Search Results (466)

Concrete waste generated from the demolition of structures constitutes a significant source of waste worldwide. Recycled concrete aggregates (RCA) obtained from this waste exhibit disadvantages such as high porosity and low mechanical strength; therefore, they are not used in pavement structures without improvement. This study investigates the feasibility of using RCA improved with waste-based stabilizers as highway subbase material. RCA was used as fine aggregate and blended with basalt aggregate (BA) at different replacement ratios. The mixtures were subjected to California Bearing Ratio (CBR) tests to determine the optimum RCA content. Subsequently, unconfined compressive strength (UCS) tests were conducted using calcium carbide slag (CCS) as an activator and sewage sludge ash (SSA) as pozzolanic material at various proportions. The experimental results indicated that the mixture containing 35% RCA exhibited the most favorable performance, while higher RCA contents resulted in significant reduction in CBR values. The highest UCS value was obtained in the mixture containing 30% waste additive by weight of RCA with a CCS:SSA ratio of 3:7. For this mixture, CBR reached 315%, and displacement measured in the cyclic plate loading test under a load of 35 kN was 2.5 mm. This mixture provides sustainable and mechanically suitable alternatives for highway subbase applications. Full article

The circular economy represents a significant opportunity to enhance the mechanical properties of bituminous mixtures, thereby contributing to sustainable development. This research compares the behaviour of traditional bituminous mixtures with sustainable ones that reuse recycled materials, industrial waste products, or additives that improve mechanical or rheological properties. The methodology employed comprised the acquisition of fatigue resistance laws from 4-point bending tests on prismatic specimens. This facilitated the analytical determination of the number of axles of 13 tons that the section of pavement with sustainable material can support for comparison with the axles supported in the conventional mix. The findings corroborate the utilization of sustainable bituminous mixtures in pavement sections, employing the maximum circularity criterion. The fatigue laws calculated must permit the use of different calculation methods or other applications in green infrastructures, such as cycling lanes or pedestrian areas. On sections with an AADT of between 800 and 25 HV/day, all of the analyzed bituminous mixtures with sustainable materials prolong the service life of the road. There were increases in service life of between 25.5% and 6.6%, respectively, which satisfactorily achieved an increase in pavement service life based on the criterion of maximum circularity. Full article

This study examines the influence of virgin polyethylene (vPE), recycled polyethylene (rPE), and Aerosil (A) on the performance of bitumen binders modified with partially devulcanized rubber (DVR). The experimental program included morphology analysis, determination of devulcanization degree, dynamic viscosity measurements, shear stress–shear rate analysis, load–displacement (F–Δl) testing, storage-stability evaluation, ring and ball softening point (R&B), penetration (P), and elastic recovery (ER) testing. The results show that DVR-rPE-modified bitumen binders exhibit 20–35% higher viscosity and up to 25% greater elongation at the break compared to DVR-vPE-modified bitumen systems, indicating more effective interaction with the bitumen matrix. The incorporation of Aerosil increased viscosity ca. 1.5–2 times for DVR-rPE and DVR-vPE-modified systems, respectively. Meanwhile, top and bottom differences in R&B decreased by a factor of 1.6–5 for DVR-rPE and DVR-vPE-containing composites, respectively, demonstrating significant enhancement in structural stability during storage. Mechanical testing further revealed that DVR-rPE + A binders absorbed 10–20% more deformation energy and consistently maintained ER values above 70–80%, corresponding to a higher elastic recovery grade at 25 °C. Overall, the DVR-rPE + A system provided the most balanced improvements in rheological, mechanical, and thermal properties, confirming its potential for use in high-performance, thermally stable, and environmentally sustainable bituminous materials for pavement applications. Full article

In Mediterranean cities, high solar radiation combined with limited shading and vegetation intensifies the urban heat island (UHI) phenomenon. As the road network often covers a large portion of the cities’ surfaces and is mostly constructed using asphalt pavements, it can significantly affect the urban microclimate, leading to low thermal comfort and increased energy consumption. Recycled and waste materials are increasingly used in the construction of pavements in accordance with the principle of sustainability for minimizing waste and energy to produce new materials based on a circular economy. The scope of this study is to evaluate the effect of recycled or waste materials used in road pavements on the urban microclimate. The surface and ambient temperature of urban pavements constructed with conventional asphalt and recycled/waste-based mixtures are assessed through simulation. Two study areas comprising large street junctions near metro stations in the city of Thessaloniki, in Greece, are examined under three scenarios: a conventional hot mix asphalt, an asphalt mixture containing steel slag, and a high-albedo mixture. The results of the research suggest that the use of steel slag could reduce the air temperature by 0.9 °C at 15:00, east European summer time (EEST), while the high-albedo scenario could reduce the ambient temperature by 1.6 °C at 16:00. The research results are useful for promoting the use of recycled materials, not only as a means of sustainably using resources but also for the improvement of thermal comfort in urban areas, the mitigation of the UHI effect, and the reduction of heat stress for human health. Full article

The incorporation of reclaimed asphalt pavement (RAP) offers significant environmental benefits; however, its use is often limited by an increased susceptibility to cracking due to the insufficient elasticity of the severely aged RAP binder. This limitation is conventionally mitigated using polymers such as styrene–butadiene styrene, which, despite their effectiveness, are costly and carbon intensive. This paper introduces a low-carbon sulfur-based ternary polymer developed through TiO₂-catalyzed inverse vulcanization of elemental sulfur to be used as a modifier to address the abovementioned challenge at the asphalt mixture level. The sulfur polymer containing waste cooking oil and metal-rich biochar was incorporated into hot-mix asphalt having 25% RAP. The mixture specimens were evaluated before and after accelerated thermal and ultraviolet aging. Cracking resistance was measured using the Indirect Tensile Asphalt Cracking Test (IDEAL-CT), while resistance to rutting and moisture damage were assessed through the Hamburg Wheel Tracking Test (HWT). IDEAL-CT findings showed improved ${\mathrm{C}\mathrm{T}}_{\mathrm{I}\mathrm{n}\mathrm{d}\mathrm{e}\mathrm{x}}$ values for the modified mixture under unaged conditions and after three days of thermal aging, with smaller variations noted after prolonged thermal aging and during the combined thermal–ultraviolet aging process. Results from the HWT test revealed that the addition of the sulfur polymer did not negatively impact resistance to rutting or moisture damage; all mixtures remained significantly below rutting failure thresholds. Furthermore, a simplified environmental analysis indicated that substituting 10 wt% of petroleum binder with the sulfur polymer lowered the binder’s cradle-to-gate global warming potential by around 11%. In summary, study results showed that the newly developed sulfur polymer system has the potential to improve cracking resistance even when exposed to select accelerated aging protocols while decreasing embodied carbon, thus endorsing its viability as a sustainable modifier for asphalt mixtures. Full article

This study investigates the industrial validation of a granular additive derived from waste tire textile fibers (WTTF) developed to replace the conventional cellulose stabilizing additive in stone mastic asphalt (SMA) mixtures while enhancing their mechanical performance. Building on previous laboratory-scale findings, this work evaluates the feasibility and mechanical behavior of this recycled-fiber additive under real asphalt-plant production conditions, advancing a sustainable solution aligned with circular economy principles. Three asphalt mixtures were fabricated in a batch plant: a reference SMA (SMA-R) containing a commercial cellulose additive, an SMA incorporating the WTTF additive (SMA-F), and a reference hot mix asphalt (HMA-R). The WTTF additive was incorporated in a 1:1 proportion relative to the cellulose additive. Performance was assessed through tests of cracking resistance (Fénix test), stiffness modulus, fatigue resistance (four-point bending test), moisture susceptibility (ITSR), and resistance to permanent deformation (Hamburg wheel tracking). Industrial validation results showed that the SMA-F mixture met the design criteria and achieved superior mechanical performance relative to the reference mixtures. In particular, SMA-F exhibited greater ductility and toughness at low temperatures, reduced susceptibility to moisture-induced damage, and higher fatigue resistance, with an increase in fatigue durability of up to 44% compared to SMA-R. The results confirm that the WTTF additive is both feasible and scalable for industrial production, offering a solution that not only improves pavement mechanical performance but also promotes the valorization of a challenging waste material. Full article

The growing environmental effect of asphalt pavements has fueled interest in sustainable alternatives including the application of recycled materials and self-healing systems. This research investigates the synergistic possibilities of steel slag aggregates and steel wool fibers in hot-mix asphalt compositions to increase sustainability and let crack healing via electromagnetic induction heating. Using either recycled steel slag or natural porphyritic aggregates, two kinds of AC16 Surf S mixtures with 35/50 bitumen were created incorporating two levels of steel fiber content (2% and 4%). Based on repeated semi-circular bending (SCB) testing following regulated induction heating and confinement, a committed self-healing evaluation plan was developed. The results verified that combinations including recycled steel slag met or outperformed traditional mixes in terms of mechanical behavior. Induction heating successfully set off partial recovery of fracture toughness, with more fiber content and repeated heating cycles producing better healing values. Recovery levels ran from 14.6% to 40%, therefore proving the practicality of this approach. These results encourage the creation of asphalt mixtures with improved endurance and environmental advantages. The research offers both an approved approach for assessing healing and real-world recommendations for the construction of low-maintenance, round pavements utilizing induction-based techniques. Full article

The construction industry significantly contributes to global sustainability challenges, producing 30–40 percent of global carbon dioxide emissions and consuming large amounts of natural resources. Pervious concrete has emerged as a sustainable alternative to conventional pavements due to its ability to promote stormwater infiltration and groundwater recharge. However, the absence of fine aggregates creates a highly porous structure that results in reduced compressive strength, limiting its broader structural use. Determining compressive strength traditionally requires destructive laboratory testing of concrete specimens, which demands considerable material, energy, and curing time, often up to 28 days—before results can be obtained. This makes iterative mix design and optimization both slow and resource intensive. To address this practical limitation, this study applies Machine Learning (ML) as a rapid, preliminary estimation tool capable of providing early predictions of compressive strength based on mix composition and curing parameters. Rather than replacing laboratory testing, the developed ML models serve as supportive decision-making tools, enabling engineers to assess potential strength outcomes before casting and curing physical specimens. This can reduce the number of trial batches produced, lower material consumption, and minimize the environmental footprint associated with repeated destructive testing. Multiple ML algorithms were trained and evaluated using data from existing literature and validated through laboratory testing. The results indicate that ML can provide reliable preliminary strength estimates, offering a faster and more resource-efficient approach to guiding mix design adjustments. By reducing the reliance on repeated 28-day test cycles, the integration of ML into previous concrete research supports more sustainable, cost-effective, and time-efficient material development practices. Full article

The growing demand for sustainable pavement materials has driven increased interest in asphalt mixtures incorporating recycled crumb rubber (CR). While CR modification enhances mechanical performance and durability, its often increases initial production costs and energy demand. This study develops an integrated framework that combines machine learning (ML) and economic analysis to identify the optimal balance between performance and cost in CR-modified asphalt overlay mixtures. An experimental dataset of conventional and CR-modified mixtures was used to train and validate multiple ML algorithms, including Random Forest (RF), Gradient Boosting (GB), Artificial Neural Networks (ANNs), and Support Vector Regression (SVR). The RF and ANN models exhibited superior predictive accuracy (R² > 0.98) for key performance indicators such as Marshall stability, tensile strength ratio, rutting resistance, and resilient modulus. A Cost–Performance Index (CPI) integrating life-cycle cost analysis was developed to quantify trade-offs between performance and economic efficiency. Environmental life-cycle assessment indicated net greenhouse gas reductions of approximately 96 kg CO₂-eq per ton of mixture despite higher production-phase emissions. Optimization results indicated that a CR content of approximately 15% and an asphalt binder content of 4.8–5.0% achieve the best performance–cost balance. The study demonstrates that ML-driven optimization provides a powerful, data-based approach for guiding sustainable pavement design and promoting the circular economy in road construction. Full article

With the growing trend of incorporating waste and industrial by-products in infrastructure, airport pavements built with sustainable materials are of increasing interest. This research developed six theoretical concrete mixtures for airport pavement and evaluated their financial, social and environmental cost within a stochastic triple bottom line framework. A Monte Carlo simulation was used to capture uncertainty in key parameters, particularly material transport distances, embodied carbon, and cost variability, allowing a probabilistic comparison of conventional and sustainable mixtures. The results showed that mixtures incorporating supplementary cementitious materials, recycled concrete aggregate and geopolymer cement consistently outperformed the ordinary Portland cement benchmark across all triple bottom line dimensions. Geopolymer concrete offered the greatest overall benefit, while the mixture containing blast furnace slag aggregate demonstrated how long haulage distances can significantly erode sustainability gains, highlighting the importance of locally available materials to sustainability. Overall, the findings provide quantitative evidence that substantial triple bottom line cost reductions are achievable within current airport pavement specifications, and even greater benefits are possible if specifications are expanded to include emerging low-carbon technologies such as geopolymer cement. These outcomes reinforce the need for performance-based specifications that permit the use of recycled materials and industrial by-products in pursuit of sustainable airport pavement practice. Full article

The incorporation of utilized plastic waste into concrete mix designs for precast pavement applications presents a highly efficacious strategy, yielding demonstrably superior mechanical properties. High-density polyethylene (HDPE) is the proposed type of plastic in this study. It demonstrates remarkable performance and durability characteristics. The methodology not only significantly curtails landfill waste and incineration but also contributes to a reduction in energy consumption within the concrete sector, thereby establishing itself as a definitive sustainable solution that addresses environmental, economic, and societal imperatives. The optimal incorporation ratio for the recycled plastic within concrete matrices is determined to fall between 10% and 15%, as this range facilitates the attainment of the most desirable material properties. This study specifically focuses on plastic waste and the incorporation of recycled plastic into concrete materials. The emphasis on plastic is due to its material properties, which are particularly well-suited for concrete applications. Experimental tests are conducted on recycled concrete in comparison with the conventional concrete. The results demonstrate high mechanical properties to the recycled concrete. The novelty of this research is the type of plastic used in the concrete mix. Although most of the worldwide applications use Polyethylene Terephthalate (PET), HDPE showed exceeding properties and performance. Two important factors that influence the architectural aspect of construction materials are the heat island effect and the solar reflective index. These factors affect the energy absorption and emissivity rates of construction materials. The embodied carbon in the concrete mix impacts environmental and energy consumption rates, which directly relate to climate change, one of the Sustainable Development Goals (SDGs). Full article

Rapid urbanization and the widespread use of impervious materials have intensified the urban heat island (UHI) effect, raising surface temperatures and energy demands. Conventional concrete pavements contribute significantly due to their high thermal conductivity and low reflectivity. This study systematically investigates the development of thermally efficient concrete paver blocks using sustainable alternative fine aggregates to mitigate heat accumulation while retaining a minimum compressive strength of 35–45 MPa (recommended for medium traffic). Unlike prior isolated studies, this research offers a comprehensive comparative analysis of three sand replacements—Vermiculite powder (12.5–50%), Perlite powder (20–80%), and Crushed Glass (7.5–30%)—in M30-grade concrete. Fresh and hardened properties were evaluated through slump, density, and compressive strength tests at 7, 14, and 28 days, while infrared thermography quantified surface temperature variations under controlled heat exposure. Results showed significant thermal improvements, with optimal mixes Vermiculite 25% (VC-25), Perlite 40% (PR-40), and Crushed Glass 15% (CG-15) reducing surface temperatures by 25.1 °C, 22.2 °C, and 18.2 °C, respectively, while maintaining compressive strengths of 47.8 MPa, 38.8 MPa, and ~58 MPa. VC-25 proved superior, achieving the lowest surface temperature (26.3 °C) and 48.8% lower heat absorption than conventional concrete. The study establishes optimal replacement thresholds balancing insulation and strength, supporting SDGs 11, 12, and 13 through climate-responsive, resource-efficient construction materials. Full article

The global production of electronic waste (e-waste) has increased due to the quick turnover of electronic devices, creating urgent problems for resource management and environmental sustainability. As a result, e-waste-derived materials (EWDMs) are being explored in pavement engineering research as sustainable substitutes in line with Sustainable Development Goals (SDGs), specifically SDG 9 (Industry, Innovation, and Infrastructure), 11 (Sustainable Cities and Communities), 12 (Responsible Consumption and Production), and 13 (Climate Action). Therefore, to assess global research production and the effectiveness of EWDMs in asphalt applications, this review combines scientometric mapping and systematic evidence synthesis. A total of 276 relevant publications were identified via a thorough search of Web of Science, Scopus, and ScienceDirect (2010–2025). These were examined via coauthorship structures, keyword networks, and contributions at the national level. The review revealed that China, India, and the United States are prominent research hubs. Additionally, experimental studies have shown that EWDMs, such as printed circuit board powder, fluorescent lamp waste glass, high-impact polystyrene, and acrylonitrile–butadiene–styrene, improve the fatigue life, Marshall stability, rutting resistance (up to 35%), and stiffness (up to 28%). However, issues with long-term field durability, microplastic release, heavy metal leaching, and chemical compatibility still exist. These restrictions highlight the necessity for standardised toxicity testing, harmonised mixed-design frameworks, and performance standards unique to EWDMs. Overall, the review shows that e-waste valorisation can lower carbon emissions, landfill build-up, and virgin material extraction, highlighting its potential in the circular pavement industry and promoting sustainable paving practices in accordance with SDGs 9, 11, 12, and 13. This review suggests that further studies on large-scale field trials, life cycles, and technoeconomic assessments are needed to guarantee the safe, long-lasting integration of EWDMs in pavements. It also advocates for coordinated research, supportive policies, and standardised methods. Full article

Coal gangue, a solid waste from coal mining, has long been underutilized while posing environmental and safety risks. This study reviews the current research progress and future prospects of coal gangue as a resource in asphalt pavement. The physical and chemical properties of coal gangue were summarized, and the environmental issues caused by its accumulation were highlighted. The effects of using coal gangue as aggregates or fillers in asphalt mixture were reviewed, along with its activation methods. The research progress on using coal gangue as an aggregate or a cementitious material in mixtures stabilized with inorganic binders was also examined, emphasizing the effects of binder content and coal gangue properties on mechanical and durability performance. The findings indicate that despite its inferior physical properties, coal gangue demonstrates practical feasibility as a pavement material when appropriately incorporated and activated. Proper content enabled coal gangue to meet asphalt mixture or base material requirements, while excessive content reduced low-temperature resistance and caused structural defects. Activated or modified methods can effectively enhance interfacial interaction, high-temperature stability, or structural densification of coal gangue. Recent studies have expressed enthusiasm for innovative activation or modification methods and AI-based performance optimization, while key challenges remain regarding high activation-energy demand, limited aggregate-related research, and an incomplete understanding of interfacial mechanisms. Full article