Types Of Steel Bars Research Articles

Simulation and analysis of rust expansion cracking of reinforced concrete

Reinforced concrete is used in complex environment, and the damage of concrete protective layer caused by steel corrosion will seriously reduce the durability of the structure. In order to deal with the different corrosion morphology of steel bars in engineering, three different function expressions are proposed to describe the uniform and non-uniform corrosion of steel bars. Based on PF_CZM phase field model and adaptive refinement mesh technology, the cracking of concrete protective layer caused by different corrosion types of steel bars is simulated. The simulation results are close to the experimental or actual observed crack propagation. The research shows that the non-uniform corrosion coefficient (α) of steel bars affects the crack propagation form of protective layer. When α=1,2, the thinnest part of the protective layer will be penetrated by the main crack, and two secondary cracks will be produced on both sides. The characteristic displacement in the process of crack propagation is similar, and the maximum expansion displacement of steel bar is less than 125 μm when there is obvious crack in the protective layer. When α=4,8, the protective layer will produce two main cracks. The corrosion characteristic displacement is also similar, and the maximum expansion displacement of steel bars exceeds 180 μm when there are obvious cracks in the protective layer. However, with the increase of non-uniform corrosion coefficient, the amount of steel corrosion required for obvious damage and cracks gradually decreases, and the structure is more likely to be damaged. When non-uniform corrosion occurs in both longitudinal and transverse directions of steel bars, cracks will originate from the most serious corrosion of steel bars and spread to both sides. Compared with the two-dimensional simulation results, the simulated crack propagation morphology and the predicted structural durability results are more accurate. The coarse mesh is used to verify the adaptability of the method to the project, which provides reference for the engineering design and durability research of concrete structures.

Study on bond properties of corroded NPR (negative Poisson’s ratio) steel bar embedded in marine concrete

In this work, 48 pull-out test specimens of 150 mm × 150 mm × 150 mm have been examined to assess the bond behavior between corroded NPR (negative Poisson’ s ratio steel bar) and marine concrete with different anchorage bond length. Three variables are considered: two types of steel bar (NPR bar and HRB400 steel bar), theoretical corrosion ratio of steel bar (ρ=0,1\\%,2\\%,3\\%), anchorage length (5 or 7 times of steel bar diameter). Experiment results showed that under the same extent of bars theoretical corrosion ratio and anchorage length, the bond between NPR and marine concrete exhibits lower value than that of HRB400. Moreover, as measured mass corrosion ratio increases, the bond strength of NPR and HRB400 embedded in marine concrete shows a trend of first rising and then falling. For NPR bas, the measured mass corrosion ratio corresponding to the peak value of bond strength is about 1.8 %. Furthermore, considering the condition of ρ=0,1\\%,2\\%, NPR bar specimens with anchorage length of 7d show slightly lower bond capacity than that of specimens with anchorage length of 5d due to the inhomogeneity of bond stress distribution of steel bar and surrounding concrete. Finally, the bond stress-slip constitutive model between two types of steel bars and marine concrete considering different working conditions has been proposed.

Behavior of large-scale concrete columns reinforced with high-strength and high-toughness steel bars under axial and eccentric compression

In this paper, combined with the current era background of energy saving and emission reduction, low carbon and environmental protection, the mechanical performance of new high-strength and high-toughness steel bars (HSHTSB) in concrete structural members is studied, and HSHTSB is expected to be popularized. To investigate the compression behavior of large-scale concrete columns reinforced with HSHTSB under axial and eccentric compression, thirteen reinforced concrete (RC) columns were designed in this paper, including the five columns under axial compression and the eight columns under eccentric compression. The effects of different types of steel bars, transverse steel bar spacing, the configuration of transverse steel bars, and eccentricity on failure modes, load-deformation curves, load-strain curves, ultimate bearing capacity, deformation capacity, and energy absorption capacity were studied in detail. The results show that the cracks are more uniform for concrete columns reinforced with HSHTSB. When the transverse steel bar spacing is less than 80 mm, concrete columns reinforced with HSHTSB with eccentricity ≤200 mm (including eccentricity = 0) have obvious secondary bearing phenomenon, and significantly improve ductility and energy absorption capacity; HSHTSB as longitudinal steel bars can reach yield strength for RC columns under axial compression. For RC columns under eccentric compression, HSHTSB could not reach yield strength on both the tensile and compression side. For the RC columns of Group II, III, and IV, when the eccentricity increases from 100 mm to 400 mm, the ultimate bearing capacity decreases by 76.1%, 75.2%, and 75.1%, respectively. Different from the ordinary RC columns, the ductility decreases with the increase of eccentricity for concrete columns reinforced with HSHTSB. Compared with ordinary RC columns, the energy absorption capacity and deformation capacity of concrete columns reinforced with HSHTSB under axial compression are increased by 120.9% and 116.9%, respectively. Compared with RC columns using transverse steel bars with single-leg, the energy absorption capacity and ductility for multiple-leg can be increased by 111.5% and 103.2%, respectively. When the eccentricity increases from 100 mm to 400 mm, the ductility for columns of Group II and III decreases by 73.5% and 65.9%, respectively. The use of HSHTSB can save the number of longitudinal steel bars and the transverse steel bar spacing while maintaining the bearing capacity, and further improve the deformation capacity. Based on the section strain analysis, the analytical models of the ultimate bearing capacity for the concrete columns reinforced with HSHTSB were established with high accuracy.

Bond–Slip Law Between Steel Bar and Different Cement-Based Materials Considering Anchorage Position Function

The bond performance between steel bar and cement-based materials was the prerequisite for the two materials to work together, and previous studies showed that the bond behavior of the steel bars and cement-based materials will vary with the kinds of cement-based materials. For this reason, this paper adopted 12 direct pullout test specimens including three types of concrete and two types of steel bars. The strain of the steel bar at six measuring points was measured with a strain gauge. Based on the measured strain and free end slip of the steel bars, the distribution of steel stress, bond stress, and relative slip and the bond slip relation along the anchorage length were obtained and analyzed for different concrete and different steel bars. Based on these test results of steel strain and relative slip at six measuring points, the anchorage position function could be established in consideration of anchorage position, which was conducive to the establishment of an accurate bond–slip relationship. In addition, the anchorage length of the steel bar in Engineered Cementitious Composites (ECC) calculated from the equilibrium equation of critical limit state is only half of the anchorage length calculated in the current Code for Design of Concrete Structures (GB 50010-2010) in China. It is suggested to establish the critical anchorage length formula suitable for ECC in future studies.

Bond Behavior between Recycled Concrete Containing CDW and Different Types of Steel Bars

The operation of reinforced concrete structures is directly associated with the adhesion between the steel bar and the concrete, which allows the internal forces to be transferred to the reinforcement during the process of loading the structural elements. The modification of the concrete composition, with the introduction of recycled aggregate from construction and demolition waste (CDW), affects the steel-concrete interface and can modify the bonding stress, which is also influenced by the type and diameter of the bar used. In this work, the influence of the recycled fine aggregate (RFA) and types of steel bar on the steel-concrete bond was experimentally evaluated using the pullout test. Conventional concrete and recycled concrete, with RFA replacement level of 25%, were produced. Two types of steel rebars (i.e.,plain and deformed) with diameters of 10.0 and 16.0 mm were considered in this paper. The results indicate a reduction in the adhesion stress with the introduction of recycled aggregate, but this trend is influenced by the diameter of the bar used. The use of ribbed bars modifies the stress bonslip behavior, with an increase in the average bond strength, which is also observed with the reduction of the diameter of the bar.

Comparative studies on passivation and corrosion behaviors of two types of steel bars in simulated concrete pore solution

The corrosion behavior of two types of stirrups, a plain steel bar and a ribbed steel bar, were studied in this work. The results demonstrated that a better passive state was achieved on B500, which was due to a relatively higher concentration of Fe2+ oxides at the first 2 nm depths of the film, even though B500 film had relatively less FeOx contents, because Fe2+ oxides had a better protective property than Fe3+ oxides. Furthermore, the slightly lower donor density of B500 film in the M-S analysis results presented the much less point defect in the film, showing an increase in the anti-corrosion property of passive film. These contributed to a higher chloride threshold value of B500, 4 times higher than that of S275. Therefore, compared with S275, B500 stirrups could be more suitable for the application in the severe service environment.

Effect of Cement Content on Compressive and Bonding Strength with Steel Bar Reinforcement

Concrete is the most important building material due to the availability of its constituent materials and its easy manufacturing; it is commonly reinforced with a steel bar to resist the tensile stresses. The present research discusses the effect of cement content on the bonding strength with the steel bar reinforcement as well as the concrete strength while fixing the fine/coarse aggregate proportion, the slump and the water/cement ratio. Two series have been produced by using different types of steel bars (smooth and deformed) with a different cement content of (250, 300, 350, 400 and 450 kg/m3). These two parameters were used to study the effect of the cement content and the mechanical interlocking on the bonding strength between concrete and steel bars. The results of this study showed that the compressive strength increases with the increasing of cement content up to 400 kg/m3, and then there is no significant improvement in compressive strength. However, the bonding strength with the steel bar increases even at 450 kg/m3. For any cement content, the deformed bars exhibited a better bonding strength of several times than the smooth bars.

Effects of Transverse Crack on Chloride Ions Diffusion and Steel Bars Corrosion Behavior in Concrete under Electric Acceleration.

Cracks greatly impact the durability of concrete structures due to their influence on the migration of chloride ions and the corrosion process of steel bars. This study investigates the effects of transverse cracks on chloride diffusion and the corrosion behavior of two types of steel bars (low carbon steel and corrosion resistant steel) in fly ash concrete with 1 kg/m3 solution-polymerized super absorbent polymer. Electrochemical impedance spectroscopy was used to monitor the chloride-induced corrosion behavior of steel bars in concrete. The chloride profile around cracks was tested via chemical titration. The corrosion products diffusion area was photographed and measured to evaluate the influences of cracks on the corrosion degree of steel bars. Transverse cracks greatly influence the chloride ion transport. When their width is less than 0.15 mm, cracks exert little influence on both chloride diffusion and steel corrosion. When the crack width exceeds 0.15 mm, the chloride ion transmission coefficient is significantly improved and steel corrosion is accelerated. However, when the crack width exceeds 0.20 mm, this effect is gradually weakened. Based on the experimental data, a quantitative relationship between the crack width and the chloride ion transmission coefficient in electric acceleration was established.

FRP-confined concrete core-encased rebar for RC columns: Concept and axial compressive behavior

In the ultimate failure mode of columns in RC structures under seismic load, the longitudinal reinforcement generally suffers from severe buckling due to the axial compressive load, spalling of concrete cover and dilation of concrete core. Proper configuration of RC columns to postpone or prevent the buckling phenomenon can enhance the seismic performance and make full use of the strength of steel reinforcement. In this paper, a new concept and configuration of FRP-confined concrete core-encased rebar (FCCC-R) for RC columns is proposed. The concrete surrounded the longitudinal rebar is confined by an FRP tube, which can prevent the rebar from premature buckling. The axial compressive behavior of the hybrid bar considering different parameters, including the slenderness ratio, FRP tube diameter, mortar strength, and bar position was studied experimentally. Furthermore, finite element (FE) simulation was carried out and calibrated by test results. Based on the FE model, additional discussion and a parametric study was performed. Finally, the minimum FRP tube diameter required for the FCCC-R considering the compressive behavior enhancement effect was calculated, and design curves for 3 types of steel bars with nominal yield strengths of 400 MPa, 800 MPa, and 1100 MPa were proposed.

Probability Distribution of Cross-sectional radius of Corroded Steel Bars in Concrete and Its application

The impress current method is applied to acquire corroded steel bars embedded in concrete, and three-dimensional(3D) laser scanning techniques are applied on corroded steel bars to obtain the cross-sectional radius of corroded steel bars. Statistical analysis shows that with the increase of corrosion degree, the variation of radius of corroded steel bars increases linearly. For different types of steel bars, plain round steel bars have a larger sensitivity to corrosion than ribbed ones. Original radius of steel bars and mixture proportion of concrete have negligible effect on the variability of radius of corroded steel bars. A normal distribution model is obtained to describe radius data of corroded steel bars. For the convenience of practical application, the indicator,R, which is the ratio of the average to the minimum cross-sectional areas of corroded steel bars, is introduced to quantify the longitudinal variation of the cross-sectional areas. By using Monte-Carlo simulation, the indicator, R, of corroded steel bars are achieved based on the probability distribution of radius. The indicator R can be fitted well by the Gumbel distribution, and the distribution parameters increase linearly with the increases of corrosion degree.

The computational analysis of the crack width of beams reinforced with CFRP and steel bars

The aim of the paper is to explain the particular problems related to the use of FRP reinforcement in bending beams. The paper compares the aspect of Serviceability Limit State (SLS) of simply supported concrete beams reinforced with Carbon Fiber Reinforced Polymer (CFRP) bars and three various types of steel bars (the steel grades are 35G2Y, 20G2VY-b and B500SP). The computational analysis of change in crack width under the influence of various level of service live load was investigated. The calculations of beam reinforced with FRP bars was based on Italian design guideline (CNR-DT 203/2006) and the conventional reinforced concrete beams (RC) were analysed in accordance with the European standard Eurocode 2 (EN 1992-1-1:2004).

Bond behavior of steel bar embedded in recycled coarse aggregate concrete under lateral compression load

Steel bars and concrete in practical engineering is served under a complex stress state, the bond behavior of steel bar embedded in concrete, inevitably, was affected by the stress state. So, the center pull out tests were conducted to investigate the bond strength and the bond stress-slip curves of steel bar embedded in recycled coarse aggregate concrete under the action of lateral compression load. For recycled coarse aggregate concrete, the replacement percentage of recycled coarse aggregate to the sum of natural coarse aggregates and recycled coarse aggregates was 30%. The variables of two types of steel bars (deformed steel bars with diameter 14mm, 18mm, 22mm and plain steel bars with diameter 12mm), four levels of lateral compressive load (0kN, 200kN, 320kN and 450kN) were considered in the experimental study. The failure modes of center pull out specimen were observed and recorded. Based on the test results, the influences of lateral compressive stress, type of steel bars and diameter of deformed steel bars on the bond behavior of steel bar embedded in recycled aggregate concrete were studied and analysed. It was found that the pull out force and bond strength for deformed steel bar are larger than that for plain steel bar under the same lateral compressive load, the bond strength increases with the increase of lateral compressive load.

Bond behavior between steel bar and recycled aggregate concrete after freeze–thaw cycles

The bond behavior (failure modes, bond strength, bond stress-slip curves) between steel bar and recycled aggregate concrete after different cycles of freeze–thaw was studied using pullout tests. One recycled aggregate concrete, two types of steel bars: plain steel bars with diameter 12mm, deformed steel bars with diameter 14mm, 18mm, 22mm and 0, 15, 25, 50, 75cycles of freeze–thaw were considered in the experiment. Based on the experimental results, the influence of number of freeze–thaw cycles, type of steel bar, and diameter of deformed steel bar on the bond behavior between steel bar and recycled aggregate concrete was studied and analyzed. It was found that the bond strength decreases as the freeze–thaw cycles increased, the drop of bond strength between plain steel bar and recycled aggregate concrete is larger than that between deformed steel bar and recycled aggregate concrete as the freeze–thaw cycles increased, the pullout force and bond strength for deformed steel bar are larger than that for plain steel bar after the same cycles of freeze–thaw.

Comparative Study of Flexural Behavior of Corroded Beams with Different Types of Steel Bars

AbstractAn experimental study is proposed to compare the corrosion-induced flexural behavior deterioration of beams with various bar types and bar diameters. The proposed study aims to distinguish the effects of the corrosion of different rebars on the flexural behavior of reinforced concrete (RC) beams. Twenty-two RC beams were designed and four variables were considered: the type and the diameter of reinforcement, corrosion loss, and concrete cover. Corrosion was induced in the laboratory using an accelerated corrosion technique. The corrosion-induced strength loss for two types of steel bars is discussed. Extensive statistical analysis is performed to compare the flexural performance of beams with different rebars. The experimental results show that (1) corrosion has a more significant effect on the flexural behavior deterioration in beams with smooth rebars than in beams with deformed rebars; (2) the corrosion-induced performance deterioration has a monotonic decreasing relationship with reinforcement...

Corrosion Inhibition by Cr-bearing Rebar in Concrete Due to Combined Deterioration of Carbonation and Chloride Attack

With the aim of developing Cr-bearing rebars having required resistance to deteriorative environments prone to carbonation with or without chloride attack, ten types of steel bars having different Cr contents were embedded in concretes with chloride ion contents of 0, 0.3, 0.6, 1.2, and 2.4 kg/m3 to fabricate specimens assuming such deteriorative environments. After being carbonated to the reinforcement level, these concretes were subjected to corrosion-accelerating cycles of heating/cooling and drying/wetting. The time-related changes in the corrosion area ratio and corrosion loss of the Cr-bearing rebars were then measured to investigate their corrosion resistance. The results revealed that the Cr content required for corrosion resistance in a simple carbonating environment was 5% or more. The corrosion-resisting performance of Cr-bearing rebar was particularly noticeable with a Cr content of 7% or more. In a deteriorative environment prone to both carbonation and chloride attack, corrosion resistance was evident with a Cr content of 7% or more and 9% or more in concretes with chloride ion contents of 1.2 and 2.4 kg/m3, respectively.

Inspection of interfaces between corroded steel bars and concrete using the combination of a piezoelectric zirconate-titanate transducer and an electromagnetic acoustic transducer

We have conducted an inspection of the interface between a steel bar and concrete using the combination of a piezoelectric zirconate-titanate transducer (PZT) and an electromagnetic acoustic transducer (EMAT). The PZT is used for generating elastic waves by mechanical vibration and then the EMAT is used for receiving the transmitted ultrasonic guided waves. This arrangement is made in order to overcome the major shortcomings of the PZT, i.e., the requirement of a couplant, and of the EMAT, i.e., relatively low transmitted ultrasonic energy. To investigate the applicability of this technique in the field, outside the laboratory environment, the experiments are conducted on different types of steel bars: corrosion-free, naturally corroded, and zinc-coated as well as corroded bars. It is shown that the PZT-EMAT combination is very effective for inspecting the steel bar-concrete interface. Using this technique, small separation at the steel bar-concrete interface can be effectively detected for corroded as well as corrosion-free specimens. This method can be applied in the field to pre-stressed tendons and soil nails, where one side of the reinforcement is exposed.

Bond strength of cement grouted glass fibre reinforced plastic (GFRP) anchor bolts

Fibre reinforced plastic (FRP) has recently been introduced in the market in the form of bars for grouted anchor bolts. The resistance to corrosion and chemical attacks, high strength-to-weight ratio, low electromagnetic properties and ease in handling of these bars make them a better alternative to steel in some applications of grouted anchor bolts. However, to fully utilise FRP bars as tendons for cement grouted anchors, some aspects of their behaviour have to be determined, including load carrying capacity, bond strength in cement grout, long-term strength and durability in alkaline environments. In this paper, the load carrying capacity and bond strength of cement grouted glass fibre reinforced plastic (GFRP) anchor bolts are discussed in comparison with steel anchor bolts. The results of laboratory and field pull-out tests of GFRP and steel bars anchored with cement grout are presented. The pull-out tests were conducted on four types of GFRP bars and two types of steel bars installed in concrete blocks and rock mass. The experimental results have shown that the bond strength of GFRP bar anchor bolts is close to that of steel bar anchor bolts. The slip at failure of GFRP bars relative to the cement grout is greater than that of steel bars, mainly due to their low modulus of elasticity.