ABSTRACT
The distinct tensile behaviour of Ultra-High Performance Fibre Reinforced cement based Composite (UHPFRC) and its extremely low permeability, make it particularly suited for use in 30 to 50 mm thick layers (Brühwiler & Denarié 2013) in the rehabilitation/strengthening of existing reinforced concrete structures. The tensile strength of UHPFRC depends primarily on the properties of the matrix and fibres but can also vary significantly according to fibre orientation. While the former can be tailored during mix design, the latter depends on the geometric shape of the form to be cast, on the placement process and on the rheological behaviour of the material in the fresh state. This means that it is not possible to define an intrinsic tensile response for UHPFRC and it is necessary to characterize the representative fibre orientation in the real structure.
The results of an experimental campaign (Pimentel & Nunes 2016) comprising a total of 8 beams failing in bending are discussed in the paper. An NDT method developed by Nunes et al. (2016) based on the magnetic properties of the steel fibres is adopted for determining two reliable indicators of the fibre content and fibre orientation. It is shown that these indicators can be used to obtain the tensile constitutive law of UHPFRC and how this information can be used to reproduce the structural behaviour observed in the tests.
It was shown that the structural behaviour of UHPFRC strengthening layers containing reinforcement bars is not influenced by local fibre content and orientation variations. In this case, the force deformation curves obtained in the experiments could be accurately reproduced considering the tensile constitutive law of the UHPFRC corresponding to a uniform distribution of fibres. However, in the case of the layers without reinforcement bars, the behaviour could only be reproduced using the tensile constitutive laws estimated from the NDT measurements and taking into account the spatial variability.
The proposed procedure is well suited for quality control of hardened UHPFRC layers. Variation of the uniaxial tensile strength of the UHPFRC, <italic>f<sub>Ut,u</sub> </italic>: (a) Contour levels; (b) variation along the Y-axis of the <italic>f<sub>Ut,u</sub> </italic> values averaged across the X-direction. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig64_1.tif"/>
