The Design And Preparation Of The Subway Autoclaving-free Shieldsegment Tunnel Concrete

Duct piece is the important part of shield tunnel. In order to improve producing efficiency at most factories of our country, steam-curing method is adopted to enhance demolding strength at the early stage. However, during enhancing concretes early strength the steam curing also give the shield segment concretes the volume stability and the lasting quality the adverse effect, while steam curing consumed energy greatly. In 20 years the subway tunnel keeps the sustained growth, and its shield segment's formerly demand will be bigger than before. From the view of the long-term strategic angle of conserving energy and the environmental protection our country, as well as the questions of the shield segment concretes durability improvement and so on, it is necessary to develop the high performance concretes of steam curing shield segment to substitute the original steam curing shield segment concretes, the improvement concretes durability as well as the energy consumption question of shield segment production.Depending on the Wuhan science and technology research project and the Wuhan subway tunneling, superb hardening accelerating and water reducing admixture was developed and was suitable to be in the free steam curing conditions. Through optimization of mix design, the best mix design of high-performance concrete of duct piece was fixed.The influence of the different structure of polycarboxylate and the early-strength components on the cement hydromass mobility, the congealment time difference, and the rubber granulated substance early strength were investigated. Ultra strength of polycarboxylate superplasticizer compound options were identified,Systematic research about influence of each key factor on dimensional stability and durability of concrete including shrinkage and creep whose mechanism was also studied. Demouding strength was 23.5Mpa at age of 12h, diffusion coefficient of chloride ion was 5.1×10-13m2/s, shrinkage value was 1.8×10-4 at the age of 28d and值2.2 X 10-4 at the age of 90d. Dimensional stability Free steam duct piece high-performance concrete was better than steam duct piece concrete.The hydration of the different mixtures of poly-carboxylate and ultra-early-strength poly-carboxylate were investigated by hydration heat, XRD, SEM, hole structure and other microscopic test methods. The early strength machanism of concrete improved by the ultra-early-strength poly-carboxylic acid was proved. The influence rule of various key aspect to the cement hydration of the free steam curing segment performance concrete was proved through the analysis the microscopic structure of the exempts steams raises shield segment high performance concretes forming process and the hole structure distribution rule.This plan applies in the segment production of Wuhan subway tunnel and the preparation of segment has been applied in the Wuhan subway tunnel. The dimension error of segment is small, the appearance of outward is smooth, the air bubble are few and no missing edge off angle phenomenon, which satisfies the design requirements completely after the scene assembling quality.