Search Results (317)

Several variables influence the performance of hot asphalt mixtures including reclaimed asphalt pavement (RAP). Among these, the virgin bitumen’s origin, the mix production temperature and the time the mix is kept at a high temperature between mixing and compaction play a fundamental role but are often neglected. This study aimed to quantify the negative effects associated with the improper choice of these variables. Therefore, their influence on the mechanical (indirect tensile stiffness modulus and strength, Cracking Tolerance Index) and chemical (Fourier Transform Infra-Red spectroscopy) characteristics of asphalt mixtures containing 50% RA were investigated. In particular, two rejuvenators, two types of virgin bitumen (visbreaker and straight-run), two production temperatures (140 °C and 170 °C) and three conditioning times in the oven (30 min, 90 min and 180 min) were analyzed. The results showed interesting findings that allow us to recommend selecting the virgin bitumen type carefully and to avoid excessively stressing the binder during the production of the mix. Full article

The increasing demand for sustainable practices in road construction has prompted the search for environmentally friendly and cost-effective materials. This study explores the incorporation of reclaimed asphalt pavement (RAP) and Panasqueira mine waste (greywacke aggregates) as full replacements for virgin aggregates in hot mix asphalt (HMA), aligning with the objectives of UN Sustainable Development Goal 9. Three asphalt mixtures were prepared: a reference mixture (MR) with granite aggregates, and two modified mixtures (M15 and M20) with 15% and 20% RAP, respectively. All mixtures were evaluated through Marshall stability, stiffness modulus, water sensitivity, and wheel tracking tests. The results demonstrated that mixtures containing RAP and mine waste met Portuguese specifications for surface courses. Specifically, the M20 mixture showed the highest stiffness modulus, improved moisture resistance, and the best performance against permanent deformation. These improvements are attributed to the presence of stiff aged binder in RAP and the mechanical characteristics of the greywacke aggregates. Overall, the findings confirm that the combined use of RAP and mining waste provides a technically viable and sustainable alternative for asphalt pavement construction, contributing to resource efficiency and circular economy goals. Full article

Effective management and handling of construction and demolition waste (CDW) can yield significant technical and environmental benefits for road pavement construction. This article aims to provide a comprehensive and up-to-date chronological review of studies on the mechanical performance of asphalt mixtures—primarily hot mix asphalt (HMA)—incorporating recycled concrete aggregate (RCA). Since the main limitation of RCA is the presence of residual adhered mortar, the review also includes studies that applied various surface treatments (mechanical, chemical, and thermal, among others) to enhance mixture performance. The article summarizes the experimental procedures used and highlights the key findings and conclusions of the reviewed research. Although the results are varied and sometimes contradictory—mainly due to the source variability and heterogeneity of RCA—the use of these materials is technically viable. Moreover, their application can provide environmental, social, and economic advantages, particularly in the construction of low-traffic roadways. Finally, the article identifies research gaps and offers recommendations for future researches. Full article

In response to the escalating climate crisis, reducing greenhouse gas emissions (GHG) has become a top priority for both the public and private sectors. The pavement industry plays a key role in this transition, offering innovative technologies that minimize environmental impacts without compromising performance. Among these, the incorporation of recycled tire rubber and warm-mix asphalt (WMA) additives represents a promising strategy to reduce energy consumption and resource depletion in road construction. This study conducts a comparative life cycle assessment (LCA) to evaluate the environmental performance of an asphalt pavement incorporating recycled rubber and a WMA additive—referred to as R-W asphalt—against a conventional hot-mix asphalt (HMA) pavement. The analysis follows the ISO 14040/44 standards, covering material production, transport, construction, and maintenance. Two service-life scenarios are considered: one assuming equivalent durability and another with a five-year extension for the R-W pavement. The results demonstrate environmental impact reductions of up to 57%, with average savings ranging from 32% to 52% across key impact categories such as climate change, land use, and resource use. These benefits are primarily attributed to lower production temperatures and extended maintenance intervals. The findings underscore the potential of R-W asphalt as a cleaner engineering solution aligned with circular economy principles and climate mitigation goals. Full article

The application of hot in-place recycling asphalt mixtures (HIRAMs) is gaining increasing attention in highway maintenance due to its environmental and economic benefits. This paper comprehensively reviews and discusses the state-of-the-art studies in the field of hot in-place recycling (HIR). Firstly, different HIR technologies are introduced, including surface recycling, remixing, and repaving. Then, this paper provides a detailed description of the key factors influencing the road performance of HIRAMs in terms of both materials and production, such as reclaimed asphalt pavement (RAP), rejuvenators, virgin asphalt, virgin asphalt mixtures, preheating temperature, and mixing time. Furthermore, the environmental and economic benefits of HIR are compared with other preventative maintenance and recycling technologies. Finally, some challenges for the investigation of HIR are further discussed, and the corresponding suggestions are recommended for future investigation. Full article

With increasing traffic loads and the continuous deterioration of asphalt pavements, it has become necessary to explore alternative materials that enhance both performance and sustainability. This study aims to investigate the effect of using cement kiln dust (CKD) as a filler substitute in hot mix asphalt composites, focusing on the mechanical and durability properties of pavements. The results indicate that replacing conventional filler with CKD in different proportions (1.5%, 3%, 4.5%, and 6%) positively affects the properties of asphalt mixtures. Marshall stability values increased by 58.4% when using 100% CKD, indicating a significant improvement in the mixture’s ability to withstand traffic loads. Flow tests revealed that replacing CKD by up to 50% enhances the flexibility of the mixture, but exceeding this percentage makes the mixture stiffer, which may lead to premature cracking. In terms of moisture sensitivity, incorporating CKD by 25% improves the mixture’s resistance to water damage, while increasing it to 100% reduces this resistance, highlighting the need to improve the adhesion properties of asphalt. Indirect tensile strength tests have confirmed that CKD enhances the cohesion of the mixture, reducing the likelihood of cracking under pressure and contributing to longer pavement life. Based on these results, it is recommended that CKD be used for up to 50% to achieve a balanced combination of strength, flexibility, and moisture resistance, with further studies being needed to evaluate the long-term performance and potential improvements through additional material modifications. Full article

The integration of Recycled Concrete Aggregate (RCA) and Reclaimed Asphalt Pavement (RAP) into Hot Mix Asphalt (HMA) presents a sustainable solution to mitigate environmental impacts and reduce reliance on virgin materials. This study investigates the influence of RCA and RAP as partial replacements for natural limestone aggregates on the volumetric, mechanical, and performance properties of asphalt mixtures. Replacement levels of 11%, 33%, and 66% (by total aggregate weight) were evaluated through comprehensive testing, including dynamic modulus, flow number, stiffness factor, and loss modulus assessments under varying temperatures and loading frequencies. Findings indicate that recycled aggregate incorporation results in a progressive reduction in optimum asphalt binder content, voids in mineral aggregates (VMAs), and voids filled with asphalt (VFAs). While all mixtures demonstrated acceptable stiffness-frequency behavior, the 33% replacement mix provided the best balance of rutting resistance and fatigue performance, satisfying Superpave volumetric criteria. The 11% mix exhibited enhanced fatigue resistance, whereas the 66% mix, despite showing the highest rutting stiffness, failed to meet minimum volumetric thresholds and is therefore unsuitable for structural applications. Statistical analysis (one-way ANOVA) confirmed the significant effect of RCA and RAP content on the mechanical response across performance zones. The results highlight the potential of using moderate recycled aggregate levels (particularly 33%) to produce durable, sustainable, and cost-efficient asphalt mixtures. For regions with mixed distress conditions, a 33% replacement is recommended, while 11% may be preferable in fatigue-critical environments. Further research incorporating viscoelastic continuum damage models and life cycle cost analysis is suggested to optimize design strategies and quantify long-term benefits. Full article

Iraq’s extreme summer temperatures pose critical challenges to pavement durability, as conventional asphalt mixtures often fail under prolonged thermal stress. This paper provides a comparative evaluation of the high-temperature performance of unmodified (40/50 penetration grade) and polymer-modified (PG 76-10) asphalt mixtures for the asphalt course layer. Marshall stability, flow, and stiffness were measured at elevated temperatures of 60 °C, 65 °C, 70 °C, and 75 °C after short-term (30 min) and extended (24 h) conditioning. Results show that while both mixtures experienced performance degradation as the temperature increased, the polymer-modified mixture consistently exhibited superior thermal resistance, retaining approximately 9% higher stability and 28% higher stiffness, and displaying 18% lower flow deformation at 75 °C compared to the unmodified mixture. Stability degradation rate (SDR), stiffness degradation rate (SiDR), and flow increase rate (FIR) analyses further confirmed the enhanced resilience of PG 76-10, showing nearly 39% lower FIR under thermal stress. Importantly, PG 76-10 maintained performance within specification thresholds under all tested conditions, unlike the conventional 40/50 mixture. These findings emphasize the necessity of adapting mix design standards to regional climatic realities and support the broader adoption of polymer-modified asphalt binders to enhance pavement service life in hot-climate regions like Iraq. Full article

Most modified asphalts require high-temperature shearing and prolonged mixing to achieve a uniform structure, often resulting in substantial exhaust gas pollution. This study explores the utilization of polyurethane (PU) as a warm mix asphalt modifier, leveraging its favorable compatibility with asphalt at lower temperatures to mitigate emissions. To address the inherent limitations of PU-modified asphalt mixtures, namely, poor low-temperature performance and susceptibility to water damage, silane coupling agents (SCAs) are introduced to reinforce the asphalt–aggregate interfacial strength. At the microscopic level, the optimal PU content (20.8%) was determined through analysis of micro-viscosity and radial distribution functions (RDFs). SCA effects on interfacial properties were assessed using adhesion work, adhesion depth, and interfacial thermal stability. At the macroscopic level, performance metrics—including strength, high-temperature resistance, low-temperature resistance, and water stability—were evaluated against a benchmark hot mix SBS-modified asphalt mixture. The results indicate that PU-modified asphalts exhibit superior high-temperature performance and strength but slightly lower low-temperature performance and insufficient water stability. The addition of SCAs improved both low-temperature and water stability attributes, enabling the mixtures to meet specification requirements. The simulation results suggest that KH-550, which chemically reacts with isocyanate groups (-OCN) in PU, exhibits a better interfacial reinforcement effect than KH-570. Therefore, KH-550 is recommended as the preferred SCA for PU-modified asphalt mixtures in practical applications. Full article

Ferrochrome (FeCr) slag is a by-product of high-carbon ferrochromium, which is used in the manufacturing of stainless steel. In this study, FeCr was evaluated as a replacement for natural aggregates in hot-mix asphalt (HMA) bituminous base and wearing course layers. Four mixes were designed according to the Superpave mix design procedure, one control and three mixes, with FeCr slag replacing coarse, fine, or total aggregate. FeCr slag exhibited higher angularity and surface roughness than natural aggregates, resulting in an increased number of voids in mineral aggregate (VMA) and increased binder content. Performance testing using dynamic modulus, finite element analysis, and rutting evaluation using the MEPDG rut model showed that rutting increased with increased slag content. However, mixes with coarse aggregate replacement performed better than those with fine aggregate replacement. TCLP testing indicated that the FeCr slag is environmentally safe. The heavy metal leachate content was well below regulatory limits. Economic analysis showed material cost savings of up to 44% and 4% in the bituminous base and wearing course layers, respectively. The findings support the use of FeCr slag as a coarse aggregate replacement in asphalt mixes, offering both environmental and economic benefits. Full article

Background: In response to the growing demand for the real-time, in-field characterization of odorous anthropogenic emissions, this study develops and uses a MEMS-based micropacked thermal desorption Gas Chromatography system coupled with a PhotoIonization Detector (GC/PID) for Hot Mix Asphalt (HMA) plant emissions. Methods: The innovative portable device, Pyxis GC, enables the high-sensitivity profiling of Volatile Organic Compounds (VOCs), particularly aldehydes and ketones, with sub-ppb detection limits using ambient air as the carrier gas. A comprehensive experimental design optimized the preconcentration parameters, resulting in an efficient, green analytical method evaluated via the Green Analytical Procedure Index (GAPI). Sorbent comparison showed quinoxaline-bridged cavitands outperform the conventional materials. Results and conclusions: The method was successfully deployed on site for source-specific sampling at an HMA plant, generating robust emission fingerprints. To assess environmental impact, a Generalized Additive Model (GAM) was developed, incorporating the process temperature and Sum of Odour Activity Values (SOAV) to predict odour concentrations. The model revealed a significant non-linear influence of temperature on emissions and validated its predictive capability despite the limited sample size. This integrated analytical–statistical approach demonstrates the utility of MEMS technology for real-time air quality assessment and odour dispersion modelling, offering a powerful tool for environmental monitoring and regulatory compliance. Full article

Predicting the performance of hot mix asphalt (HMA) is crucial for ensuring pavement durability, especially as the use of rejuvenated reclaimed asphalt pavement (RAP) increases in sustainable construction. Indirect tensile strength (ITS) is a critical parameter that indicates a pavement’s resistance to cracking and distress under traffic loads. This study developed statistical and machine learning models—linear regression, support vector machine (SVM), and artificial neural network (ANN)—to predict ITS and ITS loss in RAP-incorporated HMA rejuvenated with waste cooking oil (WCO) and waste engine oil (WEO). The models used key input variables, including rejuvenator type and the composition of asphalt, rejuvenator, and RAP. Results showed that WCO increased initial ITS, while WEO enhanced durability by reducing ITS loss. Additionally, lower RAP and asphalt content contributed to improved pavement durability. Among the predictive models, ANN demonstrated the highest accuracy, exhibiting lower error metrics and less variation in scatterplots compared to regression and SVM models. The only exception was ITS loss percentage prediction, where the mean absolute error was nearly identical across all models. These predictive models provide valuable insights for designing and testing modified asphalt mixtures, particularly those containing RAP. By optimizing mix design and enabling proactive maintenance strategies, they contribute to the development of more durable and sustainable pavement infrastructure with the provision of accurate and workable models for prediction of ITS and loss prediction which can be used for design. Full article

Pavement materials like hot mix asphalt (HMA) and cold recycled mixes (CRMs) are typically considered isotropic. This study evaluates the anisotropy of a cold in-place recycled (CIR) material using the shear wave velocity (V_s) parameter. The piezoelectric ring actuator technique (P-RAT) is utilized to assess the V_s parameter in three directions in CIR slabs. Similarly, the ultrasonic pulse velocity (UPV) technique is employed to measure P-wave velocities. Both methods evaluate mechanical properties in multiple directions. Complex modulus tests are conducted to link velocities results to |E*| modulus. Finally, computed tomography (CT) scans are performed on the specimens in order to evaluate anisotropy resulting from aggregate alignment. The V_s obtained using P-RAT and the V_p from UPV indicate anisotropy, as the wave velocities differ across the three directions. Differences range from 0.6 to 11.6% in V_s, influenced by measurement location. UPV results are analysed in relation to the |E*| modulus master curves, demonstrating that the first peak arrival time for the P-wave corresponds with the master curve. CT scan analysis reveals that the aggregates tend to be more aligned in the direction of the compacting wheel’s displacement, which also highlights anisotropy. Full article

This study explores the correlation between road surface texture, including microtexture (texture depth) and macrotexture (wavelength) in asphalt pavement, and suspended dust generation on asphalt pavements. A detailed analysis of various pavement types, including Hot Mix Asphalt (HMA) and porous pavement, was conducted to assess their impact on dust load and concentration. For HMA pavements, deeper texture depths led to a higher dust load and concentration, attributed to the impermeable nature of the material, which causes dust to become easily suspended in the air. Conversely, porous pavements, which have air gaps in their surface layers, showed reduced dust suspension despite a higher dust load, due to the ability of these voids to trap dust and minimize air-pumping effects from tire–road contact. The study found that a macrotexture depth (MTD) exceeding 1.7 mm stabilized dust concentration, while higher surface wavelengths and silt load (sL) values above 0.1 g/m² significantly contributed to dust suspension. These findings suggest that optimizing road surface texture and aggregate size, considering the voids and depth, can help reduce suspended dust, providing a balance between road safety and environmental management. This research offers valuable insights for designing pavements that mitigate air pollution while maintaining functional performance. Full article

Zinc oxide (ZnO) exhibits promising thermochemical properties when used as an asphalt binder modifier. Its micrometric size further enhances its potential as a substitute for natural fillers (NFs) in hot-mix asphalt (HMA). This study evaluates the effect of partially and fully replacing NFs with ZnO on the mechanical performance of HMA, addressing a research gap since the influence of ZnO as a filler in asphalt mixtures has not been previously investigated. NFs were replaced by ZnO at weight-based proportions of ZnO/NF = 25, 50, 75, and 100%. Initially, the morphology of NF and ZnO particles was analyzed using Scanning Electron Microscopy (SEM). Asphalt mastics were then produced with the same ZnO/NF proportions and subjected to conventional characterization tests, including penetration, softening point, and viscosity. In the next phase, HMA samples were designed using the Marshall method, incorporating ZnO at 0, 25, 50, and 100% replacement levels (designated as Control, HMA-25, HMA-50, and HMA-100, respectively). The mechanical performance of these mixtures was assessed through indirect tensile strength (ITS) and Cantabro tests. Based on the initial results, further evaluations were conducted on the Control, HMA-50, and HMA-100 mixtures to determine their resilient modulus, fatigue behavior under stress-controlled conditions, and resistance to permanent deformation (static creep test). The findings indicate that ZnO can replace NF in HMA without compromising Marshall stability or Cantabro strength. Additionally, ZnO-modified HMAs exhibit increases in stiffness under cyclic loading, and improvements in resistance to permanent deformation, fatigue performance, and moisture damage. These enhancements occur despite a 0.5% reduction in binder content compared to the Control HMA and a slight increase in porosity. Full article