Passive Reinforcement Research Articles

Process intensification in carbonylation of formaldehyde with active and passive enhancement methods

The process intensification in carbonylation of formaldehyde by active and passive enhancement was investigated in stirred tank reactor and membrane contactor, respectively. The increase of rotational speed and decrease of reaction solution volume was advantageous to the yield of glycolic acid in active strengthening experiments, indicating that the reaction was greatly affected by the mass transfer of CO. In passive reinforcement mode, the membrane contactor composed of PTFE hollow fibers with inner diameter of 0.85 mm or 0.42 mm was used as a novel reactor to improve the process mass transfer. The effects of reaction temperature, operation pressure, reaction time and reactant concentration were systematically studied. The results showed that membrane contactor was an effective reactor for the carbonylation of formaldehyde compared to the conventional tank reactor. This study provided a reference for the process intensification of similar gas-liquid reactions.

Improving response of wind turbines by pitch angle controller based on gain-scheduled recurrent ANFIS type 2 with passive reinforcement learning

In this paper, passive reinforcement learning (RL) solved by particle swarm optimization policy (PSO–P) is used to handle an adaptive neuro-fuzzy inference system (ANFIS) type-2 structure with unsupervised clustering for controlling the pitch angle of a real wind turbine (WT). The proposed control scheme is based on gain-scheduled reinforcement learning recurrent ANFIS type 2 (GS-RL-RANFIST2) pitch angle controller to maintain the rotor speed at its rated value while smoothing the output power and the performance of the pitch angle system. The practical application of the proposed controller is evaluated by using FAST tool for a real 600 kW WT equipped with a synchronous generator with a full-size power converter (CART3, located at the National Renewable Energy Laboratory, NREL), whose results are compared with those obtained by a gain corrected proportional integral (GC-PI) controller. The results demonstrate that the GS-RL-RANFIST2, which sets the nonlinear characteristics of the system automatically and waves more uncertainties in the windy conditions, allows to increase the energy capture and smooth the output power fluctuation, and therefore, to improve the control and response of the WT.

Cover Picture: Materials and Corrosion. 5/2020

Cover:Galvanic corrosion of reinforced concrete structures is characterized by high corrosion rates, accompanied by severe loss of cross section. The visualization presents a modelling approach used by Michael Raupach in the course of his thesis. It is accounting for the polarization resistances of active and passive reinforcement as well as the concrete resistivity in a cracked concrete situation with coplanar arrangement of anodic and cathodic areas.More information can be found in: M. Raupach, Ph.D. Thesis, Schriftenreihe des deutschen Ausschusses für Stahlbeton, Berlin, Germany 1992

Effect of Cathode–Anode distance and electrical resistivity on macrocell corrosion currents and cathodic response in cases of chloride induced corrosion in reinforced concrete structures

When dealing with macrocell corrosion, it is crucial to consider the geometry and size of the structure, including the mobilizable cathode–anode distance, which is the maximum distance where passive reinforcement bars exchange current with corroding active sites. An application of the mobilizable cathode–anode distance is the corrosion of submerged regions of reinforced concrete structures where very high local anodic current densities were reported with no visual manifestation making this type of corrosion very dangerous. One possible explanation for these observations is that active steel (anode) bars in the submerged region could be coupled with a cathodic aerated zone located far away from the anode. This paper aims to study the influence of cathode–anode distance on the macrocell current. Experimental investigations were carried out on a 10 m long reinforced beam consisting of 20 segments of rebars: an anode where corrosion was initiated with chloride diffusion, and 19 identical cathodes. Different electrical connections were made between cathodes and corrosion currents were measured in order to test the impact of the cathode–anode distance on the evolution of corrosion current and the attenuation of the cathodic reaction in relation to the distance between anode and cathode. The experimental campaign was supported by numerical simulations, which confirmed the experimental results and tested the impact of electrical resistivity on the mobilizable cathode–anode distance. By connecting the anode to each cathode alone, it was found that macrocell corrosion current could be provided by cathode bars at large distances from the anode, the distance being dependent on the electrical resistivity of the structure. It was also found that, when all the cathodes were connected to the anode, the closest bar received the highest proportion of the total current, which increased with electrical resistivity, whereas the most distant bars received very limited amounts of current.

A novel self-healing composite made of thermally reversible polymer and shape memory alloy reinforcement

A novel self-healing polymer composite made of the thermally reversible polymer matrix and shape memory alloy reinforcement is introduced. The healing system is designed in such a way that by heating the structure, activation of shape recovery in shape memory alloy and chemical reversible reactions in polymer occur simultaneously. In the present healing method, the required crack closure force is provided by activating the embedded shape memory alloy wires in the polymer. Both superelastic and shape memory effects of shape memory alloy are considered on the fracture behavior of composites by investigating the passive and active reinforcement methods, respectively. Double cleavage drilled compression tests are utilized in order to study the fracture behavior and healing efficiency of composites. In the case of passive reinforcement, embedding 2% prestrained shape memory alloy wires caused 15% enhancement in the fracture toughness of composites. In this prestrain level, results of the micromechanical model are in good agreement with experiments. Promising results are also obtained for healing efficiency of composites in the case of active reinforcement. The average healing efficiency of 92% is achieved for shape memory alloy-reinforced thermally reversible epoxy composites. The excellent healing performance, without the necessity of external force and pressure, makes the present healing method as an ideal candidate for utilizing self-healing composite structures.

Comparative case study between the characteristics that the use of passive or active reinforcement in ribbed slab attributes to the construction of a garage building.

Comparative case study between the characteristics that the use of passive or active reinforcement in ribbed slab attributes to the construction of a garage building.

Response of UHPFRC Columns Submitted to Combined Axial and Alternate Flexural Loads

This paper deals with the experimental determination of ductility of ultra-high-performance fiber-reinforced concrete (UHPFRC) columns with longitudinal passive reinforcement, tested under combined axial and alternate flexural load. The influence of axial load has been studied, as well as the presence or not of a reduced shear reinforcement. One companion column made of ordinary concrete and with a high shear reinforcement ratio has also been tested for comparison. The ductility has been assessed with energy dissipation and ductility coefficient calculations. In addition, the maximum bending moment has been compared with theoretical calculation, using the material characteristics determined from characterization tests. The paper concludes that UHPFRC columns with a longitudinal reinforcement which have not been specifically designed for seismic resistance do display a ductility coefficient higher than 2 and a noticeable ability to protect the rebars from buckling, but have a rather high decrease of bending moment under the succession of series of alternate flexural load cycles.

A critical examination of corrosion rate measurement techniques applied to reinforcing steel in concrete

This paper presents an investigation of five corrosion‐monitoring techniques for reinforced concrete. The techniques studied are the potentiodynamic, galvanostatic, and coulostatic direct‐current techniques as well as electrochemical impedance spectroscopy (EIS), and the connectionless electrical pulse response analysis (CEPRA) technique. The study included monitoring corrosion rates on reinforced concrete specimens with a range of admixed chloride percentages, cover depths, and rebar diameters for 8 months. After this period, the rebars were extracted for mass loss measurements to determine the average corrosion rates. EIS was found to provide accurate measurements of active and passive corrosion rates with a simplified spectrum‐analysis procedure. Galvanostatic and potentiodynamic techniques were able to measure the corrosion rates for actively corroding reinforcements accurately, while the coulostatic technique overestimated it. For passive reinforcements, the coulostatic technique provided reliable corrosion rate estimates, while the potentiodynamic technique provided a minor overestimation, due to the fast scan rate used, and the galvanostatic technique failed in detecting passivity, due to the short measurement duration and confinement failure. Finally, the CEPRA technique provided accurate corrosion rate predictions except for passive rebars with small diameters embedded in saturated concrete.

Sectional analysis for design of ultra-high performance fiber reinforced concrete beams with passive reinforcement

Sectional flexural analysis, as performed in normal strength concrete design, requires uniaxial constitutive models. For ultra-high performance fiber reinforced concrete (UHPFRC), the constitutive model tensile backbone varies with section heights for different flexural members, due to the size-dependent stress-crack opening relation used to derive it. In this paper, several simplified size-independent constitutive models were investigated. For unreinforced sections with heights between 51 mm and 1067 mm, the elastic-perfectly-plastic tension model leads to conservative ultimate moment prediction (or results within 5%) when compared to that obtained by the size-dependent model. For reinforced sections, the difference between the two models is affected by the reinforcing condition and is even smaller than the unreinforced cases. By assuming an elastic-perfectly-plastic tension model, the flexural strength of rectangular or T section UHPFRC beams was estimated analytically. The flexural strengths are greatly influenced by the reinforcement ratio and yielding strength of the longitudinal reinforcement. Including shear strength predictive equations from past research, the load capacity and failure mode for rectangular and T beams are presented in a design chart. The impact of several factors on UHPFRC beam flexural responses were investigated, such as different compressive strength, curing conditions, and anisotropic fiber orientation distributions. The load-deflection relationships generated from beam flexural analysis were compared to experimental results for both unreinforced and reinforced beams, with or without fiber alignment. Factors affecting the first crack strength in tension (i.e., fiber orientation distribution) had greater impact on the flexural strength of UHPFRC beams than the effect of using a size-dependent model.

Mixed model for the analytical determination of critical buckling load of passive reinforcement in compressed RC and FRC elements under monotonic loading

Compressed reinforcements on reinforced concrete (RC) and steel fibre reinforced concrete (SFRC) columns are generally submitted to cyclic and monotonic loading, which can buckle. This phenomenon can cause the reduction of both ductility and peak loads, which is why design standards propose constructive details to avoid this. Although the bibliography mentions that steel fibres in concrete can delay buckling of reinforcements, design codes do not distinguish between concrete types (with and without fibres) in these constructive details. Analytical models that determine the length and critical buckling stress of reinforcements may consider this effect. Nowadays, analytical models can be classified as discrete and distributed depending on whether they consider transverse reinforcement stiffness and the stiffness of the concrete cover that concentrates on transverse reinforcements, or if they are distributed along the element, respectively. Both discrete and distributed models are valid for small transverse reinforcement separations, while distributed models that only consider the concrete cover effect are valid for large transverse reinforcement separations.This paper proposes a mixed model to determine critical buckling loads of compressed reinforcements subjected to monotonic loading to use the stress-strain relationships of reinforcing bars, including buckling, that are found in the scientific-technical literature. This model considers transverse reinforcements discretely and concrete cover distributedly. The model can be applied to any transverse reinforcement configuration, and to any concrete type (with or without fibres). An analytical equation is also proposed to determine critical compressed reinforcement loads, whose result is presented as abaci. Finally, to calibrate the model in normal-strength concrete columns under eccentric loading, with or without fibres, a programme is presented in which the critical load of longitudinal reinforcements is experimentally determined. The proposed analytical model is calibrated and a procedure to determine critical buckling loads of compressed reinforcements under monotonic loading is proposed.

Economic viability of ultra high-performance fiber reinforced concrete in prestressed concrete wind towers to support a 5 MW turbine

Abstract The Ultra-High Performance Fiber-Reinforced Concrete is a material with remarkable mechanical properties and durability when compared to conventional and high performance concrete, which allows its use even without the reinforcement. This paper proposes the design of prestressed towers for a 5 MW turbine, through regulatory provisions and the limit states method, with UHPFRC and the concrete class C50, comparing the differences obtained in the design by parametric analysis, giving the advantages and disadvantages of using this new type of concrete. Important considerations, simplifications and notes are made to the calculation process, as well as in obtaining the prestressing and passive longitudinal and passive transverse reinforcement, highlighting the shear strength of annular sections comparing a model proposed here with recent experimental results present in the literature, which was obtained good agreement. In the end, it is estimated a first value within the constraints here made to ensure the economic viability of the use of UHPFRC in a 100 m prestressed wind tower with a 5 MW turbine.

Potential differences between passive reinforcement segments in concrete components in dependency of binder type, aeration conditions and quality of the steel/concrete‐interface

For exploring the chloride threshold level of steel in concrete, respectively the onset of active reinforcement corrosion in general, the environmental and electrochemical conditions in the passive state are decisive. For reinforced concrete structures in practice, possible characteristics of the inner polarization state and the resulting potential differences, mainly forced by moisture deviations in the structure, are not commonly known. In this paper the exploration of four slab like specimens and two column bases with “real” dimensions, which are cyclically exposed to chloride solution for simulating typical moisture conditions for outdoor structures, is described. Ordinary portland cement (OPC, CEM I) and blast‐furnace slag cement (BFSC, CEM III) are used. For various, decoupled segments of the reinforcing steel potential differences are determined and depolarization measurements are performed. The concrete compositions with different binder types show considerably diverging results. The maximum of the determined potential differences is 150 mV for OPC specimens and 650 mV for BFSC specimens. The extent of instant effects of changing exposure conditions also is completely different. Generally, exposure (wetting) causes a displacement of the potential to more negative values. Other impact parameters do not lead to a clear pattern of behavior or reaction.

Design procedure and experimental study on fibre reinforced concrete segmental rings for vertical shafts

Structural fibres are used to replace partially or totally the passive reinforcement in precast concrete segments for tunnel linings constructed with TBM, showing several advantages. Fibre reinforced concrete (FRC) could also be applied with similar benefits to vertical shafts. However, to the author's knowledge, this material has not been used in such application yet. The Model Code 2010 gathers an approach for the design of FRC structural elements. This approach should be adapted according to the structural needs of precast segment, for which the transient load stages are often the most critical and specific ductility requirements should be established. The objective of this paper is twofold: propose a general analytical formulation to assess the minimum mechanical requirements that FRC must fulfil in case of partial or complete substitution of the steel rebars and confirm that it is possible to replace the rebars by using fibres in vertical shaft linings. First, the general analytical formulation is proposed. Then, the segments of the Montcada vertical shaft (Barcelona) are redesigned considering the total substitution of the traditional reinforcement by fibres. Finally, two full-scale tests of the FRC precast segments were performed to verify the suitability of the analytical formulation proposed.

Post-tensioning glulam timber beams with basalt FRP tendons

Improvements in the structural performance of glulam timber beams by the inclusion of reinforcing materials can increase both the service performance and ultimate capacity. This paper describes a series of four-point bending tests conducted, under service loads and to failure, on unreinforced, reinforced and post-tensioned glulam timber beams, where the reinforcing tendon used is 12 mm dia. basalt fibre-reinforced polymer. The research is designed to evaluate the benefits offered by including an active reinforcement in contrast to the passive reinforcement typically used within timber strengthening works, in addition to establishing the effect that bonding the reinforcing tendon has on the material's performance. Further experimental tests have also been developed to investigate the long-term implications of this research, with emphasis placed upon creep and loss of post-tensioning; however, this is ongoing and is not presented in this paper. The laboratory investigations establish that the flexural strength and stiffness increase for both the unbonded and bonded post-tensioned timbers compared to the unreinforced and reinforced beams. Timber that is post-tensioned with an unbonded basalt fibre-reinforced polymer tendon shows a flexural strength increase of 2·8% and an increase in stiffness of 8·7%. Post-tensioned beams with a bonded basalt fibre-reinforced polymer tendon show increases in flexural strength and stiffness of 15·4% and 11·5% respectively.

An Experimental Study on Reinforcing Rock Columns Using Heated Polymeric Ties

Load-bearing rock column and pillar reinforcing without a permanent visual change is an important advantage for applications in both historical and modern sites. One of the most widely seen column reinforcement methods is using steel collars which can cause a visual change on rock surfaces because of its corrosion problem and hardness. Steel collars are mostly used to reinforce rock columns with regular cross-sectional shapes, but not suitable for being used to reinforce rock columns with irregular crosssectional shapes because of their high stiffness which prevents them from being shaped by the column body. Rock column reinforcement method can be divided into two groups: active and passive reinforcement methods (Moghaddam et al. 2010; Bieniewski et al. 1969; Komurlu et al. 2013; Spencer and Gardner 2003). In passive reinforcement method, confinement pressure is supplied as a reaction to the deformation of the rock surface in contact with the reinforcing devices. On the other hand, active reinforcement pressure can increase the load-bearing capacity without a deformation of columns/pillars (Holmes et al. 2014; Windsor 1987; Kovari et al. 1983). Polymers can be divided into two groups: thermoplastics and thermosets, according to their reaction to being heated (Wigley 1971; McCrum et al. 1997; Komurlu and Kesimal 2014). Thermosets cannot be softened and extended easily by heating. Generally, their polymerization process transforms the liquid components into a plastic or rubber by cross-linking. Thermosets are not able to be remolded by heating after their initial formation (Pascault et al. 2002; Tadlaoui et al. 1993; Ebewele 2000). Therefore, thermosets are generally polymerized in molds. In case of heating with high temperatures, cross-links of thermosets are broken without melting. On the other hand, thermoplastics, also called as thermosoftening plastics, can be deformed easily and shaped by heating. Thermoplastics harden and strengthen by cooling, which can preserve the original length or shape after cooling from a temperature level depending on the type of product (Akay and Barkley 1985; Komurlu and Kesimal 2012). Therefore, the use of thermoplastics should be considered for the aim of active reinforcement pressure applied on rock columns encircled with heated ties. Polymer materials are used for different reasons varying within a large range. An important percentage of polymer usage is because of their good chemical resistivity as in applications of food packing, transport of drinking water, hot water or gases (RTMSTI 2010; Ohtomo and Ohnuma 2014; Castagnet and Grandidier 2006; Siracusa et al. 2011). Polymer materials used considering their strength values are generally engineering polymers which have better mechanical properties in comparison to most of the other polymeric materials (Troughton 2008; Komurlu 2012; Komurlu and Kesimal 2011). Also, the chemical resistance of the engineering polymers is an important reason, making them convenient to be used as an alternative to conventional engineering materials. & Eren Komurlu erenkomurlu@gmail.com; ekomurlu@ktu.edu.tr

Post-tensioning of glulam timber with steel tendons

This paper describes a series of four-point bending tests that were conducted, under service loads and to failure, on unreinforced, reinforced and post-tensioned glulam timber beams, where the reinforcing tendon used was 12mm diameter toughened steel bar. The research was designed to evaluate the benefits offered by including an active reinforcement in contrast to the passive reinforcement typically used within timber strengthening works, in addition to establishing the effect that bonding the reinforcing tendon has on the materials performance.The laboratory investigations established that the flexural strength and stiffness increased for both the reinforced and post-tensioned timbers compared to the unreinforced beams. The flexural strength of the reinforced timber increased by 29.4%, while the stiffness increased by 28.1%. Timber that was post-tensioned with an unbonded steel tendon showed a flexural strength increase of 17.6% and an increase in stiffness of 8.1%. Post-tensioned beams with a bonded steel tendon showed increases in flexural strength and stiffness of 40.1% and 30% respectively.

Memetic Algorithm Approach to Designing Precast-Prestressed Concrete Road Bridges with Steel Fiber Reinforcement

AbstractThis paper describes the influence of steel fiber-reinforcement on the design of cost-optimized, prestressed concrete, precast road bridges, with a double U-shaped crosssection and isostatic spans. A memetic algorithm with variable-depth neighborhood search is applied to the economic cost of these structures at different stages of manufacturing, transportation, and construction. The problem involved 41 discrete design variables for the geometry of the beam and the slab, materials in the two elements, active and passive reinforcement, as well as residual flexural tensile strength corresponding to the fibers. The use of fibers decreases the mean weight of the beam by 1.72% and reduces the number of strands an average of 3.59%, but it increases the passive reinforcement by 8.71% on average, respectively. Finally, despite the higher cost of the fibers, their use is economically feasible since the average relative difference in cost is less than 0.19%.

A Study on the Structural Response of a PSC Inner Containment Dome with Large Openings Due to Prestress Transfer

A linear three dimensional finite element (FE) study has been carried out to examine the structural response of a prestressed concrete (PSC) inner containment (IC) dome of reactor building (double containment system) of a typical Indian Nuclear Power Plant, having large steam generator (SG) openings with due emphasis on the local behaviour of the steel-concrete interfaces at the SG openings, due to initial prestress transfer. The predominant thrust of the study has been placed on the objective of predicting the possibilities of separation at the steel-concrete interface zones adjacent to the embedded plates (EPs) of the SG openings. Two types of modeling and analysis have been made to study the overall and local behaviour of the structure. Prestressing ducts, passive reinforcements and EPs have been included in the models in certain ways. For the FE analysis, the interface zone has been modeled using interface elements, the properties of which were derived from the results of past experiments conducted on steel plate-concrete inter-face specimens. The FE analysis results have been compared with the results of the past two FE analytical studies on the linear behaviour of the same PSC IC dome. Important observations have been made regarding dome deformation and stresses throughout the structure with special emphasis on the local behaviour of steel-concrete interfaces at and around the SG openings.

Study of Pressure and Curing Temperature in Reactive Powder Concretes (RPC) with different amounts of Metallic Microfibers

Reactive powder concrete (RPC) is one of the greatest breakthroughs in concrete technology, as it enables the manufacturing of thinner structures without passive reinforcement. That reduces the load in buildings and increases durability, especially in aggressive environments. The use of metallic microfibers is what provides the increase in tensile stress and the resulting elimination of reinforcements. However, it is also the most expensive material as well as the most difficult to obtain, which requires its maximum optimization. Therefore, the aim of this study was to compare the mechanical properties of the RPC with three amounts of metallic fibers, 1%, 3%, and 5% in volume in relation to the material total, after having determined the best curing temperature and effectiveness of the confining pressure in the fresh state. The mechanical properties studied were the axial compressive strength, flexural strength, tensile strength by splitting tensile test, and capillary absorption. The results showed that the fibers have little influence on compressive strength, since there was only a small increase as the amount of fibers was increased. However, for tensile strengths, either flexural or by splitting tensile test, the incorporation of microfibers allowed a significant improvement, obtaining gains of 392% for the flexural strength for the 5%, reaching 59MPa, in comparison with the 0%, which was 12MPa. There was also a decrease in capillary absorption. Keywords: Reactive Powder Concrete (RPC); Metallic Microfibers; Mechanical properties, Construction Materials.

A study on the evaluation of performance of the PSC inner containment dome with large openings during prestress transfer

A linear three dimensional finite element (FE) analysis has been carried out for the loading condition at pre-stress transfer of a representative test specimen for a typical pre-stressed concrete (PSC) inner containment (IC) dome with due emphasis on the local behaviour of the steel plate concrete interfaces at the steam generator (SG) openings. The FE model includes the pre-stressing ducts and passive reinforcements. The FE analysis results have been compared with the past experimental results for the same representative test specimen. Due thrust has been put on the objective of predicting the possibility of separation at the steel plate concrete interfaces.An attempt has been made in corroborating the findings of the past two FE analytical studies on the linear behaviour of the PSC IC dome (with large SG openings) of the same actual double containment reactor building of the typical 220MWe capacity Indian nuclear power plant. Finally important conclusions in line with the desired objectives have been made based on the summary observations of all the studies conducted on this typical PSC IC dome.