Reasearch And Application On The Covering Layer Materials Of Gradient Structural Concrete Segmentwith High Volume Stability

This thesis is based on Wuhan Yangtze River Tunnel Project and 863 project (Structure Design of highly anti-resistant,long life and large diameter tunnel segment material and Its Application).Aming at deficiency in durability of ordinary concrete,the worse environment and high demand for durability in river-crossing or sea-crossing tunnels,a new type material--MIF(Meso Interfacial Transition Zone Free Cement-based Material)was developed for improving durability of covering layer according to improving compactness and eliminating deficiency of cement-based material.MIF possessed higher volume stability,higher impermeability,and higher compactness.Volume stabilization and related performance of MIF was studied in this thesis,and MIF was applied to Gradient Structure Concrete Segment successfully.The main conclusions presented in this thesis are summarized as follows:1.In the principles of the hydration sequence theory,mechanism of improving Interface Transition Zone,mechanism of improving pore structures,a special type of mineral admixtures for concrete was designed which could improve volume stabilization,ITZ and pore structures.It contained 75%～85%components with high calcium and high silicon compounds and 15%～25%nano-powder material with high silicon compounds,which could decrease hydration heat,reduce drying shrinkage and autogenous shrinkage,improving pore structures of cement-based material.2.From the point view of volume of stability,strenth and durability,MIF was designed for concrete covering layer of segment.MIF was the denst structure to reject coarse aggregates and use small flint quartz and as framework,and unhydrated cement particle,mineral admixtures particle and hydration product were distributed in pore uniformly.So meso- deficiency was reduced or eliminated.MIF's workability was good,and its strength of 28d reached to C60-C80.Comparing with the HPC,its impermeability increased by one order of magnitude,and the lowest diffusion coefficients of Cl^- reached to 0.37×10^-13m²/s.Shinkage-inducing and cracking-resistance components were added into MIF,which could effectively controll the drying shrinkage in the range of 300×10^-6-500×10^-6,and show better anti-cracking capability.3.According to design principle of gradient structure and engineering properties of segment of Wuhan Yangtze River Tunnel Project,GSCS(Gradient Structure Concrete Segment)was designed tested using MIF as covering layer. Comparing with the ordinary segment,GSCS had higher strength in the concrete cover(MIF)and the main structural concrete,better impermeability and anti-cracking capability.Volume stabilization and durability of segment had improved obviously.