Corrosion Resistance Of Steel Bars Research Articles

Mechanistic study on initial passivation and surface chemistry of steel bars in nano-silica cement pastes

This work studied the passivation of steel bar in cement pastes prepared with and without nano-silica by using electrochemical measurements and surface characterization methods. The results showed that the passivation of steel bar in cement paste was dominated by the chemistry of the pore solution and the evolution over time, which are closely associated with the hydration process of the cement. The addition of nano-silica influenced the alkalinity of the pore solution in cement paste and modified the pore structure of the cement paste, which resulted in a different passivation process and a thicker passive film with a higher proportion of Fe2+ oxides. The intrinsic corrosion resistance of steel bars in concrete prepared with nano-silica was expected to be enhanced.

Effects of vibration time on compressive strength and corrosion resistance of steel bars in concrete

In this paper, In this paper, effects of vibration time (0, 10 and 20 seconds) on compressive strength and corrosion resistance of steel bar in concrete are experimentally investigated. Compressive strength of concrete was performed on cylindrical specimens of Ø100x200 mm with water cement ratio (w/c) 0.52 after 28 days curing in tap water. Cylindrical specimens of Ø100x200 mm having 16 mm diameter of steel bar are considered for corrosion study. The specimens were subjected to cyclic wetting and drying regime up to 15 cycles. In wet cycle the specimens are immersed in sea water for 3 days, while in dry cycle the specimens were placed in open air for 4 days. The corrosion activity is monitored by measuring the copper/copper sulphate (CSE) half-cell potential according to ASTM C-876. The chloride penetration depths of concretes are also measured after 28 days immersed in 10% NaCl solution. Results show that compressive strength, chloride penetration depths and corrosion of steel bars is significantly affected by vibration time.

Corrosion resistance of steel bar and chloride binding capacity of cementitious materials with internal chloride

During the construction of islands and reefs far from the mainland, local marine materials are expected to be used in concrete from the viewpoint of economy, rapid and convenient construction. As abundant chloride with local marine materials is involved into concrete, ordinary Portland cements are not recommended due to their low chloride binding capacity and poor corrosion resistance of steel bar. In the present study, geopolymer, gap-graded blended cement as well as Portland cement and inter-ground blended cement as references were mixed directly with NaCl to simulate the chloride in local marine materials, their hydration process, mechanical properties, corrosion resistance of steel bar and microstructure were compared. The results showed that the hydration processes of blended cements were accelerated after introducing NaCl, resulting in a dramatic increase in early strengths. In contrast, the compressive strengths of Portland cement and geopolymer kept constant, whereas the late flexural strengths reduced gradually. Geopolymer had slightly better corrosion resistance of steel bar than Portland cement due to low porosity and pore size refinement, and gap-graded blended cement presented a superior corrosion resistance of steel bar even in chloride-rich environment, as the chloride binding capacity of gap-graded blended cement paste was about 4 times higher than that of geopolymer.

Corrosion resistance of steel bars in mortar mixtures mixed with organic matter, microbial or other

Dissolved oxygen in pore solution is often a controlling factor determining the rate of corrosion processes of steel bars in concrete. This study reports on corrosion resistance and polarization properties of steel bars in mortar specimen mixed with aerobic microorganisms. The properties are essentially associated with the permeability of dissolved oxygen in pore solution. This could be affected via metabolic activities of aerobic Bacillus subtilis natto mixed in hardened mortar specimens. Mortar specimens with segmented steel bars were prepared using culture solution as a partial replacement of mixing water. The mortar specimens cast with a w/c ratio of 0.50 were cracked by 4-point bending test and then they were exposed to dry (4 days) and wet (3 days) cycles using tap water containing 10% NaCl in order to accelerate corrosion especially at cracked parts. Electro-chemical measurements were carried out to examine the corrosion processes by AC impedance method, half-cell potential measurements, and macrocell corrosion measurements using zero-resistance ammeters. Cathodic polarization curves were measured at the ages of 28 and 91 days before and after the specimens were exposed to chloride-induced corrosion tests through dry and wet cycles. The results indicate that the rate of oxygen permeability inferred based on limiting current density is substantially smaller in the case of mortar specimens mixed with the bacillus subtilis natto. This can be explained by the fact that the dissolved oxygen is consumed by the oxidation of organic matter, a process initially catalyzed by Bacillus subtilis natto present in hardened mortar specimen during the monitoring periods. Based on the results obtained, the addition of culture solution containing Bacillus subtilis natto reacting with dissolved oxygen resulted in higher resistance against corrosion processes, which was confirmed by the results of half-cell potential and microcell and macrocell corrosion current density. There is a strong possibility that the reduced dissolved oxygen in pore solution through the aerobic processes could enhance the corrosion resistance in cracked mortar specimens.

Carbonation treatment of recycled concrete aggregate: Effect on transport properties and steel corrosion of recycled aggregate concrete

Old cement mortars attached on recycled concrete aggregates (RCA) seriously affects the durability of the recycled aggregate concrete (RAC). Revealing the variation of the transport properties of cement mortar after subjecting to accelerated carbonation treatment is crucial with respect to understanding the effects of carbonated RCA on the durability of RAC. In this paper, cement mortars were used to study the transport properties after they were treated by accelerated carbonation. The corrosion behavior of steel bars in the concrete incorporating the carbonated RCA was also evaluated. The experimental results indicated that the water absorption and sorptivity, resistance to chloride ion penetration, as well as the bulk electrical conductivity of the cement mortar was decreased after subjecting the accelerated carbonation treatment. Extending the treatment from 1 day to 7 days only resulted in a marginal improvement of the transport properties. A significant decrease in the local porosity at the edge of cement mortar determined by Scanning electron microscopy-backscattered image was observed, agreeing well with the concentrated calcium carbonate (CC) contents detected in the surface layer by TGA. The determination of the spatial gradients of the porosity and carbonates/portlandite contents illustrated that even only with the external layer (0–10 mm) carbonated, a considerable improvement of transport properties of the cement mortar could still be achieved. The corrosion test in the new concrete prepared with the carbonated RCA also confirmed that the corrosion resistance of steel bars in the RAC was improved.

Effects of Coatings Containing Organic Ashes on the Corrosion Performance of Reinforcements

The aim of this study is to investigate the corrosion performance of reinforcement steels coated with a coating containing wheat straw, sunflower stalk, and corn stalk ashes and moreover to discuss the effect of the coating on the concrete durability. By replacing calcite with different amounts of these organic ashes in the dye production, innovative corrosion inhibitive coating types were introduced. These coating types have been applied both on the reinforcement steels and concrete surface. In order to understand the effects of the coating types produced with these organic ashes, the steel bars coated with them containing 6% of the organic ashes as fine aggregate were embedded into concrete samples. The samples were cured both in tap water and 3.5% NaCl solution for 180 days, and the mass losses of the steel bars were determined. Also, the inhibition efficiency of the coating was determined by using the galvanic cell method and accelerated corrosion tests. Furthermore, mass loss, compressive strength, abrasion resistance, freeze‐thaw property, and capillary water permeability of the reinforced concrete samples with the produced coating were investigated. Test results showed that the minimum mass loss ratio in reinforcement was observed as 0.185% in samples coated with all three organic ash‐added mixes. Also, for the same samples compressive strength loss was the lowest as 14%. As a result, the durability of concrete and the corrosion resistance of steel bars improve with the addition of wheat straw, sunflower stalk, and corn stalk ashes into the coating and they could be used as environment‐friendly corrosion inhibitors.

Ion-triggered calcium hydroxide microcapsules for enhanced corrosion resistance of steel bars.

Herein, we synthesized Ca(OH)2 microcapsules with ion-responsive shells composed of cross-linked poly-ionic liquids (CPILs). By exchanging PF6− with Cl− in water, the hydrophobic poly-ionic liquids (PILs) on the shell are converted to hydrophilic channels. The encapsulated Ca(OH)2 can permeate through the hydrophilic channels and release OH−. Meanwhile, the Cl− content can be reduced. The release rate of Ca(OH)2 is influenced by the content of monomers and concentration of Cl− ions in water. SO42− can also trigger the release of Ca(OH)2 from the microcapsule. With these microcapsules, Q235 steel exhibited promising corrosion resistance in simulated seawater. These results indicate that encapsulation of corrosion inhibitors is highly desirable for enhanced corrosion resistance of steel bars and the proposed approach can be used to encapsulate various corrosion inhibitors and functional materials for a wide range of applications.

Effect of silica fume and steel slag coarse aggregate on the corrosion resistance of steel bars

This study evaluates the corrosion resistance of concrete cylindrical specimens. The concrete samples were prepared from electric arc furnace steel slag (EAFSS) with percentages equal to 0%, 20%, 40%, 60%, 80% and 100%, and were examined as a partial replacement of ordinary coarse aggregate (dolomite). Silica fume with 20% replacement of the weight of the used cement was utilized in order to study its effect on the corrosion resistance of the embedded steel bars. Twenty cylindrical specimens, with a diameter equal to 50mm and a height of 200mm, were prepared and merged in NaCl solution with 3.5% concentration. Subsequently, the electrochemical behavior of the specimens was assessed using linear polarization resistance technique and open circuit voltage. The results indicated that rebar in the concrete specimens which contains steel slag was found to be resisting corrosion efficiently better than the control specimens which incorporates dolomite as coarse aggregate.

Influence of nano-silica addition on durability of UHPC

This study aims at studying the effect of nano-silica (nS) addition to ultra-high performance concrete (UHPC) on the corrosion resistance of steel bars embedded in the latter. In order to conduct a comparative study, a high performance concrete (HPC) and an UHPC without nS were also considered in the experimental program. An accelerated corrosion test along with multi-steps potentiodynamic polarization technique, including Tafel plot and linear polarization resistance (LPR), was used to determine the corrosion rate of the samples tested. The accelerated corrosion tests showed that the time to cracking in HPC is less than half the time in UHPC. It was found that nS addition to UHPC effectively reduces the corrosion rate of steel bars embedded in the latter.

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.

The influence of EAF dust on resistivity of concrete and corrosion of steel bars embedded in concrete

Essentially, when electrical current flows easily in concrete that has large pores filled with highly connective pore water, this is an indication of a low resistivity concrete. In concrete, the flow of current between anodic and cathodic sites on a steel reinforcing bar surface is regulated by the concrete electrical resistance. Therefore, deterioration of any existing reinforced concrete structure due to corrosion of reinforcement steel bar is governed, to some extent, by resistivity of concrete. Resistivity of concrete can be improved by using SCMs and thus increases the concrete electrical resistance and the ability of concrete to resist chloride ingress and/or oxygen penetration resulting in prolonging the onset of corrosion. After depassivation it may slow down the corrosion rate of the steel bar. This indicates the need for further study of the effect of electric arc furnace dust (EAFD) addition on the concrete resistivity. In this study, concrete specimens rather than mortars were cast with different additions of EAFD to verify the electrochemical results obtained and to try to understand the role of EAFD addition in influencing the corrosion behaviour of reinforcing steel bar embedded in concrete and its relation to the resistivity of concrete. The results of these investigations indicated that the corrosion resistance of steel bars embedded in concrete containing EAFD was improved, which may link to the high resistivity found in EAFD-concrete. In this paper, potential measurements, corrosion rates, gravimetric corrosion weight results and resistivity measurements will be presented and their relationships will also be discussed in details.

Some Considerations for Applicability of Seawater as Mixing Water in Concrete

According to the report of the World Meteorological Organization (WMO), more than half of the world’s population will not have enough drinking water by 2025. To save drinking water, use of seawater in the concrete industry seems imperative. In the present study, the possibilities of seawater as a material of concrete are discussed as a result of the literature-based and experimental investigations. From the results of the literature-based study, more than half of the papers collected in this study had positive opinions about concrete mixed with seawater by adding the mineral admixture such as blast furnace slag (BFS). In addition, some results of long-term exposure tests indicated the high possibility of using seawater as a material of concrete. The experimental data obtained in this study indicated that the addition of BFS might contribute significantly to the corrosion resistance of steel bar, because of the low oxygen environment around steel bar and chloride immobilization.

Effects of Coating/Electroplating on Corrosion Resistance of Steel Bar in Reinforced Concrete

One of the main reasons for the damage of reinforced concrete is the expansion caused by corrosion of steel bar in concrete. In this paper, the equivalent circuit that inflects corrosion process of steel bars in reinforced concrete was analyzed, with the A.C.Impedance Spectrum method. And the effects of surface treatment of the bars on corrosion resistance of the reinforced concrete were investigated. Study results show that the surface coating (plating) on the built-in reinforcement can effectively prevent corrosion of steel bar, thereby enhancing the durability of concrete structures.

Effects of Coating/Electroplating on Corrosion Resistance of Steel Bar in Reinforced Concrete

One of the main reasons for the damage of reinforced concrete is the expansion caused by corrosion of steel bar in concrete. In this paper, the equivalent circuit that inflects corrosion process of steel bars in reinforced concrete was analyzed, with the A.C.Impedance Spectrum method. And the effects of surface treatment of the bars on corrosion resistance of the reinforced concrete were investigated. Study results show that the surface coating (plating) on the built-in reinforcement can effectively prevent corrosion of steel bar, thereby enhancing the durability of concrete structures.

Effect of steel manufacturing process and atmospheric corrosion on the corrosion-resistance of steel bars in concrete

This paper presents results of a study conducted to evaluate the effect of steel manufacturing process and the surface condition of reinforcing steel on their corrosion-resistance when embedded in concrete. Steel bars produced by water quenching and air-cooling were utilized. The corrosion-resistance of fresh bars, i.e., those that were clean and shiny, and those exposed to atmosphere and accelerated salt spray, when embedded in concrete, was evaluated. The corrosion-resistance of the clean and corroded reinforcing steel bars was assessed by measuring corrosion potentials and corrosion current density. Accelerated impressed current technique was also utilized to evaluate the corrosion-resistance of clean and corroded reinforcing steel bars in concrete. A longer time-to-initiation and lower rate of reinforcement corrosion was noted in the concrete specimens prepared with water-quenched steel bars compared to similar bars manufactured by the hot-rolling process. Similarly, the rate of reinforcement corrosion in the concrete specimens prepared with corroded steel bars, exposed to atmosphere for 12 months and salt spray, was less than that on the unexposed bars. The data developed in this study also indicate that the surface layer formed on the water-quenched steel bars, due to the cooling process, provides protection to the metal substrate as against the loose mill scale formed on the steel bars produced by the air-cooling process.