Water Stability Of Asphalt Mixture Research Articles

Influence of Acidity and Alkalinity of Water Environment on Water Stability of Asphalt Mixture: Phase II-Microscopic Erosion Mechanism

Acidity and alkalinity of water environments have been proven to influence the water stability of asphalt mixture. However, the relevant influencing mechanism still remains unclear. To fulfill this research gap, this study conducted a series of microscopic tests, aiming at unveiling the microscopic erosion mechanism of the water environment on the water stability of asphalt mixture for better moisture stability achieved. Specifically, the asphalt-aggregate interfacial transition zone (ITZ) samples were prepared by combining #70 asphalt with limestone and granite, respectively, which were then immersed in water solutions at 3 different pH levels (pH = 3.0, 7.0, and 11.0) for 7 days. The chemical composition and microstructure of the asphalt film on the surface of the ITZ samples pre and post-treatment were scrutinized using the Fourier Transform Infrared Spectroscopy (FTIR) and the Atomic Force Microscope (AFM), while the development of microcracks at the asphalt-aggregate interface were identified and traced utilizing the Scanning Electron Microscope (SEM). The test results indicate that after treatment with acidic and alkaline aqueous solutions, the asphalt film’s surface is enriched with polar components such as asphaltenes, resins, and aromatic fractions. The migration of these polar components to the surface of the asphalt film reduces the adhesion between asphalt-aggregate, leading to the formation of microcracks at the asphalt-aggregate interface. The most severe crack development occurs in alkaline water environment, followed by acidic water environment. It is interestingly noted that the adhesion at the asphalt-granite interface is improved under the acidic environment. This improvement may be attributed to the covalent nature of silica, which hinders the adsorption of ions from acidic solution into the asphalt film. This hindrance effectively prevents water intrusion at the asphalt-aggregate interface, thereby reducing the adhesion loss. These findings can help elucidate the mechanism of water damage in asphalt pavement exposed to real-world conditions and enhance its water stability with effective countermeasures proposed.

Effect of aging on micromechanical behavior of asphalt surfaces using an atomic force microscope

The micro-mechanical properties of asphalt surfaces are significantly impacted by short-term aging during construction and long-term aging in service. This, in turn, affects macroscopic characteristics such as asphalt-aggregate adhesion and water stability of asphalt mixtures. The study investigated different aging processes had different impacts on the micromechanical properties of the asphalt on the surface. The short-term aging process had the most significant effects, while the subsequent long-term aging had similar but less important effects. The adhesion, surface energy, and Young's modulus of five different types of asphalt using atomic force microscopy (AFM) in their original state, after short-term aging through the Rolling Thin Film Oven Test (RTFOT), and after long-term aging through the RTFOT+Pressure Aging Vessel (PAV). The results showed that ZH and SK asphalts had a distinct "bee structure", and aging had varying effects on adhesion, surface energy, and Young's modulus in different areas (peak, valley, and other region). Before and after asphalt aging, the adhesion and surface energy approximately followed the order other region > peak > valley, while Young's modulus approximately followed the peak>valley> other region. This indicates that the bumpy "bee structure" does not always correspond to higher modulus or lower adhesion. It was also found that ZH asphalt and SK asphalt with a "bee structure" exhibited better aging resistance compared to KL asphalt without a "bee structure". The study also revealed that aging led to decreased adhesion and surface energy, while increasing Young's modulus. This finding indicates that as asphalt ages, adhesion decreases and asphalt elasticity increases. Additionally, it was observed that the modified asphalt showed less change in adhesion, surface energy, and Young's modulus after aging compared to the matrix asphalt, indicating that SBS modifiers contribute to improving the aging resistance of asphalt. These results will provide a good reference for understanding the microscopic changes in asphalt aging properties.

Water Stability of Fibers-Enhanced Asphalt Mixtures under Static and Dynamic Damage Conditions.

Water damage is one of the major distresses of asphalt pavements. Existing methods for investigating the water stability of asphalt mixtures rely primarily on static water test methods, the tensile strength ratio (TSR) test, and the retained Marshall stability (RMS) test, which evaluate the strength and stability loss after freeze-thaw damage or hot water immersion, respectively. However, these methods do not accurately replicate the actual dynamic water damage conditions to pavement. Therefore, in this study, a variety of damage conditions, including static water conditions and dynamic water pressure conditions, were used to investigate the effects of lignin fibers (LFs), polyester fibers (PFs), and polypropylene fibers (PPFs) on the water stability of asphalt mixtures. First, three fibers-enhanced SMA gap-gradation asphalt mixtures were designed. Then, TSR and RMS were measured under traditional static water damage conditions and new dynamic water pressure damage conditions to evaluate the effect of fiber types on the water stability of asphalt mixtures. Finally, the void rate of asphalt mixtures and its changes under dynamic water damage conditions were further revealed with the help of CT scanning technique. Results showed that, among these three types of fibers, PFs-enhanced asphalt mixture exhibited excellent stability under both static and dynamic water conditions, and the CT scanning test also indicated that the PFs can significantly reduce the increase rate of voids in asphalt mixtures after dynamic water pressure damage. This study identified the potential of incorporating suitable type of fiber to enhance the performance of asphalt mixture under dynamic water pressure damage.

Study on road performance of asphalt mixture based on POE/PA6 modifier

A POE/PA6 modifier with increased reactivity was prepared using the twin-screw extrusion granulation process and added to the asphalt mixture. The effect of the POE/PA6 modifier on high-temperature stability, low-temperature anti-cracking, and water stability of asphalt mixture was studied. The results show that compared with the asphalt mixture mixed with recycled PE, the asphalt mixture mixed with POE/PA6 has nearly four times the rutting resistance of the former at 70°C and 1.0 MPa, the fracture energy and flexibility index are twice the former at -10°C, and the maximum bending strain and water stability are also significantly improved. This modifier shows a good engineering application prospect in highway construction and maintenance under high temperatures and heavy load traffic environments.

Influence of acidity and alkalinity of water environments on the water stability of asphalt mixture: Phase I - molecular dynamics simulation

The pH of water environments surrounding asphalt pavements is not constant at 7.0. Previous studies have demonstrated that the erosion of asphalt mixtures is more severe in acidic or alkaline water environments. However, the underlying mechanism remains unclear. To fulfill this research gap, the molecular dynamics (MD) simulation was employed in this study to explore the erosion influence of three different aqueous solutions on asphalt and asphalt-aggregate interface. Asphalt-solution systems and asphalt-aggregate systems under the different water environments were established. Through investigating the nanostructure change of the asphalt and asphalt-aggregate interface, the relative concentration (RC) and mean square displacement (MSD) of asphalt molecules, and the adhesion work between asphalt and aggregate were analyzed. The results show that the nanostructure of asphalt changes under acidic and alkaline water conditions, which further results in the decrease of the asphalt cohesion. In addition, the study revealed that the acidic and alkaline water solutions promote the molecular migration of SARA (saturates, aromatics, resins, and asphaltene) components, leading to the molecule reorganization at the asphalt-aggregate interface, finally affecting the bonding performance of asphalt-aggregate and the water stability of asphalt mixtures. These findings are anticipated to provide new insights into the influence of acidic and alkaline water environments on the water stability of asphalt mixture from the molecular scale perspective.

Exploring the short-term water damage characteristics of asphalt mixtures: The combined effect of salt erosion and dynamic water scouring

In icy or snowy conditions, improper application and uneven dispersion of deicing salts on roadways can lead to saltwater accumulation, subsequently causing roadway scouring when vehicles transit. This study aims to assess the combined influence of salt erosion and dynamic water scouring on short-term water damage of asphalt mixtures. A custom-designed dynamic water scouring simulation apparatus is used, employing three diverse deicing salt solutions as agents for dynamic water scouring. Numerous iterations of dynamic water scouring tests are conducted on two types of graded asphalt mixtures. Post-scouring, alterations in air void content and water stability are evaluated through void content tests, Marshall water immersion tests, and freeze-thaw splitting tests. Additionally, the GM (1,N) damage prediction model from gray theory is applied for data modeling and prediction. The results reveal a significant impact of the combined effects of salt erosion and dynamic water scouring on the short-term performance of asphalt mixtures. In the early phase, dynamic water scouring primarily influences the asphalt composite, augmenting micro-cracks and causing aggregate disintegration. The intermediate phase sees the disintegration of the asphalt membrane by deicing salts, disrupting adhesion between asphalt and aggregate, and progressively leading to the emergence of new micro-cracks. During later stages, dynamic water scouring continues to deteriorate the asphalt composite, building on the erosion instigated by deicing salts, resulting in the expansion of newly formed micro-cracks and further aggregate disintegration. Among the three deicing salts, CH4N2O exhibits the most pronounced impact on short-term water damage, followed by NaCl, while CH2CH3OH has the least effect. Increasing the fine aggregate proportion in the asphalt mixture enhances water damage resistance. The GM (1,N) damage prediction model effectively anticipates air void content and water stability of asphalt mixtures. The research outcomes offer theoretical and technical support for understanding the durability and service lifespan of asphalt pavements in cold regions.

IMPACT OF DEICING SALT ON THE PERFORMANCE OF ASPHALT MIXTURES IN NORTHWEST CHINA: AN INVESTIGATION INTO MECHANICAL PROPERTIES AND INFLUENTIAL FACTORS

Currently, the primary form of high-grade highways is constituted by asphalt concrete pavement. Winter conditions often result in ice and snow accumulation on these pavements, precipitating severe traffic incidents. Statistically, around 15%-30% of such incidents are directly linked to icy and snowy conditions. Hence, when roads are laden with ice and snow, the most cost-effective and efficient countermeasure remains the dispersal of deicing salt onto the road surface. Particularly in China's northwestern region, which experiences low precipitation and consistent droughts, the deicing salts applied during winter aren't diluted or transported away by water flow. Consequently, the soil surrounding the roads retains a higher concentration of deicing salts than other regions, leading to a pronounced impact on the pavement's service life. This investigation aims to experimentally emulate the impact of this high-salt environment on the mechanical properties of asphalt mixtures, followed by an analysis of the crucial factors that influence the asphalt mixtures' durability. The current study employs measures such as high-temperature rut testing, Marshall water immersion testing, and freeze-thaw splitting testing to investigate the damage patterns of mechanical properties in asphalt mixtures under varying grading, diverse deicing salt solutions, and differing frequencies of dry-wet cycles. In addition, the study employs grey correlation entropy analysis to ascertain the interdependence among factors influencing the performance of asphalt mixtures. The findings reveal that after undergoing 0, 5, 10, 15, 20, 25, and 30 dry-wet cycles in solutions of 20% industrial salt (NaCl), 15% urea (CH4N2O), and 20% anhydrous ethanol (CH2CH3OH), both the high-temperature stability and water stability of asphalt mixtures with AC-13 and AC-16 gradings displayed varying levels of decline. Overall, an enhancement in the fine aggregate percentage in asphalt mixtures can augment the asphalt concrete's resistance to deicing salt erosion. As per the grey correlation entropy analysis, gradation variances exerted the most significant impact on diverse mechanical properties, followed by the type of deicing salt solution, with the least significant impact attributed to the frequency of dry-wet cycles. Thus, judicious selection of road materials and structural design can effectively counter the erosive action of deicing salts, thereby enhancing the service life of the road surface.

Influence of Deicer on Water Stability of Asphalt Mixture under Freeze–Thaw Cycle

In seasonal frozen soil areas, the repeated freeze–thaw cycle of internal moisture in asphalt mixture in winter and spring will accelerate the peeling of asphalt film and aggravate the water damage of asphalt pavement. It is of great significance to carry out the attenuation law of mechanical properties of asphalt mixture under freeze–thaw cycles to prevent and reduce the economic losses caused by water damage to asphalt pavement. This study will investigate the impact of deicer application on the water stability of asphalt mixtures within the climatic conditions prevalent in Northwest China. Specifically, freeze–thaw cycle tests were administered to two types of dense-graded asphalt mixtures under three distinct deicer solutions and three disparate low-temperature environments. The Marshall water immersion test and freeze–thaw splitting test were employed to evaluate the water stability of asphalt mixtures subject to multiple factors, and the relative importance of each factor was statistically analyzed using the acquired data. Results demonstrated that AC-13 and AC-16 asphalt mixtures (AC is asphalt-concrete, which is asphalt concrete, and 13 or 16 represents the maximum particle size of aggregate (13 mm or 16 mm)), saturated in 15% CH4N2O, 20% NaCl, and 20% CH2CH3OH solutions, underwent a varying number of freezing–thawing cycles (0, 5, 10, 15, 20, 25, and 30) at temperatures of −5 °C, −15 °C, and −25 °C, respectively, displayed a discernible decline in their residual stability MS0 and freeze–thaw splitting tensile strength ratio TSR. This decline was particularly marked when temperatures dropped below the solution’s freezing point. Disregarding the fixed factors of weather variation (different low-temperature environments) and road service duration (number of freezing–thawing cycles), the aggregate grading imposed a more pronounced influence on asphalt mixture water stability than the presence of deicers.

Evaluation of the microscale structure and performance of asphalt mixtures under different design methods

Asphalt mixture design methods have an important influence on both the microscale structure formed and the corresponding properties. This research compared the performance of asphalt mixtures with the Balanced design method, Marshall design method, and Superpave design method. CT scans were performed on the mixture specimens under different design methods to analyze the mixtures' void distribution law and skeleton structure stability. Then, the water stability of asphalt mixtures with different skeleton structures was evaluated by the water immersion Marshall test and freeze–thaw splitting test, and the effects of temperature and loading frequency on the dynamic modulus of asphalt mixtures under different skeleton structures were assessed by uniaxial compression dynamic modulus test. Finally, based on the time–temperature equivalence principle and Sigmoid model, the master curves of the dynamic modulus of asphalt mixtures under different design methods were constructed. The results showed that the number of coarse aggregate contact points and the average coordination number of asphalt mixtures were relatively larger under the Balanced design method, and the residual strength ratio of asphalt mixture under the Marshall design method was 1.4% larger than that of the Balanced design method, and the residual strength ratio of specimens under Superpave design method was 6.1% larger than that of the Balanced design method. At the same time, based on the differences in the air void of the specimens under different design methods and the different skeleton structures, the dynamic modulus laws under the action of different frequencies were obtained, and the mechanism of the influence of the skeleton structure on the dynamic modulus of the mixture was revealed. This research has important implications for the durability improvement of asphalt mixtures.

Asphalt mixture with nucleus-shell structural microwave enhanced aggregate: Structure design, preparation and performance

The natural aggregates in asphalt mixture with poor electromagnetic loss have poorer microwave absorption capacity and lower microwave energy utilization. The nucleus-shell structural microwave enhanced aggregate (NSSA) consisting with external microwave absorbing and heat collecting structure layer (ESL) and internal limestone was designed to enhance the microwave absorption capacity. The composition and thickness of the ESL were determined. The microwave heating efficiency, microwave energy utilization rate and water stability of asphalt mixture with NSSA and the influence of NSSA on the distribution of electromagnetic field intensity were studied by laboratory test and numerical simulation. The electromagnetic parameters test results show that the ESL had better impedance matching with air when the SiC: Fe3O4: cement: water = 1:2:15:6.3. The ESL thickness should not exceed 4.68 mm considering the penetration ability of 2.45 GHz electromagnetic wave. The microwave heating test results show that the heating rate and energy utilization rate of NSSA were 1.76 times and 5.93 times higher than those of limestone. Furthermore, the asphalt mixture with NSSA had higher heating rate, temperature uniformity and energy utilization rate. The overall water stability of asphalt mixture with NSSA remained the same or even better because the ESL wrapped the pores inside the limestone. The simulation results show that the asphalt mixture with NSSA had larger electromagnetic field intensity and better uniformity of electromagnetic field distribution during microwave heating. In conclusion, the NSSA and the asphalt mixture with NSSA has better microwave absorption capacity and microwave energy utilization rate.

Performance and Microstructure Characterizations of Halloysite Nanotubes Composite Flame Retardant–Modified Asphalt

To solve the problems of low flame retardant efficiency and weak low-temperature performance of asphalt modified by conventional flame retardants (CFR), in this study, halloysite nanotubes (HNTs) and CFR were used to prepare nanocomposite flame retardants (NCFR) to modify asphalt. A fluorescence microscope (FM), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope/energy dispersive spectrometer (SEM/EDS) were used to characterize the microstructure of NCFR-modified asphalt. An oxygen index meter, Cleveland open cup, and cone calorimeter were used to test the flame retardant properties of the asphalt. A dynamic shear rheometer, bending beam rheometer, and force ductility tester were used to test the rheological properties of asphalt. At the same time, flame retardant–modified asphalt mixtures were prepared to verify the flame retardancy and road performance of the flame retardant–modified asphalt. The research results showed that the asphalt modified with 8% CFR and 1% HNTs (MA/CFR/1% HNTs) showed better dispersibility. The increase of limiting oxygen index and self-ignition temperature and the decrease of heat release rate and smoke production rate of MA/CFR/1% HNTs indicated that it has good flame retardancy. At 64°C, compared with modified asphalt (MA), the rutting factor of MA/CFR/1% HNTs increased by 88.17%, the creep recovery increased, and the irreversible creep decreased, indicating that its high-temperature performance improved significantly. At −18°C, compared with that of MA/CFR, the low-temperature creep stiffness of MA/CFR/1% HNTs decreased by 36 MPa and the creep rate of MA/CFR/1% HNTs increased by 0.034, indicating that only 1% HNTs can improve the effect of degraded CFR on the low-temperature performance of MA. Simultaneously, MA/CFR and MA/CFR/1% HNTs can improve the high-temperature performance and water stability of asphalt mixtures. Adding 1% HNTs to a MA/CFR-modified asphalt mixture can improve the low-temperature performance of the asphalt mixture to the level of the low-temperature performance of the modified asphalt mixture. In summary, the modification of asphalt with 1% HNTs and 8% CFR can effectively improve the flame retardant efficiency and significantly improve the road performance of asphalt.

Effect and mechanism of waste glass powder silane modification on water stability of asphalt mixture

The loss of adhesion is one of the primary mechanisms of water damage in asphalt mixes containing waste glass powders (WGPs), which is mainly attributed to the smooth surface of the glass may undermine the bitumen–aggregate adhesion and accelerate the stripping. In this study, the WGPs surface was roughened by different types and content of silane coupling agent (SCA), and the surface modification mechanism was illustrated based on the chemical reaction process. Then the adsorption capacity of WGPs on SCA was studied through UV–vis tests, and the effects of the SCA on the chemical composition of WGP and asphalt were investigated by FT-IR tests. At the same time, the adhesion performance between modified WGPs and asphalt was studied by the sessile drop test and column wicking test. Furthermore, the immersion Marshall tests were completed to study the water stability of the asphalt mixture after the replacement of filler with modified WGPs. Results show that the optimal modified time of WGPs is 75 min. During the modified process, a ≡Si-O-Si≡ skeleton structure is generated between the SCA and WGPs, and the amino group in SCA reacts with the carboxylic acid of the asphalt to form a new chemical bond. In addition, adding 10 % KH550 SCA to modify the WGPs will provide the most superior improvement for the adhesion work, stripping work and water stability.

Influence of low-temperature polyurethane solid-solid PCMs particles on the pavement performance of asphalt mixtures

In order to slow down the cooling rate of the mixture and reduce the low temperature cracking of asphalt pavement in large temperature difference areas, low-temperature polyurethane solid-solid phase change materials (LPSPCMs) were prepared by prepolymer method. The researches show that LPSPCMs have good phase change heat storage performance and thermal stability performance, and can be applied to hot mix asphalt mixtures. The LPSPCMs particles were incorporated into the asphalt mixture, and the road performance of the LPSPCMs particulate asphalt mixture was tested and analyzed and found: as LPSPCMs particles change the abrasion resistance and embedded effect between asphalt mixes, with the increase of LPSPCMs particles, the high-temperature performance of asphalt mixes first increased and then decreased. The water stability of asphalt mixtures gradually decreases with the increase of LPSPCMs particles content because relative to limestone aggregates, LPSPCMs particles adhere poorly to asphalt. The thermal stress restrained specimen test (TSRST) showed that the cracking temperature of the asphalt mixture gradually decreased with the increase of LPSPCMs particles contents because of the phase change temperature control effect of LPSPCMs particles indicated that LPSPCMs particles improve the low-temperature performance of asphalt mixtures. On this basis, the correlation between the evaluation index of the phase change temperature adjustment effect and the improvement effect of the low-temperature performance of the mixture was established.

The effect of morphology of ZnO particle on properties of asphalt binder and mixture

To study the effects of the morphology of ZnO particles on the properties of asphalt binder and asphalt mixture, the micro ZnO particles with different morphologies (agglomerate, sphere, rod and flower), whose average size were 2 µm, were made by the homogeneous precipitation and hydrothermal methods. A series of tests, including the softening point, bending beam rheometer (BBR), dynamic shear rheological (DSR), Marshall test, rutting test and so on, were used for evaluating the properties of asphalt binder and asphalt mixture. The analysis of variance (ANOVA) and the maximum relative difference (MRD) were introduced to study the effects of the morphology of ZnO particles on the properties of asphalt binder and asphalt mixture. Finally, the optimal morphology of the ZnO particle was recommended. The results show that the morphology of the ZnO particle has a significant effect on the rutting factor, has an effect on the viscosity in the situation of the dosages of SBS are 0% and 4%, has no effect on the low temperature ability of asphalt binder. In terms of asphalt mixture, the morphology of the ZnO particle has a noticeable effect on the high temperature stability, has an effect on the low temperature ability, has almost no effect on the water stability of asphalt mixture. Furthermore, the rod-like ZnO particles are more conducive to promote the properties of asphalt binder and asphalt mixture. As a result, the rod-like ZnO particle is recommended.

Influence of Frequent Freeze–Thaw Cycles on Performance of Asphalt Pavement in High-Cold and High-Altitude Areas

This study explores the temperature changes and freeze–thaw cycles in certain typical high-altitude areas, finding that these areas encounter more than 120, or even more than 200, freeze–thaw cycles per year. Such frequent freeze–thaw cycles deliver significant impact on the performance of asphalt pavements, with cracks becoming a typical problem in high-altitude areas. Such factors as cold weather, large temperature differences, and frequent freeze–thaw cycles have adverse effects on the stress of asphalt pavement materials, resulting in cracks in pavements. By simulating the conditions of such frequent freeze–thaw cycles, this study explores the law of changes in the performance of roads made from asphalt and asphalt mixtures, as well as the low-temperature crack resistance properties of asphalt and asphalt mixtures in frequent freeze–thaw cycles. It is found that the performance of the three different types of asphalt binders used in the test shows basically no change after 50 freeze–thaw cycles, and the asphalt types have a significant effect on the low-temperature performance of asphalt mixtures. The modified asphalt shows a higher viscosity than the matrix asphalt, with better toughness than that of the matrix asphalt at low temperature. Frequent freeze–thaw cycles significantly influence the low-temperature splitting tensile strength and water stability of asphalt mixtures; with increased freeze–thaw cycles, the splitting strength and freeze–thaw splitting tensile strength ratio will gradually decrease to a significant level. The freeze–thaw conditions are found delivering remarkable influence on the low-temperature splitting tensile strength and water stability of asphalt mixtures. The research results of this study provide a basis for the selection of asphalt pavement materials as well as the optimal design of mixtures in high-altitude area like the Qinghai-Tibet Plateau.

Evaluation on Improvement Effect of Different Anti-Stripping Agents on Pavement Performance of Granite-Asphalt Mixture.

There are abundant granite reserves in China, but the adhesion between granite and asphalt is poor, and there are problems such as insufficient water stability, which seriously restrict the application and promotion of granite in asphalt pavement. In order to improve the adhesion between granite and asphalt, as well as the water stability of asphalt mixture, amines and polymers were selected as anti-stripping agents. First, silane coupling agent modified asphalt (SCAMA), rock asphalt modified asphalt (RMA), SBS modified asphalt (SBS), and double rock composite modified asphalt (SCA&RMA) were produced; the modification effect of different anti-stripping modified asphalts was evaluated. Then, the adhesion of different types of asphalts and granite aggregates before and after aging was evaluated by time-delayed water immersion method. Finally, AC-10 and AC-16 granite–asphalt mixtures were designed, through indoor performance test and 1/3 scale accelerated loading test, evaluating the improvement effect of granite–asphalt mixture on pavement performance. The results show that the asphalt modified by amine or organic polymers anti-stripping agent could significantly improve the adhesion between granite and asphalt. The Hamburg wheel-tracking test failed to fully reflect the whole process of high-temperature rutting failure. When evaluating the high-temperature performance and water stability of asphalt mixtures, it is recommended that the evaluation method should cover the whole failure stage of asphalt mixtures; considering the coupling effect of water and high temperature, the order of water stability of granite–asphalt mixture is proposed as follows: SCA&RMA > RMA > SBS > SCAMA > 70-A, and SCA&RMA has the best modification effect.

Study on betel nut fiber enhancing water stability of asphalt mixture based on response surface method

In recent years, there has been an increasing interest in waste fiber reinforced asphalt mixes. Waste betel nut fiber (BNF) can improve the tensile strength of asphalt mixture, while the hydrophilic groups on its surface can reduce its water stability. Therefore, this study investigated the effect of alkali-treated BNF on the water stability performance of asphalt mixtures. The effects of shear time, fiber content, and asphalt aggregate ratio on the water stability of BNF-enhanced asphalt mixtures were investigated separately by response surface methodology (RSM). The road performance of the RSM method with optimal solution and without fiber, fiber without alkali treatment, and fiber without shear was also compared. The results showed that under the AC13 gradation, the optimal solutions of multi response variables are fiber content of 0.2561%, fiber shear time of 12.78 min and asphalt aggregate ratio of 5.82%. The corresponding predicted Rdry value is 1.48 MPa, Rsaturated value is 1.27 MPa and TSR value is 88.41%. The final test results are within the 95% confidence interval, and the prediction model has good reliability. The optimal solution has the best low-temperature flexural strength and water stability. This study helps to promote the application and promotion of BNF in road construction.

Quantitative Analysis Investigation of the Water Stability of Asphalt Mixtures with Crushed Gravel Based on the Theory of Surface Free Energy

To quantitatively analyze and study the water stability of crushed gravel asphalt mixture by using surface energy theory, the surface energy parameters of crushed gravel samples at 20℃ are tested by using the gas sorption method, and the surface energy parameters of four anti-stripping agent asphalts with different dosages (0%, 0.2%, 0.4%, 0.6%) at 20℃ are tested by using the Wilhelmy plate method. Then, the binding energy of crushed gravel and anti-stripping agent asphalts with different dosages and the surface energy evaluation index of water stability are calculated. On this basis, quantitative analysis and sequencing of water stability of crushed gravel asphalt mixture were carried out. The microscopic mechanism of the anti-stripping agent's improvement on adhesion between crushed gravel and asphalt was analyzed from the angle of surface energy. Marshall test (immersion Marshall test, vacuum saturation Marshall test, freeze-thaw splitting test) with anti-stripping agent contents of 0%, 0.2%, 0.4%, and 0.6% was conducted through strict control of crushed gravel material, gradation, and oil-stone ratio. Results show that (1) the surface energy parameters of crushed gravel are dominated by polar alkali component; (2) the addition of anti-stripping agent will reduce the surface energy of asphalt, thus increasing the wettability of asphalt to aggregate; (3) the improvement of the adhesion between crushed gravel and asphalt by adding anti-stripping agent is mainly reflected in two aspects: reducing the cohesive energy of asphalt itself to increase its wettability to aggregate and increasing the surface energy acid component of asphalt to increase its adhesion binding energy to aggregate; and (4) the order of microscopic surface energy evaluation index of water stability of crushed gravel asphalt mixture is the same as that of macroscopic performance test index, thus demonstrating the accuracy of the surface energy system for quantitative analysis of the water stability of the crushed gravel asphalt mixture.

Effect and mechanism of acidic aggregate surface silane modification on water stability of asphalt mixture

This study assessed the water stability of asphalt mixtures incorporating granite aggregates. A silane coupling agent was adopted to modify the surface of the granite aggregates, and scanning electron microscopy, contact angle measurements, Fourier transform infrared spectroscopy, and X-ray fluorescence were used to analyze the micro- and meso-characteristics of the aggregates. Effects of the silane treatment on the water stability of the mixtures were further evaluated by immersion and vacuum saturation Marshall tests and freeze–thaw splitting tests. The results indicated that the silane coupling agent had grafted onto the aggregate surface via chemical interactions, resulting in obviously raised contact angles and greatly reduced hydrophilicity. Additionally, the deposited organic film also reacted with the asphalt and formed a tighter bonding interface between the asphalt and aggregates, resulting in an asphalt mixture with a higher residual stability and splitting tension strength ratio when under environmental stress.

Investigation of the Performance of the Ecofriendly Fiber-Reinforced Asphalt Mixture as a Sustainable Pavement Material

This article presents a study to evaluate the performance of the ecofriendly calcium sulfate whisker fiber- (CSWF-) reinforced asphalt mixture as a sustainable pavement material. Asphalt mixtures containing 0.2 wt.%, 0.4 wt.%, 0.6 wt.%, and 0.8 wt.% of the CSWF were designed by the Marshall method. Asphalt mixtures without fiber were also prepared as control samples. The Marshall test, wheel-tracking test, low-temperature bending test, water sensitivity test, and fatigue test were conducted to evaluate the performance of the CSWF asphalt mixture. And the mechanism of fiber reinforcement was discussed. The results showed that the CSWF could improve the high-temperature stability and low-temperature crack resistance of the asphalt mixture. Water stability of asphalt mixtures in the presence of the CSWF was also improved. When the CSWF content was 0.4 wt.% of the total mixture, the performance of the asphalt mixture is the best. Compared with the conventional asphalt mixture, the CSWF asphalt mixture not only utilized power plant waste effectively to preserve ecosystems but also improved the performance of the pavement, which is suggested to be used in sustainable pavement construction and rehabilitation.