Search Results (24)

Modernizing municipal roads requires rehabilitation strategies that ensure adequate structural performance while reducing environmental and economic burdens. Although cold in-place recycling with foamed bitumen (CIR-FB) has been widely investigated, integrated assessments combining mechanistic–empirical modeling with LCA and LCCA remain limited—particularly for municipal roads in Central and Eastern Europe, where reclaimed asphalt pavement (RAP) quality, climatic conditions and budget constraints differ from commonly studied regions. This study compares two reconstruction variants for a 1 km road section: a conventional design using virgin materials (V₁-N) and a recycling-based alternative (V2-Rc) incorporating RAP from the existing wearing and binder layers and reclaimed aggregate (RA) from the existing base. CIR-FB mixture testing (stiffness ≈ 5.25 GPa; foamed bitumen = 2.5%, cement = 2.0%) was integrated into mechanistic–empirical fatigue analysis, material-flow quantification, LCA and LCCA. The V₂-Rc variant achieved a 3–21-fold increase in fatigue life compared to V₁-N at equal thickness. Material demand decreased by approximately 27%, demolition waste by approximately 39%, and approximately 92% of the existing pavement was reused in situ. Transport work was reduced five-fold (veh-km) and more than six-fold (t-km). LCA showed a 15.9% reduction in CO₂-eq emissions, while LCCA indicated approximately 19% lower construction cost, with advantages remaining robust under ±20% sensitivity. The results demonstrate that CIR-FB, when supported by proper RAP/RA characterization, can substantially improve structural, environmental and economic performance in municipal road rehabilitation. Full article

The cold recycling (CR) technique is gaining traction, with an increasing demand for sustainable pavement construction practices. Cold in-place recycling (CIR) and cold central plant recycling (CCPR) are two strategies under the umbrella of cold recycling. These techniques use reclaimed asphalt pavement (RAP) to rehabilitate pavement, and CCPR offers the added advantage of utilizing stockpiled RAP. While many agencies have expertise in cold recycling techniques including CCPR, the lack of pavement performance data prevented the largescale implementation of these technologies. Recent studies in high-traffic volume applications demonstrate that CCPR technology can be implemented on the entire road network across all traffic levels. This reignited interest in the widespread implementation of CCPR. Therefore, the purpose of this study is to provide agencies with the most up-to-date information on CCPR to help them make informed decisions. To this end, this paper comprehensively reviews the mix-design for CCPR, the structural design of pavements containing CCPR layers, best construction practices, and the agency experience in using this technology on high-traffic volume roads to provide in-depth information on the steps to follow from project selection to field implementation. The findings specify the suitable laboratory curing conditions to achieve the optimum mix design and specimen preparation procedures to accurately capture the material properties. Additionally, this review synthesizes existing quantitative data from previous studies, providing context for the comparison of findings, where applicable. The empirical and mechanistic–empirical design inputs, along with the limitations of AASHTOWare Pavement ME software for analyzing this non-conventional material, are also presented. Full article

With the increasing demand for highway maintenance, enhancing the resource utilization of reclaimed asphalt pavement (RAP) has become an urgent and widely studied issue. Although foam asphalt cold recycling technology offers significant benefits in terms of resource utilization and energy saving, it still faces challenges, particularly the poor stability of foam asphalt mixtures. This study focuses on optimizing the performance of foam asphalt recycled mixtures through interface modification, aiming to promote the widespread application of foam asphalt cold recycling technology. Specifically, the research follows these steps: First, the optimal mix ratio of the recycled mixtures was determined based on the fundamental properties of foam asphalt and RAP. Then, zinc oxide, silane coupling agents, and amine anti-stripping agents were introduced to modify the recycled mixtures. At last, a series of tests were conducted to comprehensively evaluate improvements in road performance. The results indicate that the silane coupling agent enhances the low-temperature performance and fatigue. The fracture energy reached 526.71 J/m². Zinc oxide improves the low-temperature cracking resistance and dry shrinkage performance. Amine anti-stripping agents have minimal impact on the low-temperature performance. The linear shrinkage was reduced by 2.6%. The results of TOPSIS indicated that silane coupling agent modification exhibits superior fatigue resistance and low-temperature performance, achieving the highest comprehensive score of 0.666. Although amine-based anti-stripping agents improve fatigue life, they are not suitable for modifying foamed asphalt mixtures due to their detrimental effects on low-temperature performance and moisture resistance. Full article

Cold recycling is an advantageous technique from economic and environmental perspectives for asphalt pavement rehabilitation, interventions, and maintenance. This work covered the investigation of dynamic modulus (|E*|) test models and their effects on cold recycled asphalt mixture (CRAM) |E*| data fitting, considering different mixture parameters such as asphalt binder type and content, active filler type and content, aggregate gradation, reclaimed asphalt pavement content, and curing conditions. Multiple mixtures from a dynamic modulus test database were fitted using six different regression models and the results were analyzed by means of different residuals analysis. Finally, the effects of CRAM composition on |E*| data were graphically assessed. For the analyzed specimens, two models were found to be the most adequate for CRAM’s |E*| data regression. The analysis of CRAM composition showed a strong relation between the compaction method and the stiffness of CRAMs. Full article

Foamed asphalt cold recycled mixtures can provide an effective approach for the reutilization of reclaimed asphalt pavement (RAP), but conventional asphalt foaming technology primarily exploits matrix asphalt as the raw material. To address this issue, this study explores rubberized asphalt with cold recycling technology to develop a foamed rubber asphalt cold recycled mixture (FRCM). The semi-circular bending (SCB) test was employed to investigate its cracking resistance. Load–crack mouth opening displacement (CMOD)–time curves under various temperatures were analyzed, and digital image technique was resorted to monitor crack propagation and growth rates. Fracture toughness, fracture energy, and flexibility index were compared with those of traditional foamed matrix asphalt cold recycled mixture (FMCM). The results show that, under the same test temperature, the FRCM exhibits slower crack propagation; larger peak load; and higher fracture toughness, fracture energy, and flexibility index in comparison with the FMCM. These improvements are more pronounced at low temperatures. For both mixtures, fracture toughness and fracture energy are decreased with increasing the temperature, while the flexibility index shows the opposite trend. The rigid zone accounts for a larger portion of fracture energy at low temperatures. The findings provide technical references for improving the cracking resistance of cold recycled asphalt layers using rubberized asphalt. Full article

This paper presents gradations of both Hot In-place Recycling (HIR) and Cold In-place Recycling (CIR) and analysis of cores collected from CIR/Hot Mix Asphalt (HMA) overlay sections in Iowa. Milling samples were obtained from an HIR recycling project on IA 22 in Wellman, Iowa. It was concluded that the average gradation of HIR millings was coarser than that of CIR millings by retaining the original aggregate gradations. Cores were then extracted from CIR pavement with foamed asphalt overlaid by HMA at the right wheel path and between wheel paths at eight locations on US 34 in Mills and Wapello Counties. The cores were cut into discs to isolate the pavement layers, and the discs were fabricated into semicircular bending test specimens. Based on the Semicircular Bending (SCB) tests performed on both CIR and HMA specimens, CIR specimens with higher asphalt binder contents exhibited higher flexibility index values. Since CIR pavement layers were found to be more flexible than the HMA overlay layers, it can be speculated that CIR layers may serve as a stress-relieving layer and mitigate reflective cracking. Full article

Foamed rubber asphalt has attracted wide attention in cold-recycled pavement projects due to its excellent performance, strong construction performance and resource conservation, but the mechanism of its performance improvement after foaming is still unclear. In order to explore the difference in the performance of rubber asphalt before and after foaming, this study systematically analyzed the performance improvement mechanism of asphalt from nano, micro and macro perspectives. Molecular dynamics simulation results show that the density and modulus of rubber asphalt decrease after foaming. After foaming, the glass transition temperature of rubber asphalt decreased by 4.4 K, and the free volume fraction decreased by 4.7%, which indicated that its low-temperature toughness was enhanced. The simulation results also illustrate the performance enhancement mechanism of rubber asphalt. Rubber and asphalt are physically mixed and do not undergo chemical reactions. However, foaming makes the rubber particles more evenly distributed, helping to improve the toughness and fatigue properties of asphalt. Macroscopic test results show that the high-temperature performance and fatigue performance of foamed asphalt are reduced, while the low-temperature performance is improved. The molecular simulation results are consistent with the experimental results, providing a comprehensive explanation for the improvement mechanism of rubber asphalt performance. Full article

This study investigates the application of foam asphalt (FA) to enhance the compaction effectiveness of a hot in-place recycling asphalt mixture (HIR-AM) during the HIR process of old road surfaces. Initially, the process parameters for FA preparation were determined through expansion-rate and half-life tests. Subsequently, the study focused on evaluating the impact of FA on the compaction quality of HIR-AM. Performance assessments were conducted through rutting tests, low-temperature bending tests, Hamburg wheel tracking tests, dynamic modulus analyses, and various other experiments to evaluate the road performance of HIR-FAM. Finally, the research findings were validated through practical engineering applications, and the construction process for HIR-FAM was summarized. The research results reveal that the optimal foaming temperature for SBS asphalt is 170 °C, with an ideal water content of 1.7%. Under the same compaction temperature, HIR-FAM demonstrated a significant reduction in void content, ranging from 3.8% to 21.2% compared to HIR-AM. Moreover, a higher proportion of FA usage resulted in a more substantial decrease in void content. Compared to HIR-AM, HIR-FAM exhibited notable improvements, including an 11.6% increase in dynamic stability, a 13.4% enhancement in bending strength, a 13.3% increase in maximum bending strain, an 8.1% improvement in residual stability, and an 8.5% boost in freeze–thaw splitting strength. Furthermore, HIR-FAM demonstrated superior water-thermal stability and resistance to low-frequency loads. Paving a test road verified that the adoption of foam asphalt in thermal recycling led to a compaction density increase of over 0.79% compared to traditional in situ thermal recycling sections, with improved compaction uniformity. Full article

Cores were recovered from the right wheel path and between wheel paths at 8 locations US 34 in Mills and Wapello Counties. The cores were cut into discs to isolate the pavement layers and the discs were fabricated into semicircular bending test specimens. Asphalt contents among CIR cores varied significantly and that CIR specimens with higher asphalt binder contents exhibited higher flexibility index values. From the output of these tests, the CIR pavement layers were found to be more flexible in comparison to the HMA layers, that CIR layers have higher flexibility that allow them to serve as a stress relieving layer and mitigate reflective cracking. Full article

Environmental awareness and budgetary constraints in road construction and rehabilitation require innovative and at the same time environmentally friendly solutions in favor of resource conservation, in any type of pavement intervention. In the meantime, surface interventions in severely deteriorated pavements are insufficient, increasing as such the recycling potential of existing materials in Full Depth Reclamation (FDR). This study addresses the efficiency of an FDR process in which the recycled base course of an existing semi-rigid pavement is stabilized with Foamed Asphalt (FA). The adverse effects of FA curing, which have a significant impact on pavement evaluation, particularly in the early stages of a pavement’s life cycle, prompted the conduct of a comprehensive testing campaign at two different periods, shortly after pavement rehabilitation and five years thereafter. The campaign included nondestructive testing at the aforementioned periods using Ground Penetrating Radar (GPR) and the Falling Weight Deflectometer (FWD), which facilitate the structural evaluation of the FA base. Using the collected nondestructive testing data, the principles of Multi-Layer Elastic Theory (MLET) and Genetic Algorithms (GA) are used to investigate the performance of the FA base. Both analysis tools captured the FA strength increase in the second period, but an increased variance of the FA modulus was observed mainly in the first test period, probably due to the curing effect. In addition, GA showed an advantage over other, more conventional tools for back-analysis of pavement stiffness, resulting in an interesting correlation potential of FA modulus to a deflection-based parameter reflecting the condition of the FA layer. Overall, the study contributes to the development of a practical methodology suitable for the evaluation of non-conventional and sustainable pavement structures. Full article

The utilization of recycled materials is an important issue in the context of environmental protection. The large amounts of recycled material recovered from the demolition of asphalt road structures indicate the need to find new ways of utilizing them. In the case of road renovation projects, large amounts of recycled materials are, in most cases, recovered in the form of reclaimed asphalt pavement (RAP), reclaimed concrete (RC) and recycled aggregate (RA). To focus on the effects of the use of recovered materials (RAP, RC and RA), the same composition was used for all of the analyzed mixtures in terms of foamed bitumen (FB) and Portland cement (CEM) content. The scope of laboratory tests included the specification of the following parameters: the amount of air void content Vm, the determination of axial compression strength at +25 °C, indirect tensile strength (ITS) at +25 °C, water resistance, TSR, water and frost resistance, WR_W+M stiffness modulus (IT-CY) at 13 °C, dynamic dynamicmodulus. The plan of the experiment assumed addition recycled material in quantities between 20% and 80% in increments of 20%. The obtained results indicate that both the type and quantity of recycled material significantly affect the properties of the cold-recycled mixture with foamed bitumen. Using reclaimed asphalt pavement and recycled cement concrete guarantees high levels of stiffness in the recycled mixture. Howeverin the case of recycled aggregate, the authors did not observe any visible changes in the dynamicdynamic modulus, irrespective of the loading conditions. It was also indicated that it is necessary to reduce the quantity of reclaimed asphalt pavement in the composition of the FB-RCM mix to maintain the required air void content. Full article

The planning of road infrastructure undergoes major changes, especially in terms of sustainable development. Recycling of pavement structures involves the reuse of materials from existing pavement structures due to its timesaving and environmental benefits, as well as cost reduction. According to the recycling temperature, recycling can be hot and cold. This paper deals with cold in-place recycling and the determination of the optimum fluid content for by-product materials in mixtures compared with one containing natural zeolite. The content of bitumen emulsion and cement—which are the most used materials so far in cold recycling along with foam bitumen—was replaced with fly ash, slag or natural zeolite, and bakelite, respectively, while recycled asphalt pavement from Serbia (Žabalj) was used. Six different mixtures were made. The mixture with the addition of fly ash had the highest optimum fluid content (7.6%) compared with all test mixtures. Mixtures with slag, natural zeolite, and bakelite were in the range of a mixture containing 2% cement. Furthermore, the mixture with 3% cement had the lowest optimum fluid content (5.7%) in comparison to all the mixtures that were tested. Full article

Foamed asphalt recycling technology can effectively recover waste asphalt pavement materials and achieve the sustainable utilization of resources. This technology’s core equipment is asphalt foaming equipment. Since the asphalt foaming device’s fault data are uncertain, this work proposes a method for evaluating the device’s reliability, combining triangular intuitionistic fuzzy numbers, trapezoidal intuitionistic fuzzy numbers, and expert knowledge. Using the proposed evaluation method, the failure probability of the asphalt foaming device and the importance of the bottom event were calculated. The obtained model results were found to be consistent with the actual collected data, verifying the reliability and validity of the model. Furthermore, the asphalt viscosity is one of the key factors affecting the asphalt foaming recycling technology. In this work, the influence of different viscosities on the asphalt foaming mechanism was investigated using a theoretical analysis. Then, a computational fluid dynamics (CFD) analysis method was employed to simulate the different viscosity asphalt foaming processes, aiming to identify the most suitable one for the production of high-quality foam asphalt in the foaming asphalt viscosity range. Finally, experiments were carried out to verify the results of the analysis. The results show that the asphalt foaming device’s failure probability was around 7.512 × 10⁻², and the best foaming asphalt viscosity was in the range of 0.3~0.5 Pa·s. Full article

The paper presents the results of exploratory research on the use of reclaimed cement concrete in cold-recycled mixes with foamed bitumen. Because reclaimed cement concrete, unlike natural aggregates, is expected to have a residue of the non-hydrated cement covering the aggregate grains, which may result in a secondary cementation process after its application in a road base, this avenue was explored by tracking the time evolution of the compressive strength of the final material. The tests were performed using two mixtures, i.e., a reference mixture and a mixture containing 25% reclaimed cement concrete. The mixtures containing reclaimed cement concrete were characterized by increased uniaxial compressive strengths after each curing period (3, 4, 7, 14 and 28 days)—by 11.5 kPa on average and e.g., 498 kPa vs. 506 kPa after 28 days. The obtained differences between the mixtures were not found to be statistically significant. The small effects of the incorporation of reclaimed cement concrete were attributed to the time passed typically between the demolition and new pavement construction and to the presence of a second binding material—bitumen. Full article

Millions of tons of reclaimed asphalt pavement (RAP) and reclaimed aggregate or reclaimed inorganic binder stabilized aggregate (RAI) is produced every year in China. The cold recycled mixture (CRM) technology reduces fuel consumption, emissions, and cost and utilizes the high content of RAP. In this paper, six types of CRM with varying RAP/RAI composition and asphalt binders were investigated. The laboratory tests included strength indicators, high temperature stability, low temperature crack resistance, water stability, and dynamic modulus. A full-scale trial section was constructed after the laboratory tests. Except for low temperature failure strain without secondary compaction in the mixture design, test results illustrated that the performances of different CRMs met the specifications. The cement addition limited the thermo-viscoelastic behavior of the CRM. The RAI contents had reduced the water sensitivity of CRM, and the emulsified asphalt CRM had better performance than the foamed asphalt CRM. The performances of samples cored from the test section in the field met the specifications and were lower than that in the laboratory. The curing conditions in the field were not as effective as in the laboratory. The curing conditions and compaction method should simulate the conditions in the field to guide the CRM selection and mixture design. Full article