Insights into the mechanical and environmental behaviours of artificially phosphogypsum-based lightweight aggregate and its sustainable application

This study developed a novel phosphogypsum-based lightweight aggregate (PGLA) in an attempt to replace conventional gravel. Self-developed stabiliser, CTGU-NL, was adopted to prepare both PGLA concrete (PGLAC) and gravel concrete for comparative study. Two field test sections (PGLAC and gravel concrete) equipped with multiple sensors were constructed to monitor the time-dependent variations in nitrogen, phosphorus, and potassium concentrations, as well as electrical conductivity, temperature, and humidity. Core samples were collected at predetermined curing periods to determine the unconfined compressive strength (UCS). Thereafter, the microstructural evolution in the interfacial transition zone (ITZ) was further revealled using scanning electron microscopy (SEM) and backscattered electron (BSE) imaging. The results showed that phosphogypsum-based lightweight aggregate concrete (PGLAC) reduced the ion concentration to undetectable levels within 30 days, suggesting improved environmental compatibility. Compared to gravel concrete, the embedded ITZ of PGLAC facilitated the formation of an interlocking structure between the matrix and PGLA, which contributed to ITZ reinforcement and enhanced mechanical properties of PGLAC (28-day UCS of 31.2 MPa). Furthermore, environment and economy assessment revealed that using 1 m³ of PGLAC reduced costs by 21.68% and CO2 emissions by 4% when compared to gravel concrete.