| With the rapid development of transportation infrastructure construction in China,the transportation network extends to areas with complex terrain and geology,the proportion of tunnels in new roads and railways is increasing,and the demand for shotcrete is increasing rapidly.However,shotcrete has some shortcomings,such as low strength,poor toughness,many internal defects,and many cracks.In order to make shotcrete adapt to the tunnel with high ground stress and large deformation,it is significant to study shotcrete with high strength and toughness.In this paper,the fiber reinforced spraying cement-based materials(FRSCM)was taken as the research object.The fracture toughness was measured by the three-point bending toughness test,and the cracking risk was quantitatively evaluated by the restrained ring shrinkage test.The effects of basalt fiber content,basalt fiber length,fly ash,and silica fume on mechanical properties were studied,and the significance of influencing factors was analyzed.Based on the double K fracture model,the influences of basalt fiber on fracture parameters were studied,and a three-dimensional relationship model between fracture toughness and fiber parameters was established.The microscopic morphology of FRSCM was observed by scanning electron microscopy,which corroborated the toughening and crack resistance mechanism of the fibers,the effect of mineral dopants on the hydration products and the improvement of the transition zone at the fiber interface.The influence of basalt fiber and mineral admixtures on the cracking performance of FRSCM was studied by using the restrained ring shrinkage test,and the development trend of cracking performance was studied.The main conclusions of this paper are as follows:(1)The addition of basalt fiber effectively improves the toughness of sprayed cementbased materials.The fracture energy is increased by 20 % ～ 35 %,the fracture toughness is increased by 10 % ～ 25 %,and the instability toughness is increased by 10 % ～ 15 %.(2)Basalt fiber reduces the cracking risk of sprayed cement-based materials.The average stress rate is reduced by 40 % ～ 50 %,and the stress cracking coefficient is reduced by 15 % ～35 %.After adding mineral admixtures,the average stress rate is increased by 20 % ～ 50 %,and the stress cracking coefficient at cracking is reduced by 40 % ～ 50 %,which further reduces the cracking risk.(3)Basalt fiber plays the role of toughening and crack resistance mainly by changing the direction of crack development and preventing the expansion of micro-cracks.There is a weak interfacial transition zone between the fiber and the cement matrix.The addition of mineral admixtures can fill the pores in the interfacial transition zone and improve the interfacial bonding performance.(4)In order to obtain FRSCM with high strength,high toughness and good crack resistance,basalt fiber with 12 mm length and 0.15 % volume content was used,and 15 % fly ash and 3 %silica fume were added at the same time. |
