Search Results (158)

Periodic visual inspections are currently conducted to maintain the condition of railway bridges. These inspections rely on direct visual assessments by human inspectors, often requiring specialized equipment such as aerial ladders. However, this method is not only time-consuming and costly but also involves significant safety risks. Therefore, there is a growing need for a more efficient and reliable alternative to traditional visual inspections of railway bridges. In this study, we evaluated and compared the performance of damage detection using U-Net-based deep learning models on images captured by unmanned aerial vehicles (UAVs). The target damage types include cracks, concrete spalling and delamination, water leakage, exposed reinforcement, and paint peeling. To enable multi-class segmentation, the U-Net model was trained using three different loss functions: Cross-Entropy Loss, Focal Loss, and Intersection over Union (IoU) Loss. We compared these methods to determine their ability to distinguish actual structural damage from environmental factors and surface contamination, particularly under real-world site conditions. The results showed that the U-Net model trained with IoU Loss outperformed the others in terms of detection accuracy. When applied to field inspection scenarios, this approach demonstrates strong potential for objective and precise damage detection. Furthermore, the use of UAVs in the inspection process is expected to significantly reduce both time and cost in railway infrastructure maintenance. Future research will focus on extending the detection capabilities to additional damage types such as efflorescence and corrosion, aiming to ultimately replace manual visual inspections of railway bridge surfaces with deep-learning-based methods. Full article

Recycled concrete aggregates (RCAs) have the potential to be used as a sustainable, cost-effective, and environmentally friendly material in pavement base construction. However, there is a lack of information on the durability, strength, and hydraulic properties of RCA. The primary purpose of this study was to evaluate the properties and performances of commonly available RCAs in Oklahoma as pavement bases through laboratory testing and AASHTOWare Pavement ME simulations. For this purpose, three RCAs (RCA-1, RCA-2, and RCA-3) and a virgin limestone aggregate (VLA-1) were collected from local sources. RCA-1 and RCA-3 were produced in the field by crushing the existing concrete pavement of Interstate 40 and US 69 sections, respectively. RCA-2 was produced by crushing concrete and rubble collected in a local recycling plant. Laboratory testing for this study included particle size distribution, wash loss, optimum moisture content and maximum dry density (OMC-MDD), Los Angeles (LA) abrasion, durability indices (D_c and D_f), permeability (k), and resilient modulus (M_r). The properties of aggregates were compared and the service life (performance) of aggregate bases was studied through mechanistic analysis using the AASHTOWare Pavement ME design software (version 2.6, AASHTO, USA). The results indicated that the properties of RCAs can differ greatly based on the origin of the source materials and the methods used in their processing. Recycled aggregates from concrete pavements of interstate and state highways exhibited similar or improved performance as virgin aggregates. RCA produced in a recycling plant was found to show durability and strength issues due to the presence of inferior quality materials and contaminants. Also, the results indicated that the fine aggregate durability test is a useful tool for screening recycled aggregates to ensure quality during production and construction. Bottom-up fatigue cracking was identified as the most affected performance criterion for flexible pavements when using RCA as the base layer. The findings will help increase the use of RCA as pavement base to promote environmental sustainability. Full article

Plastic and especially microplastic (MP) pollution has posed a serious threat to the marine environment for decades. Studies on MPs have started to gain momentum especially in the Sea of Marmara (SoM), which is an international waterway, under the pressure of intense maritime traffic and exposure to domestic and industrial discharges. The aim of this study was to evaluate the MPs found in surface sediments collected from the coastal area of the SoM according to the locations and to reveal the extent of the existing pollution. This is the first study to examine MPs in both the surface sediments of the entire shorelines of the SoM, which have not been previously reported, and in the surface sediments of Çanakkale Strait. Accordingly, the highest MP abundance was detected at Yenice station (St 15) with 1286 items/kg, and the lowest MP abundance was detected at Turan Village station (St 14) with 199 items/kg. The most dominant shapes across all sampling stations and months were fiber (37%) and fragment (26%), while the most dominant color was blue (35%). According to the polymer characterization results, PE (polyethylene) was found to be the most dominant polymer type. Additionally, most stations were found to have “Moderate” and “High” pollution levels in terms of the contamination factor (CF), and regions were classified as “Moderate” and ‘High’ in terms of the pollution load index (PLI), with the St 15 station specifically exhibiting “Very High” pollution levels. Furthermore, hazard index (HI) and pollution risk index (PRI) values were also calculated regionally, revealing that regions have pollution levels classified as “High”, “Very High”, and even “Dangerous”. This study concluded that there are no areas with low pollution levels in SoM, and that the threat posed by MP pollution in this sea is increasing. Furthermore, this study found that stations with high MP pollution levels are located near river discharges and that rivers significantly contribute to MP pollution in the seas. The findings are of great importance in terms of the need to implement sustainable plans and measures to prevent pollution in the SoM and to take concrete steps to protect and ensure the sustainability of coastal ecosystems, particularly those under serious pollution threats. Full article

In contemporary construction practices, polycarboxylate superplasticizers (PCEs) have gained extensive utilization in concrete formulation owing to their exceptional dispersive properties and superior water reduction capabilities. Nevertheless, these admixtures demonstrate pronounced susceptibility to clay contamination, a critical limitation that substantially constrains their practical implementation. To mitigate this detrimental effect, multiple technical strategies have been developed to suppress clay sensitivity, with predominant approaches focusing on molecular structure optimization and incorporation of supplementary admixtures. This review systematically investigates the competitive adsorption mechanisms operating at the cement–clay interface. Through rigorous analysis of molecular architecture characteristics and synergistic admixture combinations, we comprehensively review current methodologies for enhancing the clay resistance of PCE-based systems. Furthermore, this paper proposes prospective directions for synthesizing clay-tolerant PCE derivatives, emphasizing molecular design principles and advanced formulation protocols that may inform future research trajectories in construction materials science. Full article

Leaching from cement can lead to a loss in performance and durability and can also have an environmental impact. Therefore, it is an important aspect to consider when new cements are being developed and where concrete is to be placed that could lead to the contamination of groundwater. Calibrated thermodynamic models can provide very useful predictions in a matter of seconds for any cement-based material. However, such models need to include accurate representations of the solid-solution nature of the C-S-H gels that are included for the incongruent dissolution of calcium and silica. This study presents the calibration of a thermodynamic model employing the pH-REdox-Equilibrium geochemical software 3.8.7, written in C (PHREEQC 3.8.7), to model the change in the pH and the leaching of calcium (Ca) and silica (Si) from cement against the Ca/Si ratio and over time. The predicted concentrations of Ca and Si and the pH in the leachate were calculated using three solid-solution C-S-H gel models that were taken from the cemdata18 database, namely, CSHQ, CSH3T, and tobermorite–jennite, which have not been analysed before and show good agreement. The calibrated model was used to predict leaching from a CEM II/A-L cement and a blended CEM I + fly-ash with a cement replacement level of 35%. The effect of a sulphate environment (Na₂SO₄) was also analysed. Full article

Cementitious materials are indispensable in the construction industry and in urban development worldwide because cement pastes, mortars, and concrete provide mechanical strength, high durability, and excellent stability to various structures that are used in a lot of civil works. Owing to the impact and relevance of these materials, it is indispensable to frequently seek ways to improve their properties and characteristics. In recent years, the development of nanomaterials such as nanoparticles (NPs) and nanofibers (NFs) has allowed cementitious materials to improve their mechanical, thermal, chemical, and durability properties, among others. This can be associated with the fact that nanomaterials allow for improved cement hydration by retaining water in the mix, helping to define a more uniform microstructure and, therefore, significantly reducing porosity, which prevents contamination such as from the entry of external agents into the structure. In addition to providing an overview of the effects of using nanomaterials on enhancing the properties of cementitious materials, this review includes the most widely used nanomaterial synthesis methods in recent years and the contribution of these nanomaterials to sustainable and environmentally friendly construction. Full article

This research aims to address the environmental and economic challenges associated with conventional concrete by partially replacing cement—the most polluting, expensive, and energy-intensive ingredient—with industrial paint sludge ash (PSA), a highly contaminated industrial waste that is typically landfilled. Mortar mixtures were prepared with PSA replacement levels ranging from 0% to 20% in 5% increments while maintaining a constant water-to-binder ratio of 0.48. This study comprehensively evaluated the fresh, mechanical, durability, and microstructural properties of the PSA-modified mortar to assess its potential as an ecofriendly construction material. Results showed that as PSA content increased, the fresh properties, such as workability/slump flow and setting time, decreased, while the water demand for attaining normal consistency increased. Soundness tests indicated expansion up to 15% PSA replacement, beyond which expansion became more pronounced. Compressive strength improved significantly with PSA replacements of 5% to 15% compared to the control sample, with a slight decline at 15% relative to 5% and 10%. This trend was consistent with bulk density and ultrasonic pulse velocity measurements. Furthermore, the incorporation of PSA enhanced key durability properties, including water absorption, sulfate resistance, and porosity reduction, up to 15% PSA replacement. Microstructural analysis using SEM, XRD, TGA/DTA, and FTIR confirmed that PSA inclusion led to increased mortar densification, with the 10% PSA mix exhibiting thermal stability and minimal mass loss at elevated temperatures. FTIR spectra further indicated improved composition with higher PSA content. Overall, PSA proved to be a viable partial cement replacement, offering enhanced mortar properties without compromising performance. Its use contributes to sustainability by reducing reliance on cement, lowering construction costs, and eliminating the environmental and logistical burdens of paint sludge disposal. Full article

The accumulation and improper management of mining tailings represent significant environmental and public health challenges globally, due to their potential for water contamination and the presence of heavy metals. In recent years, various studies have explored the feasibility of using mining wastes, such as tailings sludge, as partial replacements for cement in concrete mixes. The literature highlights the pozzolanic properties of mining tailings attributable to their silica and alumina content, which contribute to the improved structural characteristics, chemical resistance, and enhanced durability of concrete. This research evaluates the specific potential of gold mining tailings sludge (REMI) from the municipality of Vetas, Santander, Colombia, as a sustainable substitute in cementitious materials. Characterization methodologies including X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM) confirmed the pozzolanic behavior of REMI due to its high content of silica- and alumina-rich amorphous phases and verified negligible contamination levels (Hg and cyanide below detectable limits). Concrete mixes with varying cement substitution levels (0% to 50%) were formulated and systematically evaluated to determine optimal substitution ranges based on criteria such as density, workability, setting time, and compressive strength. Consistent with previous studies, the results revealed an optimal replacement rate between 10% and 20%, with a particular emphasis on the 20% substitution achieving mechanical strengths comparable to traditional concrete. These findings underscore the technical viability and environmental benefits of using mining tailings sludge, contributing both to sustainable waste management and the advancement of eco-efficient concrete technologies. Full article

Phosphogypsum, a byproduct of phosphate fertilizer production, poses significant environmental challenges due to its large volume, hazardous composition, and radioactivity. Conventional disposal methods, such as stockpiling and landfilling, contribute to soil and water contamination and present risks to human health. This article explores the potential of integrating phosphogypsum into a circular economy framework, focusing on reducing environmental impacts and extracting value from this industrial waste. A detailed assessment of phosphogypsum’s chemical composition, including trace metals and radionuclides, is essential for effective management. This review paper examines safe handling, storage, and disposal strategies to minimize environmental risks. Additionally, innovative reuse applications are investigated, such as incorporating phosphogypsum into construction materials like cement, plasterboard, and concrete and its use in agriculture as a soil amendment or for land reclamation. The recovery of critical elements, particularly rare earth elements (REEs), highlights its potential to reduce waste and contribute to meeting the growing demand for strategic resources. Despite its promise, challenges remain, including chemical variability and the presence of radioactive components. This article identifies the technological and regulatory steps required to enable safe, large-scale reuse of phosphogypsum, emphasizing its role in advancing sustainable resource management within a circular economy. Full article

Plastic waste management remains a significant global challenge, with limited recycling opportunities contributing to its status as one of the highest waste producers. In Australia, the recovery rate for plastic waste is 12.5%, resulting in a high percentage of plastics being landfilled. Common disposal methods, such as incineration and landfilling, are environmentally damaging, with incineration emitting harmful gases and landfilling causing contamination. Recycling, while preferable, faces difficulties due to contamination and infrastructure challenges. However, alternative solutions, such as integrating waste plastic into concrete, present an opportunity to both reduce plastic waste and enhance the economic value of recycled materials. This study evaluates the potential of waste plastic milk bottles (PMBs) in residential concrete by assessing their mechanical strength, environmental impact, and variability in greenhouse gas (GHG) emissions. This study demonstrated that replacing up to 10% of cement with silica fume-modified plastic milk bottle (SFPMB) waste granules maintained comparable compressive strength to traditional concrete. The addition of metakaolin to the SFPMB mix design (SFMKPMB) further improved the material’s strength by 28%. Life cycle assessment (LCA) results revealed reductions in global warming potential (GWP), human toxicity potential (HTP), and fossil depletion potential (FDP), with SFMKPMB showing the greatest environmental savings. A Monte Carlo simulation evaluated variability factors, revealing that additional transportation and energy requirements increased GHG emissions, though the SFMKPMB mix ultimately resulted in the lowest overall material GHG emissions. This study demonstrates the complexity of assessing “green” materials and highlights how material variability and energy use can influence the sustainability of waste-derived composites. Despite challenges, incorporating waste plastics into concrete offers a promising strategy for mitigating landfill waste and reducing environmental impacts, especially as renewable energy adoption increases. Full article

The durability degradation of concrete structures in marine and urban underground environments is largely governed by chloride-induced corrosion. This process becomes significantly more severe under the coupled action of external loading and drying–wetting cycles, which accelerate chloride transport and structural deterioration. However, the existing research often isolates the effects of mechanical loading or environmental exposure, failing to comprehensively capture the synergistic interaction between these factors. This lack of understanding of chloride ingress under simultaneous mechanical and environmental loading limits the development of reliable service life prediction models for concrete structures. In this study, a self-made loading system was employed to simulate this coupled environment, combining external loading with 108 days of drying–wetting cycles. Chloride profiles were obtained to assess the combined effects of stress level, water/binder ratio, and fiber content on chloride penetration in fiber-reinforced cementitious composites (FRCCs). To further extend the analysis, a Crank–Nicolson-based finite difference approach was developed for the numerical assessment of chloride diffusion in concrete structures after repair. This model enables the point-wise treatment of nonlinear chloride concentration profiles and provides space- and time-dependent chloride concentration distributions. The results show that using an FRCC as a repair material significantly enhances the service life of chloride-contaminated concrete structures. The remaining service life of the repaired concrete was extended by 36.82% compared to the unrepaired case, demonstrating the clear practical value of FRCC repairs in aggressive environments. Full article

The aim of this paper was to investigate the corrosion behaviour of zinc in simulated concrete solutions using resistometric sensors and to describe the kinetics of zinc corrosion. The sensors provide corrosion data information in real time; thus, it is a useful technique for observing zinc corrosion behaviour in concrete environments. The replacement of carbon steel rebar by galvanized steel in concrete is a discussable topic with contradictory results in the literature presented in the introduction. In our case, zinc resistometric sensors were used, and they showed results in good agreement with other techniques, such as corrosion potential monitoring and EIS measurements. According to our results, zinc is able to passivate in a simulated concrete solution and even in a simulated carbonated solution. The corrosion rate was reduced by almost 40 times, during the active to passive transition. The zinc remains passive even in simulated concrete solutions contaminated with low levels of chloride ions up to 0.9 wt.%. Full article

Since people spend most of their time in indoor environments, they are continuously exposed to various contaminants that threaten human health. The air quality in these settings is therefore a crucial factor in maintaining health safety. In order to reduce the concentration of indoor air pollutants and improve air quality, photocatalytic oxidation has drawn the attention of researchers. This study aims to provide a comprehensive view of the nanomaterials used in the photocatalytic oxidation of the most common pollutants in indoor environments. The effects of various parameters like humidity, airflow, deposition time, and light intensity were also evaluated, as they can significantly influence photocatalytic reactions. The most common nanomaterials used in photocatalysis are TiO₂-based and, in this study, they were classified and examined based on their morphology. TiO₂ doping with metals and non-metals has demonstrated an enhancement of its adsorption properties and photocatalytic efficiency for the removal of several pollutants. The role of carbon-based nanomaterials in photocatalysis was also evaluated due to their adsorption capabilities towards various pollutants. In addition, other less common photocatalysts such as ZnO, MnO₂, WO₃, CeO₂, and CdS also exhibited high photocatalytic activity for pollutant degradation. Applications of these photocatalysts in air purifiers, paints, and building materials e.g., concrete, glass, and wallpapers, lead to efficient reduction of pollutants in indoor settings. Full article

The global problem of water scarcity is exacerbated by the continued contamination of potable water sources. This preliminary study investigates the potential of a hazardous industrial jarosite waste to adsorb As(V) and Cr(III) from contaminated waters. The results showed that this mining waste effectively adsorbed both As(V) and Cr(III), demonstrating its potential as a low-cost and sustainable solution for water remediation along with the use of a hazardous waste that also contaminates. The adsorption process was optimized, and the effects of various parameters on the adsorption capacity were investigated. The findings of this study suggest that the use of toxic mining residues in porous concrete could provide a promising approach for the removal of toxic heavy metals from polluted water sources, contributing to the development of more sustainable and environmentally friendly water treatment technologies. A maximum adsorption of 90.6% of As(V) and 96.3% of Cr(III) was achieved, and it was verified that the industrial jarosite initially contained about 0.44% As, which was later leached during decomposition; again, the industrial jarosite was able to re-adsorb both As(V) and Cr(III). Full article

Damage to human health caused by As-contaminated water can be prevented using proper As-removal techniques, such as employing excellent arsenic adsorbents. In this study, the combined addition of Mg- and Ca-based adsorbents was investigated for the efficient removal of As from contaminated water. Following a previous study on As(V), As-removal tests targeting As(III) and several additional tests, including X-ray diffraction analysis, were conducted to clarify the mechanism of the improved performance of the combined-addition As removal. Similarly as for As(V), the combined additions of both MgCO₃ + CaO and MgCO₃ + Ca(OH)₂ improved As(III)-removal performance while inhibiting the leaching of base material components; however, they did not remove As(III) as effectively as As(V). The differences in the removal ratios of As(V) and As(III) in these combined additions were concluded to be primarily due to the different As-removal mechanisms. Mg(OH)₂ and CaCO₃ were generated, and As(III) was incorporated into the generated precipitate of Mg(OH)₂ but not into that of CaCO₃. Conversely, As(V) was incorporated into both Mg(OH)₂ and CaCO₃. Additionally, MgCO₃ + Ca(OH)₂ was evaluated as a more efficient combined-addition method because MgCO₃ + Ca(OH)₂ exhibited a higher As-removal ratio value than MgO + CaO. Proposals have been made to remove As(III) using activated carbon modified with heavy metals or transition elements, or concrete waste grafted with polymers, but these methods are complicated to prepare, costly, and involve the risk of leaching of harmful components. Adsorbents that use general Mg and Ca components as their base material do not contain such harmful components. The Mg- and Ca-based adsorbents are readily available and low-cost, and, best of all, there is no concern that they will leach harmful components. Therefore, widespread use of Mg- and Ca-based adsorbents as a measure against arsenic contamination could greatly contribute to a sustainable society. Full article