Effect of freeze-thaw cycle on deterioration of mechanical properties of fibre-reinforced geopolymer cemented aeolian sand

Cyclic freezing and thawing can irreversibly damage the microstructure of geopolymer materials in the monsoon freezing zone, thereby deteriorating their load-bearing capacity. In this study, polypropylene fibres were added in geopolymer cemented aeolian sand to carry out research on the mechanical behaviour and fine-structure damage evolution characteristics of geopolymer during its life cycle under different conditions. The results show that: with the increase of fibre doping, the bias stress value and cohesion value of the specimen are first increased and then decreased, the elastic modulus and the weakening modulus show the trend of first decreased and then increased. When the fibre content is 5 %o, the fibre is evenly dispersed in the sample, and the local best strengthening effect is achieved. When the fibre content is 7 %o, the fibre bunching phenomenon appears in the sample. With the increase in the number of freeze-thaw cycles, the bias stress value, cohesion value, and modulus of elasticity of the specimens decreased as a whole, and the phenomenon of increasing the weakening modulus and the angle of internal friction occurred. After the same number of freeze-thaw cycles, the performance degradation of the specimens doped with appropriate amount of fibre was lower than that of the specimens without fibre. The deterioration of macroscopic mechanical properties is essentially caused by the superposition and evolution of microscopic mechanical effects. During the freeze-thaw cycle, the microcracks and pores increase significantly in both number and size, and the incorporation of fibres strengthens the connection of the matrix inside the specimen, optimizes the internal spatial structure, and reduces the fatigue damage produced by freeze-thaw on the specimen. The related research results are of great significance for assessing the safety of inservice geopolymer structures in cold regions, and provide a reference basis for optimizing the frost resistance of pipe trench backfill geopolymer in seasonally frozen areas.