Collaborative effects of red mud and phosphogypsum on geotechnical behavior of cement-stabilized dredged clay

Red mud (RM) and phosphogypsum (PG) are two typical industrial waste around the world, which are being generated and landfilled massively per year. This study investigates the collaborative effects of RM and PG on geotechnical properties of cement-stabilized dredged clay. Unconfined compressive strength (UCS) tests, isotropically consolidated undrained triaxial (ICUT) tests and one-dimensional consolidation tests were performed. The strength and deformation characteristics of stabilized clay were examined with 16% cement and different proportions of RM and PG (10%RM, 7.5%RM2.5%PG, 5%RM5%PG, 2.5%RM7.5%PG and 10%PG). The RM and PG are found complementary and effective in improving geotechnical properties of stabilized clay. The UCS of the cement-stabilized clay nearly triples at an optimal proportion of RM and PG at early curing period. The specimen with a high content of RM has stronger cementation bonds and exhibits a brittle behavior during undrained shearing process. A high content of PG, whereas, results in a lower peak strength but a larger failure strain of the specimen. The specimen with a high content of PG also exhibits a much smaller compression index at pre-yield stage. In addition, the evolution in microstructure of stabilized clay with different RM/PG proportions is explored using a series of microscopic tests. It is shown that the collaborative effects of RM and PG are dependent upon the cementation strengthening effects of alkaline RM and pore-filling effects of ettringite generated from PG. The role of ettringite significantly relies on the surrounding void space considering the pore-filling effects and the potential cementation damage.