Properties Of Binders Research Articles

Fractional derivative Burgers models describing dynamic viscoelastic properties of asphalt binders

The Burgers model is ineffective in the representation of dynamic viscoelastic properties of asphalt binders; the existing fractional derivative Burgers (FDB I) model has limitations in its application and construction concept. Consequently, this study started by deriving the constitutive equations of the FDB I model and proposed a new application idea of Abel dashpot to construct the second fractional derivative Burgers (FDB II) model. Then, dynamic modulus formulas for the FDB II model were derived. On this basis, the frequency sweep tests of base and two polyphosphoric acid (PPA) modified asphalt binders were carried, and the dynamic viscoelastic properties of three different asphalt binders were described using three different models, and in-depth comparisons and analysis are carried out. The results show that both fractional derivative Burgers (FDB) models can simultaneously express the dynamic viscoelastic properties of asphalt binders with a set of parameters. Both FDB models perform better than traditional Burgers model in the representation of dynamic viscoelastic properties, and fitting results of master curves no longer exhibit oscillation properties like the traditional Burgers model. The R2 of FDB models could reach above 0.99, while R2 of traditional Burgers model was only 0.9349 at minimum. Among them, the FDB II model performs best. Five parameters of the FDB II model have relatively clear physical meanings. The new application concept of fractional dashpots was verified its theoretical feasibility and application advantages, which will provide a new idea for further application and development of fractional derivative constitutive models.

Effects of Fly Ash Geopolymer Hot Mix Asphalt Additive on the Rheological Properties of Unaged and Short-Term Aged Asphalt Binder

Asphalt pavement has the advantages of driving comfort and convenient maintenance, which has been widely applied to highway construction. However, due to the continuously increased traffic volume, it is recognized that asphalt binder and mixtures with enhanced characteristics are needed to guarantee the durability of the functional performance of transportation infrastructures. This study was carried to evaluate the effect of fly ash geopolymer additive on the rheological properties of unaged and short-term aged asphalt binder. In the respect, asphalt binder 80/100 and 60/70 penetration grade with 0, 3, 5, 7, 9 and 11% fly ash geopolymer by weight of asphalt binder were prepared. The results indicated that the addition of FAG significantly increases the stiffness (G*) and decreases the phase angle (δ) for both unaged and short-term aged modified asphalt binder compared to the control asphalt binder. This can be proved that presence of FAG significantly improved rutting parameter i.e G*/sin δ compared to control in which capable to resist rutting at higher temperature. In terms of failure temperature, highest failure temperature of 9% FAG modified asphalt binder indicated that the binder is less susceptible to be rutting at high pavement temperature for both unaged and short-term aged, respectively. Overall research conclusions are that 9% of FAG is proposed as the minimal content to be used as an additive in asphalt binder for further mixture evaluations.

Boosting Hot Mix Asphalt Dynamic Modulus Prediction Using Statistical and Machine Learning Regression Modeling Techniques

The prediction of asphalt mixture dynamic modulus (E*) was investigated based on 1128 E* measurements, using three regression and thirteen machine learning models. Asphalt binder properties and mixture volumetrics were characterized using the same feeding features in the NCHRP 1-37A Witczak model. However, three aggregate gradation characterization approaches were involved in both modelling techniques: the NCHRP 1-37A gradation parameters, Weibull distribution factors, and Bailey method parameters. This study evaluated the performance of these models based on various performance indicators, using both statistical and machine learning regression modeling techniques. K-fold cross-validation and learning curve analysis were conducted to assess the models’ generalization capabilities. The conclusions of this study demonstrate the superiority of the ML models, particularly the Catboost ensemble learning regression (CbR). Hyperparameter optimization and residual analysis were performed to fine-tune and confirm the heteroscedasticity of the CbR model. The Bailey-based CbR model showed the highest coefficient of determination (R2) of 0.998 and the lowest root mean square error (RMSE) of 220 MPa. Moreover, SHAP values interpreted the CbR model and showed the relative importance of its feeding features. Based on the findings of this study, the CbR model is suggested to accurately predict E* for a variety of asphalt mixtures. This information can be used to improve pavement design and construction, leading to more durable and long-lasting pavements.

Evaluation of asphaltenes a potential alternative for cement in stabilized base courses using asphalt emulsion

Stabilization of pavement base material using asphalt emulsion has been widely used to improve pavement performance. This technology produces a high-quality base course material with decreased energy consumption, carbon footprint, and raw material usage. Cement has been used as a common additive to improve these mixes strength and moisture resistance. However, some drawbacks are also associated with cement, such as negative environmental impacts, high costs, and low-temperature deficiencies. Asphaltenes is a by-product of oil-sand bitumen with little commercial value in current practice. To investigate the impact of asphaltenes on improving the rheological properties of asphalt binder, a series of binder characteristics tests using a dynamic shear rheometer, breaking time and microscopic evaluation is conducted on modified asphalt emulsion with asphaltenes. Asphaltenes is then added to asphalt emulsion-stabilized granular material, to be compared with mixtures prepared with cement. Two asphaltenes and cement-modified mixes are prepared and compared to unmodified mixtures. All mixes are tested for permanent deformation and moisture sensitivity using a Hamburg wheel tracker and flow number test, while the low-temperature properties are evaluated using indirect tensile strength tests. Dynamic modulus is also evaluated to analyze the viscoelastic behavior of the mixes. The results of this study reveal a considerable increase in the rutting resistance of asphalt mixes by adding 1% of both additives (by total weight of mix), and asphaltenes-modification shows less adverse impacts at intermediate and low temperatures than cement-modification.

Involving prediction of dynamic modulus in asphalt mix design with machine learning and mechanical-empirical analysis

Dynamic modulus (E∗) plays a dominant role in comprehensively capturing the mechanical behavior of asphalt mixture. Many researchers tried to consider E∗ as a performance indicator for a mix design stage, but the cost of time and labor for experimentally measuring the E∗ is high. Moreover, establishing harmonized E∗ criterion is unrealistic. To involve E∗ in an asphalt mix design, this paper improved the Superpave volumetric mixture design via controlling the performance (rutting) of mixtures, which were estimated by incorporating machine learning (ML) predictive models of E∗ into the mechanical-empirical approach. The data from the concatenation of the original E∗ database and volumetric properties data extracted from the NCHRP 9–19 report were involved. The different ML models including Support Vector Regression (SVR), kernel ridge regression (KRR), artificial Neural Networks (ANN), Gaussian process regression (GPR), gradient boosting (GB), and eXtreme gradient boosting (XGBoost) were optimized, trained and tested, and their performances were compared to empirical Witczak’s predictive equations. To illustrate the improved asphalt mix design, the case study was presented. Candidate asphalt mixtures were prepared by mixing the selected gradation and different asphalt content and subject to a series of E∗ predictions using the best ML model, which were then used to calculate the permanent deformation of these mixtures with elastic layered analysis and transfer functions in MATLAB. The results show that among all the ML models, XGBoost to predict the E∗ at actual scale has the largest prediction accuracy (R2 = 0.9867), and its prediction accuracy is significantly higher than Witczak’s equations. Feature importance analysis suggested that no matter which scale of E∗ is predicted, the main important factors are test conditions and asphalt binder properties. The relationship between asphalt contents and estimated rutting by the proposed procedure agrees with the engineering experience, which suggests the feasibility of the proposed asphalt mix design procedure.

Utilizing granulated blast furnace slag as an alternative cement binder

This study addresses the challenges associated with the accumulation of technogenic waste in the production of ferrous and non-ferrous metals. We present the findings of global research on the utilization of blast furnace slag as a sustainable alternative to traditional cement binders. Our scientific investigation focuses on the laboratory exploration of replacing cement binders with a highly efficient clinkerless alternative based on blast furnace slag. The fundamentals of formulating clinkerless binders from slag were thoroughly examined for binder design. Through an extensive review, we conducted tests to identify an optimal composition, constrained within the ranges of 70-90% blast-furnace granulated slag, 14% lime, 1.5-2% gypsum, 1.5-2% C-3, and 2-25% microsilica. The outcome of these tests resulted in the development of a novel binder that combines the characteristics and properties of a lime-slag binder with the advantages of a low water consumption binder. This clinker-free binder presents a sustainable solution for construction, serving as a viable substitute for traditional cement. Our findings contribute to the ongoing efforts in adopting environmentally friendly practices in the construction industry.

Characteristics of waste dry battery powder and its enhancement effect on the physicochemical properties of asphalt binder

The rationalized recycling of waste dry batteries is of great significance to the circular development of resources. In this research, the feasibility of using waste dry batteries in asphalt modification was discussed. Waste dry battery powder (WDBP) was extracted from discarded zinc-manganese dry batteries, and its composition, micromorphology and heavy metal emissions were characterized. Further, the modified asphalts with different WDBP contents were also prepared, and the enhancement effect of WDBP on the physicochemical properties of the binder was evaluated. The results indicate that WDBP mainly contains inorganic carbon and metal oxides. Under acid rain and neutral environment, the heavy metals from WDBP are mainly Zn, Mn and Cd, and their concentrations exceed the concentration limits of Class I surface water in China. The heavy metals in WDBP can be physically solidified for the use of WDBP in asphalt modification. Meanwhile, WDBP can enhance the flow deformation resistance of the binder at the medium-high temperatures, further improve its rutting resistance. However, the WDBP may be have adverse impact on the low-temperature cracking resistance of asphalt, and the WDBP modified asphalt (WDBP-MA) is more suitable for the application in the areas with heavy traffic and hot climate. In addition, the WDBP can enhance the aging resistance of asphalt. Overall, the conclusions confirm the feasibility of applying WDBP to asphalt modification, which can provide a new approach for rational recycling of waste batteries and development of modified asphalt.

Influence of NaOH molarity and Portland cement addition on performance of alkali activated cements based in silicomanganese slags

The aim of this research is to explore the potential of recycling the waste of silicomanganese slag (SiMnS) from the ferroalloy industry in the synthesis of alkali-activated cements. The influence of the concentration of the activator NaOH (4, 6, 8, and 10 M) and the partial substitution of the waste with Portland cement (PC) (10–30 wt%) on the technological properties and microstructure of binders cured at room temperature has been studied. The SiMnS binders and the hybrid cements incorporating PC have been characterized using X-ray diffraction analysis (XRD), infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) combined with energy-dispersive spectroscopy (EDS). The results indicate that compressive strength improve with an increase in molarity from 4 to 6 M from 7.8 up to 14.0 MPa, respectively, at 28 curing days. Similar mechanical properties are observed for higher molarity increments (8 M and 10 M) (12.9 and 13.6 MPa, respectively). The main reaction product formed is a (C,N)-A-S-H gel with different morphologies. Partial substitution of SiMn slag with PC led to hybrid cements with a denser structure due to a greater amount of C-S-H gel, coexisting with C,N-A-S-H gel. Therefore, the optimal combination of SiMn slag (70 wt%) and PC (30 wt%) significantly enhances the technological properties of the SiMn slag binders obtaining optimum compressive strengths of 24.7 MPa. The results of this study demonstrate that silicomanganese slag can be utilized as an environmentally friendly solution in the production of binders and hybrid cements that meet the required technical specifications and standards for use and application in the construction sector in the line of current circular economy policies and Sustainable Development Goals.

Study on rheological properties and damage mechanism of asphalt under acid-alkali precipitation corrosion

This research delved into the effects of pH precipitation on asphalt's rheological characteristics and damage mechanisms. We analyzed the shifts in asphalt's acid-alkali corrosion properties through macro and micro tests. To begin with, we conducted three cycles of bitumen corrosion tests using acidic, alkaline, and neutral solutions. Subsequently, the dynamic shear rheological test (DSR) measured the complex shear modulus, phase angle, and rutting factor before and after asphalt corrosion, revealing correlations between corrosion duration, temperature, and asphalt's rheological traits. Additionally, we evaluated post-corrosion changes in asphalt's functional groups through infrared spectrum testing, allowing us to deduce the underlying damage mechanism. Our results showed that asphalt's deformation resistance was directly related to soaking time and inversely related to temperature. The complex shear modulus exhibited an inverse relationship with temperature, while the phase angle demonstrated a direct proportionality to temperature variations. From a chemical perspective, acidic components within asphalt tend to dissolve and ionize, while alkaline substances undergo esterification and neutralization. Notably, asphalt modified with styrene–butadiene–styrene (SBS) exhibits enhanced resistance against acid and alkali corrosion, surpassing the performance of the 90# asphalt. Ultimately, this research established a theoretical framework for exploring acid-base precipitation resistance in asphalt binders, contributing to our understanding of asphalt's binder properties and broadening its applications.

Study on the effect of aging on cracking resistance of virgin asphalt binder and its evolution model

The cracking resistance of asphalt pavement is significantly affected by the aging of asphalt binder. A better understanding of the effect of aging on the cracking resistance of virgin asphalt binders can help to determine the optimum maintenance time. In this study, the rolling thin film oven test (RTFOT) and pressure aging vessel (PAV) test were conducted to simulate short-term aging and long-term aging of asphalt binders, respectively. Frequency sweep tests were conducted on two asphalt binders at different aging conditions. The Glover-Rowe (G-R) parameter, stiffness modulus (S), creep rate (m), continuous grading temperature (Tc), critical temperature difference (ΔTc), relaxation time (λ), dissipation energy ratio (Wd/Ws), low-temperature indicator ratio (m/S), low-temperature comprehensive compliance parameter (Jc) were obtained. Meanwhile, the sensitivities of different indicators to aging were analyzed and the correlations between G-R parameter and various low-temperature indicators were discussed. Subsequently, a nonlinear model of asphalt binder aging was established by a rheological indicator. The results showed that aging had a significant impact on the low-temperature properties of asphalt binder. G-R parameter, Tc, λ increased with the growth of aging severity, whereas m, ΔTc, Wd/Ws were contrary to this trend. S, m/S, Jc had no significant relationship with the degree of aging. Moreover, G-R parameter and ΔTc were very sensitive to aging. The G-R parameter had a good correlation with m, Tc, λ, ΔTc and Wd/Ws, respectively. It indicated that G-R parameter was closely related to the low-temperature properties of asphalt binders. The aging nonlinear model containing G-R parameter could exactly describe the aging evolution of virgin asphalt binder. It is helpful for the prediction of cracking resistance of asphalt binder and determination of maintenance plan.

Concrete Modification for Hot Weather Using Crushed Dolomite Stone

Crushed dolomite stone can be used as a part of concrete for hot weather. Fine dolomite as a filler is not commonly included in Portland cement. In this paper, the properties of a blended binder based on Portland cement and dolomite filler are presented. Dolomite filler was obtained from dust grains by mechanical activation in a laboratory ball mill to increase the specific surface area and its chemical activity. It is shown that the impact of mechanical activation allows to obtain dolomite filler with a median particle size of 1.4 μm and a specific surface area of 639.9 m2/kg. The content of dolomite filler in Portland cement was 10, 30 and 50%. The main properties of blended cements, i.e., the standard consistency, setting time, compressive strength, average density, and drying shrinkage, were determined on pastes. The mineralogical composition of the hydrated pastes was determined by XRD at 28 days. The presence of dolomite filler at levels higher than 10% decreases the compressive strength of blended cements. The dolomite filler decreases the water demand, shortens the setting time, and mitigates the development of drying shrinkage in the blended binder. To prevent concrete cracking, the application of dolomite filler in blended cement is relevant in hot weather due to its reduced drying shrinkage.

Effectiveness of the different eutectic phase-change materials in cooling asphalt pavement

Choosing a phase-change material (PCM) adapted to the specific phase-change temperature (Tm) required for each temperature condition is of utmost importance in cooling pavements. Eutectic phase-change materials (EPCMs) realize the customization of the desired Tm and reduce the difficulty of matching PCMs. This work aims to investigate the effectiveness of a group of binary/ternary EPCMs with Tm ranging from 30 to 60 ℃ and melting enthalpies of around 200 J/g as thermal regulation components for different asphalt. To achieve this goal, the thermal and rheological properties of phase-change asphalt binders (PCAB) were evaluated by differential scanning calorimeter, thermogravimetric, Fourier transform infrared, and multiple stress creep and recovery tests. The results showed that PCAB with latent heat improved the specific heat capacity, which brought a maximum temperature lag of 134.5 min and a maximum temperature difference of 11 ℃. Similarly, the PCAB remained chemical stability, and its thermal stability complied with the construction temperature specifications. However, the recrystallization of EPCMs was impeded by the molten asphalt binder matrix, resulting in a significant reduction in both the Tm and enthalpy. Therefore, these reductions should be taken into consideration when choosing an EPCM. Additionally, as liquid EPCM softens the binder, the absence of elasticity in solid EPCMs renders the binder stiff, thus reducing its resistance to deformation. These impacts were particularly noticeable in Styrene-Butadiene-Styrene modified asphalt due to the polymer network being dissolved by liquefication-EPCMs. To sum up, EPCMs with a higher Tm (40–60 ℃) may decrease their negative impact on deformation resistance, such as palmitic acid-myristic acid-methyl stearate mixtures.

Interweaving Elastic and Hydrogen Bond-Forming Polymers into Highly Tough and Stress-Relaxable Binders for High-Performance Silicon Anode in Lithium-Ion Batteries.

A central challenge in practically using high-capacity silicon (Si) as anode materials for lithium-ion batteries is alleviating significant volume change of Si during cycling. One key to resolving the failure issues of Si is exploiting carefully designed polymer binders exhibiting mechanical robustness to retain the structural integrity of Si electrodes, while concurrently displaying elasticity and toughness to effectively dissipate external stresses exerted by the volume changes of Si. Herein, a highly elastic and tough polymer binder is proposed by interweaving polyacrylic acid (PAA) with poly(urea-urethane) (PUU) elastomer for Si anodes. By systematically tuning molecular parameters, including molecular weights of hard/soft segments and structures of hard segment components, it is demonstrated that the mechanical properties of polymer binders, such as elasticity, toughness, and stress relaxation ability, strongly affect the cycling performance of Si electrodes. This study provides new insight into the rational design of polymer binders capable of accommodating the volume changes of Si, primarily by judicious modulation of the mechanical properties of polymer binders.

Dynamic Modulus Prediction Validation for the AASHTOWare Pavement ME Design Implementation in Egypt

Dynamic Modulus, E* is a crucial property of the hot mix asphalt (HMA). For the AASHTOWare Pavement ME design, E* is an essential material input. E* can be measured in the laboratory or predicted using different models based on some fundamental properties of the HMA. The NCHRP 1-37A and NCHRP 1-40D prediction models are the two main models adopted by the AASHTOWare to predict the E* based on the HMA mixture volumetrics, gradation, and binder properties. The main objective of this research was to validate these two prediction models using local HMA mixes for the purpose of the regional application of the AASHTOWare Pavement ME design in Egypt. For this purpose, the E* values of ten locally plant-produced HMA mixes were measured in the laboratory. The two E* prediction models were then used to estimate the E* values for the same materials. Consequently, the performance of both models was studied by comparing the measured values to the estimated values. The results showed that the NCHRP 1-40D prediction model can satisfactorily predict the E* of the Egyptian HMA mixes with minimal bias and high accuracy. The model yielded an adjusted coefficient of determination (R2) of 0.86 based on 480 E* measurements. On the other hand, the NCHRP 1-37A prediction accuracy was not satisfactory, with very poor accuracy (Adjusted R2 = 0.18) and high bias. Afterwards, the effect of the predicted E* from the NCHRP 1-40D model on the AASHTOWare Pavement ME predicted pavement performance in terms of rutting, cracking, and roughness was further studied. Accordingly, twenty-four simulation runs for typical Egyptian design cases were conducted using, first, the laboratory measured E* values and, then, the NCHRP 1-40D predicted E* values. The results showed that the NCHRP 1-40D predictions had no significant effect on the pavement performance predicted by the AASHTOWare Pavement ME with R2 of the different pavement distresses ranged from 0.980, for the AC rutting, to 0.9996 for the International Roughness Index (IRI). Hence, the NCHRP 1-40D model can be used satisfactorily to predict E* for the Egyptian HMA mixes without compromising the structural pavement design.

Operando FTIR-ATR with molecular dynamic simulations to understand the diffusion mechanism of waste tire-derived pyrolytic oil for asphalt self-healing

Recent research proves that pyrolytic oils from waste tires are effective in restoring the chemical and rheological properties of aged asphalt binders. Nonetheless, the role of oil-binder molecular interactions and bindeŕs aging degree on the diffusional behavior of the pyro-oils is still unclear. In this study, authors propose integrating operando Fourier Transformed Infrared Spectroscopy (FTIR) measurements with molecular dynamics (MD) simulations as a novel approach to unravel the diffusion mechanisms of pyro-oils in asphalt binders with self-healing purposes. The produced pyro-oils contains aliphatic and single-ring alkyl aromatic compounds as the most abundant species (ca. 80%). The operando FTIR measurements were correlated by a Fickian model, resulting in diffusion coefficients (D0) between 10-12 and 10-11 m2s−1. Moreover, MD simulations, with a molecular model of aged asphalt containing benzylic rings, sulfoxides, and hydroxyl functional groups, demonstrated that interactions of functional groups in the pyro-oil with the binder, hinder the diffusion behavior of the pyro-oil. The D0 estimated from the MD simulations agreed with those calculated from experimental data and previous reports for petro- and bio-derived rejuvenators. The predictive performance of the MD simulations developed in this study confirms to design of more resilient self-healing asphalt binders using a bottom-up strategy.

Research on low temperature properties and physical hardening effect of asphalt components

It is generally recognized in current research that asphalt binder is composed of four components, i.e., saturates, aromatics, resins and asphaltenes, and the physicochemical properties of asphalt binder are closely related to the properties of the components. In this paper, solvent precipitation and chromatographic column method were used to extract and separate a sufficient amount of four components, and different components were recombinant according to the original ratio to form components recombinant materials. Using Fourier Transform Infrared, dynamic shear rheometer and differential scanning calorimetry to characterize the chemical composition and low temperature rheological properties of single component and components recombinant materials, including amplitude sweeping, temperature sweeping, time sweeping temperature-frequency sweeping and relaxation test. The response of the material to the physical hardening effect at low-temperature isothermal storage was also explored. The test results show that, within the test temperature range, the aromatics does not produce physical hardening effect, while the saturates and resins produced a certain degree of physical hardening effect. The free volume, phase angle, and complex shear modulus have different response times to the physical hardening effect, so the free volume theory alone is not sufficient to explain the physical hardening effect. This paper proposes to use the method of area integral to evaluate the degree of response of materials to physical hardening, and to rank the materials.

Synergetic effect of superabsorbent polymer and shrinkage reducing admixture on the properties of alkali-activated slag binders

This research is to investigate the synergistic effects of superabsorbent polymer (SAP) and shrinkage-reducing admixture (SRA) on autogenous shrinkage, hydration and microstructure of alkali-activated slag system (AAS). Results revealed that the addition of SRA reduced the absorption capacity of SAP, resulting in a smaller size distribution of macrovoids throughout the AAS matrix. Nevertheless, the presence of SAP affected the ability of SRA to effectively reduce the surface tension of the pore solution of AAS. Instead, the addition of SAP resulted in an increase in surface tension by up to 14%. This phenomenon can be explained by the hydrophobic interactions between SAP networks and SRA molecules. The combination of SAP and SRA in AAS exhibited greater effectiveness in controlling autogenous shrinkage compared to using SRA alone, resulting in a reduction of around 53% compared to 46%. On the other hand, incorporating only SAP proved to be more effective, leading to a higher reduction of 90%. However, this combined effect is reported to be counteractive and dependent on the content of each component. Moreover, the hybrid system of SAP and SRA demonstrates a pronounced retardation effect on AAS hydration. The XRD patterns showed no new reaction products were formed. As revealed by SEM analysis, the microstructure of AAS containing SAP and SRA exhibited a distribution of microvoids ranging from 5 to 50 μm. This can explain the reduction of the compressive strength by incorporation a high content of SAP combined with SRA. However, incorporating a lower dosage of SAP is advantageous when combined with SRA in AAS systems. Finally, the integration of SAP and SRA had a positive influence on the properties of AAS mortars, thus compensating for the limitations of each constituent.

Effect of Simultaneous Changes in Asphalt Binder Bee Structure Components on Mechanical Properties during the Aging and Rejuvenation Process

The bee structure of an asphalt binder surface changes during the aging and rejuvenation process, and the effect of this microstructural change on the mechanical properties of the asphalt binder is not clear. Therefore, in this paper, a two-dimensional finite element model of an asphalt binder microstructure was constructed based on processed AFM images, and the contents of bee phases and bee casings were varied at the same time to analyze the stress and strain distribution law of the asphalt binder microstructure. The results of the study show that in the bee structure, the stress in the bee phase is obviously greater than that in the bee casing, and the stress in the interstitial phase is the lowest. With the simultaneous enhancement in the proportion of the bee phase and the bee casing, the stresses in the asphalt samples increased in all phase structures. Under the combined effect of the decrease in the content of the bee phase and the increase in the content of the bee casing, there is a certain degree of increase in the internal stresses and strains in the asphalt binder, the effect of the bee casing on the internal stresses in the asphalt binder is more pronounced, and the bee phase and the bee casing play better roles in resisting the external deformation due to the increase in the volume fraction. For a recycled asphalt binder, whether there is an increase in the dosage of the old asphalt binder or an enhancement in the interfacial diffusion and a fusion of new and old asphalt binders, the level of tensile strain within the recycled asphalt binder will increase to a certain extent, which, in turn, will put forward a higher requirement for its anti-cracking ability.

Utilization of Atomic Force Microscopy (AFM) in Characterizing Microscopic Properties of Asphalt Binders: A Review

Abstract Atomic force microscopy (AFM) is a powerful tool that can effectively reveal the intricate relationship between the microstructure and micromechanical properties of asphalt binders, as well as their subsequent influence on macro-level performance. Thus, it plays a crucial role in the design and development of new asphalt materials. The objective of this review is to analyze the literature on the microscopic characterization of asphalt binders using AFM and to provide a reference for designing high-performance asphalt materials based on micromechanisms. This review begins by discussing various AFM-based characterization techniques for asphalt binders, such as morphology imaging, tip modification, atomic force microscopy-infrared (AFM-IR), nanorheological tests, and in situ tests. Next, the sample preparation methods and their impact on the test results are discussed. Then the composition-structure-mechanics relationship of asphalt binders, including the chemical composition of bee structures, surface and bulk microstructures, and macroproperties of asphalt binders are analyzed. Furthermore, we summarize the current applications of AFM in asphalt studies. Lastly, we discuss the challenges and future directions of AFM-based characterization methods of asphalt binders, emphasizing the research prospects of nanorheological testing methods.

Characterization of Self-healing Properties of Asphalt Pavement Materials Containing Carbon Nanotubes: from the Binder and Mix Level based on Grey Relational Analysis

Asphalt pavement cracks not only reduce road life and affect traffic safety but also increase maintenance costs. These issues can be solved significantly if microwave heating (MH) technology is applied based on the self-healing mechanism. This work aims to adopt carbon nanotubes (CNTs) to modify asphalt binders to accelerate their self-healing properties. Thermal conductivity and diffusivity, high-temperature rheological characteristics, and fatigue resistance were conducted to investigate healing potential from binders level; semicircular bending (SCB) tests and MH test were used to assess the fracture and self-healing properties from mix level; Grey relational analysis (GRA) was employed to study the relevance of asphalt binder properties on the healing properties of mixes. Results indicated that CNTs could improve asphalt binders' thermal conductivity, thermal diffusivity, high-temperature deformation resistance, and anti-fatigue properties. However, the Jnr-diff results suggest that the content of CNTs needs to be controlled within 1.0%. From the mixtures perspective, samples with 1.0% content of CNTs can achieve the best fracture performance and healing efficiency with excellent heating uniformity and no overheating problems. Furthermore, thermal performance strongly correlates with mixtures' healing indexes. This research addresses the maintenance of asphalt pavement cracks, which is essential for long-life pavements and sustainable road development.