Multiple Stress Creep Recovery Test Research Articles

Linking Chemical Structure to the Linear and Nonlinear Properties of Asphalt Binders

The study described in this paper aims to establish the relationship between the chemical composition and rheological properties of asphalt binders in both the linear viscoelastic (LVE) and nonlinear viscoelastic (NLVE) domains. Two asphalt binders with different penetration grades were subjected to four distinct aging treatments of varying severity, resulting in changes in their chemical fingerprints. Chemical characteristics of the asphalt binders were analyzed using thin-layer chromatography (TLC), Fourier Transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC). Frequency sweep tests were conducted to evaluate the LVE behavior of the asphalt binders, while multiple stress creep recovery (MSCR) tests were employed to assess their NLVE properties. With regard to the LVE properties, rheological index ( R) and zero shear viscosity (ZSV) derived from the Christensen-Anderson-Marasteanu (CAM) model exhibited high correlations with FTIR and molecular weight distribution (MWD) parameters. Additionally, the polydispersity index (PDI) displayed a stronger correlation with LVE-based parameters. Findings from the MSCR tests revealed that the sensitivity of the percentage recovery ( %R) to chemical composition, as opposed to nonrecoverable creep compliance ( Jnr), can be largely attributed to the degree of nonlinearity. Furthermore, it was observed that lower molecular weight molecules exert a greater influence on %R in the nonlinear domain. Finally, it was found that Jnrslope is a more reliable parameter than Jnrdiff for assessing the effects of chemical makeup on stress and temperature sensitivity.

Evolution of aging depth gradient distribution in SBS-modified bitumen during the aging of field

This study investigated the distribution of aging depth gradients in styrene-butadiene-styrene modified bitumen (SBSMB) during natural aging. SBSMB was sourced from bitumen recycling tests and was stratified into upper, middle, and lower layers according to depth. To examine the effects of various aging depths, SBSMB samples from different depths were prepared for subsequent bitumen recycling tests. Then, studying the rheological performance of the SBSMB involved conducting multiple stress creep recovery tests. Subsequently, investigating the bee structure and nanoscale indicators of SBSMB at various aging depths involved utilizing atomic force microscopy testing. Finally, the Verhulst model was applied to assess the aging of SBSMB at different depths. The results have shown that natural aging has gradually diffused from the surface to the interior of the bitumen. An increase in aging time leads to a more pronounced aging effect at the upper levels and an accelerated the downward diffusion rate. This ultimately results in a gradient behavior of the rheological properties of SBSMB at different depths. The quantity of bee structures and the distribution density of bee structures in SBSMB both progressively decrease with increased aging depth. As aging time increases, the aging properties of SBSMB exhibit significant gradient behavior at different depths. Simultaneously, the Verhulst model accurately explain the aging trend of bitumen at different nanoscale depths.

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

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

Study of High-Temperature Rheological Properties of Emulsified Asphalt Residues

The residue of emulsified asphalt is its final state when it becomes part of an asphalt mixture. Therefore, the mechanical properties of the residue have a significant impact on the performance of emulsified asphalt mixtures. Dynamic shear rheological tests and fluorescence microscopy were conducted to explore the effects of emulsification and aging on the rheological properties and micro-morphology of emulsified asphalt residue. The results of both the temperature sweep and multiple stress creep recovery tests indicated that the emulsification of the asphalt had different effects on the rheological properties of the base asphalt and the styrene-butadiene-styrene (SBS)-modified asphalt. For the base asphalt, emulsification increases the complex shear modulus by about 5% and reduces irrecoverable creep flexibility by 30%. However, the physical grinding effect of the colloid mill during the emulsification process could destroy the internal spatial network structure of SBS, leading to a reduction in the complex shear modulus by about 5% and a 10% increase in irrecoverable creep flexibility. This phenomenon is similar to the aging of SBS-modified asphalt, which, in turn, leads to a decline in the performance of emulsified SBS-modified asphalt residues.

Multiple Stress Creep Recovery of High-Polymer Modified Binders: Consideration of Temperature and Stress Sensitivity for Quality Assurance/Quality Control Policy Development

High polymer-modified binders (HiPMBs) have recently been introduced in the Gulf region, where pavement structures are commonly subjected to severe climate conditions and heavy traffic loads because there is no enforcement of weight limits. Local agencies are currently modifying quality assurance/quality control (QA/QC) policies to accommodate such technology. In this study, HiPMBs produced by different refineries were subjected to physicochemical and thermal characterizations to investigate the compositional variability of industrial HiPMBs. Their thermal and stress susceptivity was then assessed through multiple stress creep recovery (MSCR) tests. The validation of the MSCR-based hierarchy was performed by assessing nine hot mix asphalts (HMAs) through repeated load permanent deformation tests and performing mechanistic-based structural analysis. Results showed that styrene-butadiene-styrene (SBS) is not the only modifier added to the bitumen, as commonly done in laboratory settings. These undisclosed modifiers disrupt the correlation between MSCR results and SBS concentration typically observed in laboratory-prepared HiPMBs, highlighting the importance of investigating plant-produced binders. Moreover, higher temperatures and stress levels returned different MSCR performance hierarchies among binders, questioning the effectiveness of the current MSCR test protocol for HiPMBs. Additionally, findings confirmed that the current MSCR testing protocol does not correctly assess the bitumen response in HMAs. A higher MSCR stress level shall be prescribed in the local QA/QC specifications to ensure the correct selection of HiPMBs in the region. This study can be used as a framework for other countries actively engaged in the implementation of HiPMBs and novel bituminous materials.

Evaluation of Asphalt Binder and Mixture Properties Utilizing Fish Scale Powder as a Biomodifier

Fish represent an abundant and underutilized waste product from the fishing industry. This study investigated the effects of incorporating fish scale powder (FSP) at various dosages (3%, 6%, 9%, and 12%) on the properties of asphalt binder and mixtures. Conventional tests, viscosity, storage stability, Fourier transform infrared spectroscopy, and multiple stress creep recovery tests were conducted on the binder. Mix design, wheel tracking, indirect tensile strength, fatigue, and ultrasonic pulse velocity tests were evaluated for the asphalt mixtures. The results showed that FSP increased binder stiffness and reduced temperature susceptibility but compromised low-temperature performance and workability regardless of dose. The storage stability test results showed improved high-temperature storage stability. In the mixtures, the permanent deformation resistance increased with increasing FSP content, decreasing the rut depth from 4.3mm for the control to 2.9mm at 12% FSP. The moisture damage resistance, indicated by the tensile strength ratio, increased from 90% for the control to 94.1% at 12% FSP. However, the fatigue life decreased from 14,010 cycles for the control sample to 11,190 cycles at 12% FSP. The dynamic and elastic modulus values before conditioning increased with higher FSP dosages, and this increasing trend was also observed after conditioning, signifying greater stiffness retention and moisture resistance of the asphalt mixtures containing higher amounts of FSP. Numerically, the 6-9% FSP range offered the optimum balance, enhancing the rutting resistance by 18% and moisture resistance by 3.2% compared to those of the control, while limiting the fatigue life to 12% and maintaining the workability. Overall, fish scale powder has potential for use as an asphalt biomodifier by transforming an environmental liability into a value-added sustainable paving material.

Thermal Oxidative Aging Effect on Chemo-Rheological and Morphological Evolution of Crumb Rubber Modified Asphalt Binders with Wax-Based Warm Mix Additives

Wax-based warm mix additives can decrease the viscosity and improve the workability of crumb rubber (CR)-modified asphalt, but the mechanism of influence on the aging performance of CR-modified asphalt is not clear. To investigate the thermal aging behavior and mechanism of wax-based warm mix CR-modified asphalt, polyethylene wax (PEW) and polyamide wax (PAW) were mixed to prepare warm mix CR-modified asphalt. The effect of thermal aging on the rheological and mechanical properties was characterized by a basic property test, frequency sweep test, and multiple stress creep recovery test. The chemical composition changes during aging were then analyzed by Fourier transform infrared spectroscopy and gel permeation chromatography. Finally, the phase morphology during thermal aging was observed by fluorescence microscopy. The results showed that compared with the degradation of CR, the oxidative aging of the asphalt binder played a dominant role in the process. Not only did PEW and PAW attach to the asphalt surface in the form of crystallization to prevent its reaction with oxygen but they also promoted the dissolution of CR, and released polymerization chains, thereby enhancing the antiaging properties of CR-modified asphalt. Furthermore, the antiaging of PAW/CR-modified asphalt was better than that of PEW/CR-modified asphalt, because the amide group of PAW reacted with CR-modified asphalt to form a polymer structure.

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

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

Development of dynamic shear-rheology-based method to improve evaluation of swelling degree of recycled crumb rubber in asphalt rubber

Inappropriate disposal of substantial scrap tires has become an unavoidable and imminent environmental concern. Asphalt rubber (AR) facilitates the value-added recycling of scrap tires into eco-friendly and durable pavement, showcasing immense potential for pollution alleviation and resource conservation. In preparing AR, the swelling effect of rubber plays a dominant role in the gel-like network formation and performance enhancement of the modified asphalt. Accordingly, it is crucial to accurately evaluate the rubber swelling degree for guiding AR preparation and mixture design. Existing research mainly relies on measuring the volume of expanded rubber particles to assess the rubber swelling degree, which requires sophisticated instruments or a cumbersome process of extracting the crumb rubber. In this study, a method was proposed to conveniently evaluate the swelling degree of crumb rubber based on the dynamic shear rheological indicators. Firstly, the base asphalt was mixed with crumb rubber at different levels of time to prepare AR binders with varying swelling degrees. The mechanical properties (i.e., elastic recovery) and physical properties (i.e., volume expansion) were measured and analyzed to investigate the impacts of swelling time on AR properties. Secondly, the rheological properties of AR with different swelling degrees were measured via temperature sweep (TS) test, multiple stress creep recovery (MSCR) test, and linear amplitude sweep (LAS) test. Thirdly, the particle effect (PE) and interaction effect (IE) values were calculated, and the swelling degrees were determined based on the variations of PE values. Relationships between swelling degrees and PE-related indicators were established to facilitate the development of the new evaluation method. Finally, the swelling degrees evaluated by the newly developed method were compared with volume expansion to validate its reliability. The results from different rheology tests were also used to verify the feasibility of the proposed method, and the prediction of swelling degree against the swelling time was established. The findings of this research provide references for evaluating the swelling degree of crumb rubber conveniently and accurately.

Chemical and Rheological Properties of Bitumen Partially Substituted with Rice-Straw-Based Lignin from Bio-Ethanol Industry Residue

The objective of this study is to evaluate the changes in the chemical and rheological properties of bitumen when partially substituted, up to 15%, with rice-straw-based lignin materials, namely isolated lignin (IL) and fermentation residue lignin (FRL), obtained from second-generation bio-ethanol industry residues. Attenuated total reflectance-Fourier transform infrared spectroscopy was used to evaluate the alterations in chemical properties. The rheological properties that were assessed include Superpave upper performance grade (PG), rutting resistance using the multiple stress creep recovery test, and fatigue resistance using the linear amplitude sweep test. The results indicated that the addition of IL and FRL materials to the base bitumen is a physical process. Furthermore, IL and FRL substituted bitumen blends exhibited distinct trends for carbonyl (C=O) and sulfoxide (S=O) functional groups with ageing, depending on the chemical structure of the additive. Specifically, the IL materials showed a reduction in the rate of increase of ageing products and a decrease in the combined ageing index, up to 10% IL dosage, suggesting some antioxidant effect within the group. The addition of IL up to 15% dosage and FRL up to 10% dosage also led to an increase in the base binder high-temperature grade from PG70-XX to PG76-XX. Moreover, both IL and FRL materials enhanced rutting resistance and reduced fatigue resistance with an increase in dosage. It is worth noting that bitumen blends with different additives showed varying trends between chemical and rheological properties.

Evolution of Rheological and Microscopic Properties of Asphalt Binders under Fuel Corrosion

Vehicle fuel leaks can adversely affect the performance of asphalt pavements. To study the mechanisms of fuel corrosion damage in asphalt, four asphalt binders were selected in this study, and the evolution of their rheological and microscopic properties was investigated. Fuel corrosion caused continuous mass loss in asphalt binders. Base asphalt lost more than 50% of its mass after 24 h of fuel corrosion, while modified asphalts had better resistance. According to dynamic shear rheometer tests and multiple stress creep recovery tests, modifiers improved the high-temperature rheological properties of these asphalt binders. As the degree of fuel corrosion deepened, the indexes characterizing the high-temperature performance deteriorated. Rubber-modified asphalt showed the best resistance to high-temperature deformation, while the performance of LDPE-modified asphalt was more stable. In contrast, fuel corrosion improved the resistance of asphalt binders to low-temperature cracking to some extent: the creep strength (S) decreased as the creep rate (m) increased, and the resistance of SBS-modified asphalt to low-temperature cracking was optimal, with a 36% decrease in S-value after 24 h of fuel corrosion. Fourier transform infrared spectroscopy tests showed that diesel corrosion was a process of this physical dissolution, with no change in the chemical functional groups. Meanwhile, by using fluorescence images and analyzing the four-component test results, we found that fuel corrosion disrupted the stabilized structure formed by the modifiers, and the heavy components in the asphalt binders were converted into light components. This study reveals the evolution of the rheological and microscopic properties of asphalt under fuel corrosion, which can provide a reference for the optimization of fuel corrosion resistance in asphalt pavement.

Experimental study on the effect of Coumarone resin on the performance of SBS-modified asphalt.

An inexpensive and high-performing solid Coumarone resin was added to Styrene-butadiene-styrene (SBS) copolymer-modified asphalt to enhance its storage stability and road performance. To assess the effect of Coumarone resin dosage on the SBS-modified asphalt, a series of laboratory tests were conducted. The composite modified asphalt's segregation test was used to evaluate its storage stability, Dynamic Shear Rheometer (DSR) and Multiple Stress Creep Recovery (MSCR) tests were employed to investigate its high-temperature performance and permanent deformation resistance, and the Bending Beam Rheology (BBR) test was utilized to measure its low-temperature performance. Fluorescence microscopy was used to observe the composite modified asphalt's microstructure, and Fourier Transform Infrared Spectroscopy (FTIR) was conducted to study the changes in chemical structure during the modification process. The results showed that Coumarone resin can improve the compatibility of SBS and asphalt, improve the high-temperature performance and deformation resistance of SBS-modified asphalt, and adding an appropriate amount of Coumarone resin can help enhance the low-temperature cracking resistance of modified asphalt. The optimal dosage of Coumarone resin recommended for SBS-modified asphalt performance enhancement is 2% under the test conditions, as determined by comparing the test results of samples with various dosages.

Enhancing aged SBS-modified bitumen performance with unaged bitumen additives

This study investigated the performance of SBS-modified bitumen (SBSMB) after aging and rejuvenation by utilizing macroscopic performance and microscopic characterization methodologies. The blending of aged SBS-modified bitumen (SBSPAV) with different proportions of SBSMB or 80–100 penetration grade base bitumen (90BB) was performed to produce SMB-rejuvenated bitumen (a blend of SBSMB and SBSPAV) and 90BB-rejuvenated bitumen (a blend of 90BB and SBSPAV). To evaluate high-temperature rutting behavior, multiple stress creep recovery (MSCR) tests were conducted on the binders, and the outcomes were analyzed using the Burgers model to elucidate their viscoelastic behaviors. Low-temperature performance was assessed using an asphalt binder cracking device (ABCD). Furthermore, the microscopic structure, roughness, and Young's modulus of the binders were investigated using an atomic force microscope (AFM). Thermal stability was assessed using a thermogravimetric analyzer (TGA). The findings indicated that SMB-rejuvenated bitumen exhibited favorable resistance to high temperatures and the ability to withstand heavy traffic loads. The stress sensitivity of 90BB-rejuvenated bitumen surpassed that of SMB-rejuvenated bitumen. The high-temperature performance rating of 90BB-rejuvenated bitumen displayed a continuous decline, indicating poor load-bearing capacity. Regardless of the unaged bitumen type, higher doses of unaged bitumen led to a gradual decrease in the rejuvenated bitumen's cracking temperature, indicating the enhancement of low-temperature performance of SBSPAV. However, both SMB-rejuvenated bitumen and 90BB-rejuvenated bitumen fell short of matching the performance level of pure SBSMB. AFM outcomes demonstrated that with increasing SMB dosage, the number of bee-like structures initially decreased before rising again, coupled with an increase in their volume. Conversely, an increase in 90BB dosage led to a gradual reduction in bee-like structures, accompanied by increased volume. The roughness of both SMB-rejuvenated bitumen and 90BB-rejuvenated bitumen exhibited improvements compared to SBSPAV, suggesting enhanced adhesion performance of the rejuvenated bitumen. TGA results unveiled lower thermal stability in 90BB-rejuvenated bitumen in comparison to SMB-rejuvenated bitumen. This study introduces a novel perspective on the design of SBS-rejuvenated bitumen.

Study on high-temperature performance evaluation of asphalt mixtures with anti-rutting additives

<abstract><p>In order to investigate the asphalt mixture enhancement due to the granular anti-rutting additives, the multiple stress creep recovery (MSCR) test and wheel tracking test were performed to examine the effects of three anti-rutting additives on the high-temperature performance of binders and mixtures, respectively. Further, the interaction mechanism between anti-rutting additives and asphalt binder was revealed via a fluorescence microscopy (FM) test. The results indicate that the incorporation of anti-rutting additives causes a substantial increase in elasticity behavior for binders, along with a massive enhancement of dynamic stability for mixtures. Further, the enhancement of performance is not conclusively determined by the compatibility between the additive and asphalt. Instead, unmelted viscous-flow additives contribute to the enhancement of mixtures by interlocking, filling voids, cementing and wrapping the aggregate, which are essential mechanisms of mixture modification. This study contributes to selecting appropriate additives in engineering and enhancing anti-rutting additives based on their modification mechanism.</p></abstract>

Investigation of the influence of the variable-intensity ultraviolet aging on asphalt properties

Currently, researches related to asphalt UV aging mostly based on constant-intensity UV radiation, which is not consistent with its real service condition. In this study, the variable-intensity and constant-intensity UV radiation conditions were proposed on the principle of constant total radiation. The UV-aged neat asphalt film thickness was 1 mm and 0.5 mm. The temperature sweep, frequency sweep, and multiple stress creep recovery tests were conducted to reveal the rheological properties of UV-aged neat asphalt. Moreover, the Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) tests were performed to reveal the microscopic properties of UV-aged asphalt. Regarding the constant-intensity UV-aged asphalt with 1 mm film thickness, the rutting parameter aging index (RPAI) of 9 cycles was smaller than that of RTFO-aged asphalt. The variable-intensity UV aging induced a much larger aging effect than constant-intensity UV aging for UV-aged asphalt. The ISO and ICO under variable-intensity UV aging conditions is higher than constant-intensity UV aging for the same cycles. Besides, the asphalt thickness is an essential element affecting UV aging. The aging effect increased significantly as the film thickness decreased. SEM test results have indicated that the variable-intensity UV aging caused more microscopic morphology damage to asphalt than constant-intensity UV aging. Variable-intensity UV aging test condition proposed in this study is more accurately simulate the real service conditions. It is meaningful to propose the variable-intensity UV aging process. This study provides new ideas for simulating UV aging conditions and methods in the laboratory.

The Combined Effects of Additives on the Conventional and High-Temperature Performance Properties of Warm Mix Asphalt Binders.

The present study investigates the effects of the simultaneous use of two additives, an organosilane warm mix asphalt (WMA) agent and a grade-bumping polyolefin compound, on the conventional and high-temperature performance properties of a paving grade 50/70 bitumen and a polymer-modified 45/80-55 bitumen. The WMA agent and polyolefin additive were introduced to the binders at rates of up to 0.3% and 2%, respectively. The base asphalt binders and their blends with the additives were tested before and after aging in a rolling thin film oven test at a temperature of 143 °C. The effects of the investigated additives were found to be dependent on the type of base binder and its aging state. It was generally observed that the WMA additive decreased the performance of the asphalt binders and limited the effects of the other additive, which increased the high-temperature stiffness and non-recoverable compliance of the blends. This interaction amounted to as much as an approx. 20% decrease in high-temperature stiffness and non-recoverable compliance of the binders. The additives caused a small increase in the elasticity of the binders and improved their creep performance when measured in multiple stress creep recovery tests.

Effect of polyisobutylene on low-temperature thermoreversible aging properties in asphalt binders

In order to study the influence of polyisobutylene (PIB) on pavement performance of asphalt binders, two asphalt binders with large differences in wax content and the similar performance grades were selected as the base asphalt binders, and three kinds of waxes and PIB were selected as additives. Extended bending beam rheometer (Ex-BBR) test, double-edge-notched tension (DENT) test, multiple stress creep recovery (MSCR) test and rotational viscosity test were used to study the effect of PIB on the low, medium and high temperature properties of asphalt binders, respectively. The phase transition pattern of PIB when interacting with waxes was analyzed by variable temperature polarizing microscope (VT-PLM). The results show that PIB can be miscible with waxes and reduce the melting point of waxes by about 20∼60%. PIB can improve the low-temperature performance (reducing creep stiffness), medium-temperature performance (increasing toughness and fracture resistance), high-temperature performance (improving high-temperature deformation resistance and deformation recovery ability) and workability (reducing mixing and compaction temperature) of asphalt binders (including high-wax and wax-based warm-mixed asphalt binders). It is worth noting that PIB will aggravate the thermoreversible aging (the results of P-value analysis showed that PIB had a significant effect on the grade loss (GL) of asphalt binders), which will affect the low-temperature performance of asphalt binders during the isothermal low-temperature storage, resulting in premature damage to the pavement.

Investigating the rheological behaviour of styrene–butadiene–styrene modified asphalt

The rheological properties of the styrene–butadiene–styrene modified asphalt (SBSMA) binder have not been thoroughly investigated yet. In this study, SBSMA binders with various SBS contents and base asphalt types were prepared and analysed. Fluorescence microscopy, temperature sweeping, and multiple stress creep recovery (MSCR) tests were conducted to analyse the phase structure and rheological behaviour of SBSMA. The results indicate that the special rheological behaviour of a decreasing phase angle value in SBSMA as the temperature increases is a result of the gradual dominance of the network structure over SBSMA’s rheological behaviour. Results from MSCR tests indicate that with the increase in stress levels, the elasticity of the network structure gradually diminishes, signifying a significant stress sensitivity in the network structure. Consequently, due to the stress sensitivity of the network structure, traditional rheological indicators measured at low stress levels (such as phase angle, elastic recovery rate) may overestimate the elasticity of SBSMA at high temperatures (40–80°C).

Chemical and rheological analysis of unaged and aged bio-extended binders containing lignin

The use of alternative renewable sources to totally or partially replace bitumen is one of the most current challenges in the road pavement sector. The growing energy cost and environmental concerns lead to the necessity to find alternative solutions, by supporting at the same time sustainability and circular economy principles. Within this framework, this paper presents the application of a powder lignin, a natural bio-polymer deriving from by-products of wood pulp and paper industry, to replace part of bitumen. The bituminous blend consisting in 70% of bitumen and 30% of powder lignin (by weight) was made in laboratory through the use of a high shear stirring mixer, and a reference plain bitumen characterized by a similar consistency (i.e., same penetration grade) was used as comparison. Then, an extensive investigation on chemical and rheological properties of the bio-binder is presented. Fourier transform infrared spectroscopy (FTIR), saturates, aromatics, resins and asphaltenes (SARA), bending beam rheometer (BBR), frequency sweep tests and multiple stress creep recovery tests (MSCR) with a dynamic shear rheometer (DSR) were performed. Moreover, unaged, short- and long-term aging conditions were considered. Results indicated that powder lignin dominates the rheological behavior of the bio-binder and, from chemical analysis, it seems that it partially acts as a filler and partially as a binder. This would result in improved performances at both low and high temperatures, leading to a wider temperature range of performance grade (PG). Moreover, despite a stiffening effect is recognized, lignin also offers an antioxidant potentiality, reducing the aging susceptibility of the investigated bio-binder.

Prediction of asphalt binder elastic recovery using tree-based ensemble bagging and boosting models

The Multiple Stress Creep Recovery (MSCR) test has been proposed and implemented over the last two decades as an alternative to traditional tests, especially the elastic recovery (ER) test, to better capture rutting resistance. This paper presents a study on predicting asphalt binder ER using MSCR test results through ensemble learning methods, based on a database of more than 700 points for mostly polymer-modified binders. The ensemble approach involved tree-based Bagging (Random Forest and Extra Trees) and Boosting (Adaboost, gradient boosted decision tree, XGBoost, LightGBM, and CatBoost). The findings revealed the effectiveness of ensemble learning methods in capturing complex relationships within the data. Extra Trees and XGBoost emerged as the most accurate models based on coefficient of determination, mean absolute error, and root-mean-square error, compared to the other mentioned models and Neural Networks. These models offer precise predictions of asphalt binder ER from MSCR test results, surpassing the ER-DSR test proposed in the literature. Recovery at stress levels of 0.1 and 3.2 kPa were identified as the top influential features. In addition, clustering methods were employed to detect patterns within the dataset. The outcomes highlighted difficulties in discerning binders based on existing MSCR parameters, suggesting opportunities for refining MSCR analysis, and exploring additional tests to improve the distinction among asphalt binders. This investigation provides practical implications for states still utilizing PG-Plus, promoting the adoption of MSCR specifications for asphalt binder characterization.