Zhiyi Ye’s research while affiliated with Wuhan University of Technology and other places

This study compared the physical properties and mechanical strength development of PCBAs with water, sealed, standard, and open ambient air curing over 28 days to find a suitable curing method for the production of phosphogypsum-based cold-bonded aggregates. The types and relative amounts of hydration products, microstructural morphology and pore structure parameters were characterized utilizing XRD, TGA, FTIR, SEM and nitrogen adsorption methods. According to the results, water curing leads to rapid increases in single aggregate strength, reaching 5.26 MPa at 7 d. The standard curing condition improved the 28 d mechanical strength of the aggregates by 19.3% over others by promoting the generation of hydration products and the transformation of the C-S-H gel to a higher degree of polymerization and by optimizing the pore structure. Further, PCBAs achieved an excellent solidification of phosphorus impurities under all four curing conditions. This work provides significant guidance for selecting an optimized PCBA curing method for industrial production.

Phosphogypsum-based excess-sulphate slag cement (PESSC) shows great resistance to sulphate and chloride ion erosion, and is expected to be an effective sink of waste phosphogypsum, to alleviate environmental pressure. Understanding the effect of magnesium ions is essential for the engineering application of PESSC in marine environment. In this paper, heat evolution, pore solution composition, phases assemblage, and mechanical properties of PESSC are characterized and analysed to reveal the effect of magnesium ions on early hydration and strength development. Results demonstrate that magnesium ions prolong the induction period and lead to a longer setting time. Increasing magnesium ions concentration from 0 mol/L to 0.2 mol/L makes the acceleration period appear earlier, and affects content of hydration products such as ettringite and C-(A)-S-H gel at early stage. Compressive and flexural strength can be significantly improved with magnesium ions addition at various degrees. It turns out that seawater could be favourable for PESSC if applied in marine environment.

While traditional disposal of phosphogypsum either occupies excessive amounts of land or causes serious pollution, novel recycling of phosphogypsum is desirable. Making phosphogypsum-based cold-bonded aggregates (PCBAs) through granulation technology is a potential recycling strategy. In this study, the quality of the recycled PCBAs is assessed, considering physical properties, mechanical strength, impurity stabilization ability, and microstructure. With the increase of phosphogypsum content from 60% to 90%, 28-day bulk density of the PCBAs decreased from 1080 to 950 kg/m³, cylinder compressive strength in over dry (OD) condition decreased from 16.5 MPa to 3.9 MPa, and water absorption increased from 5.9% to 13.6%. SEM, XRD, and MIP analyses showed that as the phosphogypsum content increased, hydration products in the aggregates diminished and proportion of harmful pores (greater than200 nm) increased. Leaching test on 28-day PCBAs showed a reduced concentration of phosphorus and heavy metals in the leachate compared to the leaching of the original phosphogypsum. The study concluded that the PCBAs with the phosphogypsum content up to 80 % are qualified lightweight aggregates (LWAs) for concrete.