Mechanical Properties and Microscopic Mechanism of Phosphogypsum-Slag-Lime Solidified Sediment

The utilization of using lime as an alkaline activator to improve the activity of industrial byproducts (i.e.,phosphogypsum and slag) is an approach to solidify river and lake sediments,which can reduce energy consumption and environmental pollution and form a green development model of “treating waste with waste”.The study proposes a method of solidifying river and lake sediment using phosphogypsum-slag-lime ternary stabilizer (PSCA).Firstly,the unconfined compressive strength (UCS) test was used to study the effects of PSCA dosages and curing periods on the mechanical properties of solidified sediment.Then,scanning electron microscopy (SEM),X-ray diffraction (XRD),and mercury intrusion porosimetry (MIP) tests were used to reveal the microscopic mechanism of hydration products and pore structure.The results indicate that the strength of PSCA solidified sediment is low in the early curing stage,but the strength increases rapidly in the later stage,and the strength can reach 1.53MPa in 28 days,which is higher than those solidified by ordinary Portland cement with the same dosage.Microscopic results show that the PSCA solidified sediment contains a large amount of flocculent C-S-H products and needle-shaped ettringite crystals.The former mainly contributes to the bonding strength,while the latter mainly contributes to the filling strength.Economic and environmental analysis shows that the unit strength cost (28 days) and carbon emissions of PSCA are 59.1% and 14 times that of traditional ordinary Portland cement,respectively,exhibiting good economic and environmental benefits.Overall,this research results can provide a sustainable solidification material and technology for sediment,which has important scientific significance and practical value for the safe treatment and resource utilization of sediment and solid waste in China.