Suchergebnisse

Different mechanical rebar splicing systems are presented, and design situations where mechanical splicing has advantage over reinforcement splicing by overlapping and welding are defined in this paper. New international standards for testing and proof of systems for mechanical rebar splicing quality are considered. Mechanical splicing system for rebar and bolt connection, usable in steel and reinforced concrete structural elements connections, is presented in this paper. There are only few examples of mechanical rebar splicing in our country. The most significant one - the pylon and beam connection at Ada Bridge in Belgrade is presented in the paper. Intensive development of production and use of mechanical rebar splicing systems, research in this area, as well as the publication of international standards prescribing requirements for quality and procedures for proof of quality, represent very good base for development of the corresponding technical norms in Serbia. The legislation in this area would quicken proof of quality procedures, attest and approval issuing for individual products, leading to wider use of this system in all situations where it is in advantage over the classical reinforcement splicing. ; U radu su prikazani različiti sistemi mehaničkog nastavljanja armature i definisane neke od situacija kada mehaničko nastavljanje ima prednost u odnosu na nastavljanje armature preklapanjem i zavarivanjem. Razmatrani su novi internacionalni standardi za ispitivanje i dokaz kvaliteta sistema za mehaničko nastavljanje armature. U radu je prikazan i sistem mehaničkih spojnica za povezivanje zavrtnja i armaturnog ankera, koji se može koristiti za vezu čeličnog i armiranobetonskog elementa. Malobrojni su primeri primene mehaničkog nastavljanja armature u našoj zemlji. Jedan od značajnijih - veza pilona i grede Mosta na Adi u Beogradu - prikazan je u radu. Intenzivan razvoj proizvodnje i primene mehaničkog nastavljanja armature u svetu, istraživanja u ovoj oblasti, kao i internacionalni standardi koji propisuju zahteve u vezi s kvalitetom i procedurom dokaza kvaliteta, predstavljaju osnovu za razvoj odgovarajuće tehničke regulative u ovoj oblasti i u Srbiji, čime bi se proširila primena ovih sistema u svim situacijama kada oni predstavljaju bolje rešenje u odnosu na klasične načine nastavljanja armature. .

In composite reinforced concrete elements formed by concrete and rebar, only if these two materials work together, reinforced concrete elements can fully function. The significant factor that will ensure working together is the bond strength, which is called adherence. The higher the value of this force, the harder the rebar is to pull out from the concrete. In this experimental study, the effect of concrete additives and aggregate type on the bond strength and the amount of elongation of the reinforcement without stripping from the concrete was investigated. For this purpose, 28-day compressive strength and adherence force and reinforcement elongation amounts of the concrete mixtures produced by using mineral, chemical and fiber additives for two different aggregate series, crushed stone and gravel, and two different cement dosages, were observed. In addition, by using 3 different rebar in terms of diameter and surface properties, the effect of these properties on concrete-rebar adherence was revealed. As a result of the study, the use of crushed stone aggregate, hyperplasticizer additive, mineral additive and ribbed rebar with 18mm diameter increased the bond strength compared to the reference samples.

Corrosion is one of the pathologies that most affects the resistance of reinforced concrete. There are numerous ancient structures still in use affected by corrosion that need proper evaluation and remedial treatment for their maintenance. In this sense, there has been an increasing tendency to use nondestructive testing techniques that do not alter the reinforcement elements of such vulnerable structures. This work presents a combined methodology by using ground penetrating radar (GPR) and infrared thermography (IRT) techniques for the detection and evaluation of corrosion. The methodology was applied to the case study of an old construction that belongs to the abandoned military battery of Cabo Udra (Galicia, Spain). The combination of these complementary techniques allowed for the identification of areas with different dielectric and thermal conductivity, as well as different reflection patterns and intensity of the GPR waves. Thus, from the analysis of the GPR signals and IRT images acquired, it was possible to interpret corroded areas and moisture, along with inner damages such as cracking and debonding. These pathologies have a direct effect on the durability and sustentation of a structure, while the knowledge of their existence might be useful for engineers engaged in the design of maintenance works.

Nanomaterials became targeted materials for many important applications due to its huge surface area and quantum confinement effects. In this work TiO2 nanoparticles (30nm) were used as additive to enhance the corrosion protection of steel rebar in artificial concrete solution (Ca(OH)2 (2g), KOH (22.44mg), NaOH (8mg) in 1L of distilled water) against saline environment (3.5%NaCl) at four temperatures; 20, 30, 40, and 50á´¼C. Three different concentrations of TiO2 NPs were used namely; 1, 3, and 5% by weight. The corrosion parameters and pitting probability were followed using Tafel and cyclic polarization plots respectively. Protection enhancement was recorded at all TiO2 percent used and efficiencies of 75-86% were achieved. Using TiO2 NPs reduces but not diminished the pitting hysterias loop area. The results supported by surface morphology examination using atomic force microscope (AFM).

Corrosion is one of the pathologies that most affects the resistance of reinforced concrete. There are numerous ancient structures still in use affected by corrosion that need proper evaluation and remedial treatment for their maintenance. In this sense, there has been an increasing tendency to use nondestructive testing techniques that do not alter the reinforcement elements of such vulnerable structures. This work presents a combined methodology by using ground penetrating radar (GPR) and infrared thermography (IRT) techniques for the detection and evaluation of corrosion. The methodology was applied to the case study of an old construction that belongs to the abandoned military battery of Cabo Udra (Galicia, Spain). The combination of these complementary techniques allowed for the identification of areas with different dielectric and thermal conductivity, as well as different reflection patterns and intensity of the GPR waves. Thus, from the analysis of the GPR signals and IRT images acquired, it was possible to interpret corroded areas and moisture, along with inner damages such as cracking and debonding. These pathologies have a direct effect on the durability and sustentation of a structure, while the knowledge of their existence might be useful for engineers engaged in the design of maintenance works. ; Agencia Estatal de Investigación | Ref. RTI2018-095893-B-C21 ; Universidad de Salamanca. Cátedra Iberdrola VIII Centenario

Corrosion is one of the pathologies that most affects the resistance of reinforced concrete. There are numerous ancient structures still in use affected by corrosion that need proper evaluation and remedial treatment for their maintenance. In this sense, there has been an increasing tendency to use nondestructive testing techniques that do not alter the reinforcement elements of such vulnerable structures. This work presents a combined methodology by using ground penetrating radar (GPR) and infrared thermography (IRT) techniques for the detection and evaluation of corrosion. The methodology was applied to the case study of an old construction that belongs to the abandoned military battery of Cabo Udra (Galicia, Spain). The combination of these complementary techniques allowed for the identification of areas with different dielectric and thermal conductivity, as well as different reflection patterns and intensity of the GPR waves. Thus, from the analysis of the GPR signals and IRT images acquired, it was possible to interpret corroded areas and moisture, along with inner damages such as cracking and debonding. These pathologies have a direct effect on the durability and sustentation of a structure, while the knowledge of their existence might be useful for engineers engaged in the design of maintenance works. ; Agencia Estatal de Investigación | Ref. RTI2018-095893-B-C21 ; Universidad de Salamanca. Cátedra Iberdrola VIII Centenario

During the last 20 years, the corrosion of concrete rebars is increasily being considered a major problem due the high costs spent by some Governments on repair and of civil concrete structures. In the present paper, a brief description on the causes of this type of corrosion is offered together with some references to the costs of repairing of bridge decks published by USA researchs. Finally, the main lines of research which, in opinion of the authors have priority, are commented. ; El fenómeno de la corrosión de armaduras en hormigón, en los últimos 20 años, ha pasado a ser un problema económico de primera magnitud por los costos que supone para algunos Gobiernos la reparación y el mantenimiento de muchas Obras Públicas. En el presente artículo se hacen unas breves referencias a las causas más frecuentes que provocan esta corrosión y se dan algunas cifras ofrecidas por investigadores norteamericanos sobre los costos en reparación de puentes de hormigón armado. Finalmente, se comentan las líneas de investigación que, a juicio de los autores, son prioritarias en esta materia.

[EN]During the last 20 years, the corrosión of concrete rebars is increasily being considered a major probiem due the high costs spent by some Governments on repair and of civil concrete structures. In the present paper, a brief description on the causes of this type of corrosión is offered together with some references to the costs of repairing of bridge decks published by USA researchs. Finally, the main Unes of research which, in opinión of the authors have priority, are commented. ; [ES]El fenómeno de la corrosión de armaduras en hormigón, en los últimos 20 años, ha pasado a ser un problema económico de primera magnitud por los costos que supone para algunos Gobiernos la reparación y el mantenimiento de muchas Obras Públicas. En el presente artículo se hacen unas breves referencias a las causas más frecuentes que provocan esta corrosión y se dan algunas cifras ofrecidas por investigadores norteamericanos sobre los costos en reparación de puentes de hormigón armado. Finalmente, se comentan las líneas de investigación que, a juicio de los autores, son prioritarias en esta materia. ; Peer reviewed

The possibility of using licorice extract as a green inhibitor for steel reinforcements in chloride-contaminated simulated concrete pore solution was explored in this study. Different licorice amounts were added to alkaline solutions and then 1% NaCl was also added. Electrochemical studies, up to 24 h, and surface analysis (X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy) were performed. Results demonstrated the inhibition effectiveness of the plant extract on steel rebar corrosion, regardless of the concentration, being detected an inhibition efficiency higher than 80 % with electrochemical techniques for 0.1% licorice extract, which showed the most effective performance. Surface analysis methods confirmed the presence of licorice on the surface, through the deposition of organic molecules present in the plant extract on the surface oxide/hydroxide. DFT calculations confirmed that compounds present in licorice can be chemically adsorbed on steel oxide surface. ; This research was funded by the European Union Horizon 2020 research and innovation MSCA-IF-2019 programme under grant agreement No 892074 (NATCON project). Support from the Ministerio de Ciencia, Innovación y Universidades of Spain (RTI2018-096428-B-I00) is also acknowledged.