted to investigate the development of the microstructure of the muddy clay solidified by the one-part SL-FA based geopolymer. The experimental results showed that when the Si-Al raw material was composed of 90% slag and 10% fly ash by mass, the mass ratio of alkali activator to Si-Al raw material was 0.15, and the mass ratio of water to binder was 0.7, the 14-day compressive strength of the geopolymer solidified muddy clay could reach 1.5 MPa. It was also found that the main hydration products of the slag-fly ash based geopolymer were amorphous hydrated calcium silicate hydrates and hydrated calcium aluminate hydrates, which is the main reason for the improvement of the compressive strength of solidified clay. The micro-structure of geopolymer solidified muddy clay was connected by hydrated calcium silicate hydrates and calcium aluminate hydrates. The results provide a certain theoretical basis for the practical application of one-part slag-fly ash based geopolymer as the soil binder in the improvement of muddy clay.

Key words: geopolymer, slag, fly ash, unconfined compressive strength, micro-analysis