Rutting is a major form of high-temperature distress in asphalt pavements, significantly affecting service performance and driving safety. To investigate the evolution mechanism of rutting under coupled temperature and loading conditions, a laboratory rutting test incorporating embedded strain sensors was developed to continuously monitor internal strain responses. A transverse–longitudinal analysis method was proposed to characterize flow deformation, revealing that transverse unrecoverable deformation dominates the rutting process. The rutting evolution behavior was quantified using deformation rate, inflection point, and strain accumulation characteristics. Results show that the deformation rate exhibits an exponential decay trend with loading time, and rutting development can be divided into compaction and stable flow stages. Higher temperature, load, and hydrothermal coupling conditions significantly accelerate deformation, while larger aggregate sizes improve rutting resistance. Based on these findings, an evaluation framework integrating compaction resistance and flow resistance was established. The proposed method provides new insights into the internal deformation mechanism of asphalt mixtures and offers theoretical support for the design of rutting-resistant pavements.

IntroductionTo enhance the inherent shear resistance of in-service highway subgrade soils and effectively improve subgrade safety resilience under short-term traffic closure conditions, this study proposes a technical scheme of installing actively-compacted micro-expansive piles.MethodsUtilizing field-measured parameters of the subgrade soils and micro-expansive piles materials, a finite element model was established to analyze the effects of radial stresses (10 kPa, 50 kPa, 100 kPa) induced by various expansion rates on the stress distribution of the subgrade, as well as the influence of different diameter-to-spacing ratios (0.2, 0.4, 0.6) on the overall shear resistance of the subgrade.ResultsThe results indicate that when the diameter-to-spacing ratio is 0.2, the radial stress attenuates by 89.53%–95.82% at the midpoint between two piles, indicating a limited effective stress transmission distance. Increasing the diameter-to-spacing ratio to 0.6 reduces the attenuation to 24.05%–25.15%, resulting in a more uniform stress distribution. Under a diameter-to-spacing ratio of 0.6 and a radial stress of 100 kPa, the maximum principal stress at the limit equilibrium state of the subgrade soils within the pile-influenced depth (0–5 m) is enhanced by an average of 60.5%.DiscussionThis study demonstrates that appropriately configured radial stress and diameter-to-spacing ratios can significantly enhance the subgrade’s resistance to shear failure, providing a scientifically effective approach for improving the safety resilience of in-service highway subgrades.

To address prevalent asphalt pavement distresses such as rutting and water damage in hot and rainy regions, this study developed a nano-TiO2/Albanian rock asphalt (ARA) composite modified asphalt. This modification aims to enhance the high-temperature performance and water stability of asphalt pavements while reducing the consumption of petroleum asphalt. The mix design was optimized via the Response Surface Methodology (RSM), which determined the optimal modifier dosages to be 1.3% for nano-TiO2 and 16.0% for ARA. The road performance of the optimized composite mixture was evaluated and compared against single-modified and base asphalt mixtures. Results demonstrated that the nano-TiO2/ARA composite modified asphalt mixture possesses significantly superior high-temperature stability and water stability over both single-modified and base asphalt mixtures, while still complying with low-temperature performance specifications. It can be concluded that the nano-TiO2/ARA composite modified asphalt exhibits comprehensive excellent road performance and shows considerable potential in mitigating rutting and water damage in asphalt pavements in hot and rainy climates.

To enhance the erosion resistance of cement mortar in alternating wet and dry environments, this study investigates the mechanism by which fly ash influences cement mortar. Accelerated erosion tests were conducted to evaluate the effects of fly ash content (0 %-40 %) on the macroscopic properties (erosion depth, calcium ion leaching, mechanical properties, porosity) of mortar subjected to continuous immersion in 3 M NH4Cl solution and wet-dry cycling conditions. Microstructural and phase compositions were analysed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Findings indicate that wet-dry cycling significantly exacerbates erosion, with calcium ion leaching approximately 46 % higher than under continuous immersion. Fly ash addition effectively inhibits erosion progression, with 20 % dosage yielding the most pronounced pore structure optimisation-reducing porosity by 7.4 % after 72 days of erosion compared to the control group. whilst a 30 % fly ash content yielded optimal mechanical properties, reducing calcium ion leaching by 36.8 % and achieving the highest compressive strength retention post-erosion. Microstructural analysis indicates that fly ash consumes Ca(OH)2 through pozzolanic reactions, generating more stable C-S-H gel and acting as a microfiller to refine pores, thereby retarding the penetration and dissolution processes of erosive media.

This study addresses the root causes of rutting defects by examining the influence of environmental temperature, load, water-heat coupling, and the maximum nominal particle size of aggregates on the permanent deformation of asphalt mixtures. Through testing rutting specimens under varying experimental conditions, the patterns of permanent deformation were analyzed. The results indicate that temperature, water-heat coupling, load, and aggregate nominal particle size are significant factors affecting rutting depth and dynamic stability, with load exerting the greatest impact, followed by water-heat coupling. Using machine learning algorithms, a predictive model was developed to estimate rutting depth and dynamic stability, enabling accurate evaluation of the high-temperature deformation capacity of asphalt mixtures.

To address the issues of shrinkage cracking and durability in manufactured sand concrete in seasonally frozen regions, silica fume, fly ash, and superabsorbent polymer (SAP) were selected to prepare high-performance manufactured sand concrete. This study innovatively integrates SAP with fly ash and silica fume through a three-factor, four-level orthogonal experiment, systematically revealing their synergistic effects on workability, mechanical properties, and frost resistance—a gap in existing research. The results indicate that SAP improves the fluidity, workability, and slump of the concrete but reduces its mechanical properties. In contrast, silica fume and fly ash enhance the mechanical properties of the concrete. Notably, SAP’s dual role in mitigating shrinkage (via internal curing) and frost damage (by pore structure optimization) is quantitatively established, with a 0.18% dosage reducing drying shrinkage by 13.4% and extending freeze-thaw resistance to 300 cycles. The optimized mix proportion for high-performance manufactured sand concrete is: water-to-cement ratio of 0.37, sand ratio of 42%, SAP content of 0.18%, silica fume content of 0.00%, and fly ash content of 15%. This study fills a research gap by quantitatively establishing the effects of SAP, fly ash, and silica fume on concrete performance in cold climates.

Cities in developing nations have seen swift growth and urbanization, raising the requirements of urban arterials' road structure. In this study, the road performance and strain characteristics of modified and rubber asphalt recycled asphalt pavements with rigid and semi-rigid bases were investigated. The modulus decay rate and the shear strength of modified asphalts were studied by bending fatigue test and uniaxial penetration test, respectively. Strain and temperature sensors were installed at the bottom of asphalt and base layers on various pavement structures. The changes in strains under heavy vehicle loads were compared with the finite element simulation results to reflect its bearing capacity. The experimental results show that the rubber asphalt exhibited stable fatigue resistance, and the shear strength of the RCA modified asphalt mixture was higher than that of rubber asphalt and SBS modified asphalt mixtures. Rigid base asphalt pavements had smaller strains than semirigid ones, with upper layer strain reduced by 50 %. Rigid base asphalt pavements performed better in terms of rutting resistance and bearing capacity and had advantages in preventing fatigue cracks, but thicker rigid bases could lead to reflective cracking. Double modified asphalt structure showed better smoothness than rubber asphalt. The results of the finite element model indicated that the dynamic responses of rigid and semi-rigid base asphalt pavement structures were small, which was consistent with actual measurements. The results could provide a reference value for the design of urban road structures of long-life asphalt pavement.

Six models that can predict the thermal conductivity of medium- and high-temperature soil were reviewed. Except Si-Mo model, the other models contain a large number of parameters and have complex structures. A total of 381 soil thermal conductivity data measured by Chinese and Japanese researchers at 0°C–90°C using the probe method were collected from the published literature, and the measured database was constructed to evaluate the performance of the model. The results show that the prediction accuracy of the six models is all good, with root mean square error (RMSE) < 0.45 W/(mK) and Nash efficiency coefficient (NSE) > 0.65, and there are significant differences between the models: Chenhui Liu’s model performs best (NSE = 0.9380, RMSE = 0.1785 W/[mK]), and the deV-1 model performs relatively weak (NSE = 0.6580, RMSE = 0.4191 W/[mK]). The deviation analysis showed that the absolute deviation of thermal conductivity prediction (Δλ) tended to increase with the increase in temperature, and the maximum Δλ mostly occurred at the point where the moisture content was slightly lower than the permanent wilting point (θPWP). Combined with the measured data of high-temperature matric suction of red clay, it is speculated that this phenomenon is due to the decrease of soil water holding capacity due to the increase of temperature, which leads to the increase in θPWP calculated by the RETC software at high temperature, and thus underestimates the thermal conductivity contributed by the latent heat effect of water vapor (LHT). This paper realizes the unified evaluation of six soil thermal conductivity models in the middle and high temperature range for the first time, and the database fills the data gap of middle- and high-temperature thermal conductivity of soils with East Asian characteristics, which can provide the basis for model selection for related projects.

In a rainwater environment, the dynamic water pressure caused by vehicle wheel loads and the accumulation of water on the pavement together generate leaching effects, which impact the physical and mechanical properties of pervious concrete pavements. A self-developed hydrodynamic leaching coupling test device was used to simulate the dynamic water leaching of the pavement, and the physical and mechanical properties of the pervious concrete before and after leaching were tested. Optical microscopy (OM), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to analyze the microstructural changes during the leaching process and summarize the degradation mechanisms. The results show that under hydrodynamic leaching coupling conditions, the degradation of the physical properties of the pervious concrete occurs faster than under single hydrodynamic conditions, with the loss rates of mass, compressive strength, and splitting tensile strength reaching up to 9.04 %, 25.08 %, and 29.86 %, respectively. Under the same leaching conditions, the splitting tensile strength loss rate is higher than the compressive strength loss rate, indicating that splitting tensile strength is more sensitive to leaching than compressive strength. Under hydrodynamic action induced by vehicular traffic, the leached microstructure of pervious concrete pavement becomes loose, with microcracks connecting through pre-existing defects and gradually developing into major cracks. The leaching-induced damage is primarily attributed to crack propagation and leaching-induced abrasion. The research findings provide a deeper understanding of the deterioration behavior of pervious concrete under hydrodynamic leaching. These results can serve as a foundation for future studies aimed at mitigating leaching damage of pervious concrete pavement under coupled hydrodynamic conditions.

Free chloride ions significantly weaken the durability of cementitious materials, making the understanding of chloride ion binding mechanisms crucial for enhancing material performance. This paper systematically reviews the primary mechanisms of chloride ion binding (physical binding and chemical binding), influencing factors (different ions, pH, temperature, electric field and additive), and control methods (addition of mineral and nanomaterials). The findings suggest that further exploration of potential chloride ion binding mechanisms, development of advanced materials such as modified LDH and carbon dots, and the impact of multi-factor coupling on binding mechanisms are key directions for future research. This paper aims to deepen researchers' understanding of chloride ion binding behavior and provides practical references for improving the durability of cementitious materials in chloride environments.

This study separated four colloidal components of polyphosphoric acid (PPA) modified asphalts, which were made with three base asphalts from different oil sources and two grades of PPA. Frequency sweep tests were conducted on 27 of these oily components to obtain viscoelastic parameters according to the Williams-LandelFerry (WLF), Arrhenius, and standard logistic models. Infrared spectroscopy was used to gather molecular structural information of all components, and a semi-quantitative analysis method was applied to assess the molecular structural changes of each component. The results show that the rheological properties of the same components from different base asphalts vary to some extent, indicating differences in molecular structure. This leads to differential effects of the two grades of PPA on each oily component. Specifically, PPA significantly increases the complex modulus (G*) of the resins. Moreover, PPA with longer molecular chains shows a greater increase in the G* for the resins with lower aromaticity. Meanwhile, the G* of the aromatics and saturates exhibits distinct trends after PPA modification. First, this result indicates that PPA can indeed react with each asphalt oily component to some extent, causing changes in the rheological properties of the lighter components. Second, the significance of this reaction is determined by the aromaticity of the asphalt molecular structure and the polarity of the PPA molecules. The infrared spectroscopy results show that PPA significantly increases the polarizability of asphaltenes and resins. Furthermore, the functional groups of PPA mainly precipitate in the asphaltenes. This indicates that there is a substance transfer occurring within the asphalt during PPA modification. The study results point out that after PPA modification, the mechanical properties of the lighter components (serve as the dispersed phase) will change to varying degrees, which is also one of the important factors leading to the changes in asphalt performance. The oil-source-induced variability of PPA-modified asphalt is affected by the molecular weight and aromaticity of the asphalt molecules.

To recycle scrap steel slag and waste rubber in asphalt mixtures and improve road performance, this paper investigates the road performance of a coupling agent modified crumb rubber/SBS composite modified asphalt mixture with waste steel slag powder as filler, and explores the environmental impact of Cr6+ leaching from waste steel slag powder. The road performance of the asphalt mixture was assessed by radar plot method and the asphalt binder was tested for microscopic characterisation using atomic force microscopy. The results showed that compared with conventional asphalt mixtures (matrix asphalt and SBS modified asphalt), its high temperature rutting resistance was improved by 180% and 67.1%, tensile properties by 29% and 25.5%, and water damage resistance by 18.7% and 13.1% respectively. The low temperature performance meets the technical requirements for pavement use. The asphalt effectively inhibited Cr6+ leaching and the leaching concentration did not exceed the limit value.

This study systematically investigates the effects of two types of organic montmorillonite (OMMT-F and OMMT-C) on the physical and high-temperature properties of styrene-butadiene-styrene (SBS) modified asphalt to clarify the underlying modification mechanism. Through a combination of physical tests, Dynamic Shear Rheometer (DSR) analysis, Fluorescence Microscopy (FM), Fourier-Transform Infrared Spectroscopy (FTIR), and Atomic Force Microscopy (AFM), the results show that while OMMT content below 3% does not significantly impact flexibility, a 5% content of OMMT-F reduces penetration and ductility more severely than OMMT-C. Both OMMT types enhance high-temperature performance, as evidenced by an increased softening point and rutting factor, with FM revealing that OMMT promotes asphaltene agglomeration and AFM identifying a reinforcing honeycomb structure on the asphalt surface. FTIR analysis confirms that this modification is primarily a physical process. Collectively, these findings provide a comprehensive microscopic-level comparison of OMMT types, offering valuable insights for optimizing SBS modified asphalt and presenting significant research value and practical implications for pavement engineering.

This paper aims to investigate the composite application of nanomaterials and natural asphalt in order to enhance the road performance of asphalt pavement. The objective is to develop high-performance modified asphalt that improves the durability, reliability, and load resistance of asphalt roads while reducing resource waste and environmental pollution. The composite modified asphalt was prepared by adding different blends of Albanian natural rock asphalt (ARA) and 1% of nano titanium dioxide (Nano-TiO2), and the basic properties and rheological properties of the asphalt before and after aging were tested by using basic performance tests and temperature scanning tests. Subsequently, the microscopic morphological characteristics of the asphalt were observed by scanning electron microscope and atomic force microscope, and the number of bee structures, the area share of bee structures, root mean square roughness Rq, and arithmetic mean roughness Ra were used as microscopic quantitative indexes. The results indicate that the complex modulus and rutting coefficient of ARA/Nano-TiO2 composite-modified asphalt increase with an increase in ARA dosage when the dosage of Nano-TiO2 is 1%. The asphalt modified with Nano-TiO2 composite blended with 15% ARA exhibits higher residual needle penetration, composite modulus ratio, rutting coefficient ratio and lower softening point increment compared to 70# asphalt. The bitumen modified with titanium dioxide nanocomposite blended with 15% ARA exhibits higher Rq and Ra and a more stable phase structure before and after aging. 15% of ARA/Nano-TiO2 composite-modified asphalt has higher Rq and Ra before and after aging, and its phase structure is more stable. The results show that ARA/Nano-TiO2 composite-modified asphalt has better high-temperature deformation resistance and aging resistance than 70# and that 15% ARA is recommended as the optimum amount of composite-modified asphalt.

Fatigue cracking is one of the principal failure modes of asphalt pavement. The chief factors affecting the fatigue failure of asphalt pavement are load, environment, pavement structure and the fatigue resistance of asphalt mixture itself. Among them, the most important part is the research on the fatigue resistance of asphalt mixture, which has been studied deeply at home and abroad. This paper summarized some important research results and fatigue characterization parameters of the four-point bending fatigue test method in recent years, and suggested the future research direction of the four-point bending test. In the analysis and comparison of loading modes of four-point bending test, further research on various analysis methods is required. Researchers can appropriately refine the test method to account for nonlinear viscoelastic energy dissipation, as well as plastic and permanent deformation per cycle. The fatigue evaluation index of asphalt mixture can be comprehensively evaluated by four indicators, and can be combined with new fatigue characterization parameters in the future. It is suggested to develop a complete set of four-point bending fatigue test methods under various stress states consistent with the service state of asphalt pavement. This method can be used to eliminate the influences of environment, test condition and specimen size on the fatigue test results of asphalt mixture to improve the effectiveness and completeness of asphalt mixture fatigue performance characterization.

In order to investigate the influence of carbonation treatment on the rebound strength measurement curve of machine-made sand concrete, this study conducted research on the carbonation mechanism sand concrete rebound strength measurement curve through rebound and compressive strength tests using carbonation degree and concrete strength grade as control variables. The results showed that in the short aging period, carbonation treatment had little effect on the compressive strength of manufactured sand concrete but could cause an increase in the rebound value measured by the high-strength and heavy rebound hammers. As the strength grade of the manufactured sand concrete increased, the rebound value measured by both the high-strength and heavy rebound hammers increased accordingly. Compared with the high-strength rebound hammer, the heavy rebound hammer had higher accuracy in detecting the rebound of the carbonated manufactured sand concrete. This study established measurement curves for uncorrected and corrected carbonation depths, among which the accuracy of the corrected carbonation depth measurement curve was higher. At the same time, this measurement curve has been applied to the rebound test of the Pinglu Canal Extra-Large Bridge Project in Guangxi, China, and its practicality and reliability have been verified.

Asphalt pavement has been repeatedly subjected to vehicle loads during service. The probability and risk of water damage and asphalt deterioration of asphalt pavements is relatively higher in high temperature and rainy areas such as the Guangxi region of China. In this paper, the changes in rubbermodified asphalt and its mixtures under high temperature, water cycling, and ultraviolet light have been investigated. The coupled water-light-heat effects on asphalt pavements were simulated by developing a freeze-thaw cycle test protocol and a UV environment simulator. The high temperature performance of asphalt and asphalt mixtures before and after aging was compared and statistically analyzed by indoor tests of needle penetration, ductility, softening point, rutting factor and dynamic stability. Under water-light-heat coupling, rubberized asphalt showed a deeper degree of aging, accelerated conversion of asphalt to a highly elastic material, and an increased tendency to reduce flow capacity. The results showed decreasing dynamic stability of rubberized asphalt mixtures with decreasing needle penetration and ductility, increasing softening point, increasing rutting factor and decreasing phase angle. The effect of UV light on asphalt needle penetration was more significant, while the number of freeze-thaw cycles had a more pronounced effect on softening point.

Developments in the field of nondestructive testing (NDT) for road surfaces have gained substantial momentum owing to its advantages of noninvasiveness, and intelligent. This study considers the role of NDT in highway management, maintenance, and operation. Within this context, fourNDT methodologies are reviewed, including ground-penetrating radar, laser, infrared thermal imaging, andultrasonic technologies, in the context of their applications in asphalt pavement evaluation. The principles underlying the functionality of these techniques, coupled with their disease identification capabilities and relevant indices, were elucidated. Moreover, a comprehensive analysis of the factors influencing the precision of NDT is conducted. This review covers the distinct attributes and challenges of applying NDT technologies to asphalt pavements. It also extrapolates the development trajectory in this field by considering future directions and opportunities. The insights gained from this study are expected to galvanize the continues progress and widespread implementation of NDT technologies in asphalt pavement assessment.

Volatile organic compound (VOC) emissions are becoming an increasingly significant issue because of the increasing demand for bitumen in road engineering. This study attempted to develop a type of fume-suppressed bitumen with good comprehensive performance. Initially, 1, 2, and 3% organic montmorillonite and 2, 3, and 4% waxy warm-mix agents were utilised to modify bitumen. Subsequently, the fume suppression and physical and construction performances of the modified bitumen were evaluated, and the modified bitumen with the best comprehensive performance was determined. On this basis, constant- and variable-temperature heating modes were designed to verify the fuel suppression performance of the modified bitumen thoroughly. Finally, the modification mechanism of modified bitumen was investigated via atomic force microscopy. The results indicate that the modifier had the greatest impact on the ductility of the modified bitumen in terms of its physical performance. Although waxy warm mixed agents increase VOC emissions, organic montmorillonite can inhibit this effect. The modified bitumen, composed of 2% organic montmorillonite and 2% waxy warm mix agent, has the best comprehensive performance, with a 40.6% emission reduction rate under constant temperature heating mode and 46.4–28% range from 200 ℃ to 120 ℃ under another mode. The waxy warm mix agents and organic montmorillonite-modified bitumen developed into continuous and dispersed phase systems, respectively, leading to variations in the modified bitumen’s physical performance and VOC emission capacity. In contrast, the composite-modified bitumen exhibited a two-phase structure with the surface morphology of an ‘egg tray’. This unique structure enhances the heating surface area and facilitates heat conduction, improving the bitumen performance during construction.

Large aggregate asphalt mixtures can absorb noise, reduce water damage, effectively improve the service life of roads, and reduce environmental pressure. In this study, the fatigue characteristics of a large-sized asphalt mixture, LSAM-30, were investigated using four-point bending tests. The fatigue performance of LSAM-30 was compared to that of AC-13 and AC-20 asphalt mixtures across a range of temperatures, frequencies, and strains. The results indicated that the temperature, frequency, and strain significantly affect the fatigue performance of LSAM-30. As the temperature or frequency increased, the disparity in the fatigue performances of LSAM-30, AC-13, and AC-20 became more pronounced. Furthermore, the variations in the strain did not exhibit a clear pattern in the fatigue performance ratio among the three asphalt mixtures, with the ratio changes being minor (<5%). Additionally, an exponential-function-based predictive equation was proposed, showing how the fatigue characteristics of LSAM-30 vary with changes in frequency and temperature.