Ion Erosion Research Articles

A Review of Chloride Corrosion Resistance of Ultra-High-Performance Concret

Extending the service life of reinforced concrete structures can effectively reduce the economic, environmental, resource and energy costs throughout their life cycle. However, a large number of reinforced concrete structures often suffer from corrosion of reinforcing bars due to chloride ion erosion in various environments, which leads to deterioration of performance, the loss of functionality and even safety accidents. As a barrier between reinforcing steel and the external environment, protective layer concrete can effectively prevent chloride ions from contacting the surface of reinforcing steel, thus delaying the corrosion of reinforcing steel and improving the durability of reinforced concrete structures. Ultra-high-performance concrete has a dense microstructure due to its low water-to-cement ratio and elimination of coarse aggregates, which can greatly impede the transport of chloride ions within it, and thus it is expected to significantly improve the service life of reinforced concrete infrastructure. Based on this, this paper firstly summarizes the basic mechanism of chloride ion transport inside cementitious materials, including the movement mode and physicochemical binding mechanism of chloride ions inside the cementitious, and analyzes the current research status and improvement methods of the chloride ion penetration and chloride ion binding capacity of ultra-high-performance concrete.

Chloride ion permeability of concrete containing recycled composite powder from building demolition waste

Buildings in the marine environment are vulnerable to chloride ion erosion, which threatens the service life of concrete structures. To facilitate the application of concrete containing construction demolition waste in the marine environment, recycled composite powder concrete (RCPC) was prepared using recycled composite powder as cement substitute. The chloride ion permeability of RCPC was evaluated by chloride ion diffusion test and rapid chloride ion migration test (RCM). The chloride ion permeability of RCPC continued to enhance with growing content of recycled composite powder. During the immersion age, the surface chloride ion content of the samples containing recycled composite powder increased by an average of 18.3–65.3% over the control group, with a corresponding average increase in chloride ion diffusion coefficients ranging from 17.0% to 31.5%. The chloride ion migration coefficients in the RCM test raised by 9.5–24.7%. A series of microscopic tests such as nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and scanning electron microscope-energy dispersive spectrometer (SEM-EDS) suggested that the total porosity increased by 11.9–29.5% with the addition of recycled composite powder. The chloride ion diffusion coefficients exhibited a linear increase with growing total porosity and porosity of capillary pores, whereas an exponential increase with the porosity of transitional pores. The poor reactivity of the recycled composite powder resulted in a looser microstructure and weakened chloride binding capacity, and these factors boosted chloride ion transport. A chloride ion diffusion model of RCPC considering the time dependence of chloride ion transport was developed, and the reliability of the model was verified by experimental data.

A Review of Durability of New and Old Concrete Joints

The purpose of this study is to explore the durability of the new and old concrete joints, including chloride ion erosion, freeze-thaw phenomena, and the influence of aggregates. Firstly, taking into account the difference in material properties between the old and new concrete, this study analyzes the chloride ion transport characteristics of the joints in detail, focusing on the key areas of the joints, that is, the areas where the old concrete may have been eroded by chloride ions. Secondly, this study explores the change in the properties of the joints under freeze-thaw conditions, and the influence of different interface treatment methods on the properties of the joints. Finally, this study examines the influence of the type and content of aggregates on the durability of the joints. Through the above research, this paper aims to provide some useful guidance and suggestions for the durability design of the old and new concrete structures.

Research on the Permeability and Pore Structure Distribution Characteristics of High-Performance Mortar for Surface Treatment of Bridge Piers and Columns

In marine environments, bridge piers and columns are prone to corrosion caused by harmful media, particularly chloride ions. This corrosion can lead to cracking of the steel bars in the protective layer of the bridge piers. To enhance the corrosion resistance of concrete in bridge piers, this article introduces the use of nanoclay-modified cement mortar. This innovative material offers high-performance surface treatment options that can effectively slow down the erosion process of harmful media and reduce the risk of bridge pier column cracking. To evaluate the ion erosion resistance of this nanoclay-modified cement mortar, we conducted detailed experiments on the pore structure of cement paste. The pore structure of cement paste with different dosages of nano-kaolinite clay and the dispersion method was studied using mercury intrusion porosimetry (MIP). The fractal dimension of the pore surface area of the net cement paste was calculated from the fractal model based on thermodynamic relationships of the pore structure-related parameters obtained with mercury pressure experiments. The relationship among the multiple fractal dimensions, pore structure parameters, dispersion mode, and permeability is explored. The results show that the addition of nano-kaolinite clay particles can improve the internal pore structure of cement materials. When 1.5% nano-kaolinite clay is mechanical dispersed, the total specific pore volume and the most probable pore size are reduced by 47.83% and 56.87%, respectively, compared with the control group. The fractal dimension image of cement-based materials with nano-kaolinite clay has a range of singular points and does not have fractal characteristics in this range. Nano-kaolinite clay has a significant effect on the fractal dimension of pore size range I. The fractal dimension of the whole pore size range is not suitable for the analysis of permeability, and the fractal dimension calculated by selecting less than the critical pore size range has a good correlation with permeability.

Study on the durability deterioration law of marine concrete with nano-particles under the coupled effects of freeze-thaw cycles, flexural fatigue load and Cl− erosion

The marine concrete in cold region such as harbor, wharf and sea-bridge is inevitably subjected to the coupling effects of flexural fatigue load, freeze-thaw cycles and chloride ion (Cl−) erosion. This paper studies the durability of unreinforced concrete under the coupling effects of three factors. And in order to highlight the effects of freeze-thaw cycles, the two-factor coupling durability test of flexural fatigue load and Cl− erosion and the three-factor coupling durability test of freeze-thaw cycles, flexural fatigue load and Cl− erosion are designed. And the microstructures of various concretes are analyzed by mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The results show that under the coupling effects of three factors, on the one hand the icing of pore water can improve the deformation resistance of concrete; on the other hand, the expansion pressure can accelerate the deterioration of pores and promotes the development of fatigue cracks. The coupling effects of three factors significantly reduces the flexural fatigue life of concrete, and the more the number of freeze-thaw cycles, the more significant the adverse effects on the flexural fatigue life of concrete. The addition of nano-particles (The cement in concrete is replaced by the same content of nano-particles) can improve the adverse effects of freeze-thaw cycles on the flexural fatigue life of concrete, and enhance the flexural fatigue life of concrete. When the amount of nano-particles is optimal, the fatigue life of NC10 and NS20 is increased by 47.6% and 52.3% respectively. The Cl− erosion resistance of concrete increases firstly and then decreases with the increasing amount of nano-particles. The free Cl− content of the compression zone in NC10 and NS20 can be reduced by 22.4% and 24.2% respectively, and the free Cl− content of the tensile zone in NC10 and NS20 can be reduced by 16.6% and 20% respectively. Under the coupling effects of three factors, with the continues erosion of Cl−, the Ca/Si value and the atomic percentage of Ca in interface transition zone (ITZ) of concrete gradually are decreased, which makes the decreased extent of C–S–H gel and Ca(OH)2 in concrete. The addition of nano-particles can reduce the decrease extent of Ca atom percentage in ITZ, reduce the decomposition of C–S–H gel and Ca(OH)2, and improve the fatigue life and Cl− erosion resistance of concrete.

Machine Learning Method to Explore the Correlation between Fly Ash Content and Chloride Resistance.

Chloride ion corrosion has been considered to be one of the main reasons for durability deterioration of reinforced concrete structures in marine or chlorine-containing deicing salt environments. This paper studies the relationship between the amount of fly ash and the durability of concrete, especially the resistance to chloride ion erosion. The heat trend map of total chloride ion factor correlation displayed that the ranking of factor correlations was as follows: sampling depth > cement dosage > fly ash dosage. In order to verify the effect of fly ash dosage on chloride ion resistance, three different machine learning algorithms (RF, GBR, DT) are employed to predict the total chloride content of fly ash proportioned concrete with varying admixture ratios, which are evaluated based on R2, MSE, RMSE, and MAE. The results predicted by the RF model show that the threshold of fly ash admixture in chlorinated salt environments is 30-40%. Replacing part of cement with fly ash in the mixture of concrete below this threshold of fly ash, it could change the phase structure and pore structure, which could improve the permeability of fly ash concrete and reduce the content of free chloride ions in the system. Machine learning modeling using sample data can accurately predict concrete properties, which effectively reduce engineering tests. The development of machine learning models is essential for the decarbonization and intelligence of engineering.

Deterioration of mechanical properties and damage mechanism of flue gas desulfurization gypsum backfill under long-term erosion of chloride salt solution

Flue gas desulfurization gypsum (FGDG), a solid waste material generated by power plants, offers a cost-effective solution for preparing backfill materials. Concurrently, given that most backfill materials are exposed to mine water erosion, an investigation into the mechanical performance degradation and damage mechanisms of FGDG backfill materials subjected to prolonged chloride salt erosion is crucial for ensuring the stability of goaf backfills (by goaf, we mean the area or space that remains underground after the extraction of valuable minerals). This study explores the mechanical properties and damage mechanisms of backfill samples treated with varying concentrations of chloride. The findings indicate that over time, the mass of the sample initially decreases, experiences a slight increase, and then gradually declines. Simultaneously, the strength and structure of the sample deteriorate rapidly, followed by a partial recovery. The rebound in sample mass is attributed to an incomplete hydration reaction that continuously transforms free water into bound water. Microstructure analysis techniques, such as X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM), reveals that the degradation in mechanical strength and structure is a consequence of chloride salt erosion. Subsequent reuse is facilitated by the formation of Friedel's salt resulting from the reaction between hydration products and chloride ions, filling voids in the sample and impeding further chloride ion erosion into the deeper regions. Notably, FGDG exhibits outstanding reuse performance in prolonged and high-concentration chloride ion environments. This study serves as a reference for understanding the deterioration mechanism and practical application of backfills in chloride-rich environments.

RS-AAT with distributed permeable pipes and alkaline water: Enhancing concrete durability through chloride reduction, pH optimization, and pore structure improvement

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.

Study on the Effect of Ultra-fine Limestone Powder on the Resistance of Cement-slag Powder System to Chloride Ion Permeability

The effect of different limestone powder fineness on the chloride ion migration coefficient of the cement paste was tested using the Rapid Chloride Migration (RCM) method. The changes in the phase composition and pore structure of the paste were studied using hydration kinetics analysis, XRD and pore structure analysis. The results showed that before the chloride ion erosion, the limestone powder mainly exhibited filling effect, microcrystalline nucleation effect, and chemical activity effect. It reacted with the hydration products of cement to form calcium aluminate carbonate, which improved the strength of the hardened paste. After chloride ion erosion, the diffraction peak of calcium aluminate carbonate weakened, and Friedel’s salt was formed. With the increase of the specific surface area of limestone powder, the chemical activity of the powder became more obvious, and the generation of Friedel’s salt increased, leading to stronger resistance to chloride ion penetration. Limestone powder can reduce the porosity of the hardened paste and optimize the pore structure. When the particle size of the powder increased from 800 to 5000 mesh, the total porosity of the hardened paste decreased from 20.7% to 14.7%, and the most probable pore size decreased from 450nm to 75nm. Limestone powder with a particle size larger than 1500 mesh can fully exert its activity and play a role in solidifying chloride ions, thus improving the resistance to chloride ion penetration of limestone powder cement-based materials.

Effect of sulfate erosion on shear characteristics of slurry-reinforced coal body structural faces

To study the effect of sulfate ion erosion on grouted reinforced coal bodies, downhole grouting reinforcement was simulated by artificially prefabricating regular serrated structural surfaces and grouting them with cement. In addition, sulfate erosion tests were carried out at three erosion ion concentrations (3%, 5%, and 10%) and four erosion times (7d, 14d, 28d, and 40d) at a pressure of 0.2 MPa using self-developed constant pressure accelerated erosion equipment, and then, mechanical property tests were conducted using an MTS816 rock mechanics shear tester, which is the most effective way to test the mechanical properties of coal. The test results are as follows: (1) the shear stress–displacement curves of the specimens were of slip type at lower normal stresses and of peak shear type at higher normal stresses, (2) the shear strength of the specimen was linearly negatively correlated with the erosion time and erosion ion concentration, (3) the effect of erosion time was greater than the effect of erosion concentration on the specimen shear strength parameters, (4) sulfate erosion can only affect the degree of shear shrinkage and shear rise and cannot change the damage behavior, and (5) with an increase in erosion ion concentration and the prolongation of the erosion time, the damage morphology of the specimen was shown as the “coal body destruction–nipping fracture–climbing nipping fracture” (coal–pulp interfacial separation) damage form.

Chloride ion diffusion performance of concrete and its influence on scour resistance

Hydraulic structures are affected by many factors, and chloride ions can significantly reduce the service life of concrete. In this paper, the erosion test of chloride ion erosion is studied, the damage characterization is carried out by two-dimensional and three-dimensional characterization methods, and the numerical simulation analysis is carried out. The results show that when the water cement ratio (w/c) is 0.3, 0.4 and 0.5, the grinding depth of concrete surface reaches 21 mm, and the chloride ion concentration is stable. With the increase of w/c, the porosity increases, especially the harmful pores have the greatest influence on ion erosion. Chloride ion erosion reduces the scour resistance of concrete. When the w/c decreases from 0.5 to 0.4, the influence of ions on the scour resistance of concrete is weakened by 5.3%. Under 0.5 w/c, the exposed area of aggregate on the surface of concrete increases by 15.6%, and the average erosion rate of concrete decreases by 3.3%, 5.0% and 16.0%. With the increase of chloride ion diffusion depth, the chloride ion concentration is in good agreement with the simulated value. The interfacial transition zone around the coarse aggregate promotes ion diffusion, so that the ion concentration of the concrete surface reaches the peak. Concrete with a w/c of 0.3 has a longer life under the same conditions.

The effect of nano-SiO<SUB align="right">2 strengthening the performance of recycled concrete under ion erosion environment

The effect of nano-SiO<SUB align="right">2 strengthening the performance of recycled concrete under ion erosion environment

Coupling Effect of Cryogenic Freeze-Thaw Cycles and Chloride Ion Erosion Effect in Pre-Cracked Reinforced Concrete

Coupling Effect of Cryogenic Freeze-Thaw Cycles and Chloride Ion Erosion Effect in Pre-Cracked Reinforced Concrete

The effect of nano-SiO<SUB align="right">2 strengthening the performance of recycled concrete under ion erosion environment

The effect of nano-SiO<SUB align="right">2 strengthening the performance of recycled concrete under ion erosion environment

The sulfate transfer characteristics in recycled aggregate concrete incorporated with fly ash under percolation theory

Recycled aggregate concrete (RAC) has multiple interface transition zones (ITZs) due to its complex composition, providing convenient ion transfer channels. Therefore, it is significant to explore the changes of the internal pore structure in RAC under ion erosion conditions for quantifying and predicting ion transfer mechanisms. This paper innovatively utilizes the seepage effect for investigating the evolution of pore structures in RAC under sulfate attack. We conduct a systematic experimental study on the transport of sulfate ions in RAC with different fly ash (FA) substitution rates under dry-wet cycles. Combining backscattered electron imaging (BSE), permeation and fractal characteristics, this paper deeply explore the relationship between pore structure feature, sulfate percolation mechanism and the macroscopic properties of RAC incorporated with different amount of FA.

Durability investigation of fractured coal-gasified ash slag concrete eroded by sulfate and chlorine salts

The combined action of sulfate and chlorine salts erodes concrete structures in coastal and saline-alkali zones. The induced fractures under load also accelerate the deterioration of concrete. In this study, ion erosion tests of fractured coal-gasified ash slag (FC-GAS) concrete under dry-wet cyclic conditions were performed using ordinary concrete as the reference. The mass loss rates, the relative dynamic moduli of elasticity, and the distribution patterns of chlorine and sulfate ions of specimens in erosive environments of single sulfate salt, single chlorine salt, and mixed sulfate and chlorine salts were measured. The deterioration mechanism of FC-GAS concrete under coupled erosion by sulfate and chlorine salts was explored with SEM and XRD techniques. By introducing the influence coefficient and deterioration coefficient of the fracture width of FC-GAS concrete, a modified model describing the diffusion behavior of chlorine ions in FC-GAS concrete was established. The results show that for the concrete specimens after erosion in sulfate salt and the mixture of sulfate and chlorine salts, the mass and the relative dynamic modulus of elasticity first increased and then dropped. The deterioration of the concrete performance after soaking in the mixed solution was significantly lower than that of the specimen after dry-wet cycles in the single solution. The formation of fractures accelerated ion erosion. Chlorine and sulfate ions in the mixed solution could inhibit the diffusion of other ions. The diffraction peak strengths of the erosion products of the specimen after dry-wet cycles in the mixed solution were significantly reduced. The results calculated by the proposed modified model on the diffusion of chlorine ions in FC-GAS concrete agreed with the experimental results.

Investigation on self-healing polyurethane coating doped with lignin composites for protecting cementitious materials

Surface protective coatings are prone to cracking and failure due to the deformation of concrete structure itself and harsh service environment factors such as UV, ion erosion, and large temperature differences during the period of service. It is urgently required to develop new types of self-healing coatings to provide long-lasting protection for concrete structures and extend their service life. In this investigation, a lignin-based self-healing agent was prepared using aniline and lignin as raw materials. Its characterization was analyzed by SEM and FT-IR. By introducing the lignin-based healing agent and dynamic disulfide bonds, a new kind of self-healing polyurethane coating was prepared, and its self-healing ability was qualitatively and quantitatively evaluated, indicating that it had excellent self-healing performance. After self-healing process, the crack could withstand bending force. Moreover, with the increased temperature, the self-healing efficiency of tensile strength gradually increased, reaching a maximum of 86.42% at 60 ℃. Meanwhile, the self-healing efficiency of its elongation at break firstly increased and then gradually decreased, reaching a maximum of 93.77% at 40 ℃. This self-healing polyurethane coating had high hydrophobicity (139.4°) and excellent abrasion resistance. After 40 friction cycles, its hydrophobicity only decreased by 10.9% to 124.2°. In addition, this self-healing protective coating also showed excellent resistance to chloride ions, effectively protecting cementitious materials with the damaged surface. This work provides a new method for long-term protection of concrete structures.

Characterization of nano-SiO2 cemented soil under the coupled effects of dry-wet cycles and chlorination

In contrast to cemented soils in terrestrial natural environments, cemented soils in littoral and marine geotechnical engineering face numerous difficulties. In coastal and marine geotechnical engineering, cemented soils are frequently degraded by ion erosion, tidal scouring, and temperature variations. Long-term marine environments present numerous challenges for cemented soil foundation projects. In marine geotechnical engineering, addressing and enhancing these degradation issues has become a crucial topic. To address this engineering problem, Nano-SiO2 is added to cement-stabilized soils to enhance their engineering performance. To investigate the mechanical effects and erosion mechanisms of Nano-SiO2 cemented soil subjected to chloride ion erosion and tidal alternation scouring, laboratory experiments, including immersion erosion tests with sodium chloride solution and dry-wet cycle tests, were designed. On specimens subjected to dry-wet cycles after chloride ion erosion at varying concentrations, unconfined compressive strength tests (UCS), X-ray diffraction (XRD) experiments, and scanning electron microscopy (SEM) were performed. The objective was to investigate the impact of chloride ions and Nano-SiO2 on the microstructure and strength of cemented soil. Adding 2.5% Nano-SiO2 can promote cement hydration reactions while preventing the entry of chloride ions into the cemented soil, thereby increasing the density and compressive strength of the cement.

A new mesoscopic calculation model of chloride ion erosion in recycled coarse aggregate concrete (RAC): Characteristic fractal dimension of pore structure and service life prediction

This research investigates the influence of water-cement ratio and recycled aggregate content on the chlorine erosion resistance of RAC by conducting a combination of experimental and theoretical analysis. In addition, a mathematical equation is developed to represent the chloride ion transport mechanism in RAC, taking into account fluid mechanics, energy conservation, and pore structure evolution characteristics. Furthermore, mathematical analysis and modeling are used to forecast the life of the chloride ion erosion process. The results show that both the recycled coarse aggregate replacement rate and the water-cement ratio adversely affect the chloride erosion resistance of RAC. The chloride diffusion coefficient model based on pore structure characteristic parameters exhibits high prediction accuracy. This model helps increase the use of recycled aggregates and fosters the growth of the circular economy in the construction industry sector by offering a theoretical foundation for evaluating and maintaining the durability of RAC.

Multidimensional Transport Experiment and Simulation of Chloride Ions in Concrete Subject to Simulated Dry and Wet Cycles in a Marine Environment.

Chloride ion erosion is an important factor affecting the durability of marine engineering concrete. In particular, concrete structures in wave splash and tidal zones are subjected to dry and wet cycles and multidimensional diffusion of chloride ions. To investigate the intricate diffusion of chloride ions within concrete under these dynamic conditions, we devised a comprehensive experiment. This experiment encompasses multiple dimensions, involving dry and wet cycles, as well as static immersion. The experiment intends to reveal how chloride ions are distributed in the concrete and clarify the changes that occur in its microstructure. Based on Fick's second law, the multidimensional diffusion model of chloride ions in concrete under the dry and wet cycles and static immersion was established by comprehensively considering the effects of chloride ion exposure time, environment temperature, relative humidity, and the action of dry and wet cycles. The results show that, under the same conditions, the chloride content in concrete decreases with the increase in penetration depth but increases with the increase in the chloride diffusion dimension and exposure time. Dry and wet cycles and multidimensional diffusion of chloride ions increase the development of cracks and pores in the concrete structure and generate large quantities of C3A·CaCl2·10H2O, which will exacerbate the chloride ion transport rate and penetration depth of concrete. Under the same exposure time and penetration depth, the chloride ion content in concrete under two-dimensional (2D) and three-dimensional (3D) diffusion under dry and wet cycles was 1.09~4.08 times higher than that under one-dimensional (1D) diffusion. The correlation coefficients between the simulation results of the multidimensional transport model of chloride ions in concrete under multi-factor coupling and the experimental results were all greater than 0.95, and the model can be utilized to predict the distribution of chloride ion concentration in concrete.