Search Results (209)

Reinforced concrete structures in harsh environments are highly vulnerable to structural damage caused by rebar corrosion. However, there remains a critical shortage of high-performance, environmentally friendly repair materials that integrate both structural restoration and long-term corrosion protection functionalities to address this issue. To meet this demand, this study innovatively developed an eco-friendly, high-performance repair material using lotus leaf extract (LLE)-modified mortar and systematically evaluated its corrosion protection performance and mechanisms under chloride attack conditions. The primary chemical constituents of LLE include alkaloids and flavonoids, rich in polar functional groups such as O–H, N–H, and C–O. The LLE modifier increased the fluidity of fresh cement paste, thereby improving its construction workability. A low dosage of LLE modifier promoted cement hydration. When the LLE dosage was 0.2 wt%, the 7-day and 28-day flexural strengths of the LLE-modified mortar increased by 16.8% and 7.48%, respectively, compared to those of unmodified mortar, while the compressive strengths increased by 30.6% and 14.5%, respectively. The LLE-modified mortar demonstrated significant protection against chloride corrosion, effectively inhibiting rebar corrosion. Electrochemical corrosion results indicated that compared to unmodified mortar, the modified mortar containing 0.5 wt% LLE exhibited an 80% improvement in protection efficiency against chloride corrosion. These results demonstrate that an appropriate dosage of LLE modifier can simultaneously optimize the fundamental properties of mortar and provide excellent chloride corrosion protection. Therefore, LLE-modified mortar shows promising application potential in integrated repair and corrosion protection engineering for reinforced concrete structures. Full article

In marine environments, chloride salt ingress into concrete having a porous structure can lead to physical salt attack (PSA) deterioration. However, the slow deterioration of cement-based materials caused by PSA under current laboratory conditions limits the understanding of the mechanisms of PSA. To improve the efficiency of accelerated testing for PSA in a laboratory, this study investigates the accelerated methods for PSA deterioration of cement-based specimens exposed to NaCl solution by adjusting curing ages and water-to-cement ratios. The results indicate that specimens with shorter curing age exhibit accelerated damage due to insufficient hydration, while specimens with higher water-to-cement ratios experience expedited surface scaling due to increased porosity. Reducing curing age from 28 to 7 days shortened the deterioration time of specimens by 50%. For the 28-day-cured specimens, increasing the w/c ratio from 0.4 to 0.5 accelerated the initial damage by 25%. Despite the variations in the curing age and water-to-cement ratio, the fundamental deterioration mechanism remained consistent across specimens. Notably, deterioration predominantly occurred in regions with relatively reduced external salt crystallization, which can serve as an indicator for predicting potential deterioration locations. The findings provide a theoretical basis for enhancing the efficiency of accelerated PSA testing protocols in a laboratory environment. Full article

This article presents a probabilistic methodology for assessing corrosion initiation in reinforced concrete structures exposed to chloride ingress. The approach addresses key limitations of conventional analytical models by accounting for non-diffusive barriers and incorporating a rigorous statistical treatment of censored data to mitigate biases introduced by limited simulation durations. A combination of analytical solutions for diffusion from opposite sides with time-dependent boundary conditions is also proposed and validated. The probabilistic study includes the depassivation assessment of a hollow pier section. The blocking effect caused by rebars is statistically characterised through correction factors derived from finite element simulations. These factors are used to adjust analytical solutions, which are computationally inexpensive. Results show that neglecting the rebar blocking effect can overestimate the mean corrosion initiation time by up to 42%, while the use of censored data reduces bias in lifetime estimates. The observed frequency of censored events reached up to 20% when simulations were truncated at 100 years. The corrected analytical models closely match the finite element results, statistically validating their application. The case study indicates premature corrosion initiation (less than 10 years to achieve target reliability), underscoring the need to better reconcile the desired levels of reliability with realistic input parameters for depassivation. Full article

Precipitation-hardenable stainless steels (PHSS) are widely used in various applications in the aeronautical industry such in as landing gear supports, actuators, and fasteners, among others. This research aims to study the pitting corrosion behavior of passivated martensitic precipitation-hardening stainless steel, which underwent passivation for 120 min at 25 °C and 50 °C in citric and nitric acid baths before being immersed in solutions containing 1 wt.% sulfuric acid (H₂SO₄) and 5 wt.% sodium chloride (NaCl). Electrochemical characterization was realized employing electrochemical noise (EN), while microstructural analysis employed scanning electron microscopy (SEM). The result indicates that EN reflects localized pitting corrosion mechanisms. Samples exposed to H₂SO₄ revealed activation–passivation behavior, whereas those immersed in NaCl exhibited pseudo-passivation, indicative of an unstable oxide film. Current densities in both solutions ranged from 10⁻³ to 10⁻⁵ mA/cm², confirming susceptibility to localized pitting corrosion in all test conditions. The susceptibility to localized attack is associated with the generation of secondary oxides on the surface. Full article

Considering the harsh marine environment characterized by dry–wet cycles, freeze–thaw action, chloride penetration, and sulfate attack, four optimized ultra-high-performance concrete (UHPC) mix designs were developed. Durability was assessed via electric flux, dry–wet cycles, and rapid freeze–thaw tests to evaluate the effects of curing methods, aggregate types, and mineral admixtures on key durability indicators, including chloride ion permeability, compressive strength loss, and mass loss. Scanning electron microscopy (SEM) examined microstructural changes under various conditions. Results showed that curing method significantly affected chloride ion permeability and sulfate resistance. High-temperature curing (70 ± 2 °C) reduced 28-day chloride ion electric flux by about 50%, and the compressive strength loss rate of specimens subjected to sulfate attack decreased by 2.7% to 45.7% compared to standard curing. Aggregate type had minimal impact on corrosion resistance, while mineral admixtures improved durability more effectively. Frost resistance was excellent, with mass loss below 0.87% after 500 freeze–thaw cycles. SEM analysis revealed that high-temperature curing decreased free cement particles, and mineral admixtures refined pore structure, enhancing matrix compactness. Among all mixtures, Mix Proportion 4 demonstrated the best overall durability. This study offers valuable insights for UHPC design in aggressive marine conditions. Full article

The steep incline in the rising need for sustainable construction materials has marked the emerging trend of comprehensive research on utilizing waste glass powder (WGP) as a partial substitute for fine aggregates, such as cement, and coarse aggregates in concrete preparation. This review thoroughly examines WGP-incorporated concrete in terms of its mechanical and durability properties. It explores compressive, tensile, and flexural strength, as well as its resistance to freeze–thaw cycles, sulfate attack, and chloride ion penetration. The characteristic microstructure densification, strength development, and durability performance can be attributed to the pozzolanic activity of WGP that forms additional calcium silicate hydrate (C-S-H). The review also highlights the optimal replacement levels of WGP to balance mechanical performance and long-term stability while addressing potential challenges, such as alkali–silica reaction (ASR) and reduced workability at high replacement ratios. By consolidating recent research findings, this study highlights the feasibility of WGP as a sustainable supplementary cementitious material (SCM), promoting eco-friendly construction while mitigating environmental concerns associated with glass waste disposal. Full article

A strong application potential for Ag/AgCl ion-selective electrodes (ISEs) used as chloride sensors in cement-based material is widely accepted, but their stability and durability have not been sufficiently addressed. This paper summarizes the research status of the stability and durability of Ag/AgCl ISEs used for the non-destructive detection of chloride in cement-based materials. Four topics including working principle and fabrication methods, the factors that influence stability, research status for stability and durability studies, and the reason for durability failure of Ag/AgCl ISEs in cement-based materials are reviewed. Meanwhile, the improving methods for Ag/AgCl ISEs are proposed based on discussions of various aspects of Ag/AgCl ISEs. Full article

Portland cement is one of the most widely used construction materials employed in both large-scale structures and everyday applications. Although various materials are often added during production to enhance their performance, NaCl can be introduced in the process for various reasons. Despite this issue, existing studies lack sufficient quantitative data on the effects of NaCl on cement properties. Therefore, this study aims to investigate the physical and chemical degradation mechanisms in cement containing NaCl. Cement specimens were prepared by mixing cement, water, and NaCl, followed by stirring at 60 rpm and curing at room temperature for seven days. Microstructural changes as a function of the NaCl concentration were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Electrochemical properties were evaluated via open-circuit potential (OCP) measurements, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization tests. The results indicate that increasing the NaCl concentration leads to the formation of fine precipitates, the degradation of the cement matrix, and the reduced stability of major hydration products. Furthermore, the electrochemical analysis revealed that higher NaCl concentrations weaken the passive layer on the cement surface, resulting in an increased corrosion rate from 1 × 10⁻⁷ to 4 × 10⁻⁷ on the active polarization of the potentiodynamic polarization curve. Additionally, the pitting potential (E_pit) decreased from 0.73 V to 0.61 V with an increasing NaCl concentration up to 3 wt.%. This study quantitatively evaluates the impact of NaCl on the durability of Portland cement and provides fundamental data to ensure the long-term stability of cement structures in chloride-rich environments. Full article

This study investigates the evolution of the macro- and micro-scale properties of foamed concrete under different saline environments, including sulfate, chloride, and composite salt conditions. The research focuses on the changes in compressive strength, pore structure, and hydration products of the material. Through full-immersion tests and compressive strength measurements, combined with microstructural characterization techniques such as mercury intrusion porosimetry (MIP) and thermogravimetric analysis (TG), the deterioration mechanisms of foamed concrete under salt attack are systematically explored. The results indicate that Sulfate ions exhibit the most aggressive erosion effect, and the presence of chloride ions can produce a “passivation” effect which partially mitigates the damage caused by sulfate ions. Moreover, increasing the material density and incorporation of mineral admixtures contributes to pore structure refinement, significantly enhancing resistance to salt attack. These findings provide a theoretical basis for the practical application of foamed concrete under a complex salt erosion environment. Full article

This study focuses on the evolution of the Arousa Island Bridge, a critical infrastructure connecting, in northwestern Spain, the Arousa island to the Galician coast. Since its commissioning in 1985, the bridge has experienced damage due to corrosion, culminating in a major repair intervention in 2011 using hybrid galvanic cathodic protection. This repair was essential in addressing identified pathologies and ensuring the safety of the structure. In 2021, additional repairs needed to be completed, and a thorough study and testing campaign was conducted in 2023 which included the extraction of zinc anode samples from the bridge. The present work evaluates the effectiveness of the repair measures implemented since the intervention, with particular attention to corrosion risk and the durability of the cathodic protection system installed to mitigate corrosion risks in the reinforced concrete exposed to a harsh marine environment. A key aspect of this study is the correlation established between the indirect measurements utilized to evaluate zinc consumption within the cathodic protection system and the direct assessment obtained from the extraction of the anodes, which provides a tangible measure of this consumption. The calculated service life was updated with the measurement, and the integrity of the system was assessed. Full article

In this study, cavitation erosion tests were conducted to investigate the effects of the presence of coolant additives and chlorides on the corrosion and cavitation erosion of cylinder liners in marine diesel engines. Electrochemical experiments were conducted to evaluate the corrosion characteristics of ductile cast iron (DCI), and the corrosion potential and corrosion current density were measured. In addition, weight loss, surface roughness, and maximum surface damage depth were quantified as a function of cavitation exposure time. Furthermore, to investigate the erosion and erosion–corrosion characteristics induced by cavitation attack, the damaged surface morphology was closely examined using a scanning electron microscope (SEM) after the cavitation erosion tests. The results revealed that the coolant additive effectively protected the DCI from corrosion caused by aggressive chlorides. In particular, when an appropriate amount of additive was added to a coolant containing 100 ppm of chloride, the corrosion current density of DCI was reduced by approximately 31.7 times, significantly improving corrosion resistance. Therefore, different surface damage mechanisms corresponding to cavitation erosion and cavitation erosion–corrosion were identified depending on the presence or absence of the coolant additive during the cavitation erosion tests. Full article

This study proposes a co-hydrothermal method for the dechlorination of polyvinyl chloride (PVC) and the preparation of hydrothermal carbon. During the co-hydrothermal process, lignin was mixed with PVC, with ammonium carbonate serving as a supplementary additive. The effects of hydrothermal temperature, reaction time, and ammonium carbonate concentration on the dechlorination efficiency of PVC and the pH value of the system are discussed. The experimental results showed that the incorporation of lignin and ammonium nitrate manifested a remarkable synergistic effect, which substantially augmented the dechlorination process of polyvinyl chloride (PVC). Under optimal conditions (220 °C, 240 min), the dechlorination efficiency of PVC reached 99.43%. The hydrothermal carbon derived from the co-hydrothermal process exhibited a 73.9% higher calorific value (31.07 MJ/kg) compared with that obtained from pure PVC (17.87 MJ/kg). A physicochemical characterization demonstrated that lignin effectively enhanced the uniform dispersion of PVC particles during hydrothermal treatment. Concurrently, ammonium carbonate increased the solution’s alkalinity, facilitating a nucleophilic attack by OH⁻ on C-Cl bonds and accelerating dechlorination through intensified substitution reactions. Full article

Salt lakes and the surrounding saline soils distributed across northwestern China and Inner Mongolia impose severe physicochemical corrosion on cement-based concrete. Understanding the corrosion products and mechanisms are crucial scientific and technological factors in ensuring the durability and service life of concrete structures in these regions. In this study, various analytical techniques—including X-ray diffraction, thermogravimetric–differential thermal analysis, X-ray fluorescence, and scanning electron microscopy coupled with energy-dispersive spectroscopy—were employed to systematically analyze the corrosion products of ordinary Portland cement (OPC) and high-performance concrete (HPC) specimens after eight years of field exposure in the Qarhan Salt Lake area of Qinghai. The study provided an in-depth understanding of the physicochemical corrosion mechanisms involved. The results showed that, after eight years of exposure, the corrosion products comprised both physical corrosion products (primarily sodium chloride crystals), and chemical corrosion products (associated with chloride, sulfate, and magnesium salt attacks). A strong correlation could be observed between the chemical corrosion products and the strength grade of the concrete. In C25 OPC, the detected corrosion products included gypsum, monosulfate-type calcium sulfoaluminate (AFm), Friedel’s salt, chloro-ettringite, brucite, magnesium oxychloride hydrate 318, calcium carbonate, potassium chloride, and sodium chloride. In C60 HPC, the identified corrosion products included Kuzel’s salt, Friedel’s salt, chloro-ettringite, brucite, calcium carbonate, potassium chloride, and sodium chloride. Among them, sulfate-induced corrosion led to the formation of gypsum and AFm, whereas chloride-induced corrosion resulted in chloro-ettringite and Friedel’s salt. Magnesium salt corrosion contributed to the formation of brucite and magnesium oxychloride hydrate 318, with Kuzel’s salt emerging as a co-corrosion product of chloride and sulfate attacks. Furthermore, a conversion phenomenon was evident between the sulfate and chloride corrosion products, which was closely linked to the internal chloride ion concentration in the concrete. As the chloride ion concentration increased, the transformation sequence of sulfate corrosion products occurred in the following order: AFm → Kuzel’s salt → Friedel’s salt → chloro-ettringite. There was a gradual increase in chloride ion content within these corrosion products. This investigation into concrete durability in salt-lake ecosystems offers technological guidance for infrastructure development and material specification in hyper-saline environments. Full article

Cracks in reinforced concrete structures compromise strength and durability, particularly in high-performance centrifugal concrete (HPC) piles, where degradation can become irreversible. Despite their high density and low permeability, HPC piles remain vulnerable to cracking, sulfate attack, and chloride penetration, necessitating innovative durability solutions. While self-healing concrete has been widely studied, its application in HPC piles remains unexplored, representing a critical research gap. This study investigates the synergistic use of Bacillus sphaericus bacteria and flax fibers to enhance crack healing, permeability reduction, and mechanical performance in HPC piles. In this research, HPC specimens were fabricated using a specialized centrifugal device and casting process. During the mixing phase, bacteria and flax fibers were incorporated into the concrete. The fresh mix was then spun to form the final specimens. To evaluate bacterial self-healing performance of specimens, controlled random cracks were induced using a compression testing machine. Thereafter, a series of compressive strength tests, 30 min water absorption tests (BS 1881), scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS), and EDS mapping (MAP) were conducted to evaluate self-healing efficiency. Results demonstrated that bacterial activation upon cracking led to calcium carbonate precipitation, effectively sealing cracks, reducing permeability, and enhancing compressive strength. Optimizing bacterial and fiber content further influenced water absorption and mechanical properties in both cubic and centrifugally cast specimens. This study bridges a critical gap by introducing biomaterial-based self-healing in HPC piles, offering a sustainable, cost-effective, and long-term strategy for enhancing the durability of deep foundation systems in aggressive environments. Full article

Concrete structures in marine environments face significant degradation due to reinforcement corrosion caused by chloride ingress and sulfate attack. Poor construction quality, inadequate standards, and suboptimal design can further accelerate deterioration. Non-destructive testing (NDT) has proven valuable for durability assessment, yet its application remains limited due to the complex microstructural characteristics of concrete. This study establishes a comprehensive procedure for evaluating precast concrete degradation in marine environments using multiple characterization techniques. Two precast concrete elements with different cement types, CEM II A-L 42.5R and CEM I 42.5 R/SR, were analyzed through compressive strength tests, open porosity measurements, mercury intrusion porosimetry (MIP), ultrasonic wave transmission, and scanning electron microscopy (SEM). The results indicate that CEM I 42.5 R/SR exhibits superior compressive strength and lower porosity, making it more durable and suitable for load-bearing applications. Higher ultrasonic pulse velocity (UPV) further confirms its resilience. In contrast, CEM II A-L 42.5R shows lower mechanical performance and greater susceptibility to marine-induced degradation. Over time, pore size distribution shifts, potentially compromising mechanical integrity. SEM analysis reveals gypsum and brucite formation in degraded regions, demonstrating microstructural changes due to seawater exposure. A strong negative correlation between porosity and UPV underscores the detrimental effect of increased porosity on material density and structural stability. This study highlights the effectiveness of UPV and porosity analysis as reliable NDT techniques for assessing concrete deterioration. The strong correlation between UPV and porosity trends suggests that UPV serves as an early indicator of durability loss, enabling timely maintenance interventions. These findings provide valuable insights into material selection for enhanced structural performance in marine environments and emphasize the role of NDT in long-term structural health monitoring. Full article