Strength and its microstructure evolution of GGBS-FA geopolymer mortar under seawater

In this study, ground granulated blast-furnace slag (GGBS) and fly ash (FA) were used as binders, while NaOH (NH) and Na 2 SiO 3 (NS) served as alkali activators. Seawater (SW) was used instead of freshwater (FW) to develop a SW-GGBS-FA geopolymer for solidifying sandy soils. Geopolymer mortar specimens were tested for unconfined compressive strength (UCS) after being curing at room temperature. The results showed that the early strength of the seawater group specimens increased slowly less than that of the freshwater group specimens, while the late strength was 1.16 times higher than that of the freshwater group specimens. Factors including seawater salinity (SS), the GGBS/FA ratio, curing agent (CA) content, and the NH/ NS ratio were examined in this experiment. The results showed that the strength of the specimens was higher for SS of 1.2 %, G90:F10, CA content of 15 %, activator content was 15 %, and NH: NS of 50:50. The pore structure of the mortar specimens was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and computerized tomography (CT), revealing the mechanisms by which various factors influenced the microstructure. XRD indicated that SW-GGBS-FA geopolymer mortar newly produced Friedel salt and calcium silicate sulfate hydrate (C-S-S-H). The microstructures observed by CT and SEM showed that the pore radius of the seawater specimens was mainly less than 10 μm, and the maximum crack length was 92.55 μm. The pore radius of freshwater specimens was larger than that of seawater specimens, and the largest crack was 148.44 μm, which confirmed that Friedel salt and C-S-S-H fill the pores and increase the UCS of the specimens.