纳米SiO_(2)对玄武岩纤维增强煤矸石粉-矿粉基地质聚合物砂浆性能的影响

Effects of nano-SiO_(2) on properties of basalt fiber-reinforced coal gangue-mineral powder-based polymer mortar

【目的】为了改善煤矸石粉-矿粉基地质聚合物砂浆的脆性破坏特征,采用纳米SiO_(2)对玄武岩纤维增强煤矸石-矿粉基地质聚合物砂浆(basalt fiber-reinforced coal gangue-mineral powder-based geopolymer mortar,BGSG)进行改性。【方法】采用流动度、流变性、抗压强度、抗折强度、单轴拉伸和断裂试验并结合能量准则和微观手段研究纳米SiO_(2)增强地质聚合物砂浆的增韧机制。【结果】随着纳米SiO_(2)掺量的增加,BGSG的流动度逐渐下降,触变面积、屈服应力和塑性黏度逐渐增大;当纳米SiO_(2)掺量(质量分数)为3%时增韧效果最好,养护龄期为28 d时,纳米SiO_(2)改性BGSG的抗压强度为22.3 MPa,抗折强度为6.8MPa,极限拉伸强度为5.75 MPa,失稳韧度为0.534 MPa·m^(1/2),与未掺加纳米SiO_(2)的对照组相比,其抗压强度、抗折强度、极限拉伸强度和断裂失稳韧度分别增加29.1%、39.5%、36.9%、47.8%;微观分析表明,纳米SiO_(2)掺入并未改变地质聚合物水化产物的类型。【结论】纳米SiO_(2)参与聚合反应,促进地质聚合物凝胶的生成,从而增强BGSG的综合性能。

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 environmental 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-SiO_(2) is introduced to modify basalt fiber-reinforced coal gangue-mineral powder-based geopolymer mortar(BGSG).Methods The effects of nano-SiO_(2) 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-SiO_(2).A control group without nano-SiO_(2) was used for comparison.The impact of different nano-SiO_(2) contents(1%,2%,3%)on the performance of the geopolymer mortar,primarily composed of coal gangue powder and mineral powder,was investigated.The mechanisms by which nano-SiO_(2) affected the geopolymer mortar properties were explored using energy criteria,X-ray diffraction,infrared spectroscopy,and thermogravimetric analysis.Results and Discussion With the increase in nano-SiO_(2) content,the fluidity of BGSG decreased.When the nano-SiO_(2) 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-SiO_(2) content.At nano-SiO_(2) contents of 1%,2%,and 3%,the loop areas were 3140,4080,and 5000 Pa/s,respectively,showing increases of 21.2%,57.5%,and 93.1% compared to the control group(2590 Pa/s).The yield stress and plastic viscosity of the slurry increased with higher nano-SiO_(2) 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-SiO_(2) content.After 28 days of curing,the compressive and flexural strengths of the nano-SiO_(2) 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-SiO_(2) content,showing noticeable improvements in the slope of the rising segment and the area under the curve.Compared to the control group,the fracture energy and ductility index of the specimen with 3% nano-SiO_(2) increased by 150.7% and 70.1%,respectively.Additionally,the tensile performance of the specimens improved with the addition of nano-SiO_(2).At a 3% nano-SiO_(2) content,the ultimate tensile strength(σut)was 5.75 MPa,and the instability toughness(KIuCn)was 0.534 MPa·m^(1/2),increasing by 36.9% and 47.8%,respectively,compared to the control group.Microstructural analysis revealed that the incorporation of nano-SiO_(2) did not change the types of hydration products in the geopolymer.Conclusion Nano-SiO_(2) enhances the geopolymer mortar performance through filling,pozzolanic,and nucleation effects.Aggregate 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-SiO_(2) 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 mortar,thereby improving the toughness and ductility of the coal gangue-mineral powder-based geopolymer mortar.Furthermore,the incorporation of nano-SiO_(2) significantly enhances the tensile and fracture properties of the geopolymer.