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Waste phosphogypsum (PG) has been proved recyclable in producing qualified aggregate and binder for concrete, with a substitution rate of above 70% in aggregate and 40% in binder. Therefore, it is feasible to use phosphogypsum with high content as recyclable aggregate and binder. This paper provides a detailed description of high-content phosphogypsum-based concrete (HPGC) preparation process, together with evaluation of mechanical properties, impurity stability, and radioactivity of the concrete. The prepared HPGC is heavier than typical lightweight concrete, with reduced mechanical properties and qualified leaching performance. The compressive strength of the concrete prepared in this experiment at 28d was generally in the range of 18 MPa–40 MPa. Upon significant drop in compressive strength, critical PG content in coarse aggregate is around 80%, while the content in binder is about 60%. The concrete makes a good solidification of waste PG, with release of hazardous matters acceptable according to local building codes. Featuring a substitution rate of above 800 kg/m3, the PG concrete technology would find large-scale applications in recycling massive phosphogypsum waste. [Display omitted] • The fresh bulk density of HPGC was between 2140 and 2200 kg/m3. • The 28-d compressive strength of HPGC was generally in the range of 18Mpa–40Mpa. • The modulus of elasticity of HPGC lower than that of typical concrete. • HPGC shows good solidification capability for hazardous matters. • Consumption of phosphogypsum exceeds 800 kg per 1 m3 of HPGC produced. [ABSTRACT FROM AUTHOR]

• The waterglass coating has a low dosage, but excellent anti carbonization effect for EPSPM. • The waterglass coating can participate in the hydration reaction on the surface of EPSPM, what form a hard protective layer, and has good compatibility with the EPSC. • The waterglass coating can seal the surface pores of EPSPM. Excess-sulphate phosphogypsum slag plastering Mortar (EPSPM) is vulnerable to carbonization, thus reducing surface stabilities. This paper proposes a modification method to EPSPM by coating different modulus and amounts of waterglass (WG). Effects of WG coatings on the carbonation resistance, sand consolidation capacity, impurities stability and hydration products of EPSPM were evaluated. It turns that EPSPM coated with WG have more hydrates of ettringite and C-S-H gels in the mortar surface, which forms more compact structure than the uncoated one. The WG coatings can significantly improve the anti-carbonation and sand consolidation capacities. Meanwhile WG coating also accelerates the release of eutectic phosphorus, increases dissolved of phosphorus impurities. Coating WG of 2.4 modulus and 0.25 kg/m2 performs optimally, and is applicable for practical utilizations. [ABSTRACT FROM AUTHOR]

• The carbonation mechanism of phosphogypsum-based supersulfated cement paste and its effect on microstructure were studied. • The impact of three different CO 2 concentrations (atmospheric, 5% and 20%) on the microstructure was evaluated. • The CO 2 concentration less than 5% is recommended due to the similar microstructure with that of natural carbonation. This study investigates mechanisms of carbonation on the microstructure of phosphogypsum-based supersulfated cement (PSSC) paste at different CO 2 concentrations (atmospheric, 5% and 20%). The products was characterized using XRD, TGA, FTIR and 27Al MAS NMR. It is observed that the main hydration products of PSSC are ettringite, C-A-S-H gels and third aluminate hydrate (TAH), and the carbonation products are calcium carbonate (mainly vaterite and calcite), secondary gypsum, and C-A-S-H gels and separate TAH with varying degrees of decalcification. The quantitative analysis of BSEM images shows that the volume change of products occurring on carbonation significantly increases porosity and pore size of the PSSC paste. Results indicate that the carbonation of PSSC at different CO 2 concentrations results in a progressive carbonation degree, 5% CO 2 supports the accelerated carbonation experiment in PSSC to simulate the natural carbonation process due to the same phase composition and similar microstructure with atmospheric CO 2 and 20% CO 2 further loosens the microstructure of PSSC for the complete decomposition of ettringite and the severe decalcification of gel products. [ABSTRACT FROM AUTHOR]