Corrosion Of Reinforcing Bars Research Articles

Bond Strength and Development Length Model for Corroded Reinforcing Bars

Bond Strength and Development Length Model for Corroded Reinforcing Bars

Enhancing Structural Resilience: Microbial-Based Self-Healing in High-Strength Concrete

Concrete’s weak tensile strength renders it susceptible to cracking under prolonged loads, leading to reduced load-bearing capacity and reinforcing bar corrosion. This study investigates the effectiveness of microbial-based self-healing in high-strength concrete, focusing on two bacterial strains: Sporosarcina koreensis and Bacillus. Results demonstrate significant enhancements in micro- and macro-physical properties of high-strength bacterial concrete with Bacillus flexus and S. koreensis, surpassing the control. Bacillus flexus-infused concrete exhibits a remarkable 21.8% increase in compressive strength at 7 days and 11.7% at 56 days. Similarly, S. koreensis-treated concrete shows 12.2% and 7.4% increases at 7 and 56 days, respectively. Enhanced crack healing occurs due to calcite precipitation, confirmed by X-ray diffraction and scanning electron microscopy. Both bacterial strains achieve crack closure within 42 days, with widths of 259.7 µm and 288.7 µm, respectively. Moreover, bacterial concrete from these strains excels in durability against water, acid, and salt exposure, surpassing control concrete. These findings emphasize microbial-based self-healing’s potential in high-strength concrete, providing a practical strategy to enhance structural resilience and extend concrete infrastructure lifespan.

Synergistic protection of borate and silicate salts composite for controlling the chloride-induced pitting and uniform corrosion of steel reinforcement bars embedded in mortars

In this study, the efficacy of the combined effect of borate and silicate alkali metal salts added to mortars for controlling the chloride-induced uniform and localized corrosion of embedded steel rebars is examined. The individually added salts in mortars are found to have insignificant effects in terms of reducing the uniform corrosion rate and localized damage. However, their combination (0.50% sodium tetra borate + 0.10% sodium silicate added with respect to the weight of the binder) provides complete protection to reinforcements tested for long durations under wet/dry treatments with mortars in saline water and laboratory atmospheres. Electrochemical impedance spectroscopy, direct current cyclic polarization, polarization resistance, and visual observations are used for quantitative and qualitative evaluations of the protective effects of the tested additives. X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy analysis of the corrosion products formed on the embedded steel surfaces help explain the possible mechanisms behind the considerable improvement in the inhibitive effects of a mixed composition of borate and silicate. This combination also improves the compressive strength and workability of the mixed concrete. The results reveal that the synergistic protection provided by a mixture of borate and silicate can be attributed to the co-deposition of an iron-boron + ferrosilicate + cortensitite (an iron-silicon phase) film on the rebar surface.

Experimental and Analytical Investigation of Moment-Carrying Capacities of Reinforced Concrete Frame Systems Corroded by Accelerated Corrosion Method

Technical investigations carried out after the devastating earthquakes in Turkey in the last 25 years show that one of the main causes of damage to reinforced concrete structures is reinforcement bar corrosion. The deterioration caused by reinforcement corrosion in reinforced concrete elements reduces the parameters that define the performance level of the structure, such as ductility, stiffness, bond-slip relationship, load carrying capacity, and energy absorption capacity. Therefore, determining the specified performance levels of reinforced concrete structures exposed to corrosion before any seismic activity occurs is of great importance in preventing loss of life and property. Cross-section behavior in reinforced concrete structures represents the load-bearing element behavior In order to accurately determine the section behavior, the Moment-Curvature relationship must be defined. In this study, the structural behavior of reinforced concrete frames exposed to corrosion was examined experimentally and analytically. For this purpose, 4 of the 5 reinforced concrete frame specimens constructed were corroded at different ratios using the accelerated corrosion method. After the corrosion process was completed, in the experimental part of the study, all specimens were tested under the effect of a 20% constant axial load and reversal-cyclic loading. In the analytical study, as a result of the cross-sectional analyzes carried out by taking into account the material-mechanical properties changing with the effect of corrosion, it was determined that the calculated moment values were in high predicted with the experimentally measured moment values.

Explainable machine learning-aided efficient prediction model and software tool for bond strength of concrete with corroded reinforcement

The bond strength between concrete and reinforcement is crucial for the composite action and serviceability of reinforced concrete (RC) structures. However, it is vulnerable to deterioration from the corrosion of reinforcement bars, especially in marine structures. Thus, a precise and reliable model for the bond strength in corrosive environments is necessary to evaluate the serviceability and structural performance of corroded RC members. This study employs explainable machine learning (ML) techniques to assess the bond strength between concrete and corroded bars. Eight ML models are developed to establish the best predictive model for bond behavior, considering seven input parameters: corrosion level (CL), steel yield strength, compressive strength of concrete, concrete cover-to-bar diameter ratio, bar diameter-to-bonded length ratio, reinforcement type, and test type. The super learner (SL) model, integrating three ML models, outperforms other models and analytical methods with a large R2 value (98% on the test set) and minimal statistical errors. The SHapley Additive exPlanation (SHAP) technique identifies CL as the most influential parameter on bond strength, while the reinforcement and test types have the least effect. Finally, a user-friendly graphical user interface (GUI) tool is established to facilitate the practical implementation of the developed model and support accurate bond strength prediction in concrete with steel reinforcement under corrosive environments.

Bond Deterioration between Corroded Reinforcing Bars with Variable Diameters and Concrete at Elevated Temperatures

Bond Deterioration between Corroded Reinforcing Bars with Variable Diameters and Concrete at Elevated Temperatures

Analysis of Durability of Watertight Concretes Modified with the Addition of Fly Ash.

The growing demand for watertight concrete structures is conducive to the development of research in this area, but their results are rarely published. In order to partially fill this gap, the authors of the publication present the results of research into the effect of fly ash addition on the watertightness of concrete. Prior to the tests, a recipe for a concrete mix with the addition of a sealing admixture modified with fly ash was developed. The following properties were analyzed: consistency of the concrete mix, air content in the concrete mix, compressive strength of concrete, depth of penetration of water under pressure, and frost resistance of concrete for F150 level. The work meets the expectations of the construction industry with respect to the production of concrete structures resistant not only to the penetration of water into concrete but also resistant to aggressive substances dissolved in water that accelerate the destruction of concrete and corrosion of reinforcement bars. Based on the test results, it was found that the addition of fly ash to the concrete mix enhances the positive impact of the applied sealing admixture, increasing the tightness of the concrete. It reduces the depth of penetration of water under pressure and therefore increases the frost resistance of concrete.

Experimental Evaluation of Bond Behavior between Corroded Reinforcing Bars and Concrete under Elevated Temperatures

Experimental Evaluation of Bond Behavior between Corroded Reinforcing Bars and Concrete under Elevated Temperatures

Multiscale finite element analysis of earthquake-induced damage on underground RC culverts: The role of reinforcing bar corrosion

This study conducted finite element (FE) analysis to investigate the effect of corrosion in the sidewall on the damage to underground reinforced concrete (RC) culverts under an earthquake. The rationality of the numerical model was validated through the analysis of quasi-static cyclic loading tests of corroded RC culverts. Based on the validated FE model, a nonlinear dynamic analysis of an underground RC culvert subjected to an earthquake was performed. Further, the global and local responses that were changed not only by the corrosion of the sidewall reinforcement, but also by shear reinforcement in the sidewall and magnitude of the earthquake were discussed comprehensively. The analysis results show that the global deformation of the underground RC culvert increases with a higher degree of corrosion of the sidewall reinforcement and that severe local shear crack damage can be concentrated on the concrete web when corrosion cracks exist. In addition, extremely serious damage was induced in the RC culvert when corrosion occurred in the sidewall without proper seismic provisions. Therefore, steel corrosion in an aging underground RC culvert with insufficient shear reinforcement should be closely monitored to prevent its collapse in the event of earthquakes.

The robustness of reinforced concrete tied arch bridges: A case study

AbstractThe robustness of a structural systems is understood as their ability to prevent or reduce the consequences of a local (exceptional and/or extreme) event. The current work aims to address the issues related to the evaluation of robustness of structures with incorporated damage. The case study of an existing reinforced concrete arch bridge is investigated in terms of robustness considering the variation of both the cracking state from concrete spalling and the corrosion of reinforcement bars. The damage variation related to these different matters is assessed both in terms of intensity and occurrence in the various structural elements of the bridge. Finally, the structural robustness index is estimated through push‐down analysis to make an overall assessment of the bridge behavior.

Experimental Study on the Mechanical Properties and Cracking Characteristics of Bacterial Concrete

Concrete has been used as a construction material for a long period. When the concrete members are exposed to extreme conditions cracks develop. When a crack opens harmful contaminants may enter the concrete matrix. Water may enter through this crack and result in the corrosion of reinforcement bars. Corrosion of the reinforcement bar also results in the formation of cracks. Compressive strength, flexural strength, split tensile strength and permeability are adversely affected by the formation of cracks. Once damaged these structures need to be repaired. Self-healing concrete is an environmentally friendly and cost-effective method for repairing small cracks. An efficient microbial agent for preparing self-healing concrete is the bacillus species. The sample preparation is done by using Bacillus subtilis. The concentration of bacillus opted for the sample preparation is cells per millilitre. The mechanical properties of bacterial concrete are experimentally evaluated and compared with that of conventional concrete. The tension in concrete is usually overlooked while evaluating the strength of reinforced concrete sections because it makes such a small contribution to member strength. Yet it makes a significant contribution to members’ performance under service loads. In this work, tension stiffening of bacterial concrete is experimentally evaluated on concrete prismatic members made of M20 grade concrete reinforced with 8mm and 12mm diameter bars. The direct tension specimen has a cross-sectional dimension of 60 X 60mm and a length of 600mm. The total length of the steel-reinforced specimens, including the bars, is 900 mm. The tension-stiffening properties of bacterial concrete are compared with that of conventional concrete.

Shear Strength Prediction of Concrete Beams Reinforced with FRP Bars and Stirrups Using Gene Expression Programming

Existing reinforced concrete (RC) structures in humid regions suffer from deterioration due to the corrosion of ordinary reinforcement bars damaging the whole system. The deterioration of the transverse reinforcement leads to shear failure, which is one of the most dangerous failure modes. Therefore, researchers suggested using fiber-reinforced polymer (FRP) bars as a replacement for reinforcement bars in humid regions to integrate sustainability and improve their serviceability and durability. A simple model that can accurately estimate the shear strength of concrete beams designed with FRP longitudinal bars and stirrups is lacking. This research proposed a simplified Gene expression programming (GEP) based model to estimate the shear strength of FRP concrete beams. Seven parameters that principally dominate the shear behavior of FRP beams were utilized to create the GEP model. The parameters are the beam width, beam depth, concrete compressive strength, FRP tensile longitudinal reinforcement ratio, area of stirrups, spacing between the stirrups, and the ultimate FRP strength of stirrups. A comparison was made between the GEP and ACI-440 models; the R2 values of the total database were 92% and 54% for the GEP and ACI models, respectively. The R2 of the GEP model is considerably higher than that measured for the ACI model, and the errors of the GEP model are low, which affirms that the GEP is superior to the ACI model in estimating the shear strength of FRP beams. The trends of the GEP and ACI-440 models and the empirical results are similar, confirming the GEP model’s consistency. Using the GEP model to estimate the shear strength of concrete beams designed with FRP longitudinal bars and stirrups is recommended.

Critical Bending Strain and Mechanical Properties of Corroded Reinforcing Bars

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マンションの老朽化認定の評価方法に関する検討 その2：判定式および判定基準

For proffer the authorization standard of the act on facilitation reconstruction of deteriorated condominium buildings, studied on evaluation methods and criteria about buildings having the risk of falling cover concrete caused by rebar corrosion. Based on the concept of the binomial test, the number of the deteriorated reinforced concrete elements which highly probable to be the reinforcing bar corrosion higher, is determined by using the data from a survey of the actual buildings. And then, each number of survey points, the criteria for certification was set.

Impact of cracks on distribution of chloride-induced reinforcement corrosion

Surface crack width is regulated in codes to limit corrosion of reinforcement bars in concrete. However, the influence of surface crack width on corrosion damages is not directly inferable from previous research.In this work, data on corroded cracked concrete specimens in chloride environments was compiled. Detailed information was included, such as crack and pit locations, local corrosion pattern, etc. Five hypotheses on the influence of transversal cracks on corrosion damage were formulated, and statistical methods were used to test them on the dataset.Transversal cracks were good indicators of the position of corrosion pits. The corrosion rate of the pit increased in proximity of a crack. With time, pits grew in depth at a slower rate but increased in number. No clear correlation between surface crack width and corrosion damage was found. Results point out discrepancies in the collected data, arguing for the need of well-defined procedures for assessing crack and corrosion damage.Further, the statistical treatment allowed for identification of bias in existing data, which was used as a research planning tool to provide guidance on the design of additional experiments. Thus, recommendations for future experimental work required to reduce the bias are given.

Performance of reinforced concrete flat slab strengthened with CFRP for punching shear

Existing reinforced concrete (RC) slabs need punching shear reinforcement due to design defects, structural damage, increased loading, corroded reinforcement bars, and change in the use or function of the buildings. Strengthening methods such as using carbon fibre reinforced polymer (CFRP) sheets as external reinforcements in the tension area have proven to be useful in increasing the punching shear capacity and ductility of RC members. Therefore, this study aims to investigate the effect of using CFRP strengthening method in two-way RC slabs. Three strengthened RC solid flat slab samples in addition to unstrengthened slab samples were tested and subjected to static load to simulate the punching shear effect at the middle of the slab. Based on the test results, the samples strengthened with CFRP showed better performance in terms of delaying the appearance of the first crack, improving the resistance of shear crack propagation, and enhancing the load-displacement and ductility capacities compared to the control sample. In addition, the failure mode of the strengthened samples with CFRP was improved and the capacity for punching shear was increased. Furthermore, the analytical model to predict the ultimate punching shear strength has good agreement with the requirements of the practical codes, thus it can be used for the design and analysis of CFRP strengthened slab.

The finite element model of chloride diffusion in pre-stressed corroded reinforcement bars of reinforced concrete structures

Introduction. The general corrosion model, made for reinforced concrete structures, must include the initiation of environmental influences such as carbonation, cracking and chloride ion penetration. It depends on the rate and degree of corrosion, corrosive effects in reduced areas, as well as the lower strength of bond between pre-stressed and unstressed reinforcement bars and concrete. The majority of earlier studies were focused on one-dimensional diffusion problems with an assumed constant corrosion rate.
 
 Materials and methods. In the aftermath of general corrosion, localized corrosion is accompanied by a release of hydrogen and alkaline water, chlorine ions. Crack propagation in reinforcement wires is calculated using the transient finite element software for chloride diffusion, which is time-dependent.
 
 Results. In most cases, the diffusion equation does not have a closed form solution, and therefore, the finite difference method can be used. The authors have shown that the corrosion rate decreases with time if current density has different water-cement ratios. If the water-cement ratio increases, the corrosion rate increases, as well.
 
 Conclusions. In a pre-stressed reinforced concrete beam, the corrosion of one bar affects the total corrosion of all bars and the reduction in the cross-sectional area of bars that does not exceed 15 %.

Numerical Investigation of FRCM-Strengthened Corroded RC Beams under Cathodic Protection

Fibric reinforced cementitious matrix (FRCM) composites have been used to improve the mechanical performance of reinforced concrete beams subjected to degradation in the past decades. Recently, dual-functional carbon fibres have been explored to provide both structural strengthening to RC beams and cathodic protection to reinforcement bars. This paper investigates the loading responses and structural behaviour of RC beams subjected to different levels of corrosion, protected by impressed current cathodic protection and structurally strengthened by external bonded FRCM. A numerical model is developed for the corroded RC beams under impressed current cathodic protection and structural strengthening by the FRCM composite. Upon validation against experimental results collected from the literature, the finite element model is then used for parametric study. A number of numerical results are generated to analyse the effects of key parameters, including the corrosion rate, degradation level of interfacial bonding properties due to anode acidification, and end anchorage, followed by detailed discussions. It is found that the significance of the corrosion of steel reinforcement bars significantly affects the load-carrying capacity of the beams. Increasing the corrosion rate from 0 to 40% reduces the load-carrying capacity of un-strengthened beams to 45% of the original capacity. Therefore, the cathodic protection provided by the C-FRCM plate is important to the reinforcement bars as it can avoid the cross-section area reduction of reinforcement bars and, thus, the main loading capacities of the beams. In this study, the degradation of the bonding properties at the interface of carbon fibre and the cementitious matrix due to anode acidification during impressed current cathodic protection is also considered. It is found that the bond strength of the C-FRCM plate has a slight effect on the load-carrying capacity of the beam. In addition, the application of end anchorage can significantly enhance both the load-carrying capacity and ductility of the beams. The rates of enhancement, if compared to the beams with no end anchorage, can reach up to 60%.

Hydration, Compressive Strength and Durability of Eco-friendly Cement Mortars Containing Recycled Brick Powder and Metakaolin

Grinding brick waste into powder for use as a supplementary cementitious material has shown to be a promising recycling method for the reuse of construction and demolition waste. However, the strength and durability of concrete containing recycled brick powder (RBP) will significantly decrease due to the poor pozzolanic activity of RBP, limiting its wider applications. This study attempted to overcome these defects through metakaolin (MK) addition. The hydration, compressive strength, durability, and environmental impact of eco-friendly mortars containing RBP and MK were investigated. The results showed that MK promoted the early-stage hydration of cement, creating a suitable hydration environment for the hydration of RBP at a later age. As a result, the volume fractions of low-density calcium silicate hydrate (C-S-H) and high-density C-S-H increased according to the nanoindentation test results. In addition, the strength, chloride penetration resistance, and reinforcement bar corrosion resistance of the blended mortars obviously improved due to the synergistic effect of RBP and MK. Lastly, we achieved CO2 emissions that were 22.1–30.2% lower and energy consumption that was 21.4–27.0% lower by incorporating 20% RBP and 5–15% MK.

Characteristics of Combined Rice and Wheat Husk Ashes as a Partial Replacement for Cement in Mortar

The potential to recycle and utilize agricultural waste as a building material has been demonstrated in a variety of applications. The goal of this study was to assess the feasibility of partially substituting combined rice and wheat husk ashes (CORWHA) for cement in mortar. The two agricultural waste ashes, rice husk and wheat husk, were evaluated separately before being combined. Both husks were burned separately in an open room to reduce volume before being cremated for 2 hours at a regulated temperature of 600 °C to eliminate carbon and generate reactivity. The chemical and physical properties of the ashes were evaluated after grinding and sieving to determine their cementitious qualities before developing and testing 12 mix proportions of CORWHA and cement for mortar production. The mixing was done at three different percentages of cement replacement: 20, 30, and 40%. According to the findings, the maximum cement replacement yielding 5.98 MPa mortar strength is 30%, with a mixed proportion of 11% wheat husk ash (WHA) and 19% rice husk ash (RHA). It was also found that 95% of RHA is silica and 1.67% is alkaline, while 63% of WHA is silica and 12.16% is alkaline, which is good for preventing porosity and corrosion of reinforcement bars. Doi: 10.28991/CEJ-2022-08-04-04 Full Text: PDF