Study on the properties and hydration mechanism of a new fluorogypsum-based filling material

WANG Chun; ZHANG Yifei; ZHU Mingli; REN Yumeng; ZHAN Shuaifei

doi:10.16186/j.cnki.1673-9787.2023080046

Abstract：Objectives Aiming to address the high cost of mine filling material and the land occupation issues caused by the accumulation of industrial solid waste,this study developed a new type of mine filling material that included industrial solid waste.Methods The optimum ratio of fluorine gypsum-based filling material was determined through orthogonal experiments.The study examined the material's mechanical properties,hydra-tion products,hydration mechanism,and microstructure.Results The results showed that the compressive strengths of the optimal ratio material at 1,7,and 28 days can reach 1.41,4.11 and 6.47 MPa,respectively,which met the basic requirements of mine filling.The slump,diffusion and bleeding rate of the paste were 22.7 cm,42.6 cm and 2.58%,respectively.The paste had good fluidity and was easy to transport.Fluorogypsum content,fly ash content and slurry concentration were the three variable factors in the material ratio.Among them,the factor that had the greatest influence on the 1-day strength was the slurry concentration,while the 7-day and 28-day strengths,and bleeding rate were most affected by the fly ash content.The factor that had the greatest influence on the slump and diffusion of the paste was the fluorogypsum content.The uniaxial failure of the backfill was shear failure,with cohesion and internal friction angles of 2.02 MPa and 32.6°,respectively.The hydration products included ettringite,calcium sulfate dihydrate and calcium silicate hydrate gel.During the hydration process,the fluoropgypsum consolidated body was transformed from an anhydrous phase to a di-hydrous phase,where the increase of ettringite and calcium silicate hydrate gel formed a dense structure,im-proving the strength of the backfill.Conclusions The filling material prepared with fluoropgypsum and fly ash instead of cement was feasible and had a low cost.The solid waste content exceeded 90%,bringing significant economic benefits and promising application prospects.