Modified Asphalt Pavement Research Articles

Synthesis of tungsten iron-oxide zeolite composites and their catalytic degradation in VOC from rubber powder modified asphalt

Tungsten iron-oxide zeolite composites with different Fe and W loadings were synthesized over NaY zeolite supports using a wet impregnation method. The composites exhibited suitable textural properties, light absorption, redox sites and acidity for photocatalytic VOC degradation. The photocatalytic activity for degrading acetaldehyde and o-xylene VOCs emitted from rubber powder modified asphalt was evaluated under solar irradiation. The 5Fe-10 W-NaY(2.8) composite achieved the highest VOC removal of 80% for acetaldehyde and 76% for o-xylene after 6 hours. Increasing Fe and W loading up to 5 wt% and 10 wt%, respectively, significantly enhanced the VOC degradation efficiency. Higher zeolite content and stronger acidity also boosted the photocatalytic performance. The degradation occurred via redox mechanisms involving photo-generated electrons, holes and reactive oxygen species, facilitated by the zeolite acid sites. The 5Fe-10 W-NaY(2.8) composite exhibited good stability over 5 reuse cycles, indicating its potential for mitigating VOC emissions from rubber powder modified asphalt pavements.

Microcosmic mechanism of PE modified asphalt based on molecular simulation

ABSTRACT This paper proposes adding waste plastics to asphalt. Using molecular dynamics to study the properties of modified asphalt after adding polyethylene (PE), and clarify its application direction according to its microscopic characteristics, in order to achieve the goals of resource recycling, environmental protection, improvement of asphalt performance and cost reduction. First, construct the molecular model of asphalt according to the four components of the asphalt molecule; construct the molecular model of PE according to the molecular formula of polyethylene; Secondly, by calculating the solubility parameters and interaction energy of asphalt and PE, the compatibility is judged. Finally, the results of the micromechanical simulations of the original and modified asphalt were compared with the test results of the rheological properties of the asphalt. The research results show that the compatibility between PE and asphalt is the best at 175°C, indicating that this temperature is the best modification temperature of asphalt; the addition of PE increases the order of asphalt molecules, and increases the mechanical modulus of asphalt and high temperature rheological properties. The combination of micro simulation and macro test makes the content of this paper more complete and provides theoretical value for the application of waste PE modified asphalt pavement.

Research on the Long-Term Acoustic Efficiency of Asphalt Mixtures Using CRM in Test Sections of Slovak Roads

Abstract The article presents the possibilities of utilizing waste from the automotive industry, namely old tires, in constructing pavements. The application of shredded rubber creates conditions for devulcanization, which improves the rheological properties of the binder and ensures its better dissolution in asphalt. The focus is on assessing the condition of the pavement surface, measuring the noise level in the vicinity of the road, and quantifying and evaluating the cost of implementing an asphalt pavement design with a crumb rubber modifier (CRM). A visual inspection was performed after 6 years of pavement life. Based on the inspection outputs, the pavement surface structure was in a favourable condition with no permanent deformations. Verifying the acoustic properties showed a noise reduction compared to the road section with the modified asphalt pavement surface. Currently, the price of rubber-modified asphalt for pavement in Slovakia is on average 10 to 15 % higher than the price of other modified mixes. However, we can conclude that pavements with CRM are economically and especially ecologically more advantageous in the long run.

Thermal Properties of Asphalt Pavements Modified with a Lightweight Silica-Based Composite

Pavements are exposed to different external factors such as traffic loading, levels of moisture, and ambient temperature fluctuations. External temperature change affects the pavement’s temperature profile and therefore its behavior. Previous research states that the pavement’s surface temperature cannot be addressed by adjusting its thermal properties because it primarily relies on the color of the surface. Furthermore, the temperature gradients in the pavement’s temperature profile can be associated with thermal cracking, which is an aspect that has not been fully investigated. The objective of this article is to analyze the temperature profile of a modified asphalt pavement and its effects on the thermal gradients in different seasons. Consequently, the thermal properties of a modified asphalt pavement with a novel silica-based composite, developed at Arizona State University (ASU), called “aMBx” were calculated. Three types of mixtures were considered in this study: Control (0% aMBx), 10% aMBx, and 30% aMBx contents by weight of asphalt binder in the mixture. Moreover, slabs of 7.5 cm and 15 cm in thickness were built to monitor the thermal behavior in the field using wireless thermocouples, where the temperature was monitored and recorded for one year. In addition, a pavement temperature model was implemented using validated software developed at ASU. The full pavement temperature profile was simulated for the three types of asphalt mixtures discussed in this study. The results showed that the pavement surface temperature can be managed by changing the thermal properties, which, in this case, was driven by the materials and thickness of the materials. The temperature gradient was lower for the aMBx-modified pavements. Therefore, it was concluded that aMBx-modified asphalt pavements may lead to lower thermal susceptibility.

Mechanical damage characteristics of CR/PPA composite modified asphalt pavement under multi-factor coupling effect in the seasonally frozen region

Asphalt pavements are inevitably affected by coupled effects of dry-wet/freeze-thaw cycles, UV radiation, temperature, and loading during service, resulting in degradation of their road performance and reduced service life. Therefore, this study used crumb rubber (CR) and polyphosphoric acid (PPA) as modifiers to prepare CR/PPA composite modified asphalt mixtures for testing. To investigate the mechanical properties of the composite modified asphalt mixtures under the action of multi-factor coupling. Meanwhile, the performance analysis of matrix asphalt and SBS modified asphalt mixtures were carried out as a comparison. Density and water penetration tests, splitting tests, beam bending tests, and four-point bending fatigue tests reveal the evolution of asphalt mixture road performance. Finally, regression fitting was performed on the test data to establish the mechanical damage model of each type of asphalt mixture. The results show that with the increase of wet-dry/freeze-thaw cycles and the increase of UV radiation time, the void ratio and water permeability coefficient increase and the splitting strength, bending and tensile strain, and fatigue life decrease for all types of asphalt mixtures. When the number of wet-dry/freeze-thaw cycles reached 8, the mechanical properties of the asphalt mixture decreased significantly, while the changes leveled off after the number of cycles reached 15. When the UV radiation time is less than 4 months, the mechanical properties of the asphalt mixture decay more slowly. However, with a further increase in radiation time, the mechanical properties decay rapidly. The water-saturated specimens have a more significant effect on the mechanical damage of each type of asphalt mixture. Compared with the other two mixtures, the composite modified asphalt mixtures have superior mechanical properties and fatigue life. The mixture performance damage model based on the least squares Levenberg-Marquardt method (L-M method) was able to simulate the experimental data well, with a minimum correlation coefficient R2 of 0.9285. In summary, the road performance of all types of asphalt mixtures under the coupling of multiple factors has deteriorated, while the composite modified asphalt mixtures have better anti-damage characteristics, with good prospects for promotion.

Study on the high-temperature and aging properties of agricultural waste-modified asphalt based on rheology.

The modifier of road materials from agricultural waste (AW) as raw material has been widely noticed. Considering the environmental impact of AW treatment and the National policy on the promotion of resource reuse, the feasibility of four AW (namely, bamboo powder, rape straw, corn cob, and wheat straw) for styrene butadiene styrene (SBS) asphalt modification is studied from the properties and mechanism perspectives. Through properties evaluation tests (such as the dynamic shear rheometer, multiple stress creep recovery, and rotating thin film oven test), the influence of four AW and different mixing amounts on the properties of SBS modified asphalt pavement is analyzed from the aspects of high-temperature deformation resistance and anti-aging properties. The results reveal that the four AW can improve the SBS asphalt's high-temperature deformation resistance and anti-aging properties, among which rape straw has the most significant improvement effect. In addition, through the fourier transform infrared spectroscopy test, the microscopic mechanism of the AW/SBS composite modified asphalt binder is revealed from the functional groups. The analysis shows that the AW is physically mixed with the SBS asphalt binder, which inhibits the growth of sulfoxide groups and the cracking of the SBS modifier during aging.

Weathering characteristics of asphalt modified by hybrid of micro-nano tire rubber and SBS

Tire rubber has been considered as the ideal candidate for improving aging durability of styrene–butadienestyrene copolymers (SBS) modified asphalt pavement. However, crosslink characteristic of tire rubber affected its dispersion in SBS modified asphalt binder (SMB) and restricted high addition dosage. In this study, microscale and nanoscale tire rubber (MNTR) hybridized SMB with the high dosage was prepared for studying its structural evolution during weathering and physical property variation. Results of gel permeation chromatography and infrared spectroscopy showed that MNTR stabilized the molecular weight distribution and decreased oxidative condensation reaction of asphalt matrix during weathering, and yet did not prevent the SBS degradation. Structural characteristics revealed that the dissolved rubber and core–shell structured carbon black nanoparticles in MNTR were implanted into the colloid structure of asphalt, inhibiting the weathering reaction including asphalt condensation and asphalt oxidation. Fraass brittleness temperature and modulated differential scanning calorimetry results verified that the hybrid modified asphalt had more stable crack resistance compared with SMB at low temperature, and dynamic shear rheometer experiment proved its stable deformation resistance and excellent elasticity at high temperature during weathering. Accordingly, the addition of high content MNTR strongly improved natural weathering resistance of SMB based on the highly hybridized colloid structure.

Research on maintenance equipment and maintenance technology of steel fiber modified asphalt pavement with microwave heating

In this article, the 166TYHB road microwave maintenance vehicle was used as the main equipment, aiming at the investigation of the application characteristics of microwave healing technology on asphalt pavement and proving the effective of microwave heating technology in practice. The heating performance and healing behavior of steel fiber modified asphalt pavement under microwave irradiation were analyzed. The maintenance technology of asphalt pavement was designed and optimized, and the corresponding relationship between the maintenance effect of 800 W microwave oven in the laboratory test and the maintenance effect of 90 kW road maintenance vehicle in practical construction was established. The test results showed that with the curing of microwave irradiation, the steel fiber modified asphalt pavement presented an excellent healing performance, and the heating rate of the surface of asphalt pavement could reach as high as 26 °C/min. Meanwhile, as there is no need to apply another raw materials during the maintenance stage, the Pavement Condition Index(PCI) of asphalt pavement could be improved to a high degree, which is much beneficial to maintain the comfortability of pavement.

Viscoelasticity of Recycled Asphalt Mixtures with High Content Reclaimed SBS Modified Asphalt Pavement

For the concerns of investigating the viscoelastic properties of recycled asphalt mixtures incorporating high content reclaimed styrene-butadiene-styrene (SBS) modified asphalt pavement (RAP-SBS), asphalt mixture performance tester (AMPT) was applied to analyze the dynamic modulus and phase angle of recycled mixtures by the influence of RAP-SBS content, temperature, loading frequency, long-term aging (LOTA), and the incorporation of a rejuvenating agent. Master curves of recycled asphalt mixture regarding dynamic modulus and phase angle are developed, and the viscoelastic properties of recycled mixtures within a wide frequency range are characterized with the Christensen–Anderson–Marastean (CAM) model. Eventually, the one-way analysis of variance (ANOVA) was applied to investigate the role of factors on the viscoelasticity of recycled mixtures. The research indicates that (1) the elastic component of recycled mixtures elevates with the increasing of RAP-SBS content and loading frequency; as a result, the high-temperature stability of it enhances, while it is prone to cracking at low temperatures; (2) RAP-SBS content should be selected according to specific characteristics of pavement. For most cases, a content of 50% is recommended; (3) the recycled mixtures incorporating high-content RAP-SBS mixed with a rejuvenating agent has outstanding aging resistance performance; (4) RAP-SBS content is observed to have a significant influence on the viscoelasticity of recycled mixtures.

Development on the Rheological Properties and Micromorphology of Active Reagent-Rejuvenated SBS-Modified Asphalt

This study aimed to improve the recycling efficiency of waste styrene–butadiene–styrene (SBS)-modified asphalt pavements and achieve sustainable road resource development. The SBS-modified asphalt aged in a pressure aging vessel (SBSPAV) was rejuvenated utilizing active reagents [i.e., methylene-bis(4-cyclohexylisocyanate) (HMDI) and 1,6-hexanediol diglycidyl ether (HDE)] and epoxy soybean oil (ESO). The HMDI type (HMDI combined with ESO) and HDE type (HDE combined with ESO) were used as rejuvenators. The rheological behavior of rejuvenated asphalt binders at medium and high temperatures was evaluated utilizing multiple stress creep recovery tests, linear amplitude sweep tests, and rotational viscosity tests. The high-temperature rutting resistance, medium-temperature fatigue resistance, and fluidity of the rejuvenated asphalt were evaluated. The micromorphology, roughness, and adhesion of the rejuvenated asphalt were evaluated by atomic force microscopy. The thermal stability of the rejuvenated asphalt was analyzed by thermogravimetric analysis. The results reveal that the HMDI-rejuvenated asphalt combines with the active hydrogen in SBSPAV to generate a stable chemical structure that benefits the rutting resistance and traffic load grade of the rejuvenated asphalt. Due to the increase in stiffness, the fatigue resistance of the HMDI-rejuvenated asphalt could be damaged to some extent. The residual epoxy functional groups in the HDE-rejuvenated asphalt are dispersed in the asphalt in an independent phase state, which reduces the elastic recovery ability. The stiffness of the rejuvenated asphalt is lowered because it has a more flexible structure. The anti-fatigue effectiveness of the HDE-rejuvenated asphalt is improved. HMDI can boost the intermolecular force of the rejuvenated asphalt while decreasing its temperature sensitivity. The viscosity of the rejuvenated asphalt gradually decreases as the HDE content increases. This occurs because HDE combines with SBSPAV to generate flexible segments, thereby increasing the flexibility of the asphalt colloids. HMDI and SBSPAV undergo a chemical reaction, which partially repairs the structure of SBS and inhibits the free diffusion of the asphalt molecules. The number of the HMDI-rejuvenated asphalt bee-like structures increases, while the volume drops and adhesion increases. The number and volume of the bee-like structures decreased and adhesion increased as the HDE content increased. This occurs because HDE contains a high concentration of light components, which minimizes the amount of asphaltene in SBSPAV. Thermogravimetric analysis tests show that the HDE-rejuvenated asphalt and HMDI-rejuvenated asphalt have good thermal stability.

Selecting the Best Performing Modified Asphalt Based on Rheological Properties and Microscopic Analysis of RPP/SBS Modified Asphalt.

As an asphalt modifier, waste polypropylene (RPP) can not only optimize the performance of asphalt but also greatly alleviate the problem of waste plastic treatment, effectively reducing environmental pollution and resource waste. In order to evaluate the influence of RPP and styrene butadiene styrene (SBS) on asphalt performance, the application of RPP in modified asphalt pavement has been expanded. In this study, a dynamic shear rheometer (DSR), bending beam rheometer (BBR) and other instruments were used to evaluate the rheological properties of composite-modified asphalt. Fourier infrared spectroscopy (FTIR) and fluorescence microscopy (FM) was employed to conduct a microscopic analysis of the modified asphalt, and the layer analysis method was adopted to determine the optimal RPP content. The test results show that the rheological properties of asphalt are significantly improved by the composite modification of RPP and SBS. In addition, the cross-linking between polymer and asphalt is further enhanced by the composite addition of RPP and SBS. The comprehensive performance of modified asphalt is optimized at the RPP content of 2%, which is suitable for applications in the cold temperate zone. The RPP/SBS composite-modified asphalt is able to improve the utilization rate of RPP and has good environmental and economic benefits, thus exhibiting excellent comprehensive performance. However, the optimal asphalt content in the mixture was not investigated, and the economic benefits brought by the utilization of RPP were not evaluated and require further study.

Evaluating the cost of collection, processing, and application of face masks in hot-mix asphalt (HMA) pavements

Human activities significantly contribution to the yearly generated plastic wastes. Moreover, the enormous increase in face masks and face shields caused by the emergence of the COVID-19 pandemic has doubled the generated plastic wastes. Although there is an added benefit of using plastic waste in construction, the cost associated with their application, specifically the face mask, has not been addressed. This paper presents a simplified and rapid estimation of the cost associated with the collection, processing, and application of face masks in hot-mix asphalt (HMA) pavements. Two scenarios, mask modified asphalt pavement and conventional asphalt pavement, are considered. The total cost is based on market price and prices from waste management facilities and plastic processing companies. Life Cycle Cost Analysis (LCCA) is used to evaluate the long-term costs of mask modified asphalt pavement and conventional asphalt pavement. Results show that no significant difference in initial total cost between the two scenarios for pavement sections with lengths less than 500m and the number of lanes less than 6. The difference in total cost begins with lengths greater than 500 m for 5 and 6 Lanes. Despite the higher initial costs for the mask modified asphalt pavement, the LCCA shows that there is a 29% maintenance cost reduction over the 40 years life cycle of the asphalt pavement. The use of LCCA shows the benefit of the selection of the most cost-effective strategy and how the use of mask modified asphalt pavement over the conventional asphalt pavement can save money over the life cycle of the asphalt and improve rutting and stiffens.

Recycled polyethylene (RPE) modified asphalt mixtures: Performance predictions using pavement Mechanistic-Empirical design and evaluation of return on investment

The objectives of this study were to evaluate the impact of using recycled polyethylene (RPE) on the predicted rutting and bottom-up fatigue cracking of RPE modified asphalt pavement sections and on the return on investment (ROI). The AASHTOWare Pavement Mechanistic-Empirical Design (PMED) was used to predict rutting and bottom-up fatigue cracking. Life-cycle cost analyses using FHWA RealCost were used to analyze the return on investment (ROI). Three Superpave 12.5-mm mixtures were evaluated: one control and two RPE modified mixtures designed using wet and dry processes. To increase the prediction accuracies, local laboratory-derived calibration coefficients were used in AASHTOWare PMED based on the repeated load permanent deformation test (RLPDT) and flexural bending beam fatigue tests. Using time versus asphalt concrete rutting and bottom-up fatigue cracking charts, the service life for initial construction and subsequent future pavement rehabilitation/preservation activities were determined for each pavement section. The ROI was then evaluated using a 30-year analysis period. The most cost-effective pavement over the 30-year analysis period was provided by the pavement section produced using the dry process followed by the wet process while the least cost-effective pavement was the control pavement section. Hence, the study presented in this paper beneficially contributed to the current state-of-the-practice by presenting how recycled plastics impact predicted rutting and bottom-up fatigue cracking performances and the return on investment (ROI) when using both wet and dry mixing processes.

Chemical and rheological characterisation of in-situ SBS modified asphalt pavement considering the effect of aging gradient

ABSTRACT Clarifying the evolution of in-service asphalt pavement aging is critical to the project-level strategy decision of pavement maintenance. However, the environmental-induced differences in field aging evolution are still unclear. To address this problem, this research aims to first characterise field aging in terms of both chemistry and rheology, and then to investigate the factors controlling the aging gradient of asphalt pavement from both the environment and the mixture itself. Field cores were collected from 14 sections of 10 highways with different in-service times, climatic conditions, and mixture types. Field-aged binder was extracted from wearing course with different depths. Laboratory-aged binder after different cycles of Pressure Aging Vessel (PAV) were also evaluated as a benchmark for field-aged binders. The rheological and chemical properties of both the field-based and lab-based aged binders were measured using dynamic shear rheometer (DSR) and Fourier transform infrared (FTIR) spectrometer, respectively. Moreover, the mortar film thickness index (Tm ) of mixture from 4 sections was characterised through image processing techniques. The changing rate of the pavement in 0–2 cm characterised by carbonyl index was closely correlated with environmental factors. Higher solar radiation, lower annual days >30°C, and thicker mortar film thickness lead to a greater aging gradient.

Experimental Study on Activated Diatomite Modified Asphalt Pavement in Deep Loess Area

In order to effectively prevent and control the rutting problem of asphalt pavement in the deep loess area of Eastern Gansu and reduce road diseases, diatomite was added into the asphalt mixture for laboratory tests. Through Marshall test and rutting test, the optimum mix proportion of the diatomite asphalt mixture, and the optimal mix amount of the diatomite in this area were determined. The pavement performance of activated diatomite asphalt pavement and SBS asphalt pavement in this area is compared and analyzed through laboratory tests and on-site road paving. The test results show that under the same ambient temperature, the activated diatomite asphalt pavement has the advantages of lower surface temperature, high stability, and low-water permeability coefficient than SBS modified asphalt pavement. In addition, by fitting the fatigue test data of these two asphalt pavements, it is found that the fatigue life of diatomite asphalt mixture is more sensitive to the change in stress level and has better fatigue resistance. Therefore, it is concluded that the use of diatomite modified asphalt pavement in the loess area can improve the temperature stability of the pavement, prolong the service life, and reduce the cost of construction, which can be popularized.

Leaching of PAHs from rubber modified asphalt pavements

The present study aimed to, for the first time, quantify the total content of 16 priority EPA PAHs in end-of-life tyre derived crumb rubber granulates and various manufactured rubberised asphalt mix designs. After identifying the availability of 16 EPA PAHs, the leaching behaviour of rubberised asphalt specimens, were evaluated using the Dynamic Surface Leaching Test (DSLT) based on CEN/TS 16637-2:2014 standard. This was prior to modelling the release mechanisms of PAHs by utilizing a mathematical diffusion-controlled leaching model. According to the results, the total content of 16 EPA PAHs in crumb rubber granulates ranged between 0.061 and 8.322 μg/g, which were associated with acenaphthene and pyrene, respectively. The total content of PAHs in rubberised asphalt specimens varied between 0.019 and 4.992 μg/g depending on the volume of crumb rubber granulates in the asphalt concrete mix design, and type of binder. Results of the leaching experiments revealed that the highest leached PAHs were benzo[b]fluoranthene, benzo[k]fluoranthene and naphthalene with a 64-days cumulative release per specimen surface area > 1 μg/m2. Acenaphthylene, fluoranthene, fluorene and indeno[1,2,3-c,d]pyrene were released in cumulative concentrations between 0.1 and 1 μg/m2. The PAHs with a cumulative release potential below 0.1 μg/m2 during DSLT were benzo[a]anthracene, benzo[a]pyrene, benzo[g,h,i]perylene and chrysene. The diffusion coefficients, which were calculated by mathematical modelling of DSLT data, revealed that the leaching process of 16 EPA PAHs from surface of rubberised asphalt concrete mix designs fitted all the criteria set by the NEN 7345 standard for diffusion-controlled leaching during all stages of leaching experiments.

Laboratory Performance and Field Case Study of Asphalt Mixture with Sasobit Treated Aramid Fiber as Modifier

The use of fiber in asphalt mixtures can improve the mixture’s tensile strength and increase its cracking resistance, but the clumping of fiber in the mixture can weaken the improvement effect. The aim of this research is to assess the properties of Sasobit treated aramid fiber modified asphalt mixture and to validate the field case study. The rutting and stripping resistance of the fiber-modified mixture was identified with the Hamburg wheel tracking device. The low-temperature cracking characteristics of the asphalt mixture were quantified with the disk-shaped compact tension test. Moreover, the dynamic modulus test was adopted to reflect the response of the mixture to different loads and frequencies. The creep slope and stripping slope decreased by 67%, and the number of passes to stripping point and fail point increased by more than 250% after fiber modification. The fracture energy, peak load, and maximum crack mouth opening displacement (CMOD) of the mixture increased more than 10% after fiber modification. The dynamic modulus, rutting parameter, and fatigue parameter of the mixture were improved after fiber modification. The fiber in the mixture improved the stiffness of the mixture at high temperatures. The tensile strength improvement at low temperatures promoted the cracking resistance of the mixture. The cracking number in the fiber modified asphalt pavement was less than that in the control asphalt pavement. Thus, fiber modification could significantly restrict the propagation of cracking in the asphalt mixture. The implementation of fiber in the project can provide experience for future fiber application in asphalt pavement.

Preparation and performances of SBS compound modified asphalt mixture by acidification and vulcanization

Polyphosphoric acid (PPA) was used to improve the performances of styrene–butadienestyrene (SBS) modified (SM) asphalt mixture further and decline the SBS content, however the negative effect of PPA on the performances of SM asphalt mixture is still unclear. The major purpose of this paper is to indicate the negative effect and provide an efficient way to solve the problem. In this paper, SM asphalt, SBS/PPA-modified asphalt (SPMA), SBS/PPA/sulfur-modified asphalt (SPSMA) were prepared, the physical properties were studied and the morphology was investigated by using scanning electron microscope (SEM). The mixtures of base asphalt (BA), SM asphalt, SPMA, SPSMA were designed and prepared in the light of Superpave mixing design method and Phoenix specifications. Universal testing machine (UTM) system was used to investigate the effect of SBS, PPA, sulfur on the properties of BA mixture. It was found that PPA declined the crack, fatigue resistance and moisture susceptibility of SM asphalt mixture and the problem can be solved well by vulcanization, the morphology change of SBS from coarse particle to threadlike one after vulcanization prompted the swelling of SBS in asphalt. Therefore SBS compound modified asphalt pavement material with better performances and lower cost can be prepared by taking advantage of acidification and vulcanization.

Mechanical Response and Structure Optimization of Nanomodified Asphalt Pavement

Nanomaterials are widely used in the preparation of modified asphalt because they can improve the high‐temperature performance of matrix asphalt and have achieved good engineering results. However, the existing research mainly focuses on the material analysis and formula development of nanomodified asphalt and has not yet been involved in the mechanical response of the nanomodified asphalt pavement structure. The mechanical response contains the horizontal tensile stress and the vertical compressive stress of SiO2 modified asphalt pavement. It is unable to propose the matching pavement structure combination for the unique material characteristics of nanomodified asphalt, which leads to the increase of the possibility of pavement diseases and material waste. Hence, considering that semirigid base is the most widely used base type in China, two different structural models of nanomodified asphalt pavement are established according to the current specifications. The effects of pavement thickness, material type, and pavement design parameters on the mechanical response of nanomodified asphalt pavement are analyzed, and then the principle of optimal mechanical performance is taken and the optimal combination of nanomodified asphalt pavement structure is proposed.

Crack resistance investigation of mixtures with reclaimed SBS modified asphalt pavement using the SCB and DSCT tests

An investigation for crack resistance of hot mix asphalt (HMA) with reclaimed SBS modified asphalt pavement (RAP-SBS) by semi-circular bending (SCB) test was conducted. The effect of RAP-SBS content and rejuvenating agent (RA) on crack resistance of recycled mixture was analyzed at medium and low temperature. Meanwhile, the horizontal strain field at crack tip and crack development characteristics of recycled mixture were analyzed by digital speckle correlation technique (DSCT). Besides, the effects of long term aging (LOTA) and freeze–thaw (F-T) cycles on the crack resistance were also analyzed. The results show that crack resistance of recycled mixture decreases in accordance with the quadratic polynomial as RAP-SBS content increases at medium and low temperature, regardless of RA. RA can significantly improve the crack resistance of mixture with high content of RAP-SBS, when RAP-SBS content is 30%, the crack resistance is close to that of virgin mixture, but the anti-aging property is poor. The mortar of recycled mixture is easy to form a weak interface, and RA can prolong the cracking time, and the horizontal strain peak at crack tip is also increased. The influence degrees of crack resistance are shown in the order from temperature, RAP-SBS content to LOTA. As RAP-SBS content increases, the sensitivity of the low temperature crack resistance to the F-T cycle increases. The exponential fitting model can express the relationship between crack resistance and F-T cycles, and the damage degree of crack resistance contains rapid damage stages and stable damage stages as F-T cycles increased.