Corrosion-inhibiting Admixture Research Articles

Experimental Study on the Effect of Corrosion-inhibiting Admixtures on Chloride Corrosion Resistance of Concrete

Compared to the different types of rust inhibitors, The effects of the internal and external coating corrosion inhibitors on the corrosion resistance of concrete were studied. The impact of the mixed rust inhibitor on the working performance, compressive strength and chloride ion permeability coefficient of concrete was investigated. The results show that the working performance, late mechanical properties, and resistance to chlorine salt erosion of concrete are better than those of reference concrete after adding the anti-rust agent. Comparing the effects of 2% and 4% internal rust inhibitors on the corrosion resistance of chloride ions, based on the control group, the chloride ion diffusion coefficient of concrete with 2% and 4% rust inhibitors decreases to the original 15.1% and 37.0%, respectively. Concrete’s chloride ion diffusion coefficient with external rust inhibitor decreases to 62.5%. In addition, the internal corrosion inhibitor has a specific water-reducing component, which reduces the water consumption of concrete and improves the compactness of concrete itself, thus improving the corrosion resistance of concrete.

Chloride transportation and electrochemical behavior of concrete containing corrosion-inhibiting admixture and its inhibition mechanism under compound salt and drying-wetting cycles

The purpose of this study is to provide an ecological corrosion-inhibiting admixture (CIA) for retarding the degradation of reinforced concrete under compound salt attack and drying-wetting cycles. The effects of CIA on the mechanical behavior, chloride transportation, and electrochemical behavior of concrete under compound salt and drying-wetting cycles were investigated. The pore contents with different sizes in concrete and the micro-morphology of rebars were analyzed by the bubble spacing coefficient analyzer and the scanning electron microscopy (SEM), respectively. The findings showed that the addition of CIA retarded the deterioration of concrete under compound salt and drying-wetting cycles. After exposure for 150 d, the weight loss rate and average free chloride concentration of concrete containing 5 % CIA decreased by 74.14 % and 51.53 % respectively, and the compressive strength was 1.49 times that of concrete without CIA. Chloride transportation was primarily dominated by diffusion and convection. Additionally, CIA significantly reduced the content of larger pores, prevented the diffusion of chloride and sulfate into the interior concrete, and formed adsorption films through a combination of physical and chemical effects, thus improving the electrochemical performance of rebars. This study is of great significance to provide new perspectives and improvement measures for mitigating the deterioration of reinforced concrete under compound salts and drying-wetting cycles.

Performance and deterioration mechanism of concrete incorporated with corrosion-inhibiting admixtures under the coupling effect of composite salt and freeze-thaw cycles

The purpose of this study is to provide multi-functional, green, low-carbon and environmental-friendly corrosion-inhibiting admixtures (CIA) to alleviate the deterioration of reinforced concrete under the coupling effect of composite salt and freeze-thaw cycles (FTCs). The effects of different contents of CIA on the performance of C30 concrete, including mechanical behavior (mass loss rate (MLR), compressive strength loss rate (CSLR) and relative dynamic elastic modulus (RDEM)), chloride ion penetration of concrete, and the electrochemical performance of rebars in concrete, were investigated. Furthermore, the deterioration mechanism of reinforced concrete was probed in detail by evaluating the pore structure parameters of concrete and the microscopic morphology of concrete and rebars via low-field nuclear magnetic resonance (NMR) and scanning electron microscope (SEM), respectively. The results showed that the mechanical behavior of concrete with CIA was prominently superior to that of concrete without CIA, with MLR decreased by 51.13–78.60%, CSLR decreased by 40.11–84.93%, and RDEM increased by 29.89–56.27% after 100 FTCs. The average content of free chloride ion in the concrete containing CIA was decreased by 12.14–55.65% under 100 FTCs due to the addition of CIA reducing the transmission path and the percentage of much detrimental pores (decreased by 39.03–85.99% after 100 FTCs). The correlation between free chloride ion content and diffusion depth conformed to Fick's second law, showing that there was a linear positive correlation between chloride diffusion coefficient (D) and FTCs. In addition, the electrochemical performance of rebars in concrete with CIA was improved owing to the good protection of CIA to rebars. This study is of great significance for improving the durability of reinforced concrete in harsh environment.

Development of Electrically Conductive Cold Weather Cement Concrete

Placing fresh cement concrete is not permitted during cold weather under normal conditions due to the risk of frost damage. On the other hand, electrically conductive concrete can be used for deicing/snow-melting applications. This paper presents laboratory investigations to develop electrically conductive cold weather concrete (ECCWC) that can be cast and cured below freezing temperatures and has sufficient electrical conductivity for Joule heating. The concrete has additive-based freeze protection (ABFP) systems that consist of optimized amounts of accelerators and corrosion-inhibiting admixtures. Several mixture proportions were made with 0.5%, 0.75%, and 1.0% carbon fibers by volume of concrete to increase the concrete’s conductivity. ECCWC specimens were mixed, cast, and cured at −5°C. The measured freezing points of fresh concrete mixtures were below −5°C. The compressive strength development of ECCWC cured at −5°C was slow compared with the strength development of conductive concrete cured at 20°C. However, ECCWC could reach 55 MPa at 28 days of age. The temperature of hardened ECCWC increased by 18.5°C within 20 min when subjected to a potential difference of 30 V (alternating current). ABFP implemented in the ECCWC mixtures reduces the risk of frost damage and provides the opportunity to place fresh conductive cold weather concrete at ambient temperatures of −5°C without the need for taking curing precautions. The developed ECCWC introduces a new method for constructing multifunctional concrete structures to be placed and cured in cold regions.

Evaluation of Greener Corrosion-Inhibiting Admixtures for Steel Reinforcements in Concrete

In this study, corrosion of thermo-mechanically treated (TMT) rebars with and without 3.5% NaCl for various concentrations (0.1%, 0.2%, 0.3% and 0.4%) of green corrosion inhibitors, namely glucosamine and stevioside, was systematically studied in simulated concrete pore solution (SCPS). Open-circuit potential measurements revealed that inhibited system showed passive behaviour compared with control system in SCPS. Potentiodynamic polarization studies revealed that inhibitor stevioside offers more than 88% inhibition efficiency at 0.3% concentration in SCPS containing 3.5% NaCl. Similarly, linear polarization resistance and impedance measurements showed higher polarization resistance and charge transfer resistance values, respectively, at 0.3% concentration for inhibited systems when compared with control (without inhibitor).In the second part, the optimized concentration of glucosamine and stevioside showed better performance against corrosion of rebar in the solution study admixed into concrete. The corrosion of TMT rebar embedded in concrete with and without inhibitors is subjected to simulated marine exposure for a period of 180 days and evaluated the corrosion inhibition. Gravimetric weight loss and electrochemical techniques were employed to study the efficacy of inhibitors in SCPS and concrete medium. It is found that the time taken for corrosion-induced cracking in concrete admixed with stevioside inhibitor is approximately 20 times that of control concrete and that stevioside inhibitor is relatively better corrosion inhibitor than other inhibitor reported.

A short-term test method to determine the chloride threshold of steel–cementitious systems with corrosion inhibiting admixtures

Now-a-days, multiple types of corrosion inhibiting admixtures (CIAs) are being used to enhance the chloride threshold (Clth) of steel–cementitious systems. However, due to the application of external potential to drive chlorides, some existing short-term test methods are not suitable to assess the Clth of S–C systems with CIAs containing anions. This paper presents the development of a Modified Accelerated Chloride Threshold (mACT) test to determine the Clth for S–C systems with CIAs. The test specimens consisted of a mortar cylinder with an embedded steel piece and electrodes forming a 3-electrode corrosion cell. The specimens were exposed to chloride solution and the linear polarization resistance tests were conducted every 3.5 days. The corrosion initiation was detected using statistical analysis of the repeated R p measurements. After corrosion initiation, the chloride content in mortar adjacent to the embedded steel piece was determined and defined as Clth. The time required to complete mACT test for an S–C system with CIAs is about 120 days. The Clth of eight specimens each with S–C system containing (i) without inhibitor, (ii) anodic inhibitor [calcium nitrite] and (iii) bipolar inhibitor [both calcium nitrite and amino alcohol] were determined. Both anodic and bipolar CIAs showed enhanced corrosion resistance. Also, the bipolar inhibitor performed better than anodic inhibitor. It was concluded that the use of CIAs could significantly delay the initiation of chloride-induced corrosion. The mACT test can be used to determine the Clth and estimate the service life during the planning and design stages of a project and help select durable materials.

Lessons Learned from the Treat Island Marine Exposure Site

The marine exposure site on Treat Island near Eastport, Maine, was built more than 75 years ago and during this period a wide range of concrete types have been placed on the site. Treat Island represents a very severe exposure condition with the highest tides in the world, salinity typical of the Atlantic Ocean and approximately 100 freeze-thaw cycles per annum. The various research programs that have used this facility have investigated the effects of numerous parameters including fibre-reinforcement, polymer-impregnation, supplementary cementing materials, sulfur concrete, high-alumina cement, ettringite-based rapid-set binders, w/cm and strength, ultra-high-performance concrete, corrosion-resistant reinforcement, impact of load and cracking, “mechanical air-entrainment”, and use of corrosion-inhibiting admixtures. Performance has been evaluated in a number of ways including visual assessment, pulse velocity, dynamic modulus, chloride profiling, and electro-chemical corrosion monitoring. The paper presents an overview of “lessons learned” with detailed information on factors affecting the rate of chloride ingress.

Long-term chloride profiles in bridge decks treated with penetrating sealer or corrosion inhibitors

The long-term influence of three corrosion-inhibiting admixtures and a penetrating sealer on deck chloride profiles were examined on nine different bridges in Wisconsin. Chloride analyses were performed after 12–16years of field exposure to a deicing salt environment. Two of the bridge decks were sealed with a tri-siloxane penetrating sealer at the end of construction without any subsequent reapplication; two were periodically sealed (using the same tri-siloxane product) beginning 4years after construction; two decks utilized corrosion inhibiting admixtures and included untreated control segments; and three decks were completely untreated. Results from the field chloride evaluations indicated that bridge decks treated with the surface-applied penetrating sealer performed comparatively better when such treatments were repeated over time. When the sealer is used early and reapplied periodically, the primary effect is to reduce the effective surface chloride concentration. Two corrosion inhibiting admixtures performed better than their corresponding control sections of the bridge deck. Corrosion inhibiting admixtures resulted in a reduced apparent diffusion coefficient compared to their respective controls. The relative reduction in the diffusion coefficient was larger when the concrete itself had a higher diffusion coefficient.

An organic corrosion-inhibiting admixture for reinforced concrete: 18 years of field experience

Long-term, well documented field experience with organic corrosion-inhibiting admixtures for reinforced concrete is scarce. The present paper contributes to closing this gap of knowledge by reporting 18 years of field performance of a proprietary inhibitor formulation based on alkanolamines (Sika FerroGard 901). Reinforced concrete elements were exposed to chloride-bearing splash water at a road in the Swiss Alps. Periodically, chloride profiles were determined and the specimens were monitored by galvanic current measurements, potential mapping, and electrical concrete resistance measurements. After 18 years, additional electrochemical measurements were undertaken on-site and selected zones of reinforcement steel were visually inspected. While in the reference concrete, corrosion initiated after approx. 8–9 years at a cover depth of 15 mm, the reinforcing steel in the concrete with inhibitor was after 18 years still essentially free from corrosion (at identical cover depth). Thus, under the conditions of the present work, the corrosion inhibitor increased the time to initiation of chloride-induced reinforcing steel corrosion by a factor of approx. 2.

Diffusivity Resistance of Concrete Systems in Chloride Rich Environment for Corrosion Protection of Embedded Steel Bars

Improving concrete performance and minimizing corrosion-induced deterioration of reinforced concrete structures are mandated Building Codes Practices and Specifications in arid regions such as the Arabian Gulf. Concrete structures resist corrosion due to the passivating properties of the hydrated cement around the steel reinforcement created by the high alkaline environment within the composite structure (pH > 12). However, the presence of chloride ions in the pore structure of the concrete destroys this passivating layer, which makes the steel reinforcement vulnerable to chloride-induced corrosion attack that accelerates degradation and deterioration of concrete structures. Corrosion activities-related tests such as Time-to-Corrosion Initiation (Modified ASTM G-109)6, and Corrosion Rate Test (Lollipop Test), can be effectively used to monitor the behavior of corrosion development, while chloride ingress characteristics tests such as Electrical Indication of Concretes Ability to Resist Chloride Ion Penetration ASTM C-1202-91)7, and the Resistance of Concrete to Chloride Ion Penetration (AASHTO T 259-80)8, are applied to evaluate the rate at which chloride ions can diffuse through concrete to onset the time-to-corrosion initiation, which will impact the structure service life and compromise its sustainability. Efforts have been made by scientists to develop mathematical simulation models that predict the service life of the structure based on Ficks Second Law for semi-finite diffusion of chloride ions, concentrated at different concrete depths. The study concluded that mineral admixtures have contributed to the enhancement of concrete performance and its resistance to chloride diffusivity, as well when in combination with corrosion-inhibiting admixture such as calcium nitrite.

Research on Antiseptic and Corrosion-Inhibiting Admixture for Concrete

Concrete buildings in coastal area are dual attacked by chloride and sulfate easily. The erosions make great damage to buildings. This research develops a new type of antiseptic and corrosion-inhibiting admixture for concrete. It is a kind of inner-adding inorganic powder and made up by compaction component, corrosion-inhibiting component and sodium nitrite. The test results show that this admixture has the ability to resistant chloride and sulfate erosion, the admixture also can prolong service life of buildings which are exposed to high concentration of chloride and sulfate.

Influence of a biopolymer admixture on corrosion behaviour of steel rebars in concrete

Among the multitude of concrete structure pathologies, corrosion of rebars is one of the most important problems of concrete durability. In the context of sustainable development, it appears of primary importance to develop new means to protect the rebars against corrosion. This study aims to develop a new eco-friendly and corrosion-inhibiting admixture based on EPS 180 exopolysaccharides, biopolymers used in coatings already studied for the corrosion inhibition on steel in seawater. C15 rebars embedded in CEMI and CEMV cement paste containing EPS 180 were immersed in natural seawater and their electrochemical behaviour was studied using open circuit potential measurements and electrochemical impedance spectroscopy. These tests highlight the decrease of the cathodic reaction kinetics due to the EPS 180 action at the rebars surface, and the absence of effect on the passive layer. Capillary imbibition tests carried out on cement paste and mortars showed that although limiting the imbibition kinetics for cement pastes, the EPS 180 did not influence the water imbibition of mortars. Tests comparing capillary imbibition of soaked cement pastes and mortars with EPS 180 solution and the same samples containing the EPS 180 admixture highlight that the corrosion inhibition induced by EPS 180 admixture is more due to the modification of the cement – rebars interface than to the clogging of the cement porous network.

Effectiveness of Surface-Applied Corrosion Inhibitors for Concrete Bridges

While the effectiveness of corrosion-inhibiting admixtures in new concrete has been well documented, there is little research on their surface-applied counterparts for existing structures. This study was undertaken to assess whether surface-applied products can delay, slow, or stop the corrosion process in contaminated concrete. A total of 348 specimens were tested using six commercially available corrosion inhibitors, at six levels of initial chloride content, and under two accelerated corrosive environments of salt-water spray and wet-dry cycles. Half of the specimens were intentionally cracked before applying the inhibitors, while the others were cracked afterward. Corrosion current and half-cell potential readings were taken weekly during the environmental exposure. Corroded bars were then assessed visually for surface rust and rib loss; and their mass loss and strength reduction were measured. Progression of chloride content over time was measured using companion concrete cubes. The inhibitors generally delayed the onset of corrosion and slowed the process, up to an initial chloride content of 0.5% by weight of cement. Each product seemed effective up to an extent in exposure time and the chloride content. However, no product stopped the corrosion process, and none purged chloride ions. The products may be most effective as preventive measures for fully hardened virgin concrete with initial chloride content below those specified to induce corrosion.

Solution Tests of Corrosion-Inhibiting Admixtures for Reinforced Concrete

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Evaluation of a composite corrosion-inhibiting admixture and its performance in concrete under macrocell corrosion conditions

The objective of this present investigation is to design a composite corrosion-inhibiting admixture system comprising of both mineral and chemical admixtures and to evaluate its performance in concrete under macrocell corrosion conditions. The newly designed corrosion-inhibiting admixture system performed very well in chloride-contaminated concrete. Steel embedded in ordinary Portland cement suffered severe corrosion. In concrete incorporating the designed admixture system, steel showed a 10-fold decrease in corrosion rate of steel embedded in concrete under accelerated macrocell corrosion conditions. The compressive strength of mortars was not affected by adding the designed admixture system.

Effect of Corrosion-Inhibiting Admixtures on Material Properties of Concrete

Several commercially available admixtures have been introduced to inhibit the onset of chloride-induced corrosion of concrete reinforcement. Properties such as workability, set time, strength gain, permeability, and interaction with other admixtures are of concern to ensure proper placement and long-term durability. This paper examines the influence on placement and material properties of a series of commercially corrosion-inhibiting admixtures under laboratory evaluation. Admixture performance was assessed within concrete specimens, relative to the potential for positive or negative effects on characteristic concrete properties. Such properties include slump, air content, heat of hydration, compressive strength, and electrical indication of chloride ion permeability, as well as measured chloride diffusion. The performance of each admixture is discussed, relative to the interrelationships between observed test results.

The Inhibition of Chloride-Induced Corrosion in Reinforced Concrete by Calcium Nitrite

Abstract Reinforcing steel in portland cement concrete is subject to accelerated corrosion in the presence of chloride ions. A corrosion-inhibiting admixture based on calcium nitrite has been shown to confer protection (that is, to inhibit corrosion) if the chloride to nitrite weight ratio (Cl−/NO2−) does not exceed 1.5. Visual observations made on rebars in limewater solutions containing chloride and nitrite ions, current and potential measurements on concrete cylinders with embedded reinforcing bars (rebars), and potential measurements on simulated concrete bridge decks were in substantial agreement.