Bond Deterioration Research Articles

Structural assessment of the coupled influence of corrosion damage and seismic force on the cyclic behaviour of RC columns

Steel bar corrosion, which is considered to be a significant degradation issue in reinforced concrete (RC) structures, may cause premature failure during seismic events. Many experimental studies have been conducted to investigate the coupled effect of steel bar corrosion and seismic force on the structural behaviour of RC columns. However, modelling of the structural response of corroded RC columns has received comparatively less attention. An accurate assessment of the structural response of corrosion-damaged RC columns may extend the life span and reduce maintenance costs. In this study, we applied the finite element method and developed a numerical model to simulate the seismic performance of corroded RC columns. The numerical model was developed to account for corrosion-induced cracking and bond deterioration between steel and concrete depending on the spatial variation of steel bar corrosion. The finite element (FE) model was validated using the results obtained from three different sets of experimental tests available in the literature with an average corrosion ratio ranging from initial to severe levels. The results obtained using the proposed numerical model demonstrated an excellent correlation with all the experimental results, thereby making it suitable for investigating the seismic behaviour of corrosion-damaged RC columns in terms of stiffness, strength, displacement capacity, and cracking pattern. After validation, the numerical model was used to investigate the effect of localised and uneven distribution of corrosion on the cyclic response of RC columns.

Performance of externally bonded fiber-reinforced polymer retrofits in the 2018 Cook Inlet Earthquake in Anchorage, Alaska

As part of the effort to improve the seismic performance of buildings in Alaska (AK), many of the deficient structures in Anchorage, AK, were retrofitted—some with externally bonded fiber-reinforced polymer (EBFRP) composite systems. The 2018 magnitude 7.1 Cook Inlet earthquake that impacted the same region offered an opportunity to evaluate the performance of EBFRP retrofits in a relatively high-intensity earthquake. This study summarizes the following findings of this field investigation: (1) the performance of EBFRP-retrofitted structures in the Cook Inlet earthquake and (2) the observations concerning the condition of FRP retrofits from over a decade of exposure in a subarctic environment. A deployment team from the National Institute of Standards and Technology (NIST) in collaboration with the University of Delaware (UD) Center for Composite Materials conducted post-earthquake inspections of EBFRP retrofits in multiple buildings to assess their performance during the earthquake and condition with respect to weathering. EBFRP debonding was documented with infrared thermography and acoustic sounding and the bond quality between EBFRP and concrete was assessed using pull-off tests. Visual inspections showed no major signs of earthquake damage in the EBFRP-retrofitted components. However, evaluation of debonding and pull-off test results suggested that outdoor conditions may have led to bond deterioration between EBFRP and concrete from installation defects that grew over time, freeze–thaw expansion from moisture present at the FRP/concrete interface, differences in thermal expansion of the materials, or a combination thereof. The carbon fiber–reinforced polymer (CFRP) bond to concrete was found to be more vulnerable to outdoor exposure than the glass fiber–reinforced polymer (GFRP) bond. Earthquake effects on FRP/concrete bond could not be assessed due to the lack of baseline data.

Using artificial neural network and non‐destructive test for crack detection in concrete surrounding the embedded steel reinforcement

AbstractBond between steel and concrete is one of the key aspects of structural design and its performance evaluation. In the past much research work has been focused on understanding bond deterioration owing to corrosion of reinforcement, however, there exists no nondestructive method to access the bond condition. In this regard, the presented experimental research work details the development of a nondestructive testing method to estimate the crack condition of concrete surrounding the steel reinforced by using ultrasonic pulse velocity test. In addition, a multilayer feedforward back propagation perceptron artificial neural network (ANN) is developed in order to avoid simplification assumptions for developing models to predict the cracking, owing to the nonlinear complex stress distribution at the steel‐concrete interface. The ANN is used to predict the crack width and to conduct sensitivity analysis of the various factors influencing the bond deterioration. A high accuracy level is achieved between the predicted and the experimental values with R2 of 0.97 and the most influential parameter is highlighted.

Deterioration of the bond behavior between CFRP and corroded steel in wet-dry cycling environment

The purpose of this paper is to investigate the deterioration of the bond behavior between CFRP and corroded steel in wet-dry cycling environment and the corrosion effects on them. By conducting the shear tests of 60 CFRP-corroded steel sing lap specimens with 5 duration levels (0, 7, 21, 42 and 84 days), the bond behavior was obtained and its relationships with duration were established. In addition, the corrosion effect on the bond strength and the bond deterioration were investigated on the basis of corrosion analysis. Results show that the wet-dry cycling environment had a significant negative impact on bond behavior between CFRP and corroded steel; those specimens with smaller non-uniform volume loss ratios, larger pit densities and moderate pit sizes may have higher bond strengths; an appropriate number of corrosion pits distributed on the steel surface could improve the resistance to the environmental erosion.

Response of Reinforced Concrete Dapped-End Beams Exhibiting Bond Deterioration Subjected to Static and Cyclic Loading

Response of Reinforced Concrete Dapped-End Beams Exhibiting Bond Deterioration Subjected to Static and Cyclic Loading

Evaluating the effect of corrosion on shear-critical RC beams by integrated NDT

Integrated non-destructive testing (NDT) method consisting of acoustic emission (AE) and digital image correlation (DIC) was used to monitor and evaluate the load-behaviour of shear-critical reinforced concrete beams subjected to corrosion. Measurement data in the forms of mechanical load, deflection, surface strain and AE signals were processed and collectively analysed to facilitate interpretation of damage development and change of structural behaviour in a more comprehensive manner. Results show that when corrosion level increases, the failure mode of the beams changes from shear to flexure, leading to an increase in beam ductility. The steel-concrete bond deterioration caused the change of internal force transfer mechanism when beams were loaded, as indicated by DIC strain maps and AE b-value analysis. Integrated NDT method demonstrates the potential to intuitively and quantitatively indicate damage development of the RC specimen.

Three-dimensional finite element modeling of RC columns subjected to cyclic lateral loading

This paper presents a detailed finite element modeling scheme to simulate the cyclic response of RC columns considering low-cycle fatigue and bond-slip of reinforcement. The modeling scheme includes a triaxial constitutive model recently proposed in the literature to simulate concrete failure under cyclic loading. For steel, a commonly used uniaxial model is enhanced to account for bar rupture using a new low-cycle fatigue criterion, which has been validated with data from fatigue tests on reinforcing bars. The bond-slip behavior of vertical reinforcing bars is modeled using a zero-thickness concrete-steel interface element. The interface element has a bond stress-slip constitutive law that predicts bond deterioration caused by generalized slip demands, tensile yielding of steel, and compression damage in concrete. The finite element models are validated with experimental data from cyclic tests on large-scale column and pile specimens which exhibited flexure-dominated responses. The models accurately simulate the lateral force–displacement response and failure of the specimens, and provide peak tensile strain demands along longitudinal bars which are similar to those measured experimentally. Sensitivity analyses are also conducted to study the effect of modeling assumptions related to low-cycle fatigue and bond-slip behavior.

Flexural tests of concrete-encased composite girders with high-strength steel angle

This study investigated the flexural behavior of concrete-encased steel angle girders (PSRC girders). Inside the concrete section, high-strength steel angles (Fy = 605 MPa) with unequal legs were used as longitudinal reinforcement, and diagonal and vertical members were bolt-connected to the longitudinal angles as transverse ties. Flexural tests were performed for three PSRC girder specimens with different reinforcement details. The tests showed that the PSRC girders all developed the peak loads exceeding the nominal strengths; however, the ductility was limited as rupture occurred near bolt holes in the longitudinal angles. Overall, the concrete damage and cracking of the PSRC girders were comparable to those in conventional reinforced concrete beams, and cover spalling and bond deterioration along the longitudinal angles were not severe. The strength, stiffness, and ductility estimated in accordance with current design codes were compared with the test results. Given the investigation results, the application and design considerations of PSRC girders were discussed.

Modeling the lateral behavior of freeze-thaw damaged reinforced concrete columns including reinforcement slip and shear effects

This paper focuses on modeling the lateral load-deformation response of reinforced concrete columns subjected to freeze-thaw cycles (FTCs). Freeze-thaw effects are accounted for by means of a non-uniform reduction in concrete strength and bond deterioration between the steel and concrete. The new column response model that is proposed includes deformations due to flexure, reinforcement slip, and shear effects, and the influence of freeze-thaw effects on each of these aspects. The slip displacement is formulated and solved using governing equations among four bond fields. The moment-rotation relationship is then developed and introduced into the zero-length spring element to compromise the rotations caused by reinforcement anchorage slip and by curvatures over the column height. A shear spring element is used in series to represent the shear backbone curve and to capture the onset of shear failure. The proposed model is validated using experimental data on freeze-thaw damaged columns with a wide range of typical design parameters. Overall, the proposed column model accurately simulates the cyclic behavior of both flexure and flexure-shear columns that experience freeze-thaw cycles.

An experimental assessment of corrosion damage and bending capacity reduction of singly reinforced concrete beams subjected to accelerated corrosion

Many existing concrete structures damaged by corrosion show signs of deterioration. The assessment of the structural performance of their components requires understanding the link between the damage such as the corrosion crack width and cross-section loss, and mechanical behavior. This paper investigates the structural behavior of corroded concrete beams reinforced with ribbed and smooth bars by studying the relation between the corrosion damage and the failure mechanism under three-point bending. Results of corrosion damage measurements indicate that corrosion crack width is a good indicator of the corrosion level. Furthermore, results of the bending tests indicate the effect of the interaction between bond deterioration and the distribution of cross-section loss on the bending behavior. Finally, relating the relative reduction in bending capacity to the average rebar cross-section loss indicates a strong correlation in the case of beams with ribbed bars while more scatter occurs in the case of those with smooth bars.

Bond Deterioration of Corroded-Damaged Reinforced Concrete Structures Exposed to Severe Aggressive Marine Environment

Cracks lead to a reduction of the bond between concrete and reinforcing steel rebars. A considerable decrease in the bond strength is more dangerous to a structural element’s safety than the loss of the cross-sectional steel reinforcement area. The purpose of this study is to evaluate the bond strength of corroded-damaged structures exposed to severely aggressive marine environments. Eighteen (18) cube specimens with dimensions of 200 mm x 200 mm were cast. They were reinforced with three (3) different diameters of deformed steel and were grouped as unconfined and confined. The specimen was accelerated under a simulated corrosive environment. The experiment results reveal that the bond strength of concrete and steel reinforcement is susceptible to corrosion levels. The degree of corrosion significantly affects the bond strength of concrete and steel. The bond strength and the average crack width have a strong correlation; a minimal amount of corrosion with a minimum crack width of 0.03 mm after cracking reduces the bond strength to an unacceptable level. Stirrups confinement has a significant influence on the bond strength; it provides an excellent means to counteract bond loss. The loss of bond directly affects the serviceability and ultimate strength of reinforced concrete structures. There is an exponential relationship between cement and steel reinforcement’s bond strength with the serviceability and residual strength of reinforced concrete structures.

Preparation of superfine cinnamon bark nanocrystalline powder using high energy ball mill and estimation of structural and antioxidant properties

Application of Food material for medicinal use is become a common and safe approach to treat various diseases. Although Nanoscience is seeming to most promising area to be explore at every aspect of existing science including medicine and pharmaceuticals. Medicinal properties and application of various spices are well explored science but their nanopowder synthesis and effect is not very much known. In this present work, we have used a commonly known spice from Indian kitchen know as Cinnamon, for synthesis of nano powder high energy ball mill instrument was used. The crystallographic study, functional group analysis, were done using modern characterization equipment such as XRD (X-ray diffraction), FTIR (Fourier transform infrared spectroscopy), SEM (Scanning Electron Microscope), and UV-Visible spectroscopy. XRD measurement confirms that crystal structure of powder milled for 5 hours and 10 hours were different. Similarly, morphology of differently milled sample found to be different from general Cinnamon powder. This might be due the formation of different fractions of particles were formed as a result of deterioration of cohesion bond due to high energy milling. The present study suggested that cinnamon superfine powder could be a potential source of natural antioxidant and thus could be useful as therapeutic agents and also open new window for the progress of surface science of food materials, which are beneficial for biomedical engineering, pharmaceutical, health, and medicine industries.

Mesoscale simulation of pull-out performance for corroded reinforcement with stirrup confinement in concrete by 3D RBSM

The confining effect of concrete cover and stirrups reduces the rate of bond deterioration due to corrosion. However, the large dispersion in recorded experimental data makes it difficult to clearly separate the influence of cover depth and stirrup confinement on bond degradation. This study utilises the discrete 3D Rigid Body Spring Model (RBSM) to conduct a meso-scale investigation regarding the effect of cover thickness and stirrup confinement on internal crack evolution and pull-out behaviour in corroded reinforced concrete models. The simulation scheme is divided into two stages. In stage 1, different degrees of corrosion are introduced, producing cracking in the cover concrete; in stage 2, the corroded main reinforcement is pulled out from the damaged concrete. 3D RBSM is advantageous because the concrete is randomly meshed to reduce mesh bias on crack propagation and the actual geometry of the deformed bars is modelled. The simulation results clarify that the presence of thicker cover delays crack initiation but increases the rate of crack opening. Stirrups do not have any significant effect on crack initiation but effectively restrict crack growth. An investigation of the internal stress in the simulation models shows that tensile stresses generated in stirrups during corrosion are responsible for reactionary confining pressure that restricts crack propagation. Load-displacement curves show reductions in pull-out capacity, stiffness and ductility with increasing corrosion damage. The relative influence of crack opening and stirrup volume on the rate of bond degradation with respect to average surface crack width are discussed and compared with published experimental results and an empirical equation.

Mitigating Bond Deterioration under Cyclic Loading and Water Exposure

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Analyzing bond-deterioration during freeze-thaw exposure in cement-based repairs using non-destructive methods

Cement-based repair materials are extensively used to rehabilitate damaged structures and extend their service life. However, these materials experience bond deterioration and strength loss during service. Traditional standardized test methods for bond determination are destructive and impose additional damage in parent structures. This paper presents findings of a unique study where a combination of force and acoustic sensors were used to determine the dynamic modulus of elasticity (Edyn), which reflects the interfacial deterioration and material damage. Flexural bond test and image analysis were performed to validate the results. The experimental study shows that the change in Edyn determined from non-destructive tests (NDTs) agree well with the change in other measurements including flexural bond strength (fr′), interfacial crack width, and mass loss after freeze-thaw exposure. Linear relationships are established between Edyn and fr′ for both cementitious and polymer-modified cementitious repair mortar with a coefficient of determination ranging from 0.87 to 0.95.

Bond behavior and shear transfer of steel section-concrete interface with studs: Testing and modeling

The premature debonding at the steel section-concrete interface is the main cause of performance degradation for SRC structures. It is expected to improve the interfacial bond behavior using headed studs that can provide mechanical interlocking. However, the bond behavior and shear transfer mechanism of the steel section-to-concrete interface with studs has not been fully understood. For this reason, push-out tests on SRC specimens were performed in this research. The effects of the presence and the position of studs on the bond behavior were studied. Further, advanced finite element models considering both bond deterioration and mechanical action were developed to reveal the internal shear transfer mechanism during the entire loading process. Finally, a parametric study was carried out to investigate the influence of other key variables on the overall bond behavior and shear transfer of interface with studs. The results indicated that the headed studs could improve the interfacial bond resistance and shear stiffness, enhance the post-peak bond behavior, and prevent brittle failure, especially for the web-welded type. The evolution of load-slip behavior could be separated into five phases, i.e. the linear ascending, nonlinear ascending, post-peak descending, stable, and stud failure phases, as a result of the progressive deterioration of adhesion and activation of studs and friction. The behaviors and bond stress distribution in these phases were found to be affected by variations in the stud diameter, stirrup ratio, concrete strength, as well as number of stud rows.

Residual capacity assessment of reinforced concrete D-Regions affected by corrosion

The repair and rehabilitation of Reinforced Concrete (RC) structures affected by the corrosion of their reinforcement is a complex task. The estimation of the residual structural capacity of corroded RC structures is becoming a crucial factor in the decision-making process of repair or demolition. Many researchers have studied the effects of reinforcement corrosion on the load capacity of RC beams (Bernoulli or B-Regions) but little attention has been paid to disturbed or D-Regions. This piece of work presents a procedure for the assessment of the residual structural capacity of D-Regions in RC members. The bond deterioration between steel and concrete, the reduction of the cross-sectional area of reinforcement, the deterioration of the concrete area of the cross-section and the softening of concrete has been taken into consideration. The accuracy of the method has been tested with experimental results which exist in relevant literature.

Bond behaviours of deformed steel rebars in engineered cementitious composites (ECC) and concrete

This paper presents the bond behaviors of deformed steel rebars in engineered cementitious composite (ECC) and concrete under direct pullout condition. A total of 12 specimens were casted and tested, it was found that the deformed steel rebar has a much higher bond strength in ECC than in concrete due to the superior tensile ductility of ECC material. A new finite element analysis (FEA) model, which considered the influences of steel ribs, was proposed and verified with the experimental results. Based on the proposed FEA model, the failure mechanisms and bond deterioration processes for both ECC and concrete specimens were analyzed and compared. It was found that the plastic area ratio for ECC specimen was as high as 32.2%, which is 3.3 times higher than that for concrete specimen. Also, the ultimate damage zone for ECC specimen is 36% lower than that for concrete specimen. It was concluded that ECC specimen has more compatible deformability with steel rebar as more ECC elements could participate in the transfer of tensile load.

Numerical simulation of bond degradation subjected to corrosion-induced crack by simplified rebar and interface model using RBSM

The bond degradation subjected to corrosion-induced crack was investigated numerically using 3D Rigid Body Spring Model (RBSM) in which rebar was modeled by solid elements without modeling explicitly the details of rebar ribs. The proposed numerical model considers both corrosion expansion and shear stress transfer behavior through the interface elements. Validation of proposed model showed that it is possible to obtain reasonable bond performance of non-corroded specimen as meso-scale models. By comparison with experimental results, the proposed model was verified to reproduce the bond deterioration considering corrosion-induced crack with different concrete cover thickness. Moreover, bond deterioration mechanism subjected to corrosion-induced crack was clarified through the crack development and stress distribution of concrete and was found to be the combined effects of degradation of the compressive stress in diagonal compression struts and ring-tension around rebar. Bond deterioration of specimen with larger concrete cover is more sensitive to formation of corrosion crack.

Numerical Study of Bond Slip between Section Steel and Recycled Aggregate Concrete with Full Replacement Ratio

In this paper, the bond deterioration mechanism of recycled aggregate concrete (RAC) with a full replacement ratio was studied through experimental and numerical simulations. To study the bond behavior and the bond slip between section steel and RAC, nine push-out specimens were designed using the control variable method. The effects of the concrete strength, the embedded length, the cover thickness, and the lateral stirrup ratio on the bond behavior and the bond slip were investigated in detail. The loading process and failure mode of the specimens were observed, and the test curves of the loading end and free end of the specimens were analyzed. Based on the experiment, the finite element method (FEM) was used to simulate the specimens, and the simulation results were analyzed by comparing the experiment data. The analysis of the results showed that the developed model is capable of representing the characteristic bond strength value between section steel and RAC with sufficient accuracy, and the main differences of bond slip between the simulation and the test results are the slippage at the limit state and the moment at which the free end starts to slip.