Surface Chloride Concentration Research Articles

The effect of crack width on chloride threshold reaching time in reinforced concrete members

In this study, the effects of changes in the surface chloride concentration and crack width have been simultaneously investigated. To estimate the corrosion occurrence in cracked reinforced concrete members, various samples with different crack widths were modelled and the finite element method was used to model chloride ingress into the concrete. The results of modelling showed that the effect of crack on the corrosion initiation (time that chloride content reach to threshold values) is dependent on surface chloride concentration, chloride threshold, and distance from the crack. In cases of cracks with higher thickness and higher surface chloride concentration, the effect of concrete cover thickness is the most important factor on increases durability of the cracked RC members.

Comparison of Three Different Methods for Measuring Chloride Transport in Predamaged Concretes

Chloride transport is an important subject for the durability of steel-reinforced concrete structures in chloride-laden environments. There are several different types of tests for determination of the chloride-transport properties of concretes. The understanding of the differences between these tests is critical for choosing the most suitable type of test. Besides, there are different factors affecting the chloride transport in concrete, such as the water/binder (w/b) ratio, cement type or mineral additives, and the stress levels (since concrete structures are designed to withstand different loads). This work aims to evaluate the applicability and feasibility of different chloride-transport tests on concretes predamaged by compression. Moreover, the combined effect of predamage caused by different stress levels and the concrete mix design (w/b ratio, mineral additives) on chloride transport in concrete were investigated. The results show that the chloride profiles and the chloride diffusion coefficients in the chloride sorption + diffusion tests are much higher than those in the chloride diffusion tests, especially for the concretes subjected to higher stress levels. This indicates that the effect of sorption on the increase of chloride ingress into concrete is more significant when the concrete has more microcracks. Sorption was found to have minimum influence on the surface chloride content. The chloride migration coefficients were found to be higher than the chloride diffusion coefficients, especially for the concretes with a higher stress level. The partial replacement of ordinary Portland cement (OPC) with ground granulated blast-furnace slag (GGBS) can significantly reduce the detrimental effects caused by the high stress levels on chloride transport in all three methods.

Corrosion Resistance of a Cr-Bearing Low-Alloy Reinforcing Steel: Effect of Surface Condition, Alkaline Solution, and Chloride Content

AbstractA Cr-bearing low-alloy (LA) reinforcing steel with two different surface conditions (polished surface and as-received ribbed surface) was investigated using various electrochemical measurem...

Chloride Penetration into Concrete under the Coupling Effects of Internal and External Relative Humidity

Chloride penetration frequently happens in an unsaturated concrete; in this case, the chloride migration is under the coupling effects of internal moisture and external relative humidity (RH). Various chloride attack tests were designed in this paper to investigate the effects of internal moisture and external RH (50–100%) on the chloride penetration into an unsaturated concrete, and the chloride content was determined to quantify the chloride migration in concrete. The results highlighted that there was a good correlation between the chloride penetration into concrete and its internal RH. The chloride ion was difficult to penetrate into concrete when its internal RH was below 50%; however, the chloride penetration rate increased when the internal RH of concrete was above 75%, and the chloride migration increased with increasing RH and exposure duration. Water evaporation in concrete increased with decreasing external RH, and an obvious increase in the surface chloride content may be observed when external RH was 50%; however, when external RH was above 75%, the inner chloride content increased and surface chloride content decreased with increasing exposure duration. Simulating the chloride penetration under wet‐dry cycling, the water migration resulted in an increase in the surface chloride content and a decrease in the inner chloride content, and the chloride crystal precipitated on the surface of concrete with a high w/c ratio.

Prediction of Chloride Distribution for Offshore Concrete Based on Statistical Analysis.

Chloride-induced corrosion is the main threat to the service life of concrete structures. In order to better investigate chloride distribution in offshore concrete, this study proposed a new prediction model based on statistical analysis as well as a large body of experimental results collected from various sources. A detailed discussion found that the key influential parameters, such as diffusion coefficient (), surface chloride concentration () and penetration depth () are all highly time-dependent. The exposure zone, water–cement ratio and service time were also considered as relevant factors. The proposed model is then validated by two alternative tests and the results suggest that it is feasible in predicting the chloride content and penetration depth of concrete structures in a marine environment under chloride attack.

A ten year record of nitrate retention and solute trends in a Wisconsin sand plains stream: temporal variation at multiple scales

Nitrate retention is an important ecosystem service provided by streams which reduces nitrogen loads to downstream ecosystems. However, most inferences about nitrate retention and uptake in streams are based on measurements at sub-annual scales. Our objective was to evaluate variation in nitration retention and solute concentrations at weekly to decadal time scales. We measured nitrate and chloride concentration, nitrate flux and nitrate retention in Emmons Creek, a groundwater-dominated, nitrate-rich stream in central Wisconsin during a 10-year period. We used a two-station mass balance approach to measure nitrate retention while accounting for groundwater inputs. Surface water nitrate concentration, nitrate yield and nitrate retention exhibited strong seasonal variation. Seasonal Kendall tests revealed positive trends for surface water discharge, nitrate and chloride concentrations and groundwater chloride concentration, but not nitrate retention. Generalized additive mixed models (GAMM), accounting for serial autocorrelations, also indicated positive trends in surface water nitrate and chloride concentrations but no trend for nitrate retention. Nitrate retention averaged 370 mg NO3-N m−2 d−1 (± 316 SD) and was highest during the spring (512 mg NO3-N m−2 d−1 ± 319), followed by summer (460 ± 322), fall (340 ± 281) and winter (165 ± 212). Nitrate retention rates in Emmons Creek were relatively high compared to most published estimates. However, our results suggest that Emmons Cr. may have saturated its capacity to retain nitrate during a period when nitrate yield from its watershed increased, which is an important finding given the increases in N availability in many regions of earth.

Effect of surface preparation on corrosion of steel rebars coated with cement-polymer-composites (CPC) and embedded in concrete

Nowadays, Cement-Polymer-Composites are widely used to coat steel rebars to delay the initiation of corrosion in reinforced concrete (RC) structures. However, Cement-Polymer-Composite (CPC) coating is sometimes inadequately applied on rusted steel and can lead to premature under film/crevice corrosion. This paper investigates the effect of such inadequate applications of CPC coating and premature corrosion on the service life of RC structures. For this, maximum surface chloride concentrations, diffusion coefficients, and chloride thresholds were determined by a one-year-long laboratory study on the specimens obtained from a 6-year-old bridge and prepared in the laboratory. Studies found that the chloride threshold of inadequately coated steel rebar (i.e., coating on ‘as received’ surface) is significantly lower than that of the adequately coated steel rebars (i.e., coating on ‘sandblasted’ surface). Also, the corrosion initiation time for systems with inadequately coated steel rebar was about 50% less than that of the systems with adequately coated steel rebars. The corrosion mechanisms were justified with micrographs. It is recommended not to use CPC coated steel rebars if adequate surface preparation (say, cleaning/sandblasting) is not implemented.

Approximation of the bridge deck diffusion coefficient and surface chloride concentration from field data

The aim of this work is to analyse the data from in-situ measurements performed on 5 reinforced concrete bridges built between 1937 and 1986, that are a part of the road network in the Czech Republic. The bridges were subjected to the field measurements in order to evaluate the ability of the concrete to protect the steel reinforcement from corrosion, namely the pH and the amount of water-soluble chlorides were evaluated on drilled core samples of concrete. Based on the actual chloride content, the diffusion coefficient and surface chloride concentration were determined. All the data were statistically summarized and the correlations among them were provided. The main focus of this study is to evaluate the non-proportional effect of the amount of chlorides per mass of concrete on the risk of corrosion initiation and to determine the unknown parameters of concrete – diffusion coefficient and surface chloride concentration, based on the numerical model of diffusion.

Service life prediction of chloride-corrosive concrete under fatigue load

Chloride corrosion has become the main factor of reducing the service life of reinforced concrete structures. The object of this paper is to propose a theoretical model that predicts the service life of chloride-corrosive concrete under fatigue load. In the process of modeling, the concrete is divided into two parts, microcrack and matrix. Taking the variation of mcirocrack area caused by fatigue load into account, an equation of chloride diffusion coefficient under fatigue load is established, and then the predictive model is developed based on Fick\'s second law. This model has an analytic solution and is reasonable in comparison to previous studies. Finally, some factors (chloride diffusion coefficient, surface chloride concentration and fatigue parameter) are analyzed to further investigate this model. The results indicate: the time to pit-to-crack transition and time to crack growth should not be neglected when predicting service life of concrete in strong corrosive condition; the type of fatigue loads also has a great impact on lifetime of concrete. In generally, this model is convenient to predict service life of chloride-corrosive concrete with different water to cement ratio, under different corrosive condition and under different types of fatigue load.

Evaluation of service-life prediction model for reinforced concrete structures in chloride-laden environments

Reinforced concrete structures are subjected to several degradation processes that often occur early, especially due to reinforcements corrosion. Therefore, the use of representative models for an accurate service-life prediction of reinforced concrete structures becomes indispensable. Thus, this study is aimed at evaluating the model proposed by Andrade to efficiently predict the chloride penetration in concrete structures. In addition, the input variables of this model, as well as the challenges in obtaining them are analyzed. Andrade’s model was applied in some case studies to verify their efficiency in predicting the chloride penetration in reinforced concrete structures in marine environments. The results indicate that for data with small exposure times, the model yielded similar responses to the chloride penetration in situ, with good results within an error range of 35%, associated with a maximum difference of only 4.6 mm between observed and calculated values. For the data with higher exposure times, the differences were significant, indicating the need for an alteration in order to best determine the increase in surface chloride concentration over time. Thus, it is suggested that the model undergoes modifications, mainly in relation to two fundamental aspects, (i) adopt the growth of the chloride surface concentration over time and (ii) consider the variability of the concrete characteristics and exposure conditions through a probabilistic approach.

Service Life Prediction Method for Concrete and Prestressed Concrete Bridges under Chloride-Aggressive Environments

Abstract The behavior of concrete and prestressed concrete bridges under chloride-aggressive environments during their service life is influenced not only by load (especially fatigue forces) but also by the corrosion environment. At present, the research of working performance and life prediction of bridges mainly focuses on the role of force or takes a single parameter as failure criterion, such as chloride ion concentration and steel bar depassivation. In this article, the service life prediction model of concrete and prestressed concrete bridges subjected to chloride-aggressive environments and fatigue is established, and the interaction of environmental effects and fatigue is taken into full account based on the mechanism of heat and mass transfer in porous media, the metal corrosion theory, and the classical mechanics theory. Taking depassivation as a demarcation point, the calculation method for the service life of concrete and prestressed concrete bridges is developed by analyzing the service life evolution process and determining the failure criterion. The service life of concrete bridges in coastal areas is calculated by the self-compiled program with MATLAB software (MathWorks, Natick, MA), and the results show good agreement with those in the project example. According to the results of the service life calculation with different increments of the number of fatigue loading cycles, ΔN, the increment of the number of fatigue loading cycles ΔN has an influence of no more than 5 % on the service life. This indicates that the calculation is converged and stable and that the calculation results are reliable. The service life of bridges is shortened with the increase of surface chloride concentration of concrete, daily vehicle traffic volume and load level, and the decrease of the concrete cover thickness. The study results are referred to predict the service life of concrete and prestressed concrete bridges under chloride-aggressive environments.

Water and chloride permeability of cement‐based mortar with additions of dehydrated cacti

AbstractBACKGROUNDThis investigation presents experimental results concerning water and chloride permeability of cement‐based mortar specimens fabricated with botanical (green) dehydrated additions such as Nopal (Opuntia ficus‐indica) and Aloe vera. Mortar without such additions served as control. The natural dehydrated additions, Nopal or Aloe vera, were mixed with ordinary Portland cement and sand at different percentages of cement replacement (0%, 1%, 2%, 4%, or 8% of the cement mass). To characterize water and chloride ion transport in such mortars, 5 × 5 × 10‐cm prisms were fabricated (three prisms per mixture).RESULTSThe results showed improvements in both water absorption‐desorption (on average: 10% decrease in capillary absorption; 6% increase in water penetration resistance; 58% decrease in effective capillary porosity; and 2% decrease in capillary sorption) and chloride transport (14% decrease in surface chloride concentration, and 31% decrease in chloride concentration at 7 cm into the mortar) within the dehydrated Nopal replacement mixtures (≤2% of the cement mass). Aloe vera additions did not improve the corresponding parameters of water and chloride ion transport into the mortar.CONCLUSIONSAddition of dehydrated Nopal (≤2% of the cement mass) powder to cement‐based material (mortar) may increase its durability as most aspects of durability are related to the absorption of aggressive agents (water, chloride ions, etc.) into the material through its network of pores. Additions of dehydrated Aloe vera did not improve the protective performance of mortar against water and chloride ion transport and are, therefore, not suitable for increasing the durability of such cement‐based materials. © 2019 Society of Chemical Industry

Study of chloride penetration profiles and surface chloride content of concrete structures exposed to marine environment evaluated at different exposure times

DOI: 10.7764/RDLC.18.3.545 Nowadays, some studies have shown the increasing chloride content of concrete surface (Cs) exposed to marine environments over time. To evaluate this behavior, a comparative analysis was conducted between the chloride profiles in tetrapods located in southern Brazil, obtained from samples extracted at 5 and 9.5 years from four microenvironments To this end, the equation of Fick's second lawconsiders the time-dependent Cs variation, a model was prepared for each exposure time profile measured from each microenvironment, which considered the Cs variation since it increased significantly from 5 to 9.5 years. The models obtained from the profiles measured at 5 years were used to estimate the profile at the exposure time of 9.5 years and then compared with the real profiles measured at 9.5 years. The same procedure was used for the profiles measured at 9.5 years, that is to say, a 5-year profile was estimated and compared with a profile measured at the same exposure time. This shows the efficiency of the model. According to the research results, profiles of about 5 years are still too premature to be used as an estimate of the residual useful life of a structure, even considering the Cs variation. However, profiles of approximately ten years can be used, and their Cs values may increase. Therefore, research of the Cs values must continue to obtain the corresponding older chloride profiles to assess the behavior of the curves and the efficiency of the suggested model.

Effect of Different Pre-exposure Loading on Chloride Penetration in Reinforced Concrete Specimens

In this study, the effect of various pre-exposure loadings on chloride penetration in concrete beams, reinforced with both normal black and epoxy-coated bars, was experimentally investigated. In-service static and fatigue loads (around 30–35% of the designed loading capacity) were applied to the RC beams before they were exposed to a designed chloride wetting/drying cycles, simulating the seawater attacks at the tidal zone, for about 1 year. At the end of the simulated seawater exposure, the chloride profiles in the uncracked and cracked concrete cover were measured. Apparent chloride diffusion coefficients and surface chloride concentrations were then estimated on the basis of the measured chloride profiles. Results indicated that the differences in initial concrete compaction, load-induced micro-cracks and visible cracks are the main factors affecting the chloride penetration and diffusion coefficients. Fatigue load-induced cracks resulted in increase in chloride penetration in specimens compared with those in unloaded and static loaded specimens with similar initial compaction.

A study of the factors affecting the surface chloride maximum phenomenon in submerged concrete samples

The chloride content analysis of the concrete exposed to chlorides often shows an initial increase in the concentration of chlorides to a maximum point within the first layers from the concrete surface, followed by a gradual reduction in the concentration of chlorides at the lower depths. A review of literature shows that very little attention has been given to the depth (Δx) at which the maximum chloride concentration (Cmax) occurs and its potential impacts on the numerical estimation of the apparent chloride diffusion coefficient (Da) and surface chloride concentration (Cs). This paper studies the influence of water-to-cement ratio (w/c), the concentration of chlorides in the environment, the time-to-exposure, and exposure duration on Cmax and Δx. Results show that w/c does not have a significant influence on Cmax. However, a significant increase in Δx is observed with an increase in the w/c. Results also show that while Cmax has time-variant properties and it increases nonlinearly with the exposure duration, exposure duration has minimal impacts on Δx. In addition, the time-to-exposure and the concentration of chlorides in the exposure environment are found to be significant factors influencing both Cmax and Δx. The findings of this study show that Δx has a significant impact on the numerical estimation of Da and Cs. Because Δx is not limited to the first millimeter of the concrete surface, as specified in ASTM C1556, care must be taken to exclude the layers that correspond to Δx.

Modeling of environmental action for submerged marine concrete in terms of surface chloride concentration

Surface chloride concentration (SCC) of concrete is an important measure for marine environmental action on oceanic concrete engineering. However, existing models of the SCC could not estimate accurately the chloride attack on concrete exposed to submerged marine environment, as they only involve part of the main influential factors. A quantitative multifactor model for environmental action of submerged marine concrete was developed in terms of the SCC in this study. First, the water‐to‐binder ratio, binder type, chloride concentration of seawater, and exposure time were investigated and adopted as major factors in the computation model of the SCC for submerged marine concrete. The two‐phase multiple nonlinear regression technique was proposed for evaluation of the correction factors for different binder type as well as undetermined coefficients. Then a multifactor computational model for the SCC of submerged marine concrete was developed on the basis of a large number of collected test data. Finally, the effectiveness and advantages of the proposed multifactor model for the SCC were demonstrated by comparison with existing models and test data.

Effects of coarse aggregates on chloride diffusion coefficients of concrete and interfacial transition zone under experimental drying-wetting cycles

Chloride ions diffusion into concrete is one of the most significant factors for reinforced concrete (RC) structures exposed to marine environment, and this can deteriorate reinforcing steel in concrete and cause steel corrosion, ultimately, shorten the durability and serviceability of RC structures. In this paper, the in-door physical experiment method was adopted to explore the effects of natural coarse aggregate on chloride concentration profiles and diffusion behaviors for concrete specimens under man-made exposure condition of drying-wetting cycles. All investigations were based on 10 concrete mixture designs containing variable volume fractions and maximum sizes of natural coarse aggregate for maximum exposure period of 170 days. The chloride profiles versus exposure time, coarse aggregate volume fraction and maximum size were discussed in this paper. The time-dependent model of surface chloride concentration, and the multifactor model of chloride diffusion coefficient of concrete specimens included exposure time, volume fraction, and maximum size of coarse aggregate were developed based on the experimental measurements. In addition, an empirical prediction model for estimating the chloride diffusion coefficient of interfacial transition zone (ITZ) by the consideration of coarse aggregate was determined. Finally, the accuracy and reasonability of the two models of chloride diffusion coefficients for concrete and ITZ considering the effects of coarse aggregate were validated in terms of the meso-scopic finite element numerical simulation method for chloride diffusion into concrete.

Chloride ingress into structural lightweight aggregate concrete in real marine environment

This study aims to characterize the chloride ingress into structural lightweight aggregate concrete (SLWAC) in real marine environment. For this, common normal weight concrete (NWC) and SLWAC produced with different water/binder ratios, types of aggregate and types and contents of binder were exposed to submerged, tidal and atmospheric conditions. Chloride profiles were obtained at 1 and 3 years of exposure and their chloride diffusion coefficients, Dcl, and surface chloride contents, Cs, were analysed. At least for water/cement ratios up to 0.55, Dcl was little affected by the type of aggregate, regardless of the exposure conditions. However, Cs and hence the chloride penetration at a given depth were higher in SLWAC with lightweight aggregates (LWA) of higher porosity or without a protective denser outer shell. SLWAC with dense LWA were able to achieve equivalent chloride penetration resistance to NWC with the same composition.

Model of time-dependent and stress-dependent chloride penetration of concrete under sustained axial pressure in the marine environment

The effect of sustained compressive loading on the chloride penetration of concrete was investigated and a self-monitoring loading device was developed. A series of prisms were loaded under five different sustained axial stress levels and four different numbers of wet/dry chloride cycles. Both the apparent chloride diffusion coefficient Da and the surface chloride concentration Cs values were time and stress dependent with a sudden change threshold value of approximately 0.3 fc. A model was proposed to predict the chloride penetration profiles of concrete under sustained axial pressure, taking both the time-dependent and the stress-dependent characteristics of Da and Cs into account.

Using RCPT determine the migration coefficient to assess the durability of concrete

Portland cement concrete and fly ash concrete were subjected to the ASTM C1202 rapid chloride permeability test (RCPT). When the RCPT was complete, the chloride profiles of the specimens were determined by collecting concrete powder samples at controlling depths. Based on Faraday's laws of electrolysis, the mass of electrolysis deposition is directly proportional to the quantity of electricity (coulombs). This study showed a same phenomenon that a linear relationship was found between the charge passed during the RCPT and the total amount of chloride obtained from the chloride profile. The total amount of chloride in the specimen can be determined by measuring the 6 h charge passed from RCPT. The chloride profile can be obtained based on the measurement of charge passed and the surface chloride content. After the completion of the RCPT, additional step taken during the modified RCPT procedure entails measuring the surface chloride content. Based on the chloride penetration depth obtained from the chloride profile, a modified RCPT method was used to compute the chloride migration coefficient and assess the chloride permeability of concrete.