Chloride Penetration Profiles Research Articles

Chloride ion permeability of Ultra-high-performance fiber-reinforced concrete under sustained load

This work aims at investigating the effect of multiple microcracks in Ultra-High Performance Reinforced Concrete (UHPFRC) occurring in service conditions on the apparent chloride diffusion which is critical to guarantee the design lifetime. First, series of preliminary static bending tests were carried out on three UHPFRC beams to characterize their flexural response as well as their microcrack distribution measured by Digital Image Correlation (DIC). Then, a special test set-up was designed to apply and maintain a sustained bending moment on the UHPFRC beams. Finally, some accelerated migration tests were carried out on the micro-cracked UHPFRC beams under sustained bending load. The results showed different chloride penetration rates and profiles in tested UHPFRC beams under different loading levels, and the influence of the microcrack's width on the apparent chloride diffusion coefficient of the considered UHPFRC was clearly identified, which is a precious information for better predicting the service lifetime of a UHPFRC structure.

Effect of crack width and wet-dry cycles on the chloride penetration resistance of engineered cementitious composite (ECC)

• Influence of crack width and wet-dry cycles on the chloride ingress in cracked ECC was investigated. • Chloride penetration profile as well as the change of total and water-soluble chloride ion content was measured. • The “maximum phenomenon” is observed for both water-soluble and bound chloride ions profiles under wet-dry cycles. • The change of the mineral phases and porosity is related with the chloride binding behaviour. The resistance of cracked ECC against chloride ingress is mainly governed by the accumulated crack width of all the cracks rather than the maximum width of multiple cracks. However, most studies focus on the influence of a single fine crack (<100 μm), which is far smaller than the accumulated crack width. To this end, this study focuses on a relatively large crack width scale. Cracks with widths of 0.1, 0.2 and 0.3 mm were notched on an ECC specimen. Both NaCl solution immersion and wet-dry cycles conditions were applied. Chloride penetration profile as well as the change of total and water-soluble chloride ion content was measured. Relationship between the bound chloride and water-soluble chloride was studied. X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) tests were carried out to show the influence of crack width and wet-dry cycles on the changes of the mineral phases, porosity and pore size distribution in the vicinity of the crack.

Analysis of alterations presented in a white-concrete façade exposed to a marine environment——A case study in Cádiz (Spain)

&lt;abstract&gt; &lt;p&gt;This study analyses the façades of a white concrete building located in Cádiz (Spain). Numerous sections of the concrete cladding on the façades have become detached and there are clear signs of reinforcement corrosion. For the purposes of this study, the arrangement of the reinforcement was evaluated by georadar (GPR). Cylindrical concrete cores measuring 10 cm in diameter by 15–18 cm in depth were extracted and their carbonation front was evaluated. Samples were characterized by physical properties determination; chemical and mineralogical analysis and the chloride penetration profiles.&lt;/p&gt; &lt;p&gt;According to the results obtained, the concrete used can be considered permeable and porous (16.5–19.7%). Only two sampling points fulfilled the minimum reinforcement coating requirements for this type of environmental exposure, in accordance with current Spanish legislation. The carbonation fronts have reached the reinforcements, causing their depassivation. Depending on the orientation of the façade, the penetration of chlorides from marine spray was observed with a maximum value of 0.250% by weight of cement, without reaching the limit states of durability.&lt;/p&gt; &lt;/abstract&gt;

Effect of Aggregate of Electric Arc Furnace Slag on Durability of Reinforced Concrete Structures in Chloride Environment (Part I)

Durability of reinforced concrete structures including electric arc furnace slag as aggregate in chloride environment is a significant topic to enable their performance stable in their service period. In this study, chloride penetration in recycled concretes including gradation of fine and coarse aggregate that is electric arc furnace (EAF) slag is tested and compared with that of reference concrete including just natural aggregate gradation. To observe chloride penetration effect, concrete samples are exposed to a saline attack firstly; and then, total chloride content and chloride penetration profiles are tested. The Part I of the study argues the effect of aggregate of electric arc furnace slag on durability of reinforced concrete structures in chloride environment in the Introduction and Background section and the Materials and Methods section. Second part of the study is going to present the Results and Discussions section and the Conclusions section. Both part have the Abstract section and Reference section differently each other.

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.

Experimental determination and numerical validation of the chloride penetration in cracked hydraulic concrete structures exposed to severe marine environment

Concrete is one of the most broadly materials that used in hydraulic structures. Both in new and service, and for various reasons, concrete structures are oftentimes cracked. The existence of cracks plays as a catalyst role of reduction the target service life. One of the main reasons of the impairment of the durability of these structures is chloride-motivated corrosion of the iron reinforcement. This paper aims to find, for the first time, the effect of cracks, experimentally and numerically, on chloride penetration in Hydraulic Concrete Structures (HCS) exposed to varied heads of seawater. The experimental results were acquired with Darcy law, by using new laboratory method called Hydraulic Pressure Tank (HPT) with artificial cracked specimens, whereas the chloride penetration profiles were obtained with development Electrical Conductivity Technique (ECT). The numerical simulation results were obtained using microstructure finite element models. A good acceptance between experimental and the numerical chloride penetration results was gotten.

ESTUDO DA VIDA ÚTIL DE ESTRUTURAS DE CONCRETO ARMADO UTILIZANDO MODELO DE DIFUSÃO DIANTE A AÇÃO DE ÍONS CLORETO

Estruturas de concreto armado estão sujeitas a inúmeras manifestações patológicas, sendo a corrosão iniciada pela difusão de íons cloreto uma das mais agressivas e onerosas. Por isso mesmo, diversos estudos têm sido conduzidos para determinar a vida útil dessas estruturas, mas ainda não há pleno consenso. Nesse sentido, este trabalho objetiva estabelecer um padrão de ensaio para determinar a vida útil de estruturas de concreto armado devido a ação dos íons cloreto, além de analisar a variação do coeficiente de difusão ao se utilizar distintas relações água/cimento. Para alcançar tais objetivos, foram adotadas normativas nacionais e internacionais para orientar as etapas de caracterização dos materiais, além da utilização de equações de modelagens de perfis de penetração de cloretos para determinar o coeficiente de difusão e, por consequência, a vida útil da estrutura. Por fim, pôde-se concluir que ao se diminuir a relação água/cimento, houve diminuição da concentração de cloretos em uma determinada camada, proporcionando assim maior vida útil para o concreto armado. Quanto à analise probabilística, foi possível notar que quanto menor a proporção de água e cimento maior o índice de confiabilidade, uma vez que a probabilidade de falhar também reduz.&#x0D; Palavras-chave: Corrosão, Difusão de Cloreto, Vita Útil.

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.

Time-Dependent and Stress-Dependent Chloride Diffusivity of Concrete Subjected to Sustained Compressive Loading

This paper studies the chloride diffusivity of concrete subjected to long-term exposure in a simulated marine environment with sustained compressive loading for up to 224 days. A series of concrete prisms were loaded under five different compressive stress levels (0, 0.2, 0.3, 0.5, and 0.7fc) and were subjected to different numbers (4, 8, 12, and 16) of wet/dry seawater exposure cycles. At the end of each exposure period, the concrete specimens were analyzed to determine their chloride penetration profile, the apparent chloride diffusion coefficient Da of the concrete, and the surface chloride content Cs. It was found that the Da and Cs values are both time and stress dependent and that these two dependencies have complex interactions. The value of Da decreases with time due to the hydration of the cement matrix, whereas the value of Cs increases over time. The effects of compressive stress on the values of Da and Cs strongly depend upon the applied stress level, which has a threshold value at approximately 30% of the ultimate compressive strength. Below this threshold, the value Cs remains constant; after this threshold, Cs increases linearly as the applied stress increases. Below the threshold, the value of Da decreases marginally as the stress level increases. However, above the threshold, Da increases rapidly with the stress level as a result of microcracking. Through regression of the chloride penetration profiles, empirical models are proposed to quantify the dependence of Da and Cs on the exposure time and stress level. The validity of these models is evaluated through comparisons with test results.

Chloride penetration in concrete exposed to cyclic drying-wetting and carbonation

In this paper, the chloride penetration process in concrete exposed to a cyclic drying-wetting and carbonation environment was experimentally characterized. In order to better represent the concrete in service, chloride penetration tests were performed on concrete with various levels of flexural loading and incorporation of supplemental cementitious materials (i.e. blast-furnace slag and low calcium fly ash). The result shows that the chloride penetration profile in concrete is a result of multiple interactive deteriorating mechanisms and dependent on the properties and stress status of concrete itself. Carbonation induces considerable chloride (both free and bound) redistribution in concrete, rendering chloride ions ingress from carbonated region towards un-carbonated region. The incorporation of supplemental cementitious materials makes concrete more vulnerable to carbonation-induced chloride movements due to its less amount of portlandite. The increased magnitude of flexural loading results in higher chloride content in concrete probably by forming some micro-cracks.

Concrete pore structure and performance changes due to the electrical chloride penetration and extraction

Electrochemical chloride extraction (ECE) has been successfully used for reinforced concrete structure repair for those exposed to chloride environment. However, the applied external power field can cause other ionic effects on the concrete pore characteristics resulting in performance changes after treatment, especially for blended cement concretes using fly ash (FA) and ground-granulated blast furnace slag (GGBS). To evaluate this, three concrete mixes, i.e. 100%PC, 70%PC/30%FA, and 50%PC/50%GGBS with w/c ratios ranging from 0.35 to 0.55 were selected. Chloride was electrically driven into the specimens to establish chloride penetration profiles with required depth and then the ECE process was applied to remove the chloride. Pore size distributions and chloride profiles of the specimens were measured at each stage of the electrical treatment to determine any changes due to the electrical chloride penetration and extraction. Accelerated carbonation and chloride re-ingress were then carried out on the ECE-treated specimens to evaluate any changes in concrete performance. The results indicate that the applied ECE treatment obtained a very effective chloride removal. However, the micropore structure characterization shows that the capillary pores increased during both chloride penetration and ECE. The chloride penetration process aggravated carbonation resistance, and the ECE process slightly increased carbonation further. The effect of ECE process on further chloride resistance was found insignificant in pure PC and PC/FA concretes, however, not in PC/GGBS concrete. The application of a hydrophobic surface treatment to retard further chloride re-ingress has been proved to be effective.

Determination of the Corrosion Probability in Reinforced Concrete Structures by Design in Situ Monitoring System

Introduction Corrosion of concrete rebar has been established as the main factor of the premature deterioration of reinforced concrete structures. The occurrence of such phenomena represents mostly the durability problems of the material, especially when the structure is subjected to the chloride ions presence (in marine or high salinity enviroment) and large amounts of carbon dioxide (CO2 ), processes known as chloride penetration and carbonation respectively[1,2,3]. Once the corrosión process has appeared in rebar, these begin to generate large stresses on the layer of concrete around them (due to the iron oxides that accumulate around the transversal area) which over time can generate microcracks, cracks and failure on the general structure[4].Given the importance of preserving civil structures, is evident the strong necessity of obtaining a system with great flexibility to perform the estimation in situ of the corrosive state, capable to dispose the information for immediate consultation anywhere with minimum internet access. Therefore, the present work shows the development and implementation of a system for in situ monitoring of corrosion, for any reinforced concrete structure based on ASTM C876-91[5] standard for measuring half-cell potential, with which it is possible to determine the corrosion probability of rebar in reinforced concrete structures. Also, the equipment performance is presented by using different reference electrodes as Copper / Copper Sulfate (Cu -CuSO4 ), silver / silver chloride (Ag / AgCl) and Zinc / Zinc Sulfate (Zn -ZnSO4 ). Experiments and Results It was obtained a system for in situ monitoring of corrosion for reinforced concrete, that allows to estimate the corrosion probability on rebar, where the user send a text message, to start the test in the system and in return, via GPRS (General Packet Radio Service), the equipment disposes the data trend on a graphic trough a web server on an internet domain (figure 1). The system was tested on a building of the University complex, where its performance was evaluated using three different reference electrodes, obtaining an error over the measurement, between the standard and the system, of 6.62% (figure 2). References (1) ROA-RODRIGUEZ, G., APERADOR, W., DELGADO, A. Calculation of Chloride Penetration Profile in Concrete Structures. International Journal of Electrochemical Science. v. 8, p. 5022-5035, Apr. 2013 (2) HA WONG, S., VELI, S. Corrosion Monitoring of Reinforced Concrete Structures - A Review. International Journal of Electrochemistry Science, v. 2, p. 1 – 28, Jan. 2007. (3) SATHIYANARAYANAN, S., PANJALI NATARAJAN, K., SARAVANAN, S., SRINIVASAN, G. Corrosion monitoring of steel in concrete by galvanostatic pulse technique. Cement & Concrete Composites, v. 28, p. 630-637, May. 2006. (4) SHAMSAD, A., Reinforcement corrosion in concrete structures, its monitoring and service life prediction––a review. Cement & Concrete Composites, v. 25, p. 459 – 471, May. 2003 (5) ASTM Standard C876-09, 1991, Standard Test Method for Corrosion Potentials of Uncoated Reinforcing Steel in Concrete. ASTM International, West Conshohocken, PA, 2003, DOI: 10.1520/C0876-09.

Probabilistic Approach for Durability Design of Concrete Structures in Marine Environments

Corrosion of steel reinforcement due to chloride penetration is a major deterioration mechanism of reinforced concrete (RC) structures exposed to marine environments. In the present paper, a probabilistic model is presented to predict the chloride penetration profile in concrete and the risk of steel corrosion considering the time dependence of both the diffusion coefficient and the surface chloride concentration of concrete. Abundant field data from two projects in China and Japan are respectively collected. The consistency between these field data and the model prediction verified the reliability of this probabilistic model, based on which further parametric analyses were carried out to investigate the effects of different design variables on the probability of steel corrosion.

Improvement of the durability of concrete with recycled aggregates in chloride exposed environment

Recycled aggregates concrete (RAC) becomes an important participant in recycled materials although there are still questionable properties of it, like chloride penetration and diffusion. An extensive experimental campaign was performed in order to evaluate the effect of recycled concrete aggregates (RCA) over some properties of concretes. Composition and mix design influence on the concrete were studied in mixes ranging from 0.45 to 0.60 w/c ratios, with 0%, 20%, 50% and 100% coarse aggregates replacement. Concretes were submitted to saline attack and the total chloride contents were determined as well as the chloride penetration profiles. Both new cement paste and RCA from different concrete mixes were analysed by XRD and SEM in order to evaluate the chlorides binding. A chloride binding phenomenon is detected in RAC which may compensate the RCA higher permeability. According to chloride diffusion results, high RCA content lead to an improvement of durability in RAC with sufficiently low w/c ratio, in terms of chlorides presence.

Strength and durability assessment of self-compacted lightweight concrete containing expanded polystyrene

This paper presents the effect of expanded polystyrene (EPS) aggregate on the strength and durability of self-compacted lightweight concrete (SCLC). SCLC mixes with different water/binder ratios and EPS contents (10, 15, 22.5 and 30 % by volume) were cured in two different curing regimes. Durability properties were investigated by water absorption, electrical resistivity, air permeability and chloride penetration profiles. Results showed that EPS mixes cured in salt/wetting regime mostly show higher levels of compressive strength. SCLC with EPS mostly has a low absorption categorized as “good” concrete quality. After 90 days, mixtures with density higher than 2,000 kg/m3 have low corrosion risk. In these mixtures, corrosion did not really pass the threshold of activity at 2.5 cm covering depth. In addition, air exclusion ratio was observed to be lower for EPS mixes with lower W/B ratio.

Assessment of service life models for determination of chloride penetration into silica fume concrete in the severe marine environmental condition

In the last decades, the Persian Gulf region has experienced significant development in marine construction. But many RC structures are showing signs of deterioration, mainly due to the chloride-induced corrosion of reinforcement. The aim of this study is assessment of basic parameters in long term chloride penetration in severe marine environmental condition. Therefore, five year-old concrete jetties were investigated depending on two parameters, (a) construction method: in situ and precast, (b) exposure conditions: atmospheric, splash and tidal zones. Also some accelerated durability tests were performed on standard samples having similar concrete mixture. Finally, theoretical chloride penetration profiles and corrosion initiation time were estimated by four service life prediction models. Experimental results showed all concrete properties are complying with relevant durability requirements and micro-environment characterization has great influence on chloride penetration. In addition, the obtained results from service life models showed the existence of various uncertainties in parameters of chloride penetration.

해양콘크리트 구조물의 염해 예측 및 유지보수 시뮬레이션시스템 개발

As both laboratory accelerated experiment and field exposure experiment were performed, at recent, the fifth field test at five year exposures was proceeded according to long period experimental plan. Field experiment, for the adoption of the developed evaluation model, which is consisted of the analysis of chloride penetration profile at gate bridges of sea-dike completed 30 years ago was carried out during upgrading the basic evaluation model with analyzing the annual field test data. The surface concentration of chlorides was replaced to the concentration of chloride of inner concrete near the surface chlorides among his research results at basic model. Maage’s suggestion function was accepted too as a diffusion coefficient of chloride after verifying the change of diffusion coefficient by analysis of annual field test data. The comparison of field data with model predictions and the estimation of remaining life time demonstrates that the proposed updated model and maintenance simulation system can be used to predict the chloride penetration profile in the marine tidal zone and appropriate repair period and cost.

Twenty-Year Field Evaluation of Alkali-Silica Reaction Mitigation

To evaluate measures to prevent alkali-silica reaction (ASR) in concrete and to correlate short-term laboratory tests to long-term performance, an outdoor exposure site was established in Kingston, ON, Canada, in 1991. Alkali-silica reactive aggregate was combined into six concrete mixtures using various cements and supplementary cementitious materials (SCMs). Both unreinforced and reinforced 0.6 x 0.6 x 2 m (24 x 24 x 79 in.) beams, and 0.2 x 1.2 x 4 m (8 x 48 x 158 in.) pavement slabs were instrumented and have been monitored for 20 years. The high-alkali cement concrete cracked at 5 years and low-alkali cement cracked after 12 years. The high-alkali cement was replaced with various amounts of SCMs. Two concretes, containing 50% ground granulated blastfurnace slag (GGBFS) and a ternary blend of 25% slag plus 3.8% silica fume interground with a high-alkali portland cement, have neither expanded nor cracked. After 14 years, cores were examined petrographically, chloride penetration profiles were made, and chloride diffusion as well as rapid chloride permeability tests, were performed.

Influence of Boundary and Initial Condition on Durability of Concrete Structures Exposed to Chloride Environment

According to investigations of apparent surface chloride contents and chloride penetration profile of concrete structures exposed to chloride environment, the influences of boundary and initial conditions, geometry parameters such as the geometry dimension and section shape, etc. were discussed. Based on the Fick’s second law of diffusion and different boundary and initial conditions, different analytical models to predict the chloride penetration profile in concrete structural members with different boundary and initial conditions were derived. Some calculations examples were made using those analytical models. Computational results show that the boundary and initial conditions have remarkable influences on chloride penetration profile and service life time of concrete structures. Using prevailing error-function solution model based on the semi-infinite assumption of chloride ingress, the prediction of service life time of concrete structures are over evaluated, in particular for the steel reinforcement in corner of the section. Some modify coefficients should be taken into consideration, concerning the influences of boundary and initial conditions.

Effectiveness of Benzotriazole as Corrosion Protection Material for Steel Reinforcement in Concrete

This paper presents results of an experimental investigation on the effectiveness of benzotriazole (BTA) as anticorrosion material for steel reinforcement in concrete structures. BTA is used in three different corrosion-protection systems: BTA inhibition, BTA coating, and BTA as a hybrid system. Reinforced concrete beams were cast, exposed to a 3% sodium chloride solution, and subjected to drying and wetting cycles to accelerate the corrosion attack. Electrochemical measurement techniques were used to evaluate the corrosion behavior of reinforcement. These measurements include macrocell corrosion current, linear polarization resistance (LPR), corrosion potential (Ecorr), and electrochemical impedance spectroscopy (EIS). Chloride penetration profiles for the concrete cover and visual inspection of the reinforcing steel bars were also obtained. The results show that a BTA-steel complex film was formed on the steel bar. This film improves the corrosion resistance of the reinforcing steel. Second, the applica...