Search Results (113)

Atmospheric corrosion, especially in coastal environments, presents a major challenge for the long-term durability of metallic and concrete infrastructure due to chloride deposition from marine aerosols. With a significant portion of the global population residing in coastal zones—often associated with intense industrial activity—there is growing demand for accurate and early corrosion prediction methods. Traditional standards for assessing atmospheric corrosivity depend on long-term empirical data, limiting their usefulness during the design stage of infrastructure projects. To address this limitation, this study develops predictive models using machine-learning techniques, namely gradient boosting, support vector machine, and neural networks, to estimate chloride deposition levels based on easily accessible climatic and geographical parameters. Our models were trained on a comprehensive dataset that included variables such as land coverage, wind speed, and orientation. Among the models tested, tree-based algorithms, particularly gradient boosting, provided the highest prediction accuracy (F1 score: 0.8673). This approach not only highlights the most influential environmental variables driving chloride deposition but also offers a scalable and cost-effective solution to support corrosion monitoring and structural life assessment in coastal infrastructure. Full article

Standalone tsunami defense structures have demonstrated limitations in mitigating wave energy during the 2011 Japan tsunami. In order to mitigate future tsunamis in Japan, multi-layered protective mechanisms have been suggested or implemented after the incident. These include heightening the destroyed or existing embankment with concrete or stones, protecting embankments with concrete blocks, compacting the landward soil, elevating the ground following the coastal embankment, and incorporating green belts. Despite extensive research on the mitigation effects of such multiple countermeasures, the optimal structural configuration remains uncertain. In this study, we evaluated the performance of a multiple mitigation system consisting of a landward forest (F) on an elevated mound (M) following a seaward embankment (E) under a range of supercritical flow conditions using a flume experiment. Several mound heights and lengths were selected to determine the optimum mound for installing the forest. The combination of E and F of 12 rows of trees on M with a minimum height of 1.8 cm (Case EMF_R12) created the greatest water cushion depth between E and M. When M was positioned without F, the water cushion between E and M was created by raising the height of the mound rather than its length. Conversely, a mound with a minimum height and length with a forest was found to be effective in creating the largest water cushion and maximum reduction of the flow energy. The highest energy reduction was between 45 and 70% in this experiment. These findings provide useful insights for developing multiple tsunami mitigation strategies that combine artificial and natural approaches. Full article

With the increasing global population and migration toward coastal regions, and the rising demand for coastal urbanization, including the development of living spaces, ports, and tourism infrastructure, the need for coastal defense structures (CDSs) is also increasing. Traditional CDSs, such as breakwaters, typically composed of hard units designed to block and divert wave and current energy, often fail to support diverse and abundant marine communities because of their impact on current and sediment transport, the introduction of invasive species, and the loss of natural habitats. Marine ecoengineering aims at increasing CDS ecological services and the development of marine organisms on them. In this study, carried out in a coral reef environment, we examined the relationship between coral colony protection levels and three factors related to their development, namely, coral fragment survival rate, larval settlement, and water motion (flow rate), across three distinct niches: Exposed, Semi-sheltered, and Sheltered. Coral survivability was assessed through fragment planting, while recruitment was monitored using ceramic settlement tiles. Water motion was measured in all defined niches using plaster of Paris Clod-Cards. Additionally, concrete barrier structures were placed in Exposed niches to test whether artificially added protective elements could enhance coral fragment survival. No differences were found in coral settlement between the niches. Flow rate patterns remained similar in Exposed and Sheltered niches due to vortex formation in the Sheltered zones. Survival analysis revealed variability between niches, with the addition of artificial shelter barriers leading to the highest coral fragment survival on the breakwater. This study contributes to the development of ways to enhance coral development with the goal of transforming artificial barriers into functional artificial reefs. Full article

Cement-based materials used in China’s coastal and salt lake areas in the northwest are exposed to long-term chloride corrosion, which deteriorates the materials and substantially reduces the durability of the structures. This study investigates the chlorine ion erosion resistance in salt spray environments of cement-based materials made with iron ore tailings (IOTs) as an aggregate (namely, IOTCs). The compressive strength, mass loss, and relative dynamic elastic modulus (RDEM) macroscopic performance of IOTC undergoing different chloride diffusion times (0–180 d) were explored in detail. Chloride ion profiles at 0–180 d were analyzed via chemical titration, while X-ray computed tomography (CT) and scanning electron microscopy (SEM) were employed to characterize microstructural evolution. The results demonstrate that IOTC exhibited superior chloride resistance compared to conventional concrete (GC). While both materials showed early strength gain (<60 d) due to hydration and pore-filling effects, IOTC experienced only a 23.9% strength loss after long-term exposure (180 d) significantly less than the 37.2% reduction in GC. Chloride profiling revealed that IOTC had 43.5% lower free chloride ions (C_f) and 32% lower total chloride ions (C_t) at 1 mm depth after 180 d, alongside reduced chloride diffusion coefficients (D_a). The CT analysis revealed that IOTC exhibited a significantly denser and more uniformly distributed pore structure than GC, with a porosity of only 0.67% under chloride-free conditions. SEM confirmed IOTC’s more intact matrix and fewer microcracks. Full article

Environmental humidity is a determining factor in the degradation of concrete structures, particularly in the corrosion process of reinforcement bars. This study analyzed four concrete mixtures with different mucilage contents replacing mixing water: 0, 5, 10, and 15%. Two sets of specimens were fabricated and subjected to a 420-day test period under two different working conditions: natural environmental conditions and high-humidity conditions. Open-circuit potential parameters were analyzed to compare the behavior of the mixtures and determine the corrosion rate. It was observed that under environmental conditions, the mixtures with 0% and 15% mucilage exhibited higher corrosion rates, with values of 0.046 and 0.049 mm/year, respectively, compared to the mixtures with low mucilage additions of 5% and 10%, which showed values of 0.041 and 0.038 mm/year, respectively. The corrosion rates of the mixtures under high-humidity conditions were 0.010 for M0, 0.009 for M1 and M2, and 0.014 for M3. The results indicate that mixtures with 5% and 10% mucilage show better corrosion protection, suggesting that this approach could be a sustainable, low-cost solution to enhance the durability of concrete structures, particularly in coastal areas with high humidity levels. It is concluded that adding nopal mucilage in low concentrations as a substitute for mixing water in concrete formulations not only modifies the properties of concrete, but also reduces the corrosion rate of reinforcement steel under high-humidity conditions, thereby extending the service life of constructions. Full article

Concrete coating technology is a key measure that enhances the durability of concrete structures. This paper systematically studies the performance, applicability, and impact of different types of anti-corrosion coatings on concrete durability, focusing on their resistance to chloride ion penetration, freeze–thaw cycles, carbonation, and sulfate corrosion. The applicability of existing testing methods and standard systems is also evaluated. This study shows that surface-film-forming coatings can create a dense barrier, reducing chloride ion diffusion coefficients by more than 50%, making them suitable for humid and high-chloride environments. Pore-sealing coatings fill capillary pores, improving the concrete’s impermeability and making them ideal for highly corrosive environments. Penetrating hydrophobic coatings form a water-repellent layer, reducing water absorption by over 75%, which is particularly beneficial for coastal and underwater concrete structures. Additionally, composite coating technology is becoming a key approach to addressing multi-environment adaptability challenges. Experimental results have indicated that combining penetrating hydrophobic coatings with surface-film-forming coatings can enhance concrete’s resistance to chloride ion penetration while ensuring weather resistance and wear resistance. However, this study also reveals that there are several challenges in the standardization, engineering application, and long-term performance assessment of coating technology. The lack of globally unified testing standards leads to difficulties in comparing the results obtained from different test methods, affecting the practical application of these coatings in engineering. Moreover, construction quality control and long-term service performance monitoring remain weak points in their use in engineering applications. Some engineering case studies indicate that coating failures are often related to an insufficient coating thickness, improper interface treatment, or lack of maintenance. To further improve the effectiveness and long-term durability of coatings, future research should focus on the following aspects: (1) developing intelligent coating materials with self-healing, high-temperature resistance, and chemical corrosion resistance capabilities; (2) optimizing multilayer composite coating system designs to enhance the synergistic protective capabilities of different coatings; and (3) promoting the creation of global concrete coating testing standards and establishing adaptability testing methods for various environments. This study provides theoretical support for the optimization and standardization of concrete coating technology, contributing to the durability and long-term service safety of infrastructure. Full article

The service of reinforced concrete structures (RCSs) in harsh coastal environments is often threatened by chloride corrosion. The penetration of chloride ions through concrete pores into the steel/concrete interface will cause the depassivation and corrosion of steel rebars, which will lead to the deterioration and failure of RCSs durability. It is important to repair and protect the corrosion damage of existing concrete structures and ensure their high durability, and the high performance of repairing and protecting materials is crucial. In this paper, a novel cement-based protective coating material with low porosity, high impermeability and chloride-corrosion resistance was designed and prepared by introducing polypropylene fiber and high-performance cement into commercial cement-based protective materials through the double modification strategy of fiber-toughening and substrate-enhancing, in order to provide a reliable corrosion protection solution for the high durability and long life of RCSs under chloride erosion environment. Based on this, the microstructure and pore structure of the double-modified coating material was systematically analyzed by SEM, XRD, X-CT and other characterization methods. The impermeability and chloride corrosion resistance of this material were scientifically evaluated, and the protection mechanism was systematically discussed. The results show that the impermeability of the double-modified coating material is about 2.8 times higher than that of the untreated mortar. At the same time, the corrosion current density was significantly reduced to 8.60 × 10⁻⁷ A·cm⁻², which was about 86% lower than that of the untreated sample (6.11 × 10⁻⁶ A·cm⁻²). The new cement-based coating material optimized by double-modification effectively inhibits the formation and propagation of microcracks in the protective coating through the bridging effect of fibers. At the same time, the regulation of cement hydration products and the densification of pore structure are realized by adjusting the composition of cement matrix. Based on the above two aspects of microstructure improvement, the chloride-corrosion protection performance of the novel cement-based protective coating material has been greatly improved. Full article

The durability of marine structures in the northern coastal areas is significantly damaged due to the double deterioration of chloride salt and freeze–thaw, and adding fiber can effectively improve the durability of marine structures. This work investigated the influence of polypropylene fiber content and salt freezing cycles on the flexural strength and durability of high-performance concrete through salt freezing cycle tests. The main experimental methods used included four-point load bending tests, relative dynamic elastic modulus tests, mass loss rate tests, and chloride ion permeability tests, with the mechanisms analyzed using SEM. The results indicated that an appropriate amount of polypropylene fibers significantly enhanced the flexural strength and durability of high-performance concrete. At a fiber content of 0.9 kg/m³, the concrete achieved the highest flexural strength. However, when the fiber content exceeded 0.9 kg/m³, excessive fibers caused uneven distribution and formed clusters, which reduced the flexural strength. At a fiber content of 1.2 kg/m³, the high-performance concrete showed optimal resistance to salt freezing and chloride ion permeability. However, exceeding this fiber content increased the concrete’s porosity, allowing harmful substances like chloride ions to penetrate more easily, thereby accelerating degradation under freeze–thaw conditions. This study contributes to a broader understanding of the durability of marine structures in coastal northern regions and provides theoretical data support for such environments. Full article

Reinforced concrete (RC) structures in coastal atmospheres commonly suffer the penetration of chloride ions, which can lead to the corrosion of reinforcements and, thus, a reduction in their structural performance under earthquakes. In recent years, time-dependent seismic fragility analysis has been widely used as an effective tool to represent the deterioration in the seismic performance of aging RC structures. However, few studies have considered the influences of varying chloride ion exposure environments due to the different distances of structures from a coastline. In light of this, this study performs a time-dependent seismic fragility analysis for aging RC frames, considering varying distances of the buildings from the coastline. To conduct this, a time-dependent reinforcement corrosion rate model that can consider the effect of the distance of a building from the coastline is established by combining a concrete surface chloride ion concentration model, an initial corrosion time model, and an electrochemical corrosion rate model. By integrating material deterioration models for reinforcements and concrete, the seismic fragility relationships for structures with different degrees of corrosion damage can be developed. A corrosion deterioration factor is then proposed to quantify the relationship between the seismic fragility function parameters and the corrosion rate. Subsequently, time-dependent fragility functions considering the effect of the distance from the coastline can be established. A nine-story RC frame designed according to the existing Chinese codes is used for illustration. The time-dependent seismic fragility relationship of the structure is developed considering different distances of buildings from the coastline. The results show that the effect of the distance of a building from the coastline varies under different categories of environment. The seismic fragility results for a structure under a III-a environment are more significantly influenced by the structural distance from the coastline compared to those for a structure under a II-a environment. Full article

Marine geophysical and geological investigations are crucial for evaluating the construction suitability of artificial fish reefs (AFRs). Key factors such as seabed topography, geomorphology, sub-bottom structure, and sediment type significantly influence AFR design and site selection. Challenges such as material sinking, sediment instability, and scouring effects should be critically considered and addressed in the construction of AFR, particularly in areas with soft mud or dynamic environments. In this study, detailed investigations were conducted approximately seven months after the deployment of reef materials in the AFR experimental zones around Xiaoguan Island, located in the western South Yellow Sea, China. Based on morphological factors, using data from multibeam echosounders and side-scan sonar, the study area was divided into three geomorphic zones, namely, the tidal flat (TF), underwater erosion-accumulation slope (UEABS), and inclined erosion-accumulation shelf plain (IEASP) zones. The focus of this study was on the UEABS and IEASP experimental zones, where reef materials (concrete or stone blocks) were deployed seven months earlier. The comprehensive interpretation results of multi-source high-resolution acoustic images showed that the average settlement of individual reefs in the UEABS experimental zone was 0.49 m, and their surrounding seabed experienced little to no scouring. This suggested the formation of an effective range and height, making the zone suitable for AFR construction. However, in the IEASP experimental zone, the seabed sediment consisted of soft mud, causing the reef materials to sink into the seabed after deployment, preventing the formation of an effective range and height, and rendering the area unsuitable for AFR construction. These findings provided valuable scientific guidance for AFR construction in the study area and other similar coastal regions. Full article

In coastal areas, the presence of concrete cracks provides pathways for hazardous ions to ingress from the exterior into the interior of concrete, while the migration of the ions further accelerates concrete deterioration and causes durability problems. The incorporation of graphene oxide (GO) into concrete can inhibit crack initiation and development starting at the nanoscale, improving the concrete microstructure, thereby affecting concrete’s resistance to hazardous ion transport and the resulting deterioration. In this study, a multi-scale transport model for cementitious materials with a GO admixture was established to predict the resistance to hazardous ions. Based on the determination of hydration types and hydration kinetics, microstructure modeling was conducted at three scales, the sub-microscale, microscale, and mesoscale, upon which transport property simulations were performed. At the microscale, the effects of both the cement paste matrix and the interfacial transition zone (ITZ) were considered. Through the simulation, it was found that the addition of GO reduced the duration of the induction period and increased the rate of hydration development after the induction period. Moreover, the incorporation of GO could reduce the porosity of cementitious materials at all simulation scales at both early and later ages. At the microscale, it improved the pore structure of the cement matrix and ITZ by reducing large pores and increasing small pores. At all three simulation scales, GO could increase the diffusion tortuosity in hydration products, suppress ion transport, and improve the resistance to hazardous ions of cementitious materials. Full article

Moisture is a critical factor leading to the deterioration of concrete structures. Hydrophobic cement-based materials, with their excellent waterproof performance, hold significant application value in humid, coastal, and cold environments. This study employed stearic acid (STA, CH₃(CH₂)₁₆COOH) as a hydrophobic agent dissolved in anhydrous ethanol using ultrasonication to create an STA–ethanol solution. In addition, the ball-milling method was used to mix STA with tuff powder (TP) to prepare hydrophobic modified tuff powder (MTP). This study investigated the effects of the STA content, water–cement (w/c) ratio, cement–sand (c/s) ratio, the replacement rate, and addition method of TP and MTP on the wettability (contact angle and sorptivity) and compressive strength of the mortar. The effects of the STA on the cement hydration were explored by microanalysis techniques, such as SEM, XRD, and FTIR, and the modification method with the best effect was recommended based on a gray correlation degree analysis. The results indicate that the STA could be successfully grafted into the mortar without affecting the types of cement hydration products. When using the STA–ethanol solution for hydrophobic modification, adding 0.9% STA by weight increased the mortar contact angle to 69.5° and reduced the sorptivity by 22%, while the 28-day compressive strength was decreased. When the w/c ratio was 0.5, the contact angle rose with the increase in the replacement rate of MTP, while the sorptivity and compressive strength decreased. The grey relational analysis showed that at a w/c ratio of 0.4, the STA–ethanol solution was a more effective modification method in terms of reducing the mortar sorptivity. Full article

The global demand for coastal urbanization is rising with the increasing population. Alas, living close to the ocean threatens human endeavors with high currents, waves, and increasing storm frequency. Accordingly, the need for more coastal defense structures (CDSs) rises. Structures built from complex units meant to prevent and/or mitigate coastal erosion and floods, additionally providing wave protection or wave attenuation, are constructed on and near natural habitats where they alter local ecosystems. Traditional CDSs mostly fail to harbor diverse and abundant communities. However, this can be changed by eco-friendly methodologies and designs that are being tested and implemented to improve CDSs’ ecological value. Some of these can be implemented during the construction period, while others can fit on existing structures, such as wave breakers and seawalls. Effective methods include augmenting surface rugosity through strategic perforations, integrating artificial panels for increased complexity, implementing soft (naturally based) engineering solutions such as geotextiles, replacing industrial concrete mixtures for CDS construction with “green concrete” and ecologically friendly mixtures, and using alternative, eco-friendly units in CDS erections. In this mini review, we suggest that by integrating sustainable practices into coastal development, we can significantly mitigate the ecological damage caused by traditional CDSs and promote more harmonious relationships between human construction and the marine environment. This shift towards environmentally conscious coastal defenses is essential and a responsibility for ensuring the long-term sustainability of our coastal communities and the health of our oceans. We present current methodologies used on breakwaters worldwide. Full article

Reinforced concrete structures are susceptible to chloride ion attack under different conditions, such as water reservoirs, coastal regions, and industrial locations. The physical and mechanical properties of concrete are known to considerably affect the ion penetration velocity. However, studies addressing the effect of coatings on the chloride ion penetration of reinforced concrete are limited. Thus, the objective of this paper is to evaluate the effects of different surface coatings on chloride ion penetration in concrete elements. Acrylic, polyurethane, and epoxy resin coatings were applied in two layers as recommended by the manufacturers. Natural environment chloride ion exposure was conducted in loco in the city of Torres, Brazil, at two marine locations with different geographical characteristics and distances from the sea. In addition, laboratory tests consisting of salt spray and penetration-by-immersion tests were conducted. The concrete’s characteristics, including its compressive strength, water absorption, and void index, were evaluated. The results indicate higher efficiency with the polyurethane coating, while the acrylic resin had the worst results, with a difference of up to 4.5 mm between them. Full article

The study area was Anin Beach, where a 1.48-km-long breakwater, consisting of a non-porous caisson, was constructed over 16 months. During this process, significant erosion occurred over a wide area behind the coast, with a maximum reduction in the beach width of 36 m observed in the central part of the coastline. As a countermeasure to prevent erosion, a submerged breakwater was installed that consisted of concrete blocks and had a length of 600 m. Following the implementation of this submerged breakwater, the beach behind it increased in width by 64 m, in proportion to the installation length, while erosion phenomena, such as the loss of coastal roads, were observed at both ends of the structure. In this study, the topographical changes caused by waves and currents were analyzed to identify their causes and establish countermeasures. Additionally, the planned measures, established before structure installation, were closely examined against the actual occurrences observed onsite through a coastline survey. Full article