Effects of nano-SiO2 on properties of basalt fiber-reinforced coal gangue-mineral powder-based polymer mortar
Objective The approach for preparing a coal gangue-mineral powder-based geopolymer mortar using coal gangue powder and mineral powder as precursors,with water glass and NaOH as alkali activators,mitigates coal gangue accumulation and environ-mental pollution.However,coal gangue-mineral powder-based geopolymers have inherent defects such as high brittleness,low toughness,and susceptibility to cracking.To improve the fracture characteristics of this geopolymer mortar,nano-SiO2 is intro-duced to modify basalt fiber-reinforced coal gangue-mineral powder-based geopolymer mortar(BGSG).Methods The effects of nano-SiO2 on the fluidity,rheology,compressive strength,flexural strength,uniaxial tensile strength,and fracture performance of the geopolymer mortar were evaluated by adjusting the content of nano-SiO2.A control group without nano-SiO2 was used for comparison.The impact of different nano-SiO2 contents(1％,2％,3％)on the performance of the geo-polymer mortar,primarily composed of coal gangue powder and mineral powder,was investigated.The mechanisms by which nano-SiO2 affected the geopolymer mortar properties were explored using energy criteria.X-ray diffraction,infrared spectros-copy,and thermogravimetric analysis.Results and Discussion With the increase in nano-SiO2 content,the fluidity of BGSG decreased.When the nano-SiO2 content reached 3％,the fluidity of the geopolymer was 110 mm,which was 38.5％lower than that of the control group(179 mm).The thixotropic loop area of BGSG expanded with higher nano-SiO2 content.At nano-SiO2 contents of 1％,2％,and 3％,the loop areas were 3 140,4 080,and 5 000 Pa/s,respectively,showing increases of 21.2％,57.5％,and 93.1％compared to the con-trol group(2 590 Pa/s).The yield stress and plastic viscosity of the slurry increased with higher nano-SiO2 content,with yield stress rising from 31.5 Pa to 72.7 Pa,and plastic viscosity from 6.95 Pa·s to 11.45 Pa·s.The optimal toughening effect was observed at a 3％nano-SiO2 content.After 28 days of curing,the compressive and flexural strengths of the nano-SiO2 modified BGSG were 22.3 MPa and 6.8 MPa,respectively,which increased by 29.1％and 39.5％compared to the control group.The P-COMD curve became fuller with increasing nano-SiO2 content,showing noticeable improvements in the slope of the rising seg-ment and the area under the curve.Compared to the control group,the fracture energy and ductility index of the specimen with 3％nano-SiO2 increased by 150.7％and 70.1％,respectively.Additionally,the tensile performance of the specimens improved with the addition of nano-SiO2.At a 3％nano-SiO2 content,the ultimate tensile strength(σul)was 5.75 MPa,and the instabil-ity toughness(KunIC)was 0.534 MPa·m1/2,increasing by 36.9％and 47.8％,respectively,compared to the control group.Microstructural analysis revealed that the incorporation of nano-SiO2 did not change the types of hydration products in the geopolymer.Conclusion Nano-SiO2 enhances the geopolymer mortar performance through filling,pozzolanic,and nucleation effects.Aggre-gate filling and polymerization reactions improve the pore structure of the matrix and the gaps between the matrix and fibers,thereby increasing the structural density.The addition of nano-SiO2 reduces inherent defects within the geopolymer,strengthens the bonding between the matrix and fibers,and inhibits the initiation and propagation of internal cracks in the geopolymer mor-tar,thereby improving the toughness and ductility of the coal gangue-mineral powder-based geopolymer mortar.Furthermore,the incorporation of nano-SiO2 significantly enhances the tensile and fracture properties of the geopolymer.
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