Reinforcing Steel Bars Research Articles

Fractional and fractal derivative-based creep models for concrete under constant and time-varying loading

In this paper, fractional and fractal derivative-based viscoelastic laws are adopted to develop linear creep models for reinforced and prestressed concrete under constant and time-varying loading. The model parameters are determined by curve-fitting the creep compliances of the spingpot and Kelvin-Voigt viscoelastic models to experimental data of basic creep in plain concrete specimens. Equilibrium and strain compatibility equations are formulated for reinforced and prestressed concrete under concentric loading which are solved simultaneously with the constitutive stress–strain equation of the selected viscoelastic model. For the case of a constant load, adoption of the fractal viscoelastic models lead to first-order differential equations that, when solved, yield analytical expressions for basic creep in reinforced and prestressed concrete. A semi-analytical solution is derived when adopting the fractional viscoelastic laws, obtained using the Laplace transform technique. Both models ensure strain compatibility and consider stress redistribution from concrete to the steel reinforcement bars. A high-level of agreement is made between the derived fractional and fractal-derivative based models and existing experimental data of creep in reinforced and pre-stressed concrete members under constant load. When the applied loading varies with time, numerical procedures are employed to approximate the fractional and fractal derivatives. It is found that creep in plain concrete members subjected to time-varying loads is accurately predicted when using the fractional derivative models. Comparisons are then made to other methods of modelling creep under time-varying stress. The primary advantage of the derived models is that only up to three parameters require calibration using basic creep tests for an accurate representation of creep and that closed-form expressions for creep can be obtained for the case of constant, sustained loading.

Assessment of the MICP potential and corrosion inhibition of steel bars by biofilm forming bacteria in corrosive environment

The porous network and micro-cracks of concrete facilitate the movement of deleterious ions inside the concrete cover which could corrode the embedded steel. The calcifying bacteria fill up the pore spaces and cracks through a self-healing mechanism, however their capability to precipitate CaCO3 in chlorides rich environment and impact on the corrosion of rebars was unknown. Therefore, the influence of 0%–5% NaCl contents was investigated on the CaCO3 producing capability of four Bacillus strains in this study. In addition, corrosion attributes of steel bars were explored upon interacting with bacteria in the simulated cracked concrete exposed to the 3.5% NaCl solution. The results indicated that on average 1.5% of NaCl content positively affects the bacterial CaCO3 production capability and B. subtilis and B. pumilus produced more CaCO3 at 7 days and 15 days, respectively. Besides, increase in NaCl content significantly altered the type of produced CaCO3 polymorph, microstructure, and crystallinity. The bacterial biofilm forming potential and effect of biofilm on corrosion of steel bars was evaluated through Tafel polarization and electrochemical impedance spectroscopy. The B. subtilis and B. safensis were the optimum strains in developing strong and sticky biofilms during both in-vitro and in-vivo studies and appeared as excellent corrosion inhibitors of reinforcing steel bars compared to the control specimen under an exposure of 3.5% NaCl. Increase in the concentration of NaCl aggregated more bacterial cells together and resulted in the secretion of maximum amount of extracellular polymeric substances. Besides, the biofilm formed by B. safensis was comparatively more uniform and thicker without any blemishes thus considered optimum strain to prevent the corrosion of rebars.

Molecular dynamics simulations of ion migration and adsorption on the surfaces of AFm hydrates

Chloride salts can cause severe corrosion damage to reinforcing steel bars in cement-based materials whereas nitrite salts inhibit corrosion. The storage and release of these two anions in cement materials occurs mainly at the interface of monosulfoaluminate (AFm) hydrates. In this paper, molecular dynamics are used to analyze the interaction between anions and AFm phases and clarify the competitive relationships between the anions at adsorption sites on the AFm surface. It was found that the ordered structure of the [Ca2Al(OH)6]+ layers of the AFm plays a key role in anion adsorption and that the mobility of ions desorbed from AFm layers decreases linearly with increasing proximity to the AFm surfaces.

Self-cleaning superhydrophobic fly ash geopolymer

Building materials with hydrophobic surfaces can exhibit increased service life by preventing moisture absorption or diffusion through their surfaces. For concrete used in construction, this hydrophobicity can prevent the corrosion of reinforcing steel bars. Geopolymers are a new cement-free binding material that have been extensively studied to replace Portland cement. However, similar to normal concrete, geopolymers are susceptible to the intake of moisture. This paper presents the fabrication of a superhydrophobic and self-cleaning surface on a fly ash geopolymer as a method to prevent moisture intake. A composite coating of polydimethylsiloxane (PDMS) solution containing dispersed polytetrafluoroethylene (PTFE) or calcium stearate (CS) microparticles was applied by dip-coating to form the hydrophobic surface. Additionally, fly ash was incorporated with the PTFE and CS microparticles to increase surface roughness and reduce material cost. The experimental results showed that the coating containing CS microparticles yielded a hydrophobic surface with a contact angle of 140°, while those containing PTFE microparticles provided a superhydrophobic surface with a contact angle of 159°. The incorporation of fly ash resulted in increased surface roughness, leading to a larger contact angle and a smaller sliding angle. A contact angle of 153° with a sliding angle of 8.7° was observed on the PTFE/fly ash-coated surface. The cleaning process was demonstrated with a test whereby dust was removed by water droplets rolling off the surface. The tested coating exhibited self-cleaning and waterproofing properties and could thus improve the sustainability of materials in building construction.

Investigating the standard sizes of steel reinforcement used in the Ghanaian industry

The study aimed to explore and determine whether the steel reinforcement bars manufactured and used in Ghana meet the standard sizes. The research adopted a positivist philosophy and a market survey approach. The various organizations manufacturing and supplying steel reinforcement were purposively selected and visited, and the different steel reinforcement bars were measured against the standard sizes. When the measured sizes were compared to the standard sizes, the results revealed that all the mild steel reinforcement bars measured did not meet the required standard sizes. The results showed that all the high tensile steel reinforcement bars met the necessary standard sizes in the Ghanaian construction market. The research empirically demonstrated that non-standard steel reinforcement bar sizes impact most project outcomes. The regulatory authority (National Standard Authority) must ensure that both manufactured and imported steel reinforcement bars meet the standard sizes on the construction market in Ghana to keep the project under control and enable the structure to achieve its maximum strength.

Contact interaction of deformable continuous media of various physical nature

An approach is proposed for modeling the contact interaction processes of reinforcement bundles with concrete, as well as for underground elements of foundations and buildings reinforced foundations by compensatory injection with adjacent soil. A special contact finite element of a continuous medium with specific properties has been constructed which makes it possible to simulate the elastic interaction of two contacting surfaces their displacement relative to each other and separation. The developed algorithm allows within the framework of a single finite element method, to calculate the joint deformation of the elements of metal reinforcing elements, concrete and “weak” soils. The proposed calculation methods are implemented within the consistent equations framework of a geometrically nonlinear three-dimensional elasticity theory. On the basis of the proposed methods, the problem of "pulling out" a steel reinforcement bar from a concrete block was solved, a comparison was made with experimental data and with the results obtained in publicly available application software packages, a good agreement was noted.

Experimental studies on flexural action of RC beams made with hybrid rebars - A brief review

Reinforced Steel bars used in concrete constructions are particularly susceptible to corrosion since they don't have enough corrosion resistance, which decreases durability and long-term performance. The main cause of steel bar corrosion is moisture interaction, which results in rust, which causes cracks and spalling, which affects durability and long-term performance. FRP bars, which have several benefits over steel bars such as strong resistance to corrosion, higher tensile strength than steel bars, and a 1/4th of the weight of steel bars, which decreases shipping and labor costs, are now entering the market as a solution to the aforementioned issues. Polypropylene fibers in concrete have high mechanical strength, stiffness, and durability. This paper tells about the type of FRP bar and Fiber that has been chosen in order to enhance the studies on the performance of flexure of RC beams made with a combination of FRP and Steel bars. From previous studies, it has been concluded that 0.25% of fibers are used as optimum dosage in terms of volume fraction in order to improve the behavior of flexure and ductility of beams made with a combination of Steel and FRP bars.

Innovative Approach for Enhancing GLULAM Performance with Reinforcing Steel Bars: A BESO-based Study

Innovative Approach for Enhancing GLULAM Performance with Reinforcing Steel Bars: A BESO-based Study

Review on flexural performance of reinforced concrete beams designed with hybrid bars

Reinforced steel bars, commonly used in concrete construction, are prone to corrosion due to their insufficient corrosion resistance, which ultimately leads to reduced durability and long-term performance. Moisture interaction is the leading cause of corrosion, which results in rust, cracks, and spalling, leading to durability and long-term performance issues. To address this problem, FRP bars are now being introduced to the market, which offer numerous benefits over steel bars, such as strong corrosion resistance, higher tensile strength, and reduced weight, leading to lower shipping and labor costs. Concrete gains mechanical stability, stiffness, durability when polypropylene fibres are used, improving the material's effectiveness. The purpose of this study is to examine the flexural behavior, load-deflection characteristics, and ductility of hybrid reinforced concrete beams. that use both GFRP bars and steel bars, as well as compare them with reinforced concrete beams that use only GFRP bars or steel bars with and without using polypropylene fibres as a supplement. In order to enhance the beams flexural strength as well as ductility, it has been identified that 0.25% of their volume should be made up of polypropylene fibres. After the experimental investigation is finished, analytical studies using ANSYS simulation will be carried out to determine the load-deflection behaviours.

Assessment of Deviation in Quality of Steel Reinforcing Bars Used in Some Building Sites in Cameroon

Assessment of Deviation in Quality of Steel Reinforcing Bars Used in Some Building Sites in Cameroon

Corrosion of steel rebars embedded in One-part Alkali activated concrete mixes

To reduce CO2 emissions and turn a variety of industrial/agricultural wastes into valuable cementitious products, alkali-activated materials (AAM) are recognized as suitable substitutes for regular Portland cement (OPC). However, the concentrated aqueous alkali solutions used in conventional two-part alkali activated materials are highly corrosive, viscous, and are difficult to handle in direct field applications. As a result, the potential for developing so-called "just add water" type one-part AAMs, as compared to traditional two-part AAM, is being explored, particularly in cast-in-situ applications. In the present study on corrosion of reinforcing steel bars in fly ash-slag (FA-GGBS) based one-part AAC mixtures, three parameters—the total binder content, the relative proportions of GGBS and Fly-ash and the percentage of sodium oxide (Na2O) - are recognized as the key factors in determining the strength and durability performance (including corrosion of rebars embedded in it) of a given AAC mix. Accordingly, experiments were conducted on AAC mixes with three binder contents (440, 460, and 480 kg/m3), three Slag/FA ratios (80/20, 70/30 and 60/40, by volume) and three alternate Na2O percentages (5, 6, and 7%, by weight of total binder content). Prismatic cylindrical test specimens of reinforced geopolymer concrete were prepared and half-cell potential and corrosion rate measurements were made after 28-, 56-, and 90 days of continuous exposure to 3% of NaCl solution, to accelerate the corrosion process. Measured corrosion current density and corrosion rates using a Electro-chemical Corrosion Analyser have indicated that the AAC mixture having a total binder content 440 kg/m3, GGBS/FS ratio of 70/30 and 6% Na2O content, exhibits best corrosion resistance amongst the various mixes tested herein, as measured up to the end of 90-days.

Comparative Analysis of Aluminum Alloy 6061-T6 and Mild Steel Tubes in Sacrificial Protection System under Blast Loading

A sacrificial cladding consist of hollow metal tubes and steel sheet, is proposed in this study to protect a square concrete panel subjected to blast loading. Herein, comparative analysis of aluminum alloy 6061-T6 (Al 6061-T6) and mild steel tubes in sacrificial cladding is done using 3-D non-linear Finite Element (FE) software ABAQUS/Explicit®. Blast load is applied through ConWep program developed by US Army. Simplified Concrete Damage Plasticity (SCDP) model is used to define the material behavior of concrete slabs of thickness 250 mm. Johnson-Cook (J-C) plasticity model is used to model the stress-strain response of Al 6061-T6 and mild steel tubes, reinforcement bars and steel sheet. Diameter (D) and thickness (t) of circular metal hollow tubes are taken from IS1161:1998. Comparative analysis of Al 6061-T6 and mild steel tubes is carried out for blast loading using TNT with scaled distance of 0.425 m/kg1/3. It was observed that mild steel tubes perform better than Al 6061-T6 tubes and save concrete panel from degradation under blast loading.

Versatile hysteretic model of reinforcing steel bars with buckling

The buckling of reinforcing steel should be considered in the design of reinforced concrete elements subjected to compression since it can influence the load-carrying capacity and energy dissipation under cyclic loading detrimentally. To capture the influence of buckling in the stress–strain behavior of steel, some models have incorporated geometric and material nonlinearities in the formulation. Others have provided phenomenological curves calibrated with experimental data. Using a lumped plasticity model and sectional analysis based on a fiber model, nonlinearities can be incorporated into the problem. However, solving the equilibrium and compatibility in the nonlinear problem involves complex and inefficient computational methods. In this work, iterations to reach moment equilibrium are avoided by utilizing an expression that relates the average axial strain to the curvature. Cyclic experimental tests collected from the literature, using slenderness values from 6 to 15 and strain range up to 10%, verify the model’s accuracy, resulting in prediction errors of the energy enclosed by the hysteretic curves of less than 4% in all cases compared to the iterative model. The results were also consistent with the experimental test results.

Extremely-ductile alkali-activated slag-based composite with a tensile strain capacity up to 22%

Highly-ductile alkali-activated slag-based composites (HD-AASC) are fiber-reinforced cement-free materials possessing pseudo strain-hardening behavior and multiple-cracking phenomena. In this research, the feasibility of developing extremely-ductile alkali-activated slag-based composite (ED-AASC) with a tensile strain capacity over 20% is presented. Specimens with a moderate amount of sand and crumb rubber particles were made by applying new mixing and curing procedures. Then the density, compressive strength, and tension tests were performed. Test results showed that the ED-AASC (R5-S8-M1 mixture) had a tensile strain capacity of 22.3%, compressive strength of 53.6 MPa, and average crack width of 212 μm. By adopting two performance indexes (fcεts and ftsεts), the performance of ED-AASC was compared with those of previous high-ductile composites; the tensile strain capacity of the composite was also compared with the minimum extensibility of steel bars for concrete reinforcement, as specified in ASTM and ISO. In addition, the sustainability of ED-AASC was evaluated.

Evaluation of the efficiency of the MasterLife CI 222 organic corrosion inhibitor additive for the protection of steel reinforcement bars in concrete

Evaluation of the efficiency of the MasterLife CI 222 organic corrosion inhibitor additive for the protection of steel reinforcement bars in concrete

Experimental Investigation of Actively Confined RC Columns Using Iron-Based Shape Memory Alloy Spiral Stirrups

Shape memory alloys (SMA) can be employed as prestressing components in the form of bars and strips in new reinforced concrete (RC) members or for reinforcing existing RC constructions because of their shape memory effect. Early research focused on retrofitting concrete components with external SMA spirals, but this technology has not been extensively used in new building. Civil engineering constructions can benefit from the development of a more affordable iron-based shape memory alloy (Fe-SMA). A good form recovery stress (prestress force) and high elastic stiffness describe this Fe-SMA. As an added benefit, it is less expensive in terms of raw materials and easier to manufacture than nickel-titanium alloys (NiTi). Industrial production of Fe-SMA strips has just recently begun. In this research under an axial compression force, three circular columns are tested experimentally. The confinement of reinforcement-type steel strips and (Fe-SMA) spiral stirrups, main reinforced steel bars, as well as numerical simulation using finite elements, are all researched. The (Fe-SMA) spiral stirrups are considered strengthening techniques, internal and external confinement. Axial compressive load, load-displacement curve, and strain-reinforcement bars are all terms used to define the cause of failure. Strengthening by Fe-SMA stirrups external reinforcement maximum gains in compressive strength of around 69.99% for stirrups steel reinforcement columns and 51.64% for Fe-SMA stirrups internal reinforcement.

Fire residual stress–strain curves of corroded thermo-mechanically treated (TMT) reinforcing steel bars

Thermo-mechanically treated (TMT) reinforcing steel bars are extensively employed in RC buildings these days because of their superior thermal- and seismic-resisting characteristics, which enable them to sustain most of their strengths during earthquakes. The distinctive cross-sectional phase distribution (CSPD) of martensite, bainite, and pearlite in TMT rebars makes them outstanding. The current study examines the extent to which TMT reinforcing steel bars' mechanical properties deteriorate as a result of exposure to a combination of corrosion-induced CSPD damage and high temperatures. The research attempted to model an accidental fire in an aging structure with corroded members as a result of exposure to extreme environmental conditions. Heated residual tensile tests on rebar specimens subjected to various combinations of corrosion-induced damage and high temperatures were used in the experiment. The results show a significant loss in the key mechanical characteristics of reinforcing steel due to the superimposition of elevated temperature exposure on corrosion-induced damage to CSPD.

Enhancing Sustainability of Corroded RC Structures: Estimating Steel-to-Concrete Bond Strength with ANN and SVM Algorithms

The bond strength between concrete and corroded steel reinforcement bar is one of the main responsible factors that affect the ultimate load-carrying capacity of reinforced concrete (RC) structures. Therefore, the prediction of accurate bond strength has become an important parameter for the safety measurements of RC structures. However, the analytical models are not enough to estimate the bond strength, as they are built using various assumptions and limited datasets. The machine learning (ML) techniques named artificial neural network (ANN) and support vector machine (SVM) have been used to estimate the bond strength between concrete and corroded steel reinforcement bar. The considered input parameters in this research are the surface area of the specimen, concrete cover, type of reinforcement bars, yield strength of reinforcement bars, concrete compressive strength, diameter of reinforcement bars, bond length, water/cement ratio, and corrosion level of reinforcement bars. These parameters were used to build the ANN and SVM models. The reliability of the developed ANN and SVM models have been compared with twenty analytical models. Moreover, the analyzed results revealed that the precision and efficiency of the ANN and SVM models are higher compared with the analytical models. The radar plot and Taylor diagrams have also been utilized to show the graphical representation of the best-fitted model. The proposed ANN model has the best precision and reliability compared with the SVM model, with a correlation coefficient of 0.99, mean absolute error of 1.091 MPa, and root mean square error of 1.495 MPa. Researchers and designers can apply the developed ANN model to precisely estimate the steel-to-concrete bond strength.

Numerical Simulation Methodology for Prefabricated Shear Walls Considering Stochastic Defects in Grouting Materials

The most used connection form for reinforced steel bars is the grouting sleeve using cement-based grouting materials. Hence, the quality of the grouting sleeve connection determines whether the performance of a precast concrete structure is equivalent to that of a cast in situ concrete structure. However, several existing reasons, namely, insufficient grouting cement or poor construction controls and even stochastic bubble holes, lead to inevitable grouting defects. The behavior of precast concrete structures is affected dramatically. Considering the cost and efficiency of the analysis of precast concrete structures, the finite element method is still the most used method, but the simulation technology of structures considering stochastic defects in grouting materials is not sufficient. Herein, a simulation method considering stochastic defects in precast concrete structures is proposed, and the application of the method to grouting sleeves and shear wall structures is performed to verify its accuracy and feasibility. The construction of stochastic defects in grouting material is first realized through the Python scripter. Secondly, the mechanical parameters are obtained from the refined finite element analysis of grouting sleeves with material defects. Finally, based on the obtained mechanical properties of grouting sleeves, the behaviors of precast shear walls under blast loading are analyzed. The simulations of grouting sleeves under uniaxial tensile loading and precast concrete shear walls under blast loading both indicate that the proposed numerical method is feasible in solving the structural issues with stochastic defects in grouting materials.

Numerical study on effect of constant and variable axial loads on RC column subjected to blast load

Explosion is an instant release of potential energy, heat, temperature and sound producing a pressure wave that travels away from the source radially on which the resulting force the blast wave is a blast load. Besides this, column especially external column as a main load bearing compressive structural component in buildings is the most critical structural element vulnerable to explosion and require an in-depth investigation on its performance against blast loads. Despite this, currently there is perceived gap and meagre of researches regarding numerical investigation on effect of presence of constant and variable axial loads on reinforced concrete column when subjected to blast load. In this study, the responses of reinforced concrete column under different scaled distance blast load scenarios accompanied by constant and axial loads were investigated. The finite element method of structural analysis was employed accompanied by nonlinear explicit time integration software LS-DYNA. The numerical analysis result revealed that RC columns subjected to large axial loads accompanied by small scaled distance blast scenario made the reinforced concrete column to suffer severe damages including crushing of concrete especially direct shear failures and breaking of reinforcing steel bars. In addition to this, comparing the nature and behaviour of variable axial loads with constant axial loads, the former loading case revealed larger nodal displacement values along height of column, and a higher displacement-time history curve was traced. On the other hand, the damage propagation nature of RC columns loaded with variable axial load was slow and progressive and different with RC columns with constant axial loads accompanied by small scaled blast scenario which was rendered to have a severely crushed concrete element without bending actions leaving the entire column inadequate for service.