Research On Shotcrete With High Durability

Since the introduction of shotcrete,because of its simple and convenient construction method,short duration,strong adaptability and good impermeability,is widely used in the tunnel engineering and support projects.However,there are always so many problems such as the strong corrosive of materials,high rebound rate,late strength loss and poor durability,especially the high rate of alkali aggregate reaction.In recent years,people began to study on these problems,hoping to solve them.The problems of shotcrete are analyzed,and it is considered that the use of alkali-free accelerator instead of the tradit ional accelerator can improve the problem of strong corrosive concrete,high resilience and late strength loss.Besides,in this paper,the durability of shotcrete with different amount of silica fume,fly ash,expansive agent,shrinkage reducing agent,air-entraining agent and high modulus polyacrylonitrile fiber was explored to produce high durability shotcrete that csetting speed is fast,the early shrinkage performance is good,the permeability is good and freezing resistance is good.Through the experimental study,it is found that the init ial setting time of the paste with the alkali-free accelerator is 2min25 s,the final setting time is 5min09 s,the 28 d compressive strength of shotcrete is 97.4% of the ordinary concrete,and all kinds of durabilities have been improved.The amount of fly ash significantly affects the impermeability and early self-shrinkage of the shotcrete,and effectively improves the impermeability of the shotcrete and suppresses the early self-shrinkage,its optimum dosage is 15%.The shrinkage and expansion agent can effectively prevent the self-shrinkage and drying shrinkage of shotcrete,improving the internal structure of shotcrete to prevent crack ing,the best dosage of them are 1% and 6%.And the air-entraining agent has a significant effect on the frost resistance of shotcrete,the best dosage is 0.02%.Besides,the high modulus polyacrylonitrile fiber which dosage is 1kg/m3 has obvious improvement effect on the self-shrinkage of shotcrete,the shrinkage rate of 24 h self-shrinkage is reduced by 26.9%,and it has a good effect on drying shrinkage and frost resistance.But it will make a slight increase of electric flux and is harmful to impermeability,but the impact is not obvious.