Abstract
To make better use of large amounts of discarded bauxite tailings (BTs), a foamed mixture lightweight soil mixed with BTs as filler (FMLSB) was proposed. Using the orthogonal experimental design method, the effects of various contents of cement, BTs, and foam on the fluidity, wet density, unconfined compressive strength, water absorption, and microstructure of FMLSB were studied. The experimental results indicate that the wet density and unconfined compressive strength increase as the contents of cement and BTs increase but decrease as the foam content increases. Water absorption increases with the reduction of the wet density, but the unconfined compressive strength exponentially increases as the wet density increases. With an increase in the contents of cement and BTs and a decrease in the foam content, fewer pores are present, and the pores are not connected with each other. The results of the range analysis show that the main factor affecting the wet density and unconfined compressive strength of the FMLSB is the foam content, followed by the cement content, and meanwhile, BTs can maintain the lightweight and high strength of FMLSB. Based on the intended engineering applications and standard specifications, the optimum composition of the FMLSB mixture is proposed. Overall, the results indicate that BTs have the potential to be used as filler to produce FMLSB and that applications of FMLSB will lead to great economic and environmental benefits in engineering construction.
Highlights
In recent years, foamed mixture lightweight soil (FMLS) has been widely used because of its lightweight, regulatory of density and strength, good workability, self-reliance after hardening, good durability, impermeability, good heat and sound insulation, and superior environmental protection
When the wet density is 890 kg/m3, the ratio of Bauxite tailings (BTs) replacing cement is 27.3%, which is lower than when the wet density is 1080 kg/m3 (28.6%). erefore, the fluidity increases with increasing wet density above 890 kg/m3. e results are similar to results reported in the previous research [27, 28], whereby increasing amounts of solid particles in a mixture increased the stiffness of the resulting cement paste, which has occurred due to the higher absorptivity of the BT particles
We can see that, due to the presence of the BTs, the bij value of the wet density is always lower than 800 kg/m3, and the bij value of the unconfined compressive strength is always larger than 1.2 MPa, indicating that FMLS mixed with BTs (FMLSB) samples containing BTs are still lightweight and have higher strengths. erefore, the density and strength are adjusted mainly by controlling the content of foam and cement, and BTs are utilized as much as possible under safe conditions to maximize the replacement rate of cement and the utilization of waste
Summary
In recent years, foamed mixture lightweight soil (FMLS) has been widely used because of its lightweight, regulatory of density and strength, good workability, self-reliance after hardening, good durability, impermeability, good heat and sound insulation, and superior environmental protection. Fly ash, silica fume, and fibres are often added to foamed concrete mixtures to customise the mechanical properties of the resulting material [7, 8]. Using the orthogonal experimental design method, the effect of the contents of cement, BTs, and foam on the fluidity, wet density, unconfined compressive strength, water absorption and microstructure of FMLSB was investigated. E novel contribution of this paper is to provide scientific basis of how to recycle large amounts of discarded BTs for use as raw materials in the production of FMLS and to reduce the total quantity of primary materials used. Recycling waste materials greatly limits the negative effects of waste products on the environment
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