Chloride Ion Diffusion Research Articles

Study of Chloride Ion Diffusion in Coral Aggregate Seawater Concrete with Different Water-Cement Ratios under Load.

This study was conducted to investigate the chloride ion transport in coral aggregate seawater concrete (CASC) with varying water-cement ratios under different loads. The ultimate compressive strength was obtained by conducting compression testing of three groups of CASC with different water-cement ratios. Steady loads of 0%, 10%, and 20% of their respective ultimate compressive strengths were applied to the concrete specimens with different water-cement ratios. After being subjected to a seawater erosion test for 30, 60, 90, 120, and 180 days, the chloride ion concentration at different depths was measured to determine the chloride ion diffusion coefficient. Meanwhile, the chloride ion diffusion coefficients of CASC were verified by comparing them with results obtained from numerical simulations performed using COMSOL software. The test results show that the internal pore space of CASC expands, leading to acceleration of the chloride ion transport rate when applied loads are increased. The initial chloride ion concentration of CASC rises as the water-cement ratio rises, and the concentration gradient formed with artificial seawater lowers, decreasing the chloride ion transport rate. When the water cement ratio decreases and the load increases, the diffusion coefficient increases. Using the numerical simulation method of COMSOL software, it was proved that the model has good applicability and accuracy in predicting chloride ion transport in CASC.

Durability enhancement mechanism of mortar using blast furnace slag fine aggregate against combined deterioration of frost and salt damage

The effect of BFS (Blast Furnace Slag Fine Aggregate) on the freezing and thawing resistance under chloride environment was evaluated, and the freezing and thawing resistance was proven to be improved by using BFS with fine grain size and by increasing the mixing ratio of BFS to natural sand. The electrical resistivity and effective chloride ion diffusion coefficient were measured in order to evaluate the effect of BFS on the resistance of the penetration of chloride ions into concrete, and the mortar using BFS had higher electrical resistivity and lower effective chloride ion diffusion coefficient than the mortar using mountain sand. In order to elucidate the reaction products at the interface between cement paste and BFS, which cause densification of the BFS interface when BFS is used as fine aggregate in concrete, an investigation and analysis of the reaction products were conducted using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As a result, it was found that a reaction phase is formed in the BFS-cement paste interfacial transition zone (ITZ), and its thickness is 0.45 to 1.4 μm. TEM observation and selected-area diffraction (SAD) analysis revealed the existence of hydrotalcite-like compounds in the BFS-cement paste ITZ. The chloride enrichment in hydrotalcite-like compounds at ITZ was confirmed by TEM observation and TEM-EDS of mortar with BFS after freeze–thaw tests under chloride environment. Therefore, it was considered to contribute to the improvement of the resistance of the penetration of chloride ions into concrete mixed with BFS.

An Investigation of Electrochemical Dechlorination of Wrought Iron Specimens from the Marine Environment

The research shows the benefits provided by the use of electrochemical treatment, with the application of impressed current combining the use of a porous medium for the dechlorination of large iron structures removed and/or located in the marine environment. Considering the previous work for the dechlorination of the paddle wheel of the shipwreck “Patris”, located in the Aegean Sea, this study aims to determine the optimum parameters of the amount of current density, the time and the use of the porous medium to stimulate the chloride ion diffusion into an alkaline solution. Specimens of wrought iron coming from the shipwreck were electrochemically treated and the efficiency of the method was verified by the determination of the chloride concentration removal using a chloride ion selective electrode. Samples of corrosion products before and after treatment were analyzed for chloride content using SEM-EDX analysis. The results found that changing the porous medium every 24 h with replenished alkaline solution and using a stainless steel mesh is the best approach for the dechlorination of the specimens. This electrochemical method, is economical and fast, and can be applied to the conservation of large iron structures in situ, coming from and/or located near a marine environment with less waste than the traditional dehlorination methods.

SIMULATION OF CHLORIDE ION TRANSPORT AND EROSION IN FRACTAL POROUS MEDIA UNDER MULTI-FIELD COUPLING

Concrete is an important part of submarine building structure, which is eroded by hydrostatic pressure and chloride ion. In this study, concrete is regarded as a dually-porous structure composed of pores and fractures. Considering hydrostatic pressure and fractal characteristics of concrete structure, a fractal model is established for chloride ion diffusion under the dual drive of concentration and pressure. Considering the effective stress caused by water pressure in pores of concrete, a fluid–solid model for chloride ion migration is proposed. The fluid–solid coupling fractal model for chloride ion migration was verified by comparing with the experimental data. The numerical simulation results show that: (1) the influence of fractal dimension on the chloride ion diffusion coefficient and chloride ion concentration is nonlinear; (2) compared with low hydrostatic pressure, high hydrostatic pressure has more significant effects on chloride ion concentration and diffusion coefficient; (3) when the effective stress and water pressure in pores are not considered, the diffusion coefficient of chloride ion is always a constant.

Formation of environmentally friendly protective Ce2O3-CeO2 conversion coatings on Al, modified by phosphate layers: chemical and electrochemical characterization

Conversion ceria coatings were deposited on substrates of Al-1050 in a solution containing CeCl3×7H2O and CuCl2×2H2O. The post-treatment of as deposited coatings was realized in phosphate-containing solutions: 0.08 M Na3PO4 or 0.22 M NH4H2PO4. The XPS characterization of the surface of samples was carried out on an AXIS Supra electronspectrometer (KratosAnalytical Ltd.). The electrochemical investigations and determination of the basic corrosion parameters (Ecor, icor, Epit, EOCP, Rp, CR, etc.) for the studied systems were carried out on a Gamry Interface 1000 (EISSFR Analyzer EIS300). Based on the XPS investigations, it was ascertained that there is a substantial influence of the “pretreatment” and “post-treatment” operations on the chemical composition and chemical state of the elements on the samples` surface. It is expressed by a strong decrease in the concentration of Аl2O3 and Ce2O3+CeO2 components in the ceria coatings at the expense of formation of AlPO4 and AlOOH, CePO4, as well as PO3-, P2O5 and P4O10 compounds with Al and Се. The comparison of the results of Rp values and concentrations of Ce3+/Се4+, Al and P shows that the changes in Rp and quantity of Се4+ and P on the surface of the studied samples are directly related. The supposed and proved formation of low-soluble corrosion products on the surface of the studied systems and accomplished synergic effect of protective action by the formed cerium and aluminum oxides/phosphates layers determine the increase of the Rp and decrease of icor and CR, respectively. It was also concluded that the mixed conversion layers are a more effective barrier for the chloride ions diffusion to the metal surface and increase the corrosion resistance of Al 1050 to pitting and general corrosion.

Durability enhancement of half-joints in RC bridges through external prestressed tendons: The Musmeci Bridge’s case study

This paper numerically investigates the effect of post-tension interventions to strengthen the deteriorated half-joints of the Musmeci Bridge in Potenza (Italy), with the primary objective of increasing the ultimate load-bearing capacity and monitoring the secondary effects in terms of preventing or limiting cracking patterns. Bearing this in mind, the study aims to investigate the role of the reinforcement detailing, of the post-tension stress and of the corroding time in the presence of chlorides, outlining the intervention ability to improve the structure’s durability. To this end, nonlinear finite element models are provided with chloride ions diffusion analysis to investigate corrosion initiation and progress in reinforced concrete elements and account for deterioration due to two scenarios (45 and 95 years). Results show the significant impact of reinforcement layout as the presence of inclined bars increases the ultimate load by about 86 %. The ultimate load improvement is in the range 50–55 % when the intervention is carried out after 45 years while it is equal to about 30–35 % if a period of 95 years is last since the construction. This latter highlights the significant influence of the intervention timeliness on structural durability.

Chloride corrosion resistance of cement mortar with recycled concrete powder modified by nano-silica

In the marine environment, the service life of coastal structures can be significantly reduced on account of chloride corrosion. This study employed nano-silica (NS) to improve the chloride corrosion resistance of mortar samples prepared with recycled concrete powder (RCP). The free chloride ion concentration and mechanical strength of mortar samples in 3.5% NaCl solution up to 12 months were measured. Rapid chloride migration (RCM) and electric flux experiments were carried out. Compared with the pure RCP mortar, the 2% NS incorporated RCP mortar experienced a significant decrease in the chloride ion diffusion coefficient, electric flux and corrosion rate of internal rebar. Moreover, the RCP mortar with 2% NS also had the slowest increase in the free chloride ion concentration and surface chloride ion concentration. The addition of RCP in cement mortar reduced the chloride corrosion resistance, while the inclusion of 2% NS compensated for the RCP induced degradation, resulting in an improvement in chloride corrosion resistance. The X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) results showed that the addition of RCP and NS consumed Ca(OH)2 to generate more C-S-H gels and C-A-S-H gels and thereby improved the physical chloride-binding ability of the sample. In addition, the formation of Friedel’s salt via the combination of chloride ion with aluminosilicate further improved the chlorine ion corrosion resistance.

Time-dependent chloride transport models for cracked concrete bridge decks under chloride attack

The aims for this study is to develop time-dependent models of chloride diffusion using the survey data of sixteen sites of cracked concrete bridge decks under the influence of chloride attack in form of de-icing salts. This is taken into account, because it is evident that the diffusion of chloride ions through cracked concrete is different from that of uncracked one. The developed models consist of two main models, containing 4 parameters for regression. From the development, the models of chloride diffusion can predict the content of chloride ions through cracked concrete bridge decks in an average sense. Based on the prediction by the developed models, the long-term content of chloride ions near cracked concrete surface is found lower than that near uncracked one, because those chloride ions penetrate deep inside bridge decks. Because of this penetration, the increase of chloride ions near the surface of cracked concrete bridge decks is slower than that of uncracked ones. Moreover, the comparison of the diffusion coefficient indicates that the diffusion of chloride ions through cracked concrete bridge decks is faster than that through uncracked one. Considering the crack-free condition of concrete bridge decks, the available critical value of chloride ions for concrete cracking of 2.0 kg/m3 tends to overestimate the initiation time of concrete cracking. However, the critical chloride value for concrete cracking is here recommended as no more than 0.355 kg/m3 for more conservative condition.

Probability-based prediction of service life and energy-use due to silane-based treatment on chloride-exposed concrete structures

This study aims at performing probability-based prediction of chloride penetration into silane-treated concrete and the cumulative amount of energy-use due to silane-based treatment. There are five random variables to be considered. With various times of silane-based treatment, this study proposes three repair plans. Here, the Latin Hypercube algorithm is embedded in a Crank-Nicolson based finite difference framework. Using this self-developed framework, various studies are observed. It is found that the prolongation of the time, that the content of chloride ions at a specific depth approaches the critical chloride amount for the corrosion of reinforcing bars, occurs due to retarding the diffusion of chloride ions in concrete with silane-based treatment. If the application of silane-based treatment is earlier and more often, the extension of the service life is longer. Focusing on either the service life prolongation or the expected cumulative amount of energy-use, it is not simple to judge the best plan because the silane-based treatment plan with earlier and more often applications is both better in extending the service life and the worst due to causing higher expected cumulative amount of energy-use. To remedy this situation, this paper introduces the ratio of the expected cumulative amount of energy-use to the benefit of silane-based treatment. Using this proposed ratio, an optimum silane-based treatment plan can be judged.

Performance evaluation of acrylate terpolymer based coating on anti-carbonation

PurposeThe purpose of this study is to examine how well reinforced concrete structures can be shielded against concrete carbonation using anti-carbonation coatings based on synthetic polymer.Design/methodology/approachApplying free radical polymerization, an acrylate terpolymer emulsion that a surfactant had stabilized was created. A thermogravimetric analysis, minimum film-forming temperature, Fourier transform infrared spectroscopy and particle size distribution are used to characterize the prepared eco-friendly water base acrylate terpolymer emulsion. Using three different percentages of the acrylate terpolymer emulsion produced, 35%, 45% and 55%, the anti-carbonation coating was formed. Tensile strength, tensile strain, elongation, crack-bridging ability, carbon dioxide permeability, chloride ion diffusion, average pull-off adhesion strength, water vapor transmission, gloss, wet scrub resistance, QUV/weathering and storage stability are the characteristics of the anti-carbonation coating.FindingsThe formulated acrylate terpolymer emulsion enhances anti-carbonation coating performance in CO2 permeability, Cl-diffusion, crack bridging, pull-off adhesion strength and water vapor transmission. The formed coating based on the formulated acrylate terpolymer emulsion performed better than its commercial counterpart.Practical implicationsTo protect the steel embedded in concrete from corrosion and increase the life span of concrete, the surface of cement is treated with an anti-carbonation coating based on synthetic acrylate terpolymer emulsion.Social implicationsIn addition to saving lives from building collapse, it maintains the infrastructure for the long run.Originality/valueThe anti-carbonation coating, which is based on the synthetic acrylate terpolymer emulsion, is environmentally benign and stops the entry of carbon dioxide and chlorides, which are the main causes of steel corrosion in concrete.

Durability of Reinforced Concrete with Additions of Natural Pozzolans of Volcanic Origin.

In this work, the properties of concrete modified with dosages of natural pozzolans (NP) in substitution of cement or superfine aggregates were evaluated. Proportions of 20/80 pozzolan/cement or pozzolan/superfine aggregates were selected for the additions of quarry and tuff pozzolans. Pozzolanic activity, durability, compressive strength, characteristic resistance, settling consistency, density, electrical resistivity, depth of water penetration, accessible porosity, and carbonation and chloride penetration were determined for the resulting concrete mixtures, and they were subsequently compared to the values obtained for the reference concrete batches without additions. The results of the cementitious mixtures supplemented with tuff (PZT) and quarry (PZQ) pozzolans, expressed in mmol/L, are consistent with the pozzolanism test, with [Ca(OH)2]/[OH-] ratios at 7 days are 6.03/60.19 for PZQ and 1.78/92.78 PZT. In addition to the pozzolanic activity at these dosages, the characteristic resistance and durability parameters required by EHE-08 were verified. Particular attention was given to the determination of the diffusion of chloride ions, introducing an instrumental modification of the accelerated integral method. The modification provides values of diffusion coefficients similar to those obtained by the other methods with the advantage of greater stability and quality of the measurement.

A Cross-Scale Framework for Modelling Chloride Ions Diffusion in C-S-H: Combined Effects of Slip, Electric Double Layer and Ion Correlation.

Water and chloride ions within pores of cementitious materials plays a crucial role in the damage processes of cement pastes, particularly in the binding material comprising calcium-silicate-hydrates (C-S-H). The migration mechanism of water and chloride ions restricted in C-S-H nanopores is complicated due to the presence of interfacial effects. The special mechanical properties of the solid-liquid interface determine the importance of boundary slip and Electric Double Layer (EDL) and ion diversity in pore solutions determines the difference of the EDL and the stability of water film slip. A cross-scale model covering slip effects, time-varying of EDL and ion correlation needs to be developed so that the interfacial effects concentrated at the pore scale can be extended to affect the overall diffusivity of C-S-H. The statistics of pore size distribution and fractal dimension were used to quantitatively compare the similarities between model and C-S-H structure, thus proving the reliability of cross-scale reconstructed C-S-H transmission model. The results show that the slip effect is the dominant factor affecting the diffusion ability of C-S-H, the contribution of the slip effect is up to 60% and the contribution rate of EDL time-varying only up to about 15%. Moreover, the slip effect is sensitive to both ion correlation and C-S-H inhomogeneity and EDL time-varying is almost insensitive to ion correlation changes. This quantification provides a necessary benchmark for understanding the destructiveness of cement-based materials in the salt rich environment and provides new insights into improving the durability of concrete by changing the solid-liquid interface on the micro-nanoscale.

Passivity of AlCrFeMnTi and AlCrFeCoNi high–entropy alloys in Hanks’ solution

The present work studies the passivation characteristic and corrosion resistance of Al20Cr5Fe50Mn20Ti5 and Al7Cr23.26Fe23.26Co23.26Ni23.26 high–entropy alloys in Hanks’ solution at 37 °C, in view of potential biomedical applications. The Al7Cr23.26Fe23.26Co23.26Ni23.26 possesses a higher corrosion resistance than Ti-6Al-4 V alloy, mainly due to the formation of a stable p–type passive film composed of Cr(OH)3, Cr2O3, CoO, Co3O4, and Ni(OH)2, leading to low vacancy concentration and limited ion conductivity. The Al20Cr5Fe50Mn20Ti5 exhibits an n–type passive film composed of Fe2O3, Fe(OH)3, TiO2, and MnO2 that promotes chloride ions adsorption and diffusion–controlled corrosion, while its microstructural precipitates allowed a selective dissolution.

Research on Impermeability of Underwater Non-Dispersible Concrete in Saline Soil.

The permeability of different strength grades of submerged non-dispersible concrete with different granulated slag admixtures in a saline soil environment simulated by different erosion solutions was investigated. The variation patterns of the chloride ion diffusion coefficient and pore characteristics were tested using NEL and MIP. The microscopic morphology of the specimens in different erosion environments and with slag doping was observed using SEM. The results showed that the impermeability of concrete in sulfate and complex salt environments was significantly reduced. The resistance of concrete to chloride ion penetration increased with the increase in strength grade, and the Cl- diffusion coefficient of C35 was 5-30% lower than those of C30 and C25 underwater non-dispersible concrete at 360 d. Meanwhile, the admixture of granulated blast-furnace slag optimized the pore size distribution and improved the matrix compactness and permeability.

CHARACTERIZATION OF CHLORIDE IONS DIFFUSION IN CONCRETE USING FRACTIONAL BROWNIAN MOTION RUN WITH POWER LAW CLOCK

In this paper, we propose a revised fractional Brownian motion run with a nonlinear clock (fBm-nlc) model and utilize it to illustrate the microscopic mechanism analysis of the fractal derivative diffusion model with variable coefficient (VC-FDM). The power-law mean squared displacement (MSD) links the fBm-nlc model and the VC-FDM via the two-parameter power law clock and the Hurst exponent is 0.5. The MSD is verified by using the experimental points of the chloride ions diffusion in concrete. When compared to the linear Brownian motion, the results show that the power law MSD of the fBm-nlc is much better in fitting the experimental points of chloride ions in concrete. The fBm-nlc clearly interprets the VC-FDM and provides a microscopic strategy in characterizing different types of non-Fickian diffusion processes with more different nonlinear functions.

Experimental Study on the Application of Cementless Material with Industrial By-Products to Steam-Cured Precast Concrete Products.

The purpose of this study was to apply a cementless binder using industrial by-products (fly ash, ground-granulated blast furnace slag, and silica fume) to precast concrete products. In this binder, calcium hydroxide was included as an alkali stimulant but Portland cement was not included. Experiments on the compressive strength and durability of this type of material were conducted and its applicability to precast concrete products was investigated using full-scale specimens. The experiments proved that high-temperature steam curing is effective at obtaining strength development and that compressive strength can be expressed as a linear function of the binder-water ratio. Experimental results of chloride ion diffusion coefficient and sulfuric acid resistance suggested that the proposed material has higher resistances than conventional cement concrete against these deterioration factors. It was also demonstrated that full-scale specimens of a box culvert and a centrifugally compacted pipe using this type of material have almost the same load-bearing capacity and deformation performance as those using conventional cement concrete. It is believed that the proposed material could be used as a construction material instead of cement concrete, contribute to reducing CO2 emission, and increase the reuse of industrial by-products.

Improving the adhesion properties of cement/epoxy interface using graphene-based nanomaterials: Insights from molecular dynamics simulation

The cement/epoxy interface is a critical component in a repair system. Normally, the adhesion properties of the epoxy coating are negatively affected by the presence of moisture or the ingress of harmful species to the interface. In this paper, the interfacial properties between the cross-linked epoxy and hydrated calcium silicate (C–S–H) using graphene (GR) and graphene oxide (GO) nanomaterials were investigated utilizing molecular dynamics (MD) simulation. Various reinforcement schemes were adopted, including adding the GR or GO layer and modifying the epoxy with GR or GO nanomaterials. In addition, three exposure systems (dry, wet, and salty) were considered. The results indicated that introducing a GO sheet at the epoxy/C–S–H interface enhanced the adhesion energy as the oxygen-containing functional groups in the GO provided better tight-binding patterns with the C–S–H surface as well as the epoxy overlay. Modifying the epoxy by GR nanosheet also increased the adhesion energy due to its suitably-oriented conformation inside the epoxy matrix. Moreover, the introduction of graphene reinforcement effectively mitigates the diffusion of moisture and chloride ions. The reported results will certainly enhance our understanding of the sustainability and durability of the epoxy-bonded concrete systems under aggressive moist and chloride environments.

Chloride ion transport behavior of concrete containing insulating glazed hollow beads exposed to high temperature

• GHBs are beneficial to improve impermeability of concrete after fire. • GHBs have great significance for improving the concrete resistance to thermal damage. • The chloride ion diffusion and remaining service life of GIC after fire was calculated. • A thermal damage permeability model was established. Concrete building structures often suffer serious damage after fire, which poses a great threat to the durability of structures. Due to the high thermal stability and pressure relief mechanism of glazed hollow beads (GHBs), GHBs are of positive significance in improving the concrete’s resistance against high temperature. In this paper, the electric flux test was utilized to investigate the chloride ion transport behaviors of concrete containing insulating GHBs (GIC) after high temperature exposure. The electron probe micro-analysis (EPMA) combined with chemical titration method was adopted as a supplement to carry out a more in-depth analysis on concrete’s permeability. The results show that the anti-chloride ion transport performance of GIC was significantly improved compared to normal concrete. Experimental permeation data were further used to prepare a thermal damage permeability model. That is then used to discuss the impact of including glazed hollow beads on concrete’s residual service life after a fire. These data provide technical guidance for the engineering design and safe operation of undersea tunnels and other structures at risk of fire and subsequent saline water intrusion.

Influence of chloride salt type on chloride ion diffusion performance of alkali-activated slag mortar

• Alkali-activated slag (AAS) mortar has better resistance to chloride ion corrosion. • Different cation types affect the D app of AAS mortar. • MIP and XRD was performed to show a decrease in porosity. • EIS was performed to show an inverse exponential relationship between R c,d and D app . This work focuses on evaluating the influence of four cationic chloride salts (NaCl, KCl, MgCl 2 and CaCl 2 ) on chloride ion diffusion characteristics of alkali-activated slag mortar. The chloride ion concentration profiles of alkali-activated slag mortar were tested in single cation and combined cation source solutions. The hydration products and mechanism of action were analyzed by XRD and MIP, and the chloride ion transmission characteristics of alkali-activated slag mortar were further analyzed in combination with EIS. The chloride ion apparent diffusion coefficient D app related to the chloride salt solutions with the four cation types decreases in the order of D app (KCl) > D app (NaCl) > D app (MgCl 2 ) > D app (CaCl 2 ). The combination of monovalent cations can promote the chloride ions diffusion of alkali-activated slag mortar, and the results of the combination of monovalent cations and divalent cations are different. The hydration products of slag are mainly C-S-H gels with low calcium to silicon ratio, which reacts with chloride salt to form Friedel's salt, which can fill the internal pores, optimize pore size distribution, and improve the resistance to chloride ion corrosion.

Effect of halophilic bacteria on reducing chloride-ion concentration in mortars

• A new biological mortar was developed to enhance the salt damage resistance. • Halophilic bacteria were used for decomposing chloride compounds in concrete. • Halomonas venusta is favorable for reducing the chloride-ion concentration. • We confirmed that the activity of bacteria in the hardened cement matrix. • We verified the potential of the developed mortar as a biomimetic material. The present pioneering study examines the significance and limitations of biological mortars originally developed to enhance the salt damage resistance of concrete. Three strains of halophilic bacterium are isolated considering the decomposition mechanism of bacteria for chloride compounds in the cement matrix, thereby reducing the chloride ion concentration in the mortar. Test results showed that Halomonas venusta exhibited a good potential in reducing the chloride-ion concentration in mortars exposed to salt attacks, indicating a lower chloride-ion diffusion coefficient and lower amounts of Friedel’s salt by consuming the chloride ions as an energy source for its activity and growth.