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About PVA Fibers : Applications : Structural
Overview
The Swiss Federal Railway wanted to save time and money without sacrificing quality, so they asked Concretum to design a new kind of tunnel.
Concretum found:
1. Much of the time and cost involved in building a tunnel using traditional techniques is the labor-intensive work required to anchor the steel bar. Drilling many holes, gluing them with expensive polymer mortar, tying steel together: all these tasks consumed time and money.
2. Steel fibers had their own problems: sinking in the mix during vibrating compaction, or when fluid self-compacting mixes were used.
3. Corrosion can be caused also by the electricity used to run the trains running down into the concrete and causing electrolysis.
Concretum then designed and installed a PVA-reinforced tunnel for Swiss Railway, passing entirely under the main Zurich railway station, and completed it in half the normal time. The total cost was one third less than conventional construction.
Railway basement without steel reinforcement
Title:
Material-Related Concrete Design: High-Performance Fiber-Reinforced Concrete for Railway-Basement
Innovation:
Use of high-modulus polymer fibers (PVA-fibers) in combination with a specially designed, low-shrinkage concrete.
Project Description:
To increase the capacity of Zurich's main station, a tunnel with an overall length of 800 meters (one half mile) was built under the existing tracks. For construction reasons the slab of the tunnel was built in two layers. The first one bears all static and dynamic loads, while the second layer thickness: 160mm or 6.3 inches) has to provide the cross-section necessary to install sleepers and tracks.
Problem:
A micromechanically-engineered concrete had to be developed for the second layer. It was decided to cast elements with a length of 12 meters directly on the existing basement layer. Even though neither steel reinforcement nor anchoring devices can be used, the Swiss Railway required the slab to remain crack free and not show any curling. All loads are expected to be carried by the roughness of the interface. In addition to this, the concrete had to fulfill stringent requirements for workability and frost resistance. A slope of 6% had to be realized without any formwork and the surface had to be unruffled and plain.
Solution:
Differential shrinkage deformations are the controlling loads in this system consisting of top layer and substrate. In a first step the concrete-matrix was developed and optimized for minimization of drying shrinkage. The resulting matrix showed only half of the final drying shrinkage that is measured for concretes made with standard matrices. Based on this matrix composition, a concrete mix-design was developed. As the use of steel reinforcement had to be obviated, a hybrid polyvinylalcohol (PVA) shortcut fiber-cocktail was applied. The resulting high performance concrete was tested in several on-site-tests. As curing is one of the crucial aspects influencing curling and cracking of the slab, intensive testing has been performed to find the optimum method for this application. Before construction began a sophisticated numerical simulation using finite-element methods, based on experimentally determined material properties, had demonstrated long-term-resistance against surface cracking and curling. Reliable consultancy was provided by the responsible site engineers during the construction period to ensure on-site quality control.
This procedure allowed the successful application of a micromechanically-engineered concrete that shows uniquely higher performance and the following results:
Time / Cost savings: 50% / 30%
Client: Swiss Federal Railway, Switzerland
© Concretum Construction Science Inc., Zurich, Switzerland |
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