Steel Reinforced Concrete Specimens Research Articles

Study on the adhesive property of sludge-modified magnesium phosphate cement reinforcement coating for steel bars

The synergistic interaction inreinforced concrete systems originates from the strong bond between steel reinforcement and concrete, enabling them to collaborateunder load and optimize structural performance. This study applied various sludge-modified magnesium phosphate cement mixtures to the surfaces of plain round steel bars and ribbed steel bars to prepare steel-reinforced concrete specimens. The characterization of the bond performance of the sludge-modified magnesium phosphate cement reinforcement coating for steel bars and concrete was achieved through analyzing the failure modes, bond strength, and slip values of different groups. Microscopic analysis was performed using a scanning electron microscope. The results revealed that the primary failure mode of the steel-reinforced concrete specimens was steel bar pull-out, with some specimens exhibiting concrete splitting failure. Coating application on plain round steel bars increased bond strength, while on ribbed steel bars, it decreased bond strength. The application of the coating slightly reduced slip values to some extent.

Concrete carbonation in tropical urban and urban/marine environments after 20 years of natural exposure

This work is part of the DURACON project, which seeks to characterize the durability of concrete exposed to environmental conditions prevailing in Ibero-America and is based on the exposure of unreinforced and reinforced concrete specimens in marine and urban environments in each participating Ibero-American country. This research presents the results obtained from exposing unreinforced and steel-reinforced concrete specimens to prevailing environmental conditions in twelve natural exposure sites in Mexico during an exposure period of approximately 20 years to determine an empirical model that allows predicting the value of the carbonation rate, k′CO2, as a function of the nth-root of time (NRT) for the concretes evaluated. The concrete specimens, plain and reinforced, exposed to the elements in these cities were manufactured with two types of concrete, one with a w/c ratio = 0.65 and the other with a w/c ratio = 0.45. The tests mainly focused on measuring the concrete carbonation front depth during the ∼ 20 years of exposure and the measurement of environmental parameters at the exposure sites, such as temperature, relative humidity, rainfall, and atmospheric CO2 concentration. The electrochemical parameters of the reinforcing steel (half-cell potential, Ecorr, and current density, icorr) in the reinforced specimens were also obtained after ∼ 20 years of exposure to corroborate which sites showed lower or higher corrosion activity. This model to obtain k′CO2 as a function of the environmental parameters of the Mexican exposure sites and the physical properties of the concretes was compared with the value of kCO2 obtained from the square root of time (SRT) model. It was found that the k′CO2 values were 30 % higher on average than the kCO2 obtained with the empirical SRT equation. However, it should be noted that k′CO2 must be linked to the corresponding nth-root of time, whereas the value of n to obtain kCO2 is constant and equal to ½. An agreement was also obtained between the probability of activation of the reinforcing steel, using the corrosion parameters (Ecorr and icorr), and the probability of eCO2 ≤ 15 mm (lowest concrete cover used in this study).

Effect of corrosion on bond slipping between steel and concrete in SRC structures

Corrosion critically impacts bond performance in steel-reinforced concrete (SRC) structures. In this study, we investigate the impact of corrosion on bond-slipping between steel components and concrete within SRC structures. Initially, SRC specimens were subjected to electrochemical corrosion tests to induce varying corrosion rates. Then, pull-out tests were conducted to study the specimens' failure modes, bond stress–slip curves, and displacement distribution. The experimental results indicate that lower corrosion rates can increase bond strength due to enhanced steel surface roughness. As the corrosion rate increased from 0% to 5%, the initial bond stress, peak bond stress, and residual bond stress increased by 133%, 101%, and 102%, respectively. However, when the corrosion rate increased from 5% to 15%, these stresses decreased by 57.1%, 49.6%, and 49.6%, respectively. Furthermore, with an increase in corrosion rate from 15% to 20%, the initial, peak, and residual bond stresses decreased by 100%, 67.6%, and 69.0%, respectively. Corrosion considerably affected the initial and peak slipping observed between the steel components and the concrete, yet its impact on residual slip was relatively minor. In addition, a nonlinear finite element model for characterising the corrosion and pull-out tests was developed and validated according to the experimental results. The numerical results showed that the four shear transfer mechanisms, including chemical bonding, micromechanical interlocking, macromechanical interlocking, and rust interface bonding, exhibited distinct behaviours at different loading stages. Finally, a parametric study was conducted using a finite element model. With variations in corrosion rates, four modes of cracking patterns on the concrete surface were observed.

A comparative analysis of corrosion assessment techniques for steel in reinforced concrete exposed to brine water environments

Abstract Corrosion assessment of steel-reinforced concrete specimens submerged in synthetic brine water with various chloride concentrations for 1–16 weeks was performed. Mass loss measurements combined with electrochemical techniques – half-cell potential, linear polarization (LP), and electrochemical impedance spectroscopy (EIS) – were employed. The results obtained from all corrosion assessments – on-site testing (half-cell potential measurements), laboratory scale (LP and EIS measurements), and destructive testing (mass loss or immersion measurements) – exhibited remarkable consistency, complementarity, and mutual supportiveness. Corrosion rate (CR) values from mass loss were close to those obtained from LP and EIS. The corrosion resistance decreased with increasing chloride concentration and immersion time, as indicated by the highest CR, Ca2+, and Fe2+ concentrations, and the lowest half-cell potential and polarization resistance. X-ray photoelectron spectroscopy investigation on the corroded steel surface revealed Fe(III) oxides and hydroxides and Fe(III) (FeCl3), corresponding to the reduction in polarization resistance in the LP and EIS results.

ИССЛЕДОВАНИЕ ПОЛЗУЧЕСТИ СТАЛЕЖЕЛЕЗОБЕТОННЫХ ОБРАЗЦОВ

The paper presents the results of investigation of creep and shrinkage of steel-reinforced concrete specimens. For this purpose, parallel tests of specimens made of the same class of concrete but with different reinforcement were carried out. Concrete specimens, specimens reinforced with bar reinforcement frames and steel reinforced concrete specimens with external sheet reinforcement were investigated. The tests were carried out in climatic rooms using spring setups to maintain a constant load acting on the specimens over time. The load on the specimens was selected based on the equality of stresses in the concrete in all series of specimens. The specimens were tested both waterproofed and non-waterproofed, and the effect of waterproofing coating on shrinkage and creep strains was evaluated for different series of specimens. A system was developed to capture information. which allows, in addition to longitudinal shrinkage and creep deformations, to determine transverse deformations, longitudinal deformations along the faces of the specimen to determine the influence of reinforcement and steel of the outer plate, to evaluate the change in longitudinal deformations from the center of the specimen to its edges, to evaluate separately the deformations of concrete and steel plate in steel-reinforced concrete specimens. The analysis of the results allowed a comparative assessment of the influence of conventional bar reinforcement as well as steel sheet of steel-reinforced concrete specimens on creep and shrinkage deformations; the influence of waterproofing coating on the test results in different series was also assessed. Based on the results of this work, extended requirements for experimental and theoretical studies of steel-reinforced concrete specimens with external sheet reinforcement to determine their design stiffnesses were formulated.

Localized corrosion propagation of steel in cracked mortar and long-term corrosion of steel reinforcement in cracked concrete in seawater environment

A custom-designed wire beam electrode (WBE) covered by cracked mortar was applied to study the localized corrosion propagation of steel reinforcement in seawater. Additionally, steel-reinforced concrete specimens with cracks were monitored by EIS methods to study the long-term corrosion of steel in a real marine environment for 1920 days. The results revealed that corrosion initiates from the crack and then propagates to other electrodes through the steel-mortar interface. The number of anodic areas first increases and then decreases. The corrosion current density of steel reinforcement in cracked concrete increases exponentially with prolonged exposure time in a real marine environment.

Structural behavior of reinforced concrete tunnel linings with synthetic fibers addition

Fiber-reinforced-concrete has been widely used in underground structures in recent years, especially in tunnel linings. Compared with steel fiber reinforced concrete, synthetic fiber reinforced concrete not only has a considerable structural bearing capacity but also shows a better corrosion resistance and durability. However, most researchers focused on the cracking resistance property of synthetic fiber reinforced concrete instead of its mechanical contribution. Besides, experiments were carried out mostly on structural components such as beams or segments. There is little information about the performance of synthetic fiber reinforced concrete in full-scale tunnel lining rings. In this study, full-scale experiments were carried out for tunnel lining specimens with synthetic fiber reinforced concrete and traditional reinforced concrete. The experimental results are compared to evaluate the different structural behaviors between the fiber-reinforced and the steel-reinforced concrete specimens. The failure mechanism of the synthetic fiber reinforced concrete tunnel lining was investigated and compared to that of the traditional RC tunnel lining. The results show that the addition of synthetic fibers can delay the occurrence of yielding state and lead to a higher yielding load compared to the traditional RC specimen. The approach of reducing steel reinforcement by adding synthetic fibers appears to be a viable method to optimize the lining design. The differences in cracks, bearing capacity, stiffness, and other mechanical behaviors between the synthetic fiber reinforced concrete and the traditional reinforced concrete tunnel lining structures are also discussed. The results show that the synthetic fiber reinforced concrete tunnel lining structure has a different failure mechanism and better performance than the traditional RC tunnel lining structures. With a 47% reduction of steel reinforcement in the lining segments, the bearing capacity and other mechanical properties of the synthetic fiber reinforced concrete tunnel lining structure can still be comparable to those of the traditional RC tunnel lining structures.

Green and recyclable demolition of steel reinforced concrete: Application and calculation model of induction heating demolition technology

In steel-reinforced concrete (SRC) structures, it is difficult to separate or recycle steel and concrete using traditional demolition methods, which create a large amount of construction waste. A green and recyclable technology for demolishing SRC structures by induction heating (IH) is proposed in this study. The magnetic field calculation model of the rectangular coil used in IH demolition (IHD) is deduced and verified using COMSOL software. This calculation model can reduce the workload of magnetic field modelling and provide guidance for IHD scheme development. In addition, IH experiments are conducted on five section steels of different sizes. Furthermore, IHD experiments are performed on five SRC specimens that incorporated the five section steels. The temperature distribution and rise laws of the IHD are obtained. The feasibility of the IHD is verified. Under the IHD experimental conditions, the section steels and concrete are separated within approximately 15 min, and the critical expansion difference is approximately 1.85 mm. The applicability of the calculation model in the coil design and IH scheme is verified. The proposed IHD is expected to provide new ideas for reducing and recycling the amount of construction waste generated from the demolition of SRC structures.

Seismic Performances of SRC Special-Shaped Columns and RC Beam Joints Under Double-Direction Low-Cyclic Reversed Loading

Steel-reinforced concrete (SRC) special-shaped column and beam frame structure is a special structural form that can meet the requirements of high bearing capacity and satisfy the esthetic requirement of buildings. In this study, a new joint design approach is adopted to focus on the seismic behavior of SRC special-shaped column and reinforced concrete (RC) beam joints under low-cyclic double-directional reactions through pseudo-static tests with a controlled stirrup distance. The joints of SRC specimens were compared with those of RC specimens by controlling the area of steel and reinforcement, and hysteresis cycle skeleton curves and load and strain hysteresis cycles were analyzed. The specimen with profiled steel was found to have better energy dissipation capacity. The energy dissipation capacity and stiffness degradation of the nodes were analyzed. The test results showed that the energy dissipation capacity of the SRC joints was better than that of the conventional concrete column joints, and the stiffness degradation of RC joints was more significant than that of SRC joints.

Flexural Performance of Small-Scale Textile-Reinforced Concrete Beams

Textile-reinforced concrete (TRC) as a novel high-performance composite material can be used as a strengthening material and component bearing load alone. The flexural performance of TRC beams strengthened with textile reinforcement such as carbon tows was experimentally examined and associated with those of steel-reinforced concrete (SRC) beams. Through four-point bending tests, this research explores the effects of textile layers and dosages of short textile fibre on the flexural strength of concrete beams. A total of 64 prism samples of size 100 mm × 100 mm × 500 mm were made, flexure-strengthened, and tested to evaluate various characteristics and the efficiency of TRC versus SRC beams. TRC beams performed exceptionally well as supporting material in enhancing concrete’s flexural capacity; in addition, TRC’s average ultimate load effectiveness was up to 56% than that of SRC specimens. Furthermore, the maximum deflection was about 37% lesser than SRC beams. The results showed that by increasing the number of layers, the TRC’s effectiveness was significantly increased, and the failure mode became more ductile.

Modelling Total-corrosion Behaviour of Reinforcing-steel in 3.5% NaCl-immersed Concrete with Cymbopogon citratus leaf-extract admixture

In this paper, the total-corrosion behaviour of reinforcing-steel embedment in concrete samples, having Cymbopon citratus (C. citratus) leaf-extract admixture, and which were immersed in 3.5% NaCl (a saline/marine simulating environment) is investigated. Electrochemical data of macrocell current measurements were obtained, as an easy to undertake corrosion monitoring technique, from the steel-reinforced concrete specimens, that had been admixed with different concentrations of the C. citratus leaf-extract, before being immersed in the corrosive test-medium. The obtained data were then rendered to prescribed specification from ASTM G109 for the modelling of the total-corrosion prevailing in the reinforcing-steel within the concrete test-samples. Results obtained showed that C. citratus leaf-extract admixture in the concrete samples led to reduction in the total-corrosion of the reinforcing-steel, and, especially, in agreements with previous works where other types of electrochemical monitoring techniques had been employed.

Effect of concrete cover on the bond-slip behavior between steel section and concrete in SRC structures

The concrete cover is one of the key factors affecting the bond performance of steel reinforced concrete (SRC) structures. The main objective of this paper was to study the effect of concrete cover on the bond-slip behavior between steel section and concrete in SRC structures. Firstly, push-out tests on SRC specimens were conducted and the failure modes, bond stress-slip curves as well as strain distribution of the specimens were investigated. The experimental results indicated that the bond strength of steel section encased in concrete could be significantly improved by increasing the concrete cover due to the enhancement in the concrete confining effect. As the concrete cover increased from 90 mm to 170 mm, the initial bond stress, ultimate bond stress, and residual bond stress increased by 76.9%, 46.6%, and 97.2%, respectively. The concrete cover also had a considerable impact on the initial and residual slips between the steel section and concrete. Further, nonlinear finite element models of push-out tests were established and verified against the test results. The numerical results demonstrated that there were three shear mechanisms including chemical adhesion, static friction, and sliding friction performing differently at each loading stage. Finally, a parametric study was carried out based on the verified FE models. Four cracking patterns of the concrete surface were observed with the variation of the ratio of concrete cover to the clear distance between the flange tip and the web side surface of concrete.

Mega columns with several reinforced steel profiles – Experimental and numerical investigations

Steel reinforced concrete (SRC) columns are widely used in super high-rise buildings, since they can provide larger load bearing capacity and better ductility than traditional reinforced concrete (RC) columns. Current design code like EN 1994-1-1 (EN 1994-1-1, 2004 [1]) (limited to one single encased profile), while AISC 360-16 (ANSI/AISC 360-16, 2016 [2]) allows the design of composite sections with two or more encased sections, although the way to perform such design is not detailed. To understand better the structural behaviour of such composite mega columns and provide a easy to use design method, a two-phase experimental campaign was conducted on scaled isolated steel reinforced concrete (ISRC) columns. Phase 1 of the study includes six 1/4-scaled ISRC columns under static loads: every two of the specimens are loaded statically with the eccentricity ratio of 0, 10%, and 15%, respectively. Phase 2 of the study includes four 1/6-scaled ISRC columns under quasi-static loads: every two of the specimens were loaded under simulated seismic loads with the equivalent eccentricity ratios of 10% and 15%, respectively. A finite element analysis was conducted as a supplement to the physical tests to provide a deeper insight into the behaviour of SRC columns. It is concluded from these experiments that sufficient composite action exists between the concrete and the steel sections for the tested SRC specimens, and that the current code provisions are applicable for the considered configuration, in predicting the flexural capacity of SRC columns when the eccentricity ratio is less than or equal to 15%. The present paper summarizes the principles and an application method for the design of such columns under combined axial compression and bending. The method is based on simplifications provided in EN 1994–1-1. The validation of the method is made using experimental and numerical results.

Detailed numerical research on the performance of unbonded prestressed SRC frame beam under vertical cyclic load

Prestress tendons can be used to improve the serviceable performance of steel reinforced concrete (SRC) beam members. To have a comprehensive understanding of the seismic behaviors of unbonded prestressed SRC beam members, fifteen frame beam specimens, including thirteen unbonded prestressed SRC ones and two ordinary SRC ones, were designed to make the numerical multi-parameter analysis. The parameters considered were the amount of unbonded tendons, rebar, flange and web thickness of steel shape. In the paper, the load-carrying capacity, strain of steels and concrete, ductility, energy dissipation, deformation restoring capacity, stiffness and strength degradation were detailed analyzed and discussed. The results indicated that increase the amount of unbonded tendons would lower the utilization efficiency of steel and decrease the energy dissipation capacity. Raising the amounts of tendons, rebar or steel shape would reduce the specimen’s ductility and the ductility coefficient had a good linear relationship with the introduced integrate reinforcement index. According to the numerical analysis, several brief design suggestions were provided for reference. Moreover, compared with the ordinary SRC specimens, it could be observed that the energy dissipation capacity of prestressed SRC members was relatively lower, while its deformation capacity was as good as ordinary SRC ones. The application of unbonded tendons in SRC beam members greatly improved its serviceability and deformation restoring capacity.

Corrosion-inhibition and compressive-strength performance of Phyllanthus muellerianus and triethanolamine on steel-reinforced concrete immersed in saline/marine simulating-environment

This paper studies the corrosion-inhibition and compressive-strength performance of Phyllanthus muellerianus leaf-extract and triethanolamine (C6H15NO3: TEA) on steel-reinforced concretes that were immersed in 3.5% NaCl medium, a saline/marine simulating-environment. Concentrations of the plant-extract and the organic chemical were employed, individually and in synergies, as admixtures in steel-reinforced concrete specimens and corrosion monitoring of corrosion rate by linear-polarisation-resistance was applied before subjecting the samples to compressive-strength testing/analyses. Results showed that Phyllanthus muellerianus outperformed TEA in anticorrosion and compressive-strength effects but the synergies exhibited further improvements on TEA performance on these test-criteria in the steel-reinforced concretes for the saline/marine test-environment.

Axial and flexural behavior of unreinforced and FRP bar reinforced circular concrete filled FRP tube columns

Fiber Reinforced Polymer (FRP) composites have emerged as a viable alternative of steel reinforcement due to higher ultimate tensile strength to weight ratio and corrosion resistance of FRP composites. Concrete Filled Fiber Reinforced Polymer Tube (CFFT) technique for new column construction has attracted significant research attention. This paper investigated the axial and flexural behavior of Concrete Filled Carbon FRP Tube (CFRP CFFT) columns with and without CFRP bar and concrete filled Glass FRP (GFRP) tube columns with and without GFRP bar. The test results of 16 circular CFFT and four steel Reinforced Concrete (RC) specimens of 203–205mm diameter and 800–812mm height have been reported in this paper. The test results showed a larger reduction in the confinement effectiveness of FRP tube than steel helices under increasing applied load eccentricity. FRP bar reinforced CFFT specimens exhibited higher axial loads, flexural loads, and deformations at peak loads than unreinforced CFFT and steel RC specimens. Experimental axial load-bending moment interaction curves of tested specimens also showed the improved performance of FRP bar reinforced CFFT specimens.

Bio-characterisation of Solanum aethiopicum leaf: prospect on steel-rebar total-corrosion in chloride-contaminated-environment

This paper investigates biochemical constituents of Solanum aethiopicum leaf, for its prospect on the total-corrosion reduction of concrete steel-rebar in the chloride-contaminated environment. Atomic absorption spectroscopy (AAS) and Fourier transform infra-red (FTIR) spectroscopy were used for assessment of inorganic and organic constituents of the leaf. Steel-rebar total-corrosion was analysed, as per ASTM G109-99a, from macrocell-current measurements in 3.5% NaCl-immersed steel-reinforced concrete samples that were admixed with different concentrations of the Solanum aethiopicum leaf-extract. By AAS, Solanum aethiopicum leaf was characterised of inorganic constituents Fe = 4645.50 μg/g, Pb = 74.1138 μg/g, Ni = 43.1162 μg/g, Cd = 6.8425 μg/g, Cu = 0.004581 μg/g and Cr = 0.0000 μg/g. By FTIR, the plant was characterised with S-, N-, O- (and a trace of Hg-) containing organic hetero-atoms. Also, the different concentrations of Solanum aethiopicum leaf-extract admixture studied reduced steel-rebar total-corrosion, with physisorption mechanism, in the 3.5% NaCl-immersed steel-reinforced concrete specimens relative to a sample without admixture.

Morinda Lucida Effects on Steel-reinforced Concrete in 3.5% NaCl: Implications for Corrosion-protection of Wind-energy Structures in Saline/Marine Environments

This paper studies effects of the leaf-extract of Morinda lucida on the corrosion-degradation of steel-reinforced concrete in 3.5% NaCl, simulating saline/marine environment (prevalent in offshore environments for wind-energy structures/installations). Electrochemical monitoring techniques and compressive-strength testing were employed for different concentrations of the leaf- extract admixture in duplicates of steel-reinforced concrete specimens, partially immersed in the corrosive-medium. Analyses of the experimental test-results according to specification ASTM G16-95 R04 showed that Morinda lucida leaf-extract combined highly-efficient corrosion inhibition, 84.82±7.76% ≤ η ≤ 95.64±1.50%, with good compressive-strength improvements in their admixed steel-reinforced concretes. These bear implications for corrosion-protection of wind-energy structures in saline/marine environments.

Utilization of waste vehicle tires in concrete and its effect on the corrosion behavior of reinforcing steels

The mechanical and physical properties of concrete specimens obtained from replacing natural coarse aggregate with waste vehicle rubber tires at levels of 2vol%, 5vol%, 7vol%, and 10vol% were studied, and the corrosion behavior of reinforcing steels was investigated in these specimens. Corrosion rates were determined by measuring the galvanic current between steel-reinforced concrete specimens both with and without chloride addition. The change in electrode potential of reinforcing steels in these concrete specimens was measured daily for a period of 60 d in accordance with the testing method in ASTM C876. The results show that the use of waste vehicle tires in concrete instead of coarse aggregate decreases the mechanical strength of the specimens, and increases the corrosion rates of the reinforcing steels embedded in the concretes.

Electrochemical chloride extraction (ECE) from steel-reinforced concrete specimens contaminated by “artificial” sea-water

Electrochemical chloride extraction (ECE) was studied in the laboratory using cylindrical concrete specimens containing chlorides from “artificial” sea-water. The ECE was carried out for 21 and 90 days, using current densities of about 1 A/m 2 of steel surface. About 60% to 50% of the initial chloride was removed from the concrete on average. Around 1% chloride by mass of cement remained around the steel after treatment. No influence on the chloride removal efficiency was found from anolyte refreshment after treatment. The quantities of chloride removed correlated well with those observed in practice. Due to the negative polarity of steel in an ECE treatment, Na +, K + and Ca ++ ions from the concrete pore solutions accumulate near the steel surface. K + ions move towards the steel rebar more quickly than the other cations analyzed in this work. Although both the chloride content and the dissolution of the steel were reduced, the repassivation of steel rebar cannot be guaranteed.