Reinforcement Corrosion Research Articles

Effect of sea salt on carbonation and CO2 uptake in cement mortar

Previous studies mainly focused on the effects of concrete carbonation on chloride ion penetration due to the resulting reinforcement corrosion. However, it is still being determined what influence sea salt, which is common in coastal areas, has on the carbonation of cement based building materials. Thus, cement mortar samples were immersed in simulated seawater and then submitted to an accelerated carbonation test at a CO2 concentration of 5 % and a relative humidity of 58 %. For the samples that underwent different carbonation cycles, weight changes and carbonation depth were measured, and the associated mechanisms were demonstrated by combined thermogravimetry and differential thermal analysis (TG-DTA), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The results showed that salt crystals do not significantly change the pore size distribution and composition of cement mortar, but effectively influence the carbonation rate. The carbonation rate of the cement mortar sample containing sea salt was 36 mm/year0.5, 36.8 % lower than that of the control sample. Carbonate crystals efficiently occupy the pore volume in the size range of 0.02–0.15 μm and significantly reduce the carbonation rate. The results can provide a research basis for estimating the carbonation rate and measuring the CO2 uptake of cement-based building materials in coastal regions.

Evaluation of Residual Structural Capacity in Corroded Reinforced Concrete Structures

Reinforcement corrosion is a critical issue that affects the durability and service life of reinforced concrete structures. This study focuses on evaluating the effectiveness of natural corrosion inhibitors in mitigating the corrosion attack on reinforced concrete beams in saline environments. The study utilizes extruded exudates/resins obtained from plants and characterizes their potential eco-friendly and non-hazardous properties. The corrosion resistance of uncoated and coated steel reinforcements is examined through exposure to a 5% sodium chloride solution for 360 days. The samples are subjected to flexural beam tests at regular intervals to assess changes in mechanical properties. The results indicate that natural corrosion inhibitors can effectively improve durability and maintain higher residual strength capacities, even under severe exposure conditions. Coated bars show higher residual capacities and yield strengths compared to uncoated bars, attributed to the protective effect of the coatings. The inhibitors also reduce corrosion rates and preserve mechanical properties like yield strength and ductility, enhancing the service life of reinforced concrete structures. The study emphasizes the use of locally available materials to counteract the negative effects of corrosion attack in marine environments.

The Effect of Corrosion on the Mechanical Properties (Diameter, Cross-Sectional Area, Weight) of the Reinforcing Steel

Corrosion of steel reinforcement is a major cause of deterioration in reinforced concrete structures, especially those located in marine environments. This study experimentally investigates the influence of corrosion on bond strength between reinforcing steel and concrete, as well as the effect on steel bar properties. Thirty-six concrete cubes reinforced with 12mm steel bars were prepared and subjected to varying corrosion conditions - non-corroded control, uncoated corroded, and coated with Anogeissus leiocarpus exudate. Specimens were immersed in 5% NaCl solution to accelerate corrosion, and tested at intervals up to 360 days. Pull-out tests showed bond strengths of corroded bars reduced by 25-30% compared to non-corroded controls. In severe cases, complete bond failure occurred in corroded specimens. Corrosion also led to reductions in bar diameter (0.04-0.05mm), cross-sectional area (0.5-1.3%), and weight (0.006-0.009kg) over time. Natural exudate coatings on steel mitigated these effects, restoring bond strength and limiting reductions to 0.01-0.02mm in diameter, and 0.003-0.005kg in weight. Graphical analysis correlated well with test data, clearly portraying deterioration trends under corrosion exposure. This study concludes corrosion causes significant weakening of bond integrity and property losses in reinforcement. Natural exudate coatings were found to effectively inhibit corrosion activity by restoring bond strength and protecting steel bars. With proper application, such eco-friendly coatings show promise as sustainable corrosion prevention alternatives for reinforced concrete infrastructure, especially in marine environments where corrosion accelerates more rapidly.

Mitigation of Steel Corrosion Threshold Utilizing Plant-Based Green Corrosion Inhibitors through Electrochemical Techniques

Corrosion of steel reinforcement is a major cause of deterioration in reinforced concrete structures. The corrosion process is influenced by the concrete-steel interface, with the alkaline concrete pore solution initially providing passivation. However, ingress of aggressive substances like chlorides can disrupt the passive layer, initiating active pitting corrosion above a threshold level often taken as 0.4% chloride by cement weight. Once the chloride threshold is exceeded, corrosion propagation depends on oxygen and moisture availability. The resulting rust formation causes expansive cracking and spalling of the concrete cover. Corrosion damage can be mitigated through use of inhibitors like calcium nitrite though high dosages impair concrete strength. Recently, plant-based organic compounds have shown promise as green corrosion inhibitors. The corrosion behavior of steel in concrete can be evaluated through impressed accelerated corrosion testing along with electrochemical techniques like half-cell potential mapping and resistivity measurements. These allow assessment of the probability of corrosion and corrosion rate. Techniques like linear polarization resistance and electrochemical impedance spectroscopy can also quantify instantaneous corrosion rate. Proper structural condition assessment and repair using both conventional and green inhibitors is crucial to control steel corrosion, maintain service life and ensure safety. Further research is needed on green corrosion mitigation methods and advanced non-destructive testing techniques.

Effect of Corrosion Inhibitors on Bond Strength of Reinforced Concrete Structures

Corrosion of steel reinforcement is a major factor affecting the durability and strength of reinforced concrete structures. This study investigated the influence of plant-derived corrosion inhibitors, applied as coatings, on the bond strength between reinforcing steel and concrete. Thirty-six 150 mm concrete cubes with 12 mm diameter embedded steel bars were prepared and divided into uncoated, corrosion inhibitor coated, and control groups. The samples were immersed in 5% sodium chloride solution over 360 days to accelerate corrosion. Pull-out testing measured the bond strength and failure load. The corroded samples showed 31-26% lower bond strength and 82-87% higher maximum slip than controls, indicating corrosion damage at the steel-concrete interface. However, inhibitor-coated samples displayed 24-36% higher bond strength and 42-43% lower maximum slip versus corroded samples. Although the coatings did not fully restore original bond strength, this demonstrates their effectiveness at protecting bond properties. Microscopic analysis revealed non-uniform, localized corrosion preferentially initiated at steel defects. Statistical correlations confirmed the direct relationship between steel weight loss and reductions in post-corrosion rebar weight due to material loss. While nominal rebar diameters showed minimal differences between sample types, localized diameter reductions and cross-sectional area increases in corroded samples highlighted discrete corrosion effects. These were mitigated in coated samples. Together with direct weight loss measurements, this proves corrosion occurred in unprotected samples. Overall, the significant recovery of bond strength, slip resistance, diameter, area, and weight in coated samples validates the success of the natural corrosion inhibitors in reducing steel deterioration and interface degradation. The results provide new insights on optimizing inhibitor coatings to maximize corrosion protection for reinforced concrete structures.

Self-healing concrete with a bacteria-based or crystalline admixture as healing agent to prevent chloride ingress and corrosion in a marine environment

Innovative solutions are needed to improve the durability of concrete structures in marine environment. Bacteria-based agents (BAS) and crystalline admixtures (CA) are explored as healing agents to enhance chloride resistance and prevent corrosion. Healing of 100 μm and 300 μm wide cracks was investigated, in combination with two conditioning methods. Either the samples were subjected to wet/dry cycles for 3 months before exposure (“healed”), or they were directly exposed to artificial seawater after crack creation (“unhealed”). After 12 months of submersion, BAS reduced chloride ingress even in the presence of cracks but showed limitations in preventing corrosion in cracked samples. In contrast, the CA series demonstrated a reduction in chloride ingress in both uncracked and cracked concrete and effectively prevented reinforcement corrosion in healed samples and samples with cracks of 100 μm. This highlights the potential of customized self-healing solutions to improve concrete durability in marine environments.

Seismic response assessment of ductile reinforced concrete columns affected by corrosion and axial load variations

The present study investigates the effect of reinforcement corrosion and axial compression ratio (ACR) on the seismic response of large-scale ductile reinforced concrete (RC) columns. 3D numerical models of sound and corroded RC columns were developed and validated with detailed experimentation. Various parameters, such as hysteresis and backbone curves, stiffness degradation, ductility, and energy dissipation, were evaluated for all the specimens. The numerical findings were then compared with the experimental findings. Subsequently, a thorough parametric study was executed to analyse the structural behaviour under varying corrosion degrees and ACR level combinations. It was observed that both sound and corroded specimens experienced significant degradation in terms of their strength, deformability, stiffness, and ductility due to elevated ACR levels. Moreover, increased ACR levels in both specimen types led to a decline in pre-peak and post-peak response trajectories, resulting in an early achievement of peak response at lower drift levels. The study’s outcome advocates the significance of incorporating ACR levels into the design philosophy of ductile reinforcements for RC columns.

Electrochemical chlorine evolution reaction to improve the desalination of sea sand

Sea sand, a vital sand and gravel resource, is rich in chloride, which causes corrosion of steel reinforcements. This study investigates the effect of the electrochemical chlorine evolution reaction (CER) on the desalination of sea sand. The results indicate that the chlorine removal efficiency (RE) of sea sand increased from 48.76 to 56.40 % under optimal conditions: a current density of 15 mA/cm2, an electrolysis time of 1 min, and a sodium sulphate-supported electrolyte concentration of 0.05 mol/L. After 30 days of resting, the dissolved chlorine content in sea sand was 0.154 %, which was 21.03 % lower than that of the control group. The electrically active chlorine-mediated desalination process demonstrated excellent dechlorination ability, facilitated the transformation of metal and organic chlorine into liquid and gaseous forms, and reduced the slow release of chloride from sea sand. Therefore, CER is expected to be an efficient method for sea sand desalination.

Hysteretic behavior of the corroded recycled aggregate concrete columns with ultra-high strength bars

The seismic behavior of six corroded recycled aggregate concrete (RAC) columns with ultra-high-strength bars (UHSB) was investigated through quasistatic test and numerical analysis. The main parameters include different corrosion ratios, axial load ratios (ALR), and stirrup ratios. The results revealed that: The damage development of the corroded specimen sped up with increasing corrosion ratio and ALR, and the corroded specimens suffered brittle shear failure due to the stirrup fracture or the concrete failure. The difference in carrying capacity of the specimens with low corrosion ratios and ALR was relatively small, while the deformation capacity was significantly reduced with increasing corrosion ratios and ALR. Reinforcement corrosion had a minor effect on the strength and stiffness degradation but would reduce the maximum cumulative energy dissipation capacity. By combining residual drift and residual crack width, the corroded specimens all could meet the limit of repairable residual drift and crack width before 4% drift, showing satisfactory resilient performance. Based on the modified corrosion models of materials, the numerical analysis showed the detrimental and coupling impact of the high ALR, high corrosion ratio, and low stirrup ratio on the carrying and deformation capacity. Through numerical analysis data, an equation was proposed that can satisfactorily predict the peak drift of the corroded columns with UHSB.

Basics and new opportunities for chemical re-alkalisation of carbonated concrete, including alkali-activated binders

Steel corrosion is one of the main factors limiting the durability of existing reinforced concrete components. Based on the corrosive circumstances, different prevention and repair methods can be applied. In the case of carbonation-initiated corrosion, chemical re-alkalisation (CRA) is one of the standard measures to counteract alteration processes in the concrete that lead to reinforcement corrosion. The current state of research on the CRA of carbonated concrete and the various materials that have been investigated in terms of their applicability for this repair measure are summarised. The review summarises current research results in the field of carbonated concrete and the proven pozzolanic reactivity of the carbonation products in contact with portlandite, which suggests an inhibitory effect on CRA, although this has not yet been investigated. There are also initial attempts that deviate from the application of classic Portland cement as a repair material, but their applicability in practice must be questioned. The use of alternative binders and the associated different compositions of pore solutions and varying alkalinity of these binders (e.g. composite cements with a high substitution rate or alkali-activated binders), have not yet been investigated for repair processes such as CRA, although the chemical composition of binders is of the greatest importance for successful application of the repair measure.

Influence of Starch Admixtures and Silver Colloids Stabilised with Starch Hydrolysates on the Course of Electrochemical Potential Difference of Reinforcing Steel in High-chloride Environment

The purpose of the conducted study was to verify whether the use of concrete admixtures with modified starches and starches modified with stabilised silver colloids affects the course of electrochemical potential difference, and hence corrosion, of reinforcing steel in a chloride environment. In the tests, cross-linked starches and products of acid hydrolysis of starch (dextrins) were used as admixtures. The 1-molar aqueous solution of sodium chloride was used as an aggressive environment. The tests consisted of measuring the potential difference generated in the reinforcement corrosion cell on the surface for a period of 60 days and then assessing the risk of corrosion. The effect of the addition of starch derivatives on the properties of cement paste was investigated through a one-way ANOVA analysis of variance followed by post hoc tests. The test results showed that the use of concrete admixtures with cross-linked starches positively affects the passivation of the steel. The likelihood of reinforcing steel corrosion when using distarch phosphate, acetylated distarch phosphate and acetylated distarch adipate admixtures is less than 5%. The results obtained showed an improved effect on the passivation of reinforcing steel in cement composites. Additionally, concrete samples may have microbicidal properties.

Chloride ingress analysis on alkali-activated slag concrete: A validated modelling framework for long-term assessment

Amidst global commitment to reduce CO2 emissions, the forthcoming decades expect to witness the prevalence of alkali-activated materials. As a predominant trigger for reinforcement corrosion, the accurate prediction of chloride ingress is paramount for the widespread application of the emerging building material. In this regard, this paper presents a novel framework tailored for analysing long-term chloride penetration into alkali-activated slag (AAS) concrete. An innovative technique for modelling chloride binding is developed and integrated into the framework. The technique can spontaneously assess time-dependent chloride binding based on the detailed phase assemblage, thereby rendering the framework applicability for the long-term analysis. The effectiveness of this model is rigorously validated against experiments. Furthermore, a series of virtual experiments are conducted by using the verified model to investigate the impact of different activators, where the distinction of resulting AAS concretes in resisting chloride ingress is elucidated. Overall, the present model is promising in delivering comprehensive understanding and robust prediction concerning long-term behaviours of next-generation AAS concrete buildings.

Electrochemical study on the effect of high volume fly ash on the corrosion of reinforcement in self compacting concrete slab panels

Electrochemical study on the effect of high volume fly ash on the corrosion of reinforcement in self compacting concrete slab panels

Carbonation and corrosion of steel in fly ash concrete, concluding investigation of five-year-old laboratory specimens and preliminary field data

Carbonation development and reinforcement corrosion were investigated on concretes exposed for a five-year period at 90% RH, 20 ℃, and 5% CO2, and for a six-year period at natural carbonation. Portland cement-based binders with 0%, 18%, and 30% fly ash were investigated. The fly ash blends showed lower carbonation resistance compared to PC both at laboratory and field exposure, a large difference in carbonation performance was observed between the laboratory exposed specimens. The carbonation rate was fastest on the laboratory specimens and showed square-root time dependency the first 2.5 years, but reduced rate at later age. Deeper carbonation depths were in general observed in the vicinity of the reinforcement compared to the unreinforced laboratory exposed specimens. Not all specimens were fully carbonated at the steel-concrete interface. The correlation between degree of carbonation of the steel-mortar interface, the open circuit potential, and the observed corrosion of the steel bars varied between binders and bar position (top or bottom). The measured corrosion rate in the laboratory exposed (90% RH, 20 ℃, and 5% CO2) carbonated concrete was on average 0.2 μA/cm2, with an upper value of 0.6 μA/cm2. The highest corrosion rate was measured in the fly ash concrete. No corrosion rate data are yet available for the field exposed concretes.

Study on electrochemical corrosion dynamics of cathode dic shield in concrete crack

Abstract Corrosion of steel reinforcement is a primary factor that negatively impacts the service life and safety of bridges made of concrete. Cathodic protection techniques are widely used to protect reinforcing bars in concrete against corrosion. However, it is inevitable that corrosion cracks will develop in the concrete during long-term operation, which will significantly shorten the cathodic current protection distance and increase the degree of corrosion of the rebar within the cracks. Therefore, electrochemical experiments and characterization of corrosion forms were carried out based on the company’s design of a rectangular connection device, we studied HRB500 steel in 3 wt.% corrosion behavior in rectangular joints under different CP current densities in NaCl solution. The results showed that with increasing experimental time, the corrosion in the crevice transitioned from activation corrosion to oxygen concentration corrosion, with the open-pore potential of the HRB500 steel inside the crevice appearing as a positive shift and the open-pore potential outside the crevice shifting from positive to negative. When implementing cathodic protection, the corrosion of HRB500 steel within the crevice is activated, while the corrosion outside the crevice changes from anodic to mixed controlled corrosion and from full to pitting corrosion. With the increase of CP current density, the corrosion process of HRB500 steel outside the gap is mainly dominated by cathode control, then gradually weakens, and the corrosion form changes from pitting to comprehensive corrosion.

Review on Repair and Rehabilitation of Cold Storage

Abstract: The purpose of the project is to gain fundamental and practical understanding on concrete repair and rehabilitation of the structures. Large number of reinforced concrete (RC) structure are deteriorating, often prematurely, and need remedial measures to reinstate their safety and/or serviceability. Consequently, the need for repair and protection has grown considerably in recent years. While costs associated with repair of deteriorating concrete structures can be substantial, costs resulting from poorly designed or executed repairs may be even higher. Repair methods need to be designed with consideration for the anticipated or desired remaining service life of the structure. A distinction must be made between repairs intended to stop deterioration fully and those merely aimed at slowing down deterioration processes for a limited period of time. Then the respective repairs will be studied and classified into cracks, corrosion of concrete reinforcement, seepage and deterioration of surface coating. Detailed study will be done on the causes for each repair and a suitable rehabilitation method will be suggested for each repair site by comparing various methods. This paper presents review of literature available on the repair and rehabilitation of cold storage and presented a complied review report.

Monitoring of Reinforced Concrete Corrosion: Active and Passive Bars Exposed to Climate

The durability of reinforced concrete structures is a significant concern, with corrosion of reinforcement being a leading cause of reduced durability. To ensure accurate models, it is necessary to calibrate or validate them with direct measurements of the structures, specifically monitoring durability-related parameters. The heterogeneity of structures and the dispersion of the parameters considered in models make this calibration or validation essential. To enable the predictive maintenance of structures, it is essential to monitor the parameters related to their durability. This article presents the results of the monitoring of the temperature, corrosion potential, resistivity, and corrosion rate of two structural components, a beam and a tendon, for over 10 months. The obtained values were correlated with the climate to which they were exposed. The corrosion rate can be correlated with the influence of climate, enabling real-time estimation of section loss. This is a necessary step towards the digitization of structures or the development of digital twins that incorporate the effect of corrosion.

Effect of steel reinforcement corrosion on progressive collapse resistant of beam-slab structure with interior column failure

To investigate the effect of steel reinforcement corrosion on the progressive collapse resistance of reinforced concrete (RC) structures, this study shows a methodology for establishing a finite element model (FEM) of a beam-slab structure by LS-DYNA software considering steel reinforcement corrosion. The reliability of this methodology was validated by experimental results. The analysis results indicate that considering the effect of the slab causes the beam-slab structure to enter the stages of tensile catenary action (TCA) and tensile membrane action (TMA) at smaller displacement. Moreover, as the corrosion time increases, the influence of the TCA on the structural resistance decreases. After prolonged corrosion, the top reinforcements of the beam at the failed column sides fail to fully utilize their tensile capacity when the structure fails. Furthermore, the corrosion of reinforcement significantly weakens the TCA and TMA to the structure, and neglecting the effect of the slab may lead to an overestimation of the weakening degree of the TCA caused by steel reinforcement corrosion. Additionally, the contribution of the slab's resistance in the beam-slab structure follows an "S"-shaped curve in relation to the displacement of the failed column, and the contribution of the slab to the structural resistance ranges between 40% and 60%.

Water-based corrosion inhibitor for prevention and repair of reinforcement in chloride and carbonated environment

This paper explores the influence of 2-aminopyridine (2AP) as water-based migratory corrosion inhibitor (M-CoI) on the corrosion resistance of reinforcing steel bars embedded in ordinary Portland cement and pozzolanic Portland cement concrete subjected to combined chloride and carbonation ingress. Two applications of 2AP are considered i.e., preventive (applied before exposure to aggressive environment) and repair (applied after corrosion initiates). Corrosion performance was assessed using electrochemical techniques and gravimetric mass loss method. The study also examines the impact of 2AP application on chloride ion concentration and carbonation depth of both concrete systems. The compressive strength of each concrete system was also measured to study the impact of M-CoI application on strength properties. Surface condition of hardened concrete and extracted rebar was evaluated by optical microscopy. Results conclude that 2AP effectively retards reinforcement corrosion when used as preventive measure by forming a homogeneous inhibitive layer on steel. However, when used as a repair technique, localised and uniform corrosion was perceived. An attempt has been made to identify the cause of non-performance of 2AP as repair measure. It was concluded that reached concentration of 1 mM was not sufficient to reduce ongoing corrosion due to the accumulation of corrosion products. The influence of the inhibitor on chloride profile and carbonation depth was found to be insignificant. It is concluded that chloride ions initiate the corrosion mechanism, while carbonation exacerbates it, particularly in blended cement concrete. Nonetheless, inhibitor application can provide similar resistance in both concrete systems.

An integrated material-structural analysis of prestress concrete affected by corrosion of non-prestressed reinforcement

Corrosion-induced concrete cracking is a significant stage of structural deterioration in prestressed concrete (PC) structures. Most current research predominantly focuses on the corrosion of prestressed steel strands, while paying limited attention to the study of non-prestressed reinforcement corrosion. In this study, an integrated material-structural numerical approach was developed to simulate corroded PC beams, considering corrosion products migration in pores and cracks. The cracking patterns and prestress losses obtained from the simulation results agreed well with experimental observations. Subsequently, using the proposed numerical approach, the interaction mechanism of the prestress level and reinforcement corrosion was investigated. The simulation results indicated that corrosion of longitudinal reinforcement leads to cross-sectional damage, causing the redistribution of stress across the section and increasing long-term deformation, ultimately resulting in prestress losses. Meanwhile, stirrup corrosion leads to an initial increase in prestress due to expansion forces when the degree of corrosion is not so high, but finally it will also lead to a degradation of mechanical performance.