Synergetic Effects of Alkaline and Sulfate-Based Waste Binders on Undrained Triaxial Behavior of Cement-Admixed Soft Clay

Abstract

The synergetic effects of alkaline red mud (RM) and sulfate-based phosphogypsum (PG) on the undrained triaxial behavior of cement-admixed clay were explored in this study. A series of isotropically consolidated undrained triaxial tests were performed on stabilized clay with respect to different admixed RM/PG proportions. The triaxial behavior of stabilized clay is presented in terms of a stress–pore pressure–strain relationship, failure mode, undrained deformation modulus, stress path, and failure envelope. Scanning electron microscopy (SEM) tests were conducted to survey microscopic evolution. The results showed that the brittleness of the specimen intensified with a high RM content, which was manifested by a predominant postpeak strength reduction. As the PG content increased, the strain-softening behavior weakened and gradually evolved into strain-hardening. The failure mode changed from local shear failure to the single cone failure and bulging failure correspondingly. The RM played a role in increasing soil cohesion, whereas PG contributed to a larger frictional angle at the postyield stage. Microscopic observations indicated that the alkali source from RM significantly promoted pozzolanic reactions and strengthened cementation bonds, which increased the peak strength, deformation modulus, and cohesion. In addition, the sulfate in PG contributed to ettringite generation among clay particles and clusters, resulting in a more ductile behavior and a larger frictional angle due to large clusters formed.