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Corrosion of reinforcing steels induced by chloride has long been a focal point of research, yet the atomic behavior and mechanism is not fully understood. In present study, we developed a reactive force field (ReaxFF) incorporating the Fe/Cl system based on Density Functional Theory calculations to elucidate atomic-scale behavior and mechanism underlying chloride-induced corrosion of reinforcing steel. Results from ReaxFF simulations employing this force field indicate that the initiation of steel corrosion is catalytically induced by chloride present in the outer layer, and the electron transfer between atoms is identified as a critical factor in corrosion. Specifically, Fe atoms become positively charged, detaching from the matrix surface and dissolving into the solution to form iron chloride compounds with surface Cl, while oxygen atoms turn negatively charged, progressively infiltrating the matrix and combining with Fe to create intricate iron oxide compounds. Furthermore, the entire dynamic process of corrosion oxidation on the surface of the ferritic matrix and the formation of product species has been fully captured. This ongoing corrosion process leads to significant matrix loss from metal surface and a reduction in structural integrity. • The Fe-Cl ReaxFF reactive force field for steel corrosion in chloride-contaminated electrolyte environment was established. • The MD simulations were employed using developed reactive force field to investigate corrosion of Fe submitted to chloride. • Behavior and mechanism of steel corrosion induced by chloride have been unveiled by developed ReaxFF MD simulations. [ABSTRACT FROM AUTHOR]

This study investigates the synergistic effects of chloride ions, carbonation, and relative humidity on rebar corrosion in mortar, elucidating the complex interactions at the rebar-mortar interface. Findings reveal that chloride ions and carbonation significantly alter the volumetric water content and resistivity of mortar, leading to non-binary corrosion behaviour through area effect, ohmic control, and anode-to-cathode ratio. In chloride-free, non-carbonated mortar, the area effect dominates, whereas the presence of chloride introduces ohmic control and a saturation-dependent anode-to-cathode ratio. In carbonated mortar, a distinctive ohmic control mechanism emerges, governed by local ionic conductivity. This study highlights the critical need to consider these combined effects for accurate prediction and mitigation of rebar corrosion in concrete structures. By advancing the understanding of these mechanisms, the research provides valuable insights for improving the durability of reinforced concrete structures exposed to harsh environmental conditions. • Effects of carbonation and chloride on water retention and resistivity in mortar. • Water affects corrosion by area effect, ohmic control, and varying anode-to-cathode ratio. • Different water saturation-dependent corrosion potential in non-/carbonated mortar. • Ohmic control in chloride-rich carbonated mortar is not governed by bulk resistivity. [ABSTRACT FROM AUTHOR]

The present study explores low-carbon steel corrosion in simulated concrete pore solutions with varying pH, focusing on the influence of chloride and/or sulfate ions. Employing electrochemical techniques, ToF-SIMS, XRD and DFT calculations, the results reveals that higher pH strengthens the passivation film and reduces corrosion by limiting corrosive ions adsorption. Notably, sulfate triggers corrosion at higher thresholds, while chloride alone significantly elevates corrosion rates. The presence of both ions shows mitigated corrosion risk due to competitive absorption onto steel interface of sulfate. The two-stage mechanism involving competitive adsorption and catalytic corrosion is initially proposed and elucidates the interaction mechanism of chloride and sulfate during steel corrosion process. • Mild steel corrosion subjected to chloride and sulfate in simulated concrete pore solutions with different pH was studied. • Electrochemical methods, ToF-SIMS, XRD and DFT were used to investigate corrosion behavior and underlying mechanism. • The two-stage mechanism involving competitive adsorption and catalytic corrosion is proposed to elucidate the mechanism. [ABSTRACT FROM AUTHOR]

Shortly after casting, offshore reinforced concrete structures are exposed to sulfate and chloride ions without undergoing any proper curing procedures, which are crucial for enhancing their strength and durability. Furthermore, there persists a lack of comprehensive understanding concerning the coupled impact of the attack of sulfate and chloride ions on cementitious materials with current existing research still yielding conflicting outcomes. This paper investigates the influence of curing on the chemical interactions between low-carbon cementitious materials (substituting 45 % of cement with industrial by-products like slag, fly ash, and metakaolin to reduce CO 2 emissions) and coupled sulfate and chloride ions. To achieve this, powder samples were obtained from prismatic-shaped specimens of ordinary Portland cement (CEM I) paste, binary, ternary, and quaternary blends. Some solid specimens were ground into powder after 24 hours post-casting while others were powdered after a 90-day curing period. Subsequently, the acquired powders underwent exposure to chloride, sulfate, and sulfate-chloride solutions over a duration of 25 days. Results indicate that curing time does not alter the interplay between sulfate and chloride ions in the cementitious matrix. Sulfate presence accelerates chloride ion ingress, while chloride presence mitigates sulfate attack in both uncured and pre-cured samples. However, the curing process accelerates sulfate attack, proven through excessive ettringite and gypsum formation, high consumption of portlandite and AFm, diminution of sulfate ions concentration in the attacking solution after 5 days of exposure, increase of pH of more than 0.5 units, aspect changes observed through visual inspections, and porosity distribution changes showed by an increase of 10 % of the total porosity in the reference mix. Additionally, curing promotes the formation of Friedel's salt, thereby attenuating chloride ions ingress. [Display omitted] • Chemical interactions of sulfate-chloride attack are highlighted. • The presence of sulfate accelerates the chloride ingress in the materials. • Chloride diffusion mitigates the sulfate attack in the materials. • Curing duration does not affect the sulfate-chloride coupling chemical process. • Raman spectroscopy serves as a quick chemical characterization technique on solutions. [ABSTRACT FROM AUTHOR]

Electroosmosis (EO) is considered as a base for methods in drying moist masonry. EO and the other transport mechanisms, namely electromigration and diffusion, that can influence EO in the bricks, were studied in four Danish bricks with different manufacturing years and locations. Brick cubes were cut from each brick type and then saturated in NaCl 0.1 M solution. A cell with four electrodes was used to measure the electroosmotic permeability coefficient using a phenomenological approach based on non-equilibrium thermodynamics. The effective diffusion coefficient for chloride and electromigration coefficient were calculated. Results showed that the EO flux obtained in the bricks did not follow either the magnitude of zeta potential or ionic content present in the bricks. It was observed that there was a correlation between the EO coefficient and the porous structure of the brick, especially with the pore connectivity, since the bricks with higher pore connectivity and, therefore, with higher effective diffusion coefficient had a higher electroosmotic coefficient. • The phenomenological approach can be a suitable method to measure electroosmosis in the bricks. • The pore structure of the bricks influences the electroosmotic flow regardless of their zeta potential. • A direct relationship exists between the electroosmosis and the effective diffusion coefficient of chloride in the bricks regardless of the ionic content of the bricks. [ABSTRACT FROM AUTHOR]

To investigate the influence of chloride exposure on hydraulic concrete, we investigated the microstructural changes and pore evolution of aeolian sand concrete (ASC) during prolonged semi-immersion in chloride solution. Our analysis included examining the mass loss rate, relative dynamic elastic modulus, and maximum depth of chloride erosion. Utilizing scanning electron microscopy (SEM), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR), we assessed the microscopic morphology and pore structure evolution. Additionally, we employed fractal theory to evaluate pore structure heterogeneity in ASC before and after exposure to chloride erosion. After 450 days of chloride erosion, ASC displayed minimal changes in mass loss rate and relative dynamic elastic modulus, with a maximum erosion depth of 9.8 mm. Chlorides adhered to the immersed end at the concrete's base and migrated from the surface to the exposed top end during erosion. The erosion depth at the top end ranged from 23.9 % to 25.9 % of that at the bottom end. Within ASC, hydration products reacted with chlorides, resulting in the formation of Friedel's salt, a characteristic corrosion crystal. Following erosion, the total porosity of ASC increased, accompanied by shifts in pore size distribution. The internal structure of ASC underwent distinctive evolution, transitioning from small to large pores. ASC consistently exhibited fractal properties both before and after erosion. The fractal dimension D 1 demonstrated an inverse relationship with pores of radius (r) less than 0.01 μm, while D 2 was directly proportional to pores with r ≤ 0.01 μm and 0.01 < r ≤ 0.1 μm, and inversely proportional to pores with 1 < r ≤ 10 μm and r > 10 μm. This study significantly contributes to the theoretical understanding of ASC's endurance mechanisms in chloride environments. [Display omitted] • Aeolian sand was used to substitute natural river sand as fine aggregate in concrete. • The microstructure change and pore evolution of aeolian sand concrete in chloride solution were investigated. • We study the mass loss rate, relative dynamic elastic modulus, and maximum erosion depth of aeolian sand concrete. • Fractal theory was used to evaluate the pore structure heterogeneity of aeolian sand concrete before and after chloride erosion. [ABSTRACT FROM AUTHOR]

The steel corrosion in Ultra-High Performance Concrete (UHPC) would cause degradation of structural performance or even structural failure. It is an urgent need to monitor and predict the steel corrosion in UHPC, however it is still a tough task. In this paper, Fiber Bragg Grating (FBG) sensors are applied for monitoring the steel corrosion process in UHPC, by combining with steel bar, which is equidistant winding with the sensors, and connected with power supply for accelerating corrosion. The UHPC specimens embedded with steel bars are surrounded by sodium chloride (NaCl) solution, and the steels are artificially corroded with different current densities for investigation. The steel corrosion in Original C60 and Marine Concrete 60 (Marine C60) are applied for comparison. The volume expansion coefficient for monitoring the steel corrosion process, is carried out by FBG sensors, and further comprehensively monitored by three grating sensors. The results suggest that the steel corrosion process in UHPC is slowly with current density lower than 100 μA/cm2, and largely increases with current density higher than 500 μA/cm2, the volume expansion coefficient of corroded steel in UHPC is in range of 2.02–2.62 in this test, which is much different from Original C60 and Marine C60. • FBG sensor has merits in monitoring the steel corrosion process in UHPC. • By observing the wavelength shift of FBG, the steel corrosion process in UHPC is monitored. • The volume expansion coefficients of corrode steel , are carried out for quantitatively predicting the corrosion condition in UHPC. • By applying there grating sensors, the steel corrosion manner in UHPC is comprehensively investigated. [ABSTRACT FROM AUTHOR]

Concrete carbonation has an important influence on chloride penetration. The chloride distribution profiles found in carbonated concrete are often different from those found in uncarbonated concrete even when they have the same exposure conditions. In this paper we present an experimental study on chloride penetration in carbonated concrete specimens when they are subjected to stationary, splash, submerged, and pressured exposure conditions. Free chloride concentration profiles were measured in the specimens to examine the effect of carbonation and exposure condition on chloride diffusion. In addition, material characterisations were carried out using x-ray radiography imaging tests and thermogravimetric analysis to understand the influence mechanism of concrete carbonation on chloride penetration in concrete. The experimental results showed that the chloride distribution curve in carbonated concrete exhibits a second peak under marine exposure conditions. The exposure condition can significantly affect the position and value of the second peak point in the profile. It is also shown that concrete carbonation can drastically change the distribution of pores in concrete, leading to a sudden change in porosity, which is the reason for the carbonated concrete to have the zone-dependent chloride variation profiles. • The chloride distribution curve in carbonated concrete exhibits a second peak under marine exposure conditions. • The exposure condition can significantly affect the position and value of the second peak point in the profile. • The different carbonation zones can be identified based on the distribution curve of the calcium carbonate. • Change in porosity caused by carbonation leads to a zone-dependent chloride variation profiles. [ABSTRACT FROM AUTHOR]

In this paper, a new approach of bidirectional electro-migration rehabilitation (BIEM) using pulse currents was proposed. The effect of the duty cycle and frequency of the square wave pulse current on the BIEM was investigated. The results showed that the desalination efficiency was improved by 10 % with the decrease of duty ratio and frequency. Furthermore, With the increase of duty ratio and frequency, the hydrogen permeation of steel bars decreased by 28.5 %. More uniform desalination efficiency was obtained by using pulse current. The half-cell potential of the rebars was also measured and it was higher for the samples using pulse currents than for those using direct currents, indicating a lower risk of corrosion after pulse current treatment. The pH value of the concrete also increased during the BIEM process. • The amount of hydrogen permeation in the rebars of concrete repaired by pulse current is reduced. • Increasing frequency and decreasing duty cycle of pulse current make the desalination efficiency distributed more evenly. • Decreasing frequency and duty cycle of pulse current will increase the efficiency of chloride ions removal. [ABSTRACT FROM AUTHOR]

The transport of chloride in cement-based materials is influenced by various factors, and the chloride diffusion coefficient in numerical models should be the steady-state value under specific conditions, which is difficult to obtain through traditional experiments. In this article, based on an improved non-contact resistivity instrument, the steady-state chloride diffusion coefficient and porosity of cement-based materials are characterized. Considering the acceleration effect of moisture convection and electric field on chloride transport, a numerical model for moisture and chloride transport coupling diffusion, convection, and electromigration is established. Based on the measured steady-state chloride diffusion coefficient and porosity values, the influence of interface transition zone (ITZ), electric field type, chloride binding effect, initial conditions, and boundary conditions on moisture and chloride transport is numerically analyzed. It is found that the increase of ITZ thickness, electric field strength, boundary concentration, and initial concentration can accelerate chloride transport. The chloride concentration distribution curve exhibits a "shoulder peak" caused by chloride binding effect, and its peak height and width are positively correlated with the chloride binding coefficient. In conclusion, this study aims to better understand the ion transport behavior inside cement-based materials under coupling of convection, diffusion, and electromigration, and identify the key factors influencing this behavior, which provide a feasible scheme for durable design of concrete construction in environments rich in erosive media. [Display omitted] • The chloride diffusion coefficient and porosity of cement-based materials were measured using the improved NC-ERM method. • A numerical model was established for cement-based materials, incorporating convection, diffusion, and electromigration. • Accelerated chloride transport was observed with ITZ thickness, electric potential difference, and concentration. [ABSTRACT FROM AUTHOR]

This research investigates the mechanical behaviour and durability of biochar-added concrete, by comparing the results with those of a standard concrete, in the case of both dry and water curing. More in detail, the corrosion behaviour of rebars embedded in biochar-added concrete during wet and dry exposure (w/d) to calcium chloride solutions was studied by corrosion potential (E cor) and potentiostatic polarization resistance (R p) monitoring, and electrochemical impedance spectroscopy (EIS) and polarization curves recording. Chlorides concentrations were measured, in coaxial cores obtained from unreinforced samples. The results show that biochar addition improves compressive strength of short and long-term dry-cured samples compared to reference concrete. Chlorides diffusion tendency in biochar-added concrete is similar to that of the traditional one. However, the onset of localized corrosion is slightly earlier, because retained water in biochar macroporosities maintains a wet environment around rebars. The results suggest that under dry curing, typical of common structures, the beneficial effects of biochar on compressive strength and the comparable chlorides permeability with respect to reference, make biochar-added concrete an environmentally friendly solution potentially exploitable for reinforced concrete structures. [Display omitted] • Biochar improves concrete compressive strength, especially when dry-cured. • Wet/dry exposure to study corrosion behaviour of rebars in biochar-added concrete. • Chlorides permeability of biochar-added concrete comparable to traditional one. • Water retention of biochar only slightly increased corrosion initiation tendency. • In water cured concrete, rebars passivation not allowed by biochar water retention. [ABSTRACT FROM AUTHOR]

Chloride solution transport in concrete under hydraulic pressure was estimated by finite element method(FEM)-based numerical analysis utilizing experimental data. The method described in this study has been proposed to predict the long-term penetration of chloride solution into concrete, which is difficult through lab-scale experiments. A numerical analysis method was proposed by assuming that the equilibrium equation of the finite element model was a transport equation based on Fick's second law. The diffusion coefficients considering hydraulic pressure necessary for Fick's second law was estimated using short-term experimental data on water and chloride penetration into concrete under hydraulic pressure conditions. Because chloride transport is affected by moisture, we analyzed chloride transport into concrete using water transport analysis. The penetration depth and concentration of water and chloride over time were quantitatively identified and compared with the experimental results for verification. The study provides insights into the durability evaluation of RC structures exposed to underwater environments. • A method to predict chloride movement in concrete under water pressure was proposed. • A FEM-based numerical analysis utilizing experimental data was suggested. • Feasibility of the numerical analysis was verified with the experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a study on the durability testing of a concrete facility located within the North Bay Port region, which has been in service for 200 months. Based on the results of 20 sets of concrete samples, an improved Kolmogorov-Smirnov (K-S) test method and gross error discrimination method are proposed to analyze the random distribution functions of the apparent chloride diffusion coefficient (D app) and the apparent surface chloride concentration (C s), and further explore the time-varying characteristics of chloride ion transmission in concrete. The research shows that the improved K-S method presented in this paper can effectively reduce the probability of type II errors by selecting a rational sample size, which can also improve detection efficiency. When the sample size does not exceed 10, the 2 σ criterion proposed in this paper can effectively identify and eliminate gross errors. In general, D app and C s follow the log-normal distribution, while the time factor (m) follows a normal distribution parameter. The value of C s basically stabilized after exposure to 80 months, whereas D app tended to stabilize after exposure to 100 months. The value of m obtained through fitting short-term experimental data is typically overestimated, and its value decreases as the exposure time prolongs. Therefore, m should also be considered a time-varying parameter that decreases with time. The tested RC structure will begin to experience rebar corrosion after 48.5–60 years of exposure to the marine environment based on the probabilistic assessment. • The 2 σ criterion was introduced to identify and rectify significant errors. • The improved K-S method was developed to minimize the likelihood of type II errors. • Chloride profiles were extracted from 200 months aged harbor concrete structures. • Both D app and C s demonstrated a good fit with the log-normal distribution. [ABSTRACT FROM AUTHOR]

The present study concerned the effect of electrochemical chloride extraction (ECE) to chloride-contaminated concrete on chloride removal with incremental depths after the ECE at 1000 mA/m2 for 2, 4 and 8 weeks. The steel reinforcement was taken as an anode, while the titanium mesh as cathode. The chloride was extracted by diluting concrete dust sample in acid solution and still water for total and free chlorides, respectively. As a result, most free chlorides were removed from concrete at the increased current density, while bound chlorides were quite removed, presumably due to a reduction of the alkalinity of concrete. • A removal of chlorides at electrochemical chloride extraction was studied. • Free chlorides were mostly removed under ECE except at near the surface. • Bound chlorides were quite removed under ECE at all depths. • The ECE lowered the alkalinity of inner concrete pore solution. [ABSTRACT FROM AUTHOR]

The corrosion and oxidation mechanisms of steel in chloride-contaminated environment were studied through the utilization of reactive molecular dynamics simulations with self-developed force fields under various applied electric fields and temperatures. The impact of variations in the external electric field on the thickness of the oxide layer and the dissolution of iron during the corrosion reaction process was scrutinized. The results reveal that under an electric field strength of 10 MV/cm, marginal corrosion was observed within the iron matrix during the simulation period. The surface lattice of the iron matrix retained a relatively intact and regular arrangement. However, under alternative external electric field conditions, as the strength of the external electric field increased, the corrosion behavior of iron in chloride ion solutions became increasingly severe, leading to deeper oxidation levels. Additionally, localized pitting on the iron matrix surface gradually evolved into larger corroded spots. Simulation results within the temperature range studied (278 K, 298 K, 318 K) suggest that temperature elevation amplifies the thermodynamic energy of chemical reactions on the iron surface, consequently leading to a reduction in the bond strength of Fe-O and increase in the corrosion extent. • The Fe-Cl ReaxFF reactive force field for steel corrosion in chloride-contaminated electrolyte environment was established. • MD simulations were employed using self-developed reactive force field to investigate steel corrosion submitted to chloride. • High temperature amplifies the thermodynamic energy of chemical reactions and leads to a reduction in bond strength of Fe-O. [ABSTRACT FROM AUTHOR]

• Method for determining time-varying D ins by natural diffusion test was studied. • The time-dependent models of D ins and D RCM were respectively established. • RCM modified factor was proposed to quantify the relationship between D ins and D RCM. • D RCM modified model was used to predict the chloride concentrations in concrete. • Reasons for the difference between D ins and D RCM were discussed in detail. Chloride diffusion coefficients, which include the chloride diffusion coefficient D RCM measured from the rapid chloride migration (RCM) test, the instantaneous chloride diffusion coefficient D ins and the apparent chloride diffusion coefficient D a determined by the chloride natural diffusion test, are the important indexes for the chloride permeability of concrete. D a denotes the average diffusion coefficient over the whole exposure period. Both D RCM and D ins essentially represent the instantaneous diffusion coefficient, which reflect the influence of real-time changing environmental factors on the chloride permeability of concrete. In this paper, the method for determining the time-dependent model of D ins was firstly studied based on Fick's second law. Subsequently, the time-dependent models of D ins and D RCM were respectively established through the chloride natural diffusion test under artificial simulation marine environment and the RCM test. According to the comparative analysis of D ins and D RCM , the RCM modified factor f (t) was proposed to quantify the relationship between D RCM (t) and D ins (t), and the modified model of D RCM was established. Finally, the suggested modified model of D RCM was applied to predict the chloride concentrations in concrete, which was verified by experimental results. Results showed that the values of D ins and D RCM were identical at the initial exposure time, while D RCM gradually came to be larger than D ins with the increasing of exposure time. The main reason for the difference between D ins and D RCM is that the process of chloride diffusion in concrete is influenced by convection and chloride binding during the chloride natural diffusion test, which can be ignored in the RCM test. [ABSTRACT FROM AUTHOR]

This study developed a methodology for quantifying the corrosion parameters such as corrosion potential, corrosion current density and Tafel slopes for rebar in simulated pore solutions and mortar with realistic rebar conditions. We quantitatively investigated the impact of depassivation duration, chloride concentration, carbonation, and relative humidity on these parameters. Specifically, in partially saturated mortar, it was observed that the critical chloride content lacked a distinct threshold. The degree of depassivation, as indicated by shifts in corrosion parameters due to chloride ions and carbonation, was influenced by humidity. • A critical review of rebar corrosion parameters in solution and concrete. • A non-submerged two-step potentiodynamic test method on rebar corrosion in mortar. • Long-term effect of chloride-induced depassivation in simulated pore solutions. • Measurements of corrosion parameters in simulated pore solutions and mortar. • Effects of chloride, carbonation, and relative humidity on the corrosion parameters. [ABSTRACT FROM AUTHOR]

• Calcium aluminate cement (CAC) imposed the high resistance to steel corrosion. • CAC had a lower chloride binding, but higher buffering to a pH in the matrix. • CAC fall had the lower chloride profile at all depths due to a low surface chloride. The present study concerns the resistance of calcium aluminate cement (CAC) against steel corrosion. Corrosion behaviour of steel, chloride binding/buffering and chloride transport were evaluated to predict the risk of steel corrosion. The CAC mortar had no corrosion of steel, irrespective of the curing temperature and CAC types, while ordinary Portland cement (OPC) indicated a severe corrosion on the steel surface. The chloride binding capacity for CAC was lower than OPC, but the buffering to a pH decrease was highly ranked in CAC paste. Moreover, ingress of chlorides at all depths was reduced in CAC, imposing the mitigated corrosion risk. [ABSTRACT FROM AUTHOR]

• The corrosion inhibition mechanism of VB1, VB3, VB6 and VC has been studied by experiments and quantum chemical calculations. • The variation characteristics of corrosion inhibition efficiency with increasing vitamin concentration are analyzed in depth. • VB6 exhibits better corrosion inhibition efficiency due to stronger bonding stability between HOMO and iron's 3d -orbital. • These four vitamins behave as different types of corrosion inhibitors, depending on the concentration they are added to. The inhibition potency of thiamine (VB1), nicotinic acid (VB3), pyridoxine (VB6) and ascorbic acid (VC) against the reinforcement corrosion and their adsorption behavior on the surface of steel bars in chloride environments are studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. Based on the density functional theory (DFT), quantum chemical calculation is also performed to further reveal the corrosion inhibition mechanism of vitamins at the electronic level. The results indicate that these four kinds of vitamins are proven to be potentially applied as corrosion inhibitors to effectively reduce the risk of chloride-induced reinforcement corrosion in a simulated concrete pore solution with 0.05 M NaCl, and VB6 shows the best corrosion inhibition effect since the bonding stability between its highest occupied molecular orbital (HOMO) and the 3d- orbital of iron is the strongest among these vitamins. Under the experimental conditions of this study, there is a specific concentration value for each vitamin to achieve the optimum corrosion inhibition efficiency (IE%). At this time, VB1 and VB3 act as anodic corrosion inhibitors, while VB6 and VC act as mixed-type corrosion inhibitors. With the increase of vitamin concentration, IE% shows a fluctuating value, which is ascribed to the further aggravated imbalance between the cathode and the anode when the cathodic reaction is inhibited due to the adsorption of polar groups on the steel surface. [ABSTRACT FROM AUTHOR]

• Analysis of UAE environment for main deterioration. • Evaluation of temperature-dependent migration coefficients. • Derivation of activity energy of chloride ion in concrete. • Quantification of temperature effect on strength and migration. • Evaluation of cross-over in strength development. In this study, strength and chloride migration tests were conducted considering nuclear power plant concrete exposed to high temperature and chloride ingress. Two temperature grades (20 ℃ and 50 ℃) were considered for curing and diffusion testing. In the curing at high temperature, cross-over behavior appeared for strength development from 7 to 14 days, however lower migration coefficients were evaluated under high temperature curing conditions. This was because even if cement hydrates were not completely stable, the absorption of chloride was still effective and the pore structure improved due to accelerated hydration. Migration test referred to NT-BUILD 492 method was performed on 40 MPa and 27 MPa concrete of 91 days curing. Activation energy for two strength grades was individually obtained during migration test with chaining temperature to 50 °C. The obtained results were compared with the previous results considering test method (diffusion and migration) and mix proportions. [ABSTRACT FROM AUTHOR]

• The effect of three replacement contents of NA by RA was evaluated. • The mechanical and durability properties of concretes were assessed. • Carbonation, chloride penetration, and service-life prediction of concretes with RA were evaluated. • Surface treatments increase the project service life against chloride penetration. The use of recycled aggregates (RA) is growing due to the environmental problems associated with extracting natural aggregates (NA) and the disposal of construction and demolition waste (CDW). However, the service-life prediction of recycled coarse aggregate concretes remains incipient. Thus, this study aimed to evaluate the effects of different replacement contents of NA by RA (25, 50, and 75 wt%) on physical (water absorption, porosity, and bulk density), mechanical properties (compressive strength and modulus of elasticity), microstructure (evaluated by X-ray microtomography), accelerated carbonation, and chloride penetration of concrete. A service life prediction analysis of RA concretes was conducted based on the chloride profile obtained and considering the application of different concrete surface treatments. The RA contents evaluated increased the carbonation and chloride diffusion coefficients by 75.7% and 43.0%, respectively, compared to the reference concrete. Nevertheless, reductions of approximately 50% on the critical chloride concentration depth of RA concretes are estimated considering the application of acrylic-based surface treatment. Therefore, applying surface treatments is promising to increase RA concretes' durability and service life, contributing to its wide use and dissemination feasibility. [ABSTRACT FROM AUTHOR]

• Produced water can successfully be used as concrete mixing water. • Produced water increases pore formation factor in low w/c systems. • Produced water reduces workability by 20% • Produced reduces setting time by 25% • Concrete with 20% produced water maintain moderate corrosion resistance. The application of alternative non-potable water sources can be leveraged to build infrastructure components that support sustainable industrial operations in regions that experience high frequency of freshwater shortages. This study examines how the use of highly saline produced water (as mixing water) in portland cement mortar impacts workability, setting time, electrical resistivity, pore formation, and microstructure. The results show that produced water decreases both mortars setting time by 30% and workability by 20%. Alkali solubility and pore solution conductivity are also influenced by the produced water-increasing pore solution conductivity by approximately 100 mS/cm. The produced water reacts with the cementitious material to form small deposits of Friedel's salts and calcite that primarily fill the smaller pores in the matrix-thus primarily influencing the pore structure of low w/c mortar systems. In the low water/cement (w/c) produced water mortar systems (0.4), both the pore formation factor (∼2X) and resistivity (∼1.5X) are significantly higher than the control (tap water mortar systems), but in the high w/c systems (0.6) both are slightly lower. The produced water mortar systems also tend to retain more moisture during dry cycling which leads to significantly lower resistivity than the control in air-dried conditions. Diluting the produced water with tap water will reduce moisture retention during dry cycling and increase resistivity. [ABSTRACT FROM AUTHOR]

• FSGC showed 38.1% to 114.2% higher strength than FGC mixes irrespective of NaCl concentration. • Influence of Cl- ions in reducing strength of GPC decreased in the presence of slag and later curing ages. • Steel bar embedded in NaCl added FSGC showed lower E cor and I cor values than FGC mixes. • Formation of C-S-H gel and higher aluminosilicate gels in FSGC confirmed its improved performance over FGC mixes. The evaluation of corrosion behaviour of rebar and changes in microstructure evolution in geopolymer concrete (GPC) in the presence of chloride ions form an important aspect of durability investigation. For this purpose, an experimental investigation was undertaken to examine the corrosion of reinforcing steel and changes in microstructure development of fly ash based geopolymer concrete (FGC) and fly ash-GGBS based geopolymer concrete (FSGC) containing chloride ions. Corrosion behaviour was evaluated through corrosion potential (E cor) and corrosion current density (I cor) and microstructural changes of GPC were examined at various ages and that at rebar level by XRD, EDS, FTIR, and FESEM analyses. Test results revealed that chloride ions had significant influence on consistency, strength, and microstructure of GPC. NaCl improved the consistency of GPC mixes. FSGC mixes showed 38.1% to 114.2% higher strength than FGC mixes at all ages irrespective of NaCl concentration. Further, GPC mixes exhibited lower strength with increase in NaCl concentration at all ages. Rebar embedded in FSGC specimens exhibited mostly less negative E cor and lower I cor compared to FGC specimens. Results of chloride analysis revealed lack of chloride binding in GPC mixes. Higher peak intensity of aluminosilicate gels and presence of C-S-H gel in FSGC mixes as identified from XRD analysis and higher atomic Ca/Si ratio in FSGC mixes obtained from EDS analysis confirmed the improved performance of FSGC mixes in terms of higher strength, lower corrosion activity and lower chloride content over FGC mixes. [ABSTRACT FROM AUTHOR]

• An in-door test for chloride diffusion under a real-time tidal cycle is carried out. • Coupling effects of coarse aggregate (CA) and rebar on chloride diffusion is studied. • Prediction model of chloride diffusion considering the CA and rebar is proposed. Chloride-induced corrosion of steel reinforcement is one of the significant factors for the durability of the reinforced concrete structures exposed to marine environments. Reinforced concrete is a multiphase composite material composed of mortar, coarse aggregate, and rebar. The coarse aggregate and rebar can both affect the chloride diffusion characteristics of concrete. Nevertheless, the current researches related to the effects of the aforementioned two impact factors on chloride diffusion in concrete either considered the coarse aggregate only, or taken into account the steel bar separately. The coupling effects of coarse aggregate and steel reinforcement on chloride transport in concrete required to be further explored and discussed. In this paper, an in-door physical experiment for chloride diffusion in plain and reinforced concrete specimens exposed to marine tidal environment was carried out. The specimens were cast using different volume fractions of coarse aggregate and diameters of steel reinforcement. The chloride concentrations for experimental specimens were measured at various exposure times, and these measurements were adopted to further investigate the common influences of coarse aggregate volume fraction and blocking effect of rebar on chloride diffusion in concrete. Using the impact factors of coarse aggregate volume fraction f (v), the direct and indirect blocking effect coefficients of rebar α (v), β r (Φ/ c) to improve the analytical solution of Fick's second law, a prediction model of chloride diffusion in concrete considering the coupling effects of coarse aggregate and steel reinforcement was proposed. The accuracy of this proposed prediction model was validated by comparing the chloride concentrations evaluated by the prediction model with the experimental measurements. The findings are expected to be useful in realistically predicting the durability of reinforced concrete structures. [ABSTRACT FROM AUTHOR]

• Chloride ions in exposure solution significantly affected formation of compounds in concrete as indicated by XRD results. • OPC exhibited 4.82 and 2.02 times higher apparent chloride diffusion coefficient than PPC and OPC plus fly ash. • PPC exhibited better performance against corrosion as compared to OPC plus fly ash followed by OPC. • Developed empirical relations for OPC and PPC predicted the I corr with higher degree of accuracy for OPC plus fly ash. • Developed empirical relation between E 0 and I corr predicted well the I corr values reported in literature. This study aims to investigate and correlate durability parameters in concrete exposed to external chloride. Tests for corrosion, chloride diffusion, and X ray diffraction (XRD) analysis were performed. Based on results, ordinary Portland cement (OPC) exhibited 4.82 and 2.02 times higher apparent chloride diffusion coefficient than Portland pozzolana cement (PPC) and OPC plus fly ash. Reinforced concrete specimens made with PPC showed better performance against corrosion as compared to those made with OPC plus fly ash followed by OPC. Concentration of chloride ions in exposure solution significantly affected microstructure of concrete as indicated by formation of compounds from XRD results. Developed empirical relationships between durability parameters for OPC and PPC predicted well the corrosion current density for OPC plus fly ash that was independent of model development. [ABSTRACT FROM AUTHOR]

Highlights • Coupling effect of mechanical load and environment load had influence on the durability performance of concrete structure. • Water and chloride penetration into concrete decreased firstly and then increased with the increase of applied load. • Applied load had an obvious influence on the frost resistance of concrete. • Coupling effect had more obvious influence on high water/ratio concrete. Abstract In cold coastal area, the destruction mechanism of reinforced concrete structures is mainly governed by a combination of factors such as self-loading, freeze–thaw and chloride erosion. In this study, ordinary cube concretes (C30 and C50, while w/c = 0.53 and 0.35 respectively) underwent a coupling effect of pressure load with stress ratio of 0, 0.3 and 0.5 and freeze–thaw cycles, following by capillary water absorption test and chloride penetration test. Concrete samples with 0.3 f c showed the best water and chloride penetration resistance under the coupling effect, followed by samples with 0.5 f c and 0 f c , which is consistent with the conclusion that under load only. Water and chloride ions penetration increased sharply when freeze–thaw cycles was over 100 times, which is different with samples without load. Outside part of concrete showed higher permeability and chloride content than inside part. MIP results confirmed that stress played an important role in the water absorption and chloride penetration of concrete under the coupling effect. These results provide important new insights into the permeability of concrete under a coupling effect. The applied load performed a more important role on the service life prediction of concrete structure. [ABSTRACT FROM AUTHOR]

• The direct correlation between corrosion-induced crack widths and bond strength was investigated. • Crack widths can be accurate indicators of bond degradation. • Under some circumstances, corrosion products can flow without developing expansive pressures. • The presence of debonding sleeves on bars subjected to corrosion affects the cracking pattern of the surrounding concrete. • Bond test provisions have limitations if used in combination with accelerated corrosion testing. Corrosion of the steel reinforcement is among the main causes of deterioration in concrete structures. Measures of corrosion levels are typically used to evaluate the subsequent reduction in steel-to-concrete bond, but results lack accuracy. In this study, a new assessment approach based on surface cracks was investigated. Specimens were subjected to accelerated corrosion using an impressed current. With a novel sealing method, mass losses were decoupled from concrete cracking. The results indicate that surface crack widths can be better indicators of bond degradation than corrosion levels. The findings can lead to more accurate assessments and reduced maintenance costs of infrastructure. [ABSTRACT FROM AUTHOR]

• Cation type associated with chloride ions significantly affected compressive strength of concrete. • Boundary potentials of different zones of corrosion were obtained in presence of chloride salts and corrosion inhibitors. • Corrosion inhibitors influenced the effect of cation type of chloride salts on passivity of reinforcing steel. • Cation type associated with chloride ions affected free chloride ion and bound chloride ion concentrations. • Sodium nitrite was more effective in enhancing passivity of steel than di-Sodium hydrogen phosphate. In this research, effect of cation type of chloride salts on corrosion behaviour of steel was determined by potentiodynamic polarization test in concrete powder electrolyte solution in presence of corrosion inhibitors. Results showed that cation type of chloride salts not only affected compressive strength of concrete but also passivity of steel and chloride binding. The decreasing trend of bound chloride concentration was C B: CaCl 2 > C B: MgCl 2 > C B: NaCl. Formation of various compounds in concrete was confirmed through XRD and FTIR spectroscopy analyses. Sodium nitrite was more effective in enhancing passivity of steel than di-Sodium hydrogen phosphate. [ABSTRACT FROM AUTHOR]

Abstract The investigation of the hydration behavior of cementitious material with sea water has drawn a great attention for several decades since the dissolved Cl− ions in sea water may significantly affect the micro scale reactions. And the evolution of micro scale reaction of fresh cementitious material will determine the later performance of the hydration products and structures. In the past, thermal analysis and image amplification equipment were normally used to reveal the changes of microstructure of cementitious materials indirectly and a directly respectively. The major drawback of these methods is that temperature is a kind of coarse experimental parameter susceptible to environmental impact so that is not able to sensitively detect tiny variation of microstructure. Also, image amplification equipment, i.e. SEM, TEM and optical microscopes could only capture instantaneous images which are insufficient to describe the continuous processes. Therefore, in this study, an attempt was made to take advantage of a non-contact monitoring method which is good at both continuously detecting the hydration process of cementitious materials and investigating the microscale chemical and physical variations of liquid phase at the micro scale, i.e., the conductive material. It is found that the replacement of regular mixing water with seawater will evidently change the early stage hydration behavior of cementitious materials. And the seawater is found to take part in the microstructural development of cementitious materials, which can change the hydration rate and hydration degree of the cement-based material structure and its electrical conductivity after deceleration of hardening. [ABSTRACT FROM AUTHOR]

Highlights • Pore structure of HFPC concrete is obviously optimized by addition of SF. • MK contributes to form more aluminate hydrates enhancing binding capacity of chloride. • The elevated temperature is detrimental to resistance of chloride penetration. Abstract As a typical kind of sulphate resistance Portland cement (SRPC), high-ferrite Portland cement (HFPC) has drawn extensive interesting, and is expected to be used in marine environment, but the low chloride resistance is a primary issue and requires to be notably enhanced. This study therefore has investigated the effects of the curing temperature and supplementary cementitious materials (SCMs) on chloride migration in HFPC precast concrete. The results show that two representative SCMs, namely, silica fume (SF) and metakaolin (MK), could significantly improve the resistance of steam cured HFPC concrete to chloride permeation. The improving mechanism of SF is based on optimization of the pore structure to retard migration of chloride, while MK is based on promotion of the chloride binding capacity. This study could give an insight into a new type of precast concrete with excellent sulphate and chloride resistance in marine environment. [ABSTRACT FROM AUTHOR]

Highlights • Temperature and slag composition greatly affect chloride binding in slag cements. • Sulphates reduces chloride binding as Friedel's salt and by sorption onto C-S-H. • Chloride binding differs in 30% slag systems from that observed in 70% slag systems. Abstract The effects of curing temperature (20 °C or 38 °C), slag composition and slag content on the hydration and chloride binding characteristics of ground granulated blast-furnace slag (ggbs) – blended cements have been studied. Two slags (CaO/SiO 2 = 1.05 or 0.94) were each blended with CEM I 52.5R at 30% and 70% replacement. Paste samples of constant 0.5 w/b ratio were hydrated for 56 days, dried and exposed to either sodium chloride or combined sodium chloride – sodium sulphate solutions. Sodium sulphate concentration was 3 g/L, while chloride concentrations varied from 0.1 to 3.0 M. Post-exposure reaction products were characterised by XRD and thermal analysis. Chloride binding was followed via Friedel's salt formation, with thermal analysis showing a decrease in Friedel's salt formation in the presence of sulphate ions. Increasing slag content changed the nature of the chloride binding mechanism significantly. Hydration of slag studied by SEM-BSE image analysis showed that the higher basicity slag was more reactive, with the degree of slag hydration increasing with temperature. An increase in the slag load reduced the degree of slag hydration. Apart from the increase in slag load, the other changes in hydration corresponded well with the chloride binding characteristics of the blends. [ABSTRACT FROM AUTHOR]

Highlights • KMP stabilized soil possesses superior early strength performance. • GM shows higher Cl immobilization, while KMP is better on immobilizing Zn. • Zn-bearing precipitates and Friedel's salt form in GM stabilized soil. • Zn and/or Cl-bearing phosphate precipitates form in KMP stabilized soil. Abstract This study presents a multi-scale evaluation of the effectiveness of two novel binders of reactive magnesia activated blast furnace slag-based binder named as GM and phosphate-based binder named as KMP to stabilize mixed zinc (Zn) and chloride (Cl) contaminated soil collected from an abandoned industrial electroplating company site. The stabilized soils cured at 1, 3, 7, and 28 days were subjected to soil pH, unconfined compressive strength, leachability and Zn speciation tests. The X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy analyses were also performed to investigate the immobilization mechanisms of Zn and Cl in the stabilized soils. The test results showed that the unconfined compressive strength of the soils stabilized with 6% wt GM or KMP after 28 days curing was significantly improved, and the leached Zn and Cl concentrations were well below their corresponding remediation goals. In general, the KMP stabilized soil possessed superior performance in terms of higher unconfined compressive strength in early curing (7 days) and lower leached Zn concentration. While the GM exhibited superior Cl immobilization in the stabilized soil. The X-ray diffraction and energy dispersive spectroscopy results indicated that the Zn-bearing precipitates and Cl-bearing Friedel's salt were the predominant mechanisms of immobilizing Zn and Cl by using GM, while the formation of phosphate-bearing precipitates containing Zn and Cl were the predominant mechanisms of immobilizing Zn and Cl by using KMP. The results demonstrate that both GM and KMP are promising binders in treating Zn and Cl-contaminated soils at electroplating industry sites. [ABSTRACT FROM AUTHOR]

Highlights • A COMSOL-PHREEQC interface is developed to model the multi-species transport. • The interface is based on the physiochemical essential processes of the transport. • The interface is verified by the two published experiments. Abstract A COMSOL-PHREEQC interface based on MATLAB language is developed to simulate a multi-dimensional and multi-species ionic transport for cement-based materials. This interface couples the physical and chemical interactions between pore solution and cement hydrates (PHREEQC) into the Nernst-Planck equations (COMSOL) using a sequential non-iterative approach (SNIA). Based on the thermodynamic insight, the phase-equilibrium model and the surface complexation model are used to express the physical and chemical interactions. In addition, the influence of the variation of the porosity on the ionic transport is considered. Moreover, two reported experiments are taken as an example to illustrate the application of the interface and to verify its accuracy. The results indicate that the developed interface can accurately predict the transport of chloride in cement-based materials. [ABSTRACT FROM AUTHOR]

• Corrosion rate of reinforcements depends on concrete cover in chloride environment. • No cracking observed after 70 years in concrete exposed to carbonation environment. • A new model includes the expansion coefficient of rusts formed in low oxygen environments. • High humidity in concrete pipes greatly delays oxygen diffusion and corrosion process. • For chloride and carbonation, 25 mm and 20 mm concrete covers respectively suffice for 100-year service-life of pipelines. In this study, concrete cores extracted from different underground reinforced concrete pipelines exposed to chloride and carbonation environments were investigated. The age of the pipelines was ranging from 43 to 70 years. The main purpose of this study was to determine the minimum concrete cover to reinforcement allowing 100 years of service life with respect to the exposure conditions of the pipelines. Chloride content at the steel–concrete interface, the carbonation depth, the reinforcement corrosion and other concrete durability related properties were assessed. The service-life of the pipelines was thoroughly discussed based on both corrosion rates measured and corrosion induced concrete cracking observed. The high humidity in concrete pipes is suspected to greatly delay oxygen renewal at the steel–concrete interface. Concrete cover of 25 mm and 20 mm seem adequate for 100 years of service life in chloride and carbonation environments respectively. [ABSTRACT FROM AUTHOR]

• SFRC specimens were prepared using 9 wt% NaCl solution. • Performance of SFRC suffered from in-situ chloride attack was monitored. • Carbonation and chloride attack on SFRC were considered together. • SFRC showed no deterioration in the mechanical properties after 14 months. In order to investigate the performance of steel fiber reinforced concrete (SFRC) suffered from chloride attack, the SFRC specimens were prepared using 9 wt% NaCl solution to accelerate the corrosion, and they were also exposed to the high humidity environment (≥90 % RH); meanwhile, the carbonation was also considered. The performance evolution of SFRC suffered from 14 months of in-situ chloride attack was monitored, including compressive strength, flexural property, splitting-tensile property, and so on. The results show that the SFRC specimens showed no deterioration in the mechanical properties after 14 months of chloride attack, while only some corrosion spots were found on the concrete surface, independently of the water to binder ratios and mineral admixtures. The carbonation accelerated the chloride-induced corrosion of steel fibers in the carbonated zone of concrete, but did not result in the reduction in the mechanical properties of SFRC within 14 months of chloride attack. [ABSTRACT FROM AUTHOR]

• Barrier protection from galvanized steel in sulfate-rich grout can be compromised. • Sulfates in alkaline solution develop poor coverage of calcium hyroxyzincate. • Corrosion development of galvanized steel captured by EN technique. Corrosion mitigation strategies for structural steel bridge elements including post tensioned steel components include the use of galvanized steel. The zinc alloy layers and subsequent precipitation of a dense surface oxide in alkaline environments provide beneficial barrier protection to mitigate corrosion. However, severe corrosion of galvanized steel components in contact with sulfate-rich deficient cementitious grout was documented to occur in less than 8 years of bridge service. Electrochemical testing and material characterization showed that the presence of sulfates in alkaline solutions allow for prolonged zinc activity and hindered passivation by the incomplete surface coverage and the precipitation of large sized calcium hydroxy zincate. OCP, LPR, and electrochemical noise (EN) testing showed greater corrosion activity of galvanized steel in chloride and sulfate solutions. EN identified local corrosion activity of the zinc associated to the porous nature of the surface oxide layer. [ABSTRACT FROM AUTHOR]

• Impact of chloride and sulfate salts on chloride transport mechanism was studied. • Inhibitors efficiency for chloride and composite exposure environments was compared. • Inhibitors are effective in reducing free chloride content and chloride diffusion. • Na 2 HPO 4 showed less chloride binding in composite and more in chloride than NaNO 2. In this study, the effect of chloride and their cations on free chloride (Cl f), chloride diffusion coefficient (D c), and chloride binding capability (C BC) of concrete treated with inhibitors, subjected to chloride and composite chloride-sulfate environments was investigated. Results revealed that in absence of sulfate, the Cl f and D c were higher for NaCl, while in presence of sulfate they were higher in CaCl 2. The D c increased and C BC decreased in presence of sulfate. Inhibitors were effective in reducing the Cl f and D c of concrete subjected to various environments. Na 2 HPO 4 showed higher C BC in chloride and lower in composite environments than NaNO 2. [ABSTRACT FROM AUTHOR]

This study contributes to the development of more sustainable systems to limit and adverse the environmental effects as well as the disintegration of artificial Portland cement (APC) concrete structures. In this context, experimental tests were carried out to develop sustainable binders using natural pozzolan (PZ) and perlite (P) with a relatively high cement substitution rate. A certain level of cement replacement with these pozzolans is very advantageous in terms of cost, energy efficiency, environmental benefits, as well as mechanical properties and durability. A number of important properties of concrete such as compressive strength, corrosion resistance, chloride penetration, sulphate resistance have been developed and noted here. The results obtained show that 10% and 20% of natural pozzolan improves the mechanical properties, and it is noted that 10% of the replacement of the cement by pozzolan and 10% of the perlite led to a reduction of the speed of NaCl corrosion. A larger replacement of pozzolan and perlite had a negative effect on corrosion. Finally, it should be noted that sulfate ions did not affect the corrosion. [ABSTRACT FROM AUTHOR]

The present study investigated the physicochemical characteristics of alkali-activated fly ash/slag (AAFS) modified by MgO and the influence of MgO on the chloride penetration resistance of AAFS. MgO was added to replace the fly ash and slag at dosages of 0%, 5% and 10% by weight of the binder. Samples were immersed in a 10 wt% sodium chloride solution for 91 days. The results showed that the formation of hydrotalcite was promoted by MgO incorporation. Hydrotalcite was found to be effective in improving chloride penetration resistance. However, there exists a threshold level upon which the amount of hydrotalcite may not further increase the chloride penetration resistance. In addition, the adsorption of chloride in AAFS can be seen not only as the result of effects of hydrotalcite but also as the combined effect of the pore network structure and pore solution chemistry. [ABSTRACT FROM AUTHOR]

Concrete structures are frequently suffered to physical and chemical damage in the service period and then cracking is unavoidable. Cracks provide rapid access to aggressive agents and have a significant effect on the durability and service life of concrete structures. In this work, water and chloride transport in cracked mortars were investigated systematically. Firstly, the dynamic process of water transport in cracked mortars was visually monitored by X-ray CT and water absorption of cracked mortar was also quantitatively investigated by the gravimetric method. Later, chloride transport in saturated and unsaturated cracked mortars was studied by natural immersion method. What’s more, the effect of gravity on chloride transport in cracked mortar was considered in this study. The results show that the threshold crack width for water absorption of cracked mortar is 0.1 mm. The effect of crack width on chloride transport in saturated and unsaturated mortars is different. The gravity effect improves the rate of chloride transport in cracked mortars. [ABSTRACT FROM AUTHOR]

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 D a and the surface chloride concentration C s values were time and stress dependent with a sudden change threshold value of approximately 0.3 f c . 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 D a and C s into account. [ABSTRACT FROM AUTHOR]

Based on the field exposure test in a marine tidal environment, the free chloride concentrations of nine concrete mixtures at different exposed times were obtained. Then the apparent chloride diffusion coefficients in concrete were calculated by Fick's second law, according to the calculated values and the time dependent characteristic, the method for analyzing the instantaneous chloride diffusion coefficient of concrete was studied. Furthermore, effects of water to binder (W/B) ratio, admixture and exposure time on the age reduction factor of apparent diffusion coefficient and instantaneous diffusion coefficient have been analyzed respectively. The suggested time dependent model of instantaneous chloride diffusion coefficient was verified by the measured chloride concentrations. Results show that the convection zone has been appeared in test concrete at 120 d exposure time, and the addition of admixtures can reduce the free chloride concentrations effectively. Besides, the instantaneous chloride diffusion coefficients are all less than the corresponding apparent chloride diffusion coefficients, the difference between them decreases with W/B ratio, but increases with admixture, except silica fume. In addition, at 360 d exposure time, the age reduction factor of instantaneous diffusion coefficients tend to be stable generally. Based on the time dependent model of instantaneous chloride diffusion coefficient in concrete at 360 d exposure time, the derived instantaneous chloride diffusion coefficients can be well coincident with the fitted calculated by the measured chloride concentrations. In addition, the relative error of chloride concentration between the values predicted by the time dependent model of instantaneous diffusion coefficients and the measured values is less than that predicted by the time dependent model of apparent diffusion coefficients. [ABSTRACT FROM AUTHOR]

The present study concerns the resistance of silica fume (SF) concrete against chloride-induced corrosion, when SF concrete is built in a chloride-bearing environment. Chloride transport and critical chloride threshold level were experimentally obtained, which were subsequently used for the Fick’s 2nd law to calculate the corrosion-free life. As a result, it was found that SF concrete had lower chloride transport in terms of the apparent diffusion coefficient, due to a refinement of the pore structure, resulting from a further formation of C-S-H gel in the cement matrix. Simultaneously, the surface chloride for SF concrete had a slightly lower range, arising from the lower capacity to bind chlorides. However, SF mortar imposed the increased corrosion risk. The chloride threshold for SF mortar accounted for 0.45% by weight of binder, while OPC produced 0.96%. Despite the increased corrosiveness in SF concrete, SF concrete produced the longer corrosion-free life, compared to OPC. From the sensitivity analysis, a reduction of the parametric values on chloride transport in SF concrete could significantly increase the corrosion-free life. For example, the apparent diffusion coefficient for SF concrete was about 74% reduced compared to OPC concrete, and thus the time to corrosion was 270% increased. [ABSTRACT FROM AUTHOR]

In this paper, a physically and chemically based model, which describes coupled ion-moisture transport, is used to simulate chloride ingress in concrete elements subjected to wetting-drying cycles in marine environment. Various assumptions are tested, in order to quantify the influence of taking into account dissolution/precipitation kinetics or to underline the differences between complex model and very simple one assuming saturated conditions in the latter case. Numerical simulations are compared to experimental chloride concentration profiles. Experimental data were obtained on OPC concrete (w/c = 0.43) specimens exposed to 6 h/6 h seawater wetting-drying cycles in lab (where RH and T are controlled). The results show that when the initial amounts of hydration products are known, the assessment of the chloride binding parameters is not needed. In addition, including reaction kinetics in the model is essential and improves the predictions compared to a pure thermodynamical approach. Moreover, according to sensitivity analysis the boundary layer thickness that reflects the evaporation kinetics and the “intrinsic” permeability are not important parameters for the studied concrete. Updating at each time step the transport properties in order to account for dissolution/ precipitation of mineral species does not change very much the chloride content profiles as well. Furthermore, simulations carried out in saturated conditions provide similar results to those obtained when accounting for wetting-drying cycles for the studied concrete. Then, it may be possible to use a simpler model (ie saturated conditions), and thus avoid the problematic assessment of the “intrinsic” permeability, to predict the service life of a RC structure cast with the concrete studied. [ABSTRACT FROM AUTHOR]

In this work, the performance of reinforced concrete (RC) beams corroded under various levels of sustained flexural loads was evaluated. A comparison was made regarding the effect of different accelerated corrosion techniques, i.e., galvanic method and artificial climate exposure method, on the corrosion characteristics and structural performance of loaded RC beams. The results show that, regardless of sustained loading, a unique strong linear relationship can be established between the average mass loss of corroded rebar and the maximum corrosion-induced crack width, for both accelerated corrosion techniques. The application of flexural loads during corrosion exacerbates the corrosion in the pure flexural zone and enlarges the spatial variation of corrosion levels in RC beams. However, neither the average mass loss ratio of corroded rebar nor the crack widths can be a reliable way to estimate the residual capacity of the beams. [ABSTRACT FROM AUTHOR]

This paper gives a quantitative comparison of how different curing methods impact the rate of drying and subsequent penetration of lime water and chloride penetration of concrete. Laboratory work is used to investigate a bridge deck concrete mixture cured by two different curing compounds, wet curing of different lengths, and then no curing. The results confirm that wet curing methods reduce the ingress of external chemicals more effectively. The wet curing for even one day provided significant improvement over both curing compounds and no curing. To confirm the findings in the field eight bridge decks were investigated that were cured with a curing compound and wet curing. The field investigation confirms the findings of the laboratory testing and emphasizes the importance of wet curing for long term durability of concrete. This paper provides important quantitative data that can be used to compare these methods and help with making decisions about different curing practices and the impact on the service life of concrete. [ABSTRACT FROM AUTHOR]

The ultrasonic velocity in concrete and the concentrations of ions at different depths along the directional flow of ion erosion were measured under the joint effect of seepage flow and stress fields. The permeability of sulfuric acid and chloride ions in concrete under different pressure head and load were analyzed (pressure head and load are perpendicular to each other). The results show that the concentrations of chloride ion and sulfate ion in different depths of concrete were increased to a certain extent either under the water head pressure or load effect. The differences in water head can induce the variation of ions concentration in the surface layer of concrete and the influenced depth can reach up to 60 mm. The load imposed a similar effect on the ions concentration of different layers and the directions of ion erosion, respectively. The ultrasonic testing results of corroded concrete are consistent with the results of ions concentration measured by spectrometry. [ABSTRACT FROM AUTHOR]

Concrete is the most consumable building material in the world. Marine aggregates are the natural sand and gravels available in the sea or dredged from seabed. Contents of chloride, sulphate and shell in the marine aggregates can influence the properties of concrete and corresponding performance of the concrete structures. However, the limitations of chloride, sulphate and shell contents are set as different threshold values in different countries and/or regions. Some of them are inconsistent or puzzling for user. This paper presents a comprehensive review on the limit values of these contents used in different countries and provides a better understanding on the rationale behind these limit values thorough analysis on the limits of chloride, sulphate and shell content in marine fine aggregates for concrete. Except discussion, in this paper, an experimental study was carried out to evaluate the corrosion of reinforcing steel in concrete mixed with DMS as well. The experimental results of corrosion potential and corrosion current density showed that the rebar in DMS concrete should be safe from corrosion when the chloride content in DMS is less than 0.18% or the total chloride content in concrete is less than 0.34%. This study can contribute to fill the knowledge gap on concrete applications on dredged marine sand (DMS) and relative research. [ABSTRACT FROM AUTHOR]

This paper presents a critical review of existing studies on the effects of using sea-sand and/or seawater as raw materials of concrete on the properties of the resulting concrete, including its workability, short- and long-term strength as well as durability. It has been shown by existing research that concrete made with sea-sand and seawater develops its early strength faster than that of ordinary concrete, but the former achieves a similar long-term strength to the latter. Existing studies have also shown that the use of sea-sand and seawater may have a significant effect on chloride-induced steel corrosion but has only a negligible effect on the carbonation process of concrete. Strong evidence exists that a combination of mineral admixtures for the concrete and reinforcement with fiber reinforced polymer (FRP) can effectively solve the durability problem associated with the abundance of chloride ions in sea-sand seawater concrete (SSC). Such use of SSC also offers a good opportunity for the incorporation of recycled coarse aggregate (RCA) in concrete, particularly those that have been chloride-contaminated, as has been demonstrated by some preliminary research. The current understanding of the behavior of SSC, as summarized in the present paper, provides a solid basis for further research in the area to enable the wide use of SSC in concrete construction worldwide, particularly when combined with FRP as the reinforcing material. [ABSTRACT FROM AUTHOR]

Sulphate containing environments are aggressive and cause damage to cementitious materials by means of cracking, spalling and strength loss. In realistic conditions, sulphates may be found in combination with e.g. chlorides. Therefore, to predict concrete’s durability, it is important to understand the (combined) attack mechanisms and estimate their effect. This study aimed to elucidate especially the influence of chlorides on magnesium sulphate attack at two different relevant temperatures (5 °C and 20 °C) and for mortars with different binders, including ordinary Portland cement (OPC), high-sulphate resistant Portland cement (HSR) and a binder composed of 50% blast-furnace slag (BFS) and 50% ordinary Portland cement. Mass change measurements were performed to examine the influence of Cl − on MgSO 4 attack, and XRD-analyses to identify phase changes. It can be concluded that the influence of Cl − on MgSO 4 attack is temperature and binder type dependent. The presence of chlorides does not affect deterioration due to magnesium sulphate for OPC and HSR at an environmental temperature of 20 °C, however, it increases the degradation when BFS is used as partial binder and/or when temperature decreases to 5 °C. The presence of BFS decreases the formation of a protecting brucite layer and favours decomposition of calcium silicate hydrates to magnesium silicate hydrates. At 5 °C the degradation involves thaumasite formation, and is more equal for the different binders and quite severe. [ABSTRACT FROM AUTHOR]