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Material properties of fibre reinforced UHPC

Author(s): N. Randl, F. Däuber
Paper category: Conference
Book title: 8th RILEM International Symposium on Fiber Reinforced Concrete: challenges and opportunities (BEFIB 2012)
Editor(s): Joaquim A.O. Barros
Print ISBN: 978-2-35158-132-2
e-ISBN: 978-2-35158-133-9
Publisher: RILEM Publications SARL
Pages: 394 - 404
Total Pages: 10
Language: English

In the frame of a research project funded by the Austrian Research Foundation (FFG) the production process and the material properties of ultra high performance fibre reinforced concrete (“UHPFRC”) have been investigated in the labs of the Carinthia University of Applied Sciences. The addition of an appropriate amount of uniformly distributed steel fibres (about 2–2,5 Vol.-%) improves the ductility of the UHPC. Several experimental investigations have been carried out in order to receive a fairly consistent and homogenous constitutive material law for both compression and tensile behaviour.
The results from compression and beam bending tests are presented, moreover from tensile splitting and uniaxial tensile tests. The compression strength of the fine-grain UHPFRC, treated with a special heat curing method, shows approximately 184 N/mm² when tested on 100 mm cubes. In order to derive the flexural strength, bending tests were performed according to the German guideline for steel fibre reinforced concrete. Furthermore, uniaxial tensile tests on cylindrical cores drilled out of a UHPC beam perpendicular and parallel to the casting direction were accomplished, thereby providing information on the tensile behaviour in different directions with respect to the fibre orientation. Splitting tensile tests completed the experimental investigations of the material properties.
The bending tests deliver in many cases more reliable and consistent values for the tensile behaviour of UHPFRC than the rather sensitive uniaxial tensile tests. The latter ones are quite difficult to perform, considering that eccentricities may severely affect the results and notches are usually required to achieve a well-defined crack and allow for a more reliable assessment of the after-peak-behaviour. Taking into account the test results, a constitutive law is proposed on the basis of the French recommendation AFGC/SETRA (2002). The approach to describe the tensile behaviour solely from bending tests is discussed.
Fibre orientation and distribution as well as allocation along the formwork and casting direction have a significant influence on the local tensile and flexural behaviour. The influence of these factors on the scatter of the test results is investigated and discussed in the paper. Not only the way of adding the fibres during the mixing procedure, but also other factors such as the concrete viscosity and the correct sequence of mixing and adding fibres, water and superplasticizer play an essential role for the dispersion of the fibres and their final distribution and orientation.
The current study gives a comprehensive overview of the main aspects and required steps to characterize the material behaviour of UHPCFRC; finally deriving a constitutive law as required to allow for the pre-design of building members.

Online publication: 2013
Publication Type: abstract_only
Public price (Euros): 0.00