Study On Application Of Shotcrete Non-alkali Liquid Accelerator In Tunnel

As China's tunnel construction enters a high-speed advancement stage,the amount of shotcrete used will increase.In the tunnel construction,the quick-setting agent plays a vital role in the performance of the shotcrete.At this stage,the amount of accelerators used in China is very large,and most of them are made of materials with strong alkalinity.In the actual construction process,the skin,eyes and other parts will be damaged,and the concrete strength will be weak.At the same time,in the process of spraying the accelerator,the effect of non-uniform addition is highly prone to occur.Therefore,it is necessary to develop new quick-setting agent products in the direction of excellent performance,liquidity and alkali-free or lowalkalias soon as possible.In this study,the coagulation experiments of two kinds of procoagulant components of A and B were selected,and the minimum solid addition amount and the amount of aqueous solution of the alkali-free liquid quick-setting admixture required for initial coagulation less than 4 min and final coagulation not more than 8 min were compared.The components A and B are used as the basis of the alkali-free liquid accelerator.Triethanolamine was used as a performance improving component,and polyacrylamide and calcium formate were used as stabilizers and dispersants.After compounding,CSL liquid alkali-free accelerator was obtained with a compressive strength of 103.5% for 28 days.The CSL-I liquid alkali-free quick-setting admixture developed in this paper has a good coagulation effect.The adaptability between CSL and cement and water reducer was studied by coagulation time test and compressive strength test.The effect of water-cement ratio,temperature,mixing time and stirring method on the effect of CSL.Based on the concrete jet test,the influence of sand ratio and maximum aggregate size on the workability of shotcrete was studied based on the large plate method.When the CSL content is 8%,the initial setting time and final setting time of the cement are 2min50 s and 6min30 s,respectively.The 1-day and 7-day strength of cement mortar increased significantly with the increase of CSL quick-setting admixture.The 28-day compressive strength ratio reached 103.5%,which was much higher than the national standard requirements for primary accelerator.The application in the project verified the performance of the accelerator,and confirmed that the accelerator has high early strength and good strength in the later stage,which has broad application prospects.