Asphalt-aggregate System Research Articles

Investigation of Adhesion and Stripping Properties in Asphalt–Aggregate Systems: Impact of NaCl Solubility and Freeze–Thaw Cycles

Investigation of Adhesion and Stripping Properties in Asphalt–Aggregate Systems: Impact of NaCl Solubility and Freeze–Thaw Cycles

Interfacial adhesion features of high-viscosity asphalt and aggregate under water conditioning: Micro perspective and molecular simulation

Interface properties between asphalt and aggregate intimately affect the service performance and long-term durability of asphalt pavement. This study seeks to explore the interfacial adhesion features of high-viscosity asphalt (HVA)-aggregate under water conditioning to provide the understanding for the moisture damage of HVA-aggregate interface and asphalt pavement. To this end, the HVA was initially suffered from different durations of water conditioning, and atomic force microscopy (AFM) test was employed to gather the microscopic phase structure and adhesion force of water-conditioned HVA and aggregate, to analyze the adhesion variations of HVA-aggregate interface. Further, molecular dynamics method was used to simulate the changing process and influencing mechanism of adhesion effect at the HVA-aggregate interface under water immersion. The findings indicated that with the increasing water immersion, Catana phase of HVAs vanished, and concave and convex structures appeared on the surface, along with pit groove dispersion phase structures. Longer immersion time resulted in augmented surface roughness of HVA and a more dispersed height distribution in the area domain, most notably during the initial stages of water immersion. Aging increased sensitivity to immersion duration in terms of surface roughness, mechanical properties and adhesion ability of HVAs. Water immersion had a diminishing effect on the mechanical properties of HVA at different aging degrees, although it increased the micro-mechanical modulus of HVAs and impaired the interface adhesion with aggregates. Under water immersion, the phase structure and mechanical properties of HVAs and the interface adhesion indexes all distinguished a prominent negative Pearson correlation (correlation coefficient |R| > 0.7000), and these factors were critical for HVA-aggregate interface adhesion, as alterations in surface phase structure and micro-mechanical traits of HVAs triggered variations in the HVA-aggregate interface adhesion. In addition, water content in the interface layer, simulation temperature and mineral anisotropy significantly affected the interfacial adhesion of HVA and aggregate in water environment. The introduction of water and the rise of temperature considerably weakened the interfacial adhesion effect of asphalt-aggregate system, and the interface adhesion failure occurred once the water layer thickness surpassed 5 Å. Comparatively, the HVA-calcite system demonstrated better interfacial adhesion competence than the HVA-α-quartz system, and the HVA-calcite {1 0 4} system showed the optimal interfacial adhesion.

Interfacial adhesion properties and debonding mechanisms in rejuvenated asphalt mixtures

The interfacial strength between asphalt and aggregate significantly affects the macroscopic properties of rejuvenated asphalt mixtures. Investigating the interfacial properties of rejuvenated asphalt mixtures contributes to understanding the adhesion mechanisms and debonding behavior, enhancing the service life of rejuvenated asphalt mixtures. In this study, molecular dynamics methods were utilized to construct interface models of virgin, aged, and rejuvenated asphalt-aggregate systems, subsequent to which asphalt-aggregate interface pull-out tests were conducted. The findings revealed that the exponential-type cohesive zone model (CZM) effectively characterize the stress-strain correlations during asphalt-aggregate interface pull-out tests. The combination of adhesive and cohesive failure is the typical damage modes at asphalt-aggregate interface. Cohesive failure tended to be the main failure mode between aged asphalt-aggregate interface, while asphalt oxidation aging notably reduced the interface tensile strength and hence the cracking resistance of asphalt mixtures. The interface failure patterns between rejuvenated and virgin asphalt were similar, demonstrating an adhesive failure at lower temperatures and a shift towards cohesion failure at higher temperatures. The interface failure usually occurred at lower temperatures especially for aged asphalt, while the incorporation of rejuvenator could effectively mitigate the cracking potential asphalt mixtures. This study simulated the interfacial failure behavior for rejuvenated asphalt mixtures, which can be a theoretical basis of using rejuvenator in recycled asphalt mixtures.

Research on the Adhesion Properties of Fast-Melting SBS-Modified Asphalt-Aggregate Based on Surface Free Energy Theory.

In order to study the adhesion properties of fast-melting SBS-modified asphalt (SBS-T) at the interface with aggregates, the contact angles of three dosages of SBS-T asphalt with three liquids (distilled water, glycerol, and formamide) were determined by the sessile drop method based on surface free energy theory. The evaluation indexes such as cohesion, asphalt-aggregate adhesion, stripping work and energy ratio of the asphalt were analyzed and the adhesion properties of the asphalt-aggregate system were investigated with the help of micromechanical methods. The results indicate that SBS-T can improve the adhesion properties of the asphalt. Furthermore, as the dosage of the modifier increases, the cohesion work, adhesion work, and energy ratio of the SBS-T asphalt exhibit a similar rise. As the spalling work reduces and the adhesion between asphalt and aggregate improves, it is noteworthy that the SBS-T asphalt-aggregate system exhibits superior adhesion performance compared to the SBS-modified asphalt-aggregate system, despite the same dosage.

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.

Investigation of the Adhesion Characteristics of a Novel Fast-Melting SBS-Based Modifier to Asphalt-Aggregate Systems Based on a Multiscale Approach

Investigation of the Adhesion Characteristics of a Novel Fast-Melting SBS-Based Modifier to Asphalt-Aggregate Systems Based on a Multiscale Approach

Variation and mechanism of asphalt-aggregate interface features under ultraviolet aging based on meso- and micro-observations

Time-dependent variation and mechanism of asphalt-aggregate interface features under ultraviolet (UV) aging have not yet been illustrated. This study explored the time-dependent variation and mechanism of asphalt-aggregate interface features under UV aging. To this end, six asphalt binders were chosen and subjected to different durations of UV aging, and then the variation behaviors of their cohesion-adhesion ability with the changing UV radiation time were analyzed through surface energy theory. Further, the microscopic attributes of asphalt binders experiencing the various UV aging durations were measured and their varying rules were investigated with a series of micro observations. Finally, the relationship between cohesion-adhesion characteristics and microscopic properties were illustrated and thus the variation mechanism of interfacial cohesion and adhesion were revealed by mathematical statistics and image presentation. The results showed that UV aging weakened the cohesion and multi-working adhesion of asphalt binders and the moisture stability of asphalt-aggregate systems, and overall presented a gradually strengthened influence on them with the prolonged UV radiation time, especially the UV radiation exceeded 6 days. The variation of phase morphology of asphalt binders under UV aging depended on the asphalt types and neat asphalt oil sources, and there existed a favorable linear relationship between Catana phase of asphalt binders and surface roughness. Adhesion force, function group and four components (saturate (S), aromatics (Ar), resin (R) and asphaltene (As)) also exhibited a gradually increasing variation as the UV radiation duration went on, and among which, the UV aging reduced the adhesion force of asphalt binders. Adhesion force Fad demonstrated the highest Pearson relevance with the cohesion and aqueous-condition adhesion and the moisture stability of asphalt-aggregate system, and the cohesion-adhesion properties of asphalt binders under UV aging met the multivariate linear mathematical relationship with the microscopic attributes screened, with the goodness-of-fit greater than 0.7000.

Thermodynamic Properties of Aggregate Coated by Different Types of Waste Plastic: Adhesion and Moisture Resistance of Asphalt-Aggregate Systems

The utilization of acidic aggregates in hot-mix asphalt (HMA) is often inevitable due to the limited supply of locally available aggregates, posing a potential threat of moisture damage to asphalt pavements. In this regard, the use of urban waste plastic to coat the low-quality aggregates is a promising way to improve the moisture resistance. This study fundamentally evaluated the compatibility between asphalt and plastic-coated aggregate by measuring surface energy, and for the first time compared the effects of different types of waste plastic including high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polypropylene (PP). The plastic-coating significantly altered the chemistry of aggregate surface by increasing the nonpolar components and reducing the polar components. Such changes remarkably increased the dry adhesion energy between asphalt and aggregate and enhanced the wettability of aggregate. For the acidic aggregates, the polymeric treatment could decrease the value of wet adhesive, which indicated the debonding tendency in the presence of water was reduced. Finally, the energy ratios of the asphalt-aggregate combinations significantly increased by the surface pretreatment, which proved the effect of waste plastic coating on improving the moisture damage resistance of asphalt mixtures. By comparison, the HDPE coating was the most effective way to enhance the compatibility with asphalt, followed by PP and LDPE coatings. The PVC and PET coatings were investigated as the least effective way. This study cannot only contribute to the potential large-scale utilization of waste plastic but also remove the obstacles of using large quantities of acidic natural aggregate in asphalt pavements.

Interfacial Performance of Asphalt-Aggregate System under Different Conditions Based on Molecular Dynamics Simulation

The interface between asphalt and aggregate directly determines the performance of asphalt mixtures but unavoidable weaknesses can be easily found at the interfacial bonding region. In order to evaluate the interfacial adhesion behavior between asphalt and aggregate at the atomic scale, asphalt binders and two mineral aggregates (quartz and calcite) were selected to build molecular models and molecular dynamics (MD) simulations were conducted. The interfacial energy between asphalt and aggregate was calculated and the mineral aggregate has a more significant influence on the energy compared to the binder types. Also, the simulation result indicates that saturate, aromatic, resin, and asphaltene (SARA) components have different interfacial energies with respect to the aggregates. This result can also be derived from the relative concentration of SARA components on the aggregate surface. Additionally, oxidation of the asphalt binder results in increased interfacial energy due to the enhanced intermolecular bonding generated by oxidized functional groups. The intrusion of water greatly reduces the interfacial energy, but the energy increases under the coupling effect of oxidation and moisture, especially for calcite. The grey relational grade theory was conducted to evaluate the factors affecting the adhesive energy, and the results show that the energy of the asphalt-aggregate is more sensitive to the asphaltene index than other factors.

Evaluating the Effect of Curing Time and Resting Time on Moisture Damage Resistance of Asphalt Mixtures Using the Pull-Off Tensile Strength (POTS) Test

This article explores the effectiveness of the Pull-off Tensile Strength (POTS) test as a tool for evaluating the moisture damage resistance of asphalt mixtures. Currently, indirect tensile strength (ITS) and the Hamburg Wheel Tracking (HWT) test are used, but they have limitations such as expensive equipment and being heavy. The POTS test is a low-cost and portable alternative. This study investigated the effect of curing time and resting time on the POTS of asphalt-aggregate systems by subjecting samples to different curing times and resting times before testing their tensile strength under dry and wet conditions. The results show that the tensile strength decreases with increasing curing time or exposure to water, indicating that the debonding process between asphalt and aggregates occurs more rapidly with aging. The tensile strength ratio (TSR) of the POTS test for all three asphalt binder types increases with resting time and curing time, with the highest values observed at a curing time of 2 h and a resting time of 5–15 min. Additionally, this study found a strong linear relationship between the tensile strength ratios of ITS and POTS tests, regardless of curing time and resting time. Overall, the POTS test is a promising alternative for evaluating moisture damage resistance in asphalt mixtures.

Investigation of the adhesion and debonding behaviors of rubber asphalt and aggregates using molecular dynamics simulation

This paper investigates the interface property between rubber asphalt and aggregates using molecular dynamics simulations to address the adhesion and debonding properties. The effect of aggregate types and rubber contents on rubber asphalt-aggregate systems' adhesion and debonding properties were investigated. The work of adhesion characterized the adhesion property while debonding characteristics were evaluated by the work of debonding and energy ratio (ER). The results show that the impact of aggregate types on the adhesion and debonding between rubber asphalt and aggregates is much more significant than rubber contents. The work of adhesion between four aggregates and rubber asphalt is evaluated as follows: microcline > albite > quartz > calcite. The reason is that the electrostatic energy can considerably contribute to the adhesion at the interface for strong alkali aggregates (microcline, albite) and rubber asphalt, while the van der Waals energy can only contribute nearly 100 mJ/m2 energy for the adhesion. The work of debonding for the four aggregates with rubber asphalt follows the order: microcline > quartz > albite > calcite. Therefore, microcline presents extraordinary performance, while calcite shows the poorest response in moisture resistance.

Surface-Roughness-Induced Control of the Interfacial Failure Mode and Bonding Strength: Atomistic Case Study in an Asphalt–Aggregate System

Surface-Roughness-Induced Control of the Interfacial Failure Mode and Bonding Strength: Atomistic Case Study in an Asphalt–Aggregate System

Influence of novel long-chain active composite rejuvenators on interfacial adhesion between aged SBS modified asphalt and aggregate

In this study, the novel long-chain active composite rejuvenators (NLCACRs) were composed of long-chain active rejuvenators (LCARs) and aromatic hydrocarbon oil (ArO). Surface free energy method (SFE method), boiling water test method (BWT method) and related parameters were used to evaluate the effect of NLCACRs on interfacial adhesion between aged SBS modified asphalt (ASBS-MA) and granite, and preliminarily predict the moisture sensitivity of asphalt-aggregate system. The results indicated that NLCACRs could increase the surface free energy of ASBS-MA, and the increased range varied with the composition and structure of NLCACRs. The NLCACRs could not only supplement the light components lost by asphalt during aging, but also reconstruct the damaged structure of aged SBS, so they were more effective for the recovery of cohesion work of ASBS-MA. NLCACRs could significantly increase the interfacial adhesion between ASBS-MA and acid granite, and decrease the moisture sensitivity of rejuvenated SBS modified asphalt (RSBS-MA)-granite system. And the results of the BWT method indicated that long-term aging decreased the adhesion grade between SBS modified asphalt and granite from G4 to G2. NLCACRs could restore the adhesion grade of ASBS-MA and granite to the level of original SBS modified asphalt. The comprehensive analysis of the influence of NLCACRs on the interfacial adhesion between ASBS-MA and aggregate showed that the theoretical law (SFE method) was consistent with that of the actual (BWT method). This study could help to explore the influence of NLCACRs on the moisture stability of aged SBS modified asphalt mixture and provide the theoretical basis for its application in practical engineering.

Estimation of the surface free energy and moisture susceptibility of asphalt mastic and aggregate system containing salt storage additive

The moisture susceptibility of asphalt mixtures containing salt storage additive is a focus. The objective of this study was to characterize adhesion characteristic of asphalt-aggregate system containing salt storage additive. The contact angle test and boiling water test were carried out to obtain the contact characteristics and stripping behaviour of them. The results indicate that the contact angle values of asphalt mastic increased with the increment of salt storage additive resulting in poor wettability. And the surface free energy values of asphalt mastic slightly reduced with increased salt storage additive, and were remarkably less than that of water leading to bad affinity with stone under moisture condition. The adhesion works under moisture condition mainly depended on stone lithology, and had good negative correlation with the stripping area ratio values from boiling water test.

Comparative analysis of thermal aging behavior and comprehensive performance of high viscosity asphalt (HVA) from cohesion, adhesion and rheology perspectives

High viscosity asphalt (HVA) has been widely utilized in the paving of large-void asphalt pavement, and it will be affected by thermal aging and exhibit different pavement performance. In this study, through a series of macroscopic and microscopic experiments, the change behaviors of cohesion, adhesion, high- and low-temperature rheological properties, microscopic phase structure and functional groups of HVA under different thermal aging conditions were first analyzed—in comparison with the three asphalts viz. styrene-butadienestyrene (SBS) modified asphalt (SBSMA), crumb rubber modified asphalt (CRMA) and neat asphalt (NA). Further, the relationship between macro-micro properties of asphalt binders was investigated by grey correlation theory, and the comprehensive performance of HVA at different aging stages and its aging resistance were contrastively evaluated via using radar chart analysis method. Results showed that aging degraded the cohesion and adhesion of asphalt binders as well as the water stability of asphalt-aggregate systems, and weakened the low-temperature property of asphalt binders—compared to the unaged sample, the short- and long-term aging reduced the cohesion work of HVA by 1.10% and 3.41%, respectively, and decreased the water stability index of HVA-limestone system by 0.54% and 1.86%, respectively. However, the variations of viscoelastic properties, temperature sensitivity, creep recovery ability and rutting resistance of HVA under aging were inconsistent with those of SBSMA, CRMA and NA. Aging decreased the microscopic surface roughness Ra of HVA and altered the intensity of functional groups at different wavenumbers, and the short- and long-term aging diminished its Ra by 21.26% and 37.85% compared to the unaged sample, respectively. Grey correlation analysis showed that the microscopic surface roughness Ra and the functional group indexes at different wavenumbers correlated well with several macroscopic indexes, which successfully explicated the variations of macroscopic properties of HVA from the micro perspective. Radar chart analysis displayed that the comprehensive performance of HVA in the original and short-term aging stages was second only to CRMA, but its comprehensive performance after long-term aging was only superior to NA; overall, HVA exhibited the most favorable anti-aging performance.

Molecular interaction of Asphalt-Aggregate interface modified by silane coupling agents at dry and wet conditions

This study investigated interfacial behavior of asphalt-aggregate system modified by silane coupling agents (SCA). Molecular dynamics (MD) were used to simulate the interface between asphalt binder and silica grafted with three SCAs with different functional groups. At dry condition, the transition zone thickness and contact angle between asphalt binder and modified aggregate surfaces were compared. At wet condition, the effects of SCAs on interaction energy and hydrogen bond were analyzed. The simulated results are in good agreement with experimental measurements reported in the literature. It was found that the SCA modification could improve the adhesion between asphalt and aggregate at both dry and wet conditions. The thicker transition zone between asphalt and aggregate after SCA modification could enhance the compatibility and improve the force transfer between asphalt and aggregate. In addition, the wettability of asphalt binder on the SCA-modified aggregate surface was found better from the simulated contact angle. The grafted SCA on aggregate surface increased the resistance of asphalt-aggregate interface to moisture damage through increased interaction energy and less potential of hydrogen bonds. Although all three types of SCAs had positive benefits on interfacial bonding of asphalt-aggregate systems, the SLA with amino group showed superior performance.

Improved Adhesion Bond between Asphalt Binder-Aggregate as Indicator to Reduced Moisture Damage

Improving the adhesion bonding strength between asphalt-aggregate combinations has a significant influence on the field performance and durability of asphalt pavement and minimizing the moisture damage that can appear in form of losing adhesion in asphalt-aggregate system by using modifiers will increase the service life of pavements.The work of adhesion, de-bonding work, wettability and energy ratios were estimated based on surface free energy theory to evaluate the potential moisture-induced damage of combinations of pure and modified asphalt binders by (Styrene–Butadiene Styrene (SBS), Butyl Rubber (BR), and anti-stripping agent BG plus) with different types of aggregate. The sessile drop method is used to determine the components of the surface energy of different aggregate and asphalt binder types by performing direct contact angle measurements.The experimental results showed that in general, the addition of SBS and BR modifiers will increase adhesion work and decrease de-bonding work and decrease ER2 and wettability for both types of asphalt binders and aggregates while the addition of an anti-stripping agent (BG plus) caused a reduction in adhesion work and de-bonding work and increase ER2 and wettability between the asphalt binder and aggregate surface and that will provide a better possible aggregate-asphalt binder bond strength and asphalt mixture’s resistance to moisture-induced damage.

Performance Evaluation of Asphalt Mixtures Modified with Recycled Polyethylene via the Wet Process

The plastics and asphalt pavement industries have shown increasing interest in recycling waste plastics in asphalt because of potential environmental benefits. One approach to incorporating recycled plastics in asphalt is the wet process, which requires mechanical blending of recycled plastics into the asphalt binder as polymer modifiers. This study was aimed at exploring the use of recycled polyethylene (rPE) and a reactive elastomeric terpolymer (RET), which was used as a potential compatibilizer to rPE, for asphalt modification. Moreover, the study evaluated the impact of both modifiers on the bond strength characteristics of asphalt-aggregate systems as well as on the rutting and cracking resistance of asphalt mixtures. To this end, a battery of laboratory performance tests was conducted on asphalt mixtures containing binders: one neat; two rPE modified; and one styrene-butadiene-styrene modified. One rPE modified binder was formulated by adding 3% rPE to a PG 58-28 neat binder, while the other was modified with 3% rPE, RET, and polyphosphoric acid. Test results indicated that the rPE-plus-RET modified binder yielded an asphalt-aggregate system with enhanced moisture resistance, before and after oxidative aging. When compared with the control mixture, using rPE alone or rPE plus RET for asphalt modification significantly improved the rutting resistance. However, the rPE and rPE-plus-RET modified mixtures were found to be more susceptible to intermediate-temperature fatigue cracking at both short-term and long-term aging conditions. Finally, adding rPE or rPE plus RET did not have a significant impact on the mixture reflective cracking and thermal cracking resistance after long-term aging.

Effects of moisture on the bonding performance of asphalt-aggregate system

Water molecules will damage the bonding performance of asphalt-aggregate system, which will seriously affect the durability of asphalt pavement. The asphalt-aggregate system were prepared using three asphalt types (SBS modified asphalt binder (SBSMA), base asphalt (SK70 and SK90)) and three aggregates (granite, diabase and limestone) with different mineral composition. Tensile tests were performed on aggregate-asphalt samples under different moisture conditioning time. It was found that the continuous moisture conditioning caused the failure mode of samples to transform from cohesive to adhesion. The time point at which the failure mode starts to change can be used to characterize the moisture sensitivity of asphalt-aggregate system. The correlation between image structure of fracture surfaces and adhesion loss was verified through collecting and processing photos of the fracture surface. In addition, the effects of microscopic indices (fraction content of asphalt binder, structural index of asphalt binder and element content of aggregate) on the moisture sensitivity of the asphalt-aggregate system were quantified. The results showed that fractions of the asphalt binder had a more significant influence on the moisture sensitivity than elements (Si, Ca) of the aggregate. The rise in resin content would increase the moisture resistance of the asphalt-aggregate system.

Establishing threshold value of surface free energy and binder bond strength parameters for basaltic asphalt mixes

The present work was undertaken to establish the possible threshold values for Surface Free Energy (SFE) and Binder Bond Strength (BBS) methods for screening asphalt-aggregate systems to ensure excellent moisture damage resistance. A total of sixteen combinations of asphalt-aggregate systems consisted of warm mix additives (WMA) and recycled asphalt pavement (RAP) and WMA-RAP combinations. In addition, the study evaluates the effects of RAP, WMA, and WMA-RAP on compatibility ratio (CR), bitumen bond strength ratio (BSR), and indirect tensile strength ratio (TSR) for different combinations of aggregate-asphalt system. The results showed that compatibility and bond strength between asphalt binders and aggregates deteriorated with the addition of RAP and WMA additives. Threshold criteria for CR and BSR values were identified as 4.80 and 0.90, respectively, with reasonably good accuracy of 90% for the SFE method and 75% for the BBS method. The threshold values, along with the practical framework established in the present study, would help the highway agencies select the most compatible asphalt-aggregate combinations.