Low-temperature Cracking Resistance Research Articles

Basic characterization of three kinds of bio-asphalt and research on the low-temperature performance of bio-asphalt mixtures

Bio-oil is a by-product of waste biomass treatment using high-pressure liquefaction, bio-enzymatic, or high-temperature thermal cracking techniques, and can alleviate the shortage of petroleum asphalt resources. This study investigated the production of bio-oil from selected raw materials, including corn stover, castor oil from castor beans, and epoxy vegetable oil from soybeans for the preparation of bio-asphalt. The properties and mechanisms of modification of the three modified bio-asphalts were explored by assessment of basic physical properties, gel permeation chromatography (GPC), temperature scanning (DSR), and thermogravimetric analysis, as well as Semi-Circular Bending (SCB), low-temperature bending, and fatigue tests. Bio-oil was found to improve the low-temperature cracking resistance of the asphalt mixtures, with the improvement further enhanced by changing the blending amount. The bio-oil was observed to negatively affect the low-temperature fatigue performance of the mixes, and the decrease in the n-value indicated that the bio-oil could make the asphalt mixtures less stress-sensitive under repeated loading, with improved anti-fatigue performance of bio-asphalt mixtures observed when the stress ratio was 0.5. Finally, the low-temperature cracking performance index of the corn stover bio-asphalt mixtures was correlated with the gray entropy. The use of the SCB fracture index was found to be more appropriate when using the semicircular bending test to characterize the low-temperature cracking performance of bio-asphalt mixtures.

A multi-gradient analysis of microscopic void characteristics' influence on the mechanical properties of open-graded friction course bituminous pavement

The mechanical properties of the open-graded friction course (OGFC) bituminous pavement are tied to its microscopic void structure, but multiple void parameters influence void formation and distribution. Solely using air voids as an indicator of pavement stability is challenging. Thus, a multi-gradient analysis of void structure factors is vital for advancing OGFC pavement's mechanical property research. This study used computerized tomography (CT) and digital image processing (DIP) to gather data on void structure distribution, size, and complexity in OGFC bituminous mixtures. Mechanical experiments assessed high-temperature deformation, low-temperature cracking, and water damage resistance. Analysis of void parameters' influence led to a predictive model for mechanical property in OGFC mixtures. The study found that as air voids increase within the 18 %–24 % range, both equivalent void diameter and void fractal dimension increase, while void count decreases. Conversely, coarser gradation and a larger nominal maximum aggregate size (NMAS) lead to increased equivalent void diameter but decreased void fractal dimension, reducing void complexity. The mechanical properties of OGFC mixtures decline with rising air voids but improve with coarser gradation and larger NMAS. The predictive model highlights the void fractal dimension and NMAS as critical indicators, with other factors showing weaker influence or multicollinearity issues that are unfit for model fitting. The findings could provide useful references for the structural design, property evaluation, and quality control of OGFC bituminous pavements in actual road construction.

Performance evaluation of SBS-modified asphalt mixtures incorporating waste tire rubber and HDPE

Based on the functional complementarity of waste tire rubber (WTR) and waste high-density polyethylene (HDPE) in asphalt, this study presents a novel approach that simultaneously utilizes WTR and HDPE for modification and substitution of styrene-butadiene-styrene (SBS) modified asphalt. Through experiments on three major indicators, the dosage ratios of the three polymers are scientifically designed using the response surface methodology, and four different ratios of SBS-HDPE-WTR are selected to prepare modified asphalt mixtures. Performance evaluations are conducted on various pavement properties, including high-temperature stability, low-temperature crack resistance, water stability, fatigue resistance, and aging resistance, by comparing them to the reference 4% SBS-modified asphalt mixture. The results demonstrate that the addition of WTR significantly improves the elastic properties and fatigue resistance of the mixture, while the addition of HDPE enhances its high-temperature stability and aging resistance. The SBS-HDPE-WTR asphalt mixtures, designed with appropriate ratios, exhibit superior high-temperature stability, low-temperature crack resistance, and fatigue resistance. Therefore, the use of these waste materials in asphalt mixtures offers a sustainable and environmentally friendly solution for the construction industry.

Secondary degradation of bio-oil degraded crumb rubber and preparation of stable degraded crumb rubber modified asphalt

Using bio-oil to desulfurize and degrade crumb rubber (CR) significantly enhances the compatibility between CR and asphalt, improving the workability of CR-modified asphalt and providing environmental and economic benefits. However, the secondary degradation of bio-oil degraded crumb rubber (ODR) in asphalt hinders the stability of ODR-modified asphalt. To optimize the mechanical performance of ODR-modified asphalt, the secondary degradation behaviors of ODR were investigated. The degree of CR degradation was determined by solubility testing, while the rheological properties and chemical structures of ODR-modified asphalt were characterized through rotational viscometer, dynamic shear rheometer, bending beam rheometer, and Fourier transform infrared spectrometer. The processes for preparing stable ODR modifier and ODR-modified asphalt were proposed to mitigate the damage caused by bio-oil and degraded CR to the high temperature mechanical properties of asphalt. The results show that at lower processing temperatures for ODR-modified asphalt, the volatilization of light components is predominant, while higher processing temperatures prompt secondary degradation of ODR. By stirring at 280°C for 2 hours to acquire moderately degraded CR, and then concentrating it at 220°C for 2 hours, a stable ODR less susceptible to secondary degradation can be obtained. The workability, temperature sensitivity, and low temperature cracking resistance of stable ODR-modified asphalt improve significantly. The reduction of ester group and increase in aromaticity restore the high temperature deformation resistance of ODR-modified asphalt. Further, the inclusion of composite SBS extends the range of rheological properties in ODR-modified asphalt, bolstering the application potential of ODR in asphalt pavement.

Rheological Properties of Silica-Fume-Modified Bioasphalt and Road Performance of Mixtures.

The objective of this research is to enhance the high-temperature antirutting and antiaging characteristics of bioasphalt. In this study, silica fume (SF) was selected to modify bioasphalt. The dosage of bio-oil in bioasphalt was 5%, and the dosage of SF was 2%, 4%, 6%, 8%, and 10% of bioasphalt. The high- and low-temperature characteristics, aging resistance, and temperature sensitivity of Bio + SF were evaluated by temperature sweep (TS), the multiple stress creep recovery (MSCR) test, the bending beam rheology (BBR) test, and the viscosity test. Meanwhile, the road behavior of the Bio + SF mixture was evaluated using the rutting test, low-temperature bending beam test, freeze-thaw splitting test, and fatigue test. The experimental results showed that the dosage of SF could enhance the high-temperature rutting resistance, aging resistance, and temperature stability of bioasphalt. The higher the dosage of SF, the more significant the enhancement effect. However, incorporating SF weakened bioasphalt's low-temperature cracking resistance properties. When the SF dosage was less than 8%, the low-temperature cracking resistance of Bio + SF was still superior to that of matrix asphalt. Compared with matrix asphalt mixtures, the dynamic stability, destructive strain, freeze-thaw splitting strength ratio, and fatigue life of 5%Bio + 8%SF mixtures increased by 38.4%, 49.1%, 5.9%, and 68.9%, respectively. This study demonstrates that the development of SF-modified bioasphalt could meet the technical requirements of highway engineering. Using SF and bio-oil could decrease the consumption of natural resources and positively reduce environmental pollution.

Research on the Mechanical, Thermal and Induction Healing Properties of Asphalt Wearing Course with Steel Fibers.

Induction healing technology can effectively repair microcracks in asphalt mixtures and is a promising maintenance technology for asphalt pavements. However, it requires the addition of steel wool fibers to asphalt mixtures and cannot be directly used to repair existing pavements. In order to improve the practicality of the induction healing technology, this article designs a wearing course asphalt mixture with induction healing function that is going to be paved above the existing road surface. The AC-10 asphalt wearing course for induction heating was prepared by adding steel fiber (SF). Analysis of the overall temperature of the surface revealed the unevenness of the temperature distribution, and the healing properties were investigated through protective heating that controlled the maximum temperature of the upper surface. The results show that the addition of SF can improve the high-temperature stability, low-temperature and intermediate-temperature crack resistance, and moisture stability of asphalt wearing courses; however, it has adverse effects on volumetric performance and skid resistance. The heating temperature increases with the increase in SF content, but higher maximum temperature heating rate causes worse heating uniformity and lower healing effect. The maximum heating rate of the sample with 10% SF reaches 3.92 °C/s, while its heating rate at minimum temperature is similar to that of the sample with 6% SF, which is only 0.7 °C/s, indicating the worst heating uniformity. The best healing effect occurs when the maximum temperature of the upper surface reaches 160 °C. The recommended optimal SF content is 6% of the asphalt volume. The asphalt mixture with 6% SF has an appropriate volume performance, moisture stability, and skid resistance; additionally, it has the best high-temperature stability, as well as low-temperature and intermediate-temperature crack resistance. Meanwhile, it also has uniform temperature distribution and efficient healing efficiency.

Low-temperature crack resistance of stone matrix asphalt mixtures under chloride salt dry-wet cycles

Given the current insufficient understanding of the low-temperature crack resistance performance and crack evolution patterns of asphalt mixtures under chlorinated salt wet-dry coupling environments, this study aims to fill this knowledge gap. We employed SMA-13 asphalt mixtures modified with different dosages of polyester fibers (0 %, 0.3 %, 0.35 %, 0.4 %, 0.45 %, 0.5 %) and tested their low-temperature crack resistance by conducting 0 to 8 wet-dry cycles in pure water and a 13.25 % chlorinated salt solution, to explore the improvement effect of polyester fibers on the performance of asphalt mixtures in such environments. The results indicate that an increase in the number of wet-dry cycles leads to a degradation of crack resistance performance across all fiber dosages, especially under the influence of chlorinated salt wet-dry coupling, where the adverse effects are more pronounced. Fracture energy analysis further confirms that 4 and 6 cycles of wet-dry cycling are effective indicators for evaluating the attenuation of low-temperature crack resistance under the long-term impact of wet-dry cycling. Through Digital Image Correlation (DIC) and Scanning Electron Microscopy (SEM) analyses, this study reveals the significant impact of wet-dry cycling on crack evolution and identifies 0.4 % as the optimal dosage of polyester fibers, significantly enhancing the low-temperature crack resistance performance of asphalt mixtures.

Evaluation of the effect of different preparation processes on the road performance of thermoplastic resin modified porous asphalt mixtures

In order to evaluate the effects of three preparation processes, namely dry process (DP), wet process (WP) and wet/dry mixing process (MP), and resin high viscosity modifier (RHVM) on the road performance of porous asphalt mixtures, the frequency scanning, multi-stress creep recovery, and bending beam rheometer tests were used to analyze the rheological performance of resin-modified high viscosity asphalt under different processes. Uniaxial compression, Wheel tracking, Semi-circular bending and Freeze-thaw indirect tensile tests were used to test the properties of resin-modified porous asphalt mixtures under different processes. The commonly used TAFPACK-Super (TPS) modifier was a control group. Finally, the changes in the microscopic morphology characteristics and chemical composition were used to illustrate the enhancement mechanism of resin modifiers. The results showed that the high-temperature deformation resistance and low-temperature cracking resistance of RHVM modified asphalt prepared by DP and MP are weaker than that of the WP. Compared to the RHVM(WP), the Jnr(3.2) of RHVM(DP) and RHVM(WP) decreased by 14.3% and 63.8%, the strength modulus of RHVM(DP) and RHVM(MP) increased by 21.5%, 28.0% and the creep rate decreased by 2.37%, 4.45%, respectively. As for the performance of asphalt mixture, compared to the RHVM(WP) asphalt mixture, the dynamic stability of RHVM asphalt mixture prepared by the DP and MP decreased by 17.3–18.2%, σs and εs of RHVM(DP) and RHVM(MP) increased by 15–35% and 21–29%, respectively. The water stability of RHVM(DP) asphalt mixtures was better than that of RHVM(WP) when the mixing time reached 180 s. RHVM(WP) asphalt mixtures have superior low-temperature cracking resistance, comparable water stability, and slightly poorer high-temperature stability than that of TPS(WP) asphalt mixture. Microscopic morphology observation found that some modifier particles and asphalt binder did not realize effective mixing under the DP and MP, and infrared spectroscopy results confirmed that TPS modifiers are mainly physically co-mingled with asphalt, while the tackifier resin in the RHVM reacts with the asphalt to form new functional groups to increase the viscosity of the asphalt.

Evaluation of Cracking Resistance of SMA-13 Hot Recycling Asphalt Mixtures Reinforced by Basalt Fiber.

In the context of green and low-carbon development, energy saving, and emission reduction, hot recycling technology (RT) has been researched, which is divided into hot central plant RT and hot in-place RT. However, due to the aged asphalt binders, the shortcomings of hot recycled asphalt mixtures have become apparent, as in comparison to new asphalt mixtures, their resistance to cracking was inferior and the cracking resistance deteriorated more rapidly. Therefore, it was very necessary to focus on the improvement of crack resistance of hot recycled asphalt mixtures. Basalt fiber has been proved to be able to effectively improve the comprehensive road performance of new asphalt mixtures. Therefore, this paper introduced basalt fiber to hot central plant recycled and hot in-place recycled asphalt mixtures, in order to improve the crack resistance of asphalt as a new type of fiber stabilizer. Firstly, six types of SMA-13 fiber asphalt mixtures were designed and prepared, i.e., hot mixtures with basalt fiber or lignin fiber, hot central plant recycled mixtures with basalt fiber or lignin fiber, and hot in-place recycled mixtures with basalt fiber or lignin fiber. Secondly, the trabecular bending test, low-temperature creep test, semi-circular bending test, and IDEAL-CT were used to comparatively study the changing patterns of low and intermediate temperature cracking resistance of hot recycled mixtures with conventional lignin fibers or basalt fibers. Finally, Pearson's correlation coefficient was used to analyze the correlation of the different cracking resistance indicators. The results show that the low and intermediate temperature cracking resistance of hot central plant recycled mixtures increased by 45.6% (dissipative energy ratio, Wd/Ws) and 74.8% (flexibility index, FI), respectively. And the corresponding cracking resistance of hot in-place recycled mixture increased by 105.4% (Wd/Ws) and 55.7% (FI). The trabecular bending test was more suitable for testing the low-temperature cracking resistance of hot recycled asphalt mixtures, while the IDEAL-CT was more suitable for testing the intermediate-temperature cracking resistance. The results can provide useful references for the utilization of basalt fiber in the hot recycling of SMA-13 asphalt mixtures.

Application of waste rice straw as fibre or filler in asphalt mixtures: materials characterisation and performance evaluation

ABSTRACT This study investigated the application of agricultural waste rice straw as fibre or filler in asphalt mixtures. Initially, the physical, chemical, mineralogical and morphological characterisation of rice straw products were analysed. Subsequently, the performance of stone matrix asphalt (SMA) mixtures containing rice straw fibre was evaluated in terms of rutting, crack resistance and moisture susceptibility, compared to cellulose fibre. Additionally, the properties of asphalt concrete (AC) mixtures incorporating rice straw filler to replace conventional mineral filler partially were examined. The findings revealed that rice straw products exhibited similar characteristics to cellulose fibre or mineral filler, indicating their suitability for use in asphalt mixtures. The appropriate addition of rice straw fibre or filler demonstrated enhancement in the high-temperature performance, low-temperature crack resistance and moisture stability of asphalt mixtures. Through experimental tests, the optimum content of rice straw fibre in SMA-13 mixtures was determined to be 0.4%, while for the rice straw filler in AC-13 mixtures, it was 20%. The mechanisms of rice straw fibre and filler added in asphalt mixtures to strengthen their road performance were binder adsorption and reinforcement effect through scanning electron microscope (SEM) images. Furthermore, rice straw filler also contributed to void filling within asphalt mixtures.

Green environmental protection and sustainable utilization of straw: Investigation for molecular dynamics of highland barley straw fiber to enhancing road performance of asphalt

This study explores the impact of highland barley straw (HBS) fiber, an environmentally friendly material, on the molecular dynamics and performance of asphalt. Despite the widespread use of fibers in enhancing asphalt performance, molecular-scale investigations are lacking. In this study, molecular dynamics software was employed to model matrix asphalt and three types of HBS fiber-modified asphalt with varying cellulose contents (8.62 wt%, 15.88 wt%, 22.06 wt%). Thermodynamic parameters mean squared displacements (MSD), radial distribution function (RDF), free volume fraction (FFV), and mechanical parameters were analyzed through simulation to understand the diffusion behavior of HBS cellulose molecules in asphalt and study the modification mechanism. The findings revealed that the 8.62 wt% cellulose-modified asphalt had the slowest diffusion rate, with the most favorable temperature for asphalt diffusion being 298.15 K. Integration of HBS cellulose molecules facilitated the self-aggregation process of asphaltene-asphaltene and improved the compatibility between asphaltene-resin, resulting in asphalt stabilization. However, the study found that moisture damage weakened the water resistance of HBS cellulose-modified asphalt binder. Specifically, modifying asphalt with 8.62 wt% cellulose increased the Young modulus by 28.37%, bulk modulus by 39.77%, and shear modulus by 26.45%, demonstrating the overall improvement achieved with the combined effect of 8.62 wt% HBS cellulose-modified asphalt. These findings have significant implications for repurposing HBS as a solid waste material and enhancing the low-temperature crack resistance of asphalt binders.

Utilization of steel slag as coarse aggregate and filler in stone mastic asphalt (SMA) mixture: Engineering performance, environmental impact and economic benefits analysis

The unquantified environmental impact and economic benefits of steel slag based asphalt mixture, as well as the difficulty in directly utilizing steel slag fine aggregate (SSFA) due to solidification, limit the utilization of steel slag in asphalt mixture. This research proposed an innovative method of using steel slag coarse aggregate (SSCA) and steel slag powder (SSP) filler prepared by grinding solidified SSFA to replace ordinary natural resources to prepare stone mastic asphalt (SMA) mixture. The feasibility of the proposed utilization method of steel slag was determined based on the analysis results of main engineering performance, environmental impact and economic benefits of steel slag SMA mixture (SSSM). The ordinary SMA mixture (OSM) was functioned as a control group. The investigated main engineering performance included fatigue performance, moisture stability, high-temperature deformation resistance and low-temperature crack resistance. Environmental impact was evaluated based on the life cycle assessment (LCA) method, and the relationship between the transportation distance of steel slag, common basalt and the emission characteristics was deeply analyzed. In addition, economic benefits were determined based on the cost calculation results. Results showed that SSSM was superior to OSM in terms of these main engineering performance. The emissions from SMA mixtures increased with the extension of transportation distance of steel slag or basalt. From the perspective of reducing emissions, choosing steel slag aggregate had advantages when the transportation distance was less than 365 km, otherwise, it was recommended to choose basalt. Under three different transportation distances (short, medium and long distance transportation), the introduction of steel slag in SMA mixture reduced the greenhouse gas emissions by 1.1%–8.6%, of which the raw material production stage contributed the most. Furthermore, SSSM exhibited higher economic benefits, with a functional unit of SSSM pavement saving the cost by 14.4%–19.8%. Therefore, using steel slag as a substitute for coarse aggregate and filler in SMA mixture can promote the reuse of solidified SSFA, reduce the environmental impact and total cost of all stages of constructing SMA pavement.

Rheological Performance Analysis of Different Preventive Maintenance Materials in Porous High-Viscosity Asphalt Pavements.

Porous asphalt pavements are widely used in rainy and wet areas for their skid resistance, noise reduction, runoff minimization and environmental sustainability. Long-term moisture vapor erosion and the destabilization of large pore structures can easily result in pavement problems such as fragmentation, spalling, cracking, and excessive permanent deformation. To this end, four different preventive maintenance materials, including the rejuvenation (RJ), cohesion reinforcement (CEM), polymerization reaction, and emulsified asphalt (EA) types, were selected in this paper to improve the high-viscosity porous asphalt pavement. The effects of the different preventive maintenance materials on the temperature sensitivity, rheological properties and fatigue performance of high-viscosity modified asphalt were evaluated through temperature sweep, frequency sweep, multi-stress creep recovery (MSCR), linear amplitude sweep (LAS), and bending beam rheometer (BBR) tests. The results showed that the four preventive maintenance materials exhibit different enhancement mechanisms and effects. RJ improves the fatigue properties, deformation resistance and low-temperature cracking resistance of aged asphalt by adding elastomeric components; CEM materials are more conducive to increasing the low-temperature crack resistance of aged asphalt; while GL1 and EA improve the viscoelastic behavior of aged asphalt, but the effect of the dosing ratio needs to be considered.

Research on material selection and low-temperature anti-cracking mechanism of hydraulic asphalt concrete panels in the alpine region

To solve the problem of asphalt concrete panel cracking at low temperatures, this study proposes to use crumb rubber as a modified material for asphalt in the impermeable layer of asphalt concrete panels and to investigate the anti-cracking performance of crumb rubber modified asphalt concrete (CRMAC) in water conservancy projects in different low-temperature environments. Taking matrix asphalt concrete (MAC), CRMAC, and SBS modified asphalt concrete (SBSMAC) as the research objects, the cracking resistance performance of the three kinds of asphalt concrete under different low-temperature conditions were comparatively analyzed by using ultra-low-temperature (−35°C) small beam bending test, which reveals the damage mechanism of asphalt concrete's low-temperature cracking and damage process; the failure temperatures of the three kinds of asphalt concrete were accurately quantified by the thermal stress restrained specimen test (TSRST), and combined with the Pearson correlation coefficient method to determine the evaluation criteria of asphalt concrete low-temperature performance. The results show that the low-temperature crack resistance of CRMAC is better than the other two asphalt concretes under the same temperature conditions. Its failure temperature reaches −43°C, which meets the low-temperature demand for asphalt concrete panels in alpine regions. This study aims to improve the low-temperature cracking resistance of asphalt concrete impermeable panels, provide new ideas for the selection of asphalt concrete panels, and lay the foundation for the application of CRMA in water conservancy projects, and open up new ways to solve the problem of waste tire accumulation.

Evaluation of the laboratory aging of field-blended crumb rubber modified binder

Field-blending approach is widely employed by the industry to introduce crumb rubber into asphalt binder. Rubber-modified binder provides satisfactory performance and benefits the environment by consuming recycled rubber manufactured from scrap tires. This work investigated the aging mechanism and post-aging performance of rubber-modified binders using laboratory aging protocols. Four rubber-modified binders containing two rubber contents (5 and 10 percent) and two particle sizes (passing 1.18 mm and 2.36 mm, respectively) were evaluated in this study. After multiple laboratory aging protocols, chemical components in aged binders were measured with Fourier transform infrared spectroscopy. Chemical analysis revealed that rubber-modified binders accumulated fewer oxidative aging products (carbonyl and sulfoxide components) than their unmodified base binder after long-term aging. Increasing rubber content and particle size increased the complex shear modulus while decreasing the phase angle of the binder. Binder viscosities were back-calculated from complex moduli and phase angles. A linear correlation between logarithmic viscosity and carbonyl area index exists for the long-term aged rubber-modified binders. This linearity can be used to predict the age-hardening of rubber-modified binders. These binders were also tested in dynamic shear rheometer to determine performance grades. Multiple stress creep recovery tests evaluated the rutting resistance of short-term aged binders. Bending beam rheometer was used to evaluate the low-temperature cracking resistance of long-term aged binders. These test results showed that rubber-modified binders provided better rutting and cracking resistance than their base binder. Statistical analysis indicated that carbonyl components correlated to the binder performance at various aging statuses.

Macro-microscopic study on the crack resistance of polyester fiber asphalt mixture under dry-wet cycling and neural network prediction

Asphalt mixture is a composite material with a complex multiphase dispersed system, and its macroscopic mechanical behavior is inherently related to the microstructure characteristics. To investigate the low-temperature crack resistance degradation law of polyester fiber asphalt mixture under different dry-wet cycling conditions, six polyester fiber contents (0%, 0.3%, 0.35%, 0.4%, 0.45%, and 0.5%) were dry-blended into SMA-13 asphalt mixture to prepare fiber-reinforced SCB specimens with pre-notches. Semi-circular bending tests were conducted to test the crack resistance performance of the fiber asphalt mixture after 0, 2, 4, 6, and 8 dry-wet cycles. The experimental results show that the crack resistance performance of specimens with different fiber contents decreases with the increase of dry-wet cycling times, and the influence of salt-dry-wet coupling is greater than that of water-dry-wet coupling. Under the same conditions, the crack resistance index (CRI) increases first and then decreases with the increase of polyester fiber content, reaching its maximum at a polyester fiber content of 0.4%. When the fiber is added at 0.5%, the agglomeration of polyester fibers restricts the low-temperature performance of the specimen. In addition, the DIC technology is used to analyze the trend of horizontal strain variation of specimens after different dry-wet cycles. The results indicate that with the increase of the cycle period, the strain concentration area becomes more apparent, and in the destruction stage, the full-field horizontal strain Exx in the crack concentration zone gradually increases, while the crack resistance decreases. Finally, addressing the limitations of traditional BP neural networks in solving nonlinear problems, a particle swarm optimization algorithm is proposed to optimize the BP neural network, and a PSO-BP neural network model is constructed. Through the analysis of evaluation indicators, it is found that the PSO-BP neural network has improved generalization ability compared to the traditional BP neural network model, and overfitting is reduced, making it an effective tool for predicting the low-temperature performance of polyester fiber asphalt mixtures.

Investigation of the self-healing, road performance and cost–benefit effects of an iron tailing/asphalt mixture in pavement

As a solid waste, iron tailings urgently need to be addressed to prevent further environmental and social issues. This study attempted to replace natural limestone filler (LSF) with 20%, 40%, 60% and 80% iron tailing filler (ITF) in an asphalt mixture to improve its microwave self-healing properties. For this purpose, the microscopic appearance and chemical composition of the ITF and LSF were first characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD) test, while their microwave heating capacity and electromagnetic loss properties were explored. The microwave thermal behaviors of asphalt mixtures containing different substitution ratios of ITF were analyzed via infrared thermography. The self-healing abilities of the various mixtures were tested by five fracture-healing cycles with three-point bending (3PB) test. In addition, the high-temperature stability, low-temperature crack resistance and water stability of the mixtures were evaluated. Furthermore, the economic and beneficial aspects of the ITF-doped mixtures were assessed by cost–benefit analysis (CBA). The experimental results suggest that an ITF with more metal oxides and better electromagnetic loss characteristics exhibits favorable microwave heating ability. After fifth crack-healing cycle, the healing capacity of the mixtures with 60% and 80% ITF increased by 2.5 and 2.75 times, respectively, compared to that of the mixture without ITF. A total of 40% is the recommended appropriate addition of ITF, which helps to improve or has less impact on the road performance. Additionally, based on the CBA method, the incorporation of more than 60% ITF into an asphalt mixture can provide considerable economic efficiency. As a consequence, the potential use of ITF as an eco-friendly filler in asphalt mixture presents new opportunities for waste recycling and resource conservation while also introducing novel approaches for self-healing pavement.

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.

Self-healing performance and rheological properties of styrene-butadiene-styrene block copolymer modified asphalt promoted by polyurea elastomers containing disulfide bonds

Self-healing asphalt is considered as one of the desirable methods to extend the service life of asphalt pavement. This research prepared a polyurea elastomer containing dynamic disulfide bonds (PUA)/styrene butadiene styrene block copolymer (SBS) composite modified asphalt. Moreover, a new asphalt self-healing performance evaluation method based on the damage process and results has been proposed. Subsequently, the self-healing ability of PUA, the distribution of modifier, the functional group and molecular weight of composite modified asphalt were characterized by fluorescence microscope, Fourier transform infrared spectroscopy (FTIR) and Gel permeation chromatography (GPC). The self-healing potential and limits of PUA/SBS composite modified asphalt was investigated through the proposed healing linear amplitude scanning (HLAS) test. Results show that the SBS content and fatigue load level are the main factors affecting the self-healing promotion effect of PUA. The critical point of healing fatigue strain (HFS) can indirectly characterize the threshold at which healing promoters exert their effects. Next, the addition of fillers will reduce the self-healing performance of PUA/SBS composite modified asphalt, but it still improves by at least 61.318% compared with SBS modified asphalt. Finally, the addition of self-healing elastomers (PUA) improves the permanent deformation resistance at high temperature and low-temperature crack resistance of SBS modified asphalt. The dynamic recombination of disulfide bonds can increase the fatigue cycle number of 4%SBS modified asphalt by 93.52% at a 5% load strain level.

Performance Evaluation of Asphalt and Asphalt Mixtures Modified by Fuel-Resistant Admixture

In the course of asphalt pavement usage, exposure to fuel infiltration accelerates particle detachment, leading to the occurrence of problems such as looseness and peeling. The aim of this study was to comprehensively evaluate the impact of a fuel-resistant modifier (FRM; 1%, 3%, 5%, 7%) on the performance of asphalt and asphalt mixture. Conventional physical tests and high–low temperature rheological tests were conducted on the fuel-resistant modified asphalt (FRMA). The results indicate that, with increased FRM content, the penetration and ductility of FRMA decreased, while the softening point increased. The high-temperature performance improved, but the low-temperature ductility declined. High–low temperature rheological test results demonstrate that the addition of FRM significantly enhanced the asphalt’s shear deformation resistance. A moderate amount of FRM modification improved the asphalt’s low-temperature crack resistance, but excessive FRM resulted in reduced flexibility. In addition, fuel-resistant modified asphalt mixture (FRMAM) specimens were prepared and evaluated for performance. In comparison to the base asphalt, FRM modification enhanced the resistance to oil erosion and peeling as well as the Marshall stability of asphalt mixtures. It reduced the scattering loss caused by fuel dissolution and improved both low-temperature indirect tensile (IDT) strength and high-temperature shear strength. A low content of FRM effectively reduced the sensitivity of asphalt mixtures to fuel infiltration, thus enhancing their road performance.