Study On Preparation And Properties Of Nickle Gypsum Composite Cementitious Materials

Nickle gypsum is a new kind of industrial by-product gypsum produced in the process of extracting nickle by high pressure acid leach method,and its properties are similar to those of phosphogypsum.At present,China's industrial by-product gypsum emissions is far more than the use,and its amount has exceed 800 million tons.The accumulation of industrial by-product gypsum occupies a large amount of land,pollutes the environment and wastes resources.In this paper,nickel gypsum composite cementitious materials were prepared by using untreated nickel gypsum,titanium slag and quicklime.However,nickle gypsum composite cementitious materials has long setting time and poor mechanical properties due to the high content of soluble phosphorus in nickel gypsum and low activity of titanium slag.Hence,this paper choose to join coagulant and highly active admixture to improve its properties.The long-term strength,water resistance and other properties of the modified nickel gypsum composite cementitious materials were studied.The foam concrete was prepared by the optimum formulation of the modified nickel gypsum composite cementitious materials,and the effects of water cement ratio,foam content and water content on the properties were studied.The results show that:The soluble phosphorus in nickel gypsum may have adverse effects on the setting time and strength of the system,and the strength of the matrix decreases with the increase of the content of nickel gypsum.Therefore,the amount of nickel gypsum should not be too high.Based on the comprehensive utilization of waste residue and the properties of nickel gypsum composite cementitious material,the content of nickel gypsum was determined to be 40%.Lime has better effect on nickle gypsum composite cementitious materials when used lime,NaOH and sodium silicate as alkali activators,and its best content is 6%t0 8%.NaOH and sodium silicate can not be activated when their content is low.Compared with nickel gypsum,titanium slag has a greater effect on the early performance of nickel gypsum composite cementitious materials.The addition of cement to replace part of the titanium slag can improve the early and late strength of the matrix.The synergistic effect of cement and quicklime greatly increased the density of matrix,and its content should not be exceed 10%.The addition of coagulants such as sulphoaluminate cement,KAl(SO4)2.12H2O and Al2(SO4)3· 18H2O significantly shortens the setting time,but has little effect on the strength.High performance admixture of metakaolin and silica fume has little effect on the setting time,but they can significantly improve the early and late strength,and the effect of metakaolin is stronger.The addition of sulphoaluminate cement and kaolin can shorten the setting time and improve the strength of matrix.When the content of Sulphoaluminate and metakaolin are 2%and 4%respectively,nickel gypsum composite cementitious materials with initial and final setting time of 132 min and 298 min,3 d,7 d and 28 d compressive strength of 6.45 MPa,13.32 MPa and 23.96 MPa were prepared.Steam curing can greatly increase the early strength,especially when the temperature is 70?,but its later strength is similar to the sample with natural curing.The strength of the modified samples increases with age,and the water resistance increased significantly.When the water cement ratio is 0.45,the dosage of water reducer is 0.25%,and the content of LiOH is 0.2%,GB A 04?A 10 foam concrete was prepared with the modified nickel gypsum composite cementitious material by changing the amount of foam.