Study On The Improvement Of Compressive Strength And Mechanism Of Slag-based Slurry Filling Material

Tailings accumulation and occupation of land,environmental pollution,goaf subsidence are serious problems caused by mining,and cemented tailings backfill technology is an effective countermeasure to solve the above problems.However,in the cemented tailings backfill technology,the traditional cement cementing materials have the problems of low compressive strength and high filling cost.The low tailings concentration and high fine particle content also have a negative impact on the compressive strength of the filling body.In order to improve the compressive strength of the filling body,this paper selects the slag powder as the main cementing material for the low-concentration ultrafine tailings,and realizes the continuous improvement of the compressive strength of the filling body through the chemical composite excitation of the slag powder and the particle size control of the filling body.Finally,the source and promotion mechanism of the compressive strength of the filling body were discussed based on the microscopic analysis and related theories.The main research contents include :(1)The optimized slag-based slurry filling material system was obtained.The composition and ratio of slag powder : modified powder : gypsum : alkaline activator(quicklime + sodium metasilicate nine water)= 580 : 218 : 143 : 59.Taking the effect of compressive strength improvement as the evaluation standard,two common sulfate activators and three alkaline activators were selected,and the best activator type and addition method were selected to form the slag-based slurry filling material system.Through the mixing experiment,the distribution ratio of each group of slag-based slurry filling material system was adjusted,and the compressive strength of the filling body prepared by the optimized ratio was significantly higher than that of ordinary Portland cement.(2)The particle size refinement of slag powder can improve the compressive strength of filling body,and has no obvious effect on the fluidity of filling slurry.Based on the original 400 mesh slag powder,600 mesh,800 mesh and 1000 mesh slag powder are added to explore the effect of particle size refinement of slag powder on compressive strength and fluidity of filling body under different ash-sand ratios.The change rule of compressive strength of filling body was explored by replacing 400 mesh slag powder with 1000 mesh.It was found that this replacement method can reach the compressive strength standard of 600 mesh and 800 mesh slag powder filling body with lower cost.(3)Tailings gradation has a great influence on the strength of backfill.The tailings W2 with good gradation and larger particle size was introduced,and the tailings W2 was partially replaced by the original tailings W1.With the increase of the replacement amount of tailings W2,the compressive strength of filling body with different ash-sand ratios at different ages increased approximately linearly,and the fluidity of filling slurry decreased gradually.(4)The main source of the compressive strength of the filling body is the condensed structure and network structure formed by C-S-H gel and ettringite.The improvement of the close packing state of the filling body and the structure of the hydration product C-S-H gel and ettringite will improve the compressive strength of the filling body.Through the analysis of porosity,XRD,TG and SEM,it is found that the main hydration products of slag-based slurry filling materials are C-S-H gel and ettringite,and the total amount of two hydration products of the paste prepared with 1000 mesh slag is higher than 400 mesh.According to the close packing model and the related theory of hydration products,it is found that the compressive strength of tailings W2 is improved by improving the close packing state of the filling body,and the particle size of slag powder is refined by increasing the amount of hydration products.