Optimization of synergy between cement, slag, and phosphogypsum for marine soft clay solidification

Ground granulated blast furnace slag (GGBS) and waste gypsum are cost-effective and environment-friendly substitute materials for Portland cement. This work aims to investigate and optimize the synergy of ordinary Portland cement (OPC), GGBS, and phosphogypsum (PG) in solidifying marine soft clay. The soft clay is treated with the ternary blending designed, and NaOH (NH), Na2SO4 (NS), calcium aluminate cement (CA), and gamma-nano-Al2O3 (NA) are used as additives to it. The effectiveness of the ternary blending and the additives is evaluated using unconfined compressive strength (UCS), consolidation, and durability tests, and the associated mechanisms are revealed by pH evaluation, X-ray diffraction (XRD), and scanning electron microscopy (SEM) tests. A high -efficiency ternary cement (TC) is developed by blending OPC, GGBS, and PG in the optimum ratio of 5:3:2. TC solidified clay (TCSC) exhibits better strength performance than cement or binary cement (OPC-GGBS/PG) so-lidified clay, due to the combined action of pozzolanic reaction and ettringite formation. The single additives, particularly NH and NS, can dramatically improve the early strength of TCSC, whereas the composite additives NS/CA and NS/NA finally result in greater strength gains. Besides, the lower compressibility and stronger sulfate resistance also verify TCSC as a preferable reinforced material over cement solidified clay, and these mechanical properties can be further improved using the composite additives. The increased basicity and the more effective role of ettringite explain the improved mechanical performance. In particular, the NS/CA and the NS/NA induce ettringite to grow in clustered and oriented patterns, providing effective pore filling and structural support, respectively.

Automated summary

This study investigates the synergy of ordinary Portland cement(OPC), ground granulated blast furnace slag (GGBS), and phosphogypsum (PG) in solidifying marine soft clay. The ternary blending of OPC, GGBS, and PG in a 5:3:2 ratio results in a high-efficiency ternary cement (TC) that exhibits better strength performance than cement or binary cement (OPC-GGBS/PG) solidified clay, due to the combined action of pozzolanic reaction and ettringite formation. The addition of NaOH (NH) and Na2SO4 (NS) dramatically improves the early strength of TC solidified clay, while the composite additives NS/CA and NS/NA result in greater strength gains. The improved mechanical performance is attributed to increased basicity and the more effective role of ettringite, with NS/CA inducing clustered growth of ettringite and NS/NA providing structural support through oriented patterns of ettringite.