A Study on the Bond Between Basalt Composite Reinforcement and Concrete

Investigation of carrying capacity performance of reinforced concrete (RC) structures is very important for structural engineering. In this study, it is aimed to examine the nonlinear carrying capacity performance of an RC laboratory structure by using three dimensional (3D) modelling approach. For this purpose, Zonguldak Bulent Ecevit University Laboratory Structure is selected and it is modeled as three dimensional by utilizing IDECAD static software. After modelling all beams, columns and floors according to 2018 Turkish earthquake code, concrete classes are determined for all bearing elements and specified concrete classes are defined for all elements of 3D model. Then, structure is analyzed for empty situation (Case 1) and structural performance of building is analyzed to this situation. In the past, a flat of this RC structure has been exposed to strong machine loads. For this reason, a machine which is fixed on the floor is placed in the 3D model and RC structure is analyzed considering nonstructural machine element loads (Case 2). According to analysis results, Case 1 is compared with Case 2 and it is clearly seen that nonstructural machine loads effect nonlinear carrying capacity performance of RC buildings.

Using recycled concrete aggregates (RCAs) as coarse aggregate in concrete has the potential to supplement current natural aggregate reserves, divert construction and demolition debris from landfills, and promote the adoption of sustainable civil infrastructure. As many of the design equations used to calculate structural concrete properties are based on empirical data for natural aggregate concrete, using these equations for RCA concrete may not be applicable. This study examined the bond of reinforcement in concrete produced using RCA as coarse aggregate. One natural aggregate (NA) and three RCA sources were evaluated and used as coarse aggregate in 14 separate concrete mixtures with four compressive strength levels. Various concrete mechanical properties, including compressive strength, splitting tensile strength, modulus of rupture, and fracture energy, were tested, and correlations between these properties and reinforcement bond were studied. The reinforcement bond was measured using 48 beam-end specimens incorporating several bonded lengths. The results showed that bond strength of RCA concrete was reduced by up to 21% in comparison to NA concrete, and that there was a strong correlation between bond strength and coarse aggregate crushing strength. A regression model was developed to relate bond strength to coarse aggregate strength, concrete compressive strength, and the bonded length. Using this model, experimentally predicted development lengths were calculated to be up to 9% greater for RCA concrete members in comparison to NA concrete members. Overall, this study was directed at providing guidance on the evaluation of multiple RCA sources and their respective impact on the bond of reinforcement in structural concrete.

Application FRP-rebar in the Manufacture of Reinforced Concrete Structures

Special Issue on Sustainable Building Structures

Steel-reinforced structural concrete is a common building material that has proven itself to be versatile, economical and affordable. Under a spectrum of operating conditions and circumstances, steel-reinforced concrete can be categorized as being both strong and durable thereby enabling in maintenance-free service during its life span. However, corrosion, or environment-induced degradation, of the steel reinforcement embedded in concrete is of concern particularly in aggressive environments, to include both aqueous and gaseous. A gradual degradation of the steel within concrete causes several problems ranging from cracking to spelling of the concrete coupled with reduced bond strength between the steel bars and the surrounding concrete. A reduction in bond strength contributes to a gradual loss in strength coupled with increased deformation, ease of initiation of flaws spanning both microscopic and macroscopic, and concurrent growth of the flaws through the microstructure. An evaluation of steel reinforcing bars coated with a new and emerging coating material is presented in this paper. Two potential applications for this type of coated bars include (a) the role of enamel-coated dowel bars for use in concrete pavements, and (b) enamel coated bars as viable reinforcement for structural concrete. The results of the study are aimed at evaluating and understanding the influence of environment on corrosion resistance of enamel coated steel reinforcing bars with concomitant influence on mechanical performance of reinforced concrete structure is presented, and comparisons are made with the performance of structural concrete reinforced with conventional steel reinforcing bars. Structural tests on beam specimens reinforced with enamel-coated steel reinforcing bars demonstrated the role of vitreous enamel coating on steel reinforcing bars and proved that the performance of reinforced concrete beams with such bars is marginally better in terms of improved flexural strength and shear strength.

[ES] Todas estructuras, especialmente las conformadas con hormigón armado, no solo deben cumplir con la seguridad necesaria bajo los Estados Límites Últimos (ULS), además es imprescindible que garanticen un comportamiento adecuado frente a condiciones de servicio. En general, los requisitos fundamentales de servicio que debe cumplir este tipo de estructuras son: la funcionalidad, comodidad para el usuario y la apariencia. Sin embargo, estos no se pueden verificar de forma directa; por lo tanto, ha sido necesario definir criterios de desempeño tales como control de deflexión, control de vibración y control de agrietamiento para dar cumplimiento a lo indicado anteriormente. Además, se dificulta el cálculo de la capacidad de servicio debido al fenómeno de agrietamiento, el efecto de rigidez por tensión, la contracción y los efectos de fluencia. Por lo tanto, el control de la fisuración en estructuras de hormigón armado generalmente se logra limitando la tensión en el refuerzo de acero y la matriz de hormigón. Siendo así que, en los diseños incluidos en códigos relevantes a hormigón, especifican la tensión máxima del refuerzo de acero después de la fisuración y el ancho máximo de fisura para los miembros estructurales de CR o FRC, no obstante los aspectos de capacidad de servicio del diseño para el hormigón reforzado con fibras de ultra alto rendimiento reforzado (R-UHPFRC), no han sido incluidos en los códigos o recomendaciones de UHPFRC. A pesar de que se han realizado muchos esfuerzos en la investigación tanto experimental como teórica sobre el comportamiento de servicio de los elementos estructurales de CR o FRC durante las últimas décadas, para el R-UHPFRC se debe desarrollar aún más su conocimiento relacionado con los requisitos para el diseño de capacidad de servicio, incluyendo su comportamiento de tensión y agrietamiento. En este marco, el objetivo principal de la presente tesis doctoral es evaluar el comportamiento de servicio de R-UHPFRC. Por tal razón, es fundamental realizar la evaluación del comportamiento de deformación y fisuración de los elementos de tracción R-UHPFRC. Para ello, se abordaron y cumplieron adecuadamente dos puntos principales. El primero, diseñar una metodología de prueba innovadora y adecuada para ejecutar los experimentos requeridos para este proyecto de doctorado. En segundo lugar, se llevó a cabo la evaluación de la respuesta de rigidez a la tensión y el comportamiento de agrietamiento del R-UHPFCR, que son parámetros primordiales para el diseño de capacidad de servicio. Para estudiar estos dos parámetros, se consideraron algunos parámetros importantes tales como: el efecto del volumen del contenido de fibra, el tipo de fibra, el efecto del tamaño, el efecto de la relación de refuerzo y el efecto de la contracción. Finalmente, para evaluar los parámetros mencionados, se presentan cuatro campañas experimentales. Cada una de ellas, representa un nivel diferente de estudio. El primero corresponde a la validación de la metodología de ensayo de tracción propuesta y examinar los datos experimentales obtenidos, para emplearlos en futuros estudios de este proyecto. El segundo nivel consistió en establecer y realizar experimentos completos con dos tipos de fibra de acero, modificando además su cantidad, es así como se utilizaron diferentes proporciones de refuerzo y sección transversal para evaluar el efecto tanto del tamaño como del contenido de fibra, respectivamente. También, en un estudio experimental específico se indagó sobre el efecto de la combinación de micro y microfibras de acero en la deformación y el comportamiento de agrietamiento de los elementos R-UHPFRC de tracción. El tercer nivel corresponde a una prueba de contracción intensiva, necesaria para obtener el valor de contracción del UHPFRC utilizado en esta investigación. El último nivel comprende la modificación de la geometría de la probeta y el uso de probetas en forma de hueso de perro para evaluar el ancho medio y máximo de fisura (valor

The progress of science and technology significantly depends on the success in creating new materials. Composite materials are a heterogeneous structure formed by a combination of reinforcing elements and isotropic binder (binder) material, currently widely used in various fields of technology. but for the economy is more important mass application. For this purpose, more thorough and long-term research and experimental implementations are carried out, which require significant intellectual and material costs. Development of structural elements using basalt fiber began in NDIBV since 1987. and experimental samples of prestressed concrete structures with basalt-plastic reinforcement. Research to identify the interaction of cement with basalt fiber and the design of effective concrete structures using basalt reinforcement. Concrete beams with basalt reinforcement were successfully tested. Unfortunately, the results of research have not been widely implemented. Therefore, this article is devoted to the problems of mass introduction into construction practice of various types of composite materials, including basalt reinforcement. The advantages and disadvantages of composite reinforcement in comparison with steel are discussed. During the theoretical and experimental studies, both positive and negative aspects of the use of basalt reinforcement were identified. So experiments have shown that basalt fiber loses strength in the environment of Portland cement stone. But this shortcoming has been overcome by the efforts of scientists, it is important to use certain defects of basalt fibers for specific conditions. There are the following main types of basalt fibers: 1) basalt continuous fibers with a diameter of 8 - 11 microns, 12 - 14 microns, 16 - 20 microns with a fiber length of 25 - 50 mm and more; 2) staple short fibers with a diameter of 6 - 12 microns and a length of 5 - 10 mm and several diameters; 3) basalt superthin fibers with a diameter of 0.5 - 1 microns with a length of 10 - 50 mm; 4) coarse basalt fibers with a diameter of 100 - 400 microns. To create structures with certain properties for specific conditions, appropriate basalt fibers are selected. According to the research results, recommendations and normative documents have been developed. Suggestions for measures to improve and successfully widely use composite elements for reinforcement of concrete structures.

Predicting bond strength of corroded reinforced concrete after high-temperature exposure: A stacking model and feature selection

The passivation behavior of steel reinforcements in concrete is significantly influenced by the environment, concrete pore solution, and the passive film formed on the steel surface. The present study used electrochemical methods to successfully characterize the passivation process of steel reinforcements in concrete. The passivation behavior of commonly used HRB400 steel reinforcement material in concrete was studied using various electrochemical parameters quantitatively. As the soaking test time increased, the OCP gradually increased and stabilized after 5 days, indicating that the steel electrode transitioned from an active state to a passive state in the simulated liquid environment of concrete. The steel reinforcement developed a protective passive film that reduced its tendency to corrode. According to EIS, after soaking for one day, the steel electrode showed significant early passivation, indicated by an increase in its arc diameter. The WE arc gradually increased in the first 5 days of immersion, suggesting dynamic passive film formation and development. Beyond 5 days, the passive film stabilized with minimal further changes in its impedance spectrum, indicating carbon steel electrode passivation. The working electrode’s impedance increased significantly on the fifth day, and gradually increased slightly after 10 days, indicating comprehensive coverage by the oxide film. Attributed to the growth and development of the oxide film, the electrode resistance reached a relatively stable state after the fifth day. The shift in corrosion potential offers an indication of the level of passivation of the steel reinforcements. The decrease in the anode Tafel slope and increase in the corrosion potential indicate the formation and stabilization of an oxide film on the steel surface, which is beneficial for its long-term durability in concrete structures. By analyzing the OCP, EIS, and dynamic potential polarization curve method data, it is possible to gain insights into the passivation behavior of steel reinforcements in concrete structures. This study aims to provide a basis for optimizing the corrosion protection of steel reinforcements in concrete structures. The significance of this study lies in a deep understanding of the passivation behavior of steel bars in concrete, providing a theoretical basis for improving the durability and lifespan of steel bars in concrete structures.

Purpose The work purpose is to establish the real technical condition of reinforced concrete and steel-reinforced concrete bridges based on the surveys and tests, as well as the analysis and synthesis of scientific and technical sources. Methodology. To achieve the goal, a review and synthesis of scientific and technical sources and regulatory documents regarding the technical condition of reinforced concrete and steel-reinforced concrete bridges and overpasses of Ukraine is carried out. It is shown that the development and implementation of new technologies for repairing the existing bridge defective structures, in particular on the highways of Ukraine is an urgent problem. A thorough analysis of experience and publications on the operation of newly built and long-term specified bridges in the mentioned environments is carried out. The data on the main unacceptable defects and faults of bridge structures as well as the causes, including concrete and reinforcement corrosion, and other defects and faults are presented. The quality indicators of reinforced concrete and steel-reinforced concrete bridge structures are considered, the problems and analysis of ensuring reliability and durability in the operation conditions on the highways of Ukraine are formulated. Results. The analysis of domestic and foreign scientific and technical sources as well as the experience of surveys and tests regarding the technical condition of reinforced concrete bridges structures in Ukraine is carried out. In particular, the analysis and synthesis of the problems of ensuring the reliability and durability of the specified bridges in the operation conditions on the highways of Ukraine is carried out. The design errors, construction defects and faults, and long-term operational faults in the mentioned environments are summarized and clarified. In addition, the obtained data are as the basis to specify the criteria and models of the destruction mechanics in relation to reinforced concrete bridge structures. In particular, based on the obtained data, the methods to determine the VAT and the residual resource of the specified bridges are created. Scientific novelty. Based on the analysis and synthesis of scientific and technical sources and a number of surveys and tests, reinforced concrete and steel-reinforced concrete structures and long-term bridges newly built after the floods in 1998 and 2001, it is possible to summarize the main reasons that significantly affect the structures degradation of both the newly built and long-term bridges. This allows generalizing the design errors, construction defects and faults, and long-term operational faults. In addition, the state data served as the basis to specify the criteria and models of the destruction mechanics in relation to reinforced concrete bridge structures. In particular, based on these data, the methods to determine the assessment of the strength and crack resistance and the VAT and the residual resource of such bridges are created. Practical significance. Based on the given data and observations of real objects for 30 years, the main faults, defects and errors of the design, construction, and long-term bridges are summarized and set up. The methods to determine the VAT and calculate the residual resource, giving an opportunity to work out the repair and restoration method to increase the durability and reliability of long-term bridges are created.

Investigation on the dynamic bond-slip behaviour between steel bar and concrete

Experimental study on the interfacial bond strength and energy dissipation capacity of steel and steel fibre reinforced concrete (SSFRC) structures

Corrosion of steel reinforcement is one of the main causes of premature deterioration in reinforced concrete (RC) structures. It causes concrete cover cracking, degrades the steel/concrete bond strength, reduces the cross section of steel bars, and consequently reduces the carrying capacity of RC structures. In general, steel corrosion in concrete structures can be divided into two stages: corrosion initiation and corrosion propagation. In this study, the effect of high performance concrete on the corrosion behavior of steel bar in RC specimens are experimentally investigated, particularly during the propagation stage. Concrete specimens with the addition of fly ash, silica fume, and calcium nitrite were fabricated and tested for over 23 years. The corrosion evolution over time was monitored with open circuit potential. During the propagation stage, the corrosion potential, concrete resistivity, and corrosion rate were also measured. Some selected concrete specimens were terminated and visual observation was conducted. Concrete powder was collected above the rebar trace and concrete core samples were drilled and sliced on selected specimens. The chloride concentration was determined. In addition, the steel bars were cleaned and the corrosion morphology was examined. The maximum corrosion pit depth was measured and the cross sectional loss of steel bars was also estimated. Results showed that during the propagation stage, a more negative corrosion potential is related to a higher corrosion rate and a lower concrete resistivity. Localized corrosion was observed on most of the steel bars, with average mass loss ranging from 1.66% to 9.86%, and a pitting factor varying from 1.12 to 2.65, respectively. Addition of fly ash, silica fume, and calcium nitrite reduced the corrosion rate, compared with ordinary Portland cement (OPC). Use of fly ash and silica fume also reduced the chloride concentration at the steel bar surface.

Theoretical effects of corrosion on lateral stress along reinforcement bars in concrete

In today’s world, concrete structures are exposed to various influences, including explosive actions. With the increasing use of fiber-reinforced concrete (FRC), it is essential to investigate its response to blast effects. As there are few studies on this topic worldwide, this research is dedicated to the question of how blast effects affect the damage and properties of six different types of reinforced concrete (RC) slabs. These samples differ in concrete classes (C30/37 and C50/60) and in the type of fibers added (steel and polypropylene). Visual inspections and non-destructive measurements are carried out before and after blasting. The damaged area of the concrete surface is determined by visual inspection, while non-destructive measurements evaluate parameters such as the rebound value of the Schmidt hammer, the electrical resistivity of the concrete, the velocity of the ultrasonic wave, and the dynamic modulus of elasticity. Equal amounts of explosives are applied to five of the RC slabs to enable a comparative analysis of the resulting damage. Based on the comparison of the measured data from these five RC slabs, conclusions are drawn regarding the effects of the explosive impacts on conventionally reinforced concrete slabs compared to those with added fibers. In addition, one of the RC slabs with steel fibers is exposed to approximately three times the amount of explosives to assess the extent of increased damage and to evaluate the suitability of military standards in the calculation of explosive charges for blasting RC elements with fibers.