Creep Recovery Research Articles

Exact solution for hygro-thermo-mechanical creep and recovery of viscoelastic laminated beam

In order to predict the creep and recovery behaviors of for viscoelastic laminated beam in hygro-thermo-mechanical (HTM) coupled condition, an exact analytical solution is proposed. This solution considers two effect mechanisms: temperature and humidity, including the expansion difference and the variation of viscoelastic properties. In the analytical model, the stresses and displacements of each lamina are described based on the hygro-thermo-elasticity theory combined with the Boltzmann superposition. By employing series expansion, the transfer matrix method, and Laplace transform, the solution is determined analytically. Notably, the entire process of Laplace inverse transformation is carried out analytically without relying on any numerical approximations. The comparison analysis indicates that the proposed solution is more computationally efficient than the finite element counterpart and is more accurate than the solutions based on transverse shear deformation assumption. By analyzing the components of the proposed solution, a modified superposition principle applicable to HTM coupled conditions and a superposition principle for creep recovery are derived. In the end, the HTM coupled behavior, the bending creep and recovery as well as the optimization of expansion coefficient are investigated in detail.

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.

Evaluation of the Thermal Stability and Micro-Modification Mechanism of SBR/PP-Modified Asphalt.

To evaluate the thermal stability of composite polymer-modified asphalt, thermoplastic elastomer styrene-butadiene rubber (SBR)/polypropylene (PP) pellets were prepared using a hot-melt blending technique, with butyl rubber powder and waste polypropylene pellets as raw materials. The effects of different evaluation indexes on the thermal stability of SBR/PP-modified asphalt were investigated using a frequency scan test and a multi-stress creep recovery (MSCR) test, and the compatibility of SBR/PP particles with asphalt was studied using the Cole-Cole diagram and microstructure images. The tests show that, firstly, the performance grade (PG) classification of asphalt can be improved by adding an SBR/PP thermoplastic elastomer to enhance the adaptability of asphalt in high- and low-temperature environments, and the evaluation separation index can reflect the high-temperature storage stability of composite-modified asphalt more reasonably. Additionally, the larger the rubber-to-plastic ratio the worse the high-temperature thermal stability of composite-modified asphalt. Moreover, the addition of additives to the composite particles can promote the SBR/PP particles in the asphalt to be more uniformly dispersed, forming a more desirable microstructure and improving the thermal stability of composite-modified asphalt. Ultimately, the semicircular curve of the Cole-Cole diagram can reflect the compatibility characteristics of the two-phase structure of SBR/PP-modified asphalt, which can be used as an auxiliary index to evaluate the compatibility of polymer-modified asphalt.

Rate dependent short-term creep and creep recovery of normal concrete

Understanding the rate effect is crucial for enhancing the safety assessment of concrete structures. It has been observed that creep of cement paste exhibits rate dependency at the micron scale. This study investigates the rate-dependent behavior of short-term creep and creep recovery in concrete at the macroscopic level. Short-term creep tests under varying loading rates were conducted in the study, using two different concrete mix proportions. The experimental results reveal that the creep strain, residual strain, and recovery strain of concrete increase with the loading and unloading rates. The study also introduces a modified fractional-order viscoelastic model, which accurately fits the experimental results of creep and creep recovery. The research concludes that as the loading time increases, the creep strain increases, mainly in the form of an increase in irrecoverable strain. The linear correlation between residual strain and creep strain is associated with the rate of loading and unloading. At a loading rate of 7 kN/s, there is a nonlinear escalation observed in the residual strain.

Evolution of Structure and Properties of SBS-Modified Asphalt during Aging Process

To explore the performance evolution mechanism of SBS-modified bitumen (SMB) during construction and service, the chemical structure, molecular weight and properties of styrene–butadiene–styrene triblock copolymer (SBS) and SMB under multiple aging levels were assessed via Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC) and a dynamic shear rheometer (DSR). The results indicate that the polybutadiene segments in SBS are susceptible to oxidative degradation, and the molecular weight of SBS decreases rapidly during the aging process. The complex modulus and temperature sensitivity of SMB show relatively small changes during the early aging stage, which is mainly attributed to the impact of SBS oxidative degradation. While its temperature sensitivity decreases sharply after double PAV aging, it means the influence of asphalt aging on its performance is dominant. And there is a significant difference in the effect of aging on the creep recovery behavior of SMB under high and low shear stresses. The percentage recovery (R) of SMB decreases and then increases under low shear stress as aging progresses. While the value R of SMB increases gradually under high shear stress with the extension of aging. Meanwhile, the viscoelastic properties of SMB have gradually transformed to those of aged matrix asphalt after serious aging, which is also confirmed by the gradual destruction and degradation of the SBS cross-linked network in the binder from a fluorescence micrograph. This research will help to understand the performance failure mechanism of SMB during service, providing a theoretical reference for the selection of maintenance and renovation opportunities during the service process of SBS-modified asphalt pavement, as well as the avenue to achieve high-performance recycling.

Influence of rejuvenator components on rheological properties of recycled bitumen in the full temperature range

Recovering aged bitumen from reclaimed asphalt pavement (RAP) is crucial for the evolution of pavement recycling. This study delves deeply into the effects of rejuvenator components on the rheological properties of rejuvenated bitumen across a wide temperature range. The investigation utilized the rolling thin film oven test (RTFOT) and the pressure aging vessel (PAV) test to simulate the short-term and long-term aging of the bitumen binder, respectively. Four distinct rejuvenators were then applied to recover the bitumen at varied aging levels. Detailed chemical analyses, encompassing the four-fraction (SARA) method and Fourier transform infrared spectroscopy (FTIR), were employed to identify the chemical compositions and key functional groups of both the rejuvenators and the rejuvenated bitumen. The rheological behavior of rejuvenated bitumen was assessed through a comprehensive series of tests, including conventional, temperature sweep, frequency sweep, multiple stress creep recovery (MSCR), linear amplitude sweep (LAS), and bending beam rheometer (BBR) tests. A Pearson correlation analysis highlighted a significant positive association between specific rejuvenator components, notably asphaltene (As), saturate (S), and aromatic (Ar), and the high-temperature performance of the rejuvenated bitumen. The findings of this research offer insights into the formulation of rejuvenators, potentially enhancing the performance of rejuvenated asphalt pavements and facilitating sustainable infrastructure advancements.

Noncovalent Conjugates of Anthocyanins to Wheat Gluten: Unraveling Their Microstructure and Physicochemical Properties.

Intake of polyphenol-modified wheat products has the potential to reduce the incidence of chronic diseases. In order to determine the modification effect of polyphenols on wheat gluten protein, the effects of grape skin anthocyanin extract (GSAE, additional amounts of 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%, respectively) on the microstructure and physicochemical properties of gluten protein were investigated. The introduction of GSAE improves the maintenance of the gluten network and increases viscoelasticity, as evidenced by rheological and creep recovery tests. The tensile properties of gluten protein were at their peak when the GSAE level was 0.3%. The addition of 0.5% GSAE may raise the denaturation temperature of gluten protein by 6.48 °C-9.02 °C at different heating temperatures, considerably improving its thermal stability. Furthermore, GSAE enhanced the intermolecular hydrogen bond of gluten protein and promoted the conversion of free sulfhydryl groups to disulfide bonds. Meanwhile, the GSAE treatment may also lead to protein aggregation, and the average pore size of gluten samples decreased significantly and the structure became denser, indicating that GSAE improved the stability of the gluten spatial network. The positive effects of GSAE on gluten protein properties suggest the potential of GSAE as a quality enhancer for wheat products.

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.

Low-pollution asphalt: Road performance, emission reduction efficacy, and modification mechanism

To further improve the emission reduction efficiency and enhance the road performance of emission reduction modified asphalt. A low-pollution asphalt (TBD-A) was prepared with tourmaline, biochar, and diatomite (TBD). A testing and evaluation method for the emission reduction efficacy of TBD-A has been proposed. The road performance of TBD-A was evaluated based on DSR, MSCR, BBR, and LAS. The evolution law of the emission reduction effect of TBD-A was clarified. Based on DSC, FTIR, and TG, the improvement mechanism of the road performance and emission reduction mechanism of TBD-A were revealed. The results show that the high-temperature performance, creep recovery ability, and fatigue life of TBD-A increase with TBD content rising. The low-temperature performance of TBD-A is superior to that of asphalt slurry. Controlling the TBD content and temperature can ensure the excellent low-temperature performance of TBD-A. The emission reduction efficacy of TBD-A increases as temperature and adsorption time rise. The comprehensive emission reduction rate of TBD-rubber-powder asphalt is the highest, reaching 64% at 190 °C. TBD and asphalt are physically blended. TBD increases asphalt's glass transition temperature while decreasing the thermal decomposition rate. The temperature stability and sensitivity of asphalt have been improved. Asphalt harmful substances are adsorbed by the multi-level pore structure of TBD, as well as are reduced and degraded by the spontaneous polarization effect.

Exploring the interplay between thermo-oxidative degradation and asphalt aging in thermoplastic polyurethane-modified asphalt: Mechanisms, properties, and performance evolution

The aging behavior of thermoplastic polyurethane-modified asphalt (TPUMA) is intricate and the mechanisms of its thermal degradation are not well understood. This study examines the viscoelastic, chemical and morphological characteristics of thermoplastic polyurethane modified asphalt (TPUMA) under different aging conditions (RTFOT/PAV). The rheological master curve model of the S parameter was used to analyze the fitting effect on TPUMA, with SBS (styrene–butadiene–styrene) modified asphalt serving as the control group. The relationship between the phase angle plateau area and polymer aging degradation was elucidated. This study investigates the impact of polymer degradation on the high-temperature rheological behavior and medium-temperature fatigue properties of asphalt through temperature sweep, multiple stress creep recovery (MSCR), and linear amplitude sweep (LAS) tests. Fourier transform infrared spectrometer (FTIR) and confocal laser scanning microscopy (CLSM) are used to qualitatively and quantitatively analyze the chemical composition and morphological evolution of TPUMA during thermal-oxidative degradation. The findings suggest that TPUMA's performance changes in the aging environment is result from the dual coupling effect of polymer degradation and asphalt oxidative hardening. The closely arranged isocyanate (-NCO) and polar component molecular chains in asphalt slow down its oxidation speed, which enhances the aging and deformation resistance of TPUMA. The successful blending of TPU and asphalt was confirmed, and the degradation degree of the polymer was quantitatively characterized by the percentage of the degraded area. The results provide insights to better understand the interplay between TPU degradation and asphalt oxidation.

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>

Mechanical and rheological properties of polyurethane-polyurea (PU-PUa) modified asphalt binder

Polyurethane (PU) is one of the common polymer modifiers used for asphalt, and the PU modified asphalt currently plays a fundamental role in road constructions. However, most of the PU as the modification could bring about an increasement in viscosity and rigidity to asphalt binders, thus leading to insufficient ductility and deformation compatibility for the materials to some extent. In the present study, a composite polymer material synthesized with polyurethane and polyurea (PU-PUa) was introduced as a modifier to the asphalt binder in an attempt to integrate their individual advantages into the asphaltic material. The curing time, tensile strength, and Fourier Transform infrared spectroscopy (FTIR) tests were conducted to determine the optimal proportion of the PU and PUa in the compound polymer, and its formation mechanism was also discussed. The fundamental properties of the asphalt binders modified with various contents of PU-PUa (5%, 10%, and 15% by weight), such as the storage stability, rheological properties, creep recovery capacity, and fatigue resistance, were investigated through the thermal storage, dynamic rheological, stress creep recovery (MSCR), and linear amplitude sweep (LAS) tests. Furthermore, in order to understand the adhesion property of the PU-PUa modified asphalt on aggregates, the pull-off tests considering both dry and water immersion conditions were performed. The test results showed that the PU-PUa could be effectively used to modify asphalt binders, and 7:3 was found to be the best proportion of the PU and PUa. The addition of PU-PUa could promote the high temperature performance, enhance the recovery ability for creep, and extend the fatigue life of the asphalt binders (for both 70# and SBS asphalt). The optimal content of PU-PUa for the modification was found to be 10% based on the storage stability and mechanical performance of the modified asphalt binders.

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.

An ultra‐tough, creep‐resistant, wear‐resistant hydrogel for cartilage replacement

AbstractAs a load‐bearing tissue, natural cartilages possess a compressive stress above 50 MPa, a water content around 60%, and a friction coefficient (FC) less than 0.1, which remains difficult for synthetic materials to realize. Herein, a facile strategy was reported to achieve this goal. The hydrogel was obtained through a three‐step strategy from polyvinyl alcohol (PVA), chitosan (CS), sodium carboxymethyl cellulose (CMC‐Na), lecithin (LS), and deionized water. First, freezing–thawing the aqueous solution of PVA and CS three times generated the precursor gel. Second, immersing it in aqueous solution of CMC‐Na to form multiple linkages (hydrogen bonds, ionic interactions, and crystallize domains). Third, it was coated with LS to form a lubrication layer. Due to the synergy of dynamic interactions, the compressive stress was 115 MPa, superior to most tough hydrogels. Owing to existence of LS, the FC was 0.03, better than the requirement for artificial cartilage. Remarkably, the FC remained stable within 50,000 wear cycles. On account of the reversible break/reformation of physical linkages, the creep recovery efficiency was 93%. The raw materials are all biocompatible and the fabrication process exclude the adoption of toxic additives. All of these features make it an ideal material for cartilage replacement.

A continuum-micromechanical model for crazing in glassy polymers under cyclic loading

A micromechanics-inspired constitutive model is developed to describe the deformation behaviour of fibrillated material within crazes in glassy polymers subjected to cyclic loading. In a finite strain setting, the model accounts for the morphology change taking place by the drawing of material from the intact bulk polymer into craze fibrils and their transition from primitive to mature fibrils. Building on previous research, fibril drawing is described as a viscoplastic process. A novel contribution of this study is the incorporation of viscoelastic deformation of existing fibrils, which is motivated by experimental observations. This new perspective allows for creep recovery, especially during the unloading phases of cyclic deformation.A parameter study which pays special attention to the role of the characteristic times scales of fibril drawing and fibril creep in relation to the imposed loading rate illustrates the performance of the model. Since the model is designed as an input to cohesive fracture simulations in glassy polymers, its response under monotonic loading is analysed and compared to existing crazing models. Of primary interest, however, is the model behaviour under cyclic loading which is investigated for different loading scenarios up to fibril failure. The study highlights the complex interplay between the two viscous mechanisms and how they influence the local deformation behaviour of the craze matter as well as the number of cycles until failure.

Influence of anelastic recovery on the cyclic creep behavior of AlCoCrFeNi2.1 eutectic high-entropy alloy

The AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) is regarded as a promising candidate for structural materials in high-temperature equipment, which may experience the cyclic creep and anelastic recovery caused by low-frequency peak-shaving loading. To investigate the influence of anelastic recovery on the microstructure and cyclic creep behavior of AlCoCrFeNi2.1 EHEA, the stress-varying (SV) tests at 800 °C are conducted to introduce the anelastic strain for comparison with the stress-constant (SC) test. The results show that the steady-state creep rate (SSCR) is accelerated with the increase in the cyclic-creep cycle and valley stress in SV tests. The anelastic recovery happened during the valley-stress holding (VSH) stage significantly alters the microstructure in the B2 phase of EHEA under SV conditions. This anelastic-recovery-related microstructural evolution is subsequently elucidated on the basis of back stress theory. Finally, the influence of microstructural evolution on the cyclic creep behaviour is revealed. The findings obtained will enhance the comprehension of high-temperature deformation mechanism of dual-phase EHEAs.

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.