This study investigated the effects of polypropylene fibre (PF) reinforcement on the mechanical behaviour of clay soil. Using clay soil and polypropylene fibres from China’s Inner Mongolia and Hebei Provinces, respectively, a series of soil samples with 0%, 1.5%, 2.25%, and 3% PF content by soil weight were subjected to compaction, shear strength, consolidation, California bearing ratio, and microstructure analyses. The study results indicate improved compaction, shear strength, consolidation, and the bearing ratio of the PF-stabilised clay soil. As the PF content increased, its maximum dry density increased and its optimum moisture content decreased; its angle of internal friction increased and its cohesion coefficient decreased; and its void ratio, consolidation coefficient, and hydraulic conductivity all decreased. Comparing the unstabilised (0% PF) and stabilised (3% PF) clay soil, the void ratio, consolidation coefficient, and hydraulic conductivity decreased from 0.96 to 0.93, from 2.52 to 2.34 cm2/s, and from 1.12 to 1.02 cm/s, respectively. The optimum PF content was determined to be 3% by the weight of the soil, as this quantity resulted in the best improvement in soil properties.

AbstractRecycling of red mud (RM) has attracted more attention in recent years due to severe environmental problems caused by landfilling. The effect of composition optimization and Nano-strengthening on the properties of a binder based on RM was studied in this paper. Results showed that modifying ratios of main oxides and adding Nano-SiO2 could obviously affect the mechanical properties and microstructure of the binder. Specimens with high SiO2/Al2O3 molar ratio (S/A) displayed considerable increase in compressive strength, while decreasing Na2O/Al2O3 molar ratio (N/A) improved the workability of the fresh mix. The compressive strength was developed significantly to be 45 MPa at 28 days by adding Nano-SiO2 with 0.4 wt.% of RM. Phase transformation and microstructure change at different stages of RM decomposition and binder geopolyerization were investigated by X-ray diffraction (XRD), Fourier transformation infrared (FTIR) and Scanning electron microscopy (SEM). The results of this study may provide a prospective method to use RM more widely in construction applications.

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The construction of buildings on expansive soils poses considerable risk of damage or collapse due to soil shrinkage or swelling made likely by the remarkable degree compressibility and weak shear resistance of such soils. In this research, rice husk ash (RHA) was added to expansive soil samples in different quantities of 0%, 4%, 8%, 12%, and 16% by weight of soil to determine their effects on the plasticity index, compaction parameters, consolidation performance, and California bearing ratio (CBR)of clay soil. The results show that the use of RHA increases the effective stress and decreases the void ratio and coefficient of consolidation. Adding 16% RHA resulted in the greatest reduction in the hydraulic conductivity, void ratio, and coefficient of consolidation. The void ratio decreased from 0.96 to 0.93, consolidation coefficient decreased from 2.52 to 2.33 cm2/s, and hydraulic conductivity decreased from 1.12 to 0.80 cm/s. The addition of RHA improved the soil properties and coefficient of consolidation due to the high density and cohesiveness of RHA. The results of this study can be used to provide a suitable basis for the treatment of expansive soil to provide improved conditions for infrastructure construction.

In this study, the effect of SiO2/Al2O3 (S/A), Na2O/Al2O3 (N/A) and H2O/Na2O (H/N) molar ratios on bending and compressive strength of geopolymer were investigated. The geopolymerization mechanism was also analyzed from microstructure difference by FTIR. The experimental results showed that compressive strength and bending strength of geopolymer has an opposite reaction under different critical molar ratios. The increase of S/A molar ratio and the decrease of N/A and H/N molar ratios have resulted in an increase of the compressive strength. However, it caused a noticeable decrease in bending strength. The microstructure of geopolymer indicated that the degree of polymerization and cohesion of geopolymer have systematical depending on these critical molar ratios, making the mechanical properties of geopolymer susceptible to different types of loads. This paper reveals the relationship between the microstructure of geopolymer and different mechanical properties and helps to selectively prepare corresponding geopolymer for different loading patterns.