Steel-concrete Bond Strength Research Articles

Experimental study on the effect of grouting volume on the tensile performance of offset semi-grouted couplers

Research results have shown that the mechanical properties of sleeve grouting connections are related to the diameter of the rebar, the sleeve, the grout, the temperature and the loading method, but research on the factor of grout volume needs to be further developed. Therefore, this paper considers the effects of three grouting volumes (50%, 75% grouting and 100% full grouting) on the tensile properties of the joint under the offset condition of the rebar. A total of 22 uniaxial tensile tests on semi-grouted steel sleeve connection specimens were carried out, mainly to study the damage morphology, load-displacement relationship, stiffness and the strain change law on the surface of the rebar and the sleeve under different grouting amount, etc. The stress mechanism of the specimens in the tensile condition was analysed, and the effective bond length calculation model was proposed with reference to the steel-concrete bond strength research theory, and the formula for calculating the maximum bond stress related to the effective anchorage length was obtained. Studies have shown that the grouting amount affects the load bearing capacity and stiffness, and that the quality of the specimen joint is reliable when the grouting volume reaches more than 75% of the design grouting volume.

Push-out resistance of concrete-filled spiral-welded mild-steel and stainless-steel tubes

Spiral welded tubes (SWTs) are fabricated by helically bending a steel plate and welding the resulting abutting edges. The cost-effectiveness of concrete-filled steel tube (CFST) columns can be enhanced by utilising such SWTs rather than the more conventional longitudinal seam welded tubes. Even though the steel-concrete interface bond strength of such concrete-filled spiralwelded steel tubes (CF-SWSTs) is an important consideration in relation to ensuring composite behaviour of such elements, especially at connections, it has not been investigated in detail to date. CF-SWSTs warrant separate consideration of their bond behaviour to CFSTs of other tube types due to the distinct weld seam geometry and fabrication induced surface imperfection patterns of SWTs. To address this research gap, axial push-out tests on forty CF-SWSTs were carried out where the effects of tube material, outside diameter (D), outside diameter to wall thickness (D/t), length of the steel-concrete interface (L) and concrete strength grade (f'c) were investigated. D, D/t and L/D values in the range 102-305 mm, 51-152.5 and 1.8-5.9 were considered while two nominal concrete grades, 20 MPa and 50 MPa, were used for the tests. The test results showed that the push-out bond strengths of CF-SWSTs of both mild-steel and stainless-steel were either similar to or greater than those of comparable CFSTs of other tube types. The bond strengths obtained experimentally for the tested CF-SWSTs, irrespective of the tube material type, were found to be well predicted by the guidelines contained in AISC-360.

Structural Deterioration Detection Using Enhanced Autoregressive Residuals

This paper presents a study on detecting structural deterioration in existing buildings using ambient vibration measurements. Deterioration is a slow and progressive process which reduces the structural performance, including load-bearing capacity. Each building has unique vibration characteristics which change in time due to deterioration and damage. However, the changes due to deterioration are generally subtler than the changes due to damage. Examples of deterioration include subtle loss of steel-concrete bond strength, slight corrosion of reinforcement and onset of internal cracks in structural members. Whereas damage can be defined as major sudden structural changes, such as major external cracks of concrete covers. Herein, a deterioration detection method which uses structural health monitoring (SHM) data is proposed to address the deterioration assessment problem. The proposed novel vibration-based deterioration identification method is a parametric-based approach, incorporated with a nonparametric statistical test, to capture changes in the dynamic characteristics of structures. First, autoregressive (AR) time-series models are fitted to the vibration response time histories at different sensor locations. A sensitive deterioration feature is proposed for detecting deterioration by applying statistical hypotheses of two-sample [Formula: see text]-test on the model residuals, based on which a function of the resulting [Formula: see text]-values is calculated. A novel AR model order estimation procedure is proposed to enhance the sensitivity of the method. The performance of the proposed method is demonstrated through comprehensive simulations of deterioration at single and multiple locations in finite element models (FEM) of 3- and 20-storey reinforced concrete (RC) frames. The method shows a promising sensitivity to detect small levels of structural deterioration prior to damage, even in the presence of noise.

Modeling Steel-Concrete Bond Strength Depletion during Corrosion

First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address

Modeling Steel-Concrete Bond Strength Depletion during Corrosion

Modeling Steel-Concrete Bond Strength Depletion during Corrosion

Bond strength evaluation of corroded steel bars via the surface crack width induced by reinforcement corrosion

The corrosion of steel bars in reinforced concrete structures induces concrete cover cracking and leads to reduction in steel–concrete bond strength. In the present study, a series of pull-out tests were carried out to investigate the potential correlations between corrosion level, surface crack width, and bond strength. The main variables are corrosion level, concrete cover depth, and spacing of stirrups. The test results indicate that the surface crack width is closely linked to the corrosion level of the tensile steel bar, and the crack propagation can be divided into three stages. It is further revealed that the bond strength decreases exponentially with the surface crack width. Based on the test results, an empirical model for estimating the bond strength using the surface crack width is formulated, which considers the pronounced limiting effect of stirrups on the bond degradation. The model is further improved by incorporating the adverse effect of the corrosion of stirrups according to the previous investigations. Comparison with existing experimental database in the literature proves that the proposed models are able to realistically predict the bond strength of corroded steel bars.

Modeling Steel Concrete Bond Strength Reduction Due to Corrosion

Reinforcement corrosion in reinforced concrete (RC) structures induces concrete cracking and leads to a reduction in both steel cross section and steel-concrete bond strength. In this paper, a new model is proposed based on a scalar damage parameter Dc that depends on the loss of cross-sectional area of steel due to corrosion. The model predictions are plotted against experimental data from the literature based on both accelerated and natural corrosion processes and compared to other existing empirical models. The proposed new model significantly improves the prediction of the bond strength of corroding steel bars and is valid for all diameters ranging between 10 and 20 mm (0.39 and 0.79 in.). Moreover, two additional parameters have been implemented in the model, allowing for the consideration of natural (localized) corrosion and the presence of stirrups. A stirrups confinement coefficient st and a pit penetration depth coefficient a have been successfully calibrated using experimental results from the literature.

Tests on the Steel–Concrete Bond Strength in Steel Reinforced Concrete (SRC) Columns After Fire Exposure

Bond behaviour between the steel and concrete is important in ensuring the interaction of different components in steel reinforced concrete (SRC) columns under various working conditions, and sufficient bond strength should be kept in these columns even after fire exposure. This paper presents the experimental results of bond strength between the embedded steel and concrete in SRC columns after fire exposure. A total of eight push-out specimens were prepared, including two unheated and six fire exposed specimens. The fire exposed specimens were heated and left cooling down in a fire furnace, and then were tested for residual bond strength. Concrete explosive spalling was found when the test specimens were heated. The elevated temperatures at the steel–concrete interface and at the location of stirrups were recorded by thermocouples. Effects of different parameters, such as fire scenario, lateral confinement, and encased steel type, on the bond behaviour were analysed. Time delay was found in the temperature increase across the concrete section, and the inner maximum temperature reached at a measurement location was 430°C during the cooling phase, which was much higher than the temperature of 180°C measured at the end of heating phase for the same location. The reduction in bond strength was as high as 54.2%, whereas the corresponding ultimate slip increased significantly from around 0.3 mm to over 4 mm due to fire exposure. An existing model was revised to predict bond stress-slip curves for SRC columns after fire exposure, and a reasonably good agreement was obtained between the measured and predicted results.

Prediction of the steel-concrete bond strength from the compressive strength of Portland cement and geopolymer concretes

The oldest and simplest bond test, which is the standard concentric pull out test, is usually used as a comparative test for different concretes in order to assess the bond with deformed bars. In this paper, two types of concrete are considered: Ordinary Portland cement (OPC) concrete and a novel concrete technology, namely geopolymer concrete (GPC). Bond strength was investigated by conducting pull-out tests on ribbed bars with a nominal diameter of 10mm and/or 12mm. The specimens were tested at various ages ranging from 1 to 28days. Compression tests were performed at all ages as well. The main objective of the extensive research program involving 260 pull-out tests was to develop empirical models correlating the steel-concrete bond strength to the mean compressive strength of concrete for both OPC and geopolymer concretes. The models developed are compared to the existing model adopted by FIP Committee.

Influence of waste rubber utilization on the fracture and steel–concrete bond strength properties of concrete

Mechanical and fracture properties of concretes in which the natural aggregate was replaced with two types, crumb rubber and/or tire chips, of waste scrap tire rubber were experimentally investigated. The concrete mixtures were produced at a constant water-to-cement ratio of 0.40 and with a cement content of 450kg/m3. A total of 19 concrete mixtures were designed by replacing the fine and coarse aggregates with crumb rubber and tire chips, respectively, at designated replacement levels of 0%, 5%, 10%, 15%, 20%, 25% and 30% by total aggregate volume. The concrete samples were tested for compressive and splitting tensile strengths, modulus of elasticity, fracture energy, characteristic length, and steel–concrete bond strength. Test results indicated that utilization of rubber significantly affected the mechanical and fracture properties of concretes. Compressive strength and modulus of elasticity of the concretes decreased while the ductility increased as the rubber had been used. Besides, the effect of rubber appeared to be more pronounced at higher rubber content and bigger size.

Recent advances in the development and application of chemically reactive enamel coating for steel bars

A new type of chemically reactive enamel (CRE) coating has recently been developed to improve the corrosion resistance of steel bars and the bond strength between the steel bars and concrete. The corrosion process of steel bars with damaged CRE coating is confined locally around the damage locations, which completely differs from the widespread corrosion process of fusion-bonded epoxy (FBE) coated steel bars. The increase in steel-concrete bond strength with CRE-coated bars can improve the system performance and integrity of reinforced concrete (RC) structures, which also differs from the reduced bond strength with FBE-coated bars. Overall, CRE coating can potentially improve the durability, serviceability, and safety of RC structures under environmental, operational, and extreme loading. Furthermore, CRE coating is simple in manufacture and comparable in cost to widely-used FBE coating. Therefore, CRE coating is a viable alternative to FBE coating for extensive applications in civil engineering. This paper introduces the characteristics of CRE coating, reviews its state-of-the-art development, and prospects its potential applications in China.

Development Length in Reinforced Concrete Structures Exposed to Steel Corrosion: A Correction Factor for AS3600 Provisions

In reinforced concrete structures, reinforcement corrosion induces concrete cracking and leads to a reduction in both the steel cross-section and the steel-concrete bond strength and ultimately affects the development length. In this paper, a new correction factor is proposed to calculate the development length of reinforced concrete structures prone to corrosion. A scalar bond damage parameter is introduced to relate bond strength reduction to corrosion. The new model agrees well with all experimental results found in the literature. The bond damage parameter is further used as a correction factor modifying the AS3600 provisions for the development length of reinforcement in reinforced concrete structures located in a saline environment. The relationship between steel-concrete bond damage and corrosion induced concrete cracking is also discussed.

Degradation of flexural strength in reinforced concrete members caused by steel corrosion

The volume expansion of reinforcements due to corrosion produces tensile stresses on the surrounding concrete, leading to radial cracks in the concrete cover and to significant reduction in the serviceability performance and durability of reinforced concrete members. In this study, a flexural strength assessment model of reinforced concrete (RC) members with corroded bars has been developed, which is an extension of the steel–concrete bond strength models based on the thick-walled cylinder theory. This model simulates the degradation of flexural strength in RC members according to the corrosion rate and flexural cracks, and is in good agreement with available experimental data.

Confinement effects on the steel–concrete bond strength and pull-out failure

In this contribution, an experimental campaign based on unconfined and actively confined pull-out tests is presented to investigate the bond stress–slip behavior. This campaign aims at underlining passive (concrete cover) and active (external pressure) confinement effects on the maximal bond stress. Experimental results are associated to a numerical approach in order to predict the evolution of the bond strength. Equations are finally proposed that distinguish splitting failure (function of the concrete tensile properties) and pull-out failure (function of the compressive concrete properties).

Effect of cathodic protection on steel–concrete bond strength using ion migration measurements

Impressed current cathodic protection (ICCP) is a widely used method to protect steel reinforcements against corrosion. Bond degradation between concrete and steel at protection and overprotection levels was studied. Two types of materials were tested: an ordinary Portland cement (OPC) and a mixture of 85% OPC and 15% fly ash (OPC/FA). Concrete specimens were immersed in a 3.5% sodium chloride (NaCl) solution. Chemical analysis of sodium, potassium and hydrogen ions was performed using atomic absorption spectrophotometry (AAS). Hydrogen ion content was monitored using electrochemical impedance spectroscopy (EIS). Mechanical behaviour was analysed by means of pullout tests , and microstructure characterisation was carried out using scanning electron microscopy (SEM). Sodium, potassium and hydrogen ions were found at the concrete–steel interface. The mechanical properties of the specimens were poorer at overprotection level than at protection level.

Effectiveness of Calcium Nitrite in Retarding Corrosion of Steel in Concrete

Corrosion of steel bars embedded in concrete admixed with 0%, 2% and 4% calcium nitrite (CN), having compressive strengths of 20 and 46 MPa was investigated. Reinforced concrete specimens were immersed in 3% NaCl solutions for 1, 7 and 15 days where 0.4A external current was applied to accelerate the chemical reactions. Corrosion rate was measured by retrieving electrochemical data via potentiodynamic polarization technique. Pull-out tests of reinforced concrete specimens were then conducted to assess the corroded steel-concrete bond characteristics. Experimental results showed that corrosion rate of steel bars and steel-concrete bond strength were dependent on concrete strength, amount of CN added and accelerated corrosion period. As concrete strength increased from 20 to 46 MPa, corrosion rate of embedded steel decreased. The addition of 2% CN to concrete of 20 MPa was not effective in retarding corrosion of steel at long time of exposure. However, the combination of higher strength concrete and 2% or 4% CN appear to be a desirable approach to reduce the effect of chloride-induced corrosion of steel reinforcement. After 1 day of corrosion acceleration, specimens without CN showed higher bond strength in both concrete mixes than those with CN. After 7 and 15 days of exposure, the higher concentration of CN, the higher bond strength in both concrete mixes achieved, except for the concrete specimen of 20 MPa compressive strength with 2% CN that recorded the highest deterioration in bond strength at 15 days of exposure.

Robustness of corroded reinforced concrete structures – a structural performance approach

The aim of this work is to provide new contributions in order to define more accurately the structural robustness concept, particularly when applied to corroded reinforced concrete (RC) structures. To fulfil such a task, several robustness indicators are analysed and discussed with special emphasis on structural-performance-based measures. A new robustness definition and a framework are then proposed for its analysis, based on the structural performance lost after damage occurrence. The competence of the proposed methodology is then tested comparing the robustness of two RC foot bridges under corrosion. The damage considered is the longitudinal reinforcement corrosion level, and load carrying capacity is the structural performance evaluated. In order to analyse corrosion effects, a finite element (FE) based on a two-step analysis is adopted. In the first step, a cross-section analysis is performed to capture phenomenons such as expansion of the reinforcement due to the corrosion products accumulation; damage and cracking in the reinforcement surrounding concrete; steel–concrete bond strength degradation; effective reinforcement area reduction. The results obtained are then used to build a 2D structural model, in order to assess the maximum load carrying capacity of the corroded structure. For each foot bridge, robustness is assessed using the proposed methodology.

Prediction of bond strength of lightweight concretes by using artificial neural networks

In the scope of this study, concrete samples planned to be used as load-bearing concrete were produced by using pumice aggregate and silica fume. Cement was replaced by silica fume, as the mineral additive, by 5 and 10% of its weight. First of all, fresh concrete properties of the produced samples were evaluated. Then, compressive strength tests were conducted on the 28th and 90th days. In addition, pull-out tests were carried out on cubic samples of 150 mm3 on the 90th day so as to detect the reinforcing steel-concrete bond strength. The data obtained at the end of the tests were used as input to the Artificial Neural Networks (ANN) method to predict bond strength values. Bond strength values predicted via the ANN method were found to be close to the bond strength values obtained via tests. In conclusion, it can be quite beneficial to predict the bond strength of normal and lightweight concrete via the ANN method by using a high number of parameters as input. Thus, it will be possible to detect the reinforcing steel-concrete bond strength in a faster and reliable manner and by doing less laboratory work. Key words: Artificial neural networks, structural lightweight concrete, pumice, bond strength.

Steel–concrete bond strength of lightweight self-consolidating concrete

The bond behavior of lightweight self-consolidating concrete (LWSCC) must be understood in order to use this type of high performance concrete in structural members. The objective of this research program is to assess the bond behavior of reinforcing steel bars embedded in LWSCC members. Three different classes of LWSCC mixtures were developed with two different types of lightweight aggregates. In addition, one normal weight SCC (NWSCC) was developed and used as a control mixture. A total of twenty four pullout tests were conducted on deformed reinforcing bars with an embedded length of either 100 or 200 mm and the load-slip responses, failure modes and bond strengths of LWSCC and NWSCC were compared. Based on the results of this study, the bond strength of deformed bars for LWSCCs are found to be less (between 16 and 38%) as compared with NWSCC. Under the conditions of equivalent workability properties and compressive strength, bond slip properties were shown to be significantly influenced by the type of lightweight aggregate used. In this study, the use of expanded shale in the production of LWSCC significantly enhanced the pullout strength when compared with lightweight slag aggregate.

The effect of a new generation surface-applied organic inhibitor on concrete properties

Abstract The influence of a new organic surface-applied corrosion inhibitor (SACI) on selected concrete properties is studied including compressive strength, tensile strength, steel–concrete bond strength, permeability, drying shrinkage, and freeze–thaw resistance. The inhibitor is an aminoalcohol-based (AMA) corrosion inhibitor and it is applied on the hardened concrete surface. The results show that the inhibitor can be used safely and it does not have any significant harmful effect on the properties of hardened concrete and it improves some properties of concrete with its pore-blocking effect.