Study on the mechanical properties of nano Al₂O₃ synergistic polyacrylonitrile fiber-reinforced geopolymers

With the rapid development of global industrialization and urbanization, the volume of solid waste has increased dramatically, and the issue of solid waste disposal is urgently needing to be addressed.GP material was created using slag (SP), fly ash (FA), and diatomaceous earth (DE) as cementitious materials, and coal gangue (CG) as fine aggregate. To enhance the strength and toughness of GP, polyacrylonitrile fibers (PAN) and nano Al₂O₃ (NA) were added for synergistic reinforcement. Strength tests were conducted on specimens cured for 28 days, and the addition of PAN fibers significantly improved the strength of GP. When a volume fraction of 0.3% of 12 mm fibers was selected, the strength improvement was the greatest. Compared with specimens without added fibers, the compressive, flexural, and splitting tensile strengths increased by 36.06%, 66.21%, and 50.6%, respectively, reaching 11.62 MPa, 1.71 MPa, and 0.91 MPa. The addition of nano Al₂O₃ (NA) with different mass fractions in synergy with PAN fibers can further enhance the strength of GP. When the NA addition amount is 2%, the strength improvement is the greatest, and the compressive, flexural, and splitting tensile strengths of GP are further increased by 17.7%, 14.37%, and 18.3%, reaching 13.69 MPa, 1.958 MPa, and 1.08 MPa. Through detailed mechanism analysis using SEM, TGA, and MIP, it was found that the addition of PAN forms a three-dimensional network structure in GP, which can withstand tensile stress caused by plastic shrinkage, thereby preventing or reducing the formation of cracks. However, the addition of NA promotes the hydration reaction, generates more gel materials, adheres to the fiber surface, increases the roughness of the fiber, increases the friction between the fiber and the matrix, fills the pores, and reduces the porosity and the number of harmful pores.Research on the synergistic enhancement of mechanical properties of geopolymers by using nanomaterials and fibers is relatively scarce, which has certain scientific research guiding value for the comprehensive utilization of solid waste materials in concrete.