Corrosion Resistance Of Rebar Research Articles

Corrosion Initiation on Reinforcing Steel with Mill Scale in Mortar

Corrosion of reinforcing steel rebar is the main cause of loss of the long-term reliability of concrete structures. When the rebar is corroded, the rust induces cracks and detachment of the cover concrete. The mill scale, a thick oxide film, is formed on the rebars when the rebar is hot rolled. The role of mill scale on the corrosion resistance of rebars in concrete has not been clarified, yet. This study studied the corrosion behavior of rebars with mill scale in mortar.The samples are commercial rebars with 19 mm diameter, which have a mill scale of several tens of micrometers in thickness. The rebars without mill scale prepared by the electrolytic polishing were used as the comparison samples. A Hyperbaric-oxygen accelerated corrosion test (HOACT) [1] was carried out using the rebars embedded in the mortar with a 5.5 mm cover thickness. To prompt the breakdown of passive film on the rebars, 2.1 M NaCl solution was mixed with the mortar. In the HOACT, pressurized oxygen gas is supplied to the sample, and the oxygen reduction reaction on the steel surface is enhanced, leading to the steel's corrosion acceleration. The oxygen pressure was 0.6 MPa and the test period was 14 days. The corrosion of the rebar with a mill scale was more significant than that without a mill scale. This result shows that the mill scale reduces the corrosion resistance of the steel rebar in concrete [2].To investigate the effect of the mill scale on the corrosion resistance of the rebar, anodic polarization measurements of the rebars with and without the mill scale were carried out in a saturated Ca(OH)2 solution containing Cl-. The pitting potential of the rebar with mill scale was more noble than that of the sample without mill scale. However, when the mill scale was scratched, the pitting potential was significantly shifted to the less noble direction, and it was below that of the rebar without the mill scale. These results show that the mill scale improves the corrosion resistance of the rebar in concrete, in contrast, the corrosion resistance of the rebar with a defective mill scale becomes even worse than that of the rebar without the mill scale [2].[1] K. Doi, S. Hiromoto, H. Katayama, E. Akiyama, J. Electrochem. Soc., 165(9), C582-C589 (2018).[2] K. Doi, S. Hiromoto, T. Shinohara, K. Tsuchiya, H. Katayama, E. Akiyama, Corrosion Science, 177, 108995 (2020).

Effect of Nanoparticle-Incorporated Cementitious Coating on the Corrosion Resistance of Rebars in Chloride Medium

Effect of Nanoparticle-Incorporated Cementitious Coating on the Corrosion Resistance of Rebars in Chloride Medium

Parameter Identification for Thermo-Mechanical Constitutive Modeling to Describe Process-Induced Residual Stresses and Phase Transformations in Low-Carbon Steels

Reinforcing steel bars (rebars) are widely manufactured using the Tempcore™ process. Several studies have been conducted analyzing the effect of the heat treatment route on the strength and corrosion resistance of rebars, but knowledge of its effects on the residual stresses of the finished product are largely lacking. This paper presents experimental investigations to identify the material parameters necessary to simulate the Tempcore™ process using thermo-elasto-plastic constitutive modeling in order to study the generation of residual stresses during the manufacturing process. Mechanical parameters such as yield strength at elevated temperatures and elastic constants were determined experimentally. A continuous cooling transformation diagram needed to model the phase transformations was also identified and is presented here. Residual stress distributions in the surface region of the rebar were characterized using X-ray diffraction. Further characterizations of microstructure, chemical composition, and hardness were carried out. The constitutive modeling approach for the numerical simulation is briefly described for which the experimentally determined parameters are required as input.

Electrochemical and physico-mechanical characterizations of fly ash-composite cement

In this paper, the corrosion of C-steel in OPC-fly ash-composite cement pastes (OPC-FA-CCP) was examined with different fly ash (FA) contents (0, 10, 25 and 50 mass%) and immersion times in the absence and presence of spinach extract as a green-corrosion inhibitor. The effect of replacing FA in cement composition on its physical, chemical, mechanical and microstructure properties using a variety of techniques has been also studied. The results indicated a significant increase in compression strength (CS) and gel/space ratio (X) upto 90 days in the case of OPC-FA-CCP containing 10 mass% FA. At higher FA replacement levels (≈25–50 mass%), the CS and X values decreased. SEM confirmed the presence of a surface layer of amorphous-ill-crystalline C-S-H as a gel product on the FA grains, with prolonged time showing dense crystalline hydrated fibril-C-S-H products. The C-steel immersed in the pure OPC cement (FA0S) has the highest corrosion potential (Ecorr = −461 mV) vs. SCE. With the increase of the FA content the Ecorr shifts to a more negative value with an indication of the decrease in the corrosion resistance of the rebar. During the first 6 h of immersion, the increased thickness of the passive film leads to a remarkable decrease in the corrosion rate. As the dipping time increases, the current corrosion density in all tested OPC-FA-CCP mixtures is unexpectedly reduced. A significant improvement in corrosion resistance of rebar was achieved in the presence of spinach extract. All the corrosion parameters were also calculated.

Research on the influencing factors on the corrosion resistance of rebars in concrete

This paper aims to study the influence of NaNO2 contents, water-cement ratios, mineral admixtures (fly ash and fine mineral powder) on the corrosion resistance of rebars in concrete. Electrical resistance and the corrosion current were established in order to research the anti-corrosive performances of the steel reinforced concrete. In this study, the mixing dosages of NaNO2 are increased from 0% to 2.0% by mass ratio of the total mixtures. Moreover, water-cement ratio (w/c) applied in this research ranged from 0.3 to 0.5. Fly ash and slag powder ranged from 10% to 30%, meanwhile assembly unit of fly ash (10% ∼ 20%) and slag powder(10% ∼ 20%) were used to improve the corrosion resistance of rebars. The research results indicated that electrical resistance increased initially and then decreased with the increase of NaNO2 contents and water-cement ratios. When the dosage of NaNO2 was 1.0% and water-cement ratio was 0.4 respectively, steel reinforced concrete presented the maximum electrical resistance. Additionally, electrical resistance was increased by the addition of fly ash and slag powder. Resistances of steel reinforced concrete with assembly unit of fly ash (10% ∼ 20%) and slag powder (10% ∼ 20%) was higher than that with single unit of fly ash or slag powder. Moreover, the corrosion resistance coefficient (Rp) of steel reinforced concrete firstly increased and then decreased with the increase of NaNO2 content. However, the decreasing w/c and the increased amount of mineral admixtures led to an increase of Rp. Steel reinforced concrete with 30% fly ash manifested the highest Rp.

Novel anticorrosive pigments based on waste material for corrosion protection of reinforced concrete steel

The performance of concrete specimens containing reinforced rebars coated with films having silica waste and core–shell pigments containing silica as core (80–90%) covered with Zn, Sr, Zn⋅Sr phosphates (10–20%) were compared. Core–shell particles are new trend in anticorrosive pigments comprising core which is cheap material (major) covered with efficient expensive material (minor).The corrosion resistance of rebars was measured using EIS and half cell potential besides measuring the bond strength at the rebar/concrete interface. The results revealed that embedded rebars coated with paints containing the pigments exhibited better efficiency and did not affect the bond strength between rebar and concrete.

Corrosion Resistance of Mild Steel in Simulated Concrete Pore Solution in Presence of Chloride Ions - An Overview

Concrete is one of the most widely used engineering materials for construction. Its durability is a major problem affecting the service life of the engineering structures. Various technologies such as cathodic protection and the use of corrosion inhibitors are used to improve the durability of reinforced concrete. Various organic and inorganic inhibitors, and also extracts of natural products have been used as corrosion inhibitors. Corrosion resistance of rebars has been evaluated by electrochemical studies such as polarization study and AC impedance spectra. The protective films formed on the metal surface have been analyzed by NMR, FTIR spectra, SEM, AFM and XRD.

The Corrosion Behavior of Rebar in Stressed Mortars

The corrosion behavior of stainless steel and carbon steel in the mortars suffered stress is studied by electrochemical tests. The results show that the corrosion of rebar is accelerated as the magnitude of stress increasing. Under the same stress magnitude, compressive stress more seriously degraded the corrosion resistance of rebar than tensile stress in mortar in an aggressive environment.

Influence of melted incinerator ash on durability and corrosion behaviour of reinforced concrete

This study investigates the effects of incinerator bottom ash (IBA) fineness and the cooling process of molten IBA on the durability of concrete and the corrosion of rebar. Two finenesses of an original IBA, i.e. pulverized incinerator bottom ash (PIBA) powder with maximum particle sizes of 0.6 and 0.074 mm, were used to partially replace Portland cement at 20 per cent by weight. In addition, the powder was also obtained by melting the PIBA (<0.6 mm) in an electric-furnace at 1450 °C for 1 h and chilling it by quenching in water (WIBA, water-cooled melted incinerator bottom ash) and air (AIBA, air-cooled melted incinerator bottom ash). The powder was then ground in a ball mill until the particle size reached less than 0.074 mm. This study also presents the experimental results on the compressive strength, mercury intrusion porosimetry, scanning electron microscopy (SEM), and X-ray diffraction of concrete samples containing different types of IBA. This study uses the initial surface absorption test and rapid chloride penetration test to measure the absorption and the ability of different concrete samples to resist chloride ions. Cylindrical specimens were cast and exposed to 3.5 per cent NaCl solution under a direct current density (0.5 m A/cm2) to accelerate the corrosion process. The open circuit potential and direct current polarization resistance were obtained to evaluate the rebar corrosion. Results indicate that WIBA concrete achieved a compressive strength similar to reference specimens after 28 days of curing; WIBA and AIBA exhibited an increase in unit weight and workability when used as a replacement for cement. However, IBA can be processed by melting to regain reactive pozzolanic activity, which may be used to partially replace cement. The incorporation of WIBA and AIBA decreased the total capillary pore porosity of the mortars compared to ordinary PIBA. The large particle size of PIBA produced lower hydraulic properties than finer particles. The improved properties of WIBA and AIBA resulted from the dense structure achieved by the filling effect of the pozzolanic product. Strength activity index results, SEM, X-ray analysis, and the rate of ISA observations confirm these findings. Utilizing a proper amount of WIBA and AIBA significantly improved the chloride and corrosion resistance of rebar in concrete in this study. Therefore, WIBA and AIBA can act as cementitious materials in cement-based composites.

Durability performance of rebar embedded in chloride admixed blended cement concretes

In concrete structures, permeation of chloride ions either through the pores or by visible/microcracks or contamination of chloride along with the fine and coarse aggregates increase the availability of chloride ion at the rebar level. The reduction of OH− ions by pozzolanic reaction and by replacement of cement by mineral admixtures may reduce the chloride ion tolerable limit of rebar in blended cement concretes. In the present investigation, the corrosion rate of rebar in 0·5 and 1% chloride admixed concrete was assessed periodically up to a period of 1765 days using electrochemical impedance spectroscopic technique. Ordinary Portland cement (OPC), pulverised fuel ash cement (PFAC) and blast furnace slag cement (BFSC) were evaluated in 20, 30 and 40 MPa concretes. The high Rp value of rebar obtained in blended cements indicates that the additional calcium hydrates maintains the pH and also contributes significantly to the inhibitive effects at the steel/concrete interface thus maintaining the passivity of rebar. The results reveal that the high chloride ion complexing ability and microstructural changes by the formation of additional calcium hydrates in the PFAC and BFSC concrete matrix enhancing the corrosion resistance of rebar by a factor of five times than that of OPC concrete in 0% chloride added concrete and three times in 1% chloride contaminated concrete. The reduction of OH− ions did not decrease the chloride tolerable limit of rebar in PFAC and BFSC concrete; moreover they had 1·4 times higher chloride tolerance than that of OPC concrete.