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  From the Microscope to the Tunnel: State-of-the-art Optimized Production of High Durability Precast Concrete Tunnel Lining Segments

  The beginnings of Precast Concrete Tunnel Linings (PCTL) date back to the 1930’s, when it was first used in Great Britain, and many years later in North America (1960’s). In the 1980’s it was already a consolidated technology, boosted by the increasing performance of mechanical excavation by TBM process. The main reason behind this strong development was, of course, the reduction on the costs of the projects due to fastest execution. Production of tunnel lining segments in a very fast way became mandatory.Although precast concrete was a natural choice because of availability, economy and speed of process, many constraints were raised due to fire resistance behavior (concrete spalling) and durability issues, mainly under aggressive groundwater conditions. In those cases, the solution based on double shell tunnels was still the preferred.A great deal of research has been done during the last decades, leading to the actual high level of understanding about overall concrete technology, the use of alternative raw materials (including ground granulated blast furnace, steel and synthetic fibers, new generation of mold release agents, protection coatings) and production procedures, which allowed the specification of single shell lining using PCTL with high degree of confidence, even under harsh soil and underground water conditions. The QIRP (Qatar Integrated Railway Project) is a very illustrative example of the success of such an endeavor.The upmost aim of this paper is to spread the know-how of concrete technology and best demonstrated practices accumulated during years in several projects for the use in coming ones.Keywords: Tunnel Segments, Durability, Epoxy Coating, Concrete Admixture, PP fibers.Since precast concrete has been chosen as a preferential material for tunnel linings, it was mandatory to ensure certain features regarding overall durability and fire resistance. A lot of research was conducted by independent organizations, specifically in Switzerland, where the Swiss Federal Railways (SBB) decided to launch a research project for the evaluation of concrete mix designs, targeting high durability. For the new tunnels to be constructed in Switzerland (Rail 200 and Alp Transit Project – St. Gothard Base Tunnel), the design life was 100 years, considering usual maintenance. The production of PCTL segments under such specification is critical when compared to regular poured or pumped concrete. At that time, over 80 different mixes have been tested, using several types of cement and blends, different types of additives like silica fume and GGBS, and many different admixtures, like PCE based superplasticizers.

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