Semi-flexible Pavement Material Research Articles

In situ mechanical response characteristics of Autonomous Rail Rapid Transit (ART) applied to semi-flexible asphalt pavements

Autonomous Rail Rapid Transit (ART), featuring multi-axles, high tire pressure, and complete channelization, leads to severe rutting on conventional asphalt pavements. Semi-flexible pavement materials (SFP) were applied to ART corridors to mitigate rutting. Mechanical response characteristics were obtained by embedding sensors to understand the interaction between ART and SFP. Results found that the damage of corridor pavement shifted from rutting to top-down transverse cracking after adopting SFP. Nonresidual longitudinal tensile strains primarily caused top-down transverse cracking. The compressive stress at the bottom of corridor pavement caused by ART is 41%, 36%, and 58% higher than that of the BUS, respectively, under the condition of constant speed, acceleration, and deceleration. The maximum strain response caused by ART under a high-temperature environment was ten times higher than that of buses. These findings can provide data support for numerical simulations, material failures, and structural damage of ART corridors. Highlights Mechanical responses of semi-flexible pavement materials influenced by Autonomous Rail Rapid Transit (ART) were first captured using sensors. ART with high tire pressure exhibits a multi-axial cumulative effect in high-temperature conditions, resulting in pavement strains that can be up to ten times those of buses. After adopting semi-flexible pavement, the damage in ART corridors shifted from rutting to top-down transverse cracking. Nonresidual longitudinal tensile strains are the underlying cause of top-down transverse cracking.

Development and performance verification of a water-retaining semi-flexible pavement material based on alkali-activated slag system incorporating superabsorbent polymers

Water-retaining semi-flexible pavement (WRSFP) can effectively mitigate the urban heat island (UHI) effect by reducing the pavement temperature through water evaporation. To reduce environmental impacts and enhance the water retaining capacity and mechanical properties of WRSFP, this paper investigated the effect of proportion of water-retaining grout (WRG) on workability of fresh WRG, compressive strength, flexural strength, and water absorption of hardened WRG based on alkali-activated slag (AAS) system. The optimal proportion of WRG was recommended. The microstructure of the hardened WRG was observed with a scanning electron microscope (SEM), which allowed for a better characterization and understanding of the degree of hydration and mechanical properties of WRG. The WRSFP specimens (WRSFP-20%, WRSFP-25% and WRSFP-30%) with different porosities of porous asphalt mixture (PAM) were tested for moisture susceptibility, rutting resistance and low-temperature cracking resistance. WRSFP-25% had the best moisture resistance and rutting resistance, and the worst low-temperature cracking resistance. The maximum difference of upper surface temperature between WRSFP and stone mastic asphalt (SMA), which is commonly used in pavement, was 13.3 °C. The time to reach 60 °C on the upper surface of WRSFP was 3.4 times longer than that of SMA, which showed an excellent cooling effect of WRSFP.

Predicting the mechanical properties of semi-flexible pavement material with micromechanical modeling

Semi-flexible pavement (SFP) material is a composite comprising cement, coarse aggregates and asphalt mortar, which has complex mechanical properties. Traditional experimental methods struggle to accurately quantify the effect of each phase and their interfaces on the SFP's mechanical properties. Micromechanical modelling based on finite element method offers a promising solution. In this study, a new micromechanical model for SFP is proposed, idealizing the material by representative volume elements. SFP mesostructure is represented as a simplified five element composite consisting of cement, asphalt mortar, aggregate, pore and cement-asphalt mortar interface. Periodic boundary conditions are used to simulate an infinite repetitive structure within a finite computational domain. The resulting model allows evaluating the stiffness and damage resistance of SFP in a computationally efficient manner. This model is utilized to explore the mechanical properties of SFPs and the results are compared with the experimental findings. The results show that the model captures the uniaxial compressive strength and stiffness for all materials examined. The model is further used to evaluate the effect of properties of individual elements of SFP on its stiffness and strength. The feasibility of using the proposed modelling approach to optimize the material design of SFP is discussed.

The Influence of the Application Layer of Pouring Semi-Flexible Pavement Material on Low-Temperature Stress

Pouring semi-flexible pavement material (PSFM) is widely used as a wearing layer material or below pavement due to its excellent resistance to deformation at high temperatures and under heavy loads. However, in cold regions, the material exhibits severe cracking issues. The primary objective of this study is to enhance the resistance of pouring semi-flexible pavements (SFPs) to low-temperature cracking in cold regions by strategically designing pavement structures that incorporate PSFM. To achieve this goal, we conducted indoor tests to determine the relaxation modulus and temperature shrinkage coefficient of PSFM and simulated a pavement structure using COMSOL finite element simulation. The impacts of different application layers and layer thicknesses on low-temperature stresses were investigated based on these findings. The research findings indicate that when PSFM is used as the wearing layer material, the low-temperature stress is 4.7% lower than that of typical materials used in the pavement-wearing layer. When used as the binder layer material, the low-temperature stress on the wearing layer material increases by 3.5%. As the thickness of the wearing layer increases, the low-temperature stress within the pavement structure decreases, but the low-temperature stress on the pavement surface increases. Therefore, it is recommended to use PSFM as the binder layer material and appropriately increase the thickness of the wearing layer to enhance the pavement’s resistance to low-temperature cracking.

Research on the crack resistance of semi-flexible pavement mixture based on meso-heterogeneous model

Semi-Flexible Pavement (SFP) material, prepared by pouring cement-based grouting material into the voids of a porous asphalt mixture, has good load bearing capacity and excellent resistance to rutting. It is gaining increased applications in areas where permanent deformation of asphalt mixtures is a concern. When applied as the pavement surface course, the major distress observed in SFP is cracking. Currently, there is a lack of comprehensive understanding of the cracking mechanism of SFP. To improve such understanding, this study investigated the effects of fracture parameters of asphalt mortar and asphalt-aggregate interface on the crack resistance of SFP materials through laboratory experiments and numerical simulation using the finite element method. Firstly, a three-point bending test was performed on a beam SFP specimen. A multi-scale mesoscopic heterogeneity model was then established based on the mesoscopic structure of the specimen and calibrated and validated using the load-displacement curves and the cracking process features. With the validated model, the effects of different fracture parameters on the beam cracking process were investigated. It was found that the load-bearing capacity of SFP increased with the increase of the tensile strength of asphalt mortar and asphalt-aggregate interface in a certain range, while the crack propagation rate after crack initiation also increased. An increase in the fracture energy of asphalt mortar and asphalt-aggregate interface delayed the crack propagation rate, but with an attenuative effect with the increase of fracture energy. Based on the actual test conditions, the desirable range of key cracking parameters of SFP materials were recommended.

Analysis of the grouting fullness and road performance of hot-recycled semi-flexible pavement materials

In order to enhance the utilization efficiency of reclaimed asphalt pavement (RAP) and contribute to sustainable waste management, the implementation of hot recycling technique is employed to produce semi-flexible pavement materials. This research endeavor aims to scrutinize the performance characteristics of semi-flexible pavement materials manufactured through hot recycling. To attain this objective, the grout construction issue is simulated with the aid of ABAQUS software, enabling a comprehensive investigation into the impact of various load positions, surface areas, and grout heights on the horizontal and bending features of the pavement. The findings of the study indicate that the judicious incorporation of reclaimed asphalt pavement (RAP) into the hot recycled asphalt mixture as a semi-flexible pavement material exhibits an acceptable grouting rate, outstanding resistance to high temperatures, water stability, and fatigue resistance. Such exceptional properties render these materials qualified for usage in road surfaces under heavy traffic conditions, elevated summer temperatures, and other challenging utilization scenarios [1]. Moreover, it is demonstrated that higher grouting fullness contributes to superior road performance characteristics in the context of semi-flexible pavement.

Correlation analysis of the gradation design parameters and mechanical performance of semi-flexible pavement

Semi-flexible pavement (SFP) has been widely used for ant-rutting performance and resistance in heavy load conditions. The asphalt mixture skeleton was the central part in the complex-skeleton material system. However, few studies have been made on the connection of asphalt mixture skeleton composition and performance on semi-flexible pavement material. Therefore, the relationship between the skeleton gradation volumetric characteristic and mechanical properties of semi-flexible pavement material was investigated. Eight gradations with different coarse aggregate contents were constituted. The mechanical performances were conducted to establish the relationship between primary gradation performance. The result shows that the porosity of the asphalt matrix and Cantabro abrasion test are related to the composition of gradation. The tensile performance, shear characteristics, and compressive strength were affected by the voids filled asphalt (VFA), porosity, and fine aggregate to asphalt ratio (FB), respectively. The Burgers model accurately reflected the creep curves of the semi-flexible pavement material specimens. The creep modulus was related to the VFA, porosity, and effective asphalt content (Pbe). The gradation design parameters of open-gradation asphalt mixtures for semi-flexible pavement materials could be obtained based on the target performance. It is possible to reduce material testing times based on the correlation analysis effectively.

Experimental and numerical analyses on the fracture characteristics of cement-asphalt mastic-aggregate interface

The stiffness and failure properties of cement-asphalt mastic-aggregate (C-AM-A) interface are among the most important factors affecting the performance of pouring semi-flexible pavement materials (SFP). Therefore, determining the characteristics of C-AM-A interface are essential for guiding the design of SFP from the perspective of interface enhancement. In this study, the failure characteristics of C-AM-A interfaces are examined experimentally and numerically. Firstly, the effects of temperature and the proportion of cement substituting limestone filler on the bonding strength of C-AM-A interface are analyzed via pull-off tests. Then, an innovative test method based on a three-point bending test of C-AM-A beam is proposed to investigate the influence of test temperature and asphalt mastic type on the fracture characteristics of the C-AM-A interface. Finally, based on the cohesive surface techniques, numerical modeling of C-AM-A beam under three-point bending was applied to study the effect of cohesive parameters on the interfacial fracture characteristics. The results show that the interface bonding strength decreased significantly with the increase of temperature. Using cement as a filler improves the bonding strength, fracture strength, stiffness and fracture energy of C-AM-A interface as compared to the case when limestone filler is used. As the temperature increases from −10 °C to 20 °C, the failure mode of the C-AM-A interface first alters from adhesive failure to mixed failure mode, and then to cohesive failure. It suggests that enhancing the adhesion of C-AM-A interface is more advantageous for improving the fracture resistance at low temperatures, while increasing the interface cohesion is more important at relatively high temperatures. The laboratory test methods, the numerical model and methodology developed in this study are useful to study the failure behavior of C-AM-A interface and optimize the performance of SFP from the perspective of interface enhancement.

Influence of the composite interface on the mechanical properties of semi-flexible pavement materials

Semi-flexible pavement (SFP) materials, composed of porous asphalt mixture (PAM) and cement-based grouting material, are multiphase composites commonly used in roadway construction. However, damage frequently occurs at the composite interface of two-phase materials, and most SFP research has focused on the design of grouting material, with insufficient attention given to the composite interface. This paper aims to investigate the effect of bonding properties between organic PAM and inorganic grout on the mechanical properties of SFP. To investigate the different bonding properties of the SFP asphalt-grout interface, a simple method was employed, in which PAM specimens were immersed in a silane coupling agent solution to form a layer of coupling agent on the PAM surface. A series of SFP specimens were created using PAM with a porosity of 28–30%, and different strength grouting materials (40 MPa, 60 MPa, 70 MPa), and three laboratory tests were conducted to evaluate their mechanical properties. The results demonstrated that the interfacial bonding strength between asphalt and grouting material significantly influences the low-temperature splitting tensile strength, uniaxial penetration strength and uniaxial compression strength of SFP. Compared to specimens formed from high-strength grouting materials, SFP specimens immersed in a silane coupling agent solution exhibited superior low-temperature splitting tensile strength (2.06 MPa > 1.97 MPa, 2.63 MPa > 2.34 MPa) and shear strength (7.28 MPa > 6.46 MPa, 7.97 MPa > 7.26 MPa). As a result, this study highlights the importance of considering the bonding properties of the asphalt-grout interface in the design and preparation of SFP. The results of this study can be useful for enhancing the performance and durability of SFP materials in a more economically efficient way.

Molecular dynamics study on improvement effect of polyethylene terephthalate on adhesive properties of asphalt and cement-based composite interface

ABSTRACT Revealing the bonding mechanism between asphalt and cement-based materials is crucial for understanding the strength formation of semi-flexible pavement (SFP) materials and improving the performance indicators of SFP roads. Based on molecular dynamics simulation, the interface models of calcium silicate hydrogel (C-S-H) with virgin asphalt, polyethylene terephthalate (PET)-modified, and PET additive (PETA)-modified asphalt were established. At the molecular scale, the adsorption energy was used to predict the bond strength of the three interfaces, the radial distribution function was used to explore the interaction mode and stability of the interface and the static structure characteristics of the interface were analyzed in combination with the relative concentration. Finally, the interface’s dynamic behaviour was analyzed through mean square displacement and diffusion coefficient. The simulation results show that after adding PET and PETA, the adhesion energy between the asphalt and C-S-H gel increases by 0.72% and 17%, respectively. Modified asphalt has a smaller interfacial interaction zone and faster molecular diffusion than virgin asphalt. In addition, the interface system containing PETA exhibits stronger hydrogen bonding and significant homopolar aggregation behaviour. Overall, the adsorption effect of PETA-modified asphalt on cement-based materials was better than that of PET-modified asphalt and raw asphalt.

Preparation and Performance Improvement Mechanism Investigation of High-Performance Cementitious Grout Material for Semi-Flexible Pavement.

Semi-flexible pavement material (SFPM) combines the advantages and avoids the disadvantages of asphalt concrete flexible pavement and cement concrete rigid pavement. However, due to the problem of interfacial strength of composite materials, SFPM is prone to cracking diseases, which limits the further application of SFPM. Hence, it is necessary to optimize the composition design of SFPM and improve its road performance. In this study, the effects of cationic emulsified asphalt, silane coupling agent and styrene-butadiene latex on the improvement of SFPM performance were compared and analyzed. The influence of modifier dosage and preparation parameters on the road performance of SFPM was investigated by an orthogonal experimental design combined with principal component analysis (PCA). The best modifier and the corresponding preparation process were selected. On this basis, the mechanism of SFPM road performance improvement was further analyzed by scanning electron microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) spectral analysis. The results show that adding modifiers can significantly enhance the road performance of SFPM. Compared to silane coupling agents and styrene-butadiene latex, cationic emulsified asphalt changes the internal structure of cement-based grouting material and increases the interfacial modulus of SFPM by 242%, allowing cationic emulsified asphalt-SFPM (C-SFPM) to exhibit better road performance. According to the results of the principal component analysis, C-SFPM has the best overall performance compared to other SFPMs. Therefore, cationic emulsified asphalt is the most effective modifier for SFPM. The optimal amount of cationic emulsified asphalt is 5%, and the best preparation process involves vibration at a frequency of 60 Hz for 10 min and 28 days of maintenance. The study provides a method and basis for improving the road performance of SFPM and a reference for designing the material composition of SFPM mixes.

Experimental evaluation of the effect of recycled cross-linked polyethylene on the performance of grouted macadam mixtures

ABSTRACT Grouted Macadam (GM) mixtures – recognized as semi-flexible pavement (SFP) materials – offer strong stability in high temperatures, good durability and high load-bearing capacity. However, these materials are prone to environmental and traffic-induced cracking. Cross-linked polyethylene (XLPE), a common high-voltage cable insulation, faces disposal challenges due to limited recycling technology, often leading to burning or burial of these waste materials. In this study, to enhance GM mixture crack resistance and mitigate the environmental impact of XLPE waste accumulation, XLPE material was used in GM mixtures in two methods. In the first group, 15%, 30%, and 45% of 4.75 to 9.5 mm natural aggregates were replaced in volume, with XLPE pseudo-aggregates of the same size. In the second group, XLPE pseudo-fibers (1.9–2.2 cm in length, 1.5 mm thickness) were incorporated as additives in 0.5, 0.7, and 1 volume percentages. The results of mechanical tests on treated GM mixtures showed that adding recycled XLPE improved durability, with a 24.5% and 29.9% enhancement in samples with the most pseudo-aggregates and pseudo-fibers contents. The fracture strain tolerance (FST) index in low-temperature bending tests also increased by 53.8% and 108.9% in mixtures containing XLPE, highlighting its potential to enhance GM mixture performance in various service conditions.

Study of the Effect of Grouting Material Strength on Semiflexible Pavement Material

In this study, cement mortars with different strengths are poured into the large void matrix asphalt macadam material as a semiflexible pavement (SFP) material and the experimental research is carried out. The current research on SFP is mainly focused on the performance of grouting materials and the influence of grouting matrix materials on the overall mechanical properties of SFP and road performance. However, there are some flaws in the study of the influence of grouting material strength on the performance of SFP materials: the difference between the strengths of the selected grouting materials is relatively small, and in some studies, the chosen grouting material strength is low, which leads to insignificant improvements of SFP material performance; besides, the research indicators are also not very comprehensive. In this study, cement grouting asphalt macadam materials are selected as the research object to examine the effect of grouting material strength on the mechanical properties and road performance of SFP materials. Grouting materials with strengths of 19.8 MPa, 30.7 MPa, and 40.2 MPa were poured into the matrix asphalt macadam with a target void ratio of 24% and asphalt content of 2.9% to prepare the corresponding SFP test specimens. The SFP specimens were then subjected to the compressive test, flexural and tensile test, high-temperature stability test, and low-temperature crack resistance test, and the compressive resilient modulus was measured, thereby analyzing the effect of the cement slurry strength on the cement grouting asphalt macadam materials. The results show that when the strength of the cement mortar is 19.8 MPa, 30.7 MPa, and 40.2 MPa, the corresponding SFP material has better mechanical properties. When the strength of the grouting material is 40.2 MPa, the compressive strength of the SFP material is about the same as that of the grouting material. The strength is more than double that of 19.8 MPa and 30.7 MPa, and the flexural tensile strength and elastic modulus also have the above growth laws. The low-temperature crack resistance and high-temperature stability of the SFP material are enhanced with the increase in the strength of the grouting material. When the strength of the grouting material is 40.2 MPa, the mechanical properties and road performance of the SFP material are relatively better. This study provides a reference for strengthening the mechanical properties of SFP materials and boosting the crack resistance of SFP.

Damage characterization of pouring semi-flexible pavement material under triaxial compressive load based on X-ray computed tomography

Pouring semi-flexible pavement (SFP) material is a multi-phase composite material with complex damage characteristics and strength mechanism. Therefore, revealing the shear properties and damage characteristics of SFP is essential for understanding the strength formation mechanism of SFP and guiding the design of SFP. Firstly, the effect of porous asphalt mixture (PAM) air void on the shear properties of SFP was analyzed by triaxial compressive tests, and the Mohr-Coulomb theory was applied to analyze the shear strength mechanism of SFP. Then, the pore and crack distribution characteristics of SFP specimens at different loading stages were investigated via X-ray CT. Finally, three damage parameters (DV, DC, DE) were used to describe the damage degree of SFP specimens in different loading stages. The results show that increasing the air void of PAM can effectively improve the triaxial compressive strength and compressive modulus of SFP. The Mohr-Coulomb failure criterion can accurately describe the failure behavior of SFP at 60 °C. Increasing the air void of PAM can increase the proportion of interlocking force provided by aggregate-cement contact, which in turn increases the internal friction angle of SFP. When the air void of PAM is 25 %, SFP has the largest proportion of cement-asphalt-aggregate (C-AS-A) interface area, leading to the largest cohesion force of SFP. Moreover, during triaxial compression, C-AS-A interface crack accounts for 63.47 %, which is the main failure mode of SFP. The plane porosity, volume and surface area of 3D pores and cracks of SFP specimens increase with the increase of vertical deformation. The DE can more accurately characterize the damage status of SFP.

Material innovation preparation and performance study of semi-flexible pavement materials

Expounding the internal stability and rutting resistance of semi-flexible materials under different porosity can predict the relationship between pavement performance and material porosity. This study designed four porosities of 18%, 20%, 22%, and 25% to prepare the base asphalt mixture. Then the cement mortar was poured into the base asphalt mixture and cured for seven days under ambient temperature and humidity conditions to prepare semi-flexible pavement material. The stress-strain level of semi-flexible pavement(SFP) was analyzed by finite element software under the 20% porosity; the rutting test was used to evaluate the anti-rutting performance of SFP under different porosity. The orthogonal experiment indicated that the optimal ratio of cement mortar was 0.6 water-cement ratio, 15% mineral powder, and 35% sand. The finite element results further showed that the internal shear stress mainly causes the internal displacement and strain of the material. The shrinkage of the cement mortar was 0.168%, and the dynamic stability of SFP with porosity of 18%, 20%, 22%, and 25% were 6058, 7325, 11,053, and 12,353, respectively. The porosity and filling of cement mortar have a positive trend with the anti-rutting performance of semi-flexible pavement materials.

Optimal Design of Pouring Semi-Flexible Pavement via Laboratory Test, Numerical Research, and Field Validation

Pouring semi-flexible pavement (SFP) material is a multi-phase composite with excellent pavement performance, which consists of porous asphalt mixture (PAM) and grouting material. This research is to investigate the optimal design of SFP for the upper pavement layer in relation to air void and thickness. Firstly, the effect of PAM with different air voids on the mechanical performance of SFP is investigated by uniaxial compression tests. Secondly, the influence of the air void of PAM on the rutting resistance and water sensitivity of SFP is analyzed by wheel tracking test and Hamburg wheel tracking (HWT) test. Then, the optimal thickness of SFP is investigated by 3D finite element analysis. Finally, based on the experimental and numerical results, SFP is applied to practical engineering and the field performance was inspected. The results show that increasing the air void of PAM can significantly improve the mechanical properties and rutting resistance of SFP. However, when the air void of PAM is 25%, SFP has the highest strain energy density. According to the experimental and numerical results, as well as the construction cost of SFP, the optimal thickness range of 4–8 cm is recommended for the SFP layer. Moreover, the field performance inspection results show that after nearly 2 years of service, pavement using SFP with PAM air void of 25% and thickness of 4 cm for the upper layer has excellent rutting resistance, impermeability, and high wear resistance, which allows for undergoing heavy traffic loads.

Mechanical properties of pouring semi-flexible pavement material and engineering estimation on contribution of each phase

As a multi-phase composite material consisting of porous asphalt mixture (PAM) and grouting material, pouring semi-flexible pavement (SFP) material has very complex mechanical properties. This research is to investigate the effect of different factors on bonding strength of cement-asphalt interface, the compressive strength, compressive modulus, and compressive strain energy density of SFP and the rough engineering estimate of the contribution rate of PMA and grouting material to the above properties. Firstly, the effects of asphalt type, water-cement ratio (W/C) and curing time on the bonding strength of cement-asphalt interface is studied by pull-out tests. Then, the effects of asphalt type, different void ratio of PAM and W/C of grouting materials on the mechanical properties of SFP are investigated by uniaxial compression tests. Finally, compressive strength, compressive modulus and strain energy density are used as to estimate the contribution rate of PAM and grouting materials to SPF. The results show that: reducing the W/C of grouting material and using asphalt with higher elasticity can significantly improve the bonding strength of asphalt-cement interface and the mechanical properties of SFP; when the void ratio of PAM is 25%, the SFP has the highest strain energy density; when the curing time is 28d, the contribution rate of grouting material to SFP in term of compressive strength, compressive modulus and strain energy density is much larger than that of PAM. To make full use of the dominant role of grouting materials in the compressive strength, resistance to deformation and fracture, asphalt with higher elasticity, grouting materials with lower W/C, and PAM with void ratio of 25% should be selected for the preparation of SFP.

Performance and Fracture Analysis of Composite Interfaces for Semi-Flexible Pavement

Semi-flexible pavement is widely used in pavement engineering due to its excellent rutting resistance; however, it mainly fails due to cracking. Therefore, it is important to understand the properties of the aggregate–mortar–asphalt interfacial transition zone, to better understand the cracking mechanism of the semi-flexible pavement. In this work, we used pull-off tests and digital image analysis technology to compare and analyze the interfacial tensile strength and granite–bitumen–mortar interactions in three types of asphalt (70# matrix asphalt, PG76-22 modified asphalt and S-HV modified asphalt) at different curing ages. The analysis results showed that, for the three different bitumen materials, with settled mortar, the peak interfacial tensile strength values all occurred at approximately 14 d of curing. In addition, the order of the tensile strength followed the order of asphalt penetration degree; the order of the interfacial water damage resistance from weak to strong was 70# asphalt cementation specimen, PG76-22 modified asphalt cementation specimen, and S-HV modified asphalt cementation specimen. The results of this analysis highlight the original contributions of the optimum curing time for the composite interface of semi-flexible pavement materials prepared with different asphalts to reach optimum crack resistance.

Study on the Road Performance of Foamed Warm-Mixed Reclaimed Semi-Flexible Asphalt Pavement Material.

Warm-mixed reclaimed asphalt pavement (RAP) technology has been widely studied worldwide as a recycled environmental method to reuse waste materials. However, the aggregate skeleton structure of the warm-mixed reclaimed asphalt mixture is not stable because of the existence of the recycled materials. Warm-mixed recycled semi-flexible pavement material can solve the defects of the above materials. In this study, five different types of open-graded asphalt mixtures containing different contents of RAP were designed, and relevant laboratory tests were conducted to assess the road performance of the warm-mixed recycled semi-flexible pavement material. The test results indicated that the road performance of warm-mixed reclaimed semi-flexible pavement materials has good resistance to rut deformation ability. Furthermore, the materials also had good water stability and fatigue performance. The grey correlation analysis shows that the asphalt binder content has the most significant correlation with the high-temperature stability, and the correlation between RAP content and the fatigue performance was the greatest. Furthermore, the curing age has the most remarkable with the low-temperature crack resistance of the warm-mixed reclaimed semi-flexible material.

Study on the Adhesion Performance of Asphalt-Calcium Silicate Hydrate Gel Interface in Semi-Flexible Pavement Materials Based on Molecular Dynamics.

The interface between an asphalt binder and a calcium silicate hydrate (C-S-H) gel is a weak point of semi-flexible pavement material. In this study, the adhesion performance of asphalt-C-S-H gel interface in semi-flexible pavements at a molecular scale has been investigated. Molecular dynamics (MD) simulations were applied to establish three asphalt binders: 70# asphalt binder (the penetration is 70 mm), PG76-22 modified asphalt binder (a kind of asphalt binder that can adapt to the highest temperature of 76 °C and the lowest temperature of −22 °C), and S-HV asphalt binder (super high viscosity). The effects of different temperatures and SBS modifier contents on interfacial adhesion were explored. The obtained results showed that temperature variations had little effect on the adhesion work of the asphalt-C-S-H gel interface. It was also found that by increasing the content of SBS modifier, the adhesion work of the asphalt-C-S-H gel interface was increased. The molecular weight of each component was found to be an important factor affecting its molecular diffusion rate. The addition of SBS modifier could regulate the adsorption of aromatics by C-S-H gel in the four components of asphalt binder and improve the adsorption of resins by C-S-H gel.