Experimental Research On The Mix Proportion Based On Reducing The Shrinkage Of Shield Tunnel Segments

The problem of structural deformation and cracking caused by concrete shrinkage has always been one of the key issues in engineering research.With the application of high-volume mineral admixtures and concrete admixtures,as well as the widespread application of highstrength concrete and ultra-high-strength concrete,studying methods to reduce concrete shrinkage,accurately predicting the shrinkage deformation on the concrete macroscopic appearance,as well as simulating the uneven shrinkage deformation inside the concrete structure through the finite element analysis method,is of great significance to the durability design of the concrete structure engineering.Aiming at the problems of deformation and cracking caused by the shrinkage of the shield tunnel segment concrete,this paper aimed to reduce the shrinkage of the shield tunnel segment concrete and optimize the design of the mixing ratio with the fly ash and slag powder mixed.Through the shrinkage test under constant temperature and humidity conditions,the design mix ratio was studied,and a shrinkage prediction model that comprehensively considered the relative humidity of the environment,the size of the components,the amount of cement,the amount of fly ash and slag powder,and the amount of shrinkage reducer was proposed.The finite element method was used to simulate and analyze the shrinkage of reinforced concrete shield segments.After using the same amount of different mineral admixtures to replace cement,the strength of concrete showed a downward trend.And the reduction of concrete strength caused by replacing the cement with the same amount of fly ash was significantly greater than that of limestone powder.The shrinkage of concrete decreases with the increase of fly ash content,but it increases with the increase of slag powder used in this experiment.The incorporation of stone powder increases the shrinkage of concrete.The shrinkage of limestone coarse aggregate concrete is less than that of basalt coarse aggregate concrete.Shrinkage reducing agent can significantly reduce the shrinkage of concrete and improve the fluidity of concrete.The shrinkage of concrete decreases with the increase of the amount of shrinkage reducing agent.The logarithmic function formula and the square root hyperbolic compound function formula can better represent the relationship between the concrete drying shrinkage deformation and age under the conditions of constant temperature and humidity;the slope of the hyperbolic function and exponential function after 180 d is close to zero.The shrink fitting effect of the period is not ideal.The shrinkage prediction model that combines the final shrinkage calculation formula of the ACI(1978)model and the time history function of the CEB-FIP(1990)model can better fit the low water-to-binder ratio with mineral admixtures and shrinkage reducers Shrinkage of high-strength concrete.According to the similarity between the internal humidity field and the temperature field of the concrete,the internal humidity field of the concrete was analyzed through the thermal analysis module of the finite element software.According to the assumption that the humidity reduction rate caused by the self-drying inside the concrete was approximately linear with the square of the reciprocal of the drying time,and the internal humidity change of the concrete was approximately linear with the displacement and strain,the humidity field and structure field of the concrete were analyzed by ANSYS finite element software.According to the shrinkage test data,the important parameters of the concrete drying shrinkage process-the moisture diffusion coefficient,the surface moisture exchange coefficient,and the shrinkage coefficient were inversely calculated to obtain fitting values that met the actual physical meaning of the parameters.According to the inversely calculated parameter values,the finite element simulation of the shrinkage deformation of the reinforced concrete shield tunnel segments of the benchmark group and the shrinkage reducing agent 2% group was carried out.The incorporation of shrinkage reducing agent significantly reduced the shrinkage deformation of the tube sheet,which was reduced by more than 12% compared with the benchmark group.After 200 days,the shrinkage deformation growth rate of the 2% shrinkage reducing agent group slowed down significantly,while the benchmark group still had a higher growth rate.