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In this paper, the reinforcement embedded in concrete is taken as the research object. By measuring the corrosion rate of the reinforcement in concrete, the open circuit potential of the primary battery composed of reinforcement and calomel electrode in concrete is measured. The chloride ion concentration on the surface of reinforced concrete was measured in situ by the nano-Ag/AgCl electrode. The chloride diffusion theory and corrosion electrochemistry theory were used to study the corrosion mechanism of reinforced concrete specimens. The corrosion rate of reinforced concrete increases with the increase of time in the initial stage of corrosion and reached maximum after 15 h. The pitting of concrete reinforcement is positively related to the concentration of chloride ion in the environment. [ABSTRACT FROM AUTHOR]

• Created an environment-specific model using historical environmental data and considering GBA-based exposure conditions. • The surrogate model surpasses alternative models with over 99% accuracy across all target variables and scenarios. • Physical and environmental factors' evolving impact on durability and mechanical measurements is disclosed over time. • Impact of global warming on coastal structures underscores non-linear and discrete effects of diverse factors. Long-term exposure to coastal and marine environments accelerates the aging of reinforced concrete (RC) structures, impacting their structural safety and society impact. Traditional assessments of long-term performance deterioration in RC structures involve complex, nonlinear, and time-intensive studies of physical mechanisms. While existing machine learning (ML) methods can assess the lifetime of these structures, they often prioritize data regression over mechanistic interpretation. To enhance the efficiency and interpretability of predicting the life-cycle performance of RC structures, this study introduces a generic framework based on interpretable ensemble learning (EL) methods. The framework predicts life-cycle performance efficiently and accurately, with optimal hyperparameters automatically tuned through Bayesian optimization. Interpretability algorithms clarify the influence of environmental, durability, and mechanical parameters on structural durability and mechanical predictions. Validation employs real-world cases of RC hollow beams in the coastal area of the Guangdong-Hong Kong-Macao Greater Bay Area (GBA). The comprehensive model for RC structures integrates actual data on temperature, humidity, and surface chloride content in the GBA, considering diffusion, convection, and binding effects of chloride ions, corrosion non-uniformity, and crack impact on durability estimation. Comparative analysis with existing ML methods underscores the effectiveness of the framework. The findings highlight the dynamic evolution of feature importance rankings throughout the service life, shedding light on the continuous changes in the significance of different factors when predicting mechanical resistance. [ABSTRACT FROM AUTHOR]

In marine environments, traditional ordinary Portland cement (OPC) and reinforced concrete structures are prone to corrosion, reducing their durability and service life dramatically. Geopolymers, with exceptional corrosion resistance, have great value and application potential in marine engineering. This paper presents a comprehensive overview of the research advances on geopolymer cements and concretes in marine environments in terms of mechanical properties, durability, and structural properties. The research so far has demonstrated that geopolymers exhibit superior mechanical properties and durability due to their denser interface and lower porosity compared to OPC. However, geopolymers have significant brittleness defects, and their performance in marine environments, especially in splash and tidal zones with alternating wet and dry conditions, is severely affected. This is due to the influence of chloride ions, divalent cations, pH, and sulfate in seawater, which promote or inhibit the formation and transformation of reaction products and microstructures, thereby affecting their mechanical properties and stability. Nevertheless, the use of composite technologies such as modified precursors, fibers, and nanomaterials has a positive effect on enhancing their structural properties and durability. This provides guidance and solutions for the application of high-durability, low-carbon emission, and more sustainable building materials in maritime engineering. [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]

In order to improve the effectiveness of electro-migration repair technology, researchers have introduced new materials to address the adverse effects of electrochemical repair on concrete, such as interface softening in reinforced concrete. In this study, a dispersed solution of nano-Fe 3 O 4 was selected as the anode electrolyte. Concrete specimens were subjected to electric treatment for repair, and the entry of nano particles into the concrete under the action of an external electric field was investigated. The microstructure and mechanical properties of the repaired concrete material were analyzed using techniques such as potentiodynamic polarization curve, chemical titration, scanning electron microscopy, energy spectrum analysis, mercury intrusion porosimetry, and pull-out test. The results showed that after 15 days of electrochemical nano-repair, the passivation film on the steel reinforcement was repaired, resulting in a 57 % reduction in corrosion rate and prevention of further chloride ingress, thus improving the corrosion resistance of the reinforcement. Furthermore, the electrochemical nano-repair did not affect the outward migration of chloride ions from the concrete, with a chloride removal efficiency as high as 72.6 %. When the treatment duration was 15 days and the current density was 3 A/m2, the bond strength exhibited the greatest improvement, with an increase of 99.15 %. Compared to electrochemical chloride removal, the electrochemical nano-repair reduced the porosity in the middle and inner layers by 17.8 % and 14.8 %, respectively. Microstructural analysis revealed that the electromigrated nano-Fe 3 O 4 particles were uniformly dispersed within the concrete, replacing harmful byproducts and filling the pores. • Nanoelectric migration enhances the bonding performance of concrete. • Nanofilling concrete micro-pores with iron(III) oxide enhances the microstructure refinement of concrete. • Nano-electromigration repairs passivation film on reinforcing steel. [ABSTRACT FROM AUTHOR]

As one of potential materials for extending the lifetime of reinforced concrete serving in chloride-rich environments, phosphoaluminate cement (PAC) offers excellent chloride binding capacity and superior resistance to chloride penetration. The chloride binding behavior as well as binding routes and mechanisms of the clinker and its hydration products had not been clarified so far. This study revealed that the clinker would preferentially form Friedel's salts through a dissolution-precipitation route in NaCl solutions, thereby binding chloride. This dissolution-precipitation process led to an accumulation of Al3+ in solutions, which negatively affected the subsequent hydration reactivity of the clinker. In the hydration products , the calcium hydroaluminates, mainly as C 2 (A,P)H 8 with minor C(A,P)H 10 , could bind chloride rapidly via an ion exchange mechanism. Through the ion-exchange route, the chemical binding of calcium hydroaluminates to chloride could be completed in less than 1 hour. In contrast, the unhydrated clinker exhibited a slow chloride binding behavior until 72 hours. All these would provide theoretical guidance for using PAC cementitious materials in reinforced concrete to enhance resistance to chloride attack. [Display omitted] • Clinker and hydration product of phosphoaluminate cement all bind chloride directly. • Chloride binding behavior and mechanism differ for clinker and hydration product. • Clinker slowly binds chloride by dissolution precipitation to form Friedel's salt. • Calcium hydroaluminate rapidly binds chloride via ion exchange into Friedel's salt. [ABSTRACT FROM AUTHOR]

A numerical method considering both corrosion kinetics and ion transport is proposed to investigate the distribution of current and chloride ions in a cathodic protection system. The impact of impressed current density, concrete resistivity, chloride ion concentration, rebar arrangement, anode arrangement and thickness of protective layer on the current and ion distribution is discussed. Results show that the rebars located closest to anode exhibit the largest current and lowest chloride ion concentration. The utilization of multiple external anodes proves to be an effective means to enhance the cathodic protection's effect, but it impairs the ability of removing chloride ions. • Rebars closest to anode exhibit the largest current and minimum chloride ions. • The increase of chloride ions results in a uniform current distribution. • The ability of removing chloride ions of ICCP depends on the current of rebars. • Multiple anodes impair the ability of removing chloride ions. • A formula is proposed to determine the required ICCP current density. [ABSTRACT FROM AUTHOR]

Considering the widespread application of carbon fibre-reinforced polymer (CFRP) as a protective material for reinforced concrete (RC) structures, this study focuses on the ability of CFRP laminates with different numbers of layers bonded to the concrete surface to reduce the ingress of chloride ions. Variations in the free chloride concentration distribution in concrete before and after CFRP bonding were explored systematically. Nonlinear fitting was applied to the experimental data to establish a calculation model for the diffusion of free chloride ions in concrete with CFRP bonded to the surface, which was subsequently validated. Based on the proposed model, the reduction in the surface chloride concentration of concrete after bonding different numbers of CFRP layers was quantified as the reduction value. Moreover, recommendations for the durable design of RC structures bonded with CFRP in wet-dry cyclic environments are provided. The results indicate that the surface chloride concentration in concrete increases continuously with increasing wet-dry cycles, eventually reaching a steady state. Compared with the concrete specimens without CFRP bonding, the bonding of one, two, or three layers of CFRP led to reductions in the stable surface chloride concentration of concrete by 70.8%, 82.6%, and 84.9%, respectively. And no obvious convection zone was observed in the concrete after CFRP bonding. The validation results of the proposed calculation model demonstrated its high accuracy, making it suitable for durable design and service life prediction. • Experimental tests address the impacts of concrete bonded CFRP with different layers under dry-wet cycles on chloride ions resistance performance. • A chloride ion diffusion concentration model of concrete bonded with CFRP was established. • The anti-chloride ion penetration effect of bonding 1, 2, and 3 layers of CFRP was quantified. [ABSTRACT FROM AUTHOR]

New-to-old concrete interfaces are commonly found in reinforced concrete (RC) structures due to precast splices, repairs, and construction joints. The interfaces provide access for chloride ions, oxygen, and water, which intrude on the concrete, reducing its durability with new-to-old concrete interfaces. Although the mechanical bonding properties of new-to-old concrete interfaces have been extensively studied, there is a notable gap in the durability of old-new concrete, particularly concerning chloride ion penetration resistance. This paper examined the interface bonding properties and the chloride ion penetration resistance of old-new concrete through ultrasonic nondestructive testing and rapid chloride migration (RCM) tests. Influences of water-cement ratio, casting interval, and interface treatment were considered. The test results indicated that the interface treatment has minimal effect on ultrasonic velocity while the w/c ratio is the primary factor influencing ultrasonic velocity. The bonding quality of the interface between new and old concrete is more accurately reflected by ultrasonic velocity than by the amplitude of the first wave. The chloride penetration in the old and new concrete specimens is primarily influenced by the water-cement ratio and curing age. As the casting interval increases, the difference in the chloride penetration between the new concrete area and the old concrete area becomes more pronounced. When the strength of new concrete exceeds that of old concrete, the chloride penetration at the interface is primarily influenced by the characteristics of the old concrete. The difference in chloride migration coefficients between the interface and new concrete ranges from 40% to 54%, while the difference between the interface and old concrete is only 4.5–22.2%. However, when the new and old concrete has the same strength, the chloride penetration at the interface tends to be closer to that of new concrete. The impact of interface treatment on the depth of chloride penetration is minimal. An influence coefficient was proposed to assess the effect of the interface on the chloride penetration resistance. With a shorter casting interval, the chloride ion penetration resistance is more affected by different interface treatments. As the casting interval increases, this influence gradually diminishes. • The water-cement ratio is the primary factor influencing ultrasonic velocity. • Chloride penetration in new and old concrete depends on the w/c ratio and curing age. • Whether Interface chloride migration is closer to old or new concrete was discussed. • Proposed an coefficient to evaluate the effect of interface on chloride penetration. [ABSTRACT FROM AUTHOR]

In this paper, the mechanism of chloride ion transport in unsaturated concrete considering the nonlinear seepage effect is investigated by indoor experiments and analytical modelling. The concrete sheet imbibition test is used to reveal the nonlinear characters of seepage including water convection and moisture capillary within the unsaturated concrete in case of various water-binder ratios. For modelling purpose, an exponential function is introduced to mathematically depict the nonlinear relation between the specific discharge and hydraulic gradient during both water convection and moisture capillary processes. Based on such nonlinear seepage models, new mathematical models are proposed for the problem of chloride invasion within the reinforced concrete structure. The solution for the mathematical model of chloride transport is resolved by Laplace transform and finite difference method, of which acceptability is verified by the comparison with the results from chloride ion invasion test. The result indicates that, compared with linear seepage law, the use of the proposed nonlinear seepage solution is preferred to depict the saturation-relative humidity curves from concrete sheet imbibition test. The consideration of nonlinear seepage can result in a slower chloride transport rate, which further makes a later flow start-up time and a smaller free chloride iron concentration within the concrete. Such effect can be enhanced with the increase of nonlinear flow degree. The paper provides an effective solution to evaluate the chloride invasion within the unsaturated concrete. • Pioneer proposes solutions considering nonlinear seepage effect on chloride transport within concrete. • Considering nonlinear seepage can better describe the relationship between saturation and relative humidity. • The start-up time of nonlinear flow obviously lags behind that of linear flow. • The occurrence of nonlinear convection-diffusion and capillary diffusion seepage can slow down the penetration of chloride ions. [ABSTRACT FROM AUTHOR]

In this work, novel calibration curves and calibration surfaces of Electromagnetic (EM) characteristics are modeled as a function of the water and chloride contents of concrete. An experimental campaign was carried out on cores extracted from two types of concretes: C1 (Ordinary Portland Concrete) and C3 (62% slag + 38% clinker). The cores were initially saturated at three sodium chloride (NaCl) concentrations and then oven-dried to attain different degrees of saturation. They were tested with the electromagnetic and electrical cell to determine the dielectric permittivity and electrical resistivity, respectively, at the targeted hydric and chloride ion contents. The calibration curves and calibration surfaces, which represent the resistivity and permittivity as a function of chloride content and/or degree of saturation, were adjusted and presented for both concretes. The calibration surfaces developed herein serve as an essential tool to study complex phenomena, such as the coupled water-chloride ingress. • Developing novel calibration curves and calibration surfaces that correlate the permittivity and resistivity of concrete to its chloride and water content. • Investigating the impact of slag on the permittivity and resistivity of concrete. • Proposing a non-destructive methodology to monitor chloride and water content for reinforced concrete structures exposed to a tidal zone. [ABSTRACT FROM AUTHOR]

Reinforced concrete structures in an unsaturated state experiences significant degradation when exposed to combined chloride and sulfate attack in marine environments. For evaluating durability and predicting service life of reinforced structures, it is crucial to better understand ions diffusion, porosity variation and water saturation of concrete. Considering effect of porosity and water saturation degree on chloride diffusivity, a new diffusion-reaction model was established to investigate how concrete degrades exposed to the severe marine environment. The model was validated using experimental results from both hydrophobic and plain concrete that had undergone a 14-month exposure test at the Qingdao Wheat Island exposure station. The simulation results of the multi-ions model showed that both plain concrete and hydrophobic concrete experienced maximum reduction of chloride concentration of about 68% when compared to concrete exposed to the unsaturated condition. • A multi-ion coupling diffusion reaction model considering concrete porosity and water saturation degree was built. • Numerical simulation results are contrasted with experimental results to validate the model. • The service life was effectively influenced by water saturation degree, porosity and surface chloride ion concentration of concrete. • Hydrophobic admixture reduced influence of water saturation degree on chloride content of concrete. [ABSTRACT FROM AUTHOR]

Conventional anti-corrosion techniques provide short-term protection and are only suitable for low contaminate concrete. However, electrochemical techniques benefit highly contaminated concrete, but chlorides may reappear after some time. Developing on these techniques, Bidirectional Electromigration (BIEM) has recently received extensive interest. The present research injected an organic 2- Amino Pyridine Inhibitor into chloride-contaminated concrete under an electric field. The system's effectiveness was tested by measuring the chloride profile, inhibitor profile, change in corrosion rate and steel/concrete potentials. In addition, influence on various parameters such as initial admixed chloride content (1% and 3%), treatment duration (7 and 15 days), applied current density (1 A/m2 and 0.5 A/m2) and inhibitor concentration in the aqueous solution (0.3 M/L and 0.15 M/L) on treatment effectiveness was also investigated. The results indicated that after application of the BIEM, chlorides were extracted and inhibitors were migrated towards the steel bar. Further, chloride extraction and inhibitor migration efficiencies increased by increasing the treatment duration and current density. Additionally, results indicated that BIEM would be more effective for more severely chloride-contaminated structures. • An organic compound, 2 Amino pyridine has been employed in conjunction with ECE technique to protect RC under corrosion. • The technique effectively pushed the chloride ions away from the steel rebar. • The treatment can protect the corrosion with 99% inhibition efficiency. • The corrosion inhibitor forms a protective layer over rebar surface upon reaching its surface. [ABSTRACT FROM AUTHOR]

• Guiding principles to address deterioration due to corrosion are provided. • Available tests of determining the level of deterioration are culled from the literature. • A categorization of solution methods for protection, maintenance, and repair if offered. • A readily-available reference for practitioners and researchers on corrosion for coastal concrete structures. Deterioration due to corrosion is a key issue affecting the durability, safety, and sustainability of buildings and structures. Most cities are located in coastal areas and many reinforced concrete structures in these areas are exposed to aggressive marine environments. Therefore, it is important to provide protection and offer appropriate repair methods of buildings vulnerable to the degrading effects of corrosion. The first step of implementing recovery is determining the level of degradation undergone by exposed concrete structures. However, there is a lack of integrated guiding principles in this field. Thus, this review paper identifies the tests of determining the level of deterioration, with particular attention given to carbonation issues and chloride ion attacks. The paper also provides a categorization of solution methods for protection, maintenance, and repair, based on standards and codes culled from around the world. This research contributes to the field by providing a readily-available reference for practitioners and researchers, on the current state of knowledge on corrosion and repair strategies for coastal concrete structures. [ABSTRACT FROM AUTHOR]

• The relative importance of ITZ and bulk matrix to chloride diffusion was evaluated. • Natural diffusion tests were performed on varied aggregate volume content and size. • Using slag blocks chloride penetration effectively. • The reduction of diffusivity is mainly due to the improvement of bulk matrix. The reinforcement corrosion caused by chloride is one of the main threat to structural concrete exposed to marine environment or de-icing salts. The penetration of chloride is highly determined by the pore structure. In this study, the effect of pores on chloride diffusion of concrete made with varied aggregate volume fraction and size distribution was evaluated from the interfacial transition zone (ITZ) point of view. The pore structure was analyzed by using mercury intrusion porosimeter (MIP) in relation to the binder compositions and aggregates. Results show that the diffusivity decreases firstly with increasing aggregate content from 0 to 0.2, and followed by a slight increase in the pure cement group. The diffusivity increases for the specimens made with coarser aggregate. The addition of appropriate amount of blended materials could mitigate the influence of aggregate on the chloride diffusion. Increasing aggregate volume content or reducing the mean particle size, which increase the total intruded volume of pores superior to 100 nm, contribute most to the increase of total porosity. Considering the effect of limestone filler and slag on the pore structure within ITZ and bulk cement paste, the reduction in chloride diffusivity could be mainly due to the densification of the matrix. [ABSTRACT FROM AUTHOR]

• the pore content first increases and then decreases from outside to inside (5F → 1F) • the thickness of the voids is greater than that in normal reinforced concrete. • the porosity of different layers of PHC pipe pile varies. • the content of ITZ un-hydration products in aggregate is greater than that in rebar. • centrifugation results in the non-uniform distribution of the pores. Pre-stressed high-strength concrete (PHC) pipe pile is widely used in many large-scale projects, thus their durability has attracted more and more attention. However, in most studies, PHC pipe pile is regarded as the same as ordinary reinforced concrete, ignoring the effect of special construction processes and hollow shape on its microstructure and anti-erosion performance. In this paper, the real PHC pipe pile was cored and cut to investigate the multi-scale microstructure and the anti-erosion performance of PHC pipe pile concrete layer. The results shown that pore content first increases and then decreases with PHC pipe pile from the outer layer to the inner layer (5F → 1F) by CT, BSE and LF-NMR results, and the pore content changes most significantly around the rebar in PHC pipe pile. In rebar interfacial transition zone (ITZ), the thickness of the voids in PHC pipe pile is greater than that of normal reinforced concrete under the same water-binder ratio condition. Additionally, the content of un-hydration products in aggregate ITZ is obviously greater than that in rebar ITZ. Furthermore, the chloride ion diffusion coefficient of the concrete on the outside of the PHC pipe pile is slightly larger than that on the inside, which is closely related to the higher pore connectivity of the concrete on the outside of the PHC pipe pile. Moreover, it was found that centrifugation can not only reduce the water-binder ratio of PHC pipe pile but also affect the radial pore structure of PHC pipe pile concrete, including porosity and pore connectivity. This work finally indicated that the microstructure of PHC pipe pile concrete is quite different from that of normal reinforced concrete, providing a theoretical basis for establishing the diffusion model of PHC pipe pile concrete. [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]

• ECE treatment is capable of removing the chloride ions. • ECE has an adversely effect on bond strength and it is affected by cement type. • Silica fume blended cement has been proved to be effective. • Type of cement is an important factor to protect steel from corrosion. Electrochemical chloride extraction "ECE" has been used for reinforced concrete structures to protect steel from chloride-induced corrosion. ECE may change the performance of steel interface as represented by polarization resistance, corrosion rate and pull out bond strength. Thus, there is a need to evaluate these effects before and after ECE treatment for reinforced concrete made with different types of cements. This paper presents the evaluation of the performance changes of concrete specimens containing steel rebar with different times of (ECE) treatments. In this study; plain and blended cement which are commonly used in marine environment are investigated; two types of ordinary Portland cement "CEM I 42.5N" with different alkalis and percentages of C 3 A and two types of blended cement; SLAG cement "CEMII/B-S-42.5N" and CEM I 42.5N with 10% silica fume. Concrete mixes are subjected to either internal or external sources of chlorides. Other protective methods have been evaluated for comparison; corrosion inhibitor admixtures and cementitious surface coating. Corrosion initiation and corrosion rate were estimated by non-destructive techniques (Half-cell potential and polarization resistance), while the pull out bond strength was evaluated for all mixes before and after chloride extraction. The results indicated that applied ECE is an effective method of chloride removal, but it adversely affects the pull out bond strength irrespective of cements type. However, the use of silica fume blended cement has been proved to be effective. [ABSTRACT FROM AUTHOR]

Highlights • Chloride ions diffusion in sound/cracked RC under non-steady-state conditions. • Effects of the loads for the linear and non-linear material states are analysed. • Modified governing equations to account the no-constant diffusion are used. • Classic results (constant diffusion) vs. new ones (no-constant diffusion). • Chloride transport in damaged concrete, experimental and numerical aspects. Abstract The aim of this study is to investigate the chloride ions diffusion in sound and cracked concrete under compressive loads. The model includes the analytical setup and data analyses. The governing equations are modified to account for the no-constant chloride diffusion coefficient. With this condition it is possible to define several terms in the time domain to predict the service life of structures. The material is a saturated and hardened cement paste under non-steady-state conditions. Loads are studied for linear and non-linear material states. The predicted values at the depth of steel reinforcement ranges from 0.1 to 0.3% in 7–20 years. The ratio of the chloride diffusion coefficient under loading and no-loading is 9, whereas the chloride diffusivity coefficient in cracks is 0.9–1.3 times the chloride diffusion coefficient under loading. [ABSTRACT FROM AUTHOR]

Abstract Reinforcement bar corrosion induced by chloride ions ingress is one of the dominating causes for the deterioration of reinforced concrete structures in salty environment. Thus, it is particularly important to accurately predict chloride concentration in concretes and evaluate the structural service life. This paper presents the results of an indoor experimental investigation on chloride diffusion in plain and reinforced mortar specimens exposed to tidal zone, which is simulated by a self-design marine environment automatic simulation device. Concrete covering-layer was divided into major influence area (MIA) and secondary influence area (SIA) to accurately describe the chloride ion concentration distribution characteristics. MIA is the region affected by direct and indirect blocking effect of reinforcement bar, while SIA is the area only influenced by the indirect one. Also, the relative influence coefficient C re was defined to measure the impact of reinforcement bar on the chloride ion ingress. The results indicate that indirect blocking effect of rebar resulting from changes of material properties is the major cause for the chloride ion concentration distribution in SIA and it is only relative to the diffusion depth. Whereas, direct blocking effect of bar caused by physical obstruction to accumulate chloride ions contributes most to the chloride increase in MIA and it is correlated to the diffusion depth, exposure time and diameter of bar. Finally, an empirical prediction model of chloride concentration in concrete covering-layer considering the effect of reinforcement presence is proposed. Highlights • A self-designed artificial marine environment automatic simulation device can simulate the actual tidal fluctuation. • The influence area of rebar on chloride distribution was extended to concrete covering-layer not merely the apex of rebar. • An empirical model predicting chloride concentration in covering-layer of reinforced concrete was proposed. [ABSTRACT FROM AUTHOR]

Abstract Water and chloride ions are key parameters in the corrosion processes of reinforced concrete. Consequently, rebar corrosion is the first cause of decay in historical monuments made of concrete. Thus, developing new techniques to be able to detect or quantify water and chloride ions seems to be an interesting approach in the diagnosis of historical reinforced-concrete buildings, especially if these new techniques are non-destructive. SUSI-R© is a non-invasive microwave system based on the evanescent field dielectrometry technique. The SUSI system is equipped with a resonant probe able to analyze the tested material down to 2 cm in depth. The water content and salinity index are calculated from the resonance properties of the probe, which are a function of the material permittivity. Initially developed to quantify the moisture content and to detect the presence of salts in mural paintings, SUSI-R© was considered in this study for the analysis of concrete. In a first phase, the SUSI-R© technique was tested to follow the moisture and salt content in reinforced concrete slabs, made with CEM I or CEM III cements, after their semi-immersion in water or in a sodium chloride solution. Several series of measurements were then carried out before and during the rise of the capillary absorption front. In the second phase, the calibration of SUSI-R© was undertaken in a laboratory on prisms made with the same concretes as those used for the slabs, and which had undergone the same curing conditions. The resonance parameters were correlated to the moisture content contained in these samples, with various saturation rates, in plain water and salted water. The first results of this study showed that the technique makes it possible to follow the hydric changes in the material but also to differentiate between the two types of capillary absorption solution: plain water or salted water. Distinct evolutions of the salinity index were also distinguished according to the type of cement. The calibration in laboratory allowed the resonance parameters of the probe to be correlated with the moisture content values, and thus to quantify the moisture content of the concrete slabs investigated during the first phase of the study. [ABSTRACT FROM AUTHOR]

• Theoretical models for calculating Cl− adsorption capacity are proposed from the perspectives of thermodynamics and dynamics. • pH and Ca2+ concentration are partners in determining the Cl− adsorption capacity and potential reversal of C-S-H gels. • Elevated temperature reduces Cl− adsorption by decreasing the activity of SiOH sites and the constraints of the gel on ions. Calcium silicate hydrate (C-S-H) gel, as the main hydration phase of cement, intensely influences the penetration and diffusion of chloride ions (Cl-) by interacting with multiple ions in diverse environments, affecting the durability of reinforced concrete. However, the adsorption mechanism and critical influence factor are indistinct. To reveal the micro/nano mechanism of the adsorption characteristics for Cl-, a comprehensive investigation was conducted, which included ion adsorption experiments, thermodynamic calculations, and molecular dynamic simulations. In contrast to the prevailing opinion that Ca2+ is a potential determining ion in cement paste systems. The results indicate that pH value and concentration of Ca2+ are the partner to determine the Cl- adsorption capacity and potential reversal of C-S-H gels. They are unable to function in isolation from each other. It should be mentioned that OH− is more important than Ca2+ for ions adsorption of C-S-H gels. Compared with Ca2+, the compensation of Na+ on the surface charge and the promotion of Cl- adsorption is limited. SO 4 2- competes for adsorption sites with Cl-, and forms Na-SO 4 clusters to inhibit the diffusion and adsorption of Cl-. Furthermore, elevated temperature not only promotes the thermal movement of ions but also decreases the Ca2+ concentration and pH value. Consequently, the activity of SiOH sites is lessened, and ions are subjected to weaker constraints by the gel, resulting in the decline of Cl- adsorption capacity. Moreover, theoretical models for calculating the amount of chloride adsorbed by the C-S-H gels are proposed from the perspectives of thermodynamics and dynamics, and the simulation results are in agreement with the experiment results. [ABSTRACT FROM AUTHOR]

This study aims to investigate the efficiency of active and passive protection of the pre-corroded steel reinforcement in reinforced concrete (RC) columns using an externally bonded carbon fibre reinforced polymer (CFRP) wrap. Active protection is a novel technique used to impede corrosion achieved by employing the CFRP wrap as the anode of the impressed current cathodic protection (ICCP). Passive protection denotes the anti-corrosion behaviour of the CFRP fabric. Nine reinforced concrete columns with different degrees of corrosion (theoretical mass losses of 1%, 3%, and 6%) were prepared and then treated with different protection methods (non-protection, passive protection, and active protection) by exposing them to wet–dry cycles. By measuring the steel potential, linear polarization, and electrochemical impedance spectroscopy (EIS) of all investigated specimens, the efficiency of active protection was found to be closely related to the degree of the pre-corrosion of the protected specimens. Furthermore, the efficiency of active protection decreased with time, which may be attributed to the deterioration of the CFRP anode and CFRP/concrete interface. Passive protection was proven to be effective in every case, however, it can only slow down the corrosion process but cannot stop the elicited corrosion response. [ABSTRACT FROM AUTHOR]

In this work, the different techniques for non-destructive in situ measurement of chloride ion concentration are presented. Non-destructive (ND) in situ measurement is crucial for reliable and continuous determination of chloride ion concentration in concrete. Over the last 20 years, several studies have been performed on ND measurements. These were mainly focused on the application of electrochemical and electromagnetic techniques. Each technique has its advantages and disadvantages. Depending on the requirement of assets managers and constructors and considering the limitations, these techniques can be well applied. The main concepts and comparative analysis, in view of possibilities and limitations, of these non-destructive techniques are presented in this paper. [ABSTRACT FROM AUTHOR]

The chloride ions, imbibition in the reinforcement concrete, are detrimental to the durability of the material. In this paper, a low shrinkage and high ductile conductive cement-based mortar was developed as a novel external anode for electrochemical chloride extraction (ECE). The electricity resistivity, fracture energy and drying shrinkage of mortar with different length, volume fraction of carbon fiber were investigated to optimize mix proportion of conductive cement base mortar (CCM). Subsequently, the proposed CCM with good performance was then utilized as the anode to remove the chloride ions electrochemically from three types of reinforced concrete. The chloride ions distribution in concrete and CCM anode were obtained to evaluate the electrochemical chloride extraction (ECE) efficiency. Additionally, the microstructures, elements distribution and calcium hydroxide content of CCM anode and ITZ were achieved for the further mechanism investigation. Experimental results indicated that the ECE efficiency for CCM anode was as high as that of traditional stainless mesh anode. The CCM anode with 0.8% volume fraction of carbon fiber exhibits excellent ductile and conductivity performance. Furthermore, CCM anode thickness influences significantly on the chloride removal efficiency and residual chloride proportion in concrete and CCM anode. And 10 mm thickness of CCM anode was a suitable value to ECE treatment of reinforced concrete. The microstructure and calcium hydroxide content in CCM anode showed no degradation after 35 days of ECE treatment, which indicated that the CCM anode have an excellent cracking resistance capacity and could be re-used. [ABSTRACT FROM AUTHOR]

Since the deterioration of marine reinforced concrete structures is, to a great extent, related to the movement rate of chloride ions in concrete, it is essential to determine the chloride diffusion coefficient of concrete through experiment or theoretical prediction. This paper proposes a numerical algorithm for evaluating the chloride diffusion coefficient of concrete with crushed aggregates. In the numerical algorithm, the mesostructure of three-phase concrete is reconstructed by generating polygonal aggregates of various sizes and placing them within a simulation element with periodic boundary conditions. The random walk algorithm is then applied to the simulated three-phase concrete for computing the chloride diffusion coefficient. With this algorithm, the reasonable values of the random walk radius and the number of simulations are determined. Finally, comparisons are made between the calculation results and the experimental ones obtained from the literature to verify the numerical algorithm. Based on several numerical examples, three primary factors, the aggregate content, and the thickness and chloride diffusion coefficient of interfacial transition zone, influencing the chloride diffusion coefficient of concrete, are evaluated quantitatively. This paper concludes that the proposed numerical algorithm is effective in evaluating the chloride diffusion coefficient of concrete with crushed aggregates. [ABSTRACT FROM AUTHOR]

Corrosion attack due to chloride ions is a major problem found in steel reinforced concrete structures when subjected to marine environment. Glass fiber reinforced polymer (GFRP) has become an alternative reinforcement in marine concrete structures due to its excellent corrosion resistance, making it possible to combine with concrete composed of seawater and sea sand. However, the knowledge on the short-term and long-term properties of GFRP reinforced concrete columns is still limited. In order to facilitate the practical application of GFRP reinforced concrete in marine environment, the effect of chloride ions on the structural behaviors of GFRP reinforced concrete columns is investigated here. Numerous specimens consisting of GFRP reinforced concrete columns and steel reinforced concrete columns with different chloride concentrations were fabricated, conditioned and tested. The test results show that GFRP reinforced concrete columns cast with saturated water suffer a deterioration of 27.9% in load carrying capacity, but possess an enhancement of 104% in ductility when compared to those of specimens cast with distilled water. Meanwhile, it is observed that the GFRP reinforced concrete column possess a ductile failure mode, which indicates that the GFRP spirals can provide an effective confinement to the concrete core even in high chloride environment for a prolonged time. Such findings provide solid evidence to the feasibility and application of GFRP reinforced concrete in the offshore structures or artificial islands with great environmental and economic benefits. [ABSTRACT FROM AUTHOR]

Concrete structures have shown premature signs of deterioration by corrosion due to the penetration of chloride ions. This paper performs service life modeling and validates the results with actual data of the total chloride concentration in a reinforced concrete structure. Chloride profiles are obtained from samples collected from a bridge in southeastern Brazil after 36 years of service. The life span of the concrete structure is assessed. The model offers a suitable option for predicting the life span of concrete structures as an engineering tool for the evaluation of risk areas and the construction of durable projects. [ABSTRACT FROM AUTHOR]

Understanding the mechanism of chloride ion diffusion in cement is significant to improve the reliability of offshore reinforced concrete structures. The chloride ionic diffusivity in cement-based microstructures is predicted by pore-scale modeling using a modified lattice Boltzmann method. Both the Nernst-Planck equation for ion diffusion and the Poisson equation for electrodynamic effect are fully solved. The predicted effective diffusivities in cement-based microstructures with different porosities are in good agreements with the experiment data. The results show that the pore size distribution and Zeta potential of cement-based microstructures directly influence the effective diffusivities of chloride ions. The cement-based microstructure with smaller pore size and higher negative Zeta potential hinders chloride ions corrosion more effectively. The electrokinetic effect on the chloride ionic transport is negligible when the ratio of the maximum-probability pore size and the Debye length is higher than 32 in the cement-based microstructure. For engineering applications, we provide a predictive and easy-to-use formula by up-scaling to correlate the effective chloride ion diffusivity with electrokinetic effect in cement paste. [ABSTRACT FROM AUTHOR]

The increasing use of crushed concrete aggregates (CCA), formerly referred to as recycled concrete aggregates (RCA), has led to research into the effects of coarse CCA in higher value structural applications. Concerns exist regarding the effect on chloride ion ingress which ultimately can cause deterioration of reinforced concrete. This concern is reflected in existing European and British concrete design standards as limitations prevent their use in environments where chlorides may be present. The rapid chloride migration coefficient and rate of accelerated corrosion of structural CEM I and CEM III/A CCA concretes was measured to determine the effect on chloride ion ingress. Three sources of coarse CCA were evaluated; results show that coarse CCA generally had a detrimental effect on the chloride ion ingress of structural concrete. However, these effects can be mitigated by the inclusion of GGBS to produce structural CEM III/A concretes, thus allowing higher proportions of coarse CCA. It is recommended that the GGBS and coarse CCA content be limited to 50% and 60% respectively as this reduces the risk of a significant detrimental effect on chloride ion ingress. The results also suggest that the limitations in existing European and British standards are conservative and sustainable structural CEM III/A concrete with the inclusion of coarse CCA could be a viable option for future responsibly sourced projects, provided that a reliable and consistent source of CCA can be obtained. This is a positive outcome for the wider implementation of coarse CCA into structural concrete applications. [ABSTRACT FROM AUTHOR]

We present a method to simulate, in three dimensions, the concentration of chloride ions that penetrate into concrete with internal cracks. The method comprises the crack-propagation analysis of concrete and the diffusion analysis of chloride ions. A finite-element model with a damage model that is based on fracture mechanics for concrete was applied in the crack-propagation analysis, and we were able to reproduce the three-dimensional geometry of the internal cracks. Chloride-ion transfer through internal cracks was simulated by diffusion analysis with the simultaneous consideration of damage, and a diffusion coefficient that was expressed as a function of the damage variable obtained from crack-propagation analysis. We present a formulation of crack-propagation analysis by using the damage model and unsteady-diffusion analysis in consideration of damage. We also present a verification analysis of internal cracking in concrete to demonstrate that the crack width and the chloride concentration can be evaluated without mesh dependency. This is followed by a validation analysis. A comparison between the numerical and experimental results shows that the proposed method enables the high-accuracy simulation of chloride penetration into concrete with internal cracks. [ABSTRACT FROM AUTHOR]

• Description of the sensing principles of chloride ingress monitoring by a radiofrequency dielectric probe. • Decoupling the influence of water and chloride ingress is possible with the proposed method. • Ability of the method to monitor diffusion of chloride in concrete at different depths. The origin of rebars corrosion in concrete infrastructures is frequently associated with the ingress of chloride ions present in water. This is particularly the case of infrastructures located in marine environments or exposed to deicing salts. The present study aims at developing a radio-frequency dielectric sensor dedicated to free chloride ingress monitoring in a well-defined volume of the material. A resonant method operating in a wide frequency range is selected to separate the effects associated with the variation of the real part of the dielectric permittivity and tangent loss. As it will be shown, the method provides useful information on the presence of free chloride in concrete and can be used for the monitoring of chloride diffusion. For this purpose, considering the variation of the transmission parameter S12 value presents clearly some advantages with respect to the frequency shifts of resonances. This allows to decouple water and chloride content. [ABSTRACT FROM AUTHOR]

Sodium chloride (SC) is by far the most cost-effective deicing agent in winter road maintenance and therefore is used by road authorities worldwide. However, chloride ions foster high corrosivity, which significantly reduces the service lifetime of metals and reinforced concrete of transport infrastructures. Hence, a holistic evaluation with the main criteria of deicing performance and corrosion is demanded and, if possible, alternatives should be considered. This paper focuses on the deicing performance of sodium chloride and other common acetate-, carbonate-, chloride- and formate-based deicing agents. A newly developed test method is presented, enabling high volume testing at good repeatability. From its results a nonlinear model is derived to predict deicing performance up to five hours after application. Subsequently, this model is compared with both existing empirical and theoretical approaches for evaluating the deicing performance. In addition, the impact of added corrosion-inhibiting substances like sugars on deicing performance is investigated. Finally, a comparison of all tested substances in terms of corrosivity and deicing performance is presented, with corrosion being investigated in detail in another paper. • A new method for evaluation of deicing performance is presented (called CEDA). • CEDA is compared to other theoretical and empirical evaluation methods, showing the possible limit of the theoretical approach. • CEDA is a more reliable and more efficient testing method compared to the common SHRP method. • Statistical analysis shows the variation of the time-dependent deicing performance of different deicing agents. • Deicing performance is compared to mass loss due to corrosion, showing advantages of certain deicing agents and inhibitors. [ABSTRACT FROM AUTHOR]

• A fully coupled meso -scale electro-chemo-mechanical phase field model is proposed to simulate the corrosion mechanism in concrete structures; • The mass transport process of moisture, chloride ions and oxygen are well captured by the model; • The corrosion-induced damages in both mortar and interfacial transition zones are vividly simulated. • The model is validated by existing test data and used to reveal the effects of various structural and environmental parameters. Corrosion-induced concrete cover deterioration is a major factor affecting the serviceability of the reinforced concrete (RC) structures. The entire corrosion process, including mass transport, physical/chemical/electrochemical reactions, and cover cracking, occurs at the meso -scale. This paper developed a fully coupled meso -scale electro-chemo-mechanical phase field method to accurately simulate the corrosion mechanism in RC structures. The simulation begins with the mass transport process in the concrete, including the moisture, chloride ions and oxygen. When the chloride concentration at the rebar surface reaches a critical value, corrosion initiates and then propagates. A meso -scale phase field model is adopted for characterizing the corrosion-induced damage in both mortar and interfacial transition zones (ITZs). In addition, crack direction dependent diffusivity tensors are proposed to consider the influence of damage on the mass transport process. The proposed numerical method is verified by previously reported experimental results, showing its ability to conduct high-fidelity simulations of corrosion-induced fracture in RC structures. Parametric studies are carried out to investigate the effect of aggregate distribution, cover thickness, relative humidity, and temperature on the corrosion process. [ABSTRACT FROM AUTHOR]

Understanding the microstructures evolution and chloride migration characteristics of concrete is essential to solve the durability problem of reinforced concrete structures in ultra-deep buried rail transit projects (40 m–100 m). Herein, we developed a novel experimental system that can simulate the corrosion process under high hydraulic pressure and stray current coexistence environment. The changes in microstructures, phases, elements, minerals, and the Ca-leaching were comprehensively investigated. Further, the mechanisms of pores and cracks propagation, and migration characteristics of chloride ions were revealed. The results showed that stray current and hydraulic pressure significantly altered the microstructures of concrete, both of which led to the increase of specific surface area, porosity, pore diameter and more ink-bottle-shaped pores. The development of dominant microfractures and three types of crack propagation patterns caused by hydraulic pressure were found, and the mechanical framework for "local fracturing" was established. Migration characteristics in micro-nano scale showed chloride ions were mainly transported along the pores, and the decrease of adsorption sites was the main reason. [Display omitted] • A new device was developed to simulate the ultra-deep underground environment. • Stray current and hydraulic pressure strongly altered the microstructures of concrete. • Dominant micro fractures and three types of crack propagation patterns were found. • The mechanical framework for "local fracturing" of micro-nano cracks was established. • The decrease of adsorption sites made the chloride ions mainly migrate along the pores. [ABSTRACT FROM AUTHOR]

Chemical aggressions from the environment, such as salt ions, can damage reinforced concrete structures before they reach their service life. These deterioration mechanisms are coupled. The current research on cementitious material's durability has thus gradually shifted to the field of durability damage caused by the combined action of multiple factors. The research in this study concerns the case of combined chloride-sulfate attacks to provide a better understanding of the coupling phenomena by studying the mutual effect of the chloride and sulfate ions on the materials. The effect of the type of cement and curing duration on the chloride-sulfate attack is also investigated. Experimental results based on different investigation techniques (ICP, XRD, NMR, etc.) clearly show the competition between chloride and sulfate ions, and how the physico-chemical involved mechanisms completely change with respect to the cases of an exposure to a single type of ion. • The presence of sulfate ions reduces the chemical fixation of chloride ions. • This increases the possible risks of steel corrosion by increasing the propagation front. • The decalcification of C-S-H in the combined sulfate-chloride attack is drastically reduced. • The presence of sulfate ions decomposes the Friedel salt and turns it into ettringite. [ABSTRACT FROM AUTHOR]

[Display omitted] • Reverse water pressure eliminates the peak phenomenon in the convection zone. • Reverse-seepage technique weakens the chloride ion accumulation at the corner. • Arrangement scheme of the technique with rectangular cross-section is investigated. This paper looks at the application of the reverse-seepage technique in reinforced concrete (RC) structures with rectangular cross-sectional forms under chloride ion attack. Experiments and numerical analyses of the chloride invasion within rectangular section concrete which applied the reverse-seepage technique are performed. A two-dimensional convection–diffusion model of chloride is developed, which can be used to further investigate the effect of the shape of permeable tube arrangement and ratio of water permeable area. The results indicate that the reverse-seepage technique can greatly inhibit the chlorine accumulation effect in the corner of the rectangular cross-section under the effect of wetting–drying cycles. In addition, it is recommended that the water permeable area ratio should be set at about 0.6, and the permeable tubes should be arranged in a rectangular shape to improve the chloride ion intrusion resistance efficiency. These results have important implications for the further application of the new anti-chloride erosion technique in engineering. [ABSTRACT FROM AUTHOR]

• Raman mapping was employed to investigate the carbonation depth in a microscale. • The redistribution of the chloride due to carbonation was detected, and a chloride accumulation zone was found before the carbonation front, which directly caused the corrosion. • The corrosion mechanism of reinforcing steel in cement paste containing chloride under a CO 2 diffusion scenario was discussed and demonstrated in a schematic. Desalinated sea sand concrete (DSSC) is increasingly used to mitigate the shortage of natural river sand. However, one major concern lies in the corrosion risks of steel reinforcement embedded in DSSC under combined chloride and carbon dioxide attacks. To understand the corrosion mechanism, the corrosion process of steel reinforcement embedded in the cement paste containing chloride ions (Cl−) was monitored by electrochemical measurements, during which pH, Cl− profile and corrosion products were examined simultaneously. Raman spectroscopy was employed to evaluate the carbonation depth in microscale. Tests results showed that corrosion was initiated before the carbonation front reached the steel reinforcement. Interestingly, it was the carbonation-induced Cl− redistribution rather than the decrease of pH that dominated the corrosion initiation. Before the carbonation front, a Cl− accumulation zone was identified, and the corrosion mechanism was revealed. This study shall advance the understanding of the corrosion of steel reinforcement in DSSC for durability design of reinforced concrete structures. [ABSTRACT FROM AUTHOR]

Corrosion layers at the steel/concrete interfaces of two reinforced concrete specimens subjected to chloride ion ingress were observed and measured by SEM. A Gaussian function was used to model the distribution of the non-uniform corrosion. The physical meaning of the parameters in the Gaussian model is confirmed mathematically and the relationships among these parameters are discussed. The locations of the corrosion peaks along the rebar perimeter are also discussed. When the number of cracks at the steel/concrete interface becomes two or more, the corrosion layer has the same quantity of corrosion peaks. A multi-peak Gaussian model is proposed to describe this multiple corrosion peak situation. [ABSTRACT FROM AUTHOR]

• The chloride resistance of CFRP was investigated by the comparison of chloride profiles in RC piles with and without CFRP. • The restorative effect of CFRP was investigated via RC piles bonded with CFRP after a 2-year chloride attack numerically. • No obvious convection zone of chloride profiles was observed in the CFRP-bonded region in the dry-wet cycling zone. • A "chloride redistribution process" occurred in RC piles bonded with CFRP after a 2-year chloride attack. Carbon fiber reinforced polymer (CFRP) has been widely used as a protective or restorative material for reinforced concrete (RC) structures present in marine environment. The free chloride ion profile is an important index for evaluating the durability of RC structures. Herein, three types of specimens were employed, i.e., ordinary RC piles (UC piles), RC piles bonded with CFRP (CP piles), and RC piles bonded with CFRP after a 2-year chloride attack (AC piles). Experimental free chloride ion concentrations (C f) within UC piles and CP piles were measured by conducting an indoor test with the implementation of a marine environment simulation system. Predicted C f in the three types of piles were captured through numerical models based on Fick's II law and validated by test data. The results show that C f of CFRP-bonded segments were significantly lower than that of ordinary RC segments. No obvious convection zone of chloride profiles was observed in the CFRP-bonded region in the dry-wet cycling zone. A "chloride redistribution process" occurred in AC piles, which would reduce C f around steel rebars. Chloride resistance and thus durability enhancement to RC structures of CFRP were confirmed eventually. [ABSTRACT FROM AUTHOR]

Utilization of sea sand in reinforced concrete is limited, due to the risk of steel corrosion caused by the introduced chloride. The chloride ions can be chemically bound by chloroaluminate salts (i.e., Friedel's salt and Kuzel's salt) in Portland cement, which would be an effective way to reduce the risk. However, SO 4 2− from gypsum in Portland cement could form sulfoaluminate hydrates (e.g., monosulfate and ettringite), which would hinder the generation of chloroaluminates and weaken the chloride binding. In this study, an attempt was made to reduce this negative effect by introducing Ba2+ which had the effect of precipitating SO 4 2−. A design of barium@hydrogel capsule with core-shell structure was proposed to control the release rate of Ba2+ to avoid the disturbance to the paste setting process. Results showed that the release process of Ba2+ from the capsule was controlled by the slow swelling behavior of hydrogel in the shell structure. Since most of Ba2+ was released from the capsule after 8 h, the negative influence of Ba2+ on the early setting process of cement paste was avoided. The released Ba2+ facilitated the transformation of sulfoaluminates to chloroaluminates, thus enhancing the chloride binding capacity of Portland cement system. [ABSTRACT FROM AUTHOR]

• A database on bond strength between fly ash geopolymers and rebars is built up. • The bond strength prediction models with high accuracy are constructed. • The comparison between machine learning models and empirical models is performed. • The influence factors on bond strength of fly ash-based geopolymers are analyzed. Bond strength between fly ash-based concrete (FGPC) and rebars is a vital index for ensuring the reliability and safety of reinforced concrete members. Thus, prediction and analysis of ultimate bond strength between FGPC and rebars are performed based on machine learning data-driven methods in this paper. A latest database including 137 samples from the published papers in the last decade is established. Four machine learning algorithms that include Lasso regression, Support Vector Regression (SVR), Random Forest (RF) and Extreme Gradient Boosting (XGB) are adopt for the construction of prediction models, and model evaluations are carried out by using four metrics (R2, RMSE, MAPE and MRE). The comparison between machine learning models and empirical models based on experiments is finished. Besides that, the feature importance is analyzed based on RF and XGB models. The results show that the machine learning models have a better prediction performance than the empirical models, where the RF and XGB models are optimal estimators with R2 of over 0.84 on testing set. Lasso and SVR models possess stronger generalization ability than RF and XGB models. The relatively important influence factors are compressive strength of FGPC (fc), reactivity modulus of precursors (RM), the ratio of cover thickness to diameter of rebar (c/d) and the ratio of anchorage length to diameter of rebar (l/d). Increasing slag content, fc, RM, and c/d are beneficial to enhancement of bond strength. The recommended values of fc, RM, c/d and l/d are 50 MPa, 0.7, 4.5 and 5.0 respectively. [ABSTRACT FROM AUTHOR]

• Bond strength between non-uniformly corroded bars and concrete is discussed. • Cross-section area along the corroded bar length follows the lognormal distribution. • Uncertainties of the cross-section area of rebars and concrete strength are considered. • Probabilistic bond strength is predicted by using the Monte-Carlo method. The bond strength considering concrete strength and non-uniformly corrosion was tested by twelve beam-type specimens, and the corrosion was characterized by the 3D scanner. According to the K-S test, the cross-sectional area of the corroded bar follows the lognormal distribution at the 5% significance level, where its mean and standard deviation linearly correlate with the mass loss rate. The probabilistic bond strength is predicted by the Monte-Carlo method, incorporating the uncertainties of the cross-sectional area of rebars and the concrete strength. It is indicated that the failure probability can be decreased by decreasing mass loss rate and increasing concrete strength. [ABSTRACT FROM AUTHOR]

• The papers on the FRP-concrete bond via the EBROG method are reviewed. • The efficiency of EBROG method compared to the EBR method is affirmed. • The behavior of EBROG joints is discussed. • The influential parameters on the performance of EBROG method are evaluated. During the last decade, the externally bond reinforcement on grooves (EBROG) method has been introduced as a technique in the external strengthening of reinforced concrete (RC) members with fiber reinforcement polymer (FRP) composites. This method can postpone or eliminate premature debonding. Hence, the study of the EBROG bond has attracted a lot of attention, which is accomplished through lap shear tests. The present study aimed to review the previous studies conducted for evaluating and analyzing the influential parameters, and compare the EBROG and externally bonded reinforcement (EBR) methods. The EBROG method could considerably improve the bond behavior between FRP composites and the concrete substrate based on the results. Besides, 24.0% and 14.0% of all the EBROG bonds experienced FRP rupture mode and a combination of FRP rupture and debonding at the FRP-adhesive interface over the grooves, respectively. Further, the influence extent of a parameter relied on the values of other parameters, while the optimum values for some parameters were identified. [ABSTRACT FROM AUTHOR]

Steel corrosion is one of the damaging factors for structural concrete and has drawn engineering interest in the past decades. Macro-cell corrosion, a type of steel corrosion, is related to not only electric fields but also chemical substances of both polarized metals and electrolytes such as the concrete matrix. To investigate such multi-ion kinetics induced by macro-cell circuits, this study presents an experimental validation to build a numerical simulation platform using pseudo-concrete with which the species' chemo-electrical profiles are dynamically measured with elapsed time to obtain evidence for broad-band verification and validation. As a key species of cementing material, the authors focus on the profiles of Ca2+ concentrations as a major cation of concrete around the positive and negative electrodes, which are significantly affected by the initial saturation of calcium hydroxide and the supply of carbon dioxide. Experiments and numerical simulation applied to concrete show satisfactory correlation to reveal the governing mechanism based on polarization and the Nernst-Plank theory with multi-ion mass equation. [ABSTRACT FROM AUTHOR]

In this study, solid state embeddable reference electrode was fabricated and examined for their potential stability in high alkaline environment for the application of corrosion monitoring in reinforced concrete structure. Further, the fabricated solid state reference electrodes (SSREs) were studied in the presence and absence of chloride ion in aqueous solution in order to ensure their potential stability. The results showed that the fabricated SSRE gave stable potential in alkaline medium even in the presence of chloride ions. Steel rebar corrosion assessment studies were carried out in alkaline solution and real concrete medium using the fabricated SSRE and the results were compared with conventional saturated calomel electrode (SCE). The results indicate that the fabricated SSREs have the ability to differentiate the passive and active state of steel rebar similar to SCE. [ABSTRACT FROM AUTHOR]

• Experiments are conducted to obtain damage characteristic and mode of the dam. • A CLE method is adopted to describe the dam to penetration explosion. • A stability analysis method for damaged concrete gravity dams is put forward. • A stability index and classification criterion are proposed. The structural stability of concrete gravity dams is of primary importance. In this context, a quantitative and effective stability assessment method for concrete gravity dams subjected to penetration explosion is proposed by employing a series of analytical, numerical, and experimental approaches. Firstly, field blast test is carried out to obtain the possible damage characteristic and mode of a dam model to internal explosion. A fully coupled Lagrangian-Eulerian method is adopted to establish numerical models in this paper, and the validity of this method is discussed by comparing results obtained from this method with those obtained from the blast test. Then, the empirical and theoretical formulas of the penetration-explosion parameters for concrete gravity dams are presented, and these parameters contain penetration depth, damage mode, and damage range, which are the premise of the stability analysis. Moreover, these formulas are verified by the numerical models. Subsequently, the stability analysis method for damaged concrete gravity dams to penetration explosion is put forward. In the process of the stability analysis, structural stresses of the dam with different damage modes are gained, and then anti-overturning and anti-sliding stability analysis are conducted. In addition, a stability index and classification criterion for concrete gravity dams subjected to penetration explosion are proposed, and damage levels are quickly defined in four categories based on the criterion. Finally, a stability assessment model is established on the basic of the former analysis, which can effectively predict the stability performances of damaged concrete gravity dams under various penetration explosion attacks. [ABSTRACT FROM AUTHOR]

[Display omitted] • A fluid–solid-chemical coupled fractal model is developed. • The fractal dimension of tortuosity decreases rapidly with corrosion. • The corrosion of low porosity concrete reinforced by chloride ions can improve the transport of chloride ions. • The change of concrete porosity has nonlinear effect on steel corrosion and concrete pore structure evolution. Chloride ion invasion into reinforced concrete is a common disease. In this study, we combine the diffusion of free chloride ions, the corrosive expansion of iron, and the destruction of concrete. Considering the fractal characteristics of concrete pore structure, a fractal diffusivity model is established. A fluid–solid-chemical coupling model was established considering the non-uniform corrosion of iron. The correctness of the model is verified by comparison with experimental data. The corrosion thickness and pore structure evolution of concrete under different chloride ion concentration invasion and different porosity were simulated. The results show that: (1) the fractal dimension of tortuosity decreases gradually and then sharply at the initial stage of corrosion; (2) compared with concrete with high porosity, concrete with low porosity invaded by chloride ions has a more significant improvement in its own transport; (3) concrete porosity has nonlinear effect on steel corrosion and concrete pore structure evolution. [ABSTRACT FROM AUTHOR]

• Micro-cracks, induced by mechanical loading, were characterized in width and depth. • Sound and micro-cracked specimens were subject to pure diffusion of chloride ions. • Chloride diffusion coefficient was evaluated via colorimetric and titration methods. • In uncracked conditions good correlation subsisted between the two methods. • The effect of micro-cracks resulted more pronounced in more impervious concretes. Concrete resistance to chloride penetration is one of the main design parameters for the assessment of reinforced concrete structures durability in chloride-contaminated environments, and it is usually determined through one of the accredited accelerated tests in uncracked configuration. In this study, the resistance to chloride penetration was evaluated on six different concrete types, in uncracked and load-induced micro-cracked configurations, subject to pure diffusion and considering two different analysis techniques, colorimetric and potentiometric titration. Results showed that in uncracked conditions, good correlation subsisted between the diffusion coefficients evaluated through the two techniques. In cracked configuration (micro-cracks 10–75 μm wide and 5–45 mm deep) with both techniques a significant increase in chloride diffusion coefficient was detected for concretes with lower w/c ratio, suggesting that the effect of cracks may be more pronounced for more impervious concretes. [ABSTRACT FROM AUTHOR]