Initiation Of Reinforcement Corrosion Research Articles

Durability of Concrete Incorporating Corrosion Inhibitors Exposed to a Salt Solution of CL - +SO 4 -2

Laboratory investigations were performed in order to assess the effectiveness of three types of inhibitors, calcium nitrite, ethanolamine and Sika ferro gard 901(commercial inhibitor) with 1%, 2% and 3% concentration by weight of cement for each inhibitor to retarding corrosion of steel embedded in concrete. Concrete specimens were used to assess the effects of corrosion inhibitors on the compressive and tensile strength of concrete and corrosion of reinforcement.Some of the specimens were subjected to wetting and drying cycles and reinforcement corrosion was evaluated by measuring corrosion potentials and corrosion current density. Other concrete specimens were immersed in the salt (Cl-+So3-2) solution and reinforcement corrosion was accelerated by impressing an anodic potential of +12 V from a DC power supply and measuring the time-to-cracking of the concrete specimens.The results indicated that the concrete specimens incorporated corrosion inhibitors of calcium nitrite and Sika ferro gard 901 did not adversely affect the compressive and tensile strength of concrete. Furthermore, the time-to-cracking in specimens contains those two inhibitors (calcium nitrite and Sika ferro gard 901) were higher. Two percent of calcium nitrite followed by three percent of Sika ferro gard 901 were efficient in delaying the initiation of reinforcement corrosion and reducing the rate of reinforcement corrosion current density in the concrete specimens, while all the percentages of ethanolamine corrosion inhibitor were ineffective to delay corrosion of the rebar under the conditions of the study and it's adversely affect the strength.

Durability of Concrete Incorporating Corrosion Inhibitors Exposed to a Salt Solution of CL - +SO 4 -2

Laboratory investigations were performed in order to assess the effectiveness of three types of inhibitors, calcium nitrite, ethanolamine and Sika ferro gard 901(commercial inhibitor) with 1%, 2% and 3%concentration by weight of cement for each inhibitor to retarding corrosion of steel embedded in concrete. Concrete specimens were used to assess the effects of corrosion inhibitors on the compressive and tensile strength of concrete and corrosion of reinforcement.Some of the specimens were subjected to wetting and drying cycles and reinforcement corrosion was evaluated by measuring corrosion potentials and corrosion current density. Other concrete specimens were immersed in the salt (Cl-+So3-2) solution and reinforcement corrosion was accelerated by impressing an anodic potential of +12 V from a DC power supply and measuring the time-to-cracking of the concrete specimens.The results indicated that the concrete specimens incorporated corrosion inhibitors of calcium nitrite and Sika ferro gard 901 did not adversely affect the compressive and tensile strength of concrete. Furthermore, the time-to-cracking in specimens contains those two inhibitors (calcium nitrite and Sika ferro gard 901) were higher. Two percent of calcium nitrite followed by three percent of Sika ferro gard 901 were efficient in delaying the initiation of reinforcement corrosion and reducing the rate of reinforcement corrosion current density in the concrete specimens, while all the percentages of ethanolamine corrosion inhibitor were ineffective to delay corrosion of the rebar under the conditions of the study and it's adversely affect the strength.

The influence of reinforcement steel surface condition on initiation of chloride induced corrosion

This paper describes a part of the work in the development of a “standard” test method for determining chloride threshold values required to initiate corrosion on reinforcement in concrete. The prerequisites of the test set-up are that the test conditions should be reasonably comparable to those in service and the test method should be fairly reproducible and as rapid as possible concerning the slow diffusion nature of the investigated phenomenon. This paper presents the results from a study on the influence of steel bar surface condition on chloride induced corrosion. Various electrochemical techniques were employed in the study to monitor the corrosion behaviour of the embedded bars with three different surface conditions. It is shown that the steel surface condition has a strong effect on the corrosion initiation of reinforcement in concrete, and can likely be the most decisive parameter attributing to the variability in the reported chloride threshold values.

Climate change and corrosion damage risks for reinforced concrete infrastructure in China

A changing climate which leads to increases in atmospheric CO2 concentration, and changes in temperature and relative humidity (RH), especially in the longer term, will accelerate the deterioration processes and consequently decline the safety, serviceability and durability of reinforced concrete (RC) infrastructure. This paper presents an investigation of carbonation-induced deterioration in three typical Chinese cities (Kunming, Xiamen and Jinan) under a changing climate. The changing trends of atmospheric CO2, local temperature and RH of typical Chinese cities are projected based on the latest CO2 emission scenarios. The time-dependent analysis is based on Monte Carlo simulation, and includes the uncertainty of climate projections, deterioration processes, material properties, dimensions and accuracy of predictive models. Deterioration of RC structures is represented by the probabilities of reinforcement corrosion initiation and damage. It was found that the mean carbonation depths by 2100 may increase by up to 45% for RC structures in China due to a changing climate. It was also found that climate change can cause an additional 7–20% of carbonation-induced damage by 2100 for RC buildings in temperate or cold climate areas in China. The findings provide a basis for the development of climate adaptation strategies through the improved design of concrete structures.

Experimental investigation of the relation between damage at the concrete-steel interface and initiation of reinforcement corrosion in plain and fibre reinforced concrete

Cracks in covering concrete are known to hasten initiation of steel corrosion in reinforced concrete structures. To minimise the impact of cracks on the deterioration of reinforced concrete structures, current approaches in (inter)national design codes often limit the concrete surface crack width. Recent investigations however, indicate that the concrete-reinforcement interfacial condition is a more fundamental criterion related to reinforcement corrosion. This work investigates the relation between macroscopic damage at the concrete-steel interface and corrosion initiation of reinforcement embedded in plain and fibre reinforced concrete. Comparisons of experimental and numerical results indicate a strong correlation between corrosion initiation and interfacial condition.

Influence of temporal resolution and processing of exposure data on modeling of chloride ingress and reinforcement corrosion in concrete

The impacts of temporal resolution and processing of exposure data on the long-term chloride ingress and reinforcement corrosion in concrete were studied. Exposure data from one simulated and two real climates was processed to create boundary conditions for a one-dimensional geometry studied using a numerical heat and mass transport model that includes full coupling of heat, moisture and ion transport. Heat, moisture, and chloride concentration distributions were passed to a simplified reinforcement corrosion initiation and propagation model. The numerical study indicates that processing and temporal resolution of the exposure data has a considerable impact on long-term hygrothermal distribution, chloride ingress, and reinforcement section loss results. Use of time-averaged exposure data in the heat and mass transport model reduces the rate of chloride ingress in concrete and affects prediction of reinforcement corrosion initiation and propagation. Randomly sampled exposure data at daily, weekly, or monthly resolution yields prediction of reinforcement corrosion initiation and propagation closer to original resolution results than time-averaged exposure data.

Corrosion resistance of self-compacting concrete incorporating quarry dust powder, silica fume and fly ash

This paper presents the results of a study conducted to evaluate the corrosion resistance of self-compacting concrete (SCC) prepared using quarry dust powder (QDP), silica fume (SF) plus QDP or fly ash (FA). SCC specimens were prepared and tested for corrosion resistance, chloride permeability and chloride diffusion. The results indicated that the time to initiation of reinforcement corrosion in M4 (8% QDP plus 5% SF and w/c=0.4) specimens and M2 (8% QDP and w/c=0.38) specimens was more than that in M5 (30% FA and w/c=0.4) specimens. The corrosion current density on steel in the SCC specimens was very low in the initial stage of exposure to 5% NaCl solution and it increased with increasing period of exposure. Corrosion activation was noted on steel in M1, M3, and M5 specimens. However, it was not noted in M2 and M4 specimens even after 990days (33months) of exposure. The chloride permeability in SCC specimens incorporating QDP or FA was moderate and it was low in the specimens incorporating QDP plus SF. The lowest diffusion coefficient was noted in M2 specimens while it was the highest in M5 specimens.

Climate change adaptation for corrosion control of concrete infrastructure

Abstract The durability of concrete is determined largely by its deterioration over time which is affected by the environment. Climate change may alter this environment, especially in the longer term, causing an acceleration of reinforcement corrosion that will affect the safety and serviceability of concrete infrastructure in Australia, US, Europe, China and elsewhere. This paper reviews advanced simulation procedures to predict increases in damage (corrosion) risks under a changing climate in Australia in terms of changes in probability of reinforcement corrosion initiation and corrosion induced damage due to (i) increase in the concentration of CO2 in the atmosphere, and changes to (ii) temperature and (iii) humidity. These time and spatial variables will affect the penetration of aggressive agents CO2 and chlorides into concrete, and the corrosion rate once corrosion initiation occurs. The effectiveness of adaptation measures for new and existing buildings, bridges, and other concrete infrastructure is then assessed. Carbonation-induced damage risks may increase by more than 16% which means that one in six structures will experience additional and costly corrosion damage by 2100. We show that the impact of climate change on infrastructure deterioration cannot be ignored, but can be addressed by changes to design procedures including increases in cover thickness, improved quality of concrete, and coatings and barriers. For example, an increase in design cover of 10 mm and 5 mm for structures where carbonation or chlorides govern durability, respectively, will ameliorate the effects of a changing climate.

Threshold chloride level and characteristics of reinforcement corrosion initiation in simulated concrete pore solutions

Threshold chloride level ( C th ) and corrosion behavior of reinforced steel bar (rebar) have been studied in three kinds of simulated concrete pore solutions (SPSs). The rebars with two different surface conditions were immersed in SPSs and open circuit potential (OCP) and linear polarization resistance (LPR) were monitored with stepwise chloride addition. Different electrochemical techniques for C th s and rebar corrosion initiation of all cases are discussed and compared with results from the literature. The results indicate that C th s acquired from both OCP and LPR techniques are relatively consistent. C th s, represented by the threshold expression [Cl −] or [Cl −]/[OH −], exhibit an increasing trend with increasing SPS pH. Corrosion resistance of both sandblasted and prerusted bars can be improved by raising the pH of the SPS solution; the extent of improvement is more pronounced for sandblasted bars. Once initiated, severe pit corrosion occurs on sandblasted bars with more abrupt OCP and corrosion current density variation exhibited.

Impact of climate change on corrosion and damage to concrete infrastructure in Australia

The durability of concrete is determined largely by its deterioration over time which is affected by the environment. Climate change may alter this environment, causing an acceleration of deterioration processes that will affect the safety and serviceability of concrete infrastructure in Australia, U.S., Europe, China and elsewhere. This investigation of concrete deterioration under changing climate in Australia uses Monte-Carlo simulation of results from General Circulation Models (GCMs) and considers high greenhouse gas emission scenarios representing the A1FI schemes of the IPCC. We present the implications of climate change for the durability of concrete structures, in terms of changes in probability of reinforcement corrosion initiation and corrosion induced damage at a given calendar year between 2000 and 2100 across Australia. Since the main driver to increased concrete deterioration is CO2 concentration and temperature, then increases in damage risks observed in Australia are likely to be observed in other concrete infrastructure internationally. The impact of climate change on the deterioration cannot be ignored, but can be addressed by new approaches in design. Existing concrete structures, for which design has not considered the effects of changing climate may deteriorate more rapidly than originally planned.

Effects of Concrete Mix on Initiation of Reinforcement Corrosion and Chloride Threshold Level

The time-to-corrosion initiation (Ti) of reinforcement and the chloride threshold content (Cth) of a series of G109 concrete slabs were experimentally investigated. Results indicate that Ti is increased by decreasing water-to-cement ratio or increasing cement alkalinity. The effects of a superplasticizer on initiation of corrosion of reinforcing steel bars (rebar) depend on concrete mix. Measurements reveal that chloride contents at both active (anodic) and passive (cathodic) sites increase linearly with the logarithm of Ti regardless of concrete mix, whereas chloride contents measured at anodic sites are always greater than at cathodic sites. Defects at or nearby corrosion anodic spots could facilitate chloride accumulation: rebar corrosion would occur earlier than if no defect were present. Further analysis reveals that the weakest-link theory is applicable to predict the probability of initiation of rebar corrosion, as indicated by the Weibull distributions of Ti and Cth.

Laboratory investigation of reinforcement corrosion initiation and chloride threshold content for self-compacting concrete

Time-to-corrosion ( T i ) of reinforcement in concrete and chloride threshold content ( C th ) are important service life determinants for reinforced concrete structures in chloride-laden environments. In this study, the two determinants of a series of self-compacting concretes (SCC) and regular concretes were experimentally investigated. A new sampling approach for C th determination (milling powder from corrosion active site at the rebar/concrete interface) was adopted to accurately express chloride content resulting in corrosion occurrence. It is found that the T i and C th follow the 3-parameter Weibull distribution. The results indicate that the corrosion initiation of rebar in concrete slabs depends upon both cement alkalinity and superplasticizer. Rebar, embedded in high alkalinity cement SCC, exhibits better corrosion resistance as indicated by the longer T i , higher C th and larger Weibull modulus, m. A larger Weibull modulus indicates that anti-corrosion performance of rebar in slabs is more stable and less scattered. The effects of specific superplasticizer on rebar corrosion resistance are discussed from the viewpoint of air void amount and size distribution at the rebar/concrete interface.

Carbonates, Carbonation and the durability of Reinforced Concrete Marine Structures

SummaryRecent observations derived from actual structures show that compared to other concretes, concretes containing high levels of carbonates (such as limestones and dolomites) tend to have longer reinforcement initiation times and also much longer durations before the occurrence of active corrosion causing obvious damage. This is provided that the structures do not suffer from poor workmanship, alkali reactions or other failure mechanisms. These findings are reviewed and a small number of additional examples given. The observations are consistent with careful laboratory experiments available in corrosion science literature. However, they are not consistent with the conventional wisdom that associates reinforcement corrosion initiation with the formation of calcium carbonate within the concrete matrix, such as caused by the influx of carbon dioxide from the environment. To cause initiation other processes, such as alkali leaching, must occur to lower the pH to around 8.5 or lower. Only this level of pH is consistent with electrochemistry fundamentals for initiation of steel corrosion. These observations have implications for achieving durable concrete structures.

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.

Critical chloride content for reinforced concrete and its relationship to concrete resistivity

AbstractThe critical chloride content for initiation of reinforcement corrosion is an essential element in service life design and modelling of concrete structures. The critical content is laden with questions regarding its definition, experimental assessment and practical aspects. It should be addressed by a statistical approach. The paper discusses such issues, presents experimental evidence and considers its relationship to the electrical resistivity of concrete. A low concrete resistivity can be theoretically argued to relate to a low critical chloride content. However, only part of the experimental data supports this. The resolution of available data does not allow distinction with regard to the critical content between cement types.

Numerical Analysis of Moisture Influential Depth in Concrete and Its Application in Durability Design

Determining the moisture influential depth in concrete under drying-wetting cycles is of great interest for investigation of chloride ion transport and thus the initiation of reinforcement corrosion. In this paper, the moisture transport processes during drying and wetting are modeled by diffusion and absorption. A predictor-corrector implicit scheme of finite difference method is used to solve the partial differential equations. The stability of moisture influential depth is then analyzed with the available numerical tool for both initially saturate and unsaturated concretes. The concept of equilibrium time ratio is proposed for drying-wetting cycles by the balance between water loss and intake during drying and wetting. According to this time ratio, drying-wetting cycles are classified into drying-dominated, wetting-dominated, and equilibrium ones. For drying-dominated cycles, the drying front will penetrate gradually into material while the influential depth is determined by wetting; for wetting-dominated cycles, the wetting front will progress into material while the influential depth is determined by drying. This classification has strong engineering implication and can give a more rational division of convection and diffusion zones of chloride ion transport. The case of concrete in marine splash zone is investigated to illustrate the application of influential depth in durability design of concrete structures.

Influence of transverse crack width on reinforcement corrosion initiation and propagation in mortar beams

This paper discusses the relationship between crack widths, chloride diffusivity, and corrosion rate of cracked mortar beams. Flexural loads are introduced to generate crack widths ranging from 29 to 390 µm. The specimens were subjected to accelerated corrosion by immersion in a 5% NaCl solution and a constant voltage of 12 V. In addition, salt ponding tests were conducted to determine the chloride ion transport properties. The results showed that as the crack width increased, the effective diffusion coefficient (corrosion initiation) and mass loss of steel reinforcing bars due to the accelerated corrosion (corrosion propagation) also increased. For crack widths less than about 135 µm, the effect of crack width on the effective diffusion coefficient and mass loss of steel reinforcing bars embedded in mortar specimens was found to be marginal when compared with the virgin specimens. Therefore, it was concluded that the effect of crack width on the corrosion initiation and propagation period was more pronounced when the crack width is greater than about 135 µm. Moreover, a significant amount of self-healing was observed for the cracks that have widths below 50 µm when subjected to the NaCl solution exposure.

硫酸侵食に伴うコンクリート中の鉄筋の腐食性状およびその検査手法

In this paper, corroding process of reinforcement in concrete and mortar subjected to sulfuric acid attack was investigated by visual observation, by measuring profile of sulfate ion and pH with respective indicators, and by measuring corrosion area and weight loss of reinforcement. Application of the electro-chemical monitoring methods (half-cell potential, polarization resistance, and concrete resistivity), which are usually used for reinforcement subjected to chloride induced corrosion, to the sulfuric acid attack was also discussedObtained results showed that sulfate ion affected the corrosion initiation of reinforcement before the cover concrete was dissolved, and that the corrosion initiation can be detected by the concrete resistivity.

Life Cycle Modeling of Corrosion Affected Concrete Structures—Initiation

Control and monitoring of reinforcement corrosion in concrete is of significant practical importance if premature failure of reinforced concrete structures is to be prevented. The detection of the initiation of reinforcement corrosion in concrete marks the beginning of whole life performance assessment for reinforced concrete structures. This paper attempts to present the concept of whole life performance assessment for structures and apply it to reinforced concrete structures located in a marine environment. Models used in the whole life assessment are developed and their statistics derived. A merit of the developed models is that they are derived from data representing concrete structures in real service conditions. The emphasis of the paper is to develop a reliability-based method to estimate the initiation time of reinforcement corrosion in concrete structures. This method can equip structural engineers and asset managers with confidence in decision making in regard to the maintenance and repairs of corroded reinforced concrete structures. It has been shown in the paper that the initiation time for reinforcement corrosion in concrete structures located in a marine environment is negligibly short for the service life consideration.

Effectiveness of corrosion inhibitors in contaminated concrete

Four types of corrosion inhibitors (calcium nitrite at two dosages, calcium nitrate at three dosages and two organic inhibitors at their recommended dosages) were evaluated at five different levels of contamination, i.e., 0.8% chloride; 0.8% chloride plus 1.5% SO 3; seawater; brackish water; and unwashed aggregates. Concrete specimens were used to assess the effect of corrosion inhibitors on the compressive strength of concrete and reinforcement corrosion. The results indicated that the corrosion inhibitors investigated in this study did not adversely affect the compressive strength of concrete. Furthermore, calcium nitrite was efficient in delaying the initiation of reinforcement corrosion in the concrete specimens contaminated with chloride, while both calcium nitrite and calcium nitrate mitigated the corrosive effects of chloride plus sulfate salts or sea water. In the concrete specimens prepared with brackish water or unwashed aggregates, all the inhibitors were effective in reducing the rate of reinforcement corrosion. The type and dosage of corrosion inhibitor were observed to be dependent on the nature and level of contamination.