Suchergebnisse

[EN] The corrosion resistance of ultra-high performance concrete (UH) made with different fibre contents and under distinct curing conditions was studied. No signs of carbonation were observed after 1 year of accelerated carbonation testing (3% CO2). The fibreless UHs¿ electrical resistivity was above 5000 ¿·m, although these values were 2-fold higher than a UH with 1% fibres and approximately 5-fold higher than a UH with 2% fibres. Concrete resistance to chloride penetration was also extremely high (the diffusion coefficient equalled 1.3·10¿13 m2/s) and curing temperatures of 60 °C or 90 °C improved even more these properties, while lack of curing made them slightly worse. Given these excellent properties, the corrosion rate in specimens submerged in chloride solution for 1 year was negligible (iCORR from 0.007 to 0.025 µA/cm2). These values remained stable with time, unlike the 50 MPa concrete at 2 months when iCORR starting to increase and was 12-fold higher after 1 year. The time estimated for corrosion onset in UH is on average about 150-fold higher than that of 50 MPa. ; Authors thank to the Spanish Government the financial support of project BIA2016-78460-C3-3-R and to the European Union¿s Horizon 2020 the financial support of ReSHEALience project (Grant Agreement No. 760824). Furthermore, authors would like to express their gratitude for the support of the Universitat Politecnica de Valencia. Funding for open access charge: CRUE-Universitat Politecnica de Valencia. The predoctoral scholarship granted to Josep Ramon Lliso Ferrando within the program "Formacion de Personal Investigador" from the Universitat Politecnica de Valencia (FPI-UPV-2018) is also gratefully acknowledged. ; Valcuende Payá, MO.; Lliso-Ferrando, JR.; Ramón Zamora, JE.; Soto Camino, J. (2021). Corrosion resistance of ultra-high performance fibre- reinforced concrete. Construction and Building Materials. 306:1-10. https://doi.org/10.1016/j.conbuildmat.2021.124914 ; S ; 1 ; 10 ; 306

[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] This paper presents a Potentiostatic Step Voltammetry approach to corrosion rate measurement of reinforcements in concrete. We have termed this approach PSV-TE since it is based on the Tafel extrapolation method, but with the added advantage that long and slow potentiodynamic scans are no longer required to obtain the Tafel slopes. In this way, the irreversible polarization of rebars is prevented, so PSV-TE is considered to be a non-destructive method. The Tafel slopes are obtained by fitting the current-time response of the system to a theoretical model which we have outlined and validated previously. In this way, the concrete's electrical resistance and double layer capacity are also obtained. In this study, the optimal PSV-TE design has been established and validated on a range of reinforced concrete specimens. Results show minimal deviation between PSV-TE and reference methods. Therefore, PSV-TE is part of the corrosion monitoring system we have patented. ; This work was supported by a pre-doctoral scholarship granted to Jose Enrique Ramon Zamora by the Spanish Ministry of Science and Innovation [grant number FPU13/00911]. We would also like to acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through the national program of oriented research, development and innovation to societal challenges [project number BIA2016-78460-C3-3-R]. The research activity reported in this paper has been performed in the framework of the ReSHEALience project which has received funding from the European Union's Horizon 2020 research and innovation program [number 760824]. We extend our appreciation to Rafa Calabuig and Jesus Martinez, Material Laboratory technicians of the ETSIE of the Universitat Politecnica de Valencia, for their invaluable cooperation in the experimental work. ; Ramón, J.; Gandía-Romero, JM.; Bataller Prats, R.; Alcañiz Fillol, M.; Valcuende Payá, MO.; Soto Camino, J. (2020). Potential step voltammetry: An approach to corrosion rate measurement of reinforcements in ...

[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. ...

Concrete carbonation is one of the main triggers of the corrosion process and hence of the premature deterioration of concrete reinforcements. In order to monitor and control the carbonation process, a potentiometric sensor using thick-film technology was developed. This paper includes the results of the research carried out to characterise the pH sensor, including the materials, response time, sensitivity, detection limit, reproducibility, reversibility and the study of chloride interference. The sensors have been studied in pore solutions and concrete specimens. The study shows that the thick-film sensor has a potentiometric response to variations in pH and is capable of providing continuous, real-time information on the progress of the carbonation front. ; The pre-doctoral scholarship was granted to Roman Bataller Prats by the Research Staff Training Program, "Formacion de Personal Investigador (FPI) 2012" from Universitat Politecnica de Valencia and to Jose Enrique Ramon Zamora by the University Faculty Training Program FPU13/0091, "Formacion del Profesorado Universitario (FPU) 2013" from the Spanish Ministry of Science and Innovation. The financial support from the Spanish Government and the European FEDER funds MAT2012-38429-004-04. ETSIE (UPV) by their support to the laboratory is also gratefully acknowledged. ; Gandía-Romero, JM.; Campos, I.; Valcuende Payá, MO.; García Breijo, E.; Marcos Martínez, MD.; Paya Bernabeu, JJ.; Soto Camino, J. (2016). Potentiometric thick-film sensors for measuring the pH of concrete. Cement and Concrete Composites. 68(2016):66-76. https://doi.org/10.1016/j.cemconcomp.2016.02.006 ; S ; 66 ; 76 ; 68 ; 2016