Study On The Uniaxial Compression Constitutive Relationship Of Cast-in-situ Phosphogypsum

Phosphate gypsum(PG)is the by-product of phosphate fertilizer industry.As of 2015,the cumulative accumulation of phosphogypsum in China has reached 300 million tons.A large amount of untreated phosphogypsum is exposed to the natural environment,which not only occupies a lot of land resources,but also causes serious harm to the ecosystem.China’s “the 13 h Five-Year Plan" for eco-environmental protection clearly calls for increasing the utilization of industrial solid wastes and encourages the application of phosphogypsum to various building materials and their additives.The application of cast-in-situ phosphogypsum as building material in structural engineering is a new direction to realize low cost and large-scale resource utilization of phosphogypsum.Due to the lack of relevant research results,the engineering application of cast-in-situ phosphogypsum is limited.In this paper,the mechanical properties of cast-in-situ phosphogypsum and its uniaxial constitutive relation model are studied by combining experimental research,theoretical analysis and numerical simulation.The main work and conclusions in this paper include:(a)The uniaxial compressive test of 16 groups of cast-in-situ phosphogypsum prism specimens is carried out.Failure modes of cast-in-situ phosphogypsum specimens and the characteristics of uniaxial compressive stress-strain curves are determined.And the mechanical properties of the cast-in-situ phosphogypsum are obtained,such as axial compression strength,elastic modulus and Poisson ratio.The influences of the additive component retarder,water-reducing agent and glass is analyzed.(b)According to the geometrical characteristics of 16 groups of cast-in-situ phosphogypsum uniaxial compressive stress-strain curves,polynomial,trigonometric and rational fraction functions are selected to fit the curves of the uniaxial compression of the cast-in-situ phosphogypsum.The error analysis results show that the fitting curves accord well with the test results when the piecewise mathematical model with ascending section as polynomial model and descending section as rational fraction model is adopted.The uniform equation of the uniaxial compressive stress-strain curve of cast-in-situ phosphogypsum can satisfy the geometrical characteristics of the test curve and provide a reasonable mathematical model for the constitutive relationship of the cast-in-situ phosphogypsum under uniaxial compression condition.(c)A constitutive model of cast-in-situ phosphogypsum is established by curve fitting and mathematical derivation.By comparing the theoretical and the experimental curves of the uniaxial compression test group,the rationality of constitutive relation model is preliminarily tested.(d)A three-dimensional model of cast-in-situ phosphogypsum prism is established by finite element software ABAQUS,and the proposed uniaxial compressive constitutive relation of the cast-in-situ phosphogypsum is used in the simulation of the prism in axial compression condition.The finite element analysis results are in good agreement with the experimental results.The result shows that the cast-in-situ phosphogypsum finite element model can simulate the uniaxial compressive test well.The numerical simulation results are in good agreement with the experimental results.It is further verified that the uniaxial compressive constitutive relation model of cast-in-situ phosphogypsum is reasonable and reliable.