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Massive discharge of ammonia nitrogen wastewater not only causes eutrophication of the water body but also has a toxic effect on humans and living things. How to deal with ammonia nitrogen wastewater is a crucial topic for researchers. Here, a novel catalyst of Pt@Ti–Si where platinum was supported on a composite oxide of titanium oxide (TiO 2) and silicon oxide (SiO 2) via a one-pot method was successfully synthesized for catalytic wet air oxidation (CWAO) of ammonia with a high concentration (more than 2000 ppm). Due to the improved specific surface area of SiO 2 and the excellent acid-base resistance of TiO 2 , the prepared composite oxide-supported platinum catalyst has excellent catalytic performance and good stability for CWAO with a high concentration of ammonia. At 200 °C and the O 2 pressure of 2 MPa for 2 h, the 1%Pt@Ti10–Si1 catalyst has a 96.32% conversion of 2470 ppm ammonia and 97.15% selectivity to N 2 and has good catalytic performance even after five cycles. Under the same reaction conditions, when the chloride concentration in the system is 3000–10000 ppm, the CWAO reaction can be inhibited at an early stage and promote conversion and selectivity at a later stage. The results show that the catalyst has good tolerance to chloride ions, and the treated ammonia nitrogen wastewater can be used for subsequent biochemical processes. Therefore, the developed novel catalyst in this study is effective for the CWAO of highly concentrated ammonia and has potential industrial application value. [Display omitted] [ABSTRACT FROM AUTHOR]

• PVDF-50 membrane shows highest reported nitrate over chloride selectivity. • Performance PVDF-50 membrane in electrodialysis independent of applied current density. • Nitrate-selectrodialysis (NO 3 -SED) system designed to boost nitrate concentration and simultaneously lower chloride levels. The depletion of natural resources and the escalating environmental concerns associated with pollution necessitate innovative approaches for sustainable resource management. In this study, we investigated the selective separation of nitrate from chloride in electrodialysis (ED) using a recently introduced PVDF-based anion-exchange membrane (PVDF-50) and two commercially available membranes (ACS and AMX from Neosepta). Experimental ED data show that the membrane PVDF-50 presents a higher value of nitrate over chloride selectivity compared with the two commercial membranes, the highest reported in literature. However, recognizing that completely preventing the permeation of chloride ions into the concentrate stream was not feasible, we explored the potential of a system in which anion-exchange membranes presenting different monovalent selectivity were alternated. In this approach, referred to as nitrate-selectrodialysis (NO 3 -SED), the different selectivity of PVDF-50 and AMX membranes was leveraged to demonstrate the possibility of increasing nitrate concentration, while simultaneously reducing chloride levels in a stream. This approach proves highly advantageous in applications where mitigating chloride contamination is a significant concern while recovering nitrate. [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]

In this paper, a new model for chloride diffusion in cracked concrete is presented. The model was developed within a standard continuum damage mechanics framework but newly considers both an irreversible damage variable and a strain field, gaps identified through a literature review, offering a more comprehensive description of the diffusion-like processes in concrete with small and moderate cracks than current models. The model utilizes a realistic dependence for the diffusion coefficient on the damage state and employs a bi-logistic mapping function or an S-curve mapping function to effectively describe the non-linear effects of cracks on diffusion in concrete. The dependence on the strain field introduced by this model not only allows examination of diffusion in opening cracks, it also enables the process of crack closing to be simulated, whatever the irreversible damage variable may be. This paper also proposes a novel calibration procedure for experimental testing involving the use of the Brazilian splitting test on samples enclosed in a steel ring. This innovative approach simplifies the process of creating a portfolio of cracks with varying widths. In the calibration tests described here, samples were subjected to natural diffusion while chloride content was monitored in inlet and outlet chambers attached to the samples, eliminating the need for laborious chloride profiling. Our in-depth examination of chloride diffusion in cracked concrete is applicable to analyses of corrosion in steel-reinforced concrete structures worldwide, with the new calibration procedure offering a straightforward method for populating the model with realistic material parameters, thus providing a valuable tool for accurately predicting chloride penetration in real-world scenarios. • Development of a new continuum model for diffusion in damaged concrete. • Modeling of increased diffusion in cracks and the decrease during crack closure. • Constructing a non-linear mapping function for damage and equivalent strain. • Developing new calibration based on natural diffusion in cracked samples. • Identifying the bi-logistic function as the best candidate for solving real-world scenarios. [ABSTRACT FROM AUTHOR]

[Display omitted] NiFe-based layered double hydroxide (LDH) is a promising electrocatalyst for alkaline water electrolysis because of the low cost and earth abundance of Ni and Fe, as well as their characteristic layered structure resulting in high electrocatalytic performance. However, its hydrogen evolution reaction (HER) activity is still insufficient compared to existing catalysts. Additionally, the hydrothermal method, a common LDH fabrication method, can be time-consuming and complicated. Herein, we suggest a facile route for the preparation of HER catalyst within tens of seconds using one-pot electrodeposition with only a few ionic additives. A trace amount of Pt ion was added to enhance the HER performance and chloride (Cl−) ion was used to increase the specific surface area of the catalyst as well as to control the reduction of Pt ion for Pt-O bonding. Consequently, the 2.5 mmol Cl− ion treated NiFePt LDH (NiFePt_Cl LDH) requires an overpotential of only 52 mV to reach a current density of 100 mA cm−2 and significantly improved durability, with an overpotential increase of only 7 mV at 100 mA cm−2 after 1,000 cyclic voltammetry scans. [ABSTRACT FROM AUTHOR]

The present research work investigates the effect of mix parameters such as fly ash-ground granulated blast furnace slag (GGBS) blends (85 %/15 %, and 70 %/30 %), NaOH solution molarity (10 M and 14 M), different salts (i.e., 3.5 % NaCl and 3.5 % NaCl plus 3.5% MgSO 4) on workability, compressive strength, chloride content, sulfate ion concentration, and microstructure of geopolymer concrete (Gc). Cube specimens were made for compressive strength test at the age of 7, and 28 days. Further, free chloride and total chloride contents of geopolymer concrete mixes were determined. The sulfate ion concentration and pH values of pore solutions made from different geopolymer concrete mixes were also determined. The effect of mix parameters on phase composition of geopolymer concrete mixes was evaluated by X-ray diffraction (XRD) analysis and the morphology of geopolymer concrete was studied by Field emission scanning electron microscope (FESEM) analysis. The results showed that the workability of geopolymer concrete decreased with increase in GGBS content and concentration of NaOH solution. With addition of salt, the slump value of geopolymer concrete increased. The compressive strength was increased with GGBS content and molarity of NaOH solution. The control geopolymer concrete mixes exhibited higher compressive strength than that added with salt. Free chloride and total chloride contents mostly reduced with increase in GGBS content in geopolymer concrete mixes. The increase in GGBS proportion and NaOH solution concentration reduced the concentration of sulfate ions in geopolymer concrete pore solutions contaminated with chloride-sulfate salt. From the XRD analysis, albite, nepheline, anorthoclase, and C-S-H gel peak intensities were mostly increased with age and GGBS replacement level. FESEM analysis showed formation of denser microstructure in geopolymer concrete made with 14 M NaOH solution than that made with 10 M NaOH solution. Overall, the geopolymer concrete made with higher GGBS content and higher concentration of NaOH solution exhibited improved performance through formation of denser microstructure leading to enhanced mechanical property and also reduced the concentration of aggressive ions i.e., chloride and sulfate ions in the pore solution of geopolymer concrete. • The addition of chloride and sulfate salt led to increase in workability and decrease in strength of geopolymer concrete. • The increase in GGBS content led to decrease in free chloride content. • Higher GGBS content and NaOH solution molarity reduced sulfate ion concentration in mixes added with chloride-sulfate salt. • The halite and gypsum were identified in geopolymer concrete admixed with both chloride and sulfate salts. [ABSTRACT FROM AUTHOR]

This paper investigated the Electrochemical Chloride Extraction (ECE) process in concrete with carbonated surface layers. First, the ECE model for surface carbonated concrete was proposed based on pore size distribution function. Subsequently, to validate the model, concrete cube specimens exposed to natural coastal environments were modified and designed for ECE tests. Based on the validated ECE model, parametric studies were conducted. Parametric studies show that increasing the thickness of the surface carbonation layer up to 20 mm leads to a 57% increase in extraction duration, whereas the thickness of the partially carbonated zone has a relatively minor impact on the ECE process. The parametric study shows that the surface carbonated zone will pose hindrances to the extraction of chloride ions. Due to the simultaneous presence of concrete carbonation and chloride ion ingress in the actual marine atmospheric environment, considering the actual carbonation depth is of significant importance for predicting chloride ion migration during Electrochemical Chloride Extraction. [ABSTRACT FROM AUTHOR]

The ingress of chloride ions is a serious threat for concrete structures. Superabsorbent polymers (SAPs) are interesting additions to cementitious systems due to their property of absorbing water during mixing and releasing it at a later time to provide internal curing, thereby reducing shrinkage and promoting durability. In addition, SAPs can improve the regain in impermeability of cracks by swelling and blocking the crack and promoting autogenous healing. The current study investigates the influence of the addition of SAPs without additional mixing water to the chloride ingress in cracked mortar via diffusion and quasi-steady-state migration testing. Filtration tests showed that the charge-screening effect in a NaCl solution is more dominant than for cement filtrate solution during swelling of SAPs. After wet/dry cycling for a month, subsequent chloride diffusion tests with 2 and 6 weeks of exposure showed that the addition of SAPs improved the performance with respect to a reference mix with the same total water-to-cement ratio. A reference mix with the same effective water-to-cement ratio as the SAP mix had a comparable performance to the SAP mix. One set of chloride diffusion experiments showed that the SAP mix was the only one successfully preventing chloride ingress into the deepest zone of the crack. The superior performance of the series with SAPs was also confirmed by migration testing where cracked and healed specimens obtained a migration coefficient which was only 12 % higher than uncracked specimens. [ABSTRACT FROM AUTHOR]

The durability of concrete is significantly affected by the chloride solidification property of the binder. This study investigated the chloride-binding capacity and penetration process of metallurgical slag (MS)-based binder and mortar. It also analysed the influence of the ratio of steel slag (SS) to granulated blast furnace slag (GBFS). The results showed that the C–S–H gels and Friedel's salt (Fs) bound more chloride ions in high- and low-concentration NaCl solutions, respectively. In a 0.1 mol/L NaCl solution, Fs captured 0.01–0.04 mmol/g Cl–. However, in a 5 mol/L NaCl solution, the chloride bound by the C–S–H gels was 0.07–0.20 mmol/g. In addition, the increase of the SS to GBFS ratio (SGR) promoted the generation of Fs through the activity promoting of GBFS and reduced the Cl content captured by the C–S–H gels by improving calcium ions and their unstable connections with silicate chain oxygen. The increasing SGR decreased the percentage of pores smaller than 10 nm, reaching a minimum of 22.6 % at R3. However, the chloride resistance of R3 also exhibited the highest C s of 1.01 % and the lowest D a of 8.54 × 10–12 m2/s among MS-based mortars due to a 0.10 % decrease in porosity. Furthermore, the chloride-binding capacity and resistance performance of MS-based binders were all better than those of ordinary Portland cement. • The MS binder of 1:9 SGR had highest compressive strength and bound chloride content. • At a 0.1 mol/L NaCl solution, Fs captured 0.01–0.04 mmol/g Cl–. • At a 5 mol/L NaCl solution, C–S–H gels bound 0.07–0.20 mmol/g Cl–. • The SGR increasing caused the decrease of <10 nm pores percentage and mortar porosity. [ABSTRACT FROM AUTHOR]

To enhance the compactness of concrete in coastal areas and impede the ingress of chloride solutions into the structures, Cementitious capillary crystalline waterproofing material (CCCW) was internal incorporated into concrete. This study employed one-dimensional chloride immersion diffusion tests and wet-dry cycle tests to emulate the deterioration of concrete under natural conditions due to chloride ions. The optimal dosage of CCCW was determined by conducting chemical titration to measure the chloride ion concentration at various depths within the specimens. Subsequently, the influence of incorporating CCCW on the compressive strength of concrete under chloride conditions was assessed. Finally, employing experimental methods such as MIP, SEM and EDS, the pores within cementitious materials and the formation of internal crystals was examined at a microscopic level. Research indicates that in chloride salt environments, the penetration of salt solutions can trigger the formation of spider silk biomimetic shape crystalline structures within the internal pores of CCCW. thereby enhancing the compactness of concrete to achieve a self-healing effect while preventing the intrusion of chloride salt solutions. [Display omitted] • Utilized a kind of CCCW Material to enhance the compactness of the cementitious matrix. • Microscopic experiments are performed to evaluate crystals from different perspective, providing comprehensive analysis and evaluation. • The effect of adding CCCW materials on the compressive strength and chlorine salt resistance of concrete was studied. [ABSTRACT FROM AUTHOR]

Steel structures often experience significant durability degradation over time due to extreme environments. To better understand the impact of chloride environments on the mechanical properties of steel compression members, accelerated corrosion tests were conducted on H-shaped steel short columns with applied current. Monotonic tensile tests were also performed on steel specimens, and axial compression tests were carried out on H-shaped steel short columns with varying degrees of corrosion. The results revealed that the corrosion rate increased with higher current intensity and longer electrification duration while changing with different chloride ion concentrations. As the corrosion rate increased, the steel material exhibited a linear decrease in yield strength, ultimate strength, and elastic modulus. Consequently, the mechanical properties of the H-shaped steel columns, such as stiffness, ductility coefficient, and load-bearing capacity, were adversely affected. Based on these findings, a predictive formula was proposed to estimate the ultimate load-bearing capacity of H-shaped steel columns with different degrees of corrosion in chloride salt environments. The experimental results were further validated through numerical simulations, and parameter analysis indicated a negative correlation between flange width-to-thickness ratio, web height-to-thickness ratio, and ultimate load-bearing capacity of H-shaped steel columns. Finally, a random corrosion pit generation algorithm is proposed, effectively simulating the actual corrosion pit distribution and calculating the ultimate bearing capacity of columns. • The deterioration model for mechanical properties with corrosion ratio and various parameters in accelerated corrosion tests, demonstrating a linear relationship. • Secondary development of Abaqus software using Python language to randomly generate corrosion pits on the surface of the model, making the numerical simulation results more accurate. • A random corrosion pit generation algorithm is proposed to simulate the actual corrosion pit distribution and obtain the ultimate bearing capacity. [ABSTRACT FROM AUTHOR]

[Display omitted] • A number of copperII) chloride complexes with caffeine (1, 1a, 1b, 1c, 2) were prepared, their composition and structure being determined by the synthetic method and the solvent type; the synthetic scheme of the compounds interrelations is developed. • Recrystallization from organic solvents results in formation of a linear polymeric- or cyclic oligomeric structures (compounds 1a , 1b , 1c). • Four-nuclear copper(II) bromide complex with acetamide (3) has been prepared and studied. Four bromide ions in it are non-equivalent to the other four and this fact may result in modification of the exchange integral between bonded copper ions. • DFT calculation for copper(II) halide compounds with the considered ligands were performed for a number of possible reactions. • Theoretical calculations demonstrate that thermodynamic stability of the complexes rises with the growth of a number of copper atoms and chloride bridges, but increasing water content has an opposite effect. The present article is devoted to the consideration of the interconversions of copper(II) chloride complexes with caffeine (caf) ([CuII 2 (μ 2 -Cl) 2 (caf) 2 (H 2 O) 2 ] (1), [CuII 3 (μ-Cl) 6 (caf)(H 2 O)] n (1a), [Cu 4 (μ 2 -Cl) 6 (μ 4 -O)(caf) 4 ] (1b) , 2[CuII(caf)Cl 2 ].0.25 THF (1c) , [CuII(caf) 2 Cl 2 ] (2)) , depending on the synthesis conditions, and to studies on the four-nuclear copper(II) bromide complex with acetamide (AcAm) ([Cu 4 (μ 2 -Br) 6 (μ 4 -O)(AcAm) 4 ] (3)). The results obtained have been confirmed by different methods (powder XRD, single crystal XRD analysis, IR-, ESI-MS-, EPR-spectroscopy, and magnetic properties studies). Two bromide ions in (3) are non-equivalent to the other four and this fact may result in the modification of the exchange integral between bonded copper ions. Single crystal XRD data have been compared with the results of DFT calculations. It has been found that the thermodynamic stability of the complexes grows with an increase in the number of copper atoms and bridging chloride ions and a decrease in the number of water molecules in the formula unit of the compound. The calculation results for complexes with acetamide are in a good correlation with those of caffeine and experimental data. [ABSTRACT FROM AUTHOR]

An Oscillating Water Column (OWC) power plant is typically a partially immersed concrete structure that generates energy by moving waves, forcing air to flow back and forth through the turbine to produce a consistent amount of energy. Due to the repeated air pressure application, chloride penetration can be accelerated in the OWC structure. However, long-term studies on chloride penetration monitoring are lacking. Therefore, the water-soluble chloride content of concrete subjected to repeated air pressures was measured after 108 months of the OWC structure. The results were analyzed, along with measurements taken 31 months after OWC completion. Concrete powder samples were collected from three areas: the bypass room, which was subjected to repeated air pressure; the tidal zone, which was subjected to alternate dry/wet conditions of seawater; and the splash zone in the offshore atmosphere. The collected samples were then titrated. Fick's 2nd law was used to derive diffusion coefficients. The experimental results indicated that the concrete in the bypass room had the highest water-soluble chloride content. Compared with the results obtained 31 months after completion, the water-soluble chloride content and diffusion coefficient decreased over time. This is attributed to the relatively small effect of air pressure and the clogging of pores owing to the accumulation of chloride ions on the surface. Comparing the measurements in 2017 and 2023, the splash zone exhibits the highest increase over time. This is attributed to the lower initial chloride penetration, which makes diffusion easier owing to the higher concentration differences compared to other locations. In the future, ensuring the reliability of the chloride penetration behavior in concrete subjected to repeated air pressures through periodic monitoring of the chloride content will be crucial. Additionally, research is needed to establish the crystallization and pore-clogging phenomena in concrete subjected to repeated air pressures through microstructural and chemical analyses. • The chloride content of concrete in ocean wave power plants was measured. • The effects of marine environment and repeated pressure have been analyzed. • The long-term behavior of the actual structure was analyzed. • The chloride content increased on the surface of the concrete in repeated pressure. • As the depth of concrete increases, the effect of repeated pressure decreases. [ABSTRACT FROM AUTHOR]

The rapid development of marine concrete structures and the sharp shortage of freshwater resources contribute to the wide investigation of seawater-mixed ultra-high-performance concrete (SWUHPC). However, few studies have investigated the chloride ions (Cl-) binding mechanism of SWUHPC. Herein, the chloride binding experiments and molecular dynamics (MD) simulation were carried out to reveal the physically and chemically bound Cl- mechanisms of SWUHPC. The results of the experiments clearly demonstrate that the addition of silica fume (SF) led to a significant decrease in the capacity of Cl- binding. Conversely, the incorporation of metakaolin (MK) resulted in a marked increase in the content of chemically bound Cl-. Furthermore, it is revealed through MD simulations that the amount of physically bound Cl- heavily depends on the Ca/Si ratio of C-S-H. A higher Ca/Si ratio results in a stronger electrostatic effect of the C-S-H surface on Cl-, which increases the physical binding of Cl- via Ca-Cl bonds. In addition, it is found that Al[6] and Ca in the interlayer region of C-A-S-H formed the main structure layer (Ca 4 Al 2 (OH) 12 2+) of Friedel's salt, and then chemically adsorbed Cl- in the pore solution. These findings provide novel nanoscale insights regarding the physically and chemically bound Cl- mechanisms of SWUHPC. • SF reduced the Cl- binding while MK improved the chemically bound Cl- of SWUHPC. • The higher the Ca/Si, the more Ca-Cl bonds are formed to physically adsorb Cl-. • Al [6] and Ca of C-A-S-H formed the main structure layer of Friedel's salt. [ABSTRACT FROM AUTHOR]

Inspired by the easy chemical binding of chloride ions with aluminum, dredged sludge (DS) has the potential to be used in cement to reduce the adverse effects of seawater mixing and accelerate its hardening. Herein, a detailed investigation into the fresh properties, hydration behavior and chloride binding of seawater-mixed sintered sludge cement (SSSC) paste is carried out utilizing methods such as Vicat apparatus, jumping table test, isothermal calorimetry, the bellows technique, SEM, MIP, DTG, ion chromatography and thermodynamic simulation. The research reveals that calcination at 800 ℃ promotes the thermodynamic decomposition of Clinochlore, Calcite and Muscovite in DS, with amorphous phase content ranging from 9.3% to 47.2% and mainly composed of activated alumina. Compared to fresh water mixing, the initial and final setting times of SSSC paste shortens by up to 12.1% and 10.9%, respectively. Meanwhile, the addition of sintered sludge ash (SSA) results in an accelerated onset of autogenous shrinkage in the cement paste, with the degree and pace of shrinkage rising of up to 29.7% and 110.9%, respectively. Amorphous alumina released by SSA facilitates the re-dissolution of aluminate clinker and expedites the formation of AFm phases when mixed with seawater, especially Friedel's salt. Comparatively, seawater mixing results in lower Portlandite content, heightened autogenous shrinkage, and increased cumulative heat release, suggesting a pronounced improvement in the pozzolanic activity of SSA. Moreover, the concentration of leached chloride ions shows a gradual decrease with the rising addition of SSA, which is attributable to the chemical binding of Friedel's salt and physical adsorption due to increased pore tortuosity. [Display omitted] ● The calcination at 800 °C increases the amorphous phase in DS from 9.3% to 47.2%, with Al 2 O 3 as the main component. ● The redissolution of aluminate clinker and the accelerated formation of AFm caused by seawater are retained in SSSC paste. ● The larger reaction rate constants in SSSC paste explain the increase in autogenous shrinkage and hydration heat. ● The increase in Friedel's salt and pore tortuosity reduces the chloride ion leaching concentration of SSSC paste. [ABSTRACT FROM AUTHOR]

This paper explored the penetration of chloride into concrete damaged by high-cycle compressive fatigue loading. Two environmental conditions including immersion and wetting-drying cycles were prepared for experimentally investigating the transport performance of chloride in fatigue-damaged concrete. Additionally, a prediction model was developed with the damage index of residual strain. Test results revealed that both apparent diffusion coefficients and contents of chloride at each depth increased in fatigue-damaged concrete, indicating that the fatigue damage significantly degraded the resistance of concrete to chloride penetration. Furthermore, for fatigue damaged concretes with extremely different fatigue cycles and load levels but the same residual strain, the chloride ion content profiles were highly overlapped, which demonstrated the reasonability of selecting residual strains as fatigue damage indexes. The applicability of the transport model was firstly validated with the measured chloride contents and then the chloride transport behavior in gradient fatigue-damaged concrete was investigated numerically using the validated model. The numerical results indicated that the chloride transport was more sensitive to the residual strain at the exposed edge than to the residual curvature and the effect of the later can be neglected. • Fatigue loading definitely accelerate the penetration of chloride ions into concrete. • Transport model of chloride was developed in terms of the residual strain. • The rates of chloride transports were more sensitive to the residual strain at the exposed edge. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) as a novel and green nanomaterial exhibit a promising application in enhancing the chloride binding capacity of cement to extend the service life of reinforced concrete (RC) structures. However, their size influence on the enhancement of chloride binding is still a research gap, enormously hindering the further employment of CDs toward cement system. Herein, their size-induced effect on chloride binding actions of cement is comprehensively unveiled using CDs with various sizes for the first time. Specifically, three kinds of CDs with different sizes are controllably prepared through simply altering the calcinating time of citric acid. And the relationship between sizes of CDs and chloride binding capacity of cement is confirmed through the equilibrium tests. More importantly, the mechanism for the effect of CDs sizes on chloride binding is reasonably proposed according to the alteration analyses of phase compositions. The consequences demonstrate that the chloride binding capacity in cement modified by CDs with average sizes of 1.73, 5.79, and 12.37 nm increases by 41%, 20%, and 14% respectively, compared with that of the blank group after 28-d immersion in 3 mol/L NaCl solution. This testifies that the chloride binding capacity of CDs-incorporated cement is negatively correlative with CDs sizes. The related mechanism is that CDs with smaller sizes can provide more nucleation sites to promote cement hydration, further advancing the production of C–S–H gels and monosulfate (Ms), thus more markedly enhancing the physical adsorption and chemical binding of chloride ions in cement pastes. This work would guide the preparation of CDs with more suitable sizes to improve the chloride binding ability of cement, thus anticipated to extend the service life of RC structures in coastal environment, ultimately reducing the CO 2 emission from cement industry. [Display omitted] • CDs with different sizes are controllably synthesized only changing the calcinating time of citric acid. • Size-induced influence of CDs on chloride binding performance of cement is firstly unveiled. • Effect mechanism of CDs sizes on chloride binding behavior of cement is revealed. [ABSTRACT FROM AUTHOR]

Reverse-seepage and Saturation based Active Anti-corrosion Technology (RS-AAT) is a novel and environmentally-friendly approach that enhances the ability of unsaturated concrete in marine alternating wet-dry areas to resist chloride ion intrusion. Comprehending its influence on ions transport and the pore structure within the concrete is vital for assessing the rationality of the technique and further predicting its service life. In this study, cross-section specimens of cast in situ concrete piles with RS-AAT were exposed to a chloride wet-dry cycling environment for 150 days. Spatiotemporal variation patterns of chloride ion content, pore fluid pH, and pore structure in the concrete cover were investigated by free chloride titration, pH determination, and mercury intrusion porosimetry (MIP). The findings indicate that RS-AAT can effectively inhibit chloride ion intrusion into the protective layer of concrete. Moreover, implementing alkaline water in RS-AAT elevates the pore fluid pH and improves the compactness of the pore structure, especially diminishing the harmful pore ratio. Besides, increasing the number of distributed permeable pipes reinforces these effects and reduces the technology's dependence on water pressure. This insight demonstrates the viability of using alkaline water and distributed permeable pipes in RS-AAT to bolster the resistance of concrete structures to chloride ion erosion in an environmentally sustainable manner. • A novel approach (RS-AAT) to restrain chloride invasion into unsaturated concrete. • Extra-supplemental seepage solution (alkaline/deionized) actively alter pore fluid pH. • Alkaline water reduces the proportion of harmful pore levels. • Distributed permeable pipes decrease the needs of pressure. [ABSTRACT FROM AUTHOR]

The durability of ultra-high performance concrete (UHPC) with initial micro-cracking subjected to coupled freeze-thaw and chloride salt (FT-CS) attacks was investigated. The initial micro-cracking was introduced under controlled condition in the laboratory by pre-tensioning the dog-bone specimens and unloading them at a target strain of 1500 με. The micro-cracked UHPC specimens were then submerged in a sodium chloride solution with the concentration of 4 wt % and subjected to freeze-thaw (F-T) cycles. The micro-cracked UHPCs exhibited excellent chloride penetration resistance as evidenced by the consistently low chloride ion concentration (generally less than 0.5%) and the limited penetration depth (not exceeding 6 mm) even after undergoing 300 cycles of the coupled FT-CS attacks. The tensile strength and compressive strength of the micro-cracked UHPC were improved by 28.0% and 18.3% at 200 F-T cycles, respectively. The improvement in the mechanical properties can be attributed to the self-healing effect which densified the fiber-matrix interface and the matrix. Secondary hydration and carbonation were confirmed quantitatively by thermogravimetric test and qualitatively by scanning electron microscopy test. However, the detrimental effects stemming from the coupled FT-CS attacks outweighed the beneficial effect of self-healing at 300 F-T cycles, resulting in a decline in mechanical performance. [ABSTRACT FROM AUTHOR]

It is important to study the corrosion resistance of reinforcing steel in various chloride salt environment. In this study, the corrosion performance of reinforcing steel inside mortar mixed with a new deoxyribonucleic acid (DNA) primer inhibitor in various chloride salt solutions (NaCl, KCl, CaCl 2 , MgCl 2) was investigated. The results indicate that the chloride salt types have a significant effect on corrosion resistance of reinforcing steel in cement mortar mixed with DNA primer inhibitor, and the rule is NaCl ≈ KCl > CaCl 2 >MgCl 2. The new DNA primer inhibitor can maintain the good corrosion inhibition performance in cement mortar. NaCl and KCl can inhibit DNA primer inhibitor condensation and dissolution of calcium hydroxide, which can promote the formation of a better protective film compared with CaCl 2 and MgCl 2. MgCl 2 and CaCl 2 can lead to relatively high porosity and accelerate the diffusion of chloride ions to the steel surface than NaCl and KCl. • DNA primer inhibitor has good corrosion inhibition properties in cement mortar. • The corrosion resistance of steel follows the law NaCl ≈ KCl > CaCl 2 > MgCl 2. • NaCl and KCl can inhibit DNA primer inhibitor condensation. • The corrosion degree of steel immersed in NaCl and KCl solutions is relatively low. • Cement mortars exposed to MgCl 2 and CaCl 2 solutions tend to chloride ion diffusion. [ABSTRACT FROM AUTHOR]

Recycled concrete aggregate (RCA) is an important form for reusing of waste concrete. However, the presence of corrosive ions, specifically chloride ions, which are absorbed on the surface of RCA or infiltrated from the external environment, significantly affects the mechanical performance and durability of recycled aggregate concrete (RAC). This paper aims to suppress the erosion and diffusion of chloride ions in RAC by adding calcined layered double hydroxides (LDOs), utilizing the restructuring and anions exchange properties of LDOs. The dissolution ratio of chloride ions carried by RCA and the adsorption efficiency of LDOs on the leaching ions were analyzed using the silver nitrate titration method. The maximum chloride adsorption capacity of the LDOs is 31.052 mg/g. Additionally, the inhibitory effect and mechanism of LDOs on chloride ion attack were detailed evaluated by the techniques combining mercury intrusion porosimetry (MIP), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM and EDS), rapid chloride migration coefficient method (RCM), and electrochemical impedance spectrum. The results indicate that LDOs exhibit a good adsorption effect on chloride ions leaching from RCA, and the adsorption efficiency is negative correlation with the pH value. Furthermore, the small size effect of LDOs plays a filling role in the pores of concrete, increasing the compactness and penetration resistance of chloride ions of RAC. This work provides a promising approach to enhance the mechanical and durability properties of RAC by incorporating with LDOs utilizing its chloride ion capture feature and nano-filling effect. And the findings of this research can also be extended to the use of LDOs for treatment of other corrosive anions, such as SO 4 2− and CO 3 2− in RAC, demonstrating its applicability in a broader context. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ag/Ti 3 C 2 T x MXene was synthesised via dry impregnation and sonochemistry method. • Nanocomposite performance in chloride removal was optimised using RSM-CCD method. • Formulated composite could remove chloride ions up to 92% at optimal conditions. • Nanocomposite showed promising reusability/stability to supply chloride-free water. Unsafe levels of chloride in drinking water can make it unpalatable, susceptible to infrastructure corrosion and prone to heavy metals mobility. Conventional chloride mitigation strategies are subjected to inefficient performance and costly operation, necessitating innovations for more sustainable, affordable, and scalable technologies. In this study, silver nanoparticles-modified Ti 3 C 2 MXene nanocomposite (AgMX) is synthesised via dry impregnation method for effective removal of chloride ion from water. The composite physicochemical properties were thoroughly characterised using various analytical techniques, including TEM, SEM, XRD, EDS, BET, zeta potential and pH pzc analysis. The experimental testing was optimised using CCD-RSM method in terms of adsorbent dosage (0.2–2 g/L), reaction time (1–17 min), and chloride concentration (10–90 mg/L). Under optimal conditions (adsorbent:1.55 g/L, time: 12.19 min, & concentration: 52.17 mg/L), a promising chloride removal of 91.8 % was achieved. Langmuir model showed the best fit to adsorption isotherm (R2: 0.9852) comparing to Freundlich and Dubinin-Kaganer-Radushkevich (DKR) isotherms, while pseudo-second-order kinetic model offered the closest data to the experimental results (R2: 9893) compared to the pseudo-first-order, Elovich and Intraparticle diffusion models R2: 0.2335,0.1212 and 0.2050, respectively. The composite reusability and regeneration potential after four repeated cycles were found practically efficient as ≥ 68 % and ≥ 84 %, respectively. The outcomes of this study can demonstrate the efficiency of the formulated composite as a promising material for the sustainable treatment of chloride-contaminated water. [ABSTRACT FROM AUTHOR]

Chloride attack on reinforced concrete is considered the most important aspect in concrete durability investigation. This study is carried out to investigate effect of curing condition on the chloride binding capacity of fly ash geopolymer pastes containing a range of cast in chloride contents (NaCL), varying from 1%, 2% and 4% by mass of binder. The applied curing regimes were normal, oven, steam and microwave. The impact of induced chlorides on the compressive strength and on the chloride binding capacity of fly ash geopolymers under different curing conditions is determined. A detailed microstructure and phase composition analysis were conducted through SEM and XRD tests. It was observed that applying thermal curing conditions could increase the chloride binding capacity to the formed geopolyric hydration product. High curing temperatures promote the precursor dissolution reactions and will increase the overall generation of polymerization reaction products, while under normal curing a lot of fly ash grains did not fully react. Therefore, thermal curing is important in the activation of geopolymerization process that increase aluminosilicate gel and result in dense and less porous geopolymer matrix and yields in high compressive strength. This results in the physical adsorption and chemical binding of chloride ions on the gel surface, and hence reducing the rate of chloride ingress. It was concluded that the ingress of chlorides can be particularly controlled better through binding the free chloride ions under steam and microwave curing in the fly ash geopolymer concrete. [ABSTRACT FROM AUTHOR]

Electrochemical kinetics of corroded steel bars is of importance in evaluating corrosion process and subsequent structural deterioration under different aggressive environments. This paper presents an experimental programme to investigate corrosion kinetics of steel bars in pseudo-transparent concrete subjected to different levels of chloride contamination and alkalinity in pore solution. The results show that corrosion current density increased with the rise of chloride content in simulated pore solution until C l − / [ O H − ] ratio reached around 10. However, further chloride contamination with C l − / O H − = 12.5 , 15 or 20 tended to reduce current density. The phenomenon of decreasing corrosion rate and increasing corrosion potential when concrete was severely contaminated by chloride ions has not been widely reported in previous publications. An electrochemical mechanism was proposed based on the concepts of thermodynamics, anodic and cathodic polarisation kinetics to explain this extraordinary phenomenon, in which the decrease of corrosion current density when C l − / [ O H − ] ratio increased from 10 to 20 was due to the rises of both anodic and cathodic Tafel slopes. On the other hand, a more neutralised pore solution in pseudo-transparent concrete induced a greater corrosion current density. When pH value was larger than 13, corrosion current density was negligible, while it substantially increased once pH value decreased to lower than 12.5. • Corrosion rate increases with a rise of chloride content until C l − / [ O H − ] ratio reaches 10 • Further chloride contamination with C l − / O H − = 12.5 , 15 or 20 decreases corrosion rate • Corrosion rate is negligible when pH is larger than 13 with no chloride attack • A more neutralised pore solution with a smaller pH induces a greater corrosion rate • Electrochemical mechanisms account for variations of corrosion rate under different corrosive environments [ABSTRACT FROM AUTHOR]

Chloride attack in the marine environment adversely affects the durability of ordinary Portland cement-sulfoaluminate cement-ground granulated blast furnace slag (OPC-SAC-GGBFS) repair materials, leading to the premature failures of repair engineering. In this research, CaLiAl-LDHs (CLA-LDHs) was synthesized by a modified co-precipitated method, and the characterisation and adsorption behaviour for chloride ions were investigated. In addition, the impact of the synthesized CLA-LDHs on the mechanical properties, chloride binding capacity and hydration process of OPC-SAC-GGBFS repair materials were systematically researched. The obtained results revealed that the adsorption capacity of CLA-LDHs for chloride ions was 41.47 mg/g, and the adsorption process conformed better to the quasi second-order model and Langmuir isotherm model. The chloride binding capacity of OPC-SAC-GGBFS was enhanced by adding CLA-LDHs, mainly due to the formation of more FS/LDHs-Cl. Furthermore, the addition of CLA-LDHs promoted the early hydration of OPC-SAC-GGBFS, shortened the setting time, improved the early mechanical properties, but slightly reduced the mechanical properties at 28 d. It is noteworthy that the mechanical properties of OPC-SAC-GGBFS at −10 °C was significantly enhanced by CLA-LDHs. [Display omitted] • CLA-LDHs was synthesized and its adsorption behavior for chloride was investigated. • The chloride binding capacity and early mechanical properties of OPC-SAC-GGBFS were enhanced using CLA-LDHs. • The improvement mechanism of CLA-LDHs on the performance of OPC-SAC-GGBFS was analyzed. [ABSTRACT FROM AUTHOR]

The high concentration of chloride (Cl-) ions in wastewater poses environmental risks. The bismuth oxide (Bi 2 O 3)-based Cl- removal method has gained significant attention due to its high selectivity towards Cl- ions. However, it still faces challenges related to strong acid condition and excessive dosage. Herein, the mixed-ferrites (M-Fe 3 O 4) nanoparticles with broadband absorption property were combined with Bi 2 O 3 to form to the magnetite Bi 2 O 3 (FBO) composites. Due to the space separation of M-Fe 3 O 4 nanoparticles in the thin Bi 2 O 3 flakes, FBO had a loose structure, and its sample after 100 °C treatment (FBO-100) possessed weak crystallinity and the largest specific surface area, which enabled it to possess the highest Cl- removal efficiency of 98.4% at pH = 1 in the dark. Under UV-Vis-NIR irradiation, the Cl- removal efficiencies of FBO-100 at pH = 2, 3, and 5 increased from 71.4%, 56.3%, and 54.5% to 84.6%, 65.5%, and 58.0%, respectively. During the light-irradiated Cl- removal process, the heterostructures of Bi 2 O 3 /M-Fe 3 O 4 , Bi 2 O 3 /BiOCl/M-Fe 3 O 4 , and BiOCl/M-Fe 3 O 4 were successively built, and the oxidative photocorrosion of Bi 2 O 3 caused by holes played the predominant role in improving the Cl- removal efficiency, compared with the •OH, Cl•, and O 2 •− radicals. FBO-100 had stable cyclic Cl- removal performance and high safety, which is expected to be of a good application prospect for Cl- removal. [Display omitted] • Low-crystallinity magnetite Bi 2 O 3 flat thin flakes (FBO-100) were synthesized. • FBO-100 had a high Cl- removal efficiency of 98.4% at pH = 1 in the dark. • The Cl- removal efficiencies of FBO-100 at pH = 5 reached 54.5% in the dark. • The increment of Cl- removal efficiency reached 13.2% with light irradiation. • The oxidative photocorrosion of Bi 2 O 3 caused by holes played the predominant role. [ABSTRACT FROM AUTHOR]

This paper studies the time-dependent horizontal bearing characteristic and seismic fragility analysis of carbon fiber reinforced polymers (CFRP) composite pipe piles under chloride corrosion. A diffusion model of chloride ions in CFRP composite pipe piles is established based on Fick's second law, allowing for the prediction of corrosion initiation time of CFRP composite pipe piles. The flexural stiffness of composite pipe piles for different CFRP replacement ratios is calculated, and the time-dependent horizontal bearing capacity of CFRP composite pipe pile is calculated using the finite difference method. Considering the uncertainties of structural modeling and earthquake waves, an analysis is conducted to study the effect of earthquakes on piles with different CFRP replacement ratios at various service times. The seismic fragility curves are then derived. The research results show that with the increase of service time, the flexural stiffness of CFRP composite pipe piles decreases. Moreover, higher CFRP replacement ratios result in reduced loss of pile bending stiffness and greater stability of the flexural bearing capacity. As the service time increases, the failure probability of composite pipe piles under seismic action exhibits a smaller increase, particularly for higher CFRP replacement ratios, thereby resulting in a lower loss of seismic performance. [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]

This study investigates the effects of various mineral admixtures, such as fly ash, metakaolin, and limestone powder, on the mechanical, chloride, and sulfate resistance properties of alkali-activated slag (AAS). The resistance of alkali-activated concrete (AAC) to chloride and sulfate is evaluated using the rapid chloride migration (RCM), wetting-drying cycles, SEM and XRD, TG/DTG. The results reveal that introducing fly ash improves workability but degrades the strength and durability of AAS. The 15% slag substitution by metakaolin is recommended to improve durability. Incorporating 15% limestone powder increases the compressive strength and reduces porosity due to filling and nucleation effects. The replacement ratio of 30% for each mineral admixture induces a considerable Ca2+ dilution, resulting in reducing the strength and durability of AAC. Under short-term wetting-drying cycles, the continued hydration of raw materials under MgSO 4 erosion and the subsequent production of gypsum, hydrotalcite, and brucite from the matrix initially increase the AAC strength. However, the continued substitution of calcium in the C-(A)-S-H gel by magnesium and precipitation of gypsum under excessive cycles adversely deteriorates the compressive strength. The chloride migration degree in AAC is closely related to the porosity. Although the porous gel N-A-S-H facilitates chlorine migration in accelerated tests, it prevents further chlorine penetration by adsorbing chloride ions in large quantities, exhibiting the dominant effect on chloride immobilization. The formation of Friedel's salt, stemming from the chemical bonding of chloride, is present only in the high-calcium specimen G100 and the highly reactive aluminum specimen G85M15. Improvements in the gel chemistry and porosity are key factors in bolstering the durability of AAC. The findings of this study contribute to advancing the application of eco-friendly AAC in marine environments. • Alkali-activated slag-based concretes (AACs) with different mineral admixtures are developed and evaluated. • The mechanisms on sulfate erosion and binding, chloride migration and binding of the designed AACs are explored. • Optimized alkali-activated system for marine concrete is proposed considering strength, pore structure and durability. [ABSTRACT FROM AUTHOR]

• The increase of FA content improved SAAM's capacity to bind chloride. • CaAl-LDH was the most effective in reducing the content of free Cl-. • Chloride binding capacity of MgAl-LDH was compromised by less strength loss. The chloride binding mechanism of alkali-activated materials (AAM) under various granulated blast furnace slag (GBFS)/fly ash (FA) ratios is investigated in this work. Two types of layered double hydroxides (LDH), i.e., MgAl-LDH and CaAl-LDH, and active magnesium oxide (MgO) were added to reduce the concentration of free chloride in AAM. The results demonstrate that the ratio of GBFS to FA has non-negligible influence on the AAM's ability to bind chloride. The content of bound chloride increased by 3.78%-17.42% as the FA content in seawater-based alkali-activated materials (SAAM) raised. The chloride binding forms of SAAM were mainly chemical binding by the hydrated calcium aluminate (AFm) phase and physical adsorption by calcium (alumino) silicate hydration (C-(A)-S-H) gels when the FA dosage is less than 20% in SAAM. When the FA mass ratio in SAAM was larger than 20%, the chloride binding form of SAAM was mainly the physical adsorption by calcium (sodium) alumino-silicate hydrate ((C, N)-A-S-H) gels. Among the three additive materials, CaAl-LDH was the most effective in reducing the free chlorine content by 11.34%. While for MgAl-LDH, the chloride binding capacity was compromised by the less strength loss. In this work, seawater was used as the mixing water to introduce chloride ions, the results of which could provide a reference for the application of seawater in future projects. [ABSTRACT FROM AUTHOR]

This paper aims to evaluate the inhibitive effect of sepiolite-supported Mg-Al layered double hydroxides nanocomposite (SEP@LDH) on chloride-induced corrosion of steel in simulate concrete pore solution, which was synthesized by the in-situ coprecipitation method. The results show that the nanocomposite possesses a more superior corrosion protection performance than the pure LDH. The potential mechanism can be attributed to the reduction in agglomeration and increase in dispersion of LDH layers, leading to a stronger chloride binding capacity and simultaneous release of more nitrate ions. • The SEP@LDH has a stronger chloride binding capacity than pure LDH due to the reduced agglomeration of nanosheets. • The SEP@LDH exhibits an excellent corrosion inhibition effect on steel. • The inhibition effect is ascribed to the adsorption of corrosive chloride ions and release of inhibitive nitrate ions. [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]

[Display omitted] • Phosphoaluminate cement hydrates exhibit excellent chloride binding capacity. • Chemically bound chloride due to hydration products accounted for up to 80% • C(A,P) H 10 and C 2 (A,P)H 8 chemically bind with chloride to Friedel's salt. • Al(OH) 3 and Fe(OH) 3 gels bind the chloride by weak physical adsorption. • Freundlich and Elovich models fits well for chloride binding of PAC hydrates. Phosphoaluminate cement (PAC) has the potential to prepare the anti-corrosive coatings for rebar due to with high compactness and resistance to chloride. Whereas, the reports of the binding type, its ratio and binding capacity of PAC for chloride ions are not found up to now. Thus, the chloride binding performance of PAC hydration products, as well as the binding isotherms and kinetic models, were investigated in this work. The experimental results showed that the binding capacity of the fully hydrated sample reached 21.03 mg/g in 0.56 mol/L NaCl solution. Up to 80 % of this total was non-water-soluble chloride, dominated by the chemical binding of calcium hydroaluminates (i.e., C(A,P) H 10 and C 2 (A,P)H 8). The water-soluble chloride at 20 ℃ accounted for only 20 % and was mainly adsorbed physically by Al(OH) 3 and Fe(OH) 3 gels. The whole chloride binding process of hydration products was well described using Freundlich isotherm and Elovich kinetic models. Its non-water-soluble bound chloride was more suitable for D-R isotherm and Elovich kinetic models, while the water-soluble bound chloride was more applicable to Freundlich isotherm and PSO kinetic models. These data will offer theoretical support for the rational use of PAC in constructions exposed to high chloride environments, such as the ocean. [ABSTRACT FROM AUTHOR]

• Manganese was found to precipitate as MnO 2 in sulfuric acid solutions. • The presence of Cl- ions prevented manganese compound precipitation. • Chloride-containing solutions generated Cl 2 gas during leaching. • Sulfate–chloride solutions achieved higher extractions compared to H 2 SO 4 or HCl. The current paper studies the impact of chlorides on NMC111 (LiNi 1/3 Mn 1/3 Co 1/3 O 2) leaching mechanism. Experiments were conducted in chloride (HCl) and mixed sulfate–chloride (H 2 SO 4 –NaCl) solutions as well as in sulfate solution (H 2 SO 4 , reference), in the absence of external reductants. The results suggest no major differences in the leaching performance between studied lixiviants at 30 °C (∼75% for Li, ∼35% for Co, Ni, Mn), and increasing the temperature to 80 °C mainly improved the dissolution of lithium (>90% in all lixiviants). However, the leaching behavior of manganese was found to be different – in sulfate solutions, Mn precipitated as MnO 2 with only 6% Mn left in solution after 2 h (at 80 °C), whereas in chloride-containing solutions, dissolved Mn remained soluble (30–40% extraction). The presence of chlorides also supported cobalt and nickel extraction, the mixed H 2 SO 4 –NaCl system resulting in extractions of 55% for Co and 58% for Ni at 80 °C. The increase in the dissolutions is suggested to be explained by the experimentally verified reaction between Cl- ions and NMC111, resulting in Cl 2 formation and simultaneous NMC dissolution. The results indicate that hydrometallurgical battery recycling processes may face challenges with manganese extraction to solution when operating at increased temperatures, and that the presence of chloride ions can help to mitigate such difficulties by inhibiting unwanted precipitation of manganese compounds, producing Cl 2 gas as a result. Nevertheless, as the final extractions were low even in the most effective lixiviant (55% Co, 58% Ni, 39% Mn at 80 °C), the use of additional reductants is necessary to ensure high metal leaching efficiencies also in such chloride-containing systems. [ABSTRACT FROM AUTHOR]

• High-dispersity and low-cost N-GQDs are firstly used to increase the chloride binding of cement. • The addition of 0.2 wt% N-GQDs makes the chloride binding of cement paste boost by 134%. • The chloride binding mechanism of cement pastes modified by N-GQDs is proposed. One of the most primary reasons for durability deterioration of reinforced concrete (RC) structures is reinforcement corrosion caused by chloride ion invasion. However, there is still a lack of efficient additives to enhance the anti-chloride-corrosion behavior of RC structures. Herein, highly dispersed and cost-efficient N-doped graphene quantum dots (N-GQDs) are firstly applied to significantly increase the chloride binding performance of cement. Specifically, N-GQDs with high dispersity and low cost are successfully synthesized by one-step hydrothermal method. And the typical equilibrium test determines that after 14-day exposure to 3 M NaCl solution, the incorporation of 0.2 wt% (by weight of cement) N-GQDs makes the chloride binding ability of cement paste sharply boost by 134%. Moreover, in light of phase compositions analyses from XRD, TGA and SEM, the chloride binding mechanism of cement pastes modified by N-GQDs is rationally ascribed to the fact that the addition of N-GQDs enormously increases the physically adsorbed chloride ions and slightly promotes chemically bound chloride ions. This work firstly provides a novel carbon-based nanomaterial to efficiently enhance the chloride binding of cement, expected to improve the durability of RC structures. [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]

• The variations in the adhesive properties of asphalt-aggregate under combined thermal-oxygen aging and chloride salt erosion. • Utilized both internal and interfacial erosion models for comprehensive analysis. • The spatial distribution of asphaltene exhibited a certain correlation with adhesion properties. • Differences in molecular weight, spatial configuration and polarity lead to different distribution and diffusion of asphalt components. In this investigation, various Atomic Force Microscopy (AFM) probes were used to characterize changes in the adhesion properties of aged asphalt under different concentrations of chloride salt. The characterization included analyzing the surface morphology, roughness parameters, height-height correlation function (HHCF), and force-distance curves of the asphalt. Additionally, Molecular Dynamics (MD) simulation was employed to reveal the underlying mechanisms that govern changes in adhesion properties between aged asphalt and aggregate when subjected to chloride salt erosion. Interfacial erosion and internal erosion models were constructed to facilitate a comprehensive analysis from multiple perspectives. The results demonstrate that chloride salts interact with the interface between asphalt and silica aggregates, engaging in competitive adsorption with the asphalt. The strength of this competitive adsorption is influenced by the constituents of the asphalt and the concentration gradient of chloride salts both within and outside the asphalt matrix. Under this concentration gradient, polar components are attracted to the asphalt surface by chloride ions, forming triangular adsorption structures with water molecules and aggregates such as asphaltene. Components with lower polarity exhibit distinct distributions and diffusion states due to variations in molecular weight and spatial configuration. As the concentration of chloride salts increases, the concentration gradient intensifies, resulting in enhanced transformations, migrations, and dissolutions of asphalt components. Consequently, the micro-morphology of the asphalt tends to smoothen, the HHCF undergoes significant modifications, roughness decreases, and the adhesion performance between asphalt and aggregate weakens. Moreover, at higher concentrations, the formation of precipitated chloride salt crystals disrupts the continuity of the asphalt, further compromising interfacial adhesion performance. This study is expected to provide theoretical guidance for the modification of asphalt and the improvement of asphalt pavement lifespan in complex service environments. [ABSTRACT FROM AUTHOR]

• A variable testing temperature was implemented in the dry-wet cycle test. • Effect of dry-wet ratio on mechanical properties and chloride corrosion resistance of concrete was investigated. • Higher dry-wet ratio exacerbates the deterioration of concrete performance. • Cumulative damage caused by variable temperature dry-wet cycle accelerates chloride erosion. Numerous factors influence the concrete performance in dry-wet cycle environment, with dry-wet ratio and temperature being particularly significant. In this paper, the effect of dry-wet ratios (1:3, 1:1, and 3:1) on the chloride corrosion resistance of concrete was studied, and the variable test temperature and constant test temperature were implemented in the dry-wet cycle. The deterioration law of chloride corrosion resistance of concrete was investigated, and the microstructure, phase composition, and pore structure were examined. The results showed that the deterioration degree of concrete performance was intensified by a higher dry-wet ratio. Compared with D1W3 (the dry-wet ratio is 1:3), the compressive strength, splitting tensile strength, flexural strength, mass, and relative dynamic elasticity modulus (RDEM) of D3W1 (the dry-wet ratio is 3:1) exposed to 72 dry-wet cycles decreased by 11.05%, 19.40%, 8.33%, 1.09%, and 6.14%, respectively, while the peak chloride content and erosion depth increased by 40.98% and 22.75%. Compared to the dry-wet cycle with constant temperature, the cumulative damage caused by the dry-wet cycle with variable temperature was greater, resulting in more severe deterioration of concrete performance. Variable temperature accelerated the diffusion rate and penetration depth of chloride ions. The peak chloride content and erosion depth of D1W3 were 27.08% and 18.44% higher than those of control group after 72 dry-wet cycles. Microscopic analysis confirmed that higher dry-wet ratio and variable temperature cycles accelerated the decay of mechanical strength and the decline of chloride erosion resistance. [ABSTRACT FROM AUTHOR]

[Display omitted] • HCl is an effective leaching agent. • The Cl- activity is foremost important during leaching. • The pH, stirring, and oxidant addition speed determine the selectivity. • 98–99 % pure oxides were produced. The redox equilibria – also taking chloro–complexation into account – and the thermodynamics of the HCl – Co – Ni – Mn system have been examined. The leaching efficiencies of the LiCoO 2 (LCO), LiNiMnCoO 2 (NMC111), and LiFePO 4 (LFP) black masses were studied in the 1 – 10 M HCl concentration and the 25 – 95 °C temperature ranges. A minimum of 2 M HCl concentration with an 80-minute contact time at 95 °C was sufficient to achieve > 98 % leaching yields from the LCO material. By increasing the HCl concentration to 6 M, the leaching time could be halved. The NMC cathode material could even be leached completely at 80 °C with 2, 4, 8, and 10 M HCl in 50, 40, 10, and 8 min, respectively. The same yield could be achieved even at only 25 °C using 6, 8, and 10 M HCl for ∼ 310, 125, and 50 min, respectively. A relation was found between the chloride ion activity and the leaching yields, while the evolution of Cl 2 was also examined to help explain leaching kinetics. The purity of the graphite residue reached 99.9 % (referring to Co, Ni, Mn, Li) after two cross-current leaching steps. The oxidative precipitation – using hypochlorite solutions - partially generated by utilizing the Cl 2 from leaching - was examined in the 1–6 pH range showing that selectivity significantly increases with decreasing pH, but the degree of reagent utilization also decreases. Kinetic factors were also pointed out to markedly affect selectivity. The combined hydrolytic–oxidative precipitation process could recover 96–98 % pure raw oxides, which were further refined to 98–99.8 % purity by scrubbing in acidic MnSO 4 and CoSO 4 solutions. [ABSTRACT FROM AUTHOR]

Chloride ions, omnipresent environmental pollutants, can have devastating and irreversible effects on sustainable water ecosystems worldwide. Herein, bismuth oxide (Bi 2 O 3) was employed as an antichlor to effectively dislodge chloride, and systematic investigations were conducted to assess the effect of various factors on dechlorination. Response surface methodology with Box-Behnken designs was used to optimise the dechlorination process, and the control parameters were determined by fitting high quality predictive model incorporating saliency variables and interactions. Furthermore, X-Ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS) were performed to determine the phase composition, micromorphology and binding energy of the dechlorinated products. The optimum parameters for dechlorination, as determined by response surface methodology (RSM), were found to be pH 0.53, bismuth trioxide multiple of 1.48, and initial chloride concentration of 3.62 g/L, giving a theoretical removal rate of 90.0563 %. The data analysis presented provides evidence that response surface methodology is a reliable approach for optimizing the interaction effects of dechlorination process parameters, resulting in improved performance in the removal of almost non-removable chloride. • Bismuth trioxide successfully used as a recycle dechlorination agent. • The effect of different parameters was evaluated using design expert software. • Response Surface Methodology was applied for process optimization. • The morphology and characterization of dechlorination products were investigated. [ABSTRACT FROM AUTHOR]

• Revealing the coupling effects on chloride ion transport caused by carbonation, FT cycles, loading states and levels, temperature, and saturation. • Modelling essentially the chloride ion transport under the coupling effects of carbonation, FT cycles, loading states and levels, temperature, relative humidity, saturation and concrete deterioration. • Revealing the degradation laws of flexural capacity of the multi-factor corroded beams. Reinforced concrete (RC) structures are often exposed to coinstantaneous deterioration effects such as carbonation, chloride corrosion, freeze–thaw cycles and external loads which causing deterioration of concrete and reinforcement. This paper discussed the effects of carbonation, freeze–thaw cycles and sustained loads on chloride ion transport and proposed a chloride ion transport model taking porosity as the main coupling variate. The attenuation law of the corroded beams under coupling corrosion factors was studied. Through chloride immersion tests, it was found that applying freezing and thawing cycles and sustained tensile stress can enhance chloride transport capacity by coarsening the pores; Carbonation and low compressive stress can repress the chloride ion transport by densifying concrete, but the compressive stress beyond about 0.7 times the compressive strength and tensile stress would enhance the penetrating capacity due to the damage of the internal microstructure of concrete. Then, a comprehensive and unified theoretical model of chloride ion transport considering the coupling of carbonation, freeze–thaw cycle, sustained loading and other factors was proposed and verified by taking porosity as the main coupling variable quantity. This model could essentially explain the effects of various factors on chloride ion transport and has good consistency with the test results. Finally, the flexural bearing capacity of the corroded beams was tested, and the failure characteristics, crack characteristics, ultimate bearing capacity, load–displacement relationship and strain distribution of the corroded beams under different corrosion conditions were researched. The results show that the flexural capacity of the corroded beams suffered the coupling effects of multiple corrosion factors degrades, and the bearing capacity decreases with the increase of the corrosion degree of carbonation-freezing thawing cycles; The continuous tensile stress applied to the test beams in the corrosion process intensifying the degradation of bending bearing capacity and ductility, the continuous compressive stress increases the flexural capacity and improves the ductility slightly, but excessive compressive stress significantly degrades the flexural capacity; When chloride ions are used as the third kind of corrosive substance for coupling corrosion, the tensioned or without-load corroded beams have obvious degradation in bending bearing capacity, while the corrosion beams bearing continuous compressive stress have no obvious degradation in bending bearing capacity. [ABSTRACT FROM AUTHOR]

The synergistic corrosion resistance microcapsules (SCRMs) were synthesized by utilizing CaAl–NO 2 LDH (NO 2 -LDH) as chloride trigger and high-performance corrosion inhibitor to hybridize self-healing microcapsules. The morphology, chemical structure and self-healing performance of the microcapsules were characterized. The chloride triggering and corrosion resistance property of the SCRMs were evaluated. The interaction of hybrid wall, NO 2 -LDH and chloride ion was calculated by first-principles. The findings revealed that the microcapsules show regular spherical with obvious core-wall structure. EDS and chemical structure measurements confirmed that NO 2 -LDH was successfully embedded within the microcapsule wall. The SCRMs showed excellent corrosion resistance property in simulated chloride-contaminated concrete pore solution (SCPS), and the highest inhibition efficiency was 97.85%. The microcapsule wall was hybridized by NO 2 -LDH species through chemical pathways. The first-principles calculation results confirmed that Ca and Al species are the main factors for chloride ion immobilization of hybrid wall. The ion exchange process of microcapsules destroys the molecular force of NO 2 -LDH@ethyl cellulose hybrid wall and improves the mechanical triggering efficiency of microcapsules in cement-based composites. [Display omitted] • CaAl–NO 2 LDH was employed as the chloride trigger and corrosion inhibitor to prepare synergistic corrosion resistance microcapsules. • The mechanism of hybridization and corrosion resistance was discussed through experimental characterization and first-principles calculation. • The mechanical triggering efficiency of microcapsules in cement-based composites is improved by ion exchange. • The corrosion resistance property of rebar in cement-based composites is enhanced by synergistic corrosion resistance microcapsules through the triple effect. [ABSTRACT FROM AUTHOR]

• A diatomite-based test bar is invented for rapid test of chloride in fresh concrete. • A relationship between indicator number and chloride content is established. • The test bar has a mesoporous structure to provide a strong capillary effect. • Chloride in uptake liquid is gradually consumed to generate a coloration edge. This study employed diatomite-based materials to load silver chromate to prepare a novel rapid test bar for chloride ions in fresh concrete. Liquid uptake efficiency and coloring consistency were taken into account when optimizing the preparation. Microscopic properties were examined via multiple techniques to elucidate the mechanisms. A relationship between indicator numbers and chloride contents of fresh concrete was established. The environmental stability of test bars was examined to guarantee that they would work as expected. Results showed that the test bars, combined with the conversion relationship, are applicable and stable for detecting chloride content in fresh concrete. The primary component of test bars is made of diatomite and portlandite and has a mesoporous structure. Diatomite is in charge of capillary attraction while portlandite plays a skeleton role. When the uptake solution moves upward, chloride ions are gradually consumed. At a certain height, the chloride content is insufficient to support the chromogenic process, resulting in a certain coloration edge. [ABSTRACT FROM AUTHOR]

There are several cases worldwide wherein sulfide-bearing aggregates in concrete elements/structures have undergone oxidation and caused extensive damage. Signs of observed deterioration include map cracking, pop-outs, and secondary products that were generated from swelling. Unfortunately, it takes years to detect these signs visibly. Thus, in this study, a new methodology is proposed to activate and accelerate the potential oxidation reaction of iron sulfide minerals in concrete aggregates using chloride ions as activators or catalysts for the oxidation reaction. To promote the rapid penetration of chloride ions through concrete specimens, an electrochemical treatment is proposed consisting of two main phases, namely chloride impregnation in the specimen and impressed voltage treatment. Concrete specimens each 100 mm in diameter and 200 mm in length were made using aggregates with or without iron sulfide minerals and a mix design resembling the one used for building house foundations in the Trois-Rivières case, Canada. The results showed that chloride ions could activate the reaction and act as catalysts for the oxidation reaction of sulfide-bearing aggregates under a constant current (impressed voltage). Finally, traces of iron oxides/hydroxides and the formation of secondary sulfates (i.e., gypsum and ettringite) were observed in the concrete made with sulfide-bearing aggregates. This new procedure is promising for evaluating the oxidation potential of concrete with sulfide-bearing aggregates over a reasonable testing period. [ABSTRACT FROM AUTHOR]

Nano-SiO 2 @MgAl-layered double hydroxides (NS@MgAl-LDH) core-shell nano-composites were successfully synthesized by a co-precipitation method. The as-synthesized NS@MgAl-LDH was characterized by SEM, TEM, EDX, TGA and BET. The equilibrium, thermodynamic and kinetic studies on the chloride sorption of NS@MgAl-LDH were performed in simulated concrete pore solution (SCPS). The results show that NS@MgAl-LDH exhibits a higher specific surface area (SSA) compared to MgAl-LDH. Besides, the chloride sorption capacity of NS@MgAl-LDH is significantly higher than that of pure MgAl-LDH, which is obviously influenced by initial pH-value and amount of adsorbents addition. Also, the chloride sorption process can be fitted by the Langmuir-model thermodynamically and the pseudo-second-order kinetics kinetically. The negative values of Gibbs-free energy (ΔG0) and standard enthalpy change (ΔH0) indicate that the chloride sorption is spontaneous and exothermic. Furthermore, the outstanding chloride sorption capacity of NS@MgAl-LDH is mainly contributed to the ion-exchange of chloride ions with interlayer ions in the highly dispersed MgAl-LDH. • The NS@Mg-Al LDHs has been successfully synthesized. • The NS@Mg-Al LDHs exhibits a higher Cl− binding capacity. • The sorption processes can be better fitted by Langmuir-model. • The sorption processes are controlled by pseudo-second-order. • The sorption processes are spontaneous and exothermic in nature. [ABSTRACT FROM AUTHOR]

[Display omitted] • GO-CAFSS could effectively inhibit sea sand chloride leaching. • GO-CAFSS could mitigate GO agglomeration and improve the ITZs. • GO-CAFSS could improve both physical and chemical chloride binding capacity. • GO-CAFSS was proved to be an efficient way for sea sand chloride control. The scarcity of river sand has resulted in the inappropriate use of sea sand in numerous countries, particularly in coastal regions. Without effective desalination techniques and sufficient monitoring, the presence of chloride ions in sea sand leads to rapid reinforcement corrosion and frequent structural failures every year. In this paper, a novel pre-treatment method utilizing graphene oxide (GO) coating on amino-functionalized sea sand (GO-CAFSS), and the effects of GO-CAFSS on suppressing internal chloride leaching and performance of sea sand cement-based composites were investigated. Due to strong covalent bonds between GO and amino-functionalized sea sand, agglomeration of GO in the cement matrix is restrained, which leads to enhanced cement hydration and densified ITZs proved by combined microstructure tests. The chloride leaching test shows that the mass percentage of chloride ions leached from the surface of GO-CAFSS are effectively inhibited, from 0.082% (untreated sea sand) to 0.042%. The chloride binding experiment reveals that the treatment of sea sand cement-based composites with GO-CAFSS can enhance their chloride binding capacity by up to 39.5% after 14 days of exposure to NaCl solution. XRD/TGA test results indicate that GO can enhance the chloride binding capacity by promoting calcium silicate hydrate (C-S-H) and Friedel's salts (FS) formation, further increasing the physical adsorption and chemical substitution of remaining free chloride ions in the pore solution. It is also found that GO can contribute to the conversion of Ettringite (AFt) into FS with Cl− substituting SO 4 2− to a certain extent, especially with additional intermixed SO 4 2− brought by sea sand. Overall, GO-CAFSS is investigated to be a promising way for making high performance sea sand cement composites with harmful chloride ions effectively controlled. [ABSTRACT FROM AUTHOR]

Ground granulated blast furnace slags (GGBFS/slag) can have a range of chemical compositions, especially in alumina content that could potentially affect several concrete properties including chloride binding capacity and chloride penetration. Chloride binding capacity and diffusivity of several cement-slag combinations were assessed using two slags of 8% and 17% alumina contents and four cements, ASTM C150 Type I, ASTM C150 Type I (high alkali), ASTM C150 Type II(MH) and ASTM C595 Type IL(14) at a cement replacement level of 60%. The findings indicate slag addition improved chloride binding and lowered chloride diffusivity. Between the two slags, chloride binding capacity was higher in high alumina slag. Type I cement mixtures had the highest binding capacity while it was the lowest in Type IL cement mixtures due to lower C 3 A, C 3 S and clinker factor. Chloride diffusivity experiments showed that plain Type IL mixture had the highest chloride ion penetration while it was the lowest when blended with high alumina slag due to carboaluminate formation. Therefore, chemical, mineralogical, and physical characteristics of cement-slag combination should be considered in service life analysis of slag blended concrete mixtures. [ABSTRACT FROM AUTHOR]

[Display omitted] • Laser-Induced Breakdown Spectroscopy (LIBS) is a powerful tool for the analysis of chloride diffusion in mortar and concrete. • The LIBS measurements shows that chloride ions penetration profiles through the samples fit reasonably well Fick's second law in a modified version. • The apparent diffusion coefficients measured by LIBS for the mortar and concrete samples agree with the results obtained by other techniques. • The LIBS was used to study the aging of mortar samples, an age-factor α = 0.449 ± 0.006 was measured. In this work, the applicability of Laser-Induced Breakdown Spectroscopy (LIBS) for the analysis of chloride diffusion in mortar and concrete has been studied. The high resolution of this technique allows it to obtain a mapping of the chloride ions distribution in these materials upon being exposed to salted environments, thus providing an image of how chlorides diffuse inside them. The technique has been applied to mortar samples submerged in a salt-saturated solution for 3, 9, and 30 months. It has been demonstrated that the penetration profiles fit reasonably well Fick's second law in a modified version. The apparent diffusion coefficients for these samples were obtained (D 3months = (5.94 ± 0.05) × 10−13 m2/s; D 9months = (3.6 ± 0.6) × 10−13 m2/s; D 30months = (2.1 ± 0.8) × 10−13 m2/s). These results are in the range of the values found in other similar studies. The study of the evolution of these parameters over time revealed an age-factor α = 0.449 ± 0.006. Finally, LIBS was also applied to a concrete sample submitted to a long-period (60 months) immersion in the salt-saturated solution, giving similar good results (D 60months = (1.81 ± 0.03) × 10−13 m2/s), which demonstrates its suitability for the study of chloride diffusion in this type of material. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical approach, which comprises the chloride transportation model and cover cracking model, to predict the service life of RC seawall under chloride invasion. The chloride transportation model combined the Fick's second law and Darcy's law to model the convection-diffusion of chloride ions in the RC seawall. The governing equation for chloride migration in the RC seawall is solved with the separation of variables technique. The proposed model is validated by comparing with a corresponding finite difference solution and the experimental results. The mechanical model that represents the cracking of the concrete cover induced by the expansion pressure of the corrosion products is finally developed to predict the service life of the RC seawall under chloride invasion. Parametric studies are performed to illustrate the effects of convection-diffusion and other key variables on the chloride ions transportation and service life of the RC seawall. The results reveal that the convection effect substantially accelerates the chloride penetration process in the chloride gradient descent direction while inhibits the penetration in the opposite direction. The proposed analytical solution in conjunction with the mechanical model provides a theoretical approach for predicting the service life of RC seawall, which can be used to aid durability design of coastal structures. • Theoretical approach for predicting service life of RC seawall. • Convection-diffusion coupled diffusion model for chloride migration in RC seawall. • Mechanical model for cracking of concrete cover caused by corrosion products. • Convection accelerates corrosion and causes asymmetric chloride distribution. [ABSTRACT FROM AUTHOR]

• Cl- ions are useful to form P-zwitterion-(Cl)-Fe and zwitterion-(Cl)-Fe complexes. • LA is not recommended to be used alone in concrete for corrosion protection. • PO 4 3- ions help to form P-zwitterion-(Cl)-Fe and FePO 4 for corrosion resistance. • LA and PO 4 3- ions considerably increased the chloride threshold of steel rebar. The hybrid inhibitor performs excellently compared to either organic or inorganic inhibitor individually. In the present studies, a fixed amount i.e. 2 wt% l -arginine (LA) and 0.25 wt% trisodium phosphate dodecahydrate (TSPDH) is considered as hybrid inhibitor and its chloride threshold is determined by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) in simulated concrete pore solution and the formed passive films are characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy after 240 h of immersion. The chloride threshold of this hybrid inhibitor is 6 wt% NaCl, i.e., C3 until 216 h of immersion, whereas if the amount is increased, the steel rebar leads to corrode severely. 5 wt% NaCl containing sample, i.e., C 2 exhibits the noble OCP, highest impedance, and lowest passive current density attributed to the consumption of all zwitterion and phosphate ions in the formation of P-zwitterion-(Cl)-Fe, zwitterion-(Cl)-Fe and FePO 4 complexes with NaCl, whereas lower or higher than this amount of NaCl, the Cl- ions either lesser or greater to be formed these complexes. [ABSTRACT FROM AUTHOR]