ABSTRACT
The usage of steel fibers with hooked ends is common for specific applications in tunnelling, especially with prefabricated elements or when being used as a substitution for traditional reinforcements with SCL-constructions. Tests have shown that the hook is embedded perfectly within the concrete matrix and therefore the flexural strength of the specimen and their capability of absorbing energy is a function of this embedment and the tensile strength of the fiber itself. So called “straight” fibers - that are activating a bond of the concrete matrix along the surface of the fiber - until now have not shown a similar capability of realizing flexural strengths and therefore hooked fibers have become the mainstay for tunnelling applications, even though they also often induce workability issues on the construction sites and in fabrication plants.
With the STABILS® fiber, a new fiber type has become available, that has no hooked ends but inlying anchorage knots, therefore has a far better workability of the fresh concrete and provides equal to better performance in lab tests compared to traditional fiber types. This is even truer when “classical” cementous binders are substituted with geopolymer concrete, where the new fibers show 2-3 times the flexural strength compared to fibers with hooked ends. In this publication the authors show results from lab tests that – on the one hand – proof the workability of the fiber and – on the other hand - show that such a fiber can reach equal to better performance with comparable mix designs and fiber content. In the concrete lab of the RUB 4-point-bending tests have been conducted. We show and explain results from pure workability test as well as the results from the test of the flexural strength.
