| At present, underground engineering is in industrial scale construction in our country, many of them are tunnel shield. As the structural material and the waterproof body, tunnel shield segment influence the durability and servicelife of the tunnel a lot. Therefore, carry on the study of segment material has a significant effect on the performance of segment.The paper based on functionally graded material designed for Gradient Structural Concrete (short for GSC below). With material science and engineering requirement, this research prepared for a high early strength and low permeability material. The technology core is the low permeability material, permeation and its evaluated method of GSC material. The major work and research results are as follows:Permeation properties and durability of concrete is interdependent. The low permeability material is designed in three constituents: compact filling constituent, anti-crack constituent and interfacial zone strengthen constituent. For compact filling constituent, the binder is ternary designed for the effect of sequence hydration to fit the requirement of early strength and long term durability; Anti-crack constituent includes hybrid organic fibers and anti shrinkage agent, orthogonal experiment and individual factor experiment results show that polypropylene fibers hardly affect the permeation of silica fume concrete and the volume fraction of fibers is no more than 0.10%; interfacial zone strengthen constituent make up of the aggregates with optimum particle grade and diameter.The paper takes account of integrated test methods to study the permeability of GSC material. Chloride Diffusion Coefficient Method (NEL) was used to optimize raw material parameter; 6h electric flux method was applied for testing the chloride permeation of GSC material with age; Natural Diffusion Test and Water Penetration Test are applied for simulating the permeation of service environment approximately.Permeability of GSC material and protection layer material is interdependent. The permeability of GSC Material decrease with the lower of protection layer material permeation properties. All test results show that the permeation in decrease order as follows: structure layer material, Low Permeability Concrete (short for LPC below), Meso Interfacial Transition Zone Free Cement-based Material (short for MIF below). MIF has two orders of magnitude lower than structural material in chloride diffusion coefficient, about 0.5×10-13m2/s more or less, compared to LPC that is 3.0×10-13m2/s. And the apparent chloride diffusion coefficient is only 1/5 of structural material, the chloride permeable depth in 90 days is less than 8mm in 4 mol/L concentration of chloride ions. The depth of LPC and structural material are as much as 15mm and 2 times to MIF in chloride concentration in the surface area.Medium transportation in porous material and connectivity of pores is interdependent. That describes by percolation theory. For cement-based material, the capillary porosity and thickness of interfacial zone are two key parameters to the connectivity. Mercury test show that the ratio of capillary pore diameter large than 10 nm in cement paste, only 60% to MIF but 77% and 100% to LPC and structural material.The connectivity of above materials in decrease order as follows: MIF, LPC, structure layer material. Micro hardness and SEM tests show that interfacial zone thickness of structural material is more than 40μm, loosen in interface and a preferential orientation of large crystals of calcium hydroxide was around the aggregates, difference in hardness is 40% less than cement paste; Interfacial zone thickness of LPC reduce and its hardness in interfacial zone is 30% less than cement paste; That is 25% to MIF and the hardness value changes from interface to cement paste gradually. Both the macroscopic and microscopic experiment show that the permeability of MIF is negligible and the interfacial transition zone in common sense is attenuated dramatically. |
