Corrosion-induced Crack Width Research Articles

Bond-slip behavior between corroded rebar and lightweight aggregate concrete

The bond-slip property between the corroded steel bar and lightweight aggregate concrete (LWAC) was investigated. The effects of concrete cover, stirrups spacing, and steel bar corrosion level were experimentally studied using beam-type specimens. The results suggested that the bond strength of LWAC specimen was improved by the increase in concrete cover and the decrease in the spacing of stirrups, and the negative effect of the corrosion on bond strength was mitigated by the increasing thickness of cover and the spacing of the decreasing stirrups. The bond strength between LWAC and steel bar was negatively correlated to the corrosion level and the corrosion-induced cracking. The models for the bond degradation coefficient of LWAC specimens were established based on different forms of function, and the prediction of the exponential model showed better agreement with the test results. The model linking bond strength degradation in LWAC elements and corrosion-induced crack width was developed by considering factors including concrete covers and equivalent width of cracks.

Evaluation of corrosion damage in reinforced concrete structures in terms of the rebar’s residual cross-section

Corroding reinforced concrete structures are frequently assessed to determine the rate of corrosion propagation and the level of deterioration, which might compromise the structure’s reliability. Appropriate measures should be considered in deciding when and how to implement maintenance if safety must be ensured. However, the influential factor that governs or informs such decisions is corrosion damage quantification. Nonetheless, the current non-destructive methods of corrosion damage quantification often lead to ambiguity, and most do not evaluate corrosion damage in terms of the rebar’s cross-section loss, which is the primary effect of corrosion. To address these shortcomings, this paper proposes an effective, reliable, and less-complicated model for quantifying corrosion damage in reinforced concrete structures based on the cross-sectional area of the corroding bar. The study was conducted through experimental (laboratory-based) and numerical investigations of the relationship between the level of corrosion and the corrosion-induced crack width. Based on the investigations’ findings, appropriate relationships and essential parameters were identified, and the model was derived analytically. The derived model assesses corrosion damage in terms of the corroding bar’s residual cross-section and requires only a few input parameters, which can be obtained by non-destructive testing if not known. The model was tested against data obtained from the laboratory experiment and against other experimental and analytical data from the literature, and the results showed a good correlation.

Study on corrosion-induced cracks for the concrete with transverse cracks using an improved CDM-XFEM

Aimed to study the characteristics of corrosion-induced cracks in concrete contained transverse cracks, an improved CDM-XFEM is proposed to calculate the process of corrosion-induced cracks. It mainly includes reconstructing the fracture energy conversion equation and establishing the water transport model in transverse cracks. The numerical results are verified by the experimental results. Then the influence of transverse crack form on corrosion-induced crack width and angle are investigated. The results show that when increase the depth of transverse cracks, the total crack widths of corrosion-induced cracks will increase in an S shape curve, the angle of corrosion-induced cracks will increase linearly in the early stage and remain unchanged in the later stage. While increase the width of transverse cracks will decrease the angle of corrosion-induced cracks.

Numerical simulation and mechanism analysis of GPR-based reinforcement corrosion detection

Ground penetrating radar (GPR) has been used to detect reinforcement corrosion in some studies, but some of the conclusions obtained were that corrosion enhanced the reflected signal, and some conclusions were completely opposite, which restricted the further research of this method. In this study, the experimental setups and their corresponding signal variations of previous research were reviewed, and the effects of corrosion-induced changes on a GPR signal were analyzed through numerical modeling. The results indicated that the reduction of the rebar diameter and the widening of the corrosion-induced crack width resulted in a decrease of the reflected wave amplitude, while the filling of the corrosion product in the corrosion-induced crack increased the amplitude of the reflected wave, which were in reasonable agreement with the experimental observations in previous research.

Meso-scale modeling of concrete cracking induced by 3D corrosion expansion of helical strands

A meso-scale numerical model is established to simulate concrete cracking induced by the three-dimensional (3D) corrosion expansion of helical strands in the present study. A 3D corrosion expansion model is proposed to consider the longitudinal helix shape and transverse flower-like shape of the strand. The concrete in the model is considered as a three-phase composite material consisting of a mortar matrix, aggregate, and interfacial transition zones (ITZ) between the mortar matrix and aggregate. The rationality of the proposed model is validated, and the effects of the space helix structure and the lay length of the strand on corrosion-induced cracking are discussed. The results indicate that considering the space helix structure of a strand can effectively improve the prediction accuracy of strand corrosion-induced concrete cracking. The change in strand lay length has little effect on the critical corrosion loss of the initial damage occurrence. The critical corrosion loss at cover cracking increases with increasing strand lay length, whereas the corrosion-induced crack width decreases with increasing strand lay length.

Probabilistic estimation of flexural loading capacity of existing RC structures based on observational corrosion-induced crack width distribution using machine learning

Corrosion-induced crack width can provide effective information on the deterioration level of in situ corroded reinforced concrete (RC) structures. However, the uncertainty associated with the relationship between corrosion-induced crack width and steel corrosion in RC structures is quite large. In this study, a probabilistic framework for estimating the structural capacity of corroded RC structures using the observational corrosion-induced crack width distribution and machine learning is proposed. Based on the experimental results of corroded RC beams, random field theory, and finite element (FE) analysis, artificial samples composed of corrosion-induced crack width and steel weight loss distributions over the RC beams are generated. Two machine learning-based models are then developed using these samples to estimate the steel weight loss distribution from the observational corrosion-induced crack distribution. Finally, a Monte Carlo-based FE analysis with the estimated steel weight loss distribution as the input data is conducted to obtain the probability density function (PDF) of the structural capacity of corroded RC beams. For illustrative purposes, the effect of observational corrosion-induced crack width distribution on the PDF of flexural capacity of an existing RC beam is investigated using the proposed framework. The results show that the proposed framework using a machine learning-based model is a reliable and computationally efficient approach for estimating the structural capacity of corroded RC members and demonstrates the potential for assessing the deterioration condition of existing RC structures based on the corrosion-induced crack width distribution.

Analytical and Experimental Investigation on Corrosion-Induced Concrete Cracking

Practical experience and observation suggest that corrosion-affected reinforced concrete structures are highly susceptible to cracking. This paper presents an analytical time to corrosion-induced concrete cracking model based on fracture mechanics. The concrete cover load-bearing capacity is proposed and is used as a fracture criterion for concrete cracking. An accelerated corrosion test has been undertaken to produce data on time to corrosion-induced concrete cracking and crack width over time. A comparison between the analytical model and experimental results on time to concrete cracking and on crack width over time shows reasonable agreement. It is found that the distribution and size of the porous zone are non-uniform which is one of the main causes for discrepancy between results. The larger the porous zone is the longer it takes for concrete cover to crack due to corrosion. Although the experimental and model results exhibit similar trend, it is also found that assuming only a single propagating crack in analytical model results in an overestimation of corrosion-induced crack width. The models presented in this paper can serve as useful tool for serviceability and durability assessment of corrosion-affected reinforced concrete structures.

Concrete cracking prediction under combined prestress and strand corrosion

This study investigates strand corrosion-induced concrete cracking under various prestress experimentally and analytically. Experimental data on the critical time of cover cracking, crack width and corrosion loss obtained from the accelerated corrosion test are presented and discussed. The expansion ratio of strand corrosion products is estimated based on the infrared spectroscopy and thermal gravimetry. An analytical model, incorporating the coupled effects of prestress and strand corrosion, is proposed to predict the global process of concrete cracking from initiation to propagation. Strand rust-expansion ratio and the residual stiffness of cracked concrete are also included in the model. Results show that prestress can accelerate the corrosion-induced cracking process. By varying prestress from 0 to 75% strand tensile strength, the critical time of cover cracking decreases 22% and the crack propagation rate increases 9%. It is found that the proposed model is accurate in predicting corrosion-induced crack width in prestressed concrete beams.

Study on Corrosion-induced Crack Initiation and Propagation of Sustaining Loaded RCbeams

For 13 pieces of reinforced concrete beams with HRB500 steel bars under long-term sustained loads, at time of corrosion-induced initial crack of concrete, and corrosion-induced crack widths of 0.3mm and 1mm, corrosion of steel bars and time-varying behavior of corrosion-induced crack width were studied by the ECWD (Electro-osmosis - constant Current – Wet and Dry cycles) accelerated corrosion method. The results show that when cover thickness was between 30 and 50mm,corrosion rates of steel bars were between 0.8% and 1.7% at time of corrosion-induced crack, and decreased with increasing concrete cover thickness; when corrosion-induced crack width was 0.3mm, the corrosion rate decreased with increasing steel bar diameter, and increased with increasing cover thickness; its corrosion rate varied between 0.98% and 4.54%; when corrosion-induced crack width reached 1mm, corrosion rate of steel bars was between 4% and 4.5%; when corrosion rate of steel bars was within 5%, the maximum and average corrosion-induced crack and corrosion rate of steel bars had a good linear relationship. The calculation model predicting the maximum and average width of corrosion-induced crack is given in this paper.

Performance of reinforced concrete beams corroded under sustained service loads: A comparative study of two accelerated corrosion techniques

In this work, the performance of reinforced concrete (RC) beams corroded under various levels of sustained flexural loads was evaluated. A comparison was made regarding the effect of different accelerated corrosion techniques, i.e., galvanic method and artificial climate exposure method, on the corrosion characteristics and structural performance of loaded RC beams. The results show that, regardless of sustained loading, a unique strong linear relationship can be established between the average mass loss of corroded rebar and the maximum corrosion-induced crack width, for both accelerated corrosion techniques. The application of flexural loads during corrosion exacerbates the corrosion in the pure flexural zone and enlarges the spatial variation of corrosion levels in RC beams. However, neither the average mass loss ratio of corroded rebar nor the crack widths can be a reliable way to estimate the residual capacity of the beams.

Experimental investigation of corrosion effect on bond behavior between reinforcing bar and concrete

An experimental study is conducted in this paper to investigate the effect of corrosion and corrosion-induced cracks on the bond behavior between steel bars and concrete. An accelerated corrosion test was used to corrode the steel bars embedded in concrete specimens under laboratory condition. Two series of pull-out tests were designed. Pull-out tests on the specimens with plain and deformed reinforcing bars are performed. The bond behavior of the two types of steel bar specimens including the ultimate bond strength, bond-slip relationships for different corrosion levels are discussed. An empirical bond degradation model is proposed combining a wide range of experimental data available in the literatures. The other pull-out tests on the bonding specimens with interior strain gauges are conducted and the bond stress at various positions are derived based on the observed reinforcement strains. The experimental results show that the corrosion influence on bond strength can be ignored when the corrosion loss is less than 2.4%. The bond behavior between smooth bar and concrete is more sensitive to the corrosion than that of specimen with deformed bar. The selection of steel bars is also an alternative way to improve the bond behavior especially for the deformed bar specimens. The distribution of bond stress is more uniform for the specimen with a large corrosion-induced crack width.

Degradation and mechanism of the mechanics and durability of reinforced concrete slab in a marine environment

An experimental research was conducted to determine the corrosion and bearing capacity of a reinforced concrete (RC) slab at different ages in a marine environment. Results show that the development of corrosion-induced cracks on a slab in a marine environment can be divided into three stages according to crack morphology at the bottom of the slab. In the first stage, cracks appear. In the second stage, cracks develop from the edges to the middle of the slab. In the third stage, longitudinal and transverse corrosion-induced cracks coexist. The corrosion ratio of reinforcements nonlinearly increases with the age, and the relationship between the corrosion ratio of the reinforcements and the corrosion-induced crack width of the concrete is established. The flexural capacity of the corroded RC slab nonlinearly decreases with the age, and the model for the bearing capacity factor of the corroded RC slab is established. The mid-span deflection of the corroded RC slab that corresponds to the yield of the reinforcements linearly increases with the increase in corrosion ratio. Finally, the mechanisms of corrosion morphology and the degradation of the mechanical properties of an RC slab in a marine environment are discussed on the basis of the basic theories of steel corrosion in concrete and concrete structure design.

Reliability assessment of concrete bridges subject to corrosion-induced cracks during life cycle using artificial neural networks

Corrosion of RC bridge decks eventually leads to delamination, severe cracking and spalling of the concrete cover. This is a prevalent deterioration mechanism and demands for the most costly repair interventions during the service life of bridges worldwide. On the other hand, decisions for repairs are usually made whenever the extent of a limit crack width, reported in routine visual inspections, exceeds an acceptable threshold level. In this paper, while random fields are applied to account for spatial variation of governing parameters of the corrosion process, an analytical model is used to simulate the corrosion induced crack width. However when dealing with random fields, the Monte Carlo simulation is apparently an inefficient and time consuming method, hence the utility of neural networks as a surrogate in simulation is investigated and found very promising. The proposed method can be regarded as an invaluable tool in decision making concerning maintenance of bridges.

Effect of chloride-induced reinforcing steel corrosion on the flexural strength of reinforced concrete beams

An experimental investigation into the influence of reinforcing steel corrosion on the flexural capacity of conventionally reinforced concrete beams was conducted. Two types of specimens were constructed and the embedded flexural reinforcing bars were subjected to accelerated corrosion. Nine different corrosion damage levels were produced. An electro-migration method was used to accelerate the migration of chloride into the concrete, and a wet–dry cycle with small current was applied to speed up the corrosion of reinforcing steel bars. Corrosion-induced crack width and its relationship with the corrosion level were analysed. Based on the experimental data obtained from tests, a practicable approach is proposed to predict the residual flexural strength of corroded beams.

Analytical Model for Corrosion-Induced Crack Width in Reinforced Concrete Structures

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