The instantaneous post-cracking behaviour of fibre reinforced concrete, FRC, has been widely studied in the last decades, either by direct or indirect methods, by e.g. [1-5]. Nevertheless, the knowledge available in literature regarding the long-term response of FRC is still somehow scarce. Moreover, the major part of the studies
V.M.C.F. Cunha (H) • J.A.O. Barros • A. Abrishambaf Department of Civil Engineering, School of Engineering, ISISE,
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P. Serna et al. (eds.), Creep Behaviour in Cracked Sections of Fibre Reinforced Concrete, RILEM Bookseries 14,
mainly address the creep behaviour of concrete reinforced with synthetic fibres, by e.g. [6-8], which is understandable due to the higher susceptibility of these fibres to thermo-hygrometric environmental conditions, but the increasing use of steel FRC (SFRC) for structural applications brings renovated interested in this topic. Thus, to cope with these debilities, recently, some works regarding the creep behaviour of SFRC have been presented, by e.g. [9-12]. It is worth noting that the aforementioned studies were focused mainly on prismatic specimens, which in the case of using self-compacting concrete mixtures have a distinct fibre distribution and orientation from the one of planar structures [13-15]. Despite the availability of some standards for designing SFRC structures [16, 17], they still do not envisage the long-term behaviour of SFRC in cracked conditions. Therefore, information regarding the long-term behaviour of cracked SFRC elements, particularly of planar structures (like the outer layers of sandwich panels, thin slabs and shells), is still limited. Consequently, understanding the behaviour of cracked SFRC elements under a sustained load will help towards a more rational design and accurate prediction of the composite behaviour under serviceability conditions. To sum it up, it is important to evaluate the concrete capability to maintain the crack opening width relatively low under a sustained load, in order to guarantee the effectiveness of fibre reinforcement under serviceability conditions.
The long-term behaviour of pre-cracked steel fibre reinforced self-compacting concrete (SFRSCC) laminar structures (of relatively small thickness) will be presented and discussed. One hundred and twelve prismatic specimens were extracted from a SFRSCC panel. These specimens were notched with different orientations regarding to the expected SFRSCC flow direction, and were tested under four-point flexural sustained loading conditions. The influence of the following parameters on the creep behaviour was studied: initial crack opening level, wcr (0.3 and 0.5 mm); applied load level, (50-100 %), fibre orientation/dispersion, and distance from the casting point. Moreover, to evaluate the effect of the long-term residual crack opening on the flexural post-cracking strength, as well as on the secondary stiffness, a series of instantaneous monotonic and cyclic tests were carried out, and the corresponding force vs crack tip opening displacement (F-CTOD) curves were compared to the ones obtained by assembling the F-CTOD curves determined in the pre-crack monotonic tests, creep tests and post-creep monotonic tests. Finally, based on the results obtained from the creep tests, an equation was proposed to predict the creep coefficient for the developed SFRSCC.