CREEP OF CRACKED POLYMER FIBER REINFORCED CONCRETE UNDER SUSTAINED TENSILE LOADING

In fiber reinforced concrete (FRC), fibers are added to the fresh concrete mix in order to improve the residual tensile strength, the toughness and/or durability of a concrete element. Cur- rently, structural applications remain relatively scarce as the time-dependent behavior of FRC is still poorly understood. This paper reports the first results of an experimental campaign regarding the creep of cracked polymer FRC. In the test setup, cylindrical, notched FRC specimens are considered. The concrete is reinforced with structural polymeric fibers for use in load-bearing applications. In a first step, the material is characterized according to the European Standard EN14651. Secondly, the samples are precracked to localize the creep deformations and to monitor the crack growth in time. The samples are subjected to a sustained tensile load, whereby different load levels with respect to the individual residual strength are considered. The results of the first months of creep loading will be detailed and discussed in the paper

Recommendation of RILEM TC 261-CCF: test method to determine the flexural creep of fibre reinforced concrete in the cracked state

[EN] To date there is no clear consensus about how creep of cracked FRC structural elements should be considered. In recent years, different methodologies have been developed for multiple stress cases. The absence of a standardised methodology to evaluate flexural creep in the cracked state has hindered general comparisons and conclusions that could lead to significant advances in this topic. Since 2014, the study of the creep behaviour of cracked FRC has been coordinated by the RILEM TC 261-CCF. All the available creep methodologies were analysed in terms of procedure, equipment and results. A comprehensive Round-Robin Test (RRT) on the creep behaviour of cracked sections of FRC was proposed and undertaken by a total of 19 participant laboratories from 14 countries all over the world. The analysis and conclusions of the RRT results and the different methodologies provided the basis for this recommendation. This recommendation focuses on the test method to evaluate the flexural creep of FRC specimens in the cracked state. Guidelines on specimen production, detailed test equipment, experimental setup and test procedure as well as the definitions of the most relevant parameters are provided.Llano-Torre, A.; Serna Ros, P. (2021). Recommendation of RILEM TC 261-CCF: test method to determine the flexural creep of fibre reinforced concrete in the cracked state. Materials and Structures. 54(3):1-20. https://doi.org/10.1617/s11527-021-01675-0S120543Theodorakopoulos D (1995) Creep characteristics of glass reinforced cement under flexural loading. Cement Concr Compos 17:267–279Chanvillard G, Roque O (1999) Behaviour of fibre reinforced concrete cracked section under sustained load. High Performance Fiber Reinforced Cement Composites (HPFRCC 3) Mainz, Germany, pp 239–250, RILEM PRO 06Kurt S, Balaguru P (2000) Post crack creep of polymeric fibre-reinforced concrete in flexure. Cem Concr Res 30(2):183–190Mackay J, Trottier JF (2004) Post-crack behavior of steel and synthetic FRC under flexural creep. In: Shotcrete, Proc. 2nd Intnl. Conf. on Engineering, Cairns, Australia (2004), pp 183–192Kusterle W (2009) Viscous material behaviour of solids- creep of polymer fibre reinforced concrete. In: Proc. 5th Central European Congress on Concrete Engineering. obv, Baden, pp 95–100Arango S, Serna P, Martí-Vargas JR, García-Taengua E (2012) A test method to characterize flexural creep behaviour of pre-cracked FRC specimens. Exp Mech 52(8):1067–1078Zerbino RL, Barragan BE (2012) Long-term behaviour of cracked steel fibre-reinforced concrete beams under sustained loading. ACI Mater J 109(2):215–224Abrishambaf A, Barros JAO, Cunha VMCF (2015) Time-dependent flexural behaviour of cracked steel fibre reinforced self-compacting concrete panels. Cem Concr Res 72:21–36Buratti N, Mazzotti C (2016) Experimental tests on the long-term behaviour of SFRC and MSFRC in bending and direct tension. In: Proceedings of the BEFIB 2016, 9th RILEM international symposium on fiber reinforced concrete, pp. 163–174, Vancouver, Canada, 19–21 Sept 2016Babafemi AJ, Boshoff WP (2015) Tensile creep of macro-synthetic fibre reinforced concrete (MSFRC) under uni-axial tensile loading. Cement Concr Compos 55:62–69Vrijdaghs R, di Prisco M, Vandewalle L (2018) Uniaxial tensile creep of a cracked polypropylene fiber reinforced concrete. Mater Struct 51:5. https://doi.org/10.1617/s11527-017-1132-5Vasanelli E, Micelli F, Aiello MA, Plizzari G (2013) Long term behaviour of FRC flexural beams under sustained load. Eng Struct 56:1858–1867Bernard ES (2010) Influence of fibre type on creep deformation of cracked fibre-reinforced shotcrete panels. ACI Mater J 107(5):474–480EFNARC (2012) Testing sprayed concrete—Creep test on square panelLarive C, Rogat D, Chamoley D, Regnard A, Pannetier T, Thuaud C (2016) Influence of fibres on the creep behaviour of reinforced sprayed concrete. In: Proceedings of ITA World Tunnel Congress WTC 2016, April 22‐28, San Francisco, United StatesMonetti DH, Llano-Torre A, Torrijos MC, Giaccio G, Zerbino R, Martí-Vargas JR, Serna P (2019) Long-term behavior of cracked fiber reinforced concrete under service conditions. Construct Build Mater; 196:649–658. https://doi.org/10.1016/j.conbuildmat.2018.10.230Llano-Torre A., Martí-Vargas JR, Serna P (2020) Flexural and compressive creep behavior of UHPFRC specimens. Construct Build Mater; 244:118254. https://doi.org/10.1016/j.conbuildmat.2020.118254Serna P, Llano-Torre A and Cavalaro S H P (ed) (2017) Creep behaviour in cracked sections of fibre reinforced concrete: proceedings of the international RILEM Workshop FRC-CREEP 2016. RILEM bookseries 14 (Dordrecht: Springer)Llano-Torre A, Serna P, Cavalaro SHP (2016) International round robin test on creep behavior of FRC supported by the RILEM TC 261-CCF. In: Proceedings of the BEFIB 2016, 9th RILEM international symposium on fiber reinforced concrete, pp 127–140, Vancouver, Canada, 19–21 Sept 2016Serna P, Llano-Torre A, García-Taengua E, Martí-Vargas JR (2015) Database on the long-term behaviour of FRC: a useful tool to achieve overall conclusions. In: Proceedings of the 10th international conference on mechanics and physics of Creep, Shrinkage, and Durability of Concrete and Concrete Structures, Vienna, September 2015, pp 1544–1553Llano-Torre A., Serna P. (eds) Round-Robin test on creep behaviour in cracked sections of FRC: experimental program, results and database analysis. RILEM State-of-the-Art Reports. Springer. https://doi.org/10.1007/978-3-030-72736-9ASTM International (2015) C1812/C1812M-15e1 Standard Practice for Design of Journal Bearing Supports to be Used in Fiber Reinforced Concrete Beam Tests. West Conshohocken, PA; ASTM International. https://doi.org/10.1520/C1812_C1812M-15E0

A multi-scale finite element analysis and sectional design approach for the creep of polymeric frc

This paper presents the experimental, numerical and analytical results of a multi-scale investigation into the uniaxial tensile creep behavior of polymeric fiber reinforced concrete (FRC). In an extensive experimental program, the short-term and creep behavior of individual fibers, the fiber-matrix interface and the composite material are investigated. The short-term and creep properties are used to calibrate the material models of a finite element model with discrete fibers, which allows to determine the creep of polymeric FRC under tensile loading. A Monte-Carlo analysis is performed to assess the influence of the fiber dispersion and sustained load level on the time-dependent crack widening. Finally, the numerical results are used in a sectional approach that allows to translate the uniaxial tensile creep behavior into a flexural creep prediction. The proposed methodology can be readily implemented into design codes, to allow for the creep deformation of cracked FRC to be taken into account

A Computational Sectional Approach for the Flexural Creep Behavior of Cracked FRC

This paper presents a computational model to calculate and predict the flexural creep behavior in a cracked fiber reinforced concrete (FRC) section. The proposed model is based on uniaxial creep data and consists of three steps. In the first step, an inverse analysis algorithm is presented to model the monotonic bending behavior of a notched FRC beam in accordance with EN 14651. A simplified and numerically optimized method is compared to experimental data and a good agreement is found. In a second step, the unloading behavior of the beam is taken into account. Calibrated on experimental data, the model is able to accurately and precisely predict the unloading behavior. Further validation comes from the location of the neutral axis, and the deformation profile. In a third step, the flexural creep behavior is predicted based on the results in the second step. The creep data is supplied in uniaxial form, which allows greater applicability across various FRC mixtures. The proposed approach is able to take into account stress redistribution following fiber fracture. Furthermore, the time-dependent effects of the stress redistributions are also accounted for. As such, the model is able to predict tertiary creep and structural failure under sustained loading

A two-phased and multi-scale finite element analysis of the tensile creep behavior of polypropylene fiber reinforced concrete

Polymeric fibers can be used in concrete elements to improve the properties in the fresh or hardened state. In the latter case, structural macrofibers can be added to increase the residual load-bearing capacity after matrix cracking, and as such, can partially or entirely replace traditional reinforcement. Polymeric fiber reinforced concrete (PFRC) can be designed according to the Model Code 2010, but no design guidelines are given to take creep behavior into account, limiting the usage of FRC in structural applications. The tensile creep behavior of cracked PFRC is dependent on the creep deformation of individual fibers and on the creep behavior of the interface between fiber and matrix. Because of the different factors involved, a fundamental understanding of FRC creep can only be obtained by taking both mechanisms into account. Therefore, a numerical model with discrete treatment of individual fibers is set up. The results of the finite element analysis (FEA) is compared against experimental tests. In the experiments, the concrete cores are precracked to localize crack formation and growth and the time-dependent crack widening is measured over the crack. To calibrate the material models used in the FEA, the creep behavior of individual fibers as well as the pull-out behavior (short-term and creep) of the fiber is determined for a range of different embedded lengths and angles. In the finite element model, polypropylene fibers are randomly generated in an FRC beam. In a next step, a core is taken from the beam, and subsequently notched during which the effect of fiber cutting is simulated. The location of the crack in the numerical model is known (i.e. in the notched section) and fibers crossing this crack contribute to the load-bearing capacity of the element. An algorithm is implemented in MATLAB that calculates the embedded length of each crack-crossing fiber at both its ends. The material model governing pull-out behavior is then assigned to every load-bearing fiber based on its embedded length and angle, as determined by the multi-scale testing. The fibers are assigned a creep behavior model based on the experimental tests. Because of the low stresses involved, a linear elastic material model for concrete is adopted. The load, expressed as a percentage of the residual capacity, is imposed for 180 days on both the physical test specimen and on the numerical model and the crack widening is compared. Good agreement can be obtained and the model is able to capture crack growth of PFRC. Furthermore, the use of finite element modelling allows to determine the fiber stress in a cracked section of FRC, and based on the results presented here, an average fiber stress was obtained of 10% and 15% of the fibers ultimate strength for the two considered load ratios