Volume 45, Issue 5 (2025) Life Extension and Green Maintenance Technologies for Existing Asphalt Pavement
Special Issue
Research and Application Progress of RAP Plant-Mixed Hot Recycling Based on Oil-Stone Separation
YU Xin, GAO Yuchao, and ZHOU Jie
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.001
Driven by global sustainable development strategies, China, as a major infrastructure nation, faces multiple pressures from resource constraints, environmental challenges, and its dual carbon goals. The efficient recycling of recycled asphalt pavement (RAP) has become a core issue for the green development of road engineering. Traditional recycling technologies struggle to overcome the 30% blending bottleneck due to issues such as high RAP agglomeration rates and significant gradation variability. Oil-stone separation technology deconstructs RAP to a near-virgin state through physical crushing, offering a novel pathway for high-ratio (≥30%) and even ultra-high-ratio (≥50%) RAP recycling. This paper critically reviewed systematic research on RAP material properties, oil-stone separation technology, and plant-mixed hot recycling applications by comparing domestic and international progress. It focused on exploring agglomeration mechanisms, causes of variability, and control strategies, while analyzing the root causes of performance controversies in recycled mixtures. Finally, the paper identified current research gaps in mechanism depth, technological intelligence, standard systems, and long-term performance validation, proposing future research directions to provide theoretical guidance for advancing asphalt pavement recycling technology toward high efficiency, high value, and low-carbon development.
Mesoscopic Simulation Stu dy on Fatigue Performance of Asphalt Mixture Based on Discrete Element Method
MAO Quan, ZHENG Junqiu, MA Hui, and WANG Min
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.002
Asphalt pavement is prone to fatigue cracking during long-term service, which can lead to secondary diseases and weaken the structural durability. For in-depth revelation of the fatigue damage behavior of asphalt mixtures, in this paper, a semi-circular bending (SCB) mesoscopic model was established based on the discrete element method. The fatigue fracture behavior of three typical asphalt mixtures in Jiangsu Province's expressways, including SMA-13, SUP-20, and SUP-25, was simulated under different stress ratio conditions. The fatigue damage mechanism and evolution law of asphalt mixtures were analyzed from the aspects of fatigue life, crack propagation, and residual strength. The results show that all three mixtures exhibit typical three-stage fatigue damage characteristics, and the increase of stress ratio will significantly shorten the fatigue life and accelerate the crack development. SMA-13 shows excellent fatigue resistance due to its dense skeleton and modified asphalt mortar, followed by SUP-20, while SUP-25 performs the worst due to insufficient skeleton constraint and low mortar toughness. Meanwhile, the crack propagation paths and residual strength attenuation laws of different mixtures are significantly different, further revealing the key role of skeleton structure and asphalt mortar performance in the fatigue damage mechanism.
Evaluation Index of Pavement Structural Cracks Based on Deflection Response
ZHENG Junqiu, MA Hui, QIAO Yuelai, XU Ya, ZHOU Jie, XU Huan, and ZHU Haoran
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.003
To accurately assess the impact of structural cracks on the strength of pavement structures and establish corresponding evaluation indicators based on deflection response, field tests were conducted on multiple sections of expressways in Jiangsu Province. A falling weight deflectometer was used to test a total of 15 measurement points within a 3-meter range on both sides of each crack. The center deflection values at each measurement point were plotted into curves, and three evaluation indicators for cracks, namely deflection range, maximum influence distance on one side of the crack, and influence area, were proposed based on the characteristics of the curves. Core samples were taken directly above the selected cracks within the test sections to verify the crack types and development layers. According to the distribution and cracking conditions of the cracks in the core samples, six types of structural cracks were classified. The results show that the proposed indicators can effectively distinguish fatigue cracks from structural cracks. The coefficient of determination (R2) between deflection range and influence area is 0.75, and the Pearson correlation coefficient is 0.88. Both indicators have a good correspondence with the various stages of crack development and can be used in combination to evaluate the severity of cracks, providing practical guidance for pavement maintenance and construction.
Mechanical and Durability Properties of Flowable Solidified Soil Based on Waste Slurry from Pile Foundations
LI Hongzhen, WU Shuxin, CHE N Chen, YIN Shurui, WANG Luwen, ZHU Kongyou, and FENG Zhuangzhuang
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.004
To address the challenge of pile foundation waste slurry disposal, this study proposes a resource utilization approach based on alkali activation technology, enabling rapid solidification of the waste slurry into a flowable solidified soil suitable for engineering backfill. An orthogonal experimental design was employed to determine the optimal mix ratio of the solidifying agent, identified as cement:slag:fly ash = 0.5:0.35:0.15, with NaOH accounting for 6% of the total mass. Based on this, the mechanical and durability properties of the solidified soil were systematically investigated. Results indicate that within a certain range, both unconfined compressive strength and splitting tensile strength increase linearly with higher solidifying agent content and longer curing age, and a fitting relationship between the two was established. An increase in construction delay time weakens the mechanical performance, highlighting the need for appropriate time control during construction. In terms of durability, resistance to wet-dry cycles improves with greater solidifying agent content, though a saturation effect is observed. The water stability coefficient shows different growth trends with changes in solidifying agent content and immersion age. Freeze-thaw cycles significantly degrade the strength, and increasing the solidifying agent content does not effectively improve frost resistance. The findings provide theoretical and technical support for the engineering application of premixed flowable solidified soil.
Pavement Performance Prediction Based on Integrated Particle Swarm Optimization-Gray Back Propagation Neural Network Model
LI Xuelian, HUANG Yan, and LI Xiong
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.005
The existing performance prediction model of asphalt pavements is limited by low accuracy and a lack of historical measured data. To address this issue and maximally optimize the pavement maintenance decision, a pavement performance prediction model integrating particle swarm optimization (PSO), gray model (GM), and back propagation neural network (BPNN) was proposed based on network management. Meanwhile, the model was compared with the GM (1, 1) model, support vector regression (SVR) model, BPNN model, and PSO-BPNN model. Then, the prediction accuracy of the models was evaluated by the mean absolute error (EMAE), the root mean square error (ERMSE), and the mean absolute percentage error (EMAPE). The fitting results of the PSO-gray BPNN model were assessed by the R-squared (R2). The results indicate that by optimizing the BPNN model with the PSO algorithm and the GM model, the accuracy of the PSO-gray BPNN model is significantly improved. Based on the performance data of 14 expressways in Hubei Province, a high correlation between the predicted values of the model and the measured data is found. For the IPCI index, the value of EMAE, ERMSE, and EMAPE is reduced to 1.721 8, 2.296 8, and 1.897 1, respectively. The value of R2 could be up to 0.919. Compared to the other four models, the PSO-gray BPNN model has the smallest values of prediction error for IPCI, IRQI, IRDI, and ISRI, fully showing the superiority of the model. With higher prediction accuracy, the proposed PSO-gray BPNN model has prediction results more consistent with the actual situation, providing an accurate and reliable technical support for the prediction of pavement performance at the network level.
Quantification of Activation Degree of Aged Asphalt in RAP Fines Based on Recycled Mortar
LI Ning, WANG Ao, TANG Run, LI Jing, and LI Jin
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.006
The oil-rich RAP fine material has a high proportion and significant asphalt content, offering considerable utilization value. However, in conventional production processes, it faces challenges such as difficult heating and insufficient activation of aged asphalt. To achieve deep regeneration, this study adopted the method of preparing recycled asphalt mortar to regenerate asphalt mixtures. However, there is currently a lack of quantitative evaluation methods for the activation degree of aged asphalt in this mortar regeneration process. Therefore, it is essential to establish an activation degree evaluation index to optimize the mortar preparation process parameters. The paper calibrated recycled asphalt mortar samples with different activation degrees, studied the variation of the comprehensive performance of the recycled asphalt mortar with the dissolution time, and proposed a quantitative evaluation index for the activation degree of aged asphalt in RAP fines based on the sensitivity of different performance indicators of the recycled mortar to the activation degree. The results show that extending the dissolution time of the recycled asphalt mortar can effectively improve the mechanical properties, rheological properties, and low-temperature deformation resistance of the material. The performance improvements primarily result from enhanced tensile deformation capacity and fracture energy, rather than an increase in peak stress, thus significantly improving the fracture toughness of the mortar. Under the mortar-making conditions of indoor mechanical stirring at 160 ℃, the RAP activation degree corresponding to different performance indicators increases with the extension of dissolution time and tends to stabilize after 15 min, indicating that there is a limit value for the dissolution and integration of aged asphalt under this process condition. Based on nonlinear regression analysis, considering both fitting accuracy and sensitivity, the fitting R2 of the low-temperature coefficient is 0.998, with a maximum slope of 5.03. Therefore, the low-temperature coefficient index is determined to be the optimal indicator for the activation degree.
A Review of Pavement Condition Evaluation Index Systems in China and Abroad
CHEN Leilei, YANG-LI Wenyun, LI Wei, Muhammad Thlha, and QIAN Zhendong
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.007
With the increasingly complex operating conditions of roads, it has become a consensus among countries to improve the accuracy and systematicness of maintenance decisions. Since the pavement condition evaluation index system is the core tool supporting the judgment of schemes, its construction method and applicable ability directly affect the maintenance efficiency and resource allocation level. Based on the construction logic of the index model, the scoring mechanism of grade division, and the conditions of road grade adaptation, the characteristics of the evaluation index systems in typical countries in China and abroad were compared and sorted out. The internal causes affecting the characteristics of the index system were discussed from in-depth perspectives such as management concepts and institutional arrangements. Research findings show that some systems abroad emphasize hierarchical structural response or public experience, while in China, unified deployment and hierarchical downward management are emphasized. In China's case, the system has a certain foundation in terms of universality and standardization, but there are obvious shortcomings in threshold adjustment, scene adaptation, and system integration. Therefore, suggestions are proposed including setting dynamic thresholds in combination with maintenance goals, enhancing the adaptability to various types of road operating environments, and promoting the effective integration of evaluation results with the actual management process, which provides ideological support for the structural optimization and institutional coordination of the evaluation system.
Evaluation Indicators of L ayer-Specific Structural Strength for Asphalt Pavement Based on TSD Deflection Slope Parameters
CHEN Jun, YIN Long, REN Zhongshan, MEI W enjie, ZHAI Rui, and ZHU Haoran
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.008
Traffic speed deflectometer (TSD) has been widely used in pavement maintenance, yet an indicator system for identifying layer-specific structural strength remains lacking. On the basis of a three-dimensional finite element model incorporating viscoelastic damage, this study analyzed how surface damage density and the modulus of the base and subbase affect deflection slope. Two layer-sensitive indicators of structural strength were proposed:S10 (deflection slope 10 cm ahead of the load center) for characterizing the surface layer, and S30 (deflection slope 30 cm ahead of the load center) for reflecting the structural strength of the base layer. Simulation results show that S10 is highly sensitive to surface damage, with maximum variation amplitude exceeding 600%. S30 correlates strongly with base modulus changes, exhibiting excellent recognition capability. Measured TSD data from a typical expressway were used to validate the indicators. The results indicate that S10 and S30 exhibit distinct layer response characteristics, enabling effective differentiation of different lane conditions. The research provides a new path for mechanical interpretation of raw TSD data and establishes an applicable parameter system and a theoretical basis for evaluating the layer-specific structural strength of asphalt pavement.
Influence of Reflective Cracks on the Mesoscopic Mechanical Behavior of Asphalt Pavement Structures
MA Hui, REN Zhongshan, and WANG Min
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.009
To gain an in-depth understanding of the mechanical behavior of existing asphalt pavement structures affected by reflective cracks, a macro-meso coupled model of a typical semi-rigid base asphalt pavement was established based on a continuum-discrete coupling method. By incorporating reflective cracks with varying vertical lengths, the stress transfer paths, mesoscopic particle stress states, and displacement evolution of the pavement structure were analyzed. The results indicate that the coarse aggregate skeleton and the surrounding mortar collectively bear more than 75% of the traffic load, forming a critical load transfer system, and that a significant linear correlation exists between the vertical stress and effective stress of particles along the primary stress transfer path. The vertical propagation of reflective cracks significantly disrupts the original stress diffusion path, leading to force chain concentration, increased contact forces, and a substantial rise in effective stress. When the crack extends to the pavement surface, the displacement field of particles near the crack changes significantly, with enlarged displacement magnitudes, resulting in a pronounced degradation of fatigue performance across all structural layers.
Grading Evaluation Method for Road Section-Level Structural Cracks Based on 3D Ground-Penetrating Radar
ZHOU Lei, YIN Long, WU Dongsheng, XU Huan, CHANG Wei, and ZHU Haoran
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.010
Structural cracks are widely distributed in current expressways, yet there is a lack of targeted evaluation methods. To achieve a quantitative assessment of structural cracking conditions in semi-rigid base asphalt pavement, this study first analyzed the development process of structural cracks based on coring tests. Subsequently, combined with non-destructive testing technology using 3D ground-penetrating radar and on-site coring experience, the morphological characteristics of structural cracks at various development stages were analyzed, and the cracks were classified into mild, moderate, and severe levels according to their development layers. On this basis, road section-level evaluation indicators, namely structural cracking spacing (SD) and structural cracking condition index (I), were proposed, with their calculation methods and a five-level evaluation standard (excellent, good, medium, poor, and very poor) clearly defined. Verified through engineering applications on multiple expressways, this grading evaluation method could accurately reflect the actual status of structural cracks in semi-rigid base asphalt pavement and has certain guiding value for maintenance construction.
Research on Enhancement of Toughness Performance in Polyurethane-Modified Epoxy Asphalt
LIANG Bo, LIAO Xintao, LIAO Wei, JIANG Hui, and QIN Ruiming
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.011
To solve low toughness and high brittleness of epoxy asphalt under low-temperature conditions, in this study, polyether-type polyurethane (JMPU) and polyester-type polyurethane (JZPU) were employed to prepare modified epoxy asphalt. Firstly, the Brookfield viscosity test, infrared spectroscopy test, and fluorescence microscopy were utilized to characterize the curing process. The curing time and curing temperature of JMPU and JZPU modified epoxy asphalt were 3 h/140°C and 4 h/150°C, respectively. With styrene-butadiene-styrene block copolymer (SBS), a common modifier, as the control, the performance changes of epoxy asphalt before and after modification with different toughening agents were evaluated through mechanical tensile test, rheological property test, multiple stress creep recovery (MSCR) test, and storage stability test. The research findings indicate that the polyurethane system can effectively enhance the elongation at break, low-temperature performance, and storage stability of epoxy asphalt by forming an interpenetrating network structure (IPNs) with epoxy asphalt, while maintaining excellent high-temperature performance. The elongation at break of JMPU-modified epoxy asphalt and its low-temperature creep stiffness at ‒12°C can reach 233% and 169 MPa, respectively. Results of an aging test on the toughened and modified epoxy asphalt show that the incorporation of JMPU and JZPU effectively mitigates the adverse effects of aging on epoxy asphalt performance, evidenced by lower creep stiffness aging index and rutting factor aging index, as well as higher creep rate aging index. Therefore, the addition of the PU system as a toughening agent improves the toughness of epoxy asphalt and enhances its compatibility and anti-aging performance.
Performance of High-Elastic Modified Asphalt for Paving-Type Recycled Stress Absorption Layer
LI Jing, LIU Linlin, ZHU Qiyang, LI Ning, and LI Long
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.012
To enhance the performance of recycled high-elastic modified asphalt binder and achieve high-quality and high-content utilization of RAP fine materials in the design of stress absorbing layers, a highly permeable recycled high-elastic modified asphalt (ZGT-R) was prepared by adding SBS modifier, light component oil, and penetrant to replenish the degraded SBS molecules and reduce intermolecular forces. The conventional properties, elastic recovery, degree of fusion between new and aged asphalt, rheological properties, and micro-modification mechanism of ZGT-R and ordinary recycled high-elastic modified asphalt before and after the addition of the rejuvenator were analyzed. The results show that, compared with the two types of ordinary recycled high-elastic modified asphalt, the penetration and ductility of ZGT-R increase by 51.6% and 22.4%, respectively, and the elastic recovery also improves, demonstrating excellent anti-reflection cracking performance and regeneration effect. The higher viscosity ratio also proves that ZGT-R breaks through the limitation of the degree of fusion between new and aged asphalt. In terms of rheological properties, when the aged asphalt content is between 35% and 55%, ZGT-R exhibits lower temperature sensitivity and stress sensitivity and overall shows better anti-deformation ability. Regarding the micro-modification mechanism, the SBS in ZGT-R exhibits a dense spatial cross-linked network structure, proving the full swelling and diffusion of SBS and providing a new idea for the design of high-elastic modified asphalt for recycled stress absorbing layers.
Research on Fatigue Damage and Crack Propagation of Pre-Cut Seam Asphalt Mixture Composite Beams
HUANG Dengke and LIU Hongfu
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.013
This study investigated the influence of reflective cracking on the fatigue performance of asphalt pavements subjected to milling and resurfacing under varying service conditions. The fatigue life of composite beams was evaluated via four-point bending fatigue tests, considering the effects of different stress ratios, soaking durations, air void contents, and types of tack coat. Meanwhile, the digital image correlation (DIC) technique was employed to analyze the crack propagation behavior of composite beams. To accurately characterize the failure of composite beam specimens, the dynamic modulus was employed to define damage variables, enabling the calculation of critical fatigue damage for the composite beams. A nonlinear fatigue damage model, accounting for critical damage under multi-factor influences, was subsequently proposed. In addition, a modified Logistic function model was developed to analyze crack propagation behavior and fatigue life of composite beams under diverse stress ratios, air void conditions, and tack coat configurations. The results indicate that at different stress levels, the modulus of composite beams decreases with crack propagation, and the decay rate is proportional to the crack growth rate. At the same stress level, the modulus decay curves and crack propagation curves intersect as the life ratio increases. This intersection marks the transition from a stable state to an unstable state, beyond which cracks propagate rapidly and the modulus declines sharply until specimen failure. The modulus ratios corresponding to these intersection points are consistently within the range of 0.5‒0.6. Based on these findings, it is recommended that milled and resurfaced asphalt pavements be maintained promptly before their modulus decreases by 50%. This research provides a decision-making basis for the maintenance and management of asphalt pavements.
High-Modulus Asphalt Mixtures with High RAP Content
HUANG You, FENG Boxiong, LIU Zhaohui, WANG Shuai, and XIONG Tianle
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.014
The old asphalt mixtures are characterized by high hardness and fine aggregate, which is aligned with the characteristics of high-modulus asphalt mixtures. In view of the current problem that the utilization rate of recycled asphalt pavement (RAP) is generally low, research on high-modulus asphalt mixtures with high RAP content was carried out. Three kinds of asphalt mixtures were prepared, including RAP addition with the content of 0%, 30%, 50% and 70% respectively, the addition of the high-modulus agent (2% asphalt mixture mass), and the addition of both RAP and the high-modulus agent with low content (1% asphalt mixture mass). Comparative experimental studies were conducted on the dynamic modulus, road performance, and fatigue performance. The results show that the dynamic modulus of asphalt mixtures increases with the rising RAP content, with mixtures containing 70% RAP meeting the dynamic modulus requirement for high-modulus asphalt mixtures (10 Hz, 15°C, |E*| > 14,000 MPa). This enhancement for the dynamic modulus is comparable to the addition of the 2% high-modulus agent. Asphalt mixtures with 50% RAP content also satisfy the dynamic modulus requirement for high-modulus asphalt mixtures when a small amount (1%) of the high-modulus agent is added. Additionally, the increase in RAP content improves the high-temperature performance of the asphalt mixtures, and significantly increases the shear strength. However, low-temperature performance and fatigue performance are adversely affected. The research results can promote the recycling of asphalt pavement materials and the development of green maintenance technology.
Performance and Application of Viscosity Recovering Recycled Micro Overlay Based on Fine Separated RAP Fines
SHE Zhaoyu, CHEN Xianghui, LI Ning, XIE Zhiwei, and TANG Wei
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.015
The key to asphalt recycling lies in the appropriate selection of the recycling agent. To improve the recycling value of recycled asphalt pavement (RAP) fine materials, based on fine separated RAP fines and combined with viscosity recovering rejuvenator for recycled micro overlay mixture design, the performance of recycled asphalt binder and mixture was studied, and the influence of different rejuvenator types and RAP content was analyzed. The results show that: considering the recoverable degree of aggregate gradation and recycled asphalt performance requirements, the maximum content of fine separated RAP fines in SMA-5 recycled micro overlay is determined to be 30%; compared with ordinary recycled asphalt, the softening point, 5℃ elongation and 60℃ kinematic viscosity of recycled asphalt using viscosity recovering rejuvenator are higher, and the pull-out strength is close to that of high-viscosity asphalt; with the increase in content of fine separated RAP fines, the high temperature performance of the recycled micro overlay mixture is improved, while the low temperature crack resistance, water damage resistance and raveling resistance performance are reduced. With 30% RAP content, compared with ordinary recycled mixture, the recycled mixture using the viscosity recovering rejuvenator is 45.2% higher in low temperature crack resistance, 1.7% higher in water damage resistance, and 23.2% higher in raveling resistance; according to the engineering application, the recycled micro overlay using fine separated RAP has a good effect.
Influence of RAP Content on Performance of Micro-Surfacing Mixture
ZHANG Dabin, HUANG Jianhong, YUE Aijun, and LIN Yian
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.016
To evaluate the influence of different recycled asphalt pavement (RAP) content on the mix design and performance of micro-surfacing mixtures, mixing tests and torque shear tests were conducted to assess their workability. The mechanical and road performance were evaluated using load wheel tests, rutting tests, water immersion Marshall tests, freeze-thaw splitting tensile tests, SCB tests, fatigue durability tests, and cohesion tests. The study shows that, at the optimal asphalt-to-aggregate ratio, increasing RAP content leads to a decrease in the optimal emulsified asphalt content of the recycled micro-surfacing mixture and a reduction in workability. Correspondingly, the high-temperature rutting resistance, moisture damage resistance, and fatigue durability all weaken, while the low-temperature cracking resistance first increases and then decreases. When the RAP content is 50%, the moisture damage resistance of the recycled micro-surfacing mixture does not meet specification requirements. When the RAP content is 40%, the low-temperature cracking resistance of the recycled micro-surfacing mixture is optimal. When the curing time is extended to 80 minutes, the mechanical properties of the micro-surfacing mixture with 40% RAP content meet the requirements for opening to traffic. In summary, the micro-surfacing mixture with 40% RAP content exhibits excellent comprehensive performance and is suitable for engineering application.
Optimal Design and Engineering Practice for Plant-Mixing Hot Recycled Asphalt Mixture Based on Performance Control
ZHANG Wuxing, CAI Haiquan, WANG Weiwei, ZHOU Rui, WANG Luyue, and LI Qiang
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.017
To address the difficulty of balancing high-and low-temperature performance in hot recycled asphalt mixture design and the performance imbalance revealed during long-term service, wheel tracking test, repeated creep loading test, multiple-sequence repeated load test (MSRL), bending beam test, and semi-circular bending test were conducted under different recycled material content and asphalt content conditions. A performance-controlled mix design method was established for plant-mixed hot recycled asphalt mixture (PHM) and verified through engineering trials. The results show that under recycled asphalt pavement (RAP) contents of 25% and 30%, the optimal asphalt content can be determined using flow number (Fn), composite creep strain rate (RCCSR), and fracture energy (Gf) to evaluate high- and low-temperature performance. Based on these indicators, an optimized design method for the optimal asphalt content of PHM is proposed through the balance of high-and low-temperature performance. The mixtures designed using this optimal method exhibit superior high- and low-temperature performance, with volume indicators meeting specification requirements. Engineering practice further demonstrates that the mixture quality satisfies the control requirements for the middle layer of expressways, thereby validating the rationality and feasibility of the proposed design method.
Effects of RAP Pretreatment Methods on Durability and Carbon Reduction in High-Proportion Plant-Produced Hot-Recycled Asphalt Mixtures
ZHANG Dongying, LI Ning, LIU Xincheng, LIU Mingfeng, and XIE Tangfei
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.018
To address the poor performance of plant-produced hot recycled asphalt mixtures with high recycled asphalt pavement (RAP) content, this study employed a refined separation technology to treat RAP materials. The effectiveness of this technology in enhancing the durability of high-RAP-content recycled asphalt mixtures was verified through trial pavement construction and performance testing. In addition, the carbon reduction potential as well as the economic and social benefits of the refined separation technology were analyzed. The results demonstrate that the refined-separation recycled asphalt mixture performs significantly better than conventional crushed-and-screened recycled asphalt mixtures in terms of water-temperature cycling resistance, long-term aging resistance, high-temperature and moisture damage resistance, and fatigue resistance, while exhibiting comparable durability to virgin asphalt mixtures. From an economic and social perspective, the total cost of refined-separation recycled asphalt pavement decreases by 33% and 50% compared to conventional crushed-and-screened recycled asphalt pavement and virgin asphalt pavement, respectively. Furthermore, its energy consumption and carbon emissions decrease by 25% and 32% compared to virgin asphalt pavement, and by 25% and 24% compared to conventional crushed-and-screened recycled asphalt pavement. This technology not only achieves significant energy conservation and emission reduction but also substantially enhances the durability of high-RAP-content recycled asphalt pavements.
Study on the Road Performance of Recycled Asphalt Mixture with High RAP Percentage Based on Precision Separation Technology
WANG Haixiong, TANG Wei, GAO Xinglong, FAN Xiangyang, and YAN Chunpeng
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.019
The variability of recycled asphalt pavement (RAP) is one of the key factors limiting its high-content use in recycled asphalt mixtures (RAM). Although the RAP variability and clustering phenomenon can be effectively reduced by the precision separation (PS) technology, the road performance of RAM based on this technology requires further investigation. To address this issue, RAP materials were pre-processed using PS technology, followed by a comprehensive evaluation of the road performance of the RAM through rutting tests, freeze-thaw splitting tests, and beam bending tests. In addition, the influences of PS-RAP content and rejuvenator content on the road performance were analyzed. Results indicate that as the RAP content increases from 40% to 70%, the high-temperature performance of the RAM improves by 46.5%, while water stability, low-temperature performance, and fatigue resistance decrease by 6.5%, 39. 6%, and 73.3%, respectively. The dynamic modulus initially increases and then decreases with the RAP content. As the rejuvenator content increases to 8%, water stability, low-temperature performance, and fatigue resistance improve from 9.7%, 89.4%, and 219.6%, respectively but high-temperature performance decreases by 16.4%. All road performance indicators of the RAM under different RAP content meet the specification requirements, demonstrating that the RAP content can reach up to 70% when PS technology is applied. Considering both road performance and costs, it is recommended that the rejuvenator content be controlled within the range of 4% to 6%.
Crack Propagation Behavior of Polyurethane Grouting SMA Asphalt Mixtures
JI Guoqi, MA Hui, ZHENG Junqiu, and HUANG Yujie
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.020
To reveal the influence me chanis m of polyurethane grouting on the crack propagation behavior of SMA-13 asphalt mixtures, this paper first conducted a semi-circular bending (SCB) test to validate the effectiveness of the PFC2D discrete element model, which was employed to simulate the microscopic responses of mixtures under different notch positions and grouting conditions. The analysis focused on load-displacement curves, crack propagation paths, crack number evolution, and force chain distribution characteristics. The results indicate that polyurethane grouting significantly increases the peak load and peak displacement of the specimens, thereby enhancing the fracture load-bearing capacity and deformation tolerance, with the most pronounced effect occurring when the notch is located along the specimen's symmetry axis. Crack path analysis reveals that grouting redirects the main crack away from the original notch tip toward weaker regions, thus effectively mitigating local stress concentration and improving structural integrity. Crack evolution is characterized by the three stages of “slow accumulation, rapid propagation, and gradual stabilization”, dominated by Mode I cracks. In low-offset notch conditions, grouting delays crack initiation and reduces the propagation rates. Furthermore, microscopic force chain analysis demonstrates that grouting improves the distribution of tensile and compressive chains, leading to more continuous stress transmission paths.
Workability and Improvement Evaluation of Warm-Mixed High-Content
SBS Asphalt MixturesGUO Yongjia, JIN Yong, LUO Chufan, ZHOU Yusong, ZU Yuanzhe, DENG Xinyi, and SONG Yuhang
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.021
High-content SBS-modified asphalt has been widely used in high-grade highway pavement engineering due to its excellent mechanical properties and adaptability to heavy traffic. However, its application is hindered by high energy consumption and poor workability at elevated temperatures, which limits the development of green and efficient construction practices. In this study, on the basis of warm mix technology, a self-developed organic viscosi ty-reducing warm-mixed additive was incorporated to establish a warm-mixed asphalt mixture system with high-content SBS modification. With SMA-13 as the target gradation, the mixing and compaction workability was evaluated. A self-developed apparatus for mixing workability testing was used to determine the minimum mixing energy consumption as an evaluation indicator of mixing workability. Meanwhile, a gyratory compactor was used to obtain the compaction slope for quantifying compaction workability. The test results show that the representative torque value of the warm-mixed mixture at 155℃ is close to that of the conventional mixture at 175℃, with a 15.3% reduction in minimum mixing energy consumption. In the compaction test, the warm mix system at 140℃ achieves a slightly higher compaction slope compared to the conventional system at 160℃. Overall, the results demonstrate that warm mix technology enables a 20℃ reduction in construction temperature while significantly improving both mixing and compaction workability.
Rheology and Microstructure of Warm-Mixed High-Content SBS Modified Asphalt
WAN Lei, DONG Fuqiang, CHEN Jinzhen, CHEN Jiaqiang, SONG Yuhang, and HE Haonan
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.022
With the gradual shift of high-grade highways in China from construction to maintenance, higher performance requirements have been placed on asphalt binders. High-content SBS modified asphalt has become an inevitable choice for both new pavement construction and maintenance. However, conventional high-content SBS modified asphalt suffers from high energy consumption, excessive carbon emissions, and poor construction workability. In this study, a self-developed warm-mixed additive was introduced into high-content SBS modified asphalt, and the process was optimized to obtain warm-mixed SBS modified asphalt. The effects of the additive on the asphalt performance and the warm-mix efficiency were evaluated in terms of viscosity-temperature characteristics, rheological properties, and thermal properties, while the viscosity-reduction mechanism was further revealed through microstructural analysis. The results show that when the mixing ratio of additive A to B is 2% to 1%, the warm-mixed SBS modified asphalt exhibits optimal performance. The softening point increases by 1.8℃;the ductility at 5℃ improves by 5.7 cm, and the rotational viscosity at 135℃ decreases by 0.9 Pa·s, thereby significantly enhancing construction workability. Rheological tests demonstrate that both high- and low-temperature performance meet the PG 76-22 grade requirements. Microstructural observations confirm that no new chemical substances are generated during the viscosity-reduction process; instead, the additive functions as a lubricant in the molten state to reduce viscosity through physical action and serves as a skeleton in the solid state to reinforce the binder and improve its rheological properties.
Effect of Mineral Particle Size Distribution of BRA-Modified Asphalt on Its Rheological Performance
ZHUSHEN Yuzhe, DONG Fuqiang, ZHU Xun, ZU Yuanzhe, and JIN Yong
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.023
The grinding and blending process significantly enhances the stability of the Buton rock asphalt (BRA) and asphalt blending system, but the influence mechanism of BRA's mineral particle size distribution on the rheological performance of modified asphalt is still unclear. To this end, this study prepared BRA-modified asphalt samples with different particle size distributions to systematically analyze the effect of BRA particle size distribution on the rheological performance of BRA-modified asphalt and then conduct high-and low-temperature rheological tests. Meanwhile, the fluorescence microscopy test was adopted to analyze the phase structure of BRA-modified asphalt under different particle size distributions. The results show that D50, D90, and Dspan negatively correlate with high-temperature deformation resistance, and positively correlate with the low-temperature creep stiffness and creep rate. This suggests that reducing BRA's particle size helps to improve the high-temperature stability and low-temperature crack resistance of modified asphalt. Additionally, reducing the particle size of inorganic minerals improves their dispersion state in asphalt, which makes the structure denser and thus enhances both high-temperature rutting resistance and low-temperature flexibility.
Design and Performance of Solvent-Based Regenerated Cold Feed for Fine Screening
YAN Chunpeng, ZHU Yaoting, FAN Xiangyang, LIU Bin, and YI Zhao
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.024
To overcome the limitations of evaluatio n methods for the performance of cold patching asphalt mixtures, this paper systematically studied the pavement performance and its evaluation system of solvent-based cold patching asphalt mixtures using fully finely stripped and sieved reclaimed materials. Meanwhile, a multi-stage research approach was adopted to conduct an in-depth investigation. Firstly, the material ratio of the new solvent-based cold patching liquid was optimized based on the orthogonal test design method. Subsequently, an evaluation system covering key performance indicators and the corresponding technical standards was constructed. On this basis, the developed evaluation method was applied to conduct a comprehensive performance characterization of the new recycled cold patching asphalt mixture, with the influence laws of fiber and diluent content on the performance of cold patching materials analyzed. The results show that the optimally designed recycled cold patching mixture with fully finely stripped and sieved reclaimed materials has obvious technical advantages, which are specifically reflected in the high initial and formed strength, good cohesion, excellent construction workability, and strong water stability. The proposed performance evaluation system can effectively characterize the actual service performance of materials. When the mixture indicators meet the recommended standards, the quality of pavement pothole repair can be significantly improved, and the service life of the repaired structure can be extended.
Preparation and Road Performance of Cold Patching Materials Modified by Polyurethane Prepolymer
YANG Wei, ZHAI Xueguo, GUO Weixiong, and CHI Haozhan
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.025
Traditional cold asphalt mixtures present challenges such as inapplicability in humid environments and poor durability when used for repairing potholes in asphalt pavements. To address these issues, with polyurethane prepolymer (PUA), 70# base asphalt, and additives as raw materials, a cold patch asphalt base liquid with optimal comprehensive performance was developed using the simplex design and the ideal point method. Cold patching asphalt mixtures were also prepared, with pavement performance systematically evaluated. It indicates that the PUA content has the greatest influence on the low-temperature performance and tensile strength of the cold patching asphalt liquid. The effects of components on workability and volatility follow the order: diluent > asphalt > PUA. The prepared liquid also exhibits excellent storage stability and adhesion. Furthermore, the PUA-modified cold patch materials demonstrate good strength, high-temperature stability, low-temperature crack resistance, moisture resistance, and fatigue resistance. These findings facilitate the application of polyurethane prepolymer-modified cold patch asphalt in rapid repair projects for asphalt pavement distress.
Research on Influence of Ultra-Fine Iron Tailings Sand on Mechanical Properties of Foam Concrete
CHENG Sensen, LI Hongzhen, ZHANG Da, CHEN Chen, MA Guang, ZHOU Yunbiao, SUN Chengyin, and FENG Zhuangzhuang
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.026
To reduce the production cost of foam concrete and increase the resource utilization rate of ultra-fine iron tailings sand (UITS), this study used UITS as an admixture to replace part of the cement with the same mass to prepare foam concrete. The working properties such as fluidity and water absorption rate, and the mechanical properties such as compressive strength and flexural strength of foam concrete were studied. The microscopic pore structure and hydration products were analyzed by scanning electron microscopy (SEM). The results show that when the UITS content ranges from 0% to 60%, with the increase of UITS content, the fluidity of foam concrete shows a trend of increasing first and then decreasing, while the water absorption rate gradually increases. Both compressive strength and flexural strength monotonically decrease with the increase of UITS dosage. When the UITS content is ≤50%, the 28-day compressive strength meets the road performance requirements of the roadbed (≥1. 2 MPa). Microstructure analysis indicates that the increase in the UITS content leads to significant changes in the pore structure of foam concrete, with the number of small pores gradually decreasing and the number of large pores gradually increasing. At the same time, the generation amount of cement hydration products (such as C-S-H gel) decreases, which is in good agreement with the attenuation law of macroscopic mechanical properties. The research findings provide a preliminary theoretical basis for the application of UITS foam concrete in road engineering.
Influence of Ultra-Fine Iron Tailings Sand on Performance of Cement-Stabilized Macadam Base
MENG Delong, LI Hongzhen, CHEN Fushen, WANG Keran, JIANG Yuntao, CHEN Lei, and FENG Zhuangzhuang
Date posted: 10-27-2025
DOI: https://doi.org/10.14048/j.issn.1671-2579.2025.05.027
To study the application potential of ultra-fine iron tailings sand (UITS) as a road base material, this paper conducted unconfined compressive strength (UCS) tests and freezing and thawing tests to systematically analyze the effects of UITS content and cement content on the mechanical properties and durability of cement-stabilized UITS. Additionally, the scanning electron microscope (SEM) was employed to examine the evolution process of the microstructure. The results indicate that the appropriate UITS content can effectively improve UCS, with the optimal strength under the 20% UITS content and comparable strength to that of conventional cement-stabilized macadam under the 30% content. Increasing cement content helps enhance structural strength, but excessive UITS content damages the continuity of the microstructure, resulting in strength reduction. Additionally, the cement-stabilized UITS exhibits excellent frost resistance, with a strength retention rate exceeding 90%. SEM analysis reveals that appropriate UITS content promotes the production of stable hydration products, helping inhibit microcrack propagation caused by freezing and thawing and enhancing structural stability. This study provides solid technical support for the efficient application of UITS in road bases.
