Carbonation behavior and performance optimization of anhydrous phosphogypsum-based concrete: synergistic effect of admixtures

During the service life of concrete, carbonation is an inevitable phenomenon. This study innovatively developed a novel anhydrous phosphogypsum-based concrete (APGC) using anhydrous phosphogypsum (APG) as the primary cementitious material, synergistically combined with granulated blast furnace slag (GBFS), ordinary Portland cement (OPC), and carbide slag (CS), addressing the low utilization rate of industrial solid wastes. The carbonation performance was systematically evaluated through multi-scale characterizations (FTIR, XRD, SEM-EDS, MIP), accompanied by the first integrated environmental risk assessment of heavy metal leaching and carbon emissions for such materials. APGC exhibits exceptional high-fluidity (spread flow diameter up to 690 mm), high-strength (28-day compressive strength 78.6 MPa), and superior water resistance (softening coefficient 0.92, water absorption rate 0.74 %), enabled by GBFS-OPC synergies enhancing matrix density and alkalinity. Carbonation led to the decomposition of ettringite and the decalcification of C-S-H gel in APGC, as well as an increase in the proportion of harmful pores and porosity, resulting in APGC deterioration. A Fick's first law-based carbonation prediction model shows <10 % error, enabling service life prediction of APGC. Carbonation disrupted the chemical speciation of heavy metals in APGC, leading to increased leaching of heavy metals., yet APGC reduces carbon emissions by 49.8 % compared to conventional C60 concrete. The optimal mix design (30 % GBFS, 2 % CS, ≥5 % OPC) is expected to reduce the use of traditional Portland cement, pioneering exploration of APGC carbonation behavior and filling the research gap in phosphogypsum-based concrete durability.