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This study presents a novel methodology to evaluate the self-healing capability of Ultra High-Performance Fiber-Reinforced Concrete (UHPFRC) designed to compare conventional concrete types. The procedure used combines loading reinforced concrete elements until a fixed strain level to have a comparable total crack opening. Afterwards, water penetration to chlorides is used as an indicator of permeability. This work compares autogenous healing efficiency of a conventional concrete, a high-performance concrete, and two types of UHPFRCs with and without 0.8% of a crystalline admixture (CA) by the binder weight. The results show that all UHPFRC specimens exhibited excellent autogenous healing, higher than conventional concretes for an equivalent total crack. The self-healing results depended greatly on the crack size and the fiber content. Additionally, UHPFRCs with CA obtained the lowest water permeability after promoting self-healing for one month in water immersion and presented almost complete healing against chloride penetration. ; 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. The authors would also like to thank Sika and Penetron for providing materials for the tests and E.J. Mezquida-Alcaraz for the characterization of UHPFRC mixes with Inverse Analysis.

[EN] The aim of this experimental work was to study the porous structure of Ultra-High-Performance Fibre-Reinforced Concretes (UH) made with different fibre volume contents (0%, 1%, 2%) under several curing conditions (laboratory environment, 20 degrees C, 60 degrees C, 90 degrees C), comparing the results with those recorded for ordinary, high strength and very high strength concretes. Scanning electron microscopy, mercury intrusion porosimetry, thermogravimetry, water absorption and oxygen permeability tests were carried out. The results showed a low portlandite content in UH (in the order of 75% lower than in concrete C50) and a low degree of hydration, but they rise with curing temperature. These concretes have a very fine porous structure, with a high concentration of pores on the nanoscale level, below 0.05 mu m. Their porosity accessible to water is consequently around 7-fold lower than in conventional (C30), 6-fold lower than in high-strength (C50) and 4-fold lower than in very high-strength (C90) concretes. Their oxygen permeability is at least one order of magnitude lower than in C90, two orders of magnitude lower than in C50 and three orders of magnitude lower than in C30. The percentage of added steel fibre does not affect the UH porous structure ; This research was funded by Ministerio de Economia Y Competitividad (Agencia Estatal de Investigacion) of the Spanish Government, Grant number BIA2016-78460-C3-3-R ; Valcuende Payá, MO.; Lliso-Ferrando, JR.; Roig-Flores, M.; Gandía-Romero, JM. (2021). Porous Structure of Ultra-High-Performance Fibre-Reinforced Concretes. Materials. 14(7):1-18. https://doi.org/10.3390/ma14071637 ; S ; 1 ; 18 ; 14 ; 7

[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. ...