Corrosion Of Reinforcing Steel Bars Research Articles

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.

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%.

A closer look at corrosion of steel reinforcement bars in concrete using 3D neutron and X-ray computed tomography

Corrosion of reinforcing bars constitutes the largest threat to the durability of concrete structures. Thus, several studies have investigated the nature of the corrosion products, most using post-mortem analyses. However, corrosion products evolve when in contact with oxygen, hindering result interpretation. This work presents instead a state-of-the-art, non-destructive 3D method for the assessment of corrosion of embedded reinforcements.Multimodal neutron and X-ray tomography was used to observe, non-destructively, the characteristics of the corrosion products in two concrete samples, with the aim of investigating possible benefits of the use of this technique for reinforced concrete structures. One sample was naturally corroded, extracted from an 81-year-old bridge, the other was corroded via the galvanostatic method, resulting in corrosion-induced cracks. Quantitative and qualitative data was acquired, including the iron-to-rust volumetric ratio in macroscopic interfacial voids and the thickness of the corrosion layer at the steel concrete interface. The iron-to-rust volumetric ratio corresponded to large, soluble, corrosion products, forming in environments with low availability of oxygen for both samples.

Phase-field simulations of cover cracking in corroded RC beams

Corrosion of steel reinforcement bars is a crucial issue for the reinforced concrete structures. Being one of the most common deterioration mechanisms, corrosion severely affects the serviceability and durability of the structure as the steel reinforcement suffers from a reduction of the cross section and deterioration of the mechanical properties. Additionally, due to the steel oxidation process, residual material is formed, and the volume occupied by the reinforcement increases, leading to cracking and spalling of the concrete cover. A predictive model coupling concrete carbonation process and phase-field approach for brittle fractures is proposed to simulate the carbonation induced corrosion of rebar and the subsequent cracking phenomenon. First, a Fick diffusion law is used to describe the carbon dioxide (CO2) diffusion within the concrete which leads to a generalized corrosion process. As the corrosion evolves, the steel mass loss is converted into expansion strain due to the formation of residual material, and the damage evolution within the concrete cover is determined. After validation against examples from the literature, numerical simulations are performed, presenting a phase-field strategy capable to describe the cover cracking of corroded RC beams.

Experimental study of biopolymer in corrosion resistance for industrial exposure condition

Abstract Many RCC structures have been built in the last century but these structures are in need of repair within 10–20 years of its construction. The reason for this premature distress and deterioration points towards corrosion of steel reinforcement bars used in these structures due to weakening of concrete. The enormous number of structures that needs immediate repair and renovation opens up a huge potential for research in this area. The repair work done in a conventional way using normal cement composite did not work. Whereas repair work done with scientific approach using high and technically competent materials (like epoxies) leads to uneconomical solutions and not durable to withstand our tropical climatic conditions. India being a flourished nation with infinite resources giving us a numerous number of bio-polymers that were used in ancient times in ancient construction, if these bio polymers are identified experimentally for their benefits it would give way to eco-friendly economical and long-lasting structures. The use of corrosion inhibitor is one of the most widely used countermeasures, because of their simplicity in applications and is relatively less expensive. The natural bio polymers are organic materials available from selected plants, seeds, fruit extracts. Plant extracts corrosion inhibitors are cheap, non-toxic and environmental friendly. Organic inhibitors offer protection by adsorbing and forming a protective film on the steel surface. Turmeric, Neem extracts in concrete as corrosion inhibitor in different ratio and as a combination are to be studied at depth, as they are commonly available and there is no constraint in getting these resources throughout the year. An eco-friendly, economical, Non-Toxic and user-friendly corrosion inhibitor can be given from this experimental study. The feasibility study has been made and phytochemical analysis results give positive results for a better result giving corrosion inhibitor.

Depassivation of Steel Rebar in Concrete Investigated By Electrochemical Impedance

The degradation of concrete and the corrosion of steel-reinforcing bar are serious problem in infrastructures. The electrochemical measurements are useful to evaluate the stability of passive film formed on steel rebar in concrete, which are mainly measurements of corrosion potential [1] and polarization curve. Dawson et al. [2] applied an electrochemical impedance spectroscopy (EIS) to the investigation of rebar corrosion in concrete because the charge transfer resistance at rebar/concrete interface can be determined from the impedance spectrum. Recently, the authors developed an electrode in Fig. 1 as a sensor probe to monitor concrete degradation and rebar corrosion. A couple of electrodes, which were made of same material as steel rebar, can be embedded in concrete structure and complex impedance can be measured continuously on the basis of two-electrode method. The authors’ group has performed the following three types of impedance measurements in order to prove the of the developed sensor probe. (1) Impedance between two electrodes in aqueous solution that simulates the water quality of transition zone (laboratory test). (2) Impedance between two electrodes embedded in the concrete which was fabricated in the laboratory. (3) Field test at bridge pier of the highway in coastal marine environment. It is well known that the rebar corrosion in concrete is strongly influenced by the conditions of cover concrete. Thin water layer is formed at rebar/concrete interface due to water absorption in the concrete. The concrete is good health status and the passive film is formed on steel rebar when the pH of water layer on steel rebar is sufficiently high. The breakdown of passive film occurs by neutralization and enriched chloride ions in the water layer with the degradation of concrete. In this presentation, the authors investigate the critical values of pH and chloride concentration to maintain the passive film on steel rebar and discuss the depassivation mechanisms by the measurements of electrochemical impedance with the developed sensor probe.

Bearing Capacity Calculation and Fiber-reinforced Polymer Repair of Corroded Beam-slabs in a Wharf

Corrosion of steel reinforcement bars is a common problem for high-pile wharf in service, with the aim of solving this problem, a method to calculate the actual bearing capacity of corroded beam-slabs is proposed, in which the rate of loss of area and the reduction in strength of steel bars due to corrosion are considered. Taking Zhanjiang Port as an example, the actual bearing capacity of corroded beam slabs is calculated and is compared with that found under normal service conditions. For repair of corroded beam-slabs, a method in which fiber-reinforced polymer (FRP) bars partly replace the steel bars is proposed, and the basic assumptions and method of calculation for this mixed-reinforcement components are discussed.

Rebar Corrosion Due to Chlorides in the Presence of Different Cations

Recent attention on effects of climate change in the Pacific island countries (PIC’s) have focused on a multitude of areas which are at risk in the Pacific region. These include food security, flora and fauna, land accessibility, groundwater contamination and so on. These aspects are essential for sustainable development of the small island states in the Pacific region. One issue, which appears synonymous with climate change in the Pacific is sea-level rise. The rising sea level can have detrimental effects on civil infrastructure since its intrusion further inland can lead to deterioration of nearby civil metallic infrastructure due to corrosion. Since metropolisation of major PIC’s are mainly near the sea or along coast line, this presents a significant problem within the overall paradigm of sustainable development. In this regards, a study was undertaken to investigate the influences of different chloride salts (i.e. NaCl, KCl, MgCl2) on the corrosion of steel re-inforcing bars (rebar’s) in concrete mortars. This study is important to understand structural health conditions, especially for foundations in ground, and to understand the corrosion intensities in the presence of different cations, which can be significantly controlled by groundwater migration. The galvanostatic pulse technique was used to evaluate the effect of varying chloride contents of different salts on rebar corrosion. Results from this study are presented in an attempt to provide a conceptual model for understanding the interaction of aforementioned salts with metallic infrastructure. A holistic discussion is presented which are important for sustainable development in the PIC’s.

Durability studies on steelmaking slag concretes

Electric-arc furnace slag is proposed as a substitute for the conventional aggregate used in classical structural concrete. In the present research is studied the durability of these slag aggregate concretes and their resistance to both physical (freeze–thaw, high temperature and relative humidity) and chemical degradation (sulfate attack, alkali–aggregate reaction and marine environment), as well as their resistance to the corrosion of steel reinforcement bars (an assessment of the risks of corrosion) embedded in the concrete matrix. This approach requires laboratory studies. The main objective of this work focuses on evaluating the durability of slag concrete under the conditions specified in the Spanish structural concrete code. In general terms, the behavior of the concrete with slag aggregate was similar to or better than the reference concrete (natural aggregate), except in case of exposure to marine environments and seawater, which resulted in quicker chloride penetration. The study confirms the viability of producing steel-reinforced concrete with slag aggregate.

Reinforcement corrosion initiation and activation times in concrete structures exposed to severe marine environments

The corrosion of steel reinforcement bars in reinforced concrete structures exposed to severe marine environments usually is attributed to the aggressive nature of chloride ions. In some cases in practice corrosion has been observed to commence already within a few years of exposure even with considerable concrete cover to the reinforcement and apparently high quality concretes. However, there are a number of other cases in practice for which corrosion initiation took much longer, even in cases with quite modest concrete cover and modest concrete quality. Many of these structures show satisfactory long-term structural performance, despite having high levels of localized chloride concentrations at the reinforcement. This disparity was noted already more than 50 years ago, but appears still not fully explained. This paper presents a systematic overview of cases reported in the engineering and corrosion literature and considers possible reasons for these differences. Consistent with observations by others, the data show that concretes made from blast furnace cements have better corrosion durability properties. The data also strongly suggest that concretes made with limestone or non-reactive dolomite aggregates or sufficiently high levels of other forms of calcium carbonates have favourable reinforcement corrosion properties. Both corrosion initiation and the onset of significant damage are delayed. Some possible reasons for this are explored briefly.

Influence of Phosphate on Corrosion Products of Iron in Chloride-Polluted-Concrete-Simulating Solutions: Ferrihydrite vs Green Rust

Abstract The corrosion of steel-reinforcing bar (rebar) in concrete induced by the diffusion of chloride ions was simulated with a-iron foils dipped in various aqueous electrolytes. Sodium chloride (NaCl) was added to saturated calcium hydroxide (Ca[OH]2) solutions to simulate concrete polluted with chloride ions whereas solutions containing sodium bicarbonate (NaHCO3), sodium carbonate (Na2CO3), and NaCl were used as carbonate- and chloride-containing concrete. The corrosion process was electrochemically induced by cyclic voltammetry and galvanostatic methods. Similar experiments were performed with solutions where various amounts of trisodium phosphate (Na3PO4) were added. The galvanostatic potential dropped to ∼ −0.15 V vs standard hydrogen electrode (SHE) in the absence of phosphate, indicating that active corrosion took place, while it reached values of ∼1 VSHE with large phosphate concentrations. The corrosion products were analyzed by Mossbauer spectroscopy. They mainly consisted of iron(II) compou...

Effect of Epoxy Resin Injection in Concrete Cracks on Corrosion of Reinforcing Steel Bars

Effect of Epoxy Resin Injection in Concrete Cracks on Corrosion of Reinforcing Steel Bars