Effects of tension stiffening and shrinkage on the flexural behavior of reinforced UHPFRC beams

[EN] This paper presents a study on the flexural behavior of Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) beams, which included conventional reinforcing bars. The study focuses on critical design aspects, such as concrete shrinkage and cracking implications on the tension-stiffening phenomenon. An experimental program with two different sized flexural reinforced UHPFRC beams was run. Beams were cast and tested in a four-point bending test (4PBT) using UHPFRC with different amounts of fibers: 130 and 160 kg/m(3) (1.66% and 2.00% in vol.) to cover a wide range of strain-softening and strain-hardening constitutive UHPFRC behaviors. A nonlinear finite element model (NLFEM) was developed to validate the mechanical tensile characterization of UHPFRC when applied to reinforced elements. Both shrinkage and tension-stiffening effects were considered to improve the model. After the NLFEM simulation, very reliable results were obtained at both the service and ultimate load levels compared to the experimental ones. Finally, some aspects about the design of reinforced UHPFRC cross-sections under bending forces are addressed and satisfactorily compared to the experimental results.This work forms part of Project "BIA2016-78460-C3-1-R" supported by the State Research Agency of Spain and the project "Rethinking coastal defence and Green-energy Service infrastructures through enHancEd-durAbiLity high-performance cement-based materials-ReSHEALience", funded by the European Union Horizon 2020 research and innovation programme under GA No 760824.Mezquida-Alcaraz, EJ.; Navarro-Gregori, J.; Martí Vargas, JR.; Serna Ros, P. (2021). Effects of tension stiffening and shrinkage on the flexural behavior of reinforced UHPFRC beams. Case Studies in Construction Materials. 15:1-28. https://doi.org/10.1016/j.cscm.2021.e007461281

Influence of cracking on oxygen transport in UHPFRC using stainless steel sensors

[EN] Reinforced concrete elements frequently suffer small cracks that are not relevant from the mechanical point of view, but they can be an entrance point for aggressive agents, such as oxygen, which could initiate the degradation processes. Fiber-Reinforced Concrete and especially Ultra High Performance Concrete increase the multi-cracking behavior, reducing the crack width and spacing. In this work, the oxygen availability of three types of concrete was compared at similar strain levels to evaluate the benefit of multi-cracking in the transport of oxygen. The types of concrete studied include traditional, High-Performance, and Ultra-High-Performance Fiber-Reinforced Concrete with and without nanofibers. To this purpose, reinforced concrete beams sized 150 x 100 x 750 mm(3) were prepared with embedded stainless steel sensors that were located at three heights, which have also been validated through this work. These beams were pre-cracked in bending up to fixed strain levels. The results indicate that the sensors used were able to detect oxygen availability due to the presence of cracks and the detected differences between the studied concretes. Ultra High Performance Concrete in the cracked state displayed lower oxygen availability than the uncracked High Performance Concrete, demonstrating its potential higher durability, even when working in cracked state, thanks to the increased multi-cracking response.The authors would like to express their gratitude to the Spanish Ministry of Science and Innovation for the pre-doctoral scholarship granted to Ana Martinez Ibernon (FPU 16/00723), to the Universitat Politecnica de Valencia for the pre-doctoral scholarship granted to Josep Ramon Lliso Ferrando (FPI-UPV-2018), and the European Union's Horizon 2020 ReSHEALience project (Grant Agreement No. 760824).Martínez-Ibernón, A.; Roig-Flores, M.; Lliso-Ferrando, JR.; Mezquida-Alcaraz, EJ.; Valcuende Payá, MO.; Serna Ros, P. (2020). Influence of cracking on oxygen transport in UHPFRC using stainless steel sensors. Applied Sciences. 10(1):1-17. https://doi.org/10.3390/app10010239S117101Front Matter. (2013). fib Model Code for Concrete Structures 2010, I-XXXIII. doi:10.1002/9783433604090.fmatterYoo, D.-Y., & Banthia, N. (2016). Mechanical properties of ultra-high-performance fiber-reinforced concrete: A review. Cement and Concrete Composites, 73, 267-280. doi:10.1016/j.cemconcomp.2016.08.001Wittmann, F., & Van Zijl, G. (Eds.). (2011). Durability of Strain-Hardening Fibre-Reinforced Cement-Based Composites (SHCC). doi:10.1007/978-94-007-0338-4Li, V. C. (2003). On Engineered Cementitious Composites (ECC). Journal of Advanced Concrete Technology, 1(3), 215-230. doi:10.3151/jact.1.215Asgari, M. A., Mastali, M., Dalvand, A., & Abdollahnejad, Z. (2017). Development of deflection hardening cementitious composites using glass fibres for flexural repairing/strengthening concrete beams: experimental and numerical studies. European Journal of Environmental and Civil Engineering, 23(8), 916-944. doi:10.1080/19648189.2017.1327888Ravindrarajah, R. S., & Swamy, R. N. (1989). Load effects on fracture of concrete. Materials and Structures, 22(1), 15-22. doi:10.1007/bf02472690Bascoul, A. (1996). State of the art report—Part 2: Mechanical micro-cracking of concrete. Materials and Structures, 29(2), 67-78. doi:10.1007/bf02486196Damgaard Jensen, A., & Chatterji, S. (1996). State of the art report on micro-cracking and lifetime of concrete—Part 1. Materials and Structures, 29(1), 3-8. doi:10.1007/bf02486001Berrocal, C. G., Löfgren, I., Lundgren, K., Görander, N., & Halldén, C. (2016). Characterisation of bending cracks in R/FRC using image analysis. Cement and Concrete Research, 90, 104-116. doi:10.1016/j.cemconres.2016.09.016Correia, M. J., Pereira, E. V., Salta, M. M., & Fonseca, I. T. E. (2006). Sensor for oxygen evaluation in concrete. Cement and Concrete Composites, 28(3), 226-232. doi:10.1016/j.cemconcomp.2006.01.006Yoon, I.-S. (2018). Comprehensive Approach to Calculate Oxygen Diffusivity of Cementitious Materials Considering Carbonation. International Journal of Concrete Structures and Materials, 12(1). doi:10.1186/s40069-018-0242-yBanthia, N., Zanotti, C., & Sappakittipakorn, M. (2014). Sustainable fiber reinforced concrete for repair applications. Construction and Building Materials, 67, 405-412. doi:10.1016/j.conbuildmat.2013.12.073Berrocal, C. G., Löfgren, I., & Lundgren, K. (2018). The effect of fibres on steel bar corrosion and flexural behaviour of corroded RC beams. Engineering Structures, 163, 409-425. doi:10.1016/j.engstruct.2018.02.068Sisomphon, K., Copuroglu, O., & Koenders, E. A. B. (2012). Self-healing of surface cracks in mortars with expansive additive and crystalline additive. Cement and Concrete Composites, 34(4), 566-574. doi:10.1016/j.cemconcomp.2012.01.005Ferrara, L., Krelani, V., & Carsana, M. (2014). A «fracture testing» based approach to assess crack healing of concrete with and without crystalline admixtures. Construction and Building Materials, 68, 535-551. doi:10.1016/j.conbuildmat.2014.07.008Roig-Flores, M., Pirritano, F., Serna, P., & Ferrara, L. (2016). Effect of crystalline admixtures on the self-healing capability of early-age concrete studied by means of permeability and crack closing tests. Construction and Building Materials, 114, 447-457. doi:10.1016/j.conbuildmat.2016.03.196López, J. Á., Serna, P., Navarro-Gregori, J., & Camacho, E. (2014). An inverse analysis method based on deflection to curvature transformation to determine the tensile properties of UHPFRC. Materials and Structures, 48(11), 3703-3718. doi:10.1617/s11527-014-0434-0Lopez, J. A., Serna, P., Camacho, E., Coll, H., & Navarro-Gregori, J. (2014). First Ultra-High-Performance Fibre-Reinforced Concrete Footbridge in Spain: Design and Construction. Structural Engineering International, 24(1), 101-104. doi:10.2749/101686614x13830788505793Negrini, A., Roig-Flores, M., Mezquida-Alcaraz, E. J., Ferrara, L., & Serna, P. (2019). Effect of crack pattern on the self-healing capability in traditional, HPC and UHPFRC concretes measured by water and chloride permeability. MATEC Web of Conferences, 289, 01006. doi:10.1051/matecconf/20192890100

Direct procedure to characterize the tensile constitutive behavior of strain-softening and strain-hardening UHPFRC

[EN] There is a need to establish a complete process to characterize Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) in both strain-hardening and strain-softening tensile behavior. This process should be simple and easy to apply so that its application is direct. Therefore, this paper presents the development of a complete process to obtain the tensile constitutive parameters of UHPFRC. A simplified inverse analysis based on four-point bending tests (4PBT) to derive the tensile material properties of strain-hardening UHPFRC was adapted to be applied in the event of strain softening using a nonlinear finite element model (NLFEM). To fulfill this objective, an extensive experimental program was run with 227 UHPFRC specimens tested in 4PBT that exhibited strain-softening and strain-hardening tensile responses. As a reference, the characteristic UHPFRC tensile constitutive behavior was obtained. Finally, a predictive application capable of predicting tensile behavior using the experimental 4PBT curve as input was developed with the experimental database.This work forms part of Project "BIA2016-78460-C3-1-R" supported by the State Research Agency of Spain and the European Union's Horizon 2020 ReSHEALience Project (Grant Agreement No. 760824)Mezquida-Alcaraz, EJ.; Navarro-Gregori, J.; Serna Ros, P. (2021). Direct procedure to characterize the tensile constitutive behavior of strain-softening and strain-hardening UHPFRC. Cement and Concrete Composites. 115:1-14. https://doi.org/10.1016/j.cemconcomp.2020.103854S11411

Robustez de estructuras prefabricadas de hormigón: simulación computacional mediante applied element method

[ES] El colapso progresivo puede definirse como el proceso por el cual un daño local inicial pone en marcha una cadena de fallos, que a veces puede conducir a un colapso desproporcionado o total. Se trata de un fenómeno que a menudo puede ser desencadenado por cargas anormales causadas por eventos extremos, a los que pueden estar expuestos todo tipo de edificios. A pesar de que las estructuras prefabricadas de hormigón, cada vez más utilizadas, pueden ser especialmente vulnerables al colapso progresivo, se han realizado relativamente pocos estudios sobre la robustez de esta tipología estructural en comparación con las estructuras hormigonadas in situ. Los modelos computacionales validados a partir de resultados experimentales son una de las herramientas más prometedoras para comprender mejor la respuesta de las estructuras prefabricadas de hormigón frente a acciones accidentales. Este trabajo presenta el empleo de una nueva estrategia de modelización, el Applied Element Method, que se ha empleado para predecir el comportamiento de un edificio-probeta de hormigón prefabricado bajo diferentes escenarios de retirada de columnas. Estos resultados se han utilizado para planificar la estrategia de monitorización y el esquema de carga para las pruebas experimentales en una estructura real de dos plantas de 15 m x 12 m que se construirá y monitorizará durante la retirada repentina de tres columnas diferentes.El trabajo presentado en este artículo no habría sido posible sin la financiación recibida del Ministerio de Ciencia e Innovación para el proyecto PREBUST (BIA2017-88322-R-AR) y para la ayuda Juan de la Cierva-Incorporación (IJC2020-042642-I). Los autores desean agradecer a Pedro A. Calderón y Juan J. Moragues su inestimable ayuda y apoyo. También se agradece a Ayman El-Fouly, de Applied Science International, su inestimable colaboración.Buitrago, M.; Makoond, NC.; Mezquida-Alcaraz, EJ.; Adam, JM. (2022). Robustez de estructuras prefabricadas de hormigón: simulación computacional mediante applied element method. International Center for Numerical Methods in Engineering (CIMNE). 468-477. http://hdl.handle.net/10251/19189146847

Effect of crack pattern on the self-healing capability in traditional, HPC and UHPFRC concretes measured by water and chloride permeability

Concrete has a natural self-healing capability to seal small cracks, named autogenous healing, which is mainly produced by continuing hydration and carbonation. This capability is very limited and is activated only when in direct contact with water. High Performance Fibre-Reinforced Concrete and Engineered Cementitious Composites have been reported to heal cracks for low damage levels, due to their crack pattern with multiple cracks and high cement contents. While their superior self-healing behaviour compared to traditional concrete types is frequently assumed, this study aims to have a direct comparison to move a step forward in durability quantification. Reinforced concrete beams made of traditional, high-performance and ultra-high-performance fibre-reinforced concretes were prepared, sized 150×100×750 mm3. These beams were pre-cracked in flexion up to fixed strain levels in the tensioned zone to allow the analysis of the effect of the different cracking patterns on the self-healing capability. Afterwards, water permeability tests were performed before and after healing under water immersion. A modification of the water permeability test was also explored using chlorides to evaluate the potential protection of this healing in chloride-rich environments. The results show the superior durability and self-healing performance of UHPFRC elements

Validation of a non-linear hinge model for tensile behavior of UHPFRC using a Finite Element Model

[EN] Nowadays, the characterization of Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) tensile behavior still remains a challenge for researchers. For this purpose, a simplified closed-form non-linear hinge model based on the Third Point Bending Test (ThirdPBT) was developed by the authors. This model has been used as the basis of a simplified inverse analysis methodology to derive the tensile material properties from load-deflection response obtained from ThirdPBT experimental tests. In this paper, a non-linear finite element model (ELM) is presented with the objective of validate the closed-form non-linear hinge model. The state determination of the closed-form model is straightforward, which facilitates further inverse analysis methodologies to derive the tensile properties of UHPFRC. The accuracy of the closed-form non-linear hinge model is validated by a robust non-linear FEM analysis and a set of 15 Third-Point Bending tests with variable depths and a constant slenderness ratio of 4.5. The numerical validation shows excellent results in terms of load-deflection response, bending curvatures and average longitudinal strains when resorting to the discrete crack approach.This work forms part of Project "BIA2016-78460-C3-1-R" supported by the State Research Agency of SpainMezquida-Alcaraz, EJ.; Navarro-Gregori, J.; Lopez Martinez, JA.; Serna Ros, P. (2019). Validation of a non-linear hinge model for tensile behavior of UHPFRC using a Finite Element Model. Computers and Concrete. 23(1):11-23. https://doi.org/10.12989/cac.2019.23.1.011S112323

Preliminary study on the fresh and mechanical properties of UHPC made with recycled UHPC aggregates

[EN] The recycling of construction and demolition waste material reduces disposal of material and also the consumption of resources, therefore promoting sustainability in construction. Ultra-high performance concrete (UHPC) is a relatively new material and its feasibility to be recycled needs to be verified. This work investigates the recyclability of UHPC disposed elements, including the production of recycled aggregates and fibres from UHPC. The feasibility of recycled aggregates and fibres at different replacement rates was evaluated through the assessment of rheological and mechanical properties of the newly produced UHPC elements. Concrete mixes with replacement of aggregates at 50% and 100%, displayed compression strength comparable to original UHPC, maintaining the original deflection-hardening response. However, their workability was slightly reduced when increasing the content of the recycled material. Mixes with recycled fibres experienced residual strength losses and behaved as deflection-softening materials in the case of complete replacement.The activity described in this paper has been performed in the framework of the project 'Rethinking coastal defence and Green-energy Service infrastructures through enHancEd-durAbiLity high-performance cement-based materials-ReSHEALience', funded by the European Union Horizon 2020 Research and Innovation Programme under GA No. 760824.Roig-Flores, M.; Borg, RP.; Ruiz-Muñoz, C.; Mezquida-Alcaraz, EJ.; Gimenez-Carbo, E.; Lozano Násner, AM.; Serna Ros, P. (2022). Preliminary study on the fresh and mechanical properties of UHPC made with recycled UHPC aggregates. European Journal of Environmental and Civil engineering. 26(15):7427-7442. https://doi.org/10.1080/19648189.2021.199782674277442261

Experimental study on the steel-fibre contribution to concrete shearbehaviour

This paper aims at studying the shear contribution of steel fibres in concrete. Ten reinforced concrete (RC) and steel-fibre reinforced concrete (SFRC) initially uncracked push-off specimens were tested. Average normal and transverse strains at the vicinity of the shear plane were measured by photogrammetry with good accuracy. Experimental results reveal that constant shear stress flow assumption is adequate. SFRC specimens exhibited greater shear stiffness compared to RC. Moreover, shear effectiveness of fibres after diagonal cracking seems significantly dependent on reinforcement crossing the shear plane. Numerical modelling of RC and SFRC push-off specimens shows good global behaviour.This work forms part of the PAID-06-11 programme supported by Universitat Politecnica de Valencia, and project "FISNE" BIA2012-35776 supported by the Spanish Ministry of Economy and Competitiveness.Navarro-Gregori, J.; Eduardo José Mezquida Alcaraz; Serna Ros, P.; Echegaray-Oviedo, JA. (2016). Experimental study on the steel-fibre contribution to concrete shearbehaviour. Construction and Building Materials. (112):100-111. https://doi.org/10.1016/j.conbuildmat.2016.02.157S10011111