The effects of desulfurized gypsum on the mechanical properties of dredged clay with high initial water content stabilized by ternary geopolymer

Geopolymer is an emerging green cementitious material that can be used to stabilize dredged clay (DC) as construction materials. This paper presented an experimental study on the effects of desulfurized gypsum (DG) on the mechanical properties (e.g., stress-strain characteristics, unconfined compressive strength (UCS) and water stability) of stabilized DC with high initial water content using the ternary geopolymer based on fly ash (FA), ground granulated blast-furnace slag (GGBS) and DG. Moreover, microstructure tests were conducted to elucidate the mechanism of the mechanical enhancement of the stabilized DC. The results clearly demonstrated that DG exerted a significant influence on the mechanical properties of the stabilized DC. Notably, the incorporation of DG led to a transition from ductile to brittle behavior and a notable increase in the deformation modulus (E50). DG effectively enhances the unconfined compression strength (UCS) of stabilized DC with a high initial water content. The peak UCS for the stabilized DC sample with an initial water content of 2.0wL reached 1632.9 kPa with the mass ratio of DG to solid waste FA and GGBS (i.e., D/S) of 8%. Stabilized DC at the low D/S ratio exhibited excellent water stability, while the stabilized DC at the D/S ratio of 8% retained the highest strength after water immersion. The threshold of the D/S ratio is determined to be 8%. Microstructure characterization revealed that the strength enhancement of the stabilized DC primarily relies on the cementation effect of geopolymer gel and crystalline C-(A)-S-H, along with the filling effect of ettringite. However, a significant amount of ettringite can lead to an expansion in the DC volume and disrupt the weak cementation bonding, ultimately causing a deterioration in strength.